Effects Of Different Orthodontic Forces On Pulp Vitality, Changes Of Fos And MMP-9Expression In Dental Pulp Tissue

Effects of Different Orthodontic Forces on Pulp Vitality, Changes of Fos and MMP-9Expression in Dental Pulp TissueThe development of new methods to accelerate orthodontic tooth movement (OTM) has been sought by clinicians as a way to shorten treatment times, reduce adverse effects, and avoid root resorption and necrosis. Orthodontic movements have been considered to cause some inflammatory alterations in the dental pulp that are proportionally correlated with the magnitude, direction, and duration of the force applied. Orthodontic forces are known to produce inflammatory reactions in the periodontium, as well as cell damage, inflammatory changes, vascular changes and circulatory disturbances, even pulp necrosis in dental pulp.Several investigators have suggested that injury from orthodontic forces might be permanent and that the pulp eventually could lose its vitality. According to other researchers, however, orthodontic forces do not have significant longlasting effects on the dental pulp. Whether heavy intrusive force will cause the loss of pulp vitality is one of the concerns of this experiment. Dental pulp is a special type of loose connective tissue characterized by few cells and abundant amorphous extracellular matrix rich in proteoglycans and glycosamino glycans and poor in collagen fibers. The main functions of the dental pulp include synthesis of dentine, providing the tooth with blood and lymphatic vessels, synthesis of reparative or secondary dentine, and providing the tooth with nervous innervation. The effects of orthodontic forces on the pulp have not yet been significantly investigated.The proto-oncogene c-fos is an important member of Immediate-early gene family. The up-regulation of c-fos transcription may ultimately result in remodeling of the matrix. The Fos protein encoded by c-fos gene is an important component of the transcription factor activating protein-1(AP-1) complexes which play a key role in relative cellular proliferation and differentiation. The c-Fos protein and c-Jun families are activated, bind to form heterodimers, and ultimately form AP-1complexes. Binding of AP-1to the promoter/regulatory region of genes modulates the transcription machinery, which alters gene expression. The c-Fos protein appears to play the role of a third messenger in the cascade of events initiated by the activation of extracellular signals. The study suggested that VEGF may increase c-fos through AP-1to promote the chemotaxis, proliferation, and/or differentiation of human dental pulp cells. Another study showed c-fos was thought to play a part in the proliferation and differentiation of periodontal ligament fibroblasts. Matrix metallopeptidase-9(MMP-9) is involved in the breakdown of the extracellular matrix both in physiological and pathological processes. It degrades type IV and V collagens. MMP-9activity is under strict control by cytokines and cellular interactions, and plays an important role in tumor invasion, angiogenesis and metastasis. Recently, experimental orthodontic tooth movement in animals, mostly rats, shows an increased expression of MMP-9in the PDL and alveolar bone, and at the resorption side in gingival crevicular fluid. Interestingly, MMP-9is a well-defined AP-1target in non-neuronal cells. In the study of invasion process of mammary carcinomas, expression of c-Fos correlated with MMP-9protein levels. So far, no studies explore the following questions:whether Fos protein is involved in the remodeling process of the pulp tissue under the orthodontic force; the variation of MMP-9in the pulp tissue during the tooth movement; and whether there is a certain link between the expression of Fos protein and MMP-9.Objective:The aims of this study were to①investigate the pulp vitality, internal resorption and histologjcally the human pulp response to the heavy orthodontic intrusive force;②investigate the changes in the pulp tissue under the different intrusive force;③investigate the changes of expressions of Fos and MMP-9as functions of initial orthodontic force magnitude and time following applicance activation;④and whether there is a certain link between the expression of Fos and MMP-9.Methods:Part one:Twenty-seven patients were assigned to three groups. The control group (3subjects) was extracted the first premolars before orthodontics. The low-force group consisted of12subjects who had50g of directed orthodontic force applied to the first premolars bilaterally, and the high-force group (12subjects) applied300gforce. The forces were applied for1,4,8, or12weeks. An electric pulp tester (EPT) was then used to test for vitality, when teeth that did not respond to