Development and Use of Direct Amalgam Fillings and Gold Inlays and Onlays

Amalgam fillings have been used for well over a century and offer the most user-friendly material for restoring posterior teeth. Their low technology advantages include technique forgiveness and tolerance for conditions encountered when not using a rubber dam, such as susceptibility to contamination from blood, sulcular fluid, or saliva. Amalgams are also condensable, so contact can be more readily achieved. From the dentist’s standpoint, amalgam has been a good restorative material, being applied through a technique that is easy to learn and execute. Amalgam also has good longevity and the lowest cost of any of the restorative materials. Among amalgam’s significant deficiencies are its susceptibility to constant corrosion, inability to strengthen the teeth, inability to seal teeth initially, and lack of esthetics. Many patients and dentists are also concerned about the mercury issue, because amalgam is 50% mercury. Recently, environmental concerns about contamination of the water supply have led to increased regulations and even calls for a ban on further use, which has been instituted in some countries. Cast gold has been used for over a century. Gold is an inert material, can be alloyed to almost an ideal hardness value, so as to be kind to opposing tooth structure, and when properly applied has been shown to have a longevity of decades. Often gold is considered the “gold standard” of restorative dentistry. Its main deficiency is its color. However, when the restoration is placed in second molars or when the patient is not concerned about the color, selecting cast gold for moderate to large cavities is one of the wisest choices the dentist can make.

The esthetic inlay and onlay procedure successfully using ceramic and/or processed composites began to be used around the mid-to-late 1980s, shortly after the introduction of ceramic veneers for anterior teeth. Both treatments paralleled advances in adhesive dentistry in general. Stacked, feldspathic porcelain or indirect composite inlays and onlays were also introduced to address some of the deficiencies of direct composites, which at the time, were considerable when applied to posterior teeth. They included high wear, low strength, high shrinkage, and difficult placement, especially in light of dentists’ training in placing metals in posterior teeth, a technique quite different from what is used for direct composites. In addition, laboratory-fabricated ceramic and processed indirect composite yielded improved physical properties, improved contours, predictable ideal proximal contacts, and the potential for better, more appropriately placed functional occlusal contacts.

Indications

The two primary esthetic inlay or onlay restoration indications are as follows: (1) the patient’s desire for a nonmetal restoration, making this indication essentially patient driven, and (2) restorative considerations determined by the clinician.

Generally it is believed that a direct resin restoration should be restricted to smaller cavities, defined as those whose cavity width is one third or less of the buccal lingual width of the tooth. Once the cavity exceeds a third of the buccal lingual width, a significant amount of the functional demand is being placed on the restoration, with much less on the tooth. In these cases, indirect composite or ceramic restorations should be considered rather than direct resin restorations. Even using the maximum polymerization energy and time, direct composites that are light polymerized achieve a maximum conversion of about 60%. When the composite is secondarily processed in the laboratory, polymerization can be driven to 95% or higher and the material’s physical properties are increased accordingly. Ceramic has much higher compressive strength, flexural strength, and modulus of elasticity than direct composite.

In essence, these restorations are ideal for the moderately broken-down posterior tooth, the type of situation in which the cavity is too large or the tooth is subjected to too much functional demand, contraindicating the placement of an amalgam or direct resin restoration, yet in which the dentist may be uncomfortable preparing the whole tooth for a full-coverage crown. This consideration is becoming increasingly important as patients are educated about the benefits of modern adhesive dentistry, for example, esthetics, conservation of tooth structure, better seal, and tooth reinforcement. When patients understand the reduction of the natural tooth needed for crown restorations, they often prefer esthetic inlay or onlay restorations to preserve remaining healthy tooth structure.

