ASSESSMENT OF SHOULDER DIMENSIONS AND ANGLES OF PORCELAIN BONDED TO METAL CROWN PREPARATIONS

The metal ceramic crown is the most popular extracoronal restoration i n the United Kingdom. These restorations may fail because of fracture or esthetics. A potential cause of failure is the quality and width of the facial shoulder preparation. In this study 24 extracted human tee th were prepared to receive metal ceramic crowns by one of three denti sts. Preparations were replicated and scanned in the midfacial plane b y a coordinate measuring machine with a noncontact probe. The x, y, an d z surface coordinates were recorded. The results indicated a mean (/-SD) shoulder width value of 0.752 mm (+/-0.174 mm) and a shoulder an gle of 108.54 (+/-15.06) degrees. From these data it would appear that there are deficiencies in shoulder preparations, particularly in widt h. These inadequacies may have implications for longevity of the resto ration and periodontal health in a clinical situation.