Quantitative radiographic changes in the mandible and the tibia in systemically loaded rats fed a low-calcium diet

The combined effect of the duration of loaded physical exercise and the per centage of calcium intake on the mandible and tibia were studied in develop ing male rats. For the loaded exercise, rats ran on a treadmill at a rate o f 12 m per min for either I or 2 h per day, A total of 54 4-week-old male W istar rats were randomly assigned to one of six groups. After 4 weeks of th e diet and loaded exercise, the rats were killed and their mandibles and ti bia were removed. Each individual bone was assessed by radiography and the radiographs were then used for measurements of cortical thickness, bone len gth and bone width. All radiographic images were analyzed using a computer- based scanner image analysis system. In addition, we measured the dry weigh t both of the tibia and mandible. The results demonstrated that significant differences in cortical thickness, bone length, bone width, and bone weigh t, both of the tibia and the mandible, were detectable between the normal d iet group and the low-calcium diet group. Among the normal diet groups, sig nificant differences were found in cortical thickness, bone length, bone wi dth, and bone weight of the tibia, whereas no significant differences in ei ther cortical bone thickness, bone length or bone weight of the mandible we re detected. in contrast, among the low-calcium diet groups, no significant differences were detected in cortical thickness, bone length, bone width o r bone weight for either the tibia or the mandible. Our results suggested t hat systemic exercise, such as running, promote the linear dimensions and t he cortical thickness of the tibia in response to local stimuli. Furthermor e, sufficient calcium intake appears to be necessary to allow the effect of systemic exercise on tibial bone growth to occur. In contrast, systemic lo aded exercise does not promote either bone growth or development of the man dible even under conditions of sufficient calcium intake.