Dentists’ attitudes about the relative acceptability of the various materials used for Class II restorations have changed significantly during the past 20 years. Many dentists used to be skeptical about the potential longevity of resin-based composites (RBCs) when used in Class II locations, and amalgam was the dominant material used for posterior tooth restorations. A 2005 survey showed that although amalgam use still is relatively high in the United States, many dentists have eliminated it.1 Scientific evidence still appears to support the continued use of amalgam2; however, in my many travels around the world, I have found some countries, such as Japan, where amalgam does not appear to be used by any practitioner. It is obvious to me that amalgam use will decrease inevitably and that RBC will be used as the primary restorative material for Class II restorations.
Unfortunately, successful placement of RBC restorations still poses several challenges that make some dentists hesitate to use the material as a routine restorative for Class II situations. Can these challenges be overcome, or are there inherent problems that make RBC restorations a continuing problem?
In this article, I will discuss the challenges observed when using RBC in Class II locations and suggest potential solutions for each of them.
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OPEN CONTACT AREAS
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One of the most perplexing challenges encountered when placing Class II RBC restorations has been producing tight contact areas on a predictable basis. When RBC was introduced as a Class II restorative material, conventional amalgam matrices and wedges were used with it. As a result, a high percentage of restorations had flat proximal surfaces and open contact areas.
Currently, the most popular, predictable and successful method of producing tight contact areas is the use of sectional matrices. Popular brands are Composi-Tight (Garrison Dental Solutions, Spring Lake, Mich.) and Contact Matrix (Danville Materials, San Ramon, Calif.). Although these devices require more time to place than do amalgam matrices, their acceptance and reliability in assisting to make tight contact areas is excellent.
Other devices are used to assist in making tight contact areas—for instance, a transparent cone shaped-object that can be placed in the uncured RBC in the proximal box form of Class II preparations to hold the matrix band and the puttylike resin tightly against the adjacent tooth while curing the resin. Some of these cone-shaped attachments are placed on the light guide of curing lights. Similar clear plastic cones are on handles. The clinician places these cones in the box form, then places the light guide on the cone and directs the light through it. Additionally, small balls of cured RBC can be forced into proximal box forms to push matrix bands over to the adjacent tooth while placing the putty RBC.
With a minimal amount of experience and repeated use, the clinician can make tight contact areas on Class II RBC restorations.
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POSTOPERATIVE TOOTH SENSITIVITY
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Postoperative tooth sensitivity has been one of the most important and serious challenges in using RBC to create restorations. In the past, patients often received simple Class I or II RBC restorations and experienced lingering, painful postoperative tooth sensitivity.3–6 Frequently, this tooth sensitivity led to endodontic therapy and the necessity for an extracoronal restoration to provide strength for the endodontically treated tooth. The resultant fee for treatment of what originally was a minor carious lesion in the tooth moved from $100 or $200 up to $1,500.
I have been told by some endodontists that the largest "boom" for endodontic therapy in their careers has been pulpal death caused by Class I and II RBC restorations. It is common knowledge among restorative dentists that RBC and the technique required to place it can cause frequent, unpredictable postoperative tooth sensitivity if certain precautions are not observed. Polls of my continuing education (CE) audiences tell me that the following procedures have been successful in reducing or potentially eliminating postoperative tooth sensitivity.
Use of self-etching primers.
Many brands of self-etching primers are available that leave the "smear" layer on dentin and obturate the dentinal canals with grinding debris, primer and resin. Some examples: Clearfil SE Bond (Kuraray, New York City), Adper Prompt L-Pop (3M ESPE, St. Paul, Minn.), Brush & Bond (Parkell, Edgewood, N.Y.), OptiBond Solo Plus (Kerr, Orange, Calif.) and Xeno IV (Dentsply Caulk, Milford, Del.). Practitioners report that self-etching primers reduce postoperative tooth sensitivity, and most dentists have changed from the total-etch concept to self-etching primers.1 However, self-etching primers used alone may not solve the sensitivity challenge. As I have observed in my surveys of dentists in CE courses, some dentists report reduction but not elimination of postoperative sensitivity when they use self-etching primers alone.
