The process of healing periodontal ligaments (PDL) after transplantation has been widely examined, but the mechanism for preventing dentoalveolar ankylosis is still unclear. In this study, we focused on the role of mechanical stimuli in preventing ankylosis using an animal model of tooth transplantation assessed by histologic observation and evaluation of proliferating PDL cells. Five-week-old Sprague-Dawley male rats were divided into occluded and nonoccluded groups. The right maxillary first molars were replanted in both groups, and histologic observations were carried out after one or two weeks. The proliferative activity of PDL cells was also examined by assessing the distribution of 5-bromo-2'-deoxyuridine (BrdU). After two weeks in the nonoccluded group, ankylosis was clearly detected and PDL stricture was obvious, whereas no severe bone or root resorption was observed. On the other hand, the occluded group showed an enlarged and thickened PDL with extensive root resorption, but no ankylosis. Based on these findings, the replanted teeth were given a one-week healing period and then occlusion recovery was assessed, which resulted in decreased ankylosis and root resorption. The proliferative activity of PDL cells in the occluded group was generally higher than in the nonoccluded group. The activity of PDL cells in the recovery group was also higher than that of the nonoccluded group. These results suggest that occlusal stimuli promoted the regeneration of the PDL and prevented dentoalveolar ankylosis, whereas excessive initial force might cause severe root and bone resorption.