[Stress-generated potential (SGP) on the surface of fluid-filled monkey mandible]

Previous studies have shown that stress generated potential (SGP) with bone deformation caused by orthopedic force have an important role in regulation on bone remodeling. The purpose of this study was to evaluate the effects of the chin cap on bone remodeling by elucidating the characteristics and distribution of SGP at various parts on the mandible. Experiment was carried out using a mandible of macaca irus monkey which was kept in moisture with 0.9% saline. SGP was recorded using Ag-AgCl electrode from the 32 sections on the surface of the mandible. The force (3 kg) was applied to the chin with six load conditions. It simulated the force generated by chin cap. Temporomandibular joints and the soft tissue except masseter muscle were kept intact. The results were summarized as follows. 1. SGP was generated only when the load was applied or removed. No SGP was generated when the load was steady, even the absolute value was large. 2. When the interval between "on" and "off" of the load was shorted, generated SGP with "off" timing decreased, while that with "on" timing unchanged. 3. When the load was applied in the low pull direction under the centric occlusion, rather larger negative SGP was recorded at the chin, posterior sections of mandibular body and inferior border of the mandible. 4. When jaw was in closing position, high pull loading generated larger SGP at the alveolar bone and the mandibular body than that with low pull loading, although their electric sign was the same at each recorded sections. 5. When jaw was in opening position, low pull loading generated larger SGP at the posterior parts of the alveolar bone and the mandibular body than that in closing position. 6. When a bite block was placed between the upper and lower teeth, larger amplitude in SGP was the evidence in all the recorded sections especially around the bite block. 7. SGP recorded at the posterior part of the mandible increased with the sliding of the location of the bite block towards posterior portion. 8. The electric sign and the amplitude in SGP and that of the stress analyzed by a finite element method were similar at the each sections on the mandible. This suggests SGP is related with the stress generated in the bone. The results suggested that effects of chin-cap on the bone remodeling might be dependent on the direction of the load, tooth contact, existence of bite block, and its location. Also dynamic loading was suggested to be more effective.