Material Selection for Direct Posterior Restoratives

The posterior restorative material of choice depends on the individual clinical situation and patient. Amalgam has a long history of use and clinical success. Esthetic restorations are increasingly in demand, and include glass ionomers, compomers and composite resins. Fluoride release is a desirable attribute in a restorative material, as are wear resistance, low polymerization shrinkage and low polymerization stress. Recently, technologies have been incorporated into composite resins that lower polymerization shrinkage and stress. Introduction Material selection for restoring posterior teeth depends upon the patient’s age, caries risk, esthetic requirements, ability to isolate the tooth and functional demands placed on the restoration. Although amalgam has been an effective restorative material for Class I and II cavity preparations, patient expectations are varied and range from high functional requirements to high esthetic demands. Each material used to restore posterior teeth has specific advantages and disadvantages and these should be carefully weighed before selecting a restorative material. Compomers, glass ionomers and composite resins bond to tooth structure and may reinforce weakened tooth structure. They have proven longevity in minimally invasive preparations, are excellent thermal insulators, esthetic, and produce varying levels of fluoride release, which may inhibit recurrent caries. However, esthetic restorative materials have disadvantages. Composite resin, while the most durable of the esthetic direct restorative materials, has clinical limitations that restrict its use as a posterior restorative material, especially in areas where isolation is poor and wear is high. Resin restorations require greater attention to detail during adhesive placement, increased placement time and are technically more difficult than a similar-sized amalgam restoration. Postoperatively, sensitivity to cold is a frequent complaint with Class II restorations, due primarily to polymerization shrinkage or poor adhesive placement – both of which create leakage at the resin/tooth interface. Posterior Amalgam Restorations Amalgam has a long-term clinical history of success for several reasons: the margins corrode and seal, it has good moisture tolerance and excellent wear resistance. Although amalgam does not bond to tooth structure and has other limitations, such as galvanism, high thermal conductivity, and poor esthetics, it may be placed in areas when some contamination, especially blood and saliva, are likely and still provide good clinical results. Amalgam can be used to successfully restore decimated teeth (Figures 1, 2). Figure 1. Placement of amalgam restorations Figure 2. Polished amalgam restorations Amalgam restorations may be bonded to tooth structure with adhesives using the bonded amalgam technique. One of the most clinically successful systems is the 4-META-based Amalgambond Plus (Parkell). In amalgam bonding, the bonding agent bonds to dentin by creating a hybrid layer. The attachment of the bonding resin to amalgam, however, is largely mechanical rather than chemical. Unset amalgam is condensed into the bonding resin before it polymerizes, incorporating fingers of resin into the amalgam at the interface.1 Several clinical studies of bonded amalgam restorations have demonstrated their success.2,3,4 Belcher and Stewart compared the clinical success of amalgams that were pin-retained, retained with Amalgambond Plus with no filler powder or retained with Amalgambond Plus with filler. At two years, all restorations were intact with minimal sensitivity, good marginal adaptation and no recurrent caries. Summitt et al. recorded a six-year recall of Amalgambond-retained cuspal coverage Tytin restorations with no failures in the bonded amalgam group.