Histomorphometric evaluation of maxillary molar roots and surrounding periodontium following molar intrusion in rats.

OBJECTIVES: To investigate periodontal tissue changes during and after molar intrusion in rats. SETTING AND SAMPLE POPULATION: The Department of Orthodontics at Yonsei University. Thirty 12-week-old male rats were assigned to 1 control and 5 experimental groups (n = 5 each). MATERIALS AND METHODS: In the experimental groups, two maxillary molars were intruded for 2 weeks; the control group underwent the same procedures without the intrusion force. After 2 weeks of intrusion, rats in one of the experimental groups and in the control group were killed. In the other four experimental groups, the new molar positions were either retained or not retained with an occlusal bite block for 1 or 2 weeks prior to euthanization. Histomorphometric analysis was performed for sulcus depth, osteoclast number per unit alveolar bone length, and root resorption area per unit root surface length. RESULTS: Sulcus depth increased during intrusion (P < 0.05), but decreased after 2 weeks of retention (P < 0.05). The number of osteoclasts increased during intrusion (P < 0.05), but subsequently decreased regardless of the retention regime (P < 0.05). Root resorption area increased after molar intrusion, irrespective of the retention regimen, relative to that of the control group (P < 0.05) and was the greatest after 2 weeks of retention. CONCLUSION: These results indicated that root resorption occurred during and after molar intrusion and that the surrounding periodontium remodeled accordingly as tooth positions were altered, regardless of retention regime.