Influence of mandibular superstructure shape on implant stresses during simulated posterior biting.

摘要

STATEMENT OF PROBLEM: Theoretical considerations on the ideal implant-supported prosthetic superstructure shape lack the effect of complex mandibular deformation patterns during function. PURPOSE: This study compared implant abutment stresses for idealized superstructures with different cross-sectional shapes and material properties during a simulated, complex biting task. MATERIAL AND METHODS: A simplified and idealized 3-dimensional finite element computer model was built, which consisted of a sectioned mandible rehabilitated with 5 titanium implants and an attached superstructure beam composed of metal alloy and acrylic resin. The model was submitted to loads mimicking simultaneous bending and (to a lesser degree) torsion of the mandibular corpus during a bilateral posterior bite. Maximum and minimum principal stresses were calculated at implant abutment sites for each of 6 beam cross sections of the prosthetic superstructure and 2 types of materials. RESULTS: Predicted implant stresses varied significantly between implant sites for different superstructure shapes. The lowest principal stresses were obtained by using a superstructure with a rectangular-shaped beam oriented vertically. Contrary to former theoretical considerations, the ideal "I-beam" superstructure cross section did not yield the lowest stresses. Superstructure materials with a lower modulus of elasticity seem to not only increase implant abutment stresses overall but also slightly reduce the tensile stresses on the most anterior implants. CONCLUSION: Simulated implant abutment stresses may be significantly affected by the shape of the prosthetic superstructure, by diverse mandibular loading conditions, and to a lesser extent, by the prosthetic material properties.