Structural properties of mandibular bone following application of a bone plate.
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PURPOSE: Similarities in strain patterns between long bones and the mandible suggest that plates may induce stress shielding, resulting in deleterious long-term changes. This study is an investigation of the use of bone plates on the mandible in four adult rhesus monkeys. MATERIAL AND METHODS: A stainless steel plate was attached facially along the inferior border of each mandibular corpus. On the left, a thick (2.5-mm) plate was engaged with four screws. On the right, a thin (0.5-mm) plate was attached with one screw. Monkeys were killed a year after plate placement. At the beginning and end of the experiments, bone strain was recorded inferior to each bone plate during evoked maximal incisal clenching. After death, bone was removed from the mandibles around and under the plates and examined. Gross dimensions and density were measured. An ultrasonic technique was used to measure the material properties, including the elastic and shear moduli. RESULTS: Bone strain inferior to the plates was reduced by 34% to 53% after attachment of the thick plates. Little change in strain was found after attachment of the thin plates. However, no significant differences in structural or mechanical measurements, such as density, cortical thickness, elastic and shear moduli, and Poisson's ratios, were detected between the two sides in each monkey. CONCLUSION: Long-term placement of bone plates, and the resulting stress shielding, were found to result in structural changes in the mandibular corpus.
