[Effects of the localized thermal enhancement on new bone formation following mechanical expansion of the rat sagittal suture].

The purpose of this study was to investigate the effects of localized thermal enhancement on new bone formation in rats. Sixty four male Wistar rats of 52-day old were used as the experimental animal. The sagittal suture of the rat was expanded with the force of 75 g by means of an expansion appliance. After the force application for 2 days, the expansion appliance was fixed with a composite resin. The infrared ray was applied to the expanded sagittal suture for 20 minutes a day and the temperature, just above the sagittal suture, was measured with a biothermometer. The local heat was given for 5-days. The experimental animals were divided into 4 groups based on the increase of temperature: Control, 1 degree C, 2.5 degrees C and 4 degrees C groups. The sagittal suture of each rat was examined by both light and fluorescent microscopies. And histochemistry for acid phosphatase and tartrate-resistant acid phosphatase (TRAP) were performed. The results obtained were as follows: 1) In control and 1 degree C groups, little reaction of acid phosphatase and TRAP were observed in the sutural tissue except for the marrow and the neighboring area of the capillary vessels. 2) In 2.5 degrees C and 4 degrees C groups, an increased absorptive area of the bone and an active reaction of acid phosphatase were found in the sutural area. 3) In only 1 degree C group, an increased new bone formation was evident in the sutural area. Results obtained suggested that the degree of new bone formation depended on the temperature of tissues concerned.