Use of liquids containing glutaraldehyde and 2-hydroxyethyl methacrylate on tooth preparations.
Gluma Desensitizer (Heraeus Kulzer, Armonk, N.Y.) placed on tooth preparations has been accepted extremely well by dentists as a material that reduces or totally eliminates postoperative tooth sensitivity. Other examples of glutaraldehyde-containing solutions on the market include Micro Prime (Danville Materials) and AcquaSeal G (AcquaMed Technologies, Batavia, Ill.). Usually, placing two 30-second applications of the glutaraldehyde-containing liquid on the tooth preparation before priming and bonding it with a self-etching primer is highly successful in preventing postoperative tooth sensitivity. Dentists report near-total elimination of sensitivity when using this procedure.1,7–10
Use of resin-modified glass ionomer (RMGI) liners.
Dentists in my CE courses have reported, and I have observed, myself, another successful technique for preventing postoperative sensitivity: application of RMGI products such as Vitre-bond Plus (3M ESPE) or Fuji Lining LC (GC America, Alsip, Ill.). Placement of an RMGI liner on the deepest portions of the dentin, followed by application of self-etching primer and bond, is, in my opinion and experience, a near-foolproof procedure to prevent postoperative tooth sensitivity.7,8
Preventing the "white line" on RBC restoration margins.
The dreaded "white line" on RBC restoration margins is well-known to restorative dentists. It occurs frequently in the finishing of RBCs and has a disagreeable esthetic result, as well as the potential for initiation of future caries. The white line probably is caused by the approximately 2 percent polymerization shrinkage of restorative versions of RBC. The shrinkage may have the potential to pull the tooth cusps together slightly, thus placing the tooth in a stressful situation. The subsequent trauma caused by finishing could relax the stress and create the white line. Incremental curing of the major portion of the restoration minimizes the overall shrinkage. When curing in increments, the unavoidable polymerization shrinkage of the resin is segmented into smaller amounts, resulting in less cumulative shrinkage than when the resin is cured in larger bulk pieces. Whatever the cause of the white line, I have observed that by using careful finishing procedures, it is possible to avoid it.
I suggest the following tips for success:
- – use magnifying loupes;
- – use sharp burs, such as the 12-bladed no. 7406 bur for occlusal surfaces, the no. 7901 bur for gingival overhangs and the no. 7801 bur for occlusal grooves;
- – use a light cutting load on the burs at relatively low speed;
- – for optimum vision, avoid using water spray;
- – to avoid tooth trauma, be highly observant and cautious.
Wear of Class I and II RBCs was a significant concern for clinicians early in their use. However, many brands now show wear characteristics close to that of human enamel. Popular low-wear brand examples are Heliomolar (Ivoclar Vivadent, Amherst, N.Y.) and Filtek Supreme Plus (3M ESPE).
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REMAINING CHALLENGES FOR RESIN-BASED COMPOSITE
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In my opinion, there are not many challenges remaining for manufacturers to overcome with resin-based composites. These few challenges are as follows.
Lower polymerization shrinkage to below 1 percent.
The shrinkage of filled restorative resins (approximately 2 percent) and polymerization shrinkage of flowable resins (up to approximately 6 percent) need to be reduced significantly or, preferably, eliminated.
Match the wear characteristics of RBC to those of enamel.
Most RBC restorations wear slightly more than enamel. This wear produces potential eruption of restored and opposing teeth and resultant interdigitation of tooth cusps into the deepened fossae of the RBC-restored teeth. Such collapse produces nonworking and working contacts during occlusion and could lead to tooth fracture and temporomandibular joint dysfunction.
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SUMMARY
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Many patients now demand tooth-colored restorations. Class II RBC restorations are popular globally. Numerous resin products have shown adequate service characteristics in Class II locations. As with most oral treatment procedures, practitioners have faced numerous difficult clinical challenges as they have placed the several generations of RBC restorations. In my opinion and experience, after placing and researching Class II RBCs since 1968, this therapy has progressed to become a viable and predictable service. Doubting practitioners must take the time to study the materials and techniques and work with them until they can produce adequate Class II RBC restorations.
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OPEN CONTACT AREAS
POSTOPERATIVE TOOTH SENSITIVITY
