Pulp vascular changes following orthodontic tooth movement in rats

Orthodontists wish to achieve the desired tooth movement quickly with minimum tissue damage and little discomfort to the patient. How the vascular response of the dental pulp to orthodontic force application fits into achieving these goals has been a controversial issue in the literature. The purpose of this study was to correlate pulpal changes histomorphometrically with the type of orthodontic tooth movement and the duration of force application. Six groups of five young male Sprague-Dawley rats each received different types of tooth movement and durations of orthodontic force application were studied. The effects of tipping, intrusive and extrusive orthodontic tooth movements for 24 hours, 3 days, and 7 days were assessed relative to non-operated controls. After each experimental period, rats in each group were killed, specimens were fixed and decalcified, and sections of the maxillary first molar were stained with hematoxylin and eosin. Images of representative sections were recorded for each specimen and the total number of blood vessels was identified for each subject using image analysis software. Findings indicated a significant increase (p < 0.05) in the mean number of blood vessels in the pulp chamber after 24 hours of tipping movement. However, there was a significant decrease (p < 0.05) in the mean number of pulpal blood vessels after 24 hours of intrusive movement. The effect of tipping and intrusion relative to controls after 3 and 7 days was insignificant (p > 0.05). Also, the effect of tooth extrusion for all durations was insignificant (p > 0.05). These results indicate that both the type of orthodontic tooth movement and the duration of orthodontic force application play a role in the vascular response of the dental pulp.