CASE REPORT

Figure 2. Shade selection.	Figure 3. Crown preparation.
Figure 4. Margin etched with Tooth Conditioner 34% (DENTSPLY Caulk).	Figure 5. Excess cement prior to curing and removal.
Figure 6. Both crowns after cementation, finishing, and polishing.	Figure 7. Six months post cementation.

A 58-year-old woman wanted her yellow central incisors to be whiter like her other crowns (Figures 1a and 1b). She stated that she knew that her 2 existing crowns on the lateral incisors were not ideal (exposed margins), but at this time she only had the financial means to treat the front teeth, giving her a whiter smile. She also expressed concerns that any new crowns should not have “metal showing at the gums” like one of her crowns did.
There were no medical contraindications to dental treatment; the options given to her were either porcelain veneers or all-ceramic crowns. Due to the size of the existing composites and the stained margins around them (meaning a deep preparation for veneers), the patient chose to have crowns placed. She understood that her crown on tooth No. 10 would still be longer than the new ones. It was also explained to her that the shade of the new crowns might not exactly match her proximal crowns. The chosen shade was A1 (Figure 2). Digital photographs were taken and sent to the lab along with the rest of the case materials.
At the preparation visit she again confirmed that only the 2 front teeth would be treated at this time, and she would replace the other crowns in the future. Anesthesia was placed, and the teeth were prepared with a margin located at the crest of the gingiva (Figure 3). Master impressions were made using Exafast Putty and Exafast NDS Regular (GC America). Bite registration (Jet Blue Bite [Coltène/Whaledent]) and an alginate impression of the lower teeth were made. Temporary crowns were made (Jet [Lang Dental]) and cemented with TempBond Clear (Kerr).
At the delivery appointment, the patient requested that anesthesia be given. Nobel Biocare Procera crowns were tried in, and the patient approved both the shade and the shape. These crowns were to be cemented using G-Cem Shade A2. To ensure a good seal, the enamel at the margin was etched using phosphoric acid for 15 seconds and washed off (Figure 4). To make finishing the margins easier, one crown was cemented at a time. Figure 5 shows the excess material as the crown was seated. The cement was cured for 10 seconds, and the excess was removed. The cement was allowed to cure for 6 minutes, and the margins were finished and polished. Next, the other crown was cemented in place (Figure 6). Figure 7 shows the crowns 6 months after cementation. Notice that the gingival tissue is pink, not red and inflamed. The patient also stated that she was happy with the shade, as it blended in with her other crowns.

References

1. Craig RG, Powers JM. Restorative Dental Materials. 11th ed. St Louis, MO: Mosby; 2002:594.
2. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed prosthodontics. J Prosthet Dent. 1999;81:135-141.
3. Farah J. Temporary cements. Dental Advisor. 1998;15(9):2.
4. Weisman G, ed. Cements. Dental Products Report. 2005;39(11):114-124.
5. Piemjai M, Miyasaka K, Iwasaki Y, et al. Comparison of microleakage of three acid-base luting cements versus one resin-bonded cement for Class V direct composite inlays. J Prosthet Dent. 2002;88:598-603.
6. Attar N, Tam LE, McComb D. Mechanical and physical properties of contemporary dental luting agents. J Prosthet Dent. 2003;89:127-134.
7. Peutzfeldt A, Vigild M. A survey of the use of dentin-bonding systems in Denmark. Dent Mater. 2001;17:211-216.

Dr. Weiner received his DMD degree from Tufts University in 1986. He is a Fellow of the AGD, the American College of Dentists, and the Pierre Fauchard Academy. He has written many articles and presented numerous lectures on the topic of liners, bases, and cements. He maintains a private practice in family and cosmetic dentistry in Millis, Mass, and can be reached at (508) 376-4949 or randy@weinerdmd.com.

EFFICACY OF FLUORIDE VARNISHES

Fluoride varnishes were originally developed to prolong the contact time between fluoride and the tooth surfaces, thereby improving fluoride incorporation into the surface layers of the tooth, ie, uptake of fluoride that is firmly bound to enamel.² However, the concept of the cariostatic mechanism of fluoride has changed considerably over the past decades. In addition to fluoride incorporation into the crystalline lattice, fluoride varnishes interact with saliva and form calcium fluoride (CaF2) compounds on enamel.^2,5 These calcium fluoride deposits create a reservoir of fluoride ions, which are slowly released when the pH of plaque drops, thus acting as a prolonged source of fluoride ion.6 This has been considered the most important action mechanism of the products with high fluoride concentrations. It has been noticed that fluoride varnishes are effective when used on early white spot lesions, since a large amount of fluoride can be deposited in the porous demineralized enamel. Thus, the action of fluoride can be related to its inhibition of the demineralization processes as well as its promotion of enamel remineralization.
In numerous studies, fluoride varnishes have been shown to be clinically effective in preventing caries.^3,7-10 However, studies vary widely in their design and in the rate of caries reduction. Studies conducted between 1968 and 1985 reported an overall reduction in caries increment ranging from 18% to 77%.⁷ According to the Cochrane Review by Marinho, et al⁹, the application of fluoride varnishes 2 to 4 times a year, either in the permanent or the deciduous dentition, is associated with a substantial reduction in the caries increment.
Duraphat (Colgate Oral Pharmaceuticals) varnish has been the most extensively studied fluoride varnish, producing caries reductions in both primary and permanent dentition.^3,7-10 Several reviews report evidence of the efficacy of Duraphat, and recommend its use for caries control.^3,7-12 The National Institutes of Health Consensus Development Conference on Diagnosis and Caries Management,¹³ the Centers for Disease Control and Prevention,¹⁴ and American Dental Association Council on Scientific Affairs¹² support the beneficial effect of fluoride varnish on the permanent teeth and recommend the use of fluoride varnish for children and adults at moderate or high risk for caries as professionally applied topical fluoride, in addition to toothbrushing twice a day with fluoride toothpaste. However, since the majority of fluoride varnish studies have been conducted in children and adolescents, there is still a need for further studies on the effect of fluoride varnishes in the elderly, especially those with root caries.¹³

FLUORIDE VARNISHES AVAILABLE IN THE UNITED STATES

Several fluoride varnishes are currently available in the United States: Duraphat (Colgate Oral Pharmaceuticals), Duraflor (Pharmascience), CavityShield (OMNI Preventive Care, a 3M ESPE dental company), and Fluor Protector (Ivoclar Vivadent). Recently, several new products have been introduced to the market, such as Fluoridex Lasting Defense (NaF) Varnish (Discus Dental), VarnishAmerica (Medical Products Laboratories), DuraShield (Sultan Dental Products), AllSolutions (DENTSPLY), Vanish (OMNI Preventive Care), Colgate-Prevident (Colgate Oral Pharmaceuticals), and Flor-Opal Varnish (Ultradent Products). All of these varnishes, except Fluor Protector, contain 5% sodium fluoride (22,600 parts per million fluoride ions [F-]). Duraphat and Duraflor are packaged in a 10 ml tube, and the others are packaged individually for single-unit dose applications. CavityShield and VarnishAmerica are packaged in 0.25 ml and 0.4 ml doses for single use, and DuraShield, Vanish, and ColgatePrevident are packaged in 0.4 ml doses. Fluor-Protector contains 0.9% difluorosilane by weight (1,000 ppm F-) in polyurethane-based varnish, and sets to a thin transparent film. It comes in either a 0.4 ml vial for single-use or a 1.0 ml ampule for multiple doses. ColgatePrevident dries to a transparent enamel color, and Vanish has a white color. Flor-Opal Varnish has a unique syringe-to-syringe mixing and delivery system that eliminates separation of fluoride from the resin carrier, along with a bendable tip.
An in vivo study by Shen and Autio-Gold¹⁵ compared the uniformity of the fluoride concentration in different types of varnishes—Duraphat, Duraflor, CavityShield, and Fluor Protector. The intent was to evaluate possible ingredient separation.¹⁵ When doses from these varnish tubes were compared, Duraphat showed more uniformity and less separation of ingredients than Duraflor.15 According to the manufacturer, the individual dose units of CavityShield are intended to be mixed by hand in the provided well, which could reduce separation and thus improve uniformity. The separation problem should be kept in mind when considering other single-dose unit systems, and mixing could be indicated before clinical application. Some of these varnishes also appear as a light, yellowish-brown layer on the teeth surfaces after application. However, this discoloration is not permanent and disappears after a day or 2 with regular toothbrushing.16 For patients who do not want this light yellow color on the day of application, white varnishes could be used, such as Vanish and ColgatePrevident.
In 1994, the United States Food and Drug Administration (FDA) approved Duraphat for marketing as a medical device to be used as a cavity liner and for the treatment of hypersensitive teeth. Because caries prevention is considered a drug claim, manufacturers would have to submit appropriate clinical trial evidence for review by the FDA before they could be cleared as anticaries agents.³ In the United States, the therapeutic use of fluoride varnishes for caries prevention is referred to as “off-label” because the product is being used for purposes other than originally approved, and they can be used for caries prevention in clinical practice.¹⁷ In the states of Washington and North Carolina, treatment with fluoride varnishes is a preventive service procedure covered by Medicaid.¹⁸ Several states, such as Alaska, Idaho, Iowa, Georgia, North Carolina, Kansas, Nevada, Virginia, and Washington, have developed prevention programs, manuals, and billing procedures for fluoride varnish to be used as a caries preventive agent.⁴
Fluoride varnishes marketed in the United States have the highest fluoride concentration of any fluoride vehicle (22,600 ppm F-), and some ingestion of the fluoride can occur during the application process or after fluoride is released into the saliva. However, there are no reports of possible side effects or adverse effects for patients.¹¹ Ekstrand, et al¹⁹ evaluated the plasma fluoride concentration and urinary fluoride excretion following applicaton of Duraphat varnish. Their studies revealed that urinary fluoride concentration 12 hours after application was between 500 and 1,100 µg F-, which is well below the toxic level. The comprehensive review to determine the safety of fluoride varnish for the Cochrane Collaboration database found no information about adverse effects in the clinical trials that were reviewed.⁹ However, it was suggested that future studies collect additional data on possible side effects. Among clinicians, fluoride varnish applications have been regarded as safe even for young children, since the amount of varnish is usually less than 0.5 ml, which delivers 3 to 11 mg of fluoride ion, far below the probable toxic dose of 5 mg/kg.

CLINICAL CONSIDERATIONS

Frequency of Application

For a fluoride varnish to be effective, frequency of fluoride varnish applications should be based on an individual caries risk assessment.⁴ The most frequently prescribed regimen has been a semiannual application of varnish.²⁰ Petersson and Westerberg²¹ suggested that 3 applications of varnish in one week, conducted on an annual basis, could be more effective than seminannual application. However, this application frequency requires further study in order to be established as a standard recommendation. For high and moderate risk individuals, varnish could be recommended to be applied 2 to 4 times a year.^9,12

Indications

Figure 1. Early, noncavitated enamel lesions, ie, white-spot lesions, which have potential to remineralize with the use of fluoride varnish.

Fluoride varnishes are recommended for patients with a high or moderate risk of caries.⁴ To assess a patient’s caries risk, several risk factors can be identified through the use of clinical and sociodemographic information, which is routinely collected at annual clinical examinations. Several protocols have been developed for risk assessment. The National Institutes of Health13 published recommendations for the most helpful and consistent risk indicators in practice, which are: (1) past caries experience, (2) inadequate previous or current exposure to fluoride, (3) any physical or mental illness and any oral appliance or restoration that compromises the maintenance of optimal oral health, (4) frequent fermentable carbohydrate consumption, (5) lower salivary flow, associated with certain medical conditions and therapies, (6) high mutans streptococci levels, (7) gingival recession, especially in elderly populations, and (8) lower index of socioeconomic status.
Based on clinical findings, patients with a high caries risk with active noncavitated lesions (Figure 1) and exposed root surfaces can benefit from fluoride varnish. After periods of tooth eruption, when enamel is still not fully mineralized, patients can benefit from the mineralizing effect of fluoride varnish and the greater uptake of fluoride. Patients with reduced salivary flow, or following periodontal surgery, and patients with fixed or removable prostheses can temporarily have higher risk for decay and also benefit from fluoride varnish applications. Individuals with an eating disorder, or mentally or physically challenged individuals can also have a high caries risk. Varnish has been regarded as a safe and easy alternative for caries control in patients with special needs, such as those receiving head and neck radiation, orthodontic treatment, and those using medications that result in reduced salivary flow.¹⁸ As suction devices and trays are not needed for fluoride varnish application, varnish can be applied even for very young children and in field situations, such as the classroom.²² It has been suggested that fluoride varnish can be adopted into medical practice, applied by primary care physicians and their staff.²³
Clinically, varnish can be applied to fissures, proximal surfaces, or smooth surfaces of primary or permanent teeth. It can also be targeted only to specific tooth surfaces, and applications can be done according to individual needs. Varnish should be applied to dry, clean teeth. However, professional prophylaxis of the teeth is not essential before application. It has been shown that fluoride ions can migrate through plaque, and toothbrushing performed by the patients themselves is sufficient prior to varnish application.²⁴

Clinical Application

Figure 2. Teeth isolated with cotton rolls and dried with compressed air or with cotton gauze before fluoride varnish application.

The following steps are recommended for the clinical application of fluoride varnish:

1. Isolate the quadrant with cotton rolls, and dry with compressed air or with cotton gauze before application (Figure 2). Since varnish sets in the presence of moisture, excessive drying is not necessary.

Figure 3. When a single unit dose system is used, mix fluoride varnish in a well before application.

2. When a single-dose system is used, mix the varnish in the well that is provided (Figure 3). For the adult dentition, 0.4 ml of varnish is adequate. Due to the high concentration of fluoride, care should be taken not to exceed the recommended dose.

Figure 4. Apply fluoride varnish onto the teeth surfaces with a small disposable brush.	Figure 5. Varnish should be applied as a thin film.

3. Apply varnish on the dried teeth surfaces or specific tooth surface with a small disposable brush (Figure 4) or with the brush provided in the single-dose unit. Varnish should be applied as a thin film (Figure 5). A specific setting time is not required since varnish sets in contact with saliva. After the application, cotton rolls can be removed and the clinician can proceed to the next quadrant. The application process usually takes one to 4 minutes.

4. Instruct patients to avoid eating for 2 to 4 hours after the application and to eat a soft diet for the rest of the day. Patients should avoid brushing the same day to maximize contact between the varnish and teeth, and to achieve optimal fluoride benefit. The varnish can be brushed away with normal tooth brushing the next day. Patients should also be told about the temporary yellowish coating of the teeth when Duraphat, CavityShield, Duraflor, or similar products are used. In vivo testing has shown that Duraphat, Cavity-Shield, and Duraflor can be used without adversely affecting the hue and value (ie, the color) of aesthetic restorative materials.¹⁶ The fee for the application of fluoride varnish can be charged as a “topical fluoride application.” It has been estimated that the application costs are $1 to $4 depending on the brand used. The major expense is the time and related personnel costs required to apply the varnish.¹¹

SUMMARY

Available data suggest that fluoride varnish can be a safe and effective method for caries management. The application of varnish can be beneficial for those at risk for caries and for patients with special needs, and for those with no access to daily fluoride or other preventive methods. Even a small amount of varnish can be applied to active noncavitated lesions, assuring that a high concentration of the agent is available at the site where needed and that the total amount of active agent administered to the patient may be markedly reduced. Considering that varnish treatment is painless and can be easily performed by auxiliary dental personnel, it is a caries preventive method that can be easily applied and recommended for any age group, even young children. For high-risk caries patients with a significant cariogenic challenge, topical applications of fluoride might be insufficient and thus could be supplemented with other anticariogenic methods, such as xylitol chewing gum.²⁵

References

Dr. Autio-Gold received her DDS and PhD degrees from the University of Oulu, Finland. She has been teaching at the University of Florida in Gainesville for the past 10 years. She is currently assistant professor and Director of the Cariology Program in the Department of Operative Dentistry, University of Florida, and is a Secretary for the International Association of Dental Research Cariology Group. She can be reached at jautio-gold@dental.ufl.edu.

