Following the initial successes of Goldberg and Gershkoff (Dental Digest, 5, 11, 1947) with the placement of subperiosteal implants, interest in all types of implants emerged. As an aid to the evaluation of various designs and materials without resorting to clinical testing, finite element analyses are being conducted by a number of researchers to determine the stress system induced in bone. The present study investigates the effects of variation in the thicknesses of the periodontal membrane and cortical bone and of the model boundary on the stresses developed around a natural tooth or a tooth-shaped implant. The results show that strong effects due to the variation in these parameters can be expected. As a consequence, the problem of the analysis of any single implant must consider additional factors. These can influence overall implant design and may eventually help to explain what could appear as anomalies in clinical test results.

SummaryThe present investigation is concerned with answering some of the questions which arise when discussing the success or failure of endosteal implants on the basis of the resulting stresses caused in the surrounding bone structure. In particular, the questions examined are: 1) What affects do variations in the mechanical properties of the implant, an encapsulating membrane, and the surrounding bone, have on the stress distribution? 2) Are some implant designs more affected than others, as indicated through variation of bone properties? and 3) What is the affect of an encapsulating membrane and how does a change in its thickness affect the stress distribution? A similar study was conducted on a simulated tooth, so that a comparison may be made between implant and tooth related stress distributions. The method of analysis used to obtain answers to these questions is the finite element method.Results of the investigation show that for a fixed implant geometry, a change in implant properties causes only minor changes in the bone stress distribution. A change in the membrane and bone properties, however, has a greater affect on the resulting stress distribution. It is also shown that the presence of a protective membrane has a beneficial affect on the stress distribution in the surrounding bone structure and that an optimum thickness can be estimated. Finally, the results show that some implant designs create a situation which results in stronger dependence of stress upon the properties of the surrounding bone.

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