Variation in labial shoulder geometry of metal ceramic crown preparations: a finite element analysis

Recent studies have highlighted variations in the geometry of teeth prepared to receive metal ceramic crowns, particularly in the region of the labial shoulder, where shoulder designs have often involved less reduction than is recommended. Using two-dimensional finite element analysis, this study subjected crowns, superimposed upon preparations with clinically common labial margin designs, to loads of 200N in three different directions. The resultant stress distribution within the labial marginal porcelain was examined. Results imply that variations in the marginal preparation geometry of metal ceramic crowns influenced the stress response of the finished crown. Within the limits of this study, a crown constructed a 1.3mm chamfer preparation appeared to have the best response to a simulated load applied to the palatal/incisal surface, at 45 degrees to the long axis.