Disclosure: Dr. Autio-Gold does not have any financial interest in products or companies listed in the article.

TRAY SELECTION

Consider first the type of case that is being done. Laboratories estimate that about 85% of units are single crowns, and most of those are done with a dual-arch quadrant or triple tray. Because of their ease of use, conservation of material, and elimination of the need for an opposing impression and bite registration, dual-arch quadrant impressions have become the overwhelming choice for most dentists.  When employed properly they can be used satisfactorily; however, the overuse and abuse observed in commercial laboratories have frustrated both technicians and clinicians.
This is further complicated by the fact that many commercial laboratories employ plastic, disposable articulators to use in the fabrication process, adding to the inaccuracies that can occur. Evaluation of the 6 most popular plastic, disposable articulator systems used with dual-arch impressions found that with all systems, it was virtually impossible to maintain and repeat a centric occlusal position stop. The conclusion was that they should only be used for single units, not when the terminal unit in the arch is being prepared.¹
Another study evaluated the effect of the viscosity of the impression materials in plastic and metal dual-arch trays.2 There were statistically significant differences noted in the accuracy of the dies. Rigid materials in metal trays were the most accurate, while monophase materials in plastic trays produced dies that were dramatically shorter.

Figure 1. Dual-arch impression that was correctly taken in maximum intercuspation shows tooth-to-tooth contact anterior and posterior to the prepared tooth.	Figure 2. Soft-tissue contact with the plastic tray leading to distortion of the final impression.
Figure 3. Tooth contact with the plastic tray leading to distortion of the final impression.	Figure 4. Even soft-tissue contact with a plastic tray can cause the tray to distort.
Figure 5. CLINICIAN’S CHOICE metal Quad-Tray.	Figure 6. Photograph illustrating the difficulty in stabilizing a quadrant tray.

The 2 most common problems observed in commercial labs with dual-arch trays are tissue or tooth contact with the tray and failure to record maximum intercuspation. Recent visits to 3 commercial labs in 3 different states in 3 different regions of the country showed that only about 40% of the 100 randomly selected dual-arch quadrant impressions were in maximum intercuspation. Maximum intercuspation can be visually verified by observing tooth-to-tooth contact anterior and posterior to the prepared tooth (Figure 1). Few metal trays were observed, even though the preceding evidence, as well as the anecdotal advice of many prominent clinicians, suggest they are more accurate. Soft-tissue contact was frequently observed in plastic trays, with an occasional tooth contact to the tray (Figures 2 and 3). Any contact between soft or hard tissue and a plastic tray applies an occlusal force to the tray that is likely to cause it to distort. When the patient opens—removing the occlusal force that distorted the tray—the tray returns to its original dimension because of the memory of the plastic, and the final impression is distorted, causing inaccuracies in dies as well as occlusal and contact discrepancies (Figure 4).
A properly designed metal dual-arch tray assists in tray placement and increases the ease of reaching maximum intercuspation, as well as provides the proper rigidity to decrease the chance of 3-D distortion (Figure 5). For more involved cases where a full-arch impression is indicated, research utilizing an optical laser scanner showed that dies from a stock impression tray were as accurate as those produced from a custom tray.³ Custom trays do save money in impression material because they generally use less material. That savings is more than offset, though, by the additional cost of tray material and labor to fabricate a custom tray. Custom trays should be employed when the patient’s anatomy dictates their necessity, most commonly in cases of mandibular tori or a particularly large or small arch form.
Quadrant single-arch trays are the most difficult tray to use without introducing distortion because of the difficulty in stabilizing the tray while the material sets. It is virtually impossible to keep the tray steady—particularly on the mandibular arch—if the patient makes any kind of movement with his or her lips or tongue while swallowing. Because the clinician is unable to obtain cross-arch stabilization during setting of the impression material, movement permits a slight rocking of the tray that causes distortion (Figure 6).

TECHNIQUE CHOICES

Dentists can use a number of different techniques that employ a variety of different materials and viscosities to take impressions. Traditionally, a heavy-body tray material is utilized with a lighter body wash material that is syringed around the tooth just before the tray is seated. Since the 1980s, with the introduction of vinyl putties, several putty/wash techniques have been advocated. Various innovations of these techniques have emerged, further confusing the clinician. Although it is possible to get many different techniques to work, the final choice as to technique should center on which is least problematic and most likely to produce consistent results.
The putty/wash techniques fall into 2 basic categories: (1) a single-step procedure where the putty is loaded into the tray and inserted immediately after syringing a wash material around the prepared tooth or teeth, or (2) a 2-step procedure where the putty is used to take an impression before starting the preparation, allowed to set, and removed from the mouth. After tooth preparation is complete, the tooth has a wash material syringed over it, and the initial tray and putty impression are reinserted over the wash. Variations of this include routing out part of the putty impression around the prepared tooth to produce space for the wash, and relining the entire impression with wash material.
Statistically, laboratories see more problems with 2-step impressions than any other technique. This is a result of the difficulty in repositioning the impression in the exact same position without creating a “step” between the original putty impression and the detailed wash impression. It is much more difficult to reseat the tray than it appears, and the result is more chairside occlusal adjustments in the completed restoration. There appears to be little difference in reducing the creation of “steps” by routing out some of the material around the prepared tooth or washing the entire arch.
The single-step putty/wash technique can also be equally difficult to produce a consistent result with because the viscosity of the putty material is most often considerably lower than heavy-body tray material produced from a mixing machine or by hand- held gun extrusion mixing cartridges. The extremely stiff putty material, when seated in the mouth, forces the much thinner wash material away from the prepared tooth, and the resultant impression is captured in more putty than wash. ADA/ANSI specifications require that a wash material capture details to 20 µm, while tray materials are required to capture only 70 µm of detail.4 For this reason, most if not all of the prepared tooth should be captured in the fine detail of the wash material.
Recently, variations of these putty/wash techniques suggest that they can be successfully utilized to obtain impressions without the use of retraction cords. The concept is that the wash material can hydrostatically be forced into the gingival sulcus when the set putty impression is reseated in the mouth, thereby capturing the impression of the margins without having to place retraction cords or remove gingival tissue with a laser or electrosurgically. Some techniques further suggest that this technique can hydrostatically displace crevicular fluids as well as tissue.
Again, with these techniques the commercial laboratories report inconsistent results with their clients regardless of the brand of material used. The degree of preparation taper plays an integral role in the amount of hydrostatic pressure that is placed at the margin of the preparation during this impression technique. The greater the preparation taper, the greater the dimensional accuracy.5 Too much hydrostatic pressure at the margin causes a “pull-back” or rebound effect when the impression is removed from the mouth after setting. This is why all full-arch impressions should be held passively while setting. Any active force while the impression is setting causes an increase in elastic recoil when the impression is removed from the mouth and creates a reduction in the size of the casting. The greater the preparation taper, the less the hydrostatic pressure at the margin, creating (in theory) enough hydrostatic pressure to displace fluids and tissue, but not enough to create 3-D distortion. Unfortunately, an increase in the degree of preparation taper to fulfill the requirements to make this technique work adds to the clinician’s problems by ultimately increasing retention difficulties because of excessive taper.
Finally, the reason for using retraction cords, laser, or electrosurgical techniques is not limited to taking the impression. Precise viewing of the margin of the preparation is imperative, unless placed completely supragingival, for final preparation of the margin. Most clinicians advocate the use of a dual-cord impression technique, where the first cord is placed to fill about one half of the sulcus as soon as the contact is broken. This process expands the sulcus to allow for better visualization of the preparation margins for final preparation, and greatly benefits the procedure because the first cord is placed prior to any gingival bleeding. It is much easier to do this and prevent gingival hemorrhage than it is to arrest hemorrhage after it begins. A correctly chosen diameter of cord can be placed quickly and atraumatically. After the preparation is completed, the second cord is placed to expand the sulcus further so that the margin is visible for impression taking. The second cord is left in position for 3 to 5 minutes and removed for the impression, while the first cord is left in place to ensure hemostasis until completion of the impression, when it is removed.
If the gingival sulcus is very shallow (1 to 2 mm), particularly on anterior teeth, veneer preparations, and when the gingival margin is being placed just at or just below the height of the sulcus, it is frequently better to use only one cord. In these situations the preparation is completed supragingival, and then the retraction cord is placed, again filling about one half of the depth of the sulcus. The preparation can then be refined to the height of the sulcus or slightly below without trauma to the gingival tissues. The impression can be taken after careful removal of the retraction cord, or the cord can be left in place, as there should be adequate access to the supragingival margin to take the impression.
A colleague recently pointed out that it is appropriate to change terminology from gingival retraction to the more correct sulcus expansion. Gingival retraction, which may have been a more viable term in years past when a patient’s tissue health might have been less than ideal, is no longer descriptive of the procedure that is actually performed. When a patient has good gingival health—and there should be no reason to begin an indirect restoration until that has been achieved—the procedure that is accomplished is a temporary expansion of the sulcus to permit access for final preparation of the margin and then taking the impression. Removing the cords after completing the impression then permits the tissue to return to its normal biological position without a change in the occlusal-apical height of the tissue. Changing the terminology helps the dentist, chairside assistant, and patient more accurately visualize and then achieve the ideal result.

MATERIAL CHOICES

Figure 7. Two-dimensional representation of polymerization shrinkage that occurs toward a rigid wall and to the center of its mass when no rigid wall is present.

With the elimination of the putty viscosity as a recommended choice, the remaining choices are heavy-body, light-body, and monophase materials. To logically choose the best to use, it is important to consider how all materials react during setting and the impact that has on the previous discussion of trays and techniques.
All impression materials—polyvinyls, polyethers, polysulfides, and hydrocolloids—polymerize toward the rigid wall of the tray that has adhesive and/or perforations to retain the material. Unfortunately, the interproximal material has no tray, so it polymerizes toward its center (Figure 7). This explains why an impression of a perfectly round machined steel die produces an elliptical casting, which is observed regardless of the type or brand of material used.6 Polymerization shrinkage accounts for the 3-dimensional differences in dies made from impressions taken with the same material, but with different techniques—trays, dual-arch trays with sides, and sideless dual-arch trays. There is one material that is marketed specifically for use in the dual-arch quadrant metal tray (Inflex [CLINICIAN’S CHOICE]).
Monophase materials are limited in their clinical application. An ideal material must be resilient enough to be withdrawn from the mouth easily, particularly when mobile teeth or prepared teeth are thin. The material must also be flexible enough to be removed from the model without breaking off a thin preparation. This has led to the development of the “soft” formulas of polyethers. However, any material when used in a sideless, dual-arch tray must be firm enough to support the weight of the gypsum when the model is poured, without sagging under the weight of the stone. It appears that one viscosity of material would not be able to ideally fulfill all of these parameters simultaneously.

CONCLUSION

When the clinical procedure is limited to 1 or 2 units, the clinician may choose a dual-arch tray. A metal tray would be preferred over a plastic tray because of its rigidity and resultant dimensional stability. A tray material that is very inflexible should be used for its rigidity and ability to support gypsum when the model is poured.
When the clinical procedure calls for a full-arch impression, a stock tray coated with a compatible adhesive can be utilized with a slightly less rigid tray material to aid in removal from the mouth.
In all cases it is imperative to be able to see the preparation for final margination, and then take the impression. The dual-cord technique accomplishes both, and when done properly in the preparation sequence can lead to minimal hemorrhage or gingival trauma.

References

1. Thornton LJ. A survey on the utilization of disposable quadrant articulators. Gen Dent. 2002;50:72-76.
2. Ceyhan JA, Johnson GH, Lepe X. The effect of tray selection, viscosity of impression material, and sequence of pour on the accuracy of dies made from dual-arch impressions. J Prosthet Dent. 2003;90:143-149.
3. Brosky ME, Pesun IJ, Lowder PD, et al. Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy. J Prosthet Dent. 2002;87:204-209.
4. American National Standards Institute and American Dental Association. ANSI/ADA Specification No. 19: Dental Elastomeric Impression Materials. Chicago, Ill: American Dental Association, Council on Scientific Affairs; 2004.
5. Fenske C. The influence of five impression techniques on the dimensional accuracy of master models. Braz Dent J. 2000;11:19-27.
6. Wadhwani CP, Johnson GH, Lepe X, et al. Accuracy of newly formulated fast-setting elastomeric impression materials. J Prosthet Dent. 2005;93:530-539.

Dr. Cowie is a 1976 graduate of Northwestern University Dental School and practices in Jacksonville, Fla. He has completed close to 2,100 hours of continuing education, including continuums at the Dawson Center for Advanced Dental Studies, the Society of Occlusal Studies, and The Pankey Institute. He has presented more than 150 lectures nationally and internationally. He can be reached at (904) 771-0568, robertrcowie@netscape.net, or by visiting drcowie.com.

METHODS AND MATERIALS

In October 2005, the chairpersons of restorative dentistry departments of the 66 dental schools in the United States, Canada, and Puerto Rico received by mail a 3-page questionnaire. The packet included a cover letter that explained the survey objectives, the survey instrument, and a self-addressed return envelope. Participants were asked to complete and return the questionnaire within a 3-week period. A second mailing (with a copy of the survey included) was sent to chairpersons who had not responded to the first mailing.
Questions focused on which dental materials were taught (for the 2005-2006 academic year) in 4 distinct clinical scenarios: 1) a class II preparation within 1 mm of the pulp to be restored with amalgam; 2) a class II preparation more than 2 mm from the pulp to be restored with amalgam; 3) a class II preparation within 1 mm of the pulp to be restored with composite; and 4) a class II preparation more than 2  mm from the pulp to be restored with composite. All scenarios reflected the initial restoration of the tooth. Respondents were also asked to report the incidence of postoperative sensitivity with their current protocol. The depths of these hypothetical cavity preparations mirrored what was in the original survey, but composite restoration scenarios were not included in the 1995 survey. As a new element to the 2005 survey, dental schools were also asked about the cementation protocol taught for specific indirect restorations and any associated postoperative sensitivity. 
As in the 1995 survey, the current survey included related questions focused on cost considerations, satisfaction with the present protocol, and frequency of and responsibility for protocol review. The Statistical Package for the Social Sciences, Version 10.0 (SPSS), was used to analyze the findings and to determine any statistically significant findings.

RESULTS

Table 2 provides the most popular liners and bases taught at dental schools. In the first scenario (deep preparation with amalgam restoration), calcium hydroxide (38.5%) followed by glass ionomer (30.8%) were the most commonly taught liners. For shallow cavity preparations to be restored with amalgam, schools most often teach students to place no liner (23.1%), followed by copal varnish and glass ionomer (20.5% each).
For composite restorations in a deep cavity, the liners most frequently used were glass ionomer (35.9%) followed by calcium hydroxide (28.2%). For shallow cavity preparations restored with composite, just under half the schools (48.7%) report teaching the use of dentin bonding agents. Glass ionomer was the second most popular material (28.2%).
“Other” liners mentioned by respondents included calcium oxalate precipitate, Gluma (Hereaus Kulzer), a resin-modified glass ionomer, and what one school described as a homemade Gluma-like product.

