Influence of the occlusal interference time on masticatory muscle mechanical hyperal-gesia in rats / 北京大学学报(医学版)

ABSTRACT

Objective:To investigate the relationship between the removal time of 0.2 mm occlusal in-terference and the recovery of masticatory muscle mechanical hyperalgesia in rats.Methods:Forty male Sprague-Dawley rats (200-220 g)were randomly assigned to eight groups,with five rats in each group(1 )nave groupthese rats were anesthetized and their mouths were forced open for about 5 min (the same duration as the other groups),but restorations were not applied;(2 )sham-occlusal interference control groupbands were bonded to the right maxillary first molars which did not interfere with occlu-sion;(3 )occlusal interference group0.2 mm thick crowns were bonded to the right maxillary first molars;(4)2,3,4,5,and 6 d removal of occlusal interference groups0.2 mm thick crowns were bonded to the right maxillary first molars and removed on days 2,3,4,5,and 6.The nave group and sham-occlusal interference control group were control groups.The other groups were experimental groups. Bilateral masticatory muscle mechanical withdrawal thresholds were tested on pre-application days 1 ,2, and 3,and on post-application days 1 ,3,5,7,1 0,1 4,21 and 28.The rats were weighed on pre-application day 1 and on post-application days 1 ,2,3,4,5,6,and 7.Results:Between the nave group and the sham-occlusal interference control group,there was no significant difference in the mastica-tory muscle mechanical withdrawal threshold of bilateral temporalis and masseters at each time point.No significant difference was detected between the contralateral side and ipsilateral side in experimental groups (P>0.05 ).In the 2,3,4,and 5 d removal of occlusal interference groups,the masticatory muscle mechanical withdrawal thresholds decreased after occlusal interference and increased after removal of the crowns and recovered to the baseline on days 7,1 0,1 4,and 1 4,respectively [the masticatory muscle mechanical withdrawal thresholds of right masseter muscle were (1 37.46 ±2.08)g,(1 39.02 ± 2.1 1 )g,(1 40.40 ±0.98)g,(1 38.95 ±0.98)g,respectively].In the 6 d removal of occlusal inter-ference group,the masticatory muscle mechanical withdrawal threshold increased after removal of the crowns and became stable since day 1 4.There was a significant difference between the 6 d removal of oc-clusal interference group and the sham-occlusal interference group on day 28(P<0.05),the masticatory muscle mechanical withdrawal thresholds of right masseter muscle were (1 31 .24 ±0.76 ) g and (1 41 .34 ±1 .43)g,respectively.Conclusion:After removal of the 0.2 mm thick crown within 5 days, the mechanical hyperalgesia of the rats could reverse completely.The mechanical hyperalgesia of the rats could only be relieved,but not reverse completely after removal of the 0.2 mm thick crown on day 6.As the time went on,even minor occlusal interference could cause irreversible mechanical hyperalgesia of masticatory muscles.This study suggested that occlusal interference caused by dental treatment should be eliminated as soon as possible,to avoid irreversible orofacial pain.