Mechanical and Thermal Hypersensitivities Associated with Orthodontic Tooth Movement: A Behavioral Rat Model for Orthodontic Tooth Movement–Induced Pain

Aim: To test whether orofacial mechanical and thermal hypersensitivities occur in rats during orthodontic tooth movement (OTM). Methods: Sprague-Dawley rats (140 to 160 g) were divided into an experimental (E) group (n =7), with an active orthodontic spring placed in the right side of their mouth, and a sham (S) group (n = 7), with an inactive orthodontic spring. Mechanical sensitivity was tested preoperatively (1 day before attaching the orthodontic spring) and postoperatively (1 hour, 3 hours, 6 hours, days 1 to 7, day 14, day 21, and day 28 after orthodontic spring attachment) on the cheek, upper lip, and maxillary incisor labial gingiva bilaterally by recording the threshold for a head withdrawal response evoked by von Frey filaments. Thermal sensitivity was also tested preoperatively and postoperatively on the cheek bilaterally by applying a noxious thermal stimulus and measuring head withdrawal response duration, response score, and response percentile rate. Statistical analyses involved a mixed-model repeated-measures analysis of variance (MMRM ANOVA). Results: The mechanical and thermal sensitivities at all bilateral sites were significantly increased (P < .01) in the E group in the early postoperative period (1 to 5 days), with peaks reached on day 1, and then returned to and remained at preoperative levels until postoperative day 28. However, there was no significant change from the preoperative levels in mechanical and thermal sensitivities for the S group for all the tested sites. Conclusion: This rat OTM-induced pain model correlates with the time course of OTM-induced pain in humans and suggests that OTM-induced mechanical and thermal hypersensitivities may be useful measures of OTM-induced pain.

behavioral changes; malocclusion; orofacial; orthodontic appliances; sensitization

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