Bases

Glass ionomer represents the most popular base under amalgam or composite in a deep cavity (56.4% and 41%, respectively). For both restorative materials in shallow preparations, schools most often teach students not to use a base (Table 3). The respondents did not indicate what, if any, other materials they use, other than what is listed in Table 1.

Cements

The survey asked the respondents which cement they were teaching for use with 9 indirect restorations (Table 4). The most frequently taught cements are prefabricated post: glass ionomers and resin (30.8% each); cast post and core: glass ionomers (38.5%); PFM crown (vital tooth): glass ionomers (64.1%); PFM crown (nonvital tooth): glass ionomers (61.5%); all-ceramic crown (anterior): resin cement (82.1%); all-ceramic crown (posterior): resin cement (76.9%); porcelain veneer: resin cement (92.3%). For provisional crowns (both vital and nonvital teeth), the most common material is a noneugenol zinc oxide product (53.8% and 57.9%, respectively).

Postoperative Sensitivity

With respect to liners and bases, only one school (from Canada) reported that more than 30% of patients experience some degree of postoperative sensitivity. Thirteen schools noted that they do not keep track of that information. All other responding schools state that less than 20% of patients suffer from postoperative sensitivity.

Satisfaction With Protocol

Respondents rated their satisfaction with their schoolís choice of liner and base on a scale from 1 (not satisfied at all) to 5 (extremely satisfied). In general, respondents were very satisfied with both the liner and base protocol used at their respective schools (mean of 4.62).  Overall satisfaction with current cementing practices was also high (mean of 4.50).

Other Factors

Cost did not appear to impact a schoolís decisions regarding the use of liners, bases, and cements. The overall importance of cost was low (mean is 2.76 measured on a 5-point scale where 1 was not at all important and 5 was extremely important). Just under two thirds (61.5%) of the schools review their liner and base protocol every year, and 25.6% do so every third year or less frequently. Cementation protocol is reviewed on a similar schedule. Fifty-nine percent of the schools review it every year, and about 10 percent (10.3%) of the responding schools review their cementation protocol every other year.
Consistent with the findings in the 1995 survey, at most schools protocol review involves a group of faculty rather than a single individual.
           
DISCUSSION

In September of 1995, a survey of all North American dentals schools examined teaching preferences and practices with respect to liners and bases.⁵ That study surveyed the application of liners and bases under amalgam restorations. Results indicated that teaching institutions could not agree on which material is best in a given clinical situation. This supports Christensenís view that the subject of bases and liners is confusing. Current use varies enormously, many different procedures are successful, and unanimity of opinion is not likely to be achieved.⁸
The current report sought to determine if North American dental schools now agree on a particular protocol with respect to liners and bases. In addition, since versions of some of these materials can also be used as a cement, this study was expanded to evaluate the cementation protocols taught at dental schools.
In the mid 1990s, for a deep cavity that was to be restored with an amalgam, 46% of the schools advocated the use of a glass ionomer as a liner followed by 25% for calcium hydroxide. Today, the results are nearly reversed, with calcium hydroxide being a more popular liner. One school noted discontinuance of calcium hydroxide in favor of mineral trioxide aggregate.
In 1995, none of the responding dental schools placed dentin bonding agents under amalgams in deep restorations. Today, the situation has changed, as approximately 10% of schools now teach that technique for both deep and shallow preparations that will be restored with amalgam. This is in contrast to composite restorations, where more schools use a dentin bonding agent as the liner (more than 25% in a deep cavity preparation and almost 50% in a shallow cavity preparation). Perhaps this is due to dentin bonding agents being part of the technique for placing the composite. Further contributing to the growing popularity of dentin bonding agents is the claim that the use of this material reduces postoperative sensitivity.⁹
Copal varnish, once considered the preferred material to seal dentinal tubules and reduce postoperative sensitivity, is now taught by less than 3% of dental schools as the first material placed in a deep cavity preparation that will receive an amalgam restoration. This is compared to 12% just 10 years ago. One dental school noted that they no longer teach the use of a copal varnish as a liner, based on research conducted at that school.
Depending on the clinical scenario, more than one third of dental schools still do not advocate the use of any basing material. However, when a base is used (deep preparations), glass ionomer emerges as the material of choice.
In 1995, 78% of the responding schools reported that less than 20% of their patients suffered from postoperative sensitivity after receiving a deep amalgam restoration. Today, 96% of the schools do so, which means that postoperative sensitivity is less of a problem. The same pattern follows for shallow amalgam restorations, when 10 years ago 73% of the responding schools reported that less than 20% of their patients reported sensitivity, compared to 96% of schools responding to the 2005 survey.
As previously mentioned, the 1995 survey did not offer scenarios that included composite restorations. The placement of composite restorations is now more common, so this aspect of restorative dentistry was included in the 2005 survey. The 2005 survey indicated that only 17% of the responding schools (n=24) report more than 20% of their patients having postoperative sensitivity after receiving a deep composite restoration. For those having a shallow composite restoration, 92% of the schools (n=24) reported less than 20% of patients with postoperative sensitivity.
With respect to final cementation, glass ionomer cements were the most popular material for cementation of a cast post and core restoration. Resin and glass ionomer cements are the preferred luting agents for direct post and cores. With respect to a final cementing material and postoperative sensitivity associated with vital teeth, and using the same 20% criterion as was used for liners, only one school reported a problem. This was associated with all-ceramic crowns for anterior teeth, and that school was using a resin cement. The same school reported that 20% of its patients experience postoperative sensitivity when zinc phosphate was used in conjunction with porcelain-fused-to-metal crowns.
Further analysis did not identify any particular material that was associated with either a high or low rate of postoperative sensitivity. It is also conceivable that postoperative sensitivity that occurs after both provisional and final cementation is unrelated to the cement used. Other causes could include open margins, the teeth involved being in hyperocclusion, and gingival irritation. The survey did not ask, nor did any respondents state, how long the sensitivity lasted.
For provisional cementation, products that do not contain eugenol are the most popular. Tooth vitality is not an important variable here. It is reasonable to ask if there is any relation between this practice and the belief that noneugenol materials do not interfere with resin-based final cements.^10,11 One school stated that 30% of patients claim to have postoperative sensitivity when using a noneugenol cement for vital teeth. No reason was provided.
It is interesting to note that none of the schools are teaching the use of polycarboxylate-based materials. This is curious, since polycarboxylates are considered to be very biocompatible. The polyacrylate acid molecule is thought to be too large to enter the dentinal tubules.²
In 1995, the mean for the importance of the cost of materials was 2.36, which is lower than reported in the 2005 survey (2.76). The relatively low importance of cost may be related to the fact that those responsible for choosing the material(s) may not need to consider cost, as this is the responsibility of someone else, or may reflect the reduced cost offered to schools by manufacturers.
The degree of satisfaction that dental schools report with liners and bases is higher (4.62) than it was 10 years ago (4.11). This may be due to the fact that improved materials and techniques are currently available; there are now more options for clinicians. Additionally, clinicians may have a better understanding of the dynamic interaction of these materials at the dentin and pulpal levels.
Although there are no published articles reporting on surveys of private practitioners regarding the use of liners, bases, and cements, one could hypothesize that the materials and techniques taught in dental schools are being used by these graduates when they enter private practice. A survey of private practitioners is needed to determine if current clinical practice mirrors the findings of the 2005 dental school survey.

CONCLUSION

Consistent with findings a decade earlier, there is no consensus among dental schools in regard to the best materials to use as liners, bases, and cements. Dental schools report high satisfaction with their existing protocols. Since no single protocol is taught by all dental schools, clinicians must strongly consider clinical success once in practice as their primary criterion for choosing specific materials for different clinical situations. Careful reading of the dental materials literature is also strongly recommended.

References

1. Draheim RN. Cavity bases, liners and varnishes: a clinical perspective. Am J Dent. 1988;1:63-66.

2. Baum L, Phillips RW, Lund MR. Textbook of Operative Dentistry. 3rd ed. Philadelphia, Pa: WB Saunders; 1995:Chapter 7.

3. Ferracane JL. Materials in Dentistry: Principles and Applications. 2nd ed. New York, NY: Lippincott Williams & Wilkins; 2001:Chapter 4.

4. Cox CF, Suzuki S. Re-evaluating pulp protection: calcium hydroxide liners vs. cohesive hybridization. J Am Dent Assoc. 1994;125:823-831.

5. Weiner RS, Weiner LK, Kugel G. Teaching the use of bases and liners: a survey of North American dental schools. J Am Dent Assoc. 1996;127:1640-1645.

6. Craig RG, Powers JM. Restorative Dental Materials. 11th ed. St Louis, Mo: Mosby; 2001:Chapter 20.

7. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed prosthodontics. J Prosthet Dent. 1999;81:135-141.

8. Christensen GJ. To base or not to base? J Am Dent Assoc. 1991;122:61-62.

9. Farah J, Powers J. Self-etching bonding agents. The Dental Advisor. 2003;20:1-4.

10. Leirskar J, Nordbo H. The effect of zinc oxide-eugenol on the shear bond strength of a commonly used bonding system. Endod Dent Traumatol. 2000;16:265-268.

11. Peutzfeldt A, Asmussen E. Influence of eugenol-containing temporary cement on efficacy of dentin-bonding systems. Eur J Oral Sci. 1999;107:65-69.

Dr. Weiner received his DMD degree from Tufts University in 1986. He is a fellow of the Academy of General Dentistry, the American College of Dentists, and the Pierre Fauchard Academy. He has written many articles and presented numerous lectures on the topic of liners, bases, and cements. He maintains a private practice in family and cosmetic dentistry in Millis, Mass, and can be reached at randy@weinerdmd.com.

At one time it was thought that the toxic effects of dental materials could adversely affect the pulp, leading to pulpal inflammation and postoperative sensitivity.² Later, a new theory developed, suggesting that the influx of bacteria and their toxins into dentinal tubules caused adverse pulpal reactions. The bacteria were believed to originate in the smear layer,  or were present deep in the dentinal tubules and were inaccessible to caries-excavating procedures.³ Nevertheless, the current belief is that postoperative sensitivity is not due to bacterial contamination but is primarily due to fluid movement within gaps at the tooth-restoration interface.⁴ The fluid may also contain bacteria. With respect to restorative dentistry, one of the goals of treatment is to reduce or eliminate these gaps, which would result in a reduction and possibly elimination of postoperative sensitivity.

With this outcome in mind, materials (liners, bases, and cements) are available for placement under a restoration. Cements are indicated for luting of crowns and bridges. The use of a base below a restoration appears to be less popular than in the past (unpublished online survey by Weiner, Dentaltown.com, October 2002). Liners are materials that provide a thin coating (usually 0.5 mm) on the cut surface of a cavity preparation. Although they provide a barrier to chemical irritants, they are not used for thermal insulation or to add bulk to a cavity preparation.⁵  Materials that can be used as a liner can be classified as a varnish, calcium hydroxide, zinc phosphate, glass ionomer, or resin.

The newest type of cavity liner is resin-based. These products generally have low solubility and are available in a number of shades and viscosities. This category can be divided into 2 classes: flowable composites and dentin bonding agents. Studies confirm that placing adhesives below amalgam restorations reduces microleakage, thus supporting their use as liners.^6,7

An inherent problem when using traditional composite resins is the polymerization shrinkage that occurs. This shrinkage results in gap formation, and therefore an increase in microleakage. The flowable resin was developed in an attempt to overcome some of the problems associated with polymerization shrinkage. Although flowables have a higher polymerization shrinkage than do conventional resins, their better flow and reduced modulus of elasticity theoretically reduce microleakage by increasing adaptation of the material to the cavity preparation and by forming a stress-absorbing layer.⁸ The result is a decrease in gap formation at the flowable resin-tooth interface, which will ultimately lead to a decrease in secondary caries and pulpal inflammation and a longer-lasting restoration.⁹

Dentin bonding agents not only act as an adhesive for the resin restoration, they are also a cavity liner. This is because the material is placed in the cavity preparation prior to any restorative material. Thus, they fulfill the characteristics of a cavity liner, as mentioned previously. Dentin bonding agents can be used under composite resin, amalgam, and gold restorations. The major disadvantage of many dentin bonding agents is that these materials are technique sensitive. The use of these materials involves a number of steps, and the clinician must pay close attention to the details. Fortunately, the manufacturers of dental materials are making strides to improve the ease of use.

Twenty-five years ago the second generation of bonding products became available, but these materials did not bond to dentin (etching of the dentin was not included in the technique). In the early 1990s, the fourth generation of these materials was introduced. These materials were able to bond to dentin and involved the use of dentin primers. The use of these systems involved 3 steps: acid etching, followed by the application of a cavity primer, which was then followed by the placement of an unfilled resin-adhesive (as a cavity sealer).

The sixth generation of bonding agents was characterized by the elimination of a separate etching step. The etchant was combined with the primer, making it self-etching. The products were classified into either of 2 groups. The Type 1 products (eg, Clearfil SE, Kuraray) place the primer and adhesive in 2 different bottles, each to be applied separately. Type 2 products (eg, Adper Prompt L-Pop, 3M ESPE) have both the self-etching primer and the adhesive in the same bottle (Table).

Recently, the seventh generation of bonding agents was introduced. These include i-Bond (Heraeus Kulzer), G-Bond (GC America), and Clearfil S3 Bond (Kuraray). These are single-bottle materials that etch, prime, bond, and desensitize the cavity preparation; i-Bond also disinfects the cavity preparation. These materials involve only a single step (no mixing), so they are easier to use and save time (Table).

The reduction in postoperative sensitivity that is achieved when using self-etching agents is the result of dissolving the smear layer without exposing the dentinal tubules.¹⁰ An online survey (DentalTown.com, June 10, 2004) found that 34% of the respondents used a desensitizing agent when treating cervical sensitivity. Further, of those who currently use or have used a self-etching bonding agent, 64% responded that these products reduced postoperative sensitivity.

As previously mentioned, any existing gap at the tooth-restoration interface will result in microleakage. Seventh-generation bonding a-gents generally allow the clinician to place a resin restoration with no gap at this interface. The definition of a gap is any space larger than 0.1 um. Bacteria are larger than this, eliminating the chance that the gaps will be infected.

The i-Bond material is available in 2 dispensing systems, single-dose containers (0.2 mL) and 4-mL bottles. G-Bond and Clearfil S3 Bond are available in multidose containers. A study compared the total working time (setup, application, and cleanup) of self-etching primers, evaluating both sixth- and seventh- generation materials in unidose and multidose versions. Unidose systems had significantly shorter setup and cleanup times than did those materials provided in multidose bottles.¹¹

An important aspect of a patient recall appointment is to determine if recurrent caries is present. Radiographically, if the bonding agent is too thick, a radiolucent zone will appear on the bitewing radiograph between the cavity floor and the bottom of the restoration. This radiolucency could be interpreted as recurrent caries. Use of a bonding agent that would not cause this radiolucent zone would theoretically improve the accuracy of diagnosis. The use of seventh-generation materials is not associated with this radiolucency, as the consistency of these newer materials is thinner than the bonding agents from previous generations. Ito, et al demonstrated that applying more coats of the adhesive (Xeno III [DENTSPLY Caulk] and i-Bond) resulted in improved strength and quality of dentin adhesion.¹²  However, applying multiple layers of adhesive may create the radiolucent zone that can interfere with diagnosis. Dentists must determine which is preferred: no visible radiolucent line or an increase in dentin adhesion.

It should be noted that the manufacturer specifically recommends that i-Bond be used only on freshly prepared enamel. If it is to be used on sclerotic dentin or unprepared dentin, the clinician must etch with phosphoric acid for 30 seconds prior to use.

