| Objective: In the process of orthodontic treatment, pain is not only the most commonly happened but also the most difficult problem to solve.There are more and more research on how to reduce or eliminate pain in clinical orthodontic treatment and the mechanism of orthodontic pain.Trigeminal ganglion and spinal trigeminal nucleus can accept and transmit noxious stimulus.Some nucleotide receptors in trigeminal ganglion and spinal trigeminal nucleus play a role in mediating maxillofacial noxious stimulus.In the nervous system, nucleoside triphosphate,a kind of signal molecule,can produce a series of physiological effects by activating P2 receptors.In this study,we try to analyze the regularity of pain through behavioral study in the progress of mimic orthodontic treatment.At the same time,we try to analyze the correlation of pain occurs and expression changes of P2Y2 and P2Y6 in trigeminal ganglion and spinal nucleus of trigeminal nerve.Research on the mechanisms of occurence and remission of orthodontic pain in peripheral and central nervous system may provide a theoretical basis for developing anew type of maxillofacial analgesic drugs.Methods:A. Establish orthodontic tooth movement mode in rats. 1. Establish orthodontic tooth movement mode on rats. Forty-two male Sprague-Dawley rats were divided into one control group and six experimental groups randomly. Each group included 6 rats. Two maxillary incisors played a role as resistance. In the experimental groups,80 g force pulled the left maxillary first molars to move mesially. According to the duration of the orthodontic force,experimental groups were divided into 6 sub-groups: 12 h, 1d, 2d, 3d, 5d, 7d. The control group rats,without orthodontic tooth movement model,were feed with experimental group rats together. 2. Observation of the effect of tooth movement under orthodontic tooth movement model. Observed the movement of the left maxillary first molars on rat specimens at 12 h, 1d, 2d, 3d, 5d and 7d after force was applied. 3. Rsearch on periodontal tissue change in the process of orthodontic tooth movement.Treated all groups rats' left maxillary first molars and periodontal tissue with HE staining. Observed the reconstruction of the alveolar bone on the pressure side in the process of orthodontic tooth movement.B. Rsearch on the regularity of pain occurrence in the process of orthodontic tooth movement. 1. Behavioral study of rats during orthodontic tooth movement. Placed a rat in home-made transparent plastic box and observed the rats behavior performance through the following methods of each group.(1)Open field test: Recorded the following data with a video player: lines crossed in the first 30 seconds, lines crossed in the first 5 minutes, lines crossed to the center in the first 5 minutes and rearing time in the first 5 minutes.(2)Face grooming test : Recorded the total time of rat face grooming behavior with a video recorder within 5 minutes.According to the above measuring index to evaluate the behavior performance of rats and analyze the differences between control and experimental groups.2. CGRP m RNA and PPTA m RNA change in trigeminal ganglion in the process of orthodontic tooth movement. In trigeminal ganglions, the expression regularity of CGRP m RNA and PPTA m RNA was tested by RT-PCR method.C. P2Y2 and P2Y6 changes in trigeminal ganglion and spinal trigeminal nucleus in the process of orthodontic tooth movement. 1. In trigeminal ganglion and spinal trigeminal nucleus, the expression of P2Y2 m RNA and P2Y6 m RNA was tested by RT-PCR method. 2. In trigeminal ganglion and spinal trigeminal nucleus, the expression of P2Y2 and P2Y6 receptors was tested by Western Blot method.Results:A. The effect of tooth movement under orthodontic tooth movement model 1. The effect of tooth movement under orthodontic tooth movement model:2 days after the force was applied on the first molars,the contact of first and second molar proximal surfaces was not as close as control group rats'. Subtle gaps could be detected after the force was applied on the first molars for 3 days. Gaps broadened in the 5 d group and 7 d group rats. 2. Rsearch on reconstruction of periodontal tissue in the process of orthodontic tooth movement.Compared with control group rats, the number of bone absorptive lacunae increased and the degree of alveolar bone absorption deteriorated after force was applied on first molars for 12 hours to 7 days.There was no obvious absorption on cementum surface.B. The regularity of pain occurrence in the process of orthodontic tooth movement. 1. Results of behavioral test:(1)Results of open field test: Compared with control group, lines crossed in the first 30 seconds, lines crossed in the first 5 minutes, lines crossed to the center in the first 5 minutes and rearing time in the first 5 minutes, four parameters of experimental groups mentioned before decresed from 12 h, bottomed on 2d(P<0.05), then gradually increased from 3d, and eventually increased to the level of control group on 5~7d.(P>0.05)(2)Results of facial grooming test: The total time of face grooming behavior within 5 minutesincreased from 12 h, peaked on 2d(P<0.05),gradually decreased from 3d,and eventually decreased to the level of control group on 5~7d(P>0.05). 2. Results of change of expression of CGRP m RNA and PPTA m RNA in trigeminal ganglion: RT-PCR results showed the expression level of CGRP m RNA and PPTA m RNA in trigeminal ganglion of experimental groups increased from 12 h and reached the peak on 2d(P<0.05), then began to decrease and returned to the level of control group on 7d(P>0.05).C. P2Y2 and P2Y6 changes in trigeminal ganglion and spinal trigeminal nucleus in the process of orthodontic tooth movement 1. RT-PCR results showed:In the trigeminal ganglion and spinal trigeminal nucleus of experimental groups, the expression of P2Y2 m RNA ? P2Y6 m RNA increased from 12 h, reached the peak on 2d(P<0.05), then began to decrease and returned to the level of control group on 7d(P>0.05). 2. Western Blot results showed the expression level of P2Y2 and P2Y6 receptors in trigeminal ganglion and spinal trigeminal nucleus of experimental groups increased from 12 h,reached the peak on 2d(P<0.05), then began to decrease and returned to the level of control group on 7d(P>0.05).Conclusions:1. In the process of orthodontic tooth movement,the regularity of pain is: pain appear 12 hours afer the force was applied on the teeth, peak on 2 day, gradually decreased from 3 day,and eventually eliminate on 5~7 day.2. In the process of orthodontic tooth movement, CGRP m RNA and PPTA m RNA are involved in the pain occurrence and transmission in the trigeminal ganglion.3. In the process of orthodontic tooth movement, the expression of P2Y2 and P2Y6 increase when pain aggravate and decrease when pain relieve. There is correlation between orthodontic pain and expression change of P2Y2 and P2Y6 in the trigeminal ganglion and spinal trigeminal nucleus.This result suggests that, maybe P2Y2 and P2Y6 receptors are involved in the signal transmission in central and peripheral nerve in the process of orthodontic tooth movement. And maybe the increased expression of P2Y2 and P2Y6 is one of the biological mechanisms of orthodontic pain. |
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