Interdental design of porcelain veneers in the presence of composite fillings: Finite element analysis of composite shrinkage and thermal stresses

Purpose: This study was conducted to optimize the interdental design (wrapa round) of porcelain laminates bonded to teeth in the presence of preexistin g composite fillings. Materials and Methods: A finite element model (2-dime nsional mesh generated from a horizontal cross section of a maxillary incis or) was used to evaluate the effects of luting composite shrinkage and ther mal changes on the stress distribution within the ceramic. The mesh include d 3 restorative designs (3 degrees of interdental wrapping) and a Class III composite filling. Curing contraction of the luting composite was simulate d at baseline temperature (37 degrees C). Thermal loads from 37 to 60 degre es C and from 37 to 5 degrees C were assessed with and without preexisting composite shrinkage. Surface tangential stresses were calculated at the cer amic surface and interface. Results: Curing contraction alone generated mos tly compressive stresses (peaks at 15 MPa) at both the ceramic surface and interface. Stresses remained compressive (peaks at 20 MPa) when thermal cha nges were added, except for the conservative veneer with minimum wraparound , the margins of which showed potentially harmful tensile stress peaks (app roximate to 7 MPa). Deformation of the tooth-restoration complex tended to be more uniform for veneers with maximum wraparound. In the presence of the rmal loads alone, opposite effects were observed on the restoration surface and the interface, with compressive stresses on one side (up to 13 MPa) an d tensile stresses on the other (up to 9 MPa). This effect of proximal bend ing (explained by the nearby expansion/contraction of the composite filling ) was attenuated by the significant reduction of the bulk of the preexistin g interdental composite by the overlapping veneer. Conclusion: In the finit e element environment, the negative effect of the nearby expanding/contract ing composite fillings can be minimized by extending the veneer over the pr eexisting interdental restoration. Because of the precompressed state resul ting from composite shrinkage, ceramics showed lower temperature-induced te nsile stresses.