Prior to the development of dentin primers, it was taught that the cavity preparation should be dry before any restorative materials, including cavity liners, were placed. This degree of “dryness” was an area of controversy in dentistry. According to the manufacturers, this is not a concern when using sixth- and seventh-generation materials because they can be used equally well on wet or dry dentin. Butt and colleagues compared the dentin shear bond strength of 3 self-etching primers in the presence of moisture. They found that the moisture tolerance of these materials eliminates this as an important concern in bonding.¹³ This study confirms that cavity liners are now available that can be placed in a moist (not wet) preparation and still seal the cavity preparation.

To illustrate, a clinical case report is described that demonstrates a tooth being restored with i-Bond and Venus Composite Resin system (Heraeus Kulzer), which includes a flowable resin and a final restorative resin. Other combinations may be used, following manufacturers’ instructions.

The refractive indices of the fillers and matrix of the Venus Composite Resin system mimic the shades of the adjacent tooth, resulting in less visible margins. A shade guide is provided that is matched to the Vita shades and has 27 shades and 3 opacities. Further, since barium aluminum fluoride glass is a component of the filler, it is highly radiopaque. Due to the fact that the particle size is less than 1 um, the resin polishes to a high luster.

Treatment

Figure 1a. Tooth No. 5, preoperative view.	Figure 1b. Preoperative bite-wing radiograph.

A 33-year-old female patient presented for a recall visit, and a carious lesion was detected on the mesial surface of the maxillary right first premolar (Figures 1a and 1b). The patient requested an aesthetic restoration.

Local anesthesia was administered, and a rubber dam was placed from teeth Nos. 4 to 7.

Figure 2. Completed cavity preparation.	Figure 3. Cavity preparation with matrix and wedge in place after i-Bond was applied.

The cavity preparation was completed (Figure 2) using a No. 245 bur in a highspeed handpiece and a No. 6 round bur in a slow-speed handpiece, followed by a spoon excavator. To begin the restorative phase the tooth was fitted with a matrix (Tofflemire retainer and No. 1 Deadsoft band) and was wedged (Premier Dental Products, Figure 3). The i-Bond was then placed as per the manufacturer’s directions. A total of 3 coats of i-Bond was placed, with the application starting on the enamel and moving to the dentin. After a 30-second period, a gentle stream of air was directed into the preparation until no movement of the liquid was seen and the cavity surface had a glossy appearance. The material was then light-cured (Cotolux, Coltene/Whaledent) for 20 seconds.

Figure 4. Venus Flow in the axial-pulpal area.

Figure 5a. Completed restoration.	Figure 5b. Postoperative bite-wing radiograph.

The next step was placement of a flowable composite. The product used in this case was Venus Flow shade A2 (Heraeus Kulzer, Figure 4). To ensure proximal contact, a ContactPro (CEJ Dental) was used. The remainder of the cavity was filled with Venus Composite Resin shade A2 under shade T1. The restoration was completed by finishing with 30 fluted carbide burs (Midwest) and composite polishing tips (Politip, Ivoclar Vivadent),  followed by a slurry of pumice. The rubber dam was removed, and the occlusion was checked (Figure 5a). A postoperative bite-wing radiograph indicated that there was no discernible space between the floor of the cavity and the bottom of the restoration (Figure 5b).

A small amount of composite on the buccal surface of the teeth can be seen. This is because at the time the patient was undergoing orthodontic treatment with Invisalign, and the composite was required for that treatment.

CONCLUSION

A number of products are available for use as cavity liners. Some of these, such as glass ionomers and zinc phosphate, can also be used as bases and cements. Dentin bonding agents serve to increase the retention of a resin restoration to the cavity preparation. While doing so, they are acting as a cavity liner by sealing the dentin (as do conventional liners). Numerous dentin bonding agents are available. The recently introduced seventh-generation bonding products are much easier to use than previous materials. Their primary advantages are a reported decrease in postoperative sensitivity due to effective cavity-lining properties and a decrease in treatment time compared to earlier versions.

Dentin bonding agents are not meant to eliminate the need for other conventional liners. However, they are an addition to the cavity liners available for clinical use.

References

1. Baum L, Phillips R, Lund M. Textbook of Operative Dentistry. Philadelphia, Pa: WB Saunders; 1981:19, 2.

2. Weiner R. Liners, bases, and cements in clinical dentistry: a review and update. Dent Today. Aug 2003;22:88-93.

3. Brannstrom M. Reducing the risk of sensitivity and pulpal complications after the placement of crowns and fixed partial dentures. Quintessence Int. 1996;27:673-678.

4. Brannstrom M. Etiology of dentin hypersensitivity. Proc Finn Dent Soc. 1992;88(suppl 1):7-13.

5. Baum L, Phillips RW, Lund MR. Textbook of Operative Dentistry. 3rd ed. Philadelphia, Pa: WB Saunders; 1995.

6. Hagan K, Davis A, Belcher M, et al. Microleakage of class II restorations. J Dent Res. 2003;special issue:Abstract 933.

7. Vettraino JT, Neme A-ML, Pink FE, et al. Effect of cavity treatment on in vitro amalgam leakage. J Dent Res. 2003;special issue:Abstract 1322.

8. Bayne SC, Thompson JY, Swift EJ Jr, et al. A characterization of first-generation flowable composites. J Am Dent Assoc. 1998;129:567-577.

9. Bergenholtz G, Cox CF, Loesche WJ, et al. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol. 1982;11:439-450.

10. Farah J, Powers J. Self-etching bonding agents. The Dental Advisor. Oct 2003;20:1-2.

11. Peuker M, Janz K, Dubbe J. Comparison of total working times of self-etching adhesives. J Dent Res. 2003;special issue:Abstract 861.

12. Ito S, Tay FR, Hashimoto M, et al. Effects of multiple all-in-one adhesive coatings on dentin bonding. J Dent Res. 2004;special issue:Abstract 233.

13. Butt S, Burgess JO, Xin X. Dentin bond strength of bonding agents to moist and dry dentin. J Dent Res. 2003;special issue:Abstract 562.

Dr. Weiner received his DMD degree from Tufts University in 1986. He is a fellow of the Academy of General Dentistry, the American College of Dentists, and the Pierre Fauchard Academy. He has written many articles and presented numerous lectures on the topic of liners, bases, and cements. He maintains a private practice in family and cosmetic dentistry in Millis, Mass, and can be reached at randy@weinerdmd.com.

Continuing Education Test No. 70.1

After reading this article, the individual will learn:

• why cavity liners are used, and
• why seventh-generation bonding agents can be used as cavity liners.

1. Current understanding is that postoperative sensitivity exists due to _____ :
a. the toxic effects of dental materials.
b. the influx of bacteria into the dentinal tubules.
c. fluid movement within the gaps at the tooth-restoration interface.
d. none of the above.

2. The following is (are) a characteristic(s) of a cavity liner:
a. It is a barrier to chemical irritants.
b. It is not used for thermal insulation.
c. Materials are usually 0.5 mm thick when placed.
d. all of the above

3. Which of the following materials is NOT used as a cavity liner?
a. varnish
b. calcium hydroxide
c. zinc polycarboxylate
d. glass ionomers

4. Traditional resins undergo polymerization shrinkage, which allows a gap to form at the tooth-resin interface. Flowable resins have a higher modulus of elasticity, which promotes a reduction in microleakage.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true

5. Sixth-generation bonding agents are products that have the etchant, primer, and bonding agent in separate containers, while seventh-generation agents have the etchant, primer, and bonding agent in the same bottle.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true.

6. What percentage of respondents who currently use or have used a self-etching bonding agent report a reduction in postoperative sensitivity?
a. 34%
b. 44%
c. 54%
d. 64%

7. Bonding agents with a high film thickness will tend to exhibit a radiolucent zone on a bite-wing radiograph, and seventh generation products are not associated with this phenomenon.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true.

8. Self-etching dentin bonding agents CANNOT be used on ______:
a. sclerotic dentin without pre-etching.
b. sclerotic dentin with pre-etching.
c. dry dentin.
d. wet dentin.

To submit Continuing Education answers, download the answer sheet in PDF format (click Download Now button below). Print the answer sheet, identify the article (this one is Test 70.1), place an X in the box corresponding to the answer you believe is correct, and mail to Dentistry Today Department of Continuing Education (complete address is on the answer sheet).

The more traditional, older cements were luting materials that relied on mechanical retention, such as long axial walls, taper, and precise fit. These conventional cements filled the gap between the restoration and the tooth, and nothing more. The newer adhesive cements stabilize the entire system of components by adhesively bonding to both the restoration and the tooth. Adhesive cements bond the gap between the restoration and the tooth, creating a “monobloc.” The adhesive cements have additional required properties: they must also be functional, color matched, and biocompatible.

The choice of cement is defined by the procedure and the materials that are involved; no one cement is necessarily ideal for all purposes. The selection of a particular cement in the dental practice should be based on its strength, reliability, predictability, aesthetics, and most importantly, ease of use. Over the past decade, adhesive resin cements have become increasingly popular among dentists. After all, resin cements bond to enamel and dentin and develop micromechanical attachments to restorative metals and ceramics. On the other hand, zinc phosphate and polycarboxylate cements have no adhesion or attachment to enamel, dentin, metal, or ceramic.

While the properties of resin cements are generally far better than the earlier luting cements such as zinc phosphate and polycarboxylate, their use has been hampered by the confusion that surrounds their indications and utilization. The main culprits responsible for this uncertain state of affairs are the number of steps typically involved in the cementation procedure and the associated clinical challenges involved in the chairside application of a long and complex restorative protocol.

Ideally, a cement should function simply and effectively by adhering to all dental and restorative surfaces (enamel and dentin, metal and porcelain). It should involve little or no technique sensitivity (such as chairside mixing, multiple sequential layer applications, drying or wetting requirements, or a long self-cure setting time). Cementation should be easily performed by the dentist and the assistant, or the dentist alone.

Figure 1a. Rinse and leave moist.	Figure 1b. Automix cement directly into crown.
Figure 1c. Place crown onto preparation.	Figure 2a. Rinse tooth and damp dry.
Figure 2b. Mix primer and apply.	Figure 2c. Wait 30 seconds.
Figure 2d. Gently air dry.	Figure 2e. Apply metal primer.
Figure 2f. Place base and catalyst onto mixing pad.	Figure 2g. Mix cement.
Figure 2h. Load cement into crown.	Figure 2i. Place crown onto preparation.
Figure 3a. Rinse and damp dry.	Figure 3b. Activate capsule.
Figure 3c. Load capsule into triturator.	Figure 3d. Mix cement.
Figure 3e. Place capsule into dispenser.	Figure 3f. Load cement into coping.
Figure 3g. Place crown onto preparation.

Resin cements fall into 3 major categories, which are distinguished by their curing modes:

(1) Light-cure resin cements are typically used for thin, metal-free restorations (such as porcelain veneers) and metal-free orthodontic retainers and periodontal splints. For these cements, it is essential that the curing light reach every part of the adhesive in order to ensure polymerization. If the resin is too deep, the ceramic too thick, and not enough light reaches the photoinitiators, then the luting material will not set completely. Ultimately, bonding and restorative failure are the result.

(2) Dual-cure resin cements can be used for metal-free inlays, onlays, crowns and bridges, and where enough self-cure initiators are included, for metal and ceramo-metal restorations as well. In these applications, the beam of the curing light may reach most of the resin cement, but the dentist wants the extra assurance that the material will set in questionable areas. Typically, once the dual-cure resin has been photoinitiated, the cement immediately adjacent to the light will cure in a matter of seconds while simultaneously initiating a self-cure reaction in the remaining cement that has not been illuminated.

(3) Self-cure resin cements are used for metal inlays and onlays, metal and ceramo-metal crowns and bridges, and endo-dontic posts. These cements are not reactive to light; they polymerize by chemical reaction only when the separate components are physically mixed together.

Following are some of the important parameters that should be considered in the selection of resin cement:

(1) Film thickness. This is a measure of the minimum thickness that a particular product can assume under loading and functional pressure while maintaining its strength and other properties. Most resin cements have film thicknesses from 10 um to 30 um. It may seem at first glance that this could hinder the complete seating of a restoration. However, the typical tooth-restoration gap that is seen with a good technician is about 50 um, and often a far greater space is observed. (Zinc phosphate has a film thickness of 25 um.)

(2) Radiopacity. The visibility of the cement in subsequent recall radiographs is very important. This is what allows the dentist to distinguish between cement lines and recurring decay.

(3) Consistency. Cements run the gamut from very viscous to very fluid. The choice is a matter of personal preference. Some of the very thick resins require ultrasonic vibration during the seating of the restoration. Some cements are so thin that they will not effectively fill the gap between the tooth and the restoration.

(4) Extraoral working time. This is typically not an issue for the newest automix cement materials. Also, dentists who work with assistants have fewer working time-related problems. If the dentist is working alone or trying to seat multiple restorations concurrently, then a longer working time is appropriate. However, in most 4-handed practices that use automix cartridges or devices, a shorter extraoral working time is appropriate.

(5) Set time. As a cement is setting, it is a good idea to have constant and continuous finger or occlusal pressure on the restoration to prevent its displacement from the cavity. The fluid pressure of the unset cement tends to extrude the inlay, onlay, or crown away from the preparation into high occlusion unless there is a barrier to this movement. At the set time, the pressure is no longer required. The final steps of excess cement removal can be completed at this time.

(6) Rock-hard set time. Within a few minutes after the set time is reached, the cement becomes sufficiently hard that it cannot be penetrated with a sharp explorer. At this stage, the marginal cements can be polished with conventional procedures.

(7) Expansion. The post-cementation expansion of resin cements is unlikely to affect metal or ceramo-metal crowns and bridges. But it can be problematic for all-ceramic restorations if the rate of expansion is too great or too rapid. It is generally accepted that cements that have less than 4% linear expansion are unlikely to cause restorative failures.¹

(8) Translucence. While cements come in a variety of shades and opacities, often the best aesthetic results are created by translucent or relatively translucent resins. At the marginal interface, a color discrepancy often exists between the restoration and the tooth. An aesthetic gradient or color transition is best accomplished by an adhesive luting material that can blend into both.

Having considered the clinical and functional parameters of cements, the next major issue of concern is the ease of use. How many steps are involved in readying the prepared tooth for cementation? How many steps are involved in the preparation of the internal surface of the crown? And finally, how many separate steps are required to prepare the cement components for loading into the crown?

The clinical steps required for PFM cementation with 3 popular cements² are described in the Chart. (The common preparation steps of removing the provisional crown and cement and pumicing the tooth are common to all the cements and not included in the comparison. The common crown preparation steps of microabrading or etching the internal surface of the coping are also not listed separately.)

After seating for each of the cementation techniques described, the margins should be partially light cured and excess cement removed. Then the margins can be fully light cured and then polished after the cement is set.

Given chairside stress levels, the more straightforward a procedure, the more readily it is adapted into daily clinical use. Since chairside time is an expensive commodity (running from $5 to $10 per minute), the more efficient a cementation procedure, the more valuable to the practitioner (assuming, of course, that all other clinical parameters are comparable). Each additional step (particularly in long, involved, multiphase procedures) introduces the risk of clinical error or technique sensitivity; the greater the number of steps, the greater the overall risk.

