Assessing the quality of shoulder preparations for metal ceramic crowns

Previous work by the authors indicates a tendency for academic clinicians to under prepare and over angle shoulder preparations for metal ceramic crowns. This has implications for the final restoration in terms of contour, appearance and strength. This study analysed ninety six preparations, forty eight in vitro and forty eight in vivo, performed by six clinicians. The results show a mean shoulder width of 0.804 +/- 0.274 mm and a mean shoulder angle of 116 +/- 18 degrees for preparations performed in vitro; and 0.892 +/- 0.337 mm and 121 +/- 24 degrees for preparations performed in vivo. Thus, despite recommendations that such crowns should have 1-1.5 mm, 90 degrees shoulders, many of the preparations studied here fell short of this, indicating a lack of consistency in preparation geometry and adherence to the perceived 'ideal' preparation for a metal ceramic crown.