Margin Width, Internal Line Angle and Labial Emergence Profiles of Maxillary Metalloceramic Crowns

The purpose of this study were to compare the emergence profiles of crowns with their contralateral tooth, in vitro, and to determine if there is any association between the design of tooth preparations and the resultant emergence profile. 50 working models used for single crown construction were examined. Measurements of the faciolingual width of the crowns and contralateral teeth were taken using digital calipers. Internal line angles and the margin width of dies and the emergence profile of the corresponding crowns were measured from longitudinally sectioned polyvinylsiloxane indices mounted on a flat-bed scanner using image analysis software. Using Students t tests, no statistically significant differences (p>0.05) were found for shoulder width (mean 0.94 ± 0.23mm), internal line angle (mean 105.83 ± 13.57°) or emergence profiles (28.56 ± 12.95°) in the different (anterior, premolar or molar) preparations or crowns. The mean emergence profiles for all crowns was statistically significantly greater (p<0.001) than the contralateral tooth (mean 15.33 ± 7.77°). Using linear regression, there was a weak statistical relationship between emergence profile and margin width (Emergence profile° = 31.352 – 2.973 x margin width (mm)). There was no statistical association between the internal line angle and the resultant emergence profile. In conclusion, the emergence profiles of crowns were higher than the contralateral teeth. Maxillary metalloceramic crown preparations had shoulder widths that did not conform to recommendations in standard texts but line angles were within a satisfactory range. The margin width exerts a weak effect upon the emergence profile of the crown.