CLASS 3 COMPOSITES

A cavity that occurs between front teeth is referred to as a class 3.  Food collects between teeth.  Sugars within food are converted to acids that decalcify enamel. Continued destruction forms a hole and therefore, the term cavity.  Initially, these cavities are not visible, however, as acids continue the destructive process, a cavity becomes large enough to be visible.

A class 3 cavity has multiple walls after tooth preparation.  Composite shrinks upon curing applying stress to cavity walls.  More walls and increased size of a cavity preparation increases internal stress upon composite cure resulting in more potential for enamel fracture or restoration microleakage.  Enamel fracture leads to white lines on polishing when debris fills in open cracks.  Using a technique of layering composite minimizes internal stresses.

Lingual access is utilized to minimize filling material showing on facial surfaces.  Facial access is used if caries or an existing restoration extends to the facial.  Caries is excavated with slow speed round burs and spoon excavators to maintain tooth structure and minimize trauma to pulpal tissues.  Enamel is finished to eliminate thin areas that might facture.  A thin facial wall is left in place to avoid facial extension.

Bonding to enamel and dentin minimizes micro leakage from composite shrinkage during curing and forces of contraction expansion caused during thermal cycling as the thermal coefficient of expansion for composite is much greater than tooth structure.  Dentin bonding seals dentinal tubules for reduced sensitivity and minimizes micro leakage at the restoration dentin interface should restoration leakage occur.

A plastic matrix is placed between teeth to restrict material within a cavity preparation.  A wedge is often placed interproximally to hold a plastic strip in place and tight to tooth structure at the gingival area.  Composite material is placed and shaped with hand instruments.  Small preparations allow matrix wrapping as remaining tooth structure maintains contours.  The plastic strip is not wrapped around the tooth as an oxygen inhibited layer is lost and a wrapped matrix creates a straight interproximal contour on large restorations.  Composite is light cured, shaped and polished with sandpaper disks, burs, rubber cups, wheels, points and polishing paste .  Sandpaper strips or diamond strips are used to remove inadvertent interproximal excess.