MARGIN WIDTH, INTERNAL LINE ANGLE AND LABIAL EMERGENCE PROFILES OF MAXILLARY METALLOCERAMIC CROWNS

Abstract

The purpose of this study were to compare theemergence profiles of crowns with their contralateraltooth, in vitro, and to determine if there is anyassociation between the design of tooth preparationsand the resultant emergence profile. 50 workingmodels used for single crown construction wereexamined. Measurements of the faciolingual widthof the crowns and contralateral teeth were takenusing digital calipers. Internal line angles and themargin width of dies and the emergence profile ofthe corresponding crowns were measured fromlongitudinally sectioned polyvinylsiloxane indicesmounted on a flat-bed scanner using image analysissoftware. Using Students t tests, no statisticallysignificant differences (p>0.05) were found forshoulder width (mean 0.94 ± 0.23mm), internal lineangle (mean 105.83 ± 13.57°) or emergence profiles(28.56 ± 12.95°) in the different (anterior, premolaror molar) preparations or crowns. The meanemergence profiles for all crowns was statisticallysignificantly greater (p<0.001) than the contralateraltooth (mean 15.33 ± 7.77°). Using linear regression,there was a weak statistical relationship betweenemergence profile and margin width (Emergenceprofile° = 31.352 – 2.973 x margin width (mm)).There was no statistical association between theinternal line angle and the resultant emergenceprofile. In conclusion, the emergence profiles ofcrowns were higher than the contralateral teeth.Maxillary metalloceramic crown preparations hadshoulder widths that did not conform torecommendations in standard texts but line angleswere within a satisfactory range. The margin widthexerts a weak effect upon the emergence profile ofthe crown.