Resin-based composites, Polymerization, Light intensity, Marginal quality, Physical properties

Objectives and methods: Administration during root formation of a bisphosphonate, 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP), at a dose corresponding to 10mg P/kg body weight, has been found to interfere with the formation of acellular cementum in rats. The purpose of this study was to measure the force required to extract a tooth lacking normal acellular cementum, and to correlate this force and the ultimate periodontal strength with the morphology of the periodontal tissues at different time intervals after single or multiple injections of HEBP. Results: A single injection of HEBP given during root formation inhibited the formation of acellular cementum and resulted in a temporary reduction of the extraction force and the ultimate tensile strength. Ninety days after the injection of HEBP, both parameters were the same as in the controls. The increase in extraction force and ultimate tensile strength was associated with the onset of occlusal contact of the teeth. The organization of periodontal ligaments was improved after the teeth reached the occlusal level. After daily injections of HEBP for 3 days, there was a permanent reduction in root length and dento-alveolar ankylosis developed in the furcation area. Conclusion: (1) A single or three injections of HEBP changed the formation of acellular cementum to that of an atypical hyperplastic cementum which increased the resorption risk at this site. (2) The ultimate tensile strength was markedly reduced in teeth lacking acellular cementum.