Operative Dentistry MCQ Answer 19

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The Correct Answer is A

A Is the correct answer -It is a false statement: the reduction should incorporate a 1.5- to 2.0 mm reduction in vertical height and all occluding areas. The adhesive nature of the bonded restoration makes the traditional approach of additional preparation to protect unsupported cusps or to develop additional resistance form unnecessary. Removal of additional tooth structure to onlay cusp is contraindicated.

B. Is a true statement The hollow ground chamfer is used to expose and increased number of enamel rods for increased bond strength, increased marginal seal, and a transition for better esthetic color blend. A bevel could lead to fracture of porcelain due to the friability of the thin edge of porcelain.

c. Is a true statement: There should be well-rounded angles on the Cuspal preparation, to prevent propagation of porcelain fracture from these sharp stress points.

d. Is a true statement: GV Black’s original concepts for restorations demanded sharp, definitive line angles. These are contraindicated in any form of porcelain restoration. All line and point angles are of necessity rounded. This facilitates the laboratory fabrication and decreases the propagation of fractures within the restoration. The cavity preparation should be indented in the pulpal floor to develop even thickness of porcelain in the restoration in the central fossa region to parallel the cuspal inclines. This allows for a thickness of porcelain in the center that is similar to that on the lateral aspects of the restoration.

e. Is a true statement: The axial walls of the cavity preparation should be slightly more divergent from the pulpal floor toward the enamel surface than would be prepared for a conventional cast-metal inlay, where the 6-10 degree taper is commonly favored to develop retention. Increased taper of the axial walls allows easier placement and removal of the restoration during the true-in phase, but the taper should not be exaggerated so as to unnecessarily remove additional tooth structure.

Reference: Porcelain and Composite Inlays and Onlays. Garber DA and Goldstein RE