2000 年 13 巻 3 号 p. 544-558
As a means to recovering occlusal functions in prosthetic treatment for lost teeth, osseointegrated implants have been popularly accepted as a highly reliable method, supported by a large amount of research data. However, an excessively large load resulting from occlusal force may be concentrated at the interface between the implant surface and the bone, and it may break the osseointegration. One factor that can lead to age of break up this osseointegration is the surrounding bone thickness that supports the implant. Various type of mechanical effects created in the sirrounding bone thickness to the implant have been investigated by experimental sumulation studies, but no investigation has ficused on the relationship between the bone thickness surrounding the fuxture and the strain created in the bone. Therefore, in order to clarify this issue, fixtures were embedded in a human dry skull with a deficiency of the maxillary incisors. The experiments were carried out with a static load applied, and the distributions of strains on the bone surfaces were elucidated.
The edentulous incisor portion of the human dry skull was installed with four Brånemark system implant® fixtures.These were classified into two groups: one was the group of the same fixtures with the same installation angle, and the other was a different installation angle group. These were connected to the abutment, and a tentative occlusal plane was established from the remaining teeth cusp top; then, a superstructure was fabricated and connected to be parallel to the plane of occlusion. The load was applied to an access hole, and a 10-kgf static load was applied to each access hole. For strain measurement of the bone surface around each fixture, a strain gauge method was employed. At first the strain on the bone surface was measured using a one-piece superstructure, in order to measure the strain difference caused by differences in surrounding bone thickness and the fixture installation angle. Finally, the superstructure was cut at the mesiodistal center of each access hole, and a load was applied in the same manner as a single tooth setting implant, and the strain was measured.
The experimental results and conclusions are as follows:
1. For the coupling with the same fixture installation angle, the loading direction was made unidirectional to each fixture.
2. A large reactin force was generated against the moment that used the fixture abutment connective portion as a rotation axis, and the stress was assumed to be dispersed because of the different installation angle.
3. It was therefore suggested that stress might be concentrated on the labial side with a thinner bone wall,when the bone thickness was compared between the labial and palatal sides.
4. It was suggested that it would be rational to increase the number of connected fixtures from the viewpoint of dispersion of occlusal force, and the dynamic burden on the fixture could be alleviated.
5. The fixture was installed with a larger angle, suggesting that the strain concentrated in the apical portion.
6. It was suggested that the labial side at the portion with a thin bone wall of less than 1 mm often developed bone resorption or microfracture of the surrounding bone.
