Rubber Hardness Discrimination and Associated Bite Force in Osseointegrated Implant Patients

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To clarify the functional role of the periodontal membrane, interdental discrimination ability of rubber hardness was examined in 20 normal dentate subjects and 6 implant patients with cleft palate. One titanium implant [Branemark system] was inserted into the upper incisor site after orthodontic treatment. Five different test pieces of rubber hardness were prepared for the experiment. Each piece was placed at the site of upper implant incisor and natural incisor. The subjects were asked to assess whether a test piece was felt harder, softer or similar in hardness compared with a reference test piece. Bite forces were electrically measured with strain gauge during the discrimination. The error rate of the normal dentate subjects was 25.2【minus-plus】7.5% (mean 【minus-plus】 SD) on the left site, and 28.2【minus-plus】5.4% on the right. In the implant patients, the error rats were 23.3【minus-plus】5.0% in the natural site, and 28.0【minus-plus】8.7% in the implant site. Any differences in the error rates were not observed between subjects, and between sites examined. In the implant patients, the median of error distribution for rubber hardness in the natural site was not different from implant site (natural : 51.1【minus-plus】3.2 deg., implant : 50.2【minus-plus】2.5 deg.). However, bite forces of the patients were significantly higher than that of normal dentate subjects (p<0.001), and bite forces in the natural site were not different from those in the implant site in individual patients. These results suggested that the periodontal membrane of these implant patients may be affected by orthodontic treatment, and that, controlling bite forces, periodontal membrane in the lower teeth may play compensation in rubber hardness discrimination.