Disuse atrophy of the periodontium in mice

Right, first and second maxillary molars of albino mice were extracted at 25 days of age to observe the long-term effect of early loss of function on teeth without antagonists. Four experimental and three intact controls were sacrificed every 50 days thereafter. Molars were studied grossly as well as microscopically. Macroscopic observations showed marked gingival recession and root exposure on teeth without function. Little cuspal wear occurred on these molars, and there was an intense blackening and discoloration of the enamel. Histologic sections revealed that loss of function alone, without any apparent infection, caused a remarkable and progressive atrophy of the periodontium, leading to its almost total disappearance by 900 days. Alveolar bone was extensively resorbed, particularly interdental bone. There was an apical proliferation of the epithelial attachment, a disorientation and detachment of fibres of the periodontal ligament and a considerable resorption of cementum. Only traces of periodontal tissues remained in the interdental region at 900 days and, in some instances, fusion of root tips of adjacent molars had taken place. There was a pronounced narrowing of the interdental space, but the direction of tooth movement could not be evaluated due to extensive loss of familiar periodontal landmarks. No cemental hyperplasia or supraeruption was apparent. These severe changes, which apparently are initiated at the alveolar crest, were interpreted as being due to the almost complete lack of stimulation of the periodontal tissues by occlusal contact.