The significant advances in the techniques listed in the Chart include the elimination of the tooth preparation steps (etching and priming and bonding) for Embrace WetBond Universal Resin Cement (Pulpdent) and RelyX Unicem (3M ESPE). Capsule activation and a triturator are required for RelyX Unicem; Panavia F2.0 (Kuraray) simply is pad-mixed; and Embrace is auto-mixed with a dual-barrel syringe through a mixing tip. Panavia F2.0 is spatulated into the crown, while RelyX Unicem and Embrace are loaded directly. In each case, setting of the cement and cleanup are similarly straightforward.

CONCLUSION

Today’s resin cements offer a variety of clinical options. They are clinically easy to use and predictable, and continuing development is simplifying the cementation procedure on a regular basis. Resin cements are adhering to dental surfaces (dentin and enamel) and bonding to our commonly used restorative materials (metals and ceramics). They relate these substrates so effectively that for all intents and purposes, they behave as a monobloc, incorporated into a single, functional unit.

Material technology advances have eliminated the need to etch or prime the tooth surface and have simplified mixing and dispensing tremendously. As a result, the technique sensitivities that existed with resin cementation have mostly been overcome. With protocol simplification, the confusion that surrounded cementation has been eliminated.

References

1.CRA Newsletter. October, 2004;28(10):1.

2.CRA Newsletter. August, 2004;28(8):1-2.

Dr. Freedman is past president of the American Academy of Cosmetic Dentistry and associate director of the Esthetic Dentistry Education Center at the State University of New York at Buffalo. He is also director of postgraduate programs in aesthetic dentistry at the Eastman Dental Center in Rochester, NY, and university programs in Seoul, South Korea, and Schaan, Liechtenstein, and chairman of the Clinical Innovations Conference in London. He is the author or coauthor of 9 textbooks, more than 200 dental articles, and numerous CDs, videotapes, and audiotapes. He is a team member of REALITY and a past director of CE programs in aesthetic dentistry at the Universities of California at San Francisco, Florida, UMKC, and Baylor College. A diplomate of the American Board of Aesthetic Dentistry, he lectures internationally on dental aesthetics, dental technology, and photography. Dr. Freedman maintains a private practice limited to aesthetic dentistry in Toronto, Ontario, and can be reached at (905) 513-9191.

This article is designed to demonstrate many of the outstanding properties found in direct resin bonding techniques and to refute certain misconceptions that exist.^3,4 Important concepts include the following:

Figure 1. Fractured direct resin veneer—12.5 years post-op after preparation—note long bevels.	Figure 2. Primer and bonding adhesive in place. Primer on exposed dentin and enamel only. Adhesive on both tooth surface and composite resin. Polymerized.
Figure 3. Application of Creative Color Opaque A1 to block out underlying darkness while blending into external shade of microfill. Carried to middle of bevel only. Polymerized.	Figure 4. Initial placement of microfill B1 (used 12.5 years previsously) with 8A titanium coated instrument.
Figure 5. Continued sculpting and blending microfill with IPTC short-bladed titanium coated instrument.	Figure 6. Application of microfill complete and polymerized. Note: thorough blending of new material into the old microfill surface.
Figure 7. Use of Brasseler ET9 12 fluted carbide bur to start contouring and blending of one material into another.	Figure 8. Use of coarse FlexiDisc to complete blending of one material into another.
Figure 9. After use of the coarse disc, note the complete blending of new material into old microfill with no demarcation.	Figure 10. Continuation of polishing through various grits of FlexiDisc—medium, fine, and superfine—to complete the finishing and polishing process.

(1) Direct resin bonding truly stands the test of time.
(2) An explanation in simple terms of the science of bonding and the clinical significance of understanding it; pinpointing reasons for its failure.^5,6
(3) Direct resin bonding is a quality technique, and the aesthetic clinician must be adequately remunerated to perform to perfection.⁷
(4) Direct resin bonding is not a second-choice alternative. In fact, it frequently outperforms lab-driven techniques.⁸
(5) Composites are not only dentistry’s most useful materials, but they also conserve the most tooth structure.⁹
The versatility of these materials is so great that a wide variety of clinical situations are indicated for their use^10,11: (1) class I, II, III, IV, and V restorations of all kinds; (2) removal and replication of enamel defects; (3) diastema closure¹²; (4) incisal reinforcement; (5) tooth lengthening; (6) complete veneering; (7) restorative orthodontics/rearrangement; (8) smile development and widening; (9) development of proper canine rise, incisal guidance, and increase in vertical dimension; (10) gingival replication¹³; (11) patient and lab mock-ups; (12) temporary partials; (13) full-bonded crowns; (14) resin-retained bridges; (15) repairs of all kinds¹⁴ (composite, porcelain, porcelain and metal, exposed dark metal gingival margins, and unsightly metal [gold] margins); (16) restorative dentistry for cleft palate patients¹⁵; and (17) masking and increasing value of tetracycline stained dentition,16 the unsightly single discolored tooth, endodontic and implant access areas, and metal posts.

CASE REPORT
A patient came into my office almost 13 years ago desiring a reshaped, brighter, and lighter smile. She had previous grafting, but the recession was so severe that even though a good result was achieved, she still needed some periodontal-enhancing restorative treatment. She also required some gingival replication to create a better smile profile. At that time, we used Renamel Gingafill (Cosmedent), a gingival-colored microfill, to replicate the labial contours and to keep her from having hyper-extended teeth.

Figure 11. Finishing and polishing of proximal surfaces with 15-µm diamond strips followed by fine/superfine FlexiStrips (shown here).	Figure 12. Invisible repair completed. Things to note: (1) retention of polish long-term; (2) excellent color stability; (3) no demarcation of any kind between old and new microfill; (4) surface texture of veneers exhibits no wear; (5) no recession after 12.5 years—notice health of gingival tissue; and (6) note gingival recession on lower anteriors and compare with upper veneer—what does that tell you?
Figure 13. Smile immediately after direct placement of 8 upper anterior veneers—May 23, 1991.	Figure 14. Smile 12.5 years post-op demonstrating an invisible repair and total color stability—December 9, 2003.
Figure 15. May 23, 1991: immediate post-op.	Figure 16. December 9, 2003: same vibrant smile showing invisible repair.
Figure 17. Additional long-term results showing 8 anterior veneers 8 years post-op. Note the exceptional gingival health of all long-term results.	Figure 18. Additional long-term results showing 4 incisors veneered against existing dentition 8 years post-op.
Figure 19. Additional long-term results showing anterior veneers 10 years post-op.	Figure 20. Additional long-term results showing 6 anterior veneers 18 years post-op.

What allows such outstanding long-term results?
(1) The ability to maintain a long-term polish. The proper material selection that accurately simulates the enamel surface. The only material to date that can achieve this long-term is microfill. Why? Because the smaller and more uniform particle size allows you to polish to the most lustrous, enamel-like surface known to dentistry, and it will maintain this polish long term.¹⁷

(2) Microfill has a great resistance to wear. It exhibits minimal or no plucking because of the density of the filler and small particle size, and since it can be polished to such a high shine, the material tends to resist wear due to abrasion.

(3) Microfill has excellent tissue compatibility. It shows great margination beneath the free margin of the gingival because of the small particle size.

(4) The outstanding color stability of microfill is probably due to the small particle size and overall density of the material that prevents plucking, pitting, wear, and loss of surface texture.¹⁸

(5) Highly polished microfills offer superior aesthetics because their reflective and refractive index mimic tooth structure most accurately. Resin materials are properly pigmented to mimic natural tooth structure, and resin has more lifelike translucency and natural fluorescence that can match both natural dentition and porcelain.

(6) Invisible repairs with color-stable microfill composites are easily accomplished. The use of microfill allows for better and more invisible reparability due to its small particle size. When applied and finished properly, the new restoration blends into the old without demarcation.
Knowledge of the use of proper polishing systems makes margins between the new and old material completely disappear when one truly understands how to use them.

Of course, color stability plays an important role in your restoration. When color doesn’t change, the new and old material blend together as one, without distinction.

Figures 1 through 16 provide a detailed description of the patient’s repair. In addition, Figures 17 through 20 demonstrate other long-term results achieved with microfill composite.

CONCLUSION
All of the qualities I have described are meant to demonstrate how composite restorations can truly stand the test of time. In my personal practice, I have worked with composites for more than 30 years and completely limited my practice for the last 15 years to direct resin bonding. My patient files probably represent in dentistry today one of the largest bodies of actual clinical results working with composite resins.

References

1. Mopper KW. The subtleties of anterior direct-bonded class III restorations. Pract Periodont Aesthet Dent. 1990;2(6):17-20. (Now: Practical Procedures and Asesthetic Dentistry.)
2. Mopper KW. The value of the hands-on learning experience. J Calif Dent Assoc. 1995;23(4):37-40.
3. Meijering AC, Creugers NH, Roeters FJ, et al. Survival of three types of veneer restorations in a clinical trial: a 2.5-year interim evaluation. J Dent. 1998;26(7):563-568.
4. Garber DA. Direct composite veneers versus etched porcelain laminate veneers. Dent Clin North Am. 1989;33(2):301-304.
5. Duke ES. The science and practice of dental adhesive systems. Compend Contin Educ Dent. 2003;24(6):417-424.
6. Mopper KW. Why dentists miss shades frequently. Dent Econ. 1994;84(1):82-83.
7. Willhite C. Dramatic smile makeovers using direct resin veneers. Compend Contin Educ Dent. 1997;18(7):646-657.
8. Mopper KW. Creative solutions for everyday esthetics. Dental Practice Report. 2000;8(6):46-50.
9. ADA Council on Scientific Affairs. Direct and indirect restorative materials. J Am Dent Assoc. 2003;134(4):463-472.
10. Mopper KW. Renamel Restorative System Manual. Chicago, Ill: Cosmedent, Inc; 1994.
11. Feigenbaum N, Mopper KW. A Complete Guide to Dental Bonding. New Jersey: Johnson & Johnson Dental Products Co; 1984.
12. Mopper KW. Diastema closure: A natural for direct bonding procedures. Pract Periodont Aesthet Dent. 1990;2(1):22-28. (Now: Practical Procedures and Asesthetic Dentistry.)
13. Trushkowsky RD. Camouflage of recession with a gingival-simulating composite resin. Esthet Dent Update. 1995;6(2):41-42.
14. Fahl N Jr. Predictable aesthetic reconstruction of fractured anterior teeth with composite resins: a case report. Pract Periodontics Aesthet Dent. 1996;8(1):17-31.
15. Mopper KW. Aesthetic dilemma: restoring the quality of life in a cleft lip, cleft palate patient. Dent Today. 2000;19(6):46-53.
16. Mopper KW. Pink opaque for stained dentition. Contemp Esthet Restor Pract. 2000;4(4):40-41.
17. Miller MB, Costellanos IR. Microfills. REALITY. 2003;17:576.
18. Lu H, Roeder LB, Powers JM. Effect of polishing systems on the surface roughness of microhybrid composites. J Esthet Restor Dent. 2003;15(5):297-303.
19. Mopper KW. Porcelain versus composite: What’s the treatment of choice? Synergy 1990;Winter:1-10. (For more information, contact Dental Lab Publications, 205 Liberty Square, East Norwalk, CT 06855.)
20. Mopper KW. Dentistry’s most underutilized material—microfill: a key ingredient for successful anterior esthetics. Dental Town. 2003;4(1):20.

Dr. Mopper has been a clinician and a teacher with a practice in Winnetka, Ill, for more than 40 years. He is cofounder and chairman for Cosmedent, and researches new materials and techniques for dentistry. He is also founder and fellow of the American Academy of Cosmetic Dentistry, a fellow of the American Academy of Pediatric Dentistry and the America College of Dentistry, and a member of the America Academy of Aesthetic Dentistry. He can be reached at (847) 441-6080.

What I will offer you is a down-and-dirty look at what I term the unwritten. By unwritten Irefer to the many items left unsaid when authors seek to share their approach to posterior composite placement, such as the strategizing of how 2 or 3 or 4 adjacent multisurface resins might be placed so as to avoid utter chaos. Define chaos as having to scramble to repair an open contact that has food trap written all over it and then running 20 minutes behind in your schedule (which may grow to 30 minutes as you try to adjust the mile-high occlusion you created). We’ve all been there!

Please note: If placement of composite resins is to be profitable and satisfying (as it should be), we had better learn to place a quadrant of resin restorations with the same aplomb that we enjoyed when placing a quadrant of amalgam restorations. Scheduling an hour to place a single MOD resin won’t stoke the retirement plan in today’s economy.

THE TOOLS

I honestly admit to you that posterior composite resins were low on my list of fun things to do for the very reasons alluded to above. Add to that the fear of sensitivity and resultant paranoia about making things worse rather than better, and you’ve begun to appreciate this authors former disdain for the entire process.

This outlook has changed in the past 2 years owing to a parade of new products that have helped to streamline the placement of composite restorations. The tools currently available to us prove that the dental industry has listened to our complaints, and in keeping with good old American enterprise, its players have tried to outdo each other in an effort to meet our needs. We win!

The components that have been improved upon are, in no particular order, the rubber dam (Yes! the rubber dam), bonding agents, matrix systems, composite itself, instruments used to place and manipulate it, and gizmos used to finish and polish composite resin. Even the handpieces available to us have turned it up a notch. As is typical in articles of this nature, I will be describing the tools that I’ve adopted, but I acknowledge that they are representative of their class, knowing full well that you may be using equally effective items in your own practice.

NANO-WIZARDRY

Unless you’ve been hiding under a rock, the term nanotechnology already should be familiar to you. To keep a long story very short, this term describes a method for producing a new class of composite resin based on particle sizes in the 20- to 75-nm range (1 micron [u] = 1000 nm; composites produced in the 1990s to 2000 were based upon filler sizes of 400 to 600 nm). At 20 nm we are approaching a composite build from the atom up. Using a blend of nanomers and nanomer clusters, 3M ESPE has brought us Filtek Supreme, an all-purpose anterior/posterior composite resin designed to possess the strength of a micro-hybrid with the polishability of a microfill. This is the resin system I use for the techniques described in this article, but as noted above, the individual clinician can make his or her own choices from a number of available products. While completion of long-term studies are always needed to bear out a manufacturers claims, the thought and testing that went into Filtek Supreme are compelling to this author.1-3

First and foremost, the ability to freehand sculpt a Filtek Supreme restoration plays into the quadrant strategy that we will soon discuss. Filtek Supreme will remain exactly where you placed it last. It will not slump. It will not cure via ambient light. A Filtek Supreme restoration can be brought to a near completion state with hand instruments before final cure. Finishing time is slashed. Unlike many of its micro-hybrid relatives, Filtek Supreme will yield nicely to an 8-fluted carbide finishing bur such as those found in Garrisons G-Block Finishing and Polishing system. And as advertised, it can be brought to a near microfill finish with rubber polishing instruments. Finally, for whatever reason (perhaps Filtek Supremes low polymerization shrinkage of 2%), the dreaded white line seems to have become a thing of the past. From a clinical perspective, it seems apparent that we’ve been granted freedoms only dreamed about in the days of amalgam.

THE MATRIX: REBANDED!

Actually, it’s more about the Wedge! If you caught my. All In the Contacts article in the September 2003 issue of Dentistry Today, you received an overview of the class II matrix business. In that article I referenced Garrison Dental Solutions. Wedge Wand as a nice accompaniment to its Composi-Tight Gold sectional matrix system. My assessment has since changed from to indispensable. The Wedge Wand might even be termed the missing link. When used as instructed by Garrison, the chances of inadequate contacts all but disappear.