EPT were subsequently tested thermally (TT). First premolars were extracted in1,4,8and12week respectively. Part two:The experiment groups each (90Wistar rats) were unilaterally placed appliance activated to40and100g of initial force designed to mesially tip the maxillary first molars. Control group had5Wistar rats. The rats were killed at6,12,24,48hours,3,7,14,21and28days. Then, teeth of part one and part two were extracted, prepared for histological examination, and stained with hematoxylin and eosin, TRAP and immunohistochemistry. Pulpal measurements were made with an Image-Pro Plus analyzer and included changes of Fos and MMP-9protein, and then statistical analysis was done using SPSS.Results:Part one①The teeth in the high-force group responded negatively to EPT at T4, while a negative response occurred at T8in the low-force group. From8weeks to12weeks, the teeth in both groups responded negatively to EPT. However all the teeth still responded positively to the thermal test. There was a significant difference between the low-and high-force groups at T1,T2and T3(P<0.05). As the observation weeks passed, readings of pulp vitality increased.②During the intrusion period, mild inflammation such as odontoblast disruption, vacuolization, and moderate vascular congestion were found in both groups. Only in the highforce group, pulp stones were observed. And in both groups, there were no TRAP positive cells and smooth along the inner surface of the pulp.③The expression of Fos in both groups were increased as orthodontic force following. In8weeks and12weeks, Fos expression in the low-force group was higher than that in normal control group, with statistical difference (P<0.05和P<0.001). In4,8and12weeks, Fos expression in the high-force group was significantly higher than that in normal control group (P<0.001).④The expressions of MMP-9in both groups were increased as orthodontic force following In4weeks and8weeks, MMP-9expression in the low-force group was higher than that in normal control group, with statistical difference (P<0.001and P<0.05). In4,8and12weeks, MMP-9expression in the high-force group was significantly higher than that in normal control group (P<0.001).⑤At the same time, the expressions of Fos and MMP-9in the high-force group were higher than that in the low force group. The expression of Fos in the low-force group compared with that in the high-force group, there was significant difference in4weeks (P<0.001). The expression of MMP-9in the low-force group compared with that in the highforce group, there was significant difference in4,8and12weeks (P<0.001).⑥The expression of MMP-9in the high-force group was significantly correlated with Fos expression (P<0.001). The expression of MMP-9in the low-force group wasn't statistically correlated with Fos expression (P>0.05)Part two:①The rat teeth in the low-and high-force group, showed mild inflammation reactions including odontoblast disruption, vacuolization, moderate vascular congestion, but no necrosis performace were found. In both groups, there were no TRAP positive cells and smooth along the inner surface of the pulp.②The expression of Fos in both groups on the time were not uniform, first increase then reduce. The peak occurred on24th hours. Compared the expression of Fos in the low-force group with that in normal control group, there were statistical difference(P<0.05) in12,24,48hours and3days. Compared the expression of Fos in the high-force group with that in normal control group, there were statistical difference (P<0.05) in12,24,48hours,3,7and14days.③The expression of MMP-9in both groups on the time were not uniform, first increase then reduce. The peak occurred on48th hours. Compared the expression of MMP-9in the low-force group with that in normal control group, there were signiffcant difference (P<0.001) from12hours to7days. Compared the expression of MMP-9in the high-force group with that in normal control group, there were significant difference (P<0.001) from12hours to14days.④At the same time, the expressions of Fos and MMP-9in the high-force group were higher than that in the low-force group. The expression of MMP-9in the low-force group compared with that in the high-force group, there was statistical difference in24,48hours,7and14day s (P<0.001).⑤The expression of MMP-9in both groups were significantly correlated with Fos expression (P<0.001)Conclusions:①During experimental tooth movement with different force magnitude, no pulp necrosis and internal resorption were present based on histological analysis.②The expression of Fos and MMP-9showed not uniform on the time and a force-dependent increase characteristics.③During dental pulp tissue remodeling following tooth movement, the expression of Fos andMMP-9might have some relevance.