Histomorphometric analysis on bone dynamics in denture supporting tissue under masticatory pressure in rat

The bone dynamics under denture base has not been clarified sufficiently. The purpose of this study was to evaluate histomorphometrically the bone dynamics in denture supporting tissue with relation to the intensity of the masticatory pressure. The removable denture bases, which exerted four different regulated masticatory pressures (0.0, 1.0, 20.0 or 40.0 kPa), were inserted to the hard palate of the molar region of 22-week-old rats. The palatal tissues were excised from 1 to 12 weeks after denture insertion at intervals of 1 week and embedded in methyl-methacrylate. No bone resorption was observed throughout the experimental period in the 0.0 and 1.0 kPa groups. In the 1.0 kPa group compared with the 0.0 kPa group, bone formation parameters except for bone formation rate significantly increased at 4 weeks, but there was no significant difference between these groups in the other experimental periods. In the 20.0 and 40.0 kPa groups, bone resorption was observed until 3 and 5 weeks, respectively, and the amounts of bone resorption (AoBR) were 45 ± 25 and 104 ± 21 μm, respectively. After bone resorption, bone formation parameters in these two groups showed transiently significant decrease compared with the 0.0 kPa group, but were the same time course as the 0.0 kPa group following this decrease. In conclusion, masticatory pressure caused different time courses of the bone dynamics in denture supporting tissue depending on the initial intensity of the pressure. The AoBR responded to the initial intensity of masticatory pressure. Bone formation following bone resorption did not cause equivalent recovery of the bone surface level to the level observed in the case without bone resorption in the present study.