S-T-R-E-T-C-H I-T

Do not skip this paragraph! I’ll beat a dead horse. The rubber dam will accelerate the whole process. It will contain flying amalgam debris, handle management of soft tissue, and assist you in moisture control. But not just any rubber dam will do. You need one that can get behind the tightest contact between the rubber dam (RD) clamp arm and the retromolar tissue without tearing; one that can be applied in seconds. The Hygenic Flexi-Dam (Colt/Whaledent) is that dam. Look for the purple dam in my photos. Couple this with Colt/Whaledents Hygenic Fiesta (color-coded) RD clamp kit and you’re home free.

SPECIAL AGENT: SELF-ETCH BOND

Self-etching/self-priming bonding agents have not only accelerated my resin placement, they’ve reduced the number of root canals performed in my practice. Post-operative pain phone calls have all but disappeared; the patient wins you win. My weapon of choice: Parkells Brush and Bond. I’m partial to the little purple micro brush that is part of the system, not to mention the utter speed of application.

REV IT UP

Figure 1. NSK Americas Ti Max 400 electric high-speed handpiece.

If you haven’t had the pleasure of zipping through a quadrant of amalgam with an SS White 245 carbide bur and NSKs Ti Max 400 electric handpiece (under a Flexi-Dam of course), then dental nirvana awaits you. The Ti Maxs focused power (read: torque) will allow an operator to divest a patient of his or her 25-year-old quadrant of alloy in under 5 minutes without getting cramps in your fingers. This dream must be experienced to be appreciated (Figure 1).

The products noted above are the core players that I use. When coupled with a few extras and a strategy regarding how to start and how to finish, they will empower you to become a master at posterior resin placement. Lets dig in.

PRELIMINARIES

Before you pick up a handpiece, observe the occlusal form of the amalgams you will be replacing. Are they excessively worn and part of an occlusal landscape reminiscent of the tundra (read: flat), or are they relatively well-preserved amidst a well-defined range of cusps. Throw some articulating paper in there for good measure to see where the primary supporting points remain. This preliminary determination will guide you as to which method you might use to reconstruct the occlusal surfaces. It makes no sense to sculpt beautiful anatomy in an excessively worn quadrant and then spend 20 minutes leveling it back to tundra status.

Next, decide which tooth will be the anchor tooth, that is, the one that will be reconstructed first, around and against which the rest will be reconstructed. Typically, this will be a 3- to 4-surface restoration found in the middle of the pack.

Figure 2. Hole punch in FlexiDam with 1/4 inch slit.

Once your patient has been anesthetized, place the Flexi-Dam, preferably with the retaining clamp one tooth distal to the last tooth in the quadrant that you plan on restoring. This isn’t always possible, but sectional matrices can be employed even in the presence of a rubber dam clamp, as will be demonstrated. We use the slit technique, which employs a single hole punch from which is extended a scissors slit usually one-quarter inch in length (Figure 2). This usually allows the dam to be stretched one tooth mesial to the most forward tooth to be restored. This method, while not as moisture-proof as punching each tooth separately, is very fast and will solve most issues requiring a rubber dam. Now you are free to remove the old alloy quickly, knowing that your patient won’t be ingesting it for lunch.

What follows is my typical approach for restoring a quadrant with 2 variants. In the first case, occlusal anatomy is hand sculpted (BAC = bite adjusted after curing). In the second case, occlusal form is determined via the patient occluding into uncured composite prior to light curing (BBC = bite adjusted before curing). Please note that in order to make a point with the best photo possible, you may notice other quadrant shots mixed into the sequence.

CASE 1: THE CLASSIC MO, MOD, DO

Figure 3. Evaluating the occlusion of a deserving quadrant before preparation.

Of course the patient needed crowns, but the cost of an opposing bridge dictated that composite restorations be used to restore this lower right quadrant. Although this quadrant might have been restored more easily with the BBC method, it was done via the BAC method. As you can see in Figure 3, articulating paper (Accufilm II, double-sided, by Parkell) has been used to provide a heads-up on where the teeth occlude. Tooth No. 30 was chosen as the anchor tooth from which to begin the restoration of the quadrant.

Figure 4. Quadrant isolated, divested of amalgam, and ready to be restored.

In Figure 4, the Hygenic Flexi-Dam has been placed and secured mesially with a Wedge Wand. The alloy has been cleared, and teeth are ready for a 5-second phosphoric acid etch employed to freshen up the nonprepared bonding surfaces. This is typically followed with an application of Parkells Brush and Bond prior to composite placement.

Figure 5. The anchor tooth No. 30 is restored first using an Automatrix to assist in proximal wall formation.

In Figure 5, a Dentsply Automatrix has been employed to allow for buildup of the gingival boxes with an initial layer of flowable composite (Synergy Flow, Colt/Whaledent), followed by the first application of Filtek Supreme.

Figure 6. A second layer of Filtek Supreme is applied.	Figure 7. Full anatomic buildup of tooth No. 30.
Figure 8. Contouring by dragging out composite from central fossa against existing cusp.	Figure 9. Sharpening up the anatomy with a Garrison TN004 composite instrument.

In Figure 6, a second layer of Filtek Supreme has been freehanded onto the preparation and cured. Figure 7 demonstrates the full anatomic buildup of tooth No. 30 following angled instrument carving (AIC). AIC resin placement relies upon the remaining cuspal anatomy to guide resin shaping using the existing cusp, against which the plastic instrument is dragged beginning in the central fossa groove (Figure 8; instrument shown is Hu Friedy XTS Goldstein Flexithin Composite Instruments 1DE). Fine tuning anatomy can be accomplished easily with Garrisons TN004 extra thin blades, shown in Figure 9. Typically, 2 applications of Filtek Supreme will restore to full contour without risk of uncured resin or excessive shrinkage.

Figure 10. Using a Hu Friedy XTS instrument to roll the marginal ridge toward center, creating a more anatomic embrasure.

Marginal ridge formation is accomplished easily by setting the tip of the XTS instrument between the matrix band and composite, and rolling the leading edge composite back toward the center of the tooth to form an embrasure. Contacts between adjacent teeth occur 1 to 2 mm below the crest of the embrasure, not at the apex of the marginal ridge acommon misinterpretation (Figure 10).

Figure 11. Garrison matrix in place on tooth No. 29 ready to build against anchor tooth.	Figure 12. Restoring tooth No. 31 with Garrison section matrix and Addent Tri Max.
	Figure 13. Completed quadrant.

Once the anchor tooth (No. 30) has been completed, it is now an easy task to situate a Composi-Tight Gold matrix and retainer on the distal of tooth No. 29 and restore it in kind (Figure 11). As shown in Figure 12, an additional Composi-Tight Gold matrix can be placed on the mesial of tooth No. 31 and secured by a Wedge Wand even in the presence of a rubber dam clamp. Shown is Addents Tri Max matrix forming device used to aid in establishing a solid contact in the absence of a retainer/separator ring. Figure 13 demonstrates the completed quadrant.

TIPS ON PLACING THE SECTIONAL MATRIX

(1) Precontour the matrix in your fingers so that it will wrap around the tooth rather than hanging up on the gingivae.

(2) Plan on opening the contacts slightly and separating the boxs gingival margin 0.5 to 1 mm from the adjacent tooth for easier matrix and wedge placement.

(3) When placing the Wedge Wand, hold the top edge of the matrix with an index finger to keep it from dislodging occlusally when the wedge is placed.

(4) Attempt to place the wedge to the hub for best separation.

(5) Don’t forget to burnish the matrix in its contact area against the adjacent contact.

CASE 2: FUNCTIONAL OCCLUSAL FORMATION (FOF)

Figure 14. Another deserving quadrant.	Figure 15. Mesial wall of tooth No. 31 reconstructed via freehand placement and shaping of Filtek Supreme.
	Figure 16. Distal wall of tooth No. 30 placed against anchor tooth No. 31 with Garrison matrix. Note placement of retainer ring tynes between wedge and matrix.

Now for the ultimate time saver: note the deserving trio in Figure 14. Please follow the sequence. In Figure 15, following alloy removal and leveling of a fractured DL cusp on tooth No. 31, the mesial wall of tooth No. 31 has been reconstructed, freehand, with Filtek Supreme and a Garrison TN004 composite instrument. Tooth No. 31 has been chosen as the anchor tooth. Composite placement was preceded by phosphoric acid 5-second prep and application of Parkells Brush and Bond. Note in Figure 16 that a Garrison matrix has been placed on the distal of tooth No. 30 with subsequent construction of the distal wall of that same tooth. Note how the Wedge Wand is inserted to its hub and that the tynes of the Composi-Tight Gold retaining ring are positioned between the wedge and the sectional matrix band. Had the box been wider, placing the tynes outside of the wedge (as opposed to inside) would have made it less likely for the matrix to collapse into the box preparation.

Figure 17. Dam removed with wedge and matrix band left in place in preparation for establishing occlusion prior to final curing.

In Figure 17 the rubber dam has been removed, and the wedge and matrix left in place with the matrix leveled to estimated occlusal height. Leaving these in place prevents bleeding that would interfere with the bonding process. Additionally, a base layer of flowable resin (Synergy Flow, Colt/Whaledent) has been applied to the cavity surface well below final contour. At this point, occlusion is checked for high spots and adjusted on the pre-formed proximal walls of teeth Nos. 30 and 31. The teeth are isolated using cotton rolls during this point in the reconstruction.

Figures 18 and 19. Closed view of occlusal formation. (Imagine having to cut in that occlusion after having overbuilt and cured the surface with composite.)

In Figures 18 and 19 the patient has been instructed to occlude naturally into bulk Filtek Supreme that has been placed in the remaining occlusal voids of teeth Nos. 30 and 31. This process is repeated several times. Each time, excess resin is removed while sculpting the new occlusal surfaces around the imprint of the opposing cusps. Once satisfied that occlusal form matches the opposing dentition, the remaining uncured composite is light cured for final set. Following minor spot adjustments and contour corrections with Garrisons G-Block Finishing and Polishing system and a No. 12 disposable scalpel blade, the restoration is polished with rubber cups and points also found in the Garrison system.

Figure 20. Completed restorations: not pretty, but functional.

In Figure 20 the completed Filtek Supreme restorations can be observed after a final coating with Biscos BisCover. While departing from ideal anatomy, teeth Nos. 30 and 31 have been restored in a logical sequence that ensured sound contacts and occlusal harmony, minus the frustration associated with excessive occlusal adjustment.

It should be noted that maximum care is taken to keep the working areas dry during the “smush bite” process. Prebonding and application of base composite under the Flexi-Dam allows this author to be comfortable with adding the final occlusal layer in the manner described.

CLOSING ARGUMENT

Todays restorative tools allow the skilled operator to place direct posterior restorations that can rival or even exceed their indirect counterparts. Mastering the materials and techniques is the precondition for getting there.

Take away message: The astute operator should employ a modicum of composite strategy and strive to take advantage of todays nanotechnology, self-etching bonding agents, and matrix systems to produce near finished restorations prior to picking up the curing light. In doing so, increased productivity and job satisfaction will replace any prior frustrations formerly associated with the placement of posterior composite restorations.

References

1. Duke SE. Has dentistry moved into the nanotechnology era? Compend Contin Educ Dent. 2003;24(5):380-382.

2. Mitra SB, Wu D, Holmes BN. An application of nanotechnology in advanced dental materials. J Am Dent Assoc. 2003;134(10):1382-1390.

3. 3M ESPE Filtek Supreme Universal Restorative: Technical Product Profile. St. Paul, Minn: 3M ESPE; 2002:44. PDF available at 3m.com/intl/kr/medi/medi5/pdf/Filtek%20Supreme.pdf.

Dr. Goldstein practices general dentistry in Wolcott, Conn. He lectures and writes extensively concerning cosmetics and the integration of digital photography into the dental practice. A contributing editor to Dentistry Today, he has also authored numerous articles for Compendium, CERP, and other international dental publications. He can be contacted at martyg924@cox.net. His current speaking schedule can be found at dhapc.com, while information on his Comfort Zone Cosmetics hands-on seminars is posted at smilevision.net

In the past, the choice of composite resin for posterior teeth was limited. Today, the introduction of improved composite resins with better physical properties and handling has led to a wider range of options for the practitioner regarding which type of composite resin to use to restore posterior teeth. The categories of composite resin to restore class 2 preparations in posterior teeth include hybrid, nanofill hybrid, high-density microfill, and high-viscosity (packable) composite resins (Table 1). These composite resins have demonstrated more in vitro wear resistance than previous small-particle composite resins.^3-5 Clinical studies of the restoration of posterior teeth have shown that the current hybrid composite resins can be considered alternatives to amalgam in routine-sized preparations.^6-11 The expectation is that the nanofilled hybrids will perform as well as or better than hybrid composite resins. While dental amalgam, cast gold, and porcelain/metal are still the standards for posterior tooth restorations because of their durability and ability to resist wear, for routine-sized preparations, composite resins can now be viewed as alternatives to metal restorations.^12-13

An ideal composite resin for restoring posterior teeth should fulfill the following criteria¹⁵:

1. Wear similar to natural tooth structure or dental amalgam.
2. Does not display plastic deformation when in function.
3. Requires a simple technique for placement.
4. Demonstrates minimal shrinkage during polymerization.
5. Displays excellent marginal adaptation and sealing.
6. Possesses a radiopacity equal to or greater than enamel and dentin for ease of radiographic evaluation.
7. Employs a quick, exact, nontooth destructive finishing technique.
8. Is aesthetically pleasing in color and translucency.

Some of the difficulties associated with adhesive composite resins relate to shrinkage and gap formation during polymerization and their subsequent microleakage.¹⁶ Gap formation caused by resin shrinkage can contribute to loss of adhesion, bacterial invasion, recurrent caries, postoperative sensitivity, and pain on mastication.¹⁷ Polymerization shrinkage is one of the main factors that determines the longevity of composite resin restorations.^18,19 When light-curing, placing the light closer to the gingival wall minimizes the thickness of the composite resin and can alleviate some of these problems.²⁰

TREATMENT PLANNING
A successful posterior composite resin restoration is dependent upon a thorough evaluation of the patient’s occlusion and parafunctional habits. Placement of composite resins when a parafunctional habit such as bruxism exists can lead to greater wear of the composite as compared to a metal restoration. It is important to also remember that for patients with parafunctional habits, ceramic restorations will cause significant wear of opposing tooth structure and other restorative materials, including composite resin and metallic restorations. The rate of wear for posterior composite resin restorations is dependent on tooth position in the arch and the size of the preparation.26 Supporting cusps that are replaced with composite resin will demonstrate more wear than nonsupporting cusps. The rate of wear increases as the preparation width at the isthmus increases beyond one third of the intercusp distance.⁷ Even with these considerations, the literature supports the use of composite resin as an equivalent to amalgam in moderately sized class 1 and class 2 preparations.¹²

Some general guidelines to improve clinical success with posterior composite resins include the following:

1. Preparations in which an occlusal contact is supported by tooth structure.
2. Supragingival margins and the ability to place a dental dam.
3. Enamel margins are preferred. However, margins on cementum are acceptable if the margin is supragingival after dam placement.

In cases where initial caries is only on the proximal surface, a conservative slot preparation of the proximal surface combined with a sealant for the occlusal surface will suffice. When the caries extends into the occlusal pits and fissures or if an existing class 2 amalgam or composite resin is being replaced, an isthmus width of one fourth to one third the intercusp distance is preferred to minimize wear of the composite resin in function.

ACHIEVING PREDICTABLE PROXIMAL CONTACTS
A frequent problem with class 2 composite resin restorations has been achieving predictable, anatomic proximal contacts.^15,27 This problem directly relates to the fact that composite resins are viscous materials that cannot be condensed and pushed against matrix bands in a predictable manner. Even the most viscous packable composite resins are liquids that are not dense enough to move a matrix band in order to achieve proximal contact and adaptation via slight movement of the teeth during the placement process.²⁸ Although the use of a wedge before tooth preparation can help compensate for the thickness of the matrix band,¹⁵ modifications in matrix design, type of metal used, thickness, and retainer systems have been introduced to eliminate the problem of poor proximal contacts with composite resin restorations.

