Kayo Kasai1, Yoshiyuki Takayama, Atsuro Yokoyama. 1. Department of Oral Functional Prosthodontics, Division of Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, Kita-ku, Sapporo, Japan.
Abstract
PURPOSE: The purpose of this study was to investigate the influence of occlusal forces (the contractile forces of the masticatory muscles) during occlusal adjustment on the distribution of forces on combinations of implants and teeth during intercuspal clenching by means of finite element analysis. MATERIALS AND METHODS: Three-dimensional finite element models of the mandible, one with two implants in the molar region and the other with four implants in the premolar and molar regions, were constructed. Linearly elastic material properties were defined for all elements except the periodontal ligament, which was defined as nonlinearly elastic. The temporomandibular joints and antagonists were simplified and replaced with nonlinear springs. Antagonists were assumed to be a natural tooth or an implant and had two- or three-stage displaceability (ie, very high displaceability under tension and when the displacement was smaller than the clearance assumed to be made by occlusal adjustment, but displaceability of the antagonists themselves when the displacement was greater than the clearance). The clearance by occlusal adjustment was decided beforehand with a trial-and-error method so that the occlusal forces were distributed symmetrically under a prescribed load. Each model was evaluated under loads of 100 N, 200 N, and 800 N for the distribution of occlusal forces on the teeth and implants. RESULTS: In the case of occlusal adjustment under the total occlusal force of 40 N, the stress was concentrated at the most posteriorly located implant in all models under all loading conditions. This concentration was reduced in the case of occlusal adjustment under the total occlusal force of 200 N, except under a load of 800 N. CONCLUSION: Hard biting appeared to be better for occlusal adjustment to avoid overloading of the most posterior implant.
PURPOSE: The purpose of this study was to investigate the influence of occlusal forces (the contractile forces of the masticatory muscles) during occlusal adjustment on the distribution of forces on combinations of implants and teeth during intercuspal clenching by means of finite element analysis. MATERIALS AND METHODS: Three-dimensional finite element models of the mandible, one with two implants in the molar region and the other with four implants in the premolar and molar regions, were constructed. Linearly elastic material properties were defined for all elements except the periodontal ligament, which was defined as nonlinearly elastic. The temporomandibular joints and antagonists were simplified and replaced with nonlinear springs. Antagonists were assumed to be a natural tooth or an implant and had two- or three-stage displaceability (ie, very high displaceability under tension and when the displacement was smaller than the clearance assumed to be made by occlusal adjustment, but displaceability of the antagonists themselves when the displacement was greater than the clearance). The clearance by occlusal adjustment was decided beforehand with a trial-and-error method so that the occlusal forces were distributed symmetrically under a prescribed load. Each model was evaluated under loads of 100 N, 200 N, and 800 N for the distribution of occlusal forces on the teeth and implants. RESULTS: In the case of occlusal adjustment under the total occlusal force of 40 N, the stress was concentrated at the most posteriorly located implant in all models under all loading conditions. This concentration was reduced in the case of occlusal adjustment under the total occlusal force of 200 N, except under a load of 800 N. CONCLUSION: Hard biting appeared to be better for occlusal adjustment to avoid overloading of the most posterior implant.