Abstract:

Objective　The purpose of this study was to investigate the physiological process of healing after tooth extrac- tion and the biological reaction of toothmovement into extraction siteswith the aim of selecting optimal time of toothmovement into extraction sites clinically.Methods　Extraction of upper first molars were performed on 30 male Sprague-Dawley rats which were divided equally into 5 groups. Orthodontic appliance was placed at different time after tooth extraction in order to move the maxil- lary second molars mesially into the extraction spaces. The animalswere injected continuouslywith tetracycline and calcein for two days before appliance activation and animal sacrifice. Undecalcified mesio-distal specimans 65~100 microns of thickness were prepared. The quantification of bone remodeling parameters on tooth movement into extraction sites at different time was performed by histomorphometric measurements and computer image analysis.Results　①The bone turnover had two bone modeling process- es: resorption under pressure and formation in tension.②The bone resorption was more active on the mesial surface (pressure side) than that on the distal surface (tension side). While bone formationwasmore active on the distal surface (tension side) than that on the mesial surface (pressure side).③Both the resorptive parameters and the formative parameters across time were mani- fested by a peak at day 7 aftertooth extraction.Conclusion　①Orthodontic retraction into extraction sites should be initiated at an early stage after tooth extraction, so that the advantage of bone remodeling in extraction sites was used.②The optimal time of tooth movement into extraction sites clinically was about a week after tooth extraction.

Key words: tooth extraction, alveolar remodeling, histomorphometric measurements, experimental study