Threshold for bone resorption induced by continuous and intermittent pressure in the rat hard palate.

Osteoclastic bone resorption under the denture base has been considered to be influenced by mechanical force exerted through the denture base. However, no scientific evidence has been shown concerning whether osteoclastic bone resorption is a pressure-threshold-regulated phenomenon or merely a proportionally pressure-dependent phenomenon. In this study, a clear statistical criterion as an objective standard for the evaluation of histopathological bone resorption was established, and the relationship between the amount of continuous or intermittent compressive pressure exerted on the rat hard palate and induced osteoclastic bone resorption was studied based on this criterion. Eighty-five male rats of the Wistar strain, 15 weeks of age, were fitted with experimental dentures which were designed to exert a defined amount of continuous or intermittent compressive pressure on the intermolar region of the hard palate. No bone resorption was observed when continuous compressive pressure was < or = 1.96 kPa or when intermittent compressive pressure was < or = 9.8 kPa. In contrast, continuous compressive pressure > or = 6.86 kPa or intermittent compressive pressure > or = 19.6 kPa caused significant bone resorption in all rats studied. From these results, it was revealed that osteoclastic bone resorption under the denture base was a pressure-threshold-regulated phenomenon, and that the thresholds exist for the induction of bone resorption under the denture base by both continuous and intermittent compressive pressure, respectively. It was also clearly revealed from the results that the threshold for continuous compressive pressure is lower than that for intermittent compressive pressure.