Consistency of labial finish line preparation for metal ceramic crowns: an investigation of a new bur.
OBJECTIVE
Previous studies have reported on the difficulties inherent in preparing the labial aspect of teeth for metal ceramic crowns with consistency and also the implications for the definitive restoration of underprepared and overangled finish lines. In this study, a bur designed to prepare a 1.2-mm deep chamfer was tested and compared with two other bur kits.


METHODS
Seventy-two teeth were prepared to receive metal ceramic crowns in vitro by students using one of the two bur kits or the new bur. Using a coordinate measuring machine (CMM), replicas of the prepared teeth were scanned in the mid-labial plane, and shoulder width and cavosurface angles were measured.


RESULTS
The new bur produced preparations with a mean shoulder width and cavosurface angle of 1.146 +/- 0.241 mm and 108 +/- 11 degrees, respectively, compared with 0.626 +/- 0.234 mm and 128 +/- 14 degrees produced by a commercially available standardized crown cutting bur system and 0.626 +/- 0.218 mm and 124 +/- 15 degrees produced by the bur kit in use at our center at the time of the study. These differences were statistically significant at the 5% level, using Tukey's comparison of means.


CONCLUSIONS
Teeth prepared by the new bur had wider shoulders and lower cavosurface angles than teeth prepared either with a standardized crown cutting system or locally selected bur kit. The quality of labial preparations produced by the new bur in terms of closeness to the postulated "ideal" width and angulation warrants further investigation.
Seymour
Kevin G
KG
Department of Adult Oral Health, St. Bartholomew's and the Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, Whitechapel, London, UK.
Cherukara
George P
GP
Samarawickrama
Dayananda Y D
DY
Zou
Lifong
L
D000704:Analysis of Variance; D003442:Crowns; D003735:Dental Casting Technique; D003762:Dental Instruments / Q000145:classification; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design; D006801:Humans; D066298:In Vitro Techniques; D016876:Metal Ceramic Alloys; D015203:Reproducibility of Results; D019231:Tooth Preparation, Prosthodontic / Q000295:instrumentation*
D016876:Metal Ceramic Alloys