CASE REPORT
A patient presented with clinical and radiographic evidence of caries on the mesial and occlusal surfaces of the mandibular second molar and caries on the distal and occlusal surfaces of the mandibular first molar (Figure 1). The patient had a history of latex sensitivity, so a latex-free dental dam (Flexi-Dam [Coltene-Whaledent]) was used for the restorative procedure. The teeth were prepared with a 245 bur (SS White Burs). The preparation design had cavity walls that were convergent or parallel from the pulpal wall. The occlusal cavosurface margins were at right angles to the cusp ridges. This right angle margin allows for a bulk of composite resin at the high-stress-bearing occlusal margin that will prevent fracture of the composite resin. Also, beveling the gingival margin of a class 2 composite resin preparation should be avoided, even if it ends on enamel. Usually, a limited amount of enamel remains at the cervical margin, so beveling this margin removes the remaining enamel, which compromises adhesion.³²

Figure 1. Preoperative view of the mandibular first and second molar.	Figure 2. Class 2 preparations on the mandibular first and second molars.
Figure 3. Placement of a resin-reinforced glass ionomer liner on the pulpal and axial walls of the cavity preparations.	Figure 4. Light-curing the glass ionomer liner with an LED light.
Figure 5. The cavity preparations with glass ionomer liners.	Figure 6. Phosphoric acid etchant applied to tooth preparations.

After tooth preparation (Figure 2), a periodontal probe was used to determine the depth of the proximal boxes from the gingival margin to the marginal ridge. For each proximal box, a disposable Trimax tip was adjusted so that the marginal ridge would be lined up with the instrument when light-curing the composite resin. This occurs after liner placement.

Figure 7. After rinsing the etchant from the tooth, a single-bottle adhesive was applied.	Figure 8. Placement of 2 sectional matrices (ComposiTight with G-Ring, Garrison Dental Solutions) for a MOD preparation.

Figure 9. Supporting a sectional matrix with a bite registration paste without a separating matrix ring.

When restoring the proximal contact, a thinned, stainless steel matrix band allows shaping to achieve a positive, anatomic proximal contact. Although a sectional matrix was not used for this case, a sectional matrix with a retainer ring can be used to restore proximal surfaces of posterior teeth (Figure 8). In some cases, the retainer ring cannot be used because of anatomic variation in width of some posterior teeth. In these circumstances, a sectional matrix stabilized by a wedge can be placed, and the matrix can be supported with bite registration material (Figure 9). Since the preparations were adjacent to each other and there was difficulty placing a sectional matrix with a retainer ring, it was decided to first use a conventional matrix band to restore the mesio-occlusal segment of the second molar. The second molar with the dam clamp in place precluded the use of a matrix retainer, so the matrix was adapted to the tooth for restoration without a retainer.

Figure 10. The Gradia Direct preloaded tubes were warmed in a Calset unit (AdDent).	Figure 11. The use of the Trimax (AdDent) tip to enhance light-curing in the proximal box.

The nanofilled hybrid composite resin chosen for the restoration (Gradia Direct [GC America]) was heated with a Calset unit. Once heated, the composite resin was inserted into the proximal box of the cavity preparation, filling it to the axiopulpal line angle. The Trimax tip was placed into the composite resin, slowly pushing the tip toward the adjacent tooth. The curing light guide was placed, touching the top of the Trimax tip at right angles, and the composite resin was cured for 10 seconds (Figure 11). The space left by the Trimax tip was then backfilled to the height of the proximal box and light-cured.

Figure 12. The preparation was filled with composite resin in increments and light-cured. The final increment was shaped with a hand instrument wetted with adhesive resin.	Figure 13. The margin of the restoration was finished with an egg-shaped finishing bur.
Figure 14. Initial polishing was accomplished with an aluminum oxide-impregnated rubber abrasive point (Astropol, Ivoclar/Vivadent).	Figure 15. Final polish with a diamond polishing paste and a prophylaxis brush.

Figure 16. The restoration of the mandibular first and second molars is completed.

The dental dam was removed, and the slight excess of composite resin at the occlusal margins was finished using an egg-shaped finishing bur (Brasseler, Figure 13). Further definition of the anatomic form was accomplished with an aluminum oxide-impregnated rubber polishing point (Astropol [Ivoclar/Vivadent], Figure 14). The most difficult margin to access of any posterior class 2 restoration is the gingival interproximal margin. Finishing strips do not work well on rounded or concave root and interproximal surfaces. Likewise, rotary handpieces with rotating diamonds and burs are contraindicated for interproximal surfaces in cases such as this because they can create unnatural embrasures and notched and irregular surfaces. This margin can be best managed and finished using a Profin reciprocating handpiece with a Lamineer tip (Dentatus). The flat, safe-sided abrasive Lamineer tip allows for precise and controlled finishing and polishing of the cervical interproximal margin. An alternative instrument that can be used to remove excess resin in these areas is a 12A scalpel blade.

CONCLUSION
The concepts and techniques described in this article can be used to provide patients with durable and aesthetic posterior composite resin restorations. To ensure an anatomic proximal contact, pre-wedging, specialized matrices, and modifications to the curing phase of treatment will eliminate the problems previously encountered when restoring proximal surfaces with composite resin. Postoperative sensitivity associated with posterior composite resins can be minimized by using bondable resin or glass ionomer liners for cavity preparations of moderate depth. The problems associated with gap formation at the gingival margin due to polymerization shrinkage of the composite can be minimized by using a Trimax light curing tip.

References

1. Berry TG, Nicholson J. Traendle K. Almost two centuries with amalgam: where are we today? J Am Dent Assoc 125:382-399, 1994.
2. Lopes GC, Ferreira Rde S, Baratieri LN, et al: Direct posterior resin composite restorations: new techniques and clinical possibilities. Case reports. Quintessence Int 33(5):337-346, 2002.
3. Leinfelder KF, Beaudreau RW, Mazer RB: An in vitro device for predicting clinical wear. Quintessence Int 20(10):755-761, 1989.
4. Kawai K, Leinfelder KF: In vitro evaluation of OCA wear resistance of posterior composites. Dent Mater 11(4):246-251, 1995.
5. Barkmeier WW, Latta MA, Wilwerding TM, et al: Wear assessment of high viscosity and conventional composite restorative materials. Operative Dentistry 26:152-156, 2001.
6. Hickel R, Manhart J: Longevity of restorations in posterior teeth and reasons for failure. J Adhes Dent 3(1):45-64, 2001.
7. Wilder AD Jr, May KN Jr, Bayne SC, et al: Seventeen-year clinical study of ultraviolet-cured posterior composite Class I and II restorations. J Esthet Dent 11(3):135-142. 1999.
8. Lundin SA, Koch G: Class I and II posterior composite resin restorations after 5 and 10 years. Swed Dent J 23(5-6):165-171, 1999.
9. Raskin A, Setcos JC, Vreven J, et al: Influence of the isolation method on the 10-year clinical behaviour of posterior resin composite restorations. Clin Oral Investig 4(3):148-152, 2000.
10. Gaengler P, Hoyer I, Montag R: Clinical evaluation of posterior restorations: the 10-year report. J Adhes Dent 3(2):185-194, 2001.
11. Raskin A, Michotte-Theall B, Vreven J, et al: Clinical evaluation of a posterior composite 10-year report. J Dent 27(1):13-19, 1999.
12. Statement on posterior resin-based composites. ADA Council on Scientific Affairs; ADA Council on Dental Benefit Programs. J Am Dent Assoc 129(11):1627-1628, 1998.
13. Smales RJ, Webster DA, Leppard PI: Survival predictions of amalgam restorations. J Dent 19(5):272-277, 1991.
14. Strassler HE: Predictable and successful posterior packable Class II composite resins. Amer Dent Instit for CE 75:15-23, 2001.
15. Strassler HE, Goodman HS. Restoring posterior teeth using an innovative self-priming etchant/adhesive system with a low shrinkage hybrid composite resin. Restorative Quarterly 5(2):3-8, 2002.
16. Uno S, Shimokobe H: Contraction stress and marginal adaptation of composite restorations in dentinal cavity. Dent Mater J 13(1):19-24, 1994.
17. Terry DA: Mastering the technique of direct posterior composite resins. Cont Esthet Rest Pract 5(6):14-26, 2001.
18. Ferracane JL: Using posterior composites appropriately. J Am Dent Assoc 123(7):53-58, 1992.
19. Peutzfeldt A: Resin composites in dentistry: the monomer systems. Eur J Oral Sci 105(2):97-116, 1997.
20. Ericson D, Derand T. Increase in in-vitro curing depth of Class II composite resin restorations. J Prosthet Dent 70:219-223, 1993.
21. Maciel KT, Carvalho RM, Ringle RD, et al: The effects of acetone, ethanol, HEMA and air on the stiffness of human decalcified dentin matrix. J Dent Res 75(11):1851-1858, 1996.
22. Perdigao J, Swift EJ Jr, Heymann HO, et al: Effect of a re-wetting agent on the performance of acetone-based dentin adhesives. Am J Dent 11(5):207-213, 1998.
23. Ritter AV, Heymann HO, Swift EJ Jr, et al: Effects of different re-wetting techniques on dentin shear bond strengths. J Esthet Dent 12(2):85-96, 2000.
24. Strassler HE. Transitions from the familiar to the new: what bonding system should you use. Incisal Edge 8(7):6-7, 2003.
25. Strassler HE. Applications of total-etch adhesive bonding. Compend Contin Edu Dent 24:427-440, 2003.
26. Manhart J, Neuerer P, Scheibenbogen-Fuchbrunner A, Hickel R. Three-year clinical evaluation of direct and indirect composite restorations in posterior teeth. J Prosthet Dent 84:289-296, 2000.
27. Christensen GJ. Amalgam vs. composite resin: 1998. J Am Dent Assoc 129:1757-1759, 1998.
28. Leinfelder KF, Bayne SC, Swift EJ, Jr. Packable composites overview and technical considera
    ]]> https://www.dentistrytoday.com/sp-375100848/ Fri, 01 Aug 2003 00:00:00 +0000 https://www.dentistrytoday.com/?p=17392 Liners, bases, and cements used in clinical dentistry are an important part of restorative and prosthodontic care and are constantly being improved. However, there is some degree of confusion in terminology. For example, the term “lining cement” may be used even though the material is not intended to be used as a cement, or “cement” may be used in reference to certain glass ionomer materials, when in fact the product is not intended for use as a cement. This confusion may be related to suggestions that dentists should reevaluate the liners and bases being used.¹ A study published in 1996 indicated that many dental schools could not agree on when to use each type of material.²

    This article will review the clinical applications for liners, bases, and cements and the different types of materials that are available. Examples of products and manufacturers in each category are provided, but these are not intended to represent a comprehensive list of available products.

    CLINICAL USES

    It was generally held that the toxic effects of dental materials were responsible for pulpal inflammation. More recently, adverse pulpal reactions are believed to be caused by the influx of bacteria and their toxins into the dentin.^3,4 This can lead to pulpal inflammation and possibly necrosis of pulpal tissue.⁵ Therefore, the clinician should attempt to reduce or eliminate microleakage, which would result in reduction and possibly elimination of postoperative sensitivity.

    It has been proposed that secondary caries, marginal discoloration, and marginal gap/fracture account for the majority of failed restorations.⁶ These failures occur at the interface between the restoration and the cavity preparation. Therefore, improving the seal at this interface will reduce the need for replacement of restorations.

    One means of reducing the effects of microleakage is to prevent the development of caries via the use of appropriate restorative materials. The choice of which material to use is in part determined by the clinical situation, including the amount of remaining tooth structure. In terms of pulpal health, it is more beneficial to conserve tooth structure when possible than to remove that same tooth structure and replace it with a restorative material.⁷ Meryon demonstrated that a 0.5-mm thickness of dentin reduces toxicity of a material by 75%, and if that thickness is increased to 1.0 mm, a reduction of 91% is seen.⁸ This study used materials that were known to have toxic effects. When these materials came in contact with the test culture cells, a reduction in the number of viable cells was seen. However, when a layer of dentin (dentin powder) was placed between the test materials and the cells, an increase in the number of viable cells was seen compared to the controls. The same holds true with respect to the smear layer. An intact smear layer helps occlude the dentinal tubules and therefore provides a barrier to bacterial invasion. Since removal of the smear layer is taught (with respect to resin bonding), one must consider protection of the pulp.

    Currently, there are a number of methods for preparing a cavity, including use of a bur, air abrasives, lasers, and hand instruments. The method by which tooth structure is removed does not affect microleakage.⁹

    Table. Materials used for liners, bases, and cements

    Liner Base Cement Advantages Limitations Varnish X low cost, long history of use washes out at margins Calcium Hydroxide X X (temporary) low cost, long history of use most effective when in contact with pulp Zinc Oxide Eugenol X X X antibacterial, long history, sealing ability unable to withstand condensation forces Zinc Oxyphosphate X X long history low pH Zinc Polycarboxylate X X long history thickness may inhibit seating of casting Glass Ionomer X X X fluoride release moisture sensitive Resin X X adhesive strength moisture, technique sensitive Reprinted with permission of the Academy of General Dentistry from: Weiner R. Liners, Bases, and Cements: A Solid Foundation. Gen Dent. 2002; 50: 442-445.

     

    The available materials that can be used as either a liner, a base, or a cement can be divided into 7 categories: varnishes, calcium hydroxide, zinc oxide eugenol/noneugenol zinc oxide, zinc phosphate, zinc polycarboxylate, glass ionomer, and resin. In different situations, a material can be considered a liner, a base, or a cement (see Table).

    Many clinicians use more than one material beneath a restoration. However, caution is needed because certain materials are not compatible with each other. For example, Yang and Chan demonstrated that varnishes can reduce the surface hardness of glass ionomers.¹⁰

    Following is a definition of liners, bases, and cements, and a discussion of how the 7 categories of materials are used.

    LINERS

    Liners are materials that are placed as a thin coating (usually 0.5 mm) on the surface of a cavity preparation. Although they provide a barrier to chemical irritants, they are not used for thermal insulation or to add bulk to a cavity preparation.¹¹ Furthermore, these materials do not have sufficient hardness or strength to be used alone in a deep cavity.¹² Of the categories listed above, varnishes, calcium hydroxide, glass ionomers, and resins can be used as liners. Zinc eugenol, zinc phosphate, and zinc polycarboxylates are generally not used as liners.

    Varnish

    A varnish is defined as natural gum (copal or resin) dissolved in an organic solvent such as acetone, chloroform, or ether.¹³ After the dentin in the cavity preparation is covered with a varnish, the solvent evaporates, leaving the solute as a thin layer or film. The theory behind a varnish (example: Copalite/Cooley & Cooley) is that it seals the dentinal tubules, thus reducing the effects of micro-leakage. When amalgam is first placed, the tooth/amalgam interface is not microscopically sealed. Eventually the varnish dissolves and is replaced with the corrosion products of the amalgam.¹⁴

    There are several fluoride-containing varnishes available (examples: Duraphat, Colgate Oral Pharmaceuticals; Dura-flor, Pharmascience Inc; Fluor Protector, Ivoclar Vivadent). Although the FDA has approved these products both as cavity liners and for the treatment of sensitive teeth, they are not approved for caries prevention.¹⁵ However, in Europe, fluoride varnishes have been used in caries prevention programs/studies since 1968. The results showed a reduction in caries ranging from 18% to 77%.¹⁶ In order for these varnishes to receive approval for use as a method of caries prevention, the manufacturer would need to submit clinical studies to the FDA, in which case the varnish would be classified as a drug.

