Fracture Resistance of Resin Inlay/Outlay Designs on a Premolar

Objective: To establish a three-dimensional finite element (3D-FE) model of a maxillary first premolar tooth, and to use this model to evaluate the effects of various Class II resin composite inlay and onlay restorations on the stresses generated within the tooth model and restorations from occlusal forces. Method: An embedded intact maxillary first premolar tooth was sliced serially and scanned digitally parallel to the occlusal surface. The 64 images were assembled in a 3D FE mesh and exported to generate a 3D solid tooth model. Simulated, adhesively cemented indirect MOD inlays (Inlay1, 2.0 mm; Inlay2, 3.0 mm; Inlay3, 4.0 mm wide), and indirect MOD onlays (Onlay1, 2.0 mm; Onlay2, 3.0 mm occlusal cusp coverage), were created. The peak von Mises stress values in the five tooth models resulting from static vertical and oblique occlusal forces (300 N) were evaluated, using Patran^TMFE software. Result:  Oblique occlusal forces in particular generated high peak stress values in the large Inlay3, Onlay1 and Onlay2 restorations and, to a much lesser extent, in the functional remaining cusp structure present with the Inlay3 restoration. Except for Inlay1, oblique forces generated higher stresses in the remaining dentine than did vertical forces for all restorations. Conclusion: Simulated, adhesively cemented resin composite onlays reduce effectively, occlusal stresses in the underlying dentine of large MOD preparations. Oblique occlusal forces impart much higher stresses to large resin composite inlays than to the adjacent dentine.