Vascular changes in the periodontal ligament after removal of orthodontic forces.

Vascular changes in the periodontal ligament after release of orthodontic force and their possible contribution to relapse of relocated teeth are poorly understood. This study documented the periodontal vascular changes after 2 weeks of tooth movement and during a 3-week period after release of orthodontic force. This study is the first comprehensive quantitative description of these events. Changes in blood vessel number and density were correlated with the direction of tooth movement (initially mesial in response to force but later distal because of relapse). Application and removal of orthodontic force produced significant changes in blood vessel number and density, which were not related to changes in tissue volume. The vascular changes were dependent on the site of evaluation and the size of the blood vessel. The periodontal vascular distribution and density can be summarized as follows: (1) increased after application of orthodontic force, (2) transient decrease subsequent to removal of force, (3) transient increase during reactivated distal drift, and (4) normalization. Normalization was achieved during an interval equivalent to the duration of orthodontic force, suggesting that the vasculature could modulate interstitial tissue pressures, resulting in relapse of relocated teeth. The role of the periodontal vasculature in alveolar remodeling and in modifying interstitial tissue fluid pressures coincident to human tooth movement requires further study.