The incomplete fit of full cast crown restorations remains a critical problem for dentists, leading many researchers to study this problem. Marginal and internal accuracy of fit is valued as one of the most important criteria for the clinical quality and success of complete crowns. The geometry of tooth preparation has been the subject of many debates without clear evidence that one type of tooth preparation or method of fabrication provides consistently superior marginal fit. The objective of this study was to evaluate, by finite element analysis, the influence of different marginal geometries (shoulderless, chamfer, shoulder) on the stress distribution in teeth prepared for cast metal crowns.
A 3D model of a molar was created: intact teeth, unrestored teeth different marginal geometries: shoulderless, with chamfer, with shoulder preparations; the same tooth restored full cast metal crowns. These were exported in Ansys finite element analysis software for structural simulations.
The values of the maximal equivalent stress were higher for the shoulder preparations, but distributed under the preparation line. Regarding the stress distribution for the other two preparation designs, the largest area is present for the chamfer preparation, followed by the shoulderless preparation.
Within the limitations of the present study, the shoulder preparation is the recommended preparation design from biomechanical point of view. It is followed by the shoulderless preparation. Chamfer margins are less favorable only from this point of view. In light of these results, consideration should be given to the designs from prophylactic and biological points of view, with emphasis on conserving tooth structure and preventing preparation trauma.