COMPOSITE RESIN RESTORATIONS

FINISHING AND POLISHING AMALGAM RESTORATIONS. —When amalgam restorations are placed in the tooth, finishing and polishing of the restorations generally take place at another appointment. The appointment should be at least 24 hours after the placement of the amalgam. Polishing the amalgam smooths the surface so that plaque does not adhere to it readily and makes the restoration look more attractive. The dentist checks the margins and proximal contacts of the restoration initially. A metal filing strip can be used to remove any roughness or overhand of the restoration in the proximal area. The dentist may use finishing burs or stones in the handpiece, followed by discs and abrasive points. Before use, discs may be coated with a lubricant, or in some cases, wet with water. The abrasive points progress from a more-abrasive to a less-abrasive point until a smooth mirror-like surface is obtained on the amalgam restoration. Extra-fine pumice and dry tin oxide, or commercial silicone-mounted polishing cups, may be used for a final polishing. COMPOSITE RESIN RESTORATIONS.— The restoration of tooth surfaces that are normally easily visible are restored with tooth-colored restorative materials for an esthetic appearance. One of the most commonly used tooth-colored restorative materials is the composite resin. The three types of composite resins available are macrofilled, microfilled, and hybrid. The classification of each composite resin depends on the particle size of its inorganic filler. The macrofilled and hybrid resins have higher amounts of inorganic fillers and lower amounts of organic resin than the microfilled resins. This provides the strength needed for proximal-incisal restorations. These restorations may be prepared with or without the pin retention technique. On the other hand, because microfilled resins have a smaller particle size, they are easier to polish than macrofilled resins. Many of the recently developed hybrids achieve good polishability and esthetics—one reason for their increased popularity. Composite resin materials are available in self- curing two-paste systems and light-curing single- paste systems. Some brands offer several color selections; whereas, others are supplied in a universal shade. The shade must always be selected before the teeth are allowed to dry because dehydration results in lighter shades. The restorative material is retained in the cavity preparation by mechanical retention. Chipped or fractured teeth rely mostly on acid-etch enamel for retention of the restorative material. Acid-etching the enamel portion of cavity preparations with a 35 to 50 percent solution of phosphoric acid results in improved retention for resin restorations. A celluloid matrix may be placed before the acid-etching procedure to protect the adjacent teeth. The phosphoric acid is applied to the enamel surface of the cavity preparation and is allowed to be in contact with the enamel for 1 minute. Then the area is rinsed thoroughly with water and dried. The etched enamel surface, when dried, appears chalky white because of a slight dissolving of the surface enamel that leaves microscopic undercuts (retention). After etching the tooth, a bonding agent is applied. The dentist may need an instrument to pack the composite resin material into the cavity preparation and to avoid formation of air bubbles. When the composite resin material is applied to the etched and bonded surface, the resin invades the surface void, undercuts, and irregularities. When surfaces in the proximal area are restored, the dentist will place a celluloid matrix that will assist in preventing the composite material from adhering to adjacent teeth and also acts as a form to properly place the material (fig 4- 40). If using a light-cured system of composite resin, the light source is positioned near the restoration and exposed according to the manufacturer's instructions. These light-curing systems are discussed in Chapter 11, Volume I, "Dental Safety and Equipment." The dentist, assistant, and the patient should wear protective glasses during the light exposure. Once the resin material cures, a mechanical bond forms. This type of surface union between the restorative material and the enamel improves the retention qualities and provides a smoother cavity Figure 4-40.—Using a celluloid matrix for a proximal composite restoration. 4-26