Contraindications

Similar to all adhesive restorations, inlay or onlay restorations are contraindicated when adequate isolation and control of saliva, sulcular fluid, or blood contamination cannot be achieved for the adhesive process. Second molars, when they are the last tooth in the dental arch, can be particularly challenging esthetic inlay or onlay restorations. They frequently have short clinical crowns, can be difficult to isolate, and are subject to higher occlusal forces, particularly in patients who clench or brux. Over-engineering the restoration in these teeth may be a wise approach, meaning onlaying cusps that might not be onlayed on other teeth or proceeding to a full-coverage crown rather than placing a large multicusp onlay. It is the author’s opinion that a cast gold inlay or onlay is restoratively preferable to an esthetic one in the second molar location. Fortunately, many patients are okay with the lack of esthetics because of the reduced visibility.

Advantages

Some of the laboratory-fabricated resin systems have been in existence for 10 to over 22 years and have proven clinical efficacy. In recent years the physical properties and clinical performance of these materials have improved significantly (see Table 17-1). Although controversy exists as to which material, indirect composite or ceramic, provides the optimum long-term, durable, esthetic restoration, this author believes both indirect resin and ceramics can be used successfully. The final determination should rest with the clinician and be guided by personal preference. Numerous factors contribute to a high-quality restoration, and each must be examined with respect to the material, the fabrication process, and the clinical technique. Clearly, indirect composite materials are being fabricated with enhanced durability, wear resistance, and fit. The ultimate long-term success is a function of the materials used, the technique used by the clinician and the laboratory technician, and the patient’s care. In comparison to ceramic materials, inlay or onlay restorations composed of composite resin can generally be fabricated with greater ease in the laboratory. Resins also demonstrate improved wear compatibility against opposing tooth structure and can be repaired more easily intra-orally. For inlays, indirect composite seems to be currently the preferred material. For onlays the marketplace is weighted more toward ceramics than indirect composite but not by much. Numerous clinical trials have shown ceramic inlays or onlays to be viable restorations over time.

Options

Figure 17-1 shows a very large amalgam in the first molar replacing a cusp. In the second molar there is an occlusal amalgam. In treatment planning for the second molar, which has some recurrent caries, the amalgam restoration can easily be replaced with a direct composite because of the relatively small size. The first molar has a very large amount of amalgam in need of replacement, so the decision is between going to a full-coverage crown, which would necessitate virtually removing the three remaining cusps, or removing all the old alloy plus any associated disease, leaving the three remaining cusps, and placing a bonded esthetic onlay. The latter is far more conservative because of the tooth reinforcement achieved by bonding to a significant amount of enamel and because the three cusps are preserved. Potentially this tooth may never need to be crowned. The case in Figure 17-2 shows the advantages, both conservative and esthetic, of adhesive onlay restorations.

FIGURE 17-1 Case demonstrating the advantages (conservative and esthetic) of adhesive onlay restorations.

FIGURE 17-2 A, A very large amalgam in the first molar (replacing a cusp) and occlusal amalgam in second molar. B, Amalgam replaced with direct composite (second molar) and bonded esthetic onlay (first molar).

Figure 17-3 shows four amalgams, two in molars and two in premolars. Those in the premolars would be defined as relatively small restorations. When one also considers the amount of occlusal force premolars are subjected to, these amalgams could be replaced with direct composite resin restorations.

FIGURE 17-3 Four amalgams, two in molars and two in premolars.

The distal lingual cusp of the first molar is cracked. Because the restoration will be an onlay, and given the heavy functional demand on first molars, this author believes that an onlay is the best restoration, whether it be cast gold, ceramic, or indirect composite. This patient preferred an esthetic restoration, so an indirect composite was used. The width of the cavity in the second molar qualifies it as a small cavity, which might be well served by a direct composite restoration. However, the functional aspects of this particular tooth must also be considered. There is a greater than normal inter-tooth distance between the first and second molars as evidenced by the placement of the amalgam on the distal of the first molar well into the proximal space and the placement of the amalgam in the second molar well into the proximal space so that these two fillings contact. This creates a very large gingival embrasure and a lack of support. Although this is not a particular problem with amalgam, which has great streng/>