| Orthodontic pain, one of the most cited negative effects arising from orthodontic therapy, begins a few hours after application of an orthodontic force and lasts for approximately several days. In the past, responses of the periodontium were paid more attention in the study of the underlying mechanism for orthodontic pain. However, little attention was put in the pulp. The tooth pulp response to orthodontic force is considered as a negative effect, while the pulp has a dense sensory innervation which, upon any stimulation, conveys sensory signals perceived as pain. Accordingly, insights into the responses and regulations of the pulp following orthodontic force may become important in the prevention of orthodontic pain and in avoiding irreversible pulp damage.Calcitoningene-related peptide (CGRP), being a bioactive polypeptide which has strong effects of dilating vessels, is one of the most important pain-induced neurotransmitter as well. The neurotrophin NGF has been suggested to be an important mediator of inflammatory pain, besides a factor which can support the nourishment, promote regeneration and improve the functional recovery of damaged peripheral nerve. Therefore, to investigate the changes of CGRP and NGF in the pulp during the period of initial orthodontic tooth movement will be important to understanding the mechanism of reaction and repair of pulp following orthodontic force.According to these hints, following experiments are designed to explain the above mentioned problems.1. The changes of histomorphologic and expressions of CGRP and NGF in pulp during the experimental tooth movement in the rat.Objective: To observe histologically the pulp response and investigate the expressions of the CGRP and NGF in pulp tissues during the early phases of orthodontic tooth movement.Methods: Model of the experimental tooth movement was established by application a 5-mm long nickel-titanium closed coil spring, placed from the right maxillary first molar to the maxillary incisors to mimic clinical orthodontic tooth movement. After the specific period of tooth movement of each study group, the animals were sacrificed and specimens containing the teeth submitted to movement were processed and stained with hematoxylin and eosin for histological analysis under light microscopy. The expressions of CGRP and NGF were investigated by immunohistochemical SABC method.Results:1) Light microscopy observation revealed that the vessels in the pulp increased significantly in the 12h group and become wilder and congested in the 3d group. The results showed alteration of the odontoblastic layer, in which the nuclei had distended and diffused chromatin and the cytoplasm was more basophilic, and edema of the pulp connective tissue in the central area of the pulp in the 3d group. In the 7d group, the pulp displayed normal characteristics.2) Comparing to the control group, the expression intensity of CGRP decreased significantly in the 12h group, increased in the 24 group, reached the highest level in the 3d group, and return to normal in the 7d group.3) There had no expression of NGF in the control group. The expression intensity of NGF during the experimental tooth movement was up-regulated to a different extent, and in a time-dependent manner. Expression of NGF increased after 12 hours following orthodontic force, reached the highest at 3 days and decreased obviously at 7 days.Conclusion: The results indicate that orthodontic force may lead to temporary inflammatory reactions and corresponding up-regulated expressions of CGRP and NGF in the pulp during the period of initial orthodontic tooth movement, which means that both of them may take part in the pulp restoration process following orthodontic force.2. The evaluation of pulp status and expressions of CGRP and NGF in human dental pulp following orthodontic force. Objective: To observe the pulp status and the expressions of CGRP and NGF in human dental pulp tissues during the early phases of orthodontic tooth movement and analyze the relationship between the two aspects. Methods:According to Derringer's methods, orthodontic force (in the range of 0.5-1N in a mesial and extrusive direction) was applied to the upper first premolar teeth of the test groups. Electric testing was applied to the test teeth prior to installing appliance. The test teeth were extracted after finishing electric testing and pain questionnaire in the corresponding time after the placement of fixed appliances. Immunohistochemical method (SABC method) was used to localize and examine the expressions of CGRP and NGF in the paraffin section of decalcifying dental tissue.Results:1) Compared with control group, the intensity of pain increased in 1d group, reached the highest level in 3d group and decreased gradually.2) The susceptible rate was 48.2% in the test teeth during 3 days after the placement of fixed appliances, which was more significant greater than in the test teeth above 3 days.3) Comparing to the control group, the expression intensity of CGRP decreased significantly in the 1d group, increased in the 3d group and remained the level to 7 days. In the 15d group CGRP was as same as those in the normal group. 4) Comparing to the control group, the expression intensity of NGF during the experimental tooth movement was up-regulated to a different extent, and in a time-dependent manner. Expression of NGF increased after 1 day following orthodontic force, reached the highest at 3 days, decreased gradually after 7 days and return to normal in the 15d group.Conclusions:The results indicate that the pulp is maybe in the stress state in the early stage of orthodontic treatment, which will lead to pain and could be checked up by electric tester when serious. The present results also showed the up-regulated expressions of CGRP and NGF and suggested that both of them may take part in the pain reaction and pulp restoration in the early stage of orthodontic treatment. |
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