Ankylosis of the mouse molar after systemic administration of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP)

The proposed homeostasis between fibroblasts in the periodontal ligament and bone cells lining the inner aspect of the alveolar wall is thought to be responsible for maintaining the width of the periodontal ligament space. In the present study, we attempted to interfere with this cellular balance by systemic administration of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP). The maxillary left molars of mice were extracted. They then received a daily subcutaneous injection of HEBP (10 mg P/kg b.w.) for periods of 10, 30 or 50 days. A 2nd group of animals received HEBP without molar extraction. Control groups were injected with Ringer's solution. The animals were sacrificed after the last injection and the mandibles processed for light and electron microscopy. HEBP treatment caused a significant decrease of the width of the periodontal ligament space which was influenced by time. Ankylosis started to occur after 30 days, predominantly in the interradicular areas and was more common around unopposed teeth. At 50 days, signs of resorption were seen along the acellular cementum layer. During HEBP-administration, extensive deposition of newly formed cementum matrix was observed along the cellular cementum but this activity was not seen along the acellular cementum. It is concluded that HEBP interferes with the mechanisms that mediate preservation of the periodontal ligament width.