Behavioral assessment of masseter mechanical hyperalgesia in rats with unilateral malocclusion / 实用口腔医学杂志

ABSTRACT

Objective:To assess mechanical hyperalgesia of the bilateral masseter muscles following the induction of experimental unilateral malocclusion in rats. Methods:① An elastic rubber(3M Unitek,1/8#) was inserted between the first and sencond upper molars on the left side of 4 Sprague- Dawley rats to induce malocclusion.② The left maxillary first molar of 4 rats were filled with metal arsenic for 7 days to inactivate tooth pulp, and then a dentin pin(d 0.75 mm, long 1.5-2.0 mm,0.5-1.0 mm above the occlusion surface)was bonded in the pulp chamber to induce acute traumatic occlusion, and 4 control animals were treated as the same procedure but not raised occlusion surface.③ According to Ren's method, von Frey filaments were used to assess the muscle mechanical threshold.Head withdrawal, leg raising and crying were observed as painful actions. Results:① In gradually induced malocclusion group,hyperalgesia was induced in bilateral masseter muscles from 3 to 9 d, and the peak time was the 7th day. ②In the acute traumatic occlusion group, the ipsilateral masseter muscle was demonstrated hyperalgesia for 5-7 days, and the peak time was the 2nd day. Conclusions:Traumatic occlusion may lead to masseter muscles hyperalgesia, and there existe some differences for pain behavior between the acute and the chronic occlusion trauma.