Fracture of cusp on tooth is major cause of tooth loss. Tooth fracture may be related to the stresses exerted upon during masticatory function. The purpose of this study was to examine concept of the designs for cavity preparation. Among the several parameters in cavity designs, understanding of isthmus width factor is important, In this study, the cavity were prepared on mandibular first molar and filled with gold inlay. Modified cavity depth was 1.0㎜ and formed offset in cavity center. These models have various offset´s isthmus, 0.8㎜, 1,0㎜, 1.6㎜, in cavity. To analize the stress development in the tooth in that cavity design, 20㎏ distributive forces were applied on the inlay restoratives. The load applied onto central fossa. These models analysed with two dimensional finite element method. The result of this study were as follows;
1. The pattern of stress distribution and displacement showed no apparent differences.
2. The effect of width was significant, and found it relationship between the offset width and stress distribution was.
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