Shoulder preparations for collarless metal ceramic crowns: hand-planning as opposed to rotary instrumentation

This study was undertaken to determine whether hand-planning the gingival facial floor improved the overall fit and marginal adaptation of a collarless metal ceramic crown. An extracted central incisor was prepared conventionally. Separate impressions were made of the tooth with custom trays and poured in stone. Crowns were constructed and cemented with silicone impression material as the luting agent. The silicone film was captured in stone and sectioned. Film thickness was measured at six points on the buccal and lingual surfaces. The tooth was then modified at the gingival floor by hand-planning the margin to a smooth, flat finish, and the above procedures repeated. It was found that the fit of crowns as measured by the cement film thickness was significantly better (p less than 0.05) at the facial margin, facial, lingual incisal, and lingual surfaces for the hand-planned margins.