    Calcium Hydroxide

    It is generally believed that calcium hydroxide (CH) is ideal for direct pulp capping since it accelerates the formation of reparative dentin. There are 2 reasons for this: first, since the material is basic (pH of 11), it serves as an irritant stimulating the formation of reparative dentin; and second, the therapeutic affect of CH may be due to its ability to extract growth

    factors from the dentin matrix.¹⁷ The result is the formation of a dentin bridge, which allows pulpal repair. However, these concepts are challenged by Schuurs et al,¹⁸ who concluded that although CH causes the formation of a dentin bridge, this seal does not last. Eventually the pulp will undergo necrosis as a result of microleakage.

    Due to the fact that CH has a basic pH, it is not generally supportive of bacterial growth. When the base and catalyst portions of CH were tested separately, only the catalyst component was shown to have any antibacterial effect.¹⁹ In addition, since bacterial byproducts are acidic, CH will directly counteract this acidity and effectively neutralize these byproducts. It for this reason that CH is placed under zinc phosphate—to help reduce the acidity of the zinc phosphate. CH is available in chemical- cured forms (example: Dycal, DENTSPLY Caulk) and light-cured forms (example: Prisma VLC Dycal, DENTSPLY Caulk) .

    Glass Ionomer

    This material has been available for more than 30 years. A current version of glass ionomer (GI) is the resin-modified glass ionomer (example: Vitrebond, 3M ESPE). There are 2 clinical benefits attributed to GIs: first is their ability to ionically bond to tooth structure (between the carboxylate groups in the GI and the calcium ions in the enamel and dentin)20; and second, they release fluoride. The ability of fluoride to inhibit the formation of secondary caries is established. Prati et al²¹ demonstrated that when GI is used as a liner, a reduction in the consequences of microleakage is seen. They attributed this to its antimicrobial properties. This benefit, along with its ability to adhere to and seal the dentin,²² has made this material popular as a cavity liner.

    GIs should not be used as pulp-capping agents. Unlike calcium hydroxide, GI does not promote the formation of dentin bridges. In fact, in a clinical study, GI was found in the pulp chamber, which triggered a persistent inflammatory response and appeared to prevent the formation of dentin bridges.²³

    One restorative procedure that is often used clinically is known as the “sandwich technique.”²⁴ In this technique, the lining materials are brought to the cavosurface margin. There are 2 advantages to this technique when using GI; first, released fluoride has a beneficial effect on the tooth structure at the margin of the restoration. Donly et al,²⁵ have shown that when this technique is used, there is less recurrent caries at the margin of restorations. Second, the fluoride that is released can be subsequently replaced with externally delivered fluoride. This can be via gel, mouthrinse, or toothpaste, with the gel being most effective.²⁶ GIs, both conventional and resin modified, are available in both chemical- cured formulations (example: Ketacbond, 3M ESPE) and light-cured formulations (example: Vitrebond, 3M ESPE). The light-cured products have been shown to provide a better seal.²⁷ Hand-mixed forms (examples: Vitrebond and Ketacbond) and encapsulated/cartridge-dispensed forms (example: Fuji Lining LC, GC America) are also available.

    GIs have certain disadvantages. They are extremely sensitive to moisture. A study by Cattani-Lorente et al,²⁸ demonstrated that when GI comes in contact with water, there is a decrease in its physical properties. In addition, resin-modified GIs expand after coming in contact with water.

    Resin

    Of the materials discussed here, resins are the most recent additions to the clinician’s armamentarium. They are very versatile (generally being of high compressive and tensile strength), possess low solubility, and are available in different viscosities and different shades.

    When resins are used as a cavity liner, it is important to remember that it is the dentin bonding agent (examples: Clearfil SE Bond, Kuraray America; Excite, Ivoclar Vivadent) that comes into contact with the dentin. There are different types of dentin bonding agents, and their performance differs.²⁹ These resins are not recommended for direct pulp capping since, like glass ionomers, they do not promote the formation of dentin bridges. In fact, there is a persistent mild inflammatory pulpal response associated with resins when they are used as a direct pulp-capping agent.30 Studies do confirm, however, that adhesives placed below amalgam restorations reduce microleakage,^31,32 thus supporting the current trend toward this practice of using resin as a liner. However, the clinician must consider the logistics of using adhesive resin liners. Lining cavities with copal varnish is faster and less technique-sensitive than using adhesive resin, and resins cost more and have a limited shelf life.

    In an attempt to overcome the polymerization shrinkage associated with traditional composite resin, a new material—modified hybrid resin—has been developed. A resin with a reduced filler load, it is referred to as a flowable composite (examples: Unifil Flow, GC America; Tetric Flow, Ivoclar Vivadent). The better flow and reduced modulus of elasticity of these materials theoretically reduce microleakage by increasing adaptation and by forming a stress-absorbing layer.³³ The result is a decrease in gap formation at the flowable-resin/tooth interface, which will ultimately lead to a decrease in secondary caries and pulpal inflammation and a longer lasting restoration.³⁴ Although there is increased adaptation of the resin to the cavity preparation, the material has a reduced filler content. This leads to an increase in polymerization shrinkage. The net result, however, is a reduction in gingival microleakage when flowable resin is used, compared to a conventional composite resin.³⁵

    It has been observed that some adhesives do not bond well to dentin in deep cavity preparations. This makes them more susceptible to polymerization shrinkage stress that develops in deep cavities.³⁶ Since the bond strength to dentin near the pulp chamber is low, the polymerization shrinkage that the resin undergoes can cause a gap to form. This was the conclusion reached by Gordan et al, who also showed that the weakest bond was at the flowable-resin/tooth interface and dentin near the pulp chamber.³⁷

    One study comparing a resin-modified GI, a flowable composite, and a dentin bonding agent concluded that the resin-modified GI was associated with less microleakage than the other materials.³⁸

    BASES

    Bases can be considered as restorative substitutes for the dentin that was removed by caries and/or the cavity preparation. They act as a barrier against chemical irritation, provide thermal insulation, and can resist the condensation forces on a tooth when placing a restoration. Also, the clinician can shape and contour base materials after placement into the cavity preparation.¹¹ Varnishes and calcium hydroxide materials are not in this category.

    Zinc Oxide Eugenol

    Zinc oxide eugenol (ZOE) (example: Intermediate Re-storative Material, DENTS-PLY Caulk) materials provide an excellent seal of the cavity preparation. The ability of ZOE to reduce postoperative sensitivity is most likely due to⁴¹A disadvantage of this material is its inability to withstand the forces of condensation immediately after placement. The clinician should allow approximately 24 hours to pass prior to placing amalgam above a ZOE base.

    Zinc Oxyphosphate

    Zinc oxyphosphate (ZOP) is a powder/liquid combination that is an ideal base material since it can provide thermal insulation and will allow the condensation of amalgam several minutes after placement. The material is acidic when placed (pH of approximately 3.5), but rises to a pH of 6.9 after a week. Mixing of the material should be performed on a cold glass slab. This promotes cooling of the exothermic reaction that occurs when the powder and liquid are combined and allows the clinician to incorporate more powder with the liquid, thus increasing the physical properties.

    According to ADA Specification No. 96, packages of ZOP contain 20% more liquid than is necessary to combine with the powder. This is because some of the liquid will evaporate during use. This specification applies to zinc phosphate, zinc polycarboxylate, and GI together since they all are water-based. This is important for the clinician to consider. Since the water can evaporate, these materials can become viscous, leading to difficulty in seating crowns. Furthermore, loss of water will result in a decrease in the pH of the liquid, making the cement less biocompatible. Examples of ZOP are Zinc Cement (Mission White) and Fleck’s Cement (Mizzy).

    Zinc Polycarboxylate

    A material that is comparable to ZOP is zinc polycarboxylate (ZPC). The important difference is the liquid component. The liquid in ZPC is polyacrylic acid, which is quite viscous. Zinc polycarboxylate adheres to the tooth via an interaction be-tween the carboxylic acid and the calcium in the dentin. Polyacrylic acid has a very low pH (1.7), but the pH approaches neutrality upon mixing with the powder. This cannot harm the tooth since the relatively large size of the polyacrylic acid molecule and/or its ability to combine with protein prevents it from diffusing into dentin tubules. Durelon and Durelon Maxicaps (3M ESPE) and Hybond zinc polycarboxylate (Shofu) are examples of this product.

    Glass Ionomer and Resin

    GIs and resins are generally not used as bases. They do, however, meet a number of the characteristics of a base; eg, they can be shaped and contoured and provide a chemical barrier. When used under another restorative material, they are usually employed as a core buildup.

    There are reports in the literature that advocate the use of these materials under a final restoration.^42,43 Two studies involved teeth with large carious lesions. The first  study involved complete removal of the caries, followed by filling the cavity with either a GI or a composite resin.⁴² At a later visit, the tooth was prepared, leaving the original material as a base. The results suggested that using either a GI or a composite resin as a base under amalgam was clinically acceptable. The second  study involved partial removal of caries, then the placement of GI over calcium hydroxide.⁴² Six to 12 months later, the filling material was removed, and the dentin was found to be hard and dry. This technique resulted in a reduction in cultivable microorganisms, thought to be due to sealing the remaining caries from extrinsic substrate.

    Examples of GI products that can be used for this purpose include Ketac-Silver (3M ESPE) and Fuji II LC Core Material (GC America). Paracore (Coltene/Whaledent) and Luxacore (Zenith/DMG) are examples of resin products.

    CEMENTS

    Materials that are considered cements can be used for 2 different purposes; the first is to retain restorations or appliances in a fixed position in the mouth44. The other is as a restorative filling material, used either alone or with other materials. In this situation, the material would be referred to as a base.

    As with liners and bases, cements also reduce microleakage by sealing the interface between the tooth and the restoration. Dental cements can be categorized as either temporary (short-term) or permanent (final). They should (1) have no adverse effects on the pulp tissue, (2) be of low solubility, (3) have high compressive and tensile strength, and (4) be radiopaque.

    It has been suggested that temporary cements be available in compact kits so waste is minimal, dispensing is controlled, and mixing is easy. They should flow but not drip, be easily cleaned from both instruments and margins, and have a quick set.45 These suggestions also apply to other types of materials discussed in this article.

    Temporary cements

    Calcium hydroxide, zinc oxide eugenol/nonzinc oxide eugenol, zinc polycarboxylate, and resins can be used as temporary cements.

     

    Calcium Hydroxide

    Although not usually thought of as a temporary cement, calcium hydroxide, as cited above, is not harmful to the tooth. It is harder than ZOE-based temporary cements and is easily removed from the margins of resin and PFM crowns. Also, since it is not eugenol-based, it will not interfere with the final resin cements (see below). It is available in dentin and ivory shades.

    Zinc Oxide Eugenol/Noneugenol Zinc Oxide

    ZOE-based materials are known to provide an effective seal at the tooth/restoration interface. ZOE has been shown to have adverse effects on resin-based products.^46,47 However, others were not able to confirm this.⁴⁸ Tempbond (Kerr) and Embonte (Cadco) are 2 examples of a ZOE temporary cement.

    For those who use a resin cement as a final cement and want to be confident that the temporary cement used will not interfere with final luting, noneugenol zinc oxide temporary cements are available. Although these products (examples: Nogenol, GC America; Temrex TNE, Temrex ) do not have a sedative effect on the tooth, they are compatible with resin-based provisional restorations. In fact, since they have been shown to be stronger than  ZOE temporary cement, it is recommended that these products be used with preparations where retention is low.⁴⁸

    Zinc Polycarboxylate

    There are 2 zinc polycarboxylate temporary cements (examples: Shofu’s Hybond zinc polycarboxylate temporary cement soft kit and Ultradent’s Ultratemp) that are available. Both are eugenol-free. The Hybond product contains fluoride.

    Resin

    Provilink (Ivoclar Vivadent) and Sensitemp (Sultan Chemists) are examples of provisional resin cement. This type of temporary cement is ideal for anterior restorations due to its aesthetic qualities. Since it is a material that is bonded to the tooth, it has excellent retention properties. In fact, occasionally removal of the temporary restoration proves to be difficult. One disadvantage of this material is evident after removal of the temporary restoration. The clinician may find brown stains on the tooth.⁴⁵ This stain is a potential problem when placing all-ceramic restorations. Pumicing the preparation prior to cementation should remove the stain. Another problem that the clinician may encounter with all resin cements is due to the shade of the material. Since these materials are tooth colored, it might appear to the clinician that all excess cement has been removed from the margins prior to patient dismissal. The clinician must be very careful when removing excess cement. This is especially true with certain tooth morphology; for example, in subgingival regions in proximity to furcations and other areas of tooth concavity.⁴⁰

    Final Cements

    Zinc Oxide Eugenol

    ZOE, Type II, is used for permanent or final cementation. This material has an inorganic filler added to the powder and ortho-ethoxybenzoic acid added to the liquid. It appears that this type of cement is not particularly popular, since there are not many brands available. Also, a review of the literature did not identify any studies in which a ZOE final cement was comparatively evaluated. Fynal (DENTSPLY Caulk) is an example of this kind of cement.

    Zinc Oxyphosphate/Zinc Polycarboxylate

    The liquids in both of these mixtures are acids. Therefore, these products are self-etching. These cements may demineralize dentin, but this does not occur in a uniform manner. ZOP causes more demineralization than does ZPC.50 Both of these materials have a long history of clinical use in dentistry. In fact, a version of ZOP was introduced in the late 1800s and was known as Ames’ black copper cement. It contained copper (cupric oxide 97%) and was found to be germicidal. This product was eventually discontinued, but was reintroduced as Doc’s Best Red Copper Zinc Phosphate Cement (Cooley & Cooley). This currently available product contains 7% cupric oxide. Unlike other ZOP cements, this product has a brown color, which makes it unsuitable for all-ceramic restorations.

    ZPC has a rubbery consistency when setting. Therefore, it is best to remove all excess from the margins only when it is fully set, or the material may be pulled from under the casting. When using ZPC, the clinician should be aware that the cement-casting interface is where failure may occur (ZPC chemically adheres to the tooth). This is in contrast to ZOP, where the cement-tooth interface is where failure can occur.

    Glass Ionomer

    GI cement is available in both hand-mixed forms (examples: Fuji I Glass Ionomer Cement, GC America; CX-Plus GlasIonomer cement, Shofu)  and encapsulated/cartridge forms (examples: FujiCem, GC America; VivaglassCem, Ivoclar Vivadent). These are self-cured formulations.

    One disadvantage of using GI as a cement or luting agent is its sensitivity to moisture. In fact, Mojon et al⁵¹ suggest that when using GIs, the involved teeth should be protected from contamination from saliva for as long as 15 minutes after mixing. In contrast, the resin-modified GIs (RMGIs) are hydrophilic (water-absorbing). This presents both an advantage and a disadvantage. The advantage is that the material will expand after coming in contact with moisture, filling any marginal gaps. The disadvantage is that this same expansion can cause all-ceramic crowns to fracture. Lastly, it has been suggested that RMGIs are ideal luting agents for patients who have a high caries index. (Fluoride is released from RMGI.)52 Nevertheless, it might be difficult or impossible to remove a post cemented with this material.

    Resin

    Resin-based cements can be grouped into categories based on how they are cured. They can be either self- or chemical-cured (examples: Parapost Cemen

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