A Mechanical and Histological Study on the Functional Adaptation of the Tissue Surrounding Dental Implants

Abstract

The present study is composed of the following four experiments. (1)The relationship between the initiation of occlusion and the bone formation after implantation of the alumina implants on the mandibles of eight adult mongrel dogs was studied histologically. (2)The functional adaptation of the tissue surrounding the alumina, hydroxyapatite and titanium implants was studied histologically using six adult mongrel dogs and three adult monkeys. (3)The stress distribution around the alumina, hydroxyapatite and titanium implants was studied using the threedimensional finite element stress analysis. (4)The stress distribution around the alumina implant was studied using the two-dimensional finite element model, in which the slip and the separation between the implant and the surrounding tissue were allowed to occur.
In the case of the alumina implant under occlusion at 2,4 weeks after implantation, the implant was covered with thick fibrous connective tissue. In the case of the implant under occlusion at 8 weeks after implantation, thick fibrous connective tissue was found on a part of the implant surface. In the case of the implant under occlusion at 12 weeks after implantation, bone formation was found on the most part of the implant surface, and thin fibrous connective tissue was found at the implant-bone interface.
Thin fibrous connective tissue was found at the alumina implant-bone interface. But no fibrous connective tissue was found around the hydroxyapatite and titanium irnplants, and bone resorption and connective tissue ingrowth were found in the crestal region of the alveolar bone.
By the three-dimensional finite element stress analysis, the alumina implant with connective tissue at the implant-bone interface caused considerably uniform stress distribution without critical stress concentration in the crestal region of the alveolar bone, but the hydroxyapatite and titanium implants without connective tissue caused high stress concentration in the crestal region of the alveolar bone.Presence of connective tissue layer at the implant-bone interface reduced the stress in the crestal region.
By the finite element stress analysis with the boundary condition of the slip and the separation,the alumina implant with connective tissue at the implant-bone interface caused more favorable stress distribution than without connective tissue. The incorporation of connective tissue at the implant-bone interface was led to uniform stress distribution. The high stress concentration calculated in the crestal region of the alveolar bone was found to cause bone resorption and subsequent connective tissue ingrowth.