Objective To evaluate the interfacial stress distribution in different class Ⅳ preparation designs with composite resin restoration at centric occlusion and protrusive occlusion. Methods Three dimensional finite element model of maxillary central incisor with class Ⅳ preparation was established by spiral CT. It was designed into 1 mm and 2 mm bevels, chamfer, stair-step chamfer preparation and untreated model as control. All the models were restored with composite resin, and loaded under 100 N forming 45° with long axis. The interfacial Von Mises stress and distribution was recorded. Results The maximum Von Mises stress values of the interface at centric occlusion were obviously smaller than that of protrusive occlusion, at which the stess level of two bevels were smaller than two chamfers. Nevertheless, the distribution of stresses is more uniform in chamfers than that in bevels. Conclusion In view of stress and its distribution, the bevel and chamfer both have their superiorities. The maximum Von Mises stress values of the interface at protrusive occlusion were obviously higher than that of centric occlusion, thus class Ⅳ prepared teeth restored with composite resins should avoid biting hard food edge to edge.
