Bite force measurements for objective evaluations of orthodontic tooth movement-induced pain in rats.

Abstract

OBJECTIVE\nTo examine the reliability of bite force for evaluating orthodontic tooth movement-induced pain in rats.\n\n\nDESIGN\nOrthodontic tooth movement-induced pain was induced by mounting springs (40\u2009g) between incisors and ipsilateral molars in male Sprague-Dawley rats. Five group sets of animals were used: for the first group set, 20 rats were randomly divided into a force group (n\u2009=\u200910) and a sham group (n\u2009=\u200910); for the second group set, 20 rats were divided into a 20-g group and a 80-g group; for the third group set, 20 rats were randomly divided into either a CFA group (complete freund s adjuvant) (n\u2009=\u200910) receiving periodontal injections of CFA at baseline or a control group (n\u2009=\u200910) receiving periodontal injections of saline at baseline; for the forth group set, 24 rats were randomly divided into the following four groups: force\u2009+\u2009saline, control\u2009+\u2009saline, force\u2009+\u2009antiNGF and control\u2009+\u2009NGF (NGF: nerve growth factor). Rats in the fifth group set were used for immunostaining against CGRP. Bite force and bite frequency were measured at baseline (day 0) and following interventions (day 1, day 3, day 5, day 7 and day 14). Two-way ANOVA with repeated measures was used for statistical analysis and a p value less than 0.05 was considered statistical significance.\n\n\nRESULTS\nOur results revealed that bite force was significantly smaller in the force group than in the sham group at all time points (p\u2009<\u2009.001). As compared to the control group, periodontal injections of CFA significantly decreased bite force on the 3rd day (p\u2009<\u2009.01). Moreover, bite force was significantly higher in the force\u2009+\u2009antiNGF group than in the force\u2009+\u2009saline group (p\u2009=\u2009.01\u2009<\u2009.05) while significantly smaller in the control\u2009+\u2009NGF group than in the control\u2009+\u2009saline group (p\u2009<\u2009.05). Bite force was similar between the force\u2009+\u2009antiNGF group and the control\u2009+\u2009saline group (p\u2009=\u2009.71\u2009>\u2009.05) and between the control\u2009+\u2009NGF group and the force\u2009+\u2009saline group (p\u2009=\u2009.58\u2009>\u2009.05). Similar results were found for bite frequency.