Effect of Number of Implants and Cantilever Design on Stress Distribution in Three-unit Fixed Partial Dentures: a Three-dimensional Finite Element Analysis

Although dental implants have been successfully used for the rehabilitation of fully edentulous and partially edentulous patients, patient’s various conditions constrict the application of implant, or make dental treatment using dental implants very complex and difficult. Implantsupported cantilever prostheses represent that conditions. Becker and Kaiser insisted that alignment problems, extensive bone grafting, esthetic restrictions, poor bone quality and non-osseointegration of implants are advantageous conditions for implant-supported cantilever prostheses. However, the application of cantilever to implant-supported prostheses has been controversial. Although no dentists are willing to make cantilever prostheses which are unfavorable biomechanically, the case that a dentist has to use the cantilever prostheses exists obviously. There have been several clinical reports about successful application of various implants for the past decade. Meanwhile, the clinical reports which studied implantsupported cantilever fixed prostheses were limited. Therefore, implant-supported cantilever fixed prostheses remain a challenge to a dentist. Due to the difficulty of the experiment about implantsupported cantilever prostheses in patient’s mouth, in vitro studies or finite element studies have been done since 1990’ s. However, these studies were mostly for distal cantilever, and consistent studies concerning mesial cantilever were definitely lacking. As a result, the comparative study between mesial cantilever prostheses and distal cantilever prostheses was absent. Although mesial cantilever prostheses have been perceived to be more favorable than distal cantilever prostheses, a study about the difference of stress distribution between mesial cantilever prostheses and distal cantilever prostheses is demanded. Rangert et al insisted that if a three-unit posterior prosthesis is supported by two implants and has a cantilever tooth, the bending moment may be doubled when compared with a prosthesis in which both ends are supported. They, furthermore, suggested that three-implant support per se is not a guarantee for eliminating bending overload, so the addition of a third implant offset to the other two will reduce the bending by approximately two-thirds. However, it should not be overlook the fact that their insistence was EFFECT OF NUMBER OF IMPLANTS AND CANTILEVER DESIGN ON STRESS DISTRIBUTION IN THREE-UNIT FIXED PARTIAL DENTURES: A THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS