Effects of experimental occlusal hypofunction, and its recovery, on mandibular bone mineral density in rats

The aim of this investigation was to examine the effects of experimental occlusal hypofunction, and recovery, on mandibular bone mineral density (BMD) using peripheral quantitative computed tomography. A metal cap was inserted between the upper and lower incisors of 40 male Wistar rats (aged 6 weeks) to prevent the molars from biting. The rats were divided into two equal groups: 'hypofunction' and 'recovery' animals. In addition, there was a third group comprising 20 control animals. The recovery animals were anaesthetized at 4 weeks in order to remove the metal cap using pliers. The rats were killed under deep anaesthesia, after which the mandibles were immediately removed and fixed in 10 per cent neutral formalin. After 2, 4, 6, and 8 weeks, BMD was measured in the cancellous and cortical bone in the first molar region. Data were analysed using one-way analysis of variance. At 6 and 8 weeks, in the hypofunction group, cancellous bone density decreased on the buccal and lingual sides, at the bifurcation of the root and at the root apex. In the recovery group, the density on the buccal and lingual sides had recovered to the normal levels, compared with the control group. However, density of the bifurcation of the root and the root apex recovered by only 30 and 50 per cent, respectively. At 6 and 8 weeks, cortical bone density in the hypofunction group had reduced in the lingual basal and lingual middle cortical bone areas. Cortical bone density in the lingual basal and lingual areas recovered to control group levels at 6 weeks. Recovery of occlusal hypofunction may restore decreased BMD of both cancellous and cortical bone.