Résumé
Objective@#To investigate the effect of low level laser on osteoclast and collagen fiber remodeling during the process of tooth retention after tooth movement in rats and to provide the experimental basis for clinical application.@*Methods @# In total, 20 eight-week-old Wistar rats were selected to establish a mesial movement model of the maxillary first molar and then randomly divided into four groups after the appliance was removed. In total, 5 rats were included in each group, including baseline group (without force as blank control), control group (without any intervention after removing the force appliance), retention group (teeth were wrapped with orthodontic ligature wires that were screwed into hemp flower as fixed retention to maintain the space between the first molar and incisor after appliances were removed) and retention and low energy laser irradiation group (teeth were wrapped with the orthodontic ligature wires that were screwed into hemp flower as fixed retention and low energy laser irradiation was applied on days 0, 3, 6, 9 and 12 after appliance removal). Two weeks later, all the rats were sacrificed and the first molar tissue blocks of each group were collected. The distribution of osteoclasts and collagen fiber were studied by HE staining, TRAP staining and Masson staining to illustrate the process of alveolar bone and collagen fiber remodeling.@*Results @# Two weeks after appliances were removed, collagen fibers were deposited on both sides of the root in the baseline group, but no osteoclasts were observed in the distal side of the root. In the control group, collagen fibers on the two sides of the root were not obvious and osteoclasts were active on the distal side. In the retention group, collagen fibers were obvious on the two sides of the root and the osteoclasts on the distal side were less active than the control group. Regarding the retention and low energy laser irradiation group, collagen fibers were significantly obvious and osteoclasts were not seen. The difference was statistically significant between the retention and low energy laser irradiation group and the other three groups (P＜0.05). @*Conclusion@#These results suggest that fixed retention with simultaneous low level laser can effectively promote the synthesis of collagen fibers and inhibit the activity of osteoclasts during the process of tooth retention after movement, thus reducing the possibility of molar recurrence.
Résumé
Objective@#To investigate the expression and function of the TNF signaling pathway in the early stage of orthodontic tooth movement with periodontitis and to provide evidence to study the early inflammatory response in patients with periodontitis orthodontic treatment. @*Methods@#Sixteen SD rats were randomly divided into four groups: group A--12 h of orthodontic tooth movement of the bilateral maxillary first molars in rats with periodontitis; group B--periodontitis model of the bilateral maxillary first molars without orthodontic tooth movement; group C--12 h of orthodontic tooth movement of the same teeth in rats with healthy periodontium; group D--control group without operations. The bilateral maxillary first molars and surrounding periodontal tissue of each group were collected for gene chip detection. Pathway enrichment analysis, qRT-PCR and GO (gene ontology) analysis were performed to identify differential genes involved in the TNF signaling pathway. @*Results @#Gene chip results showed that the TNF signaling pathway was significantly upregulated in group A, group B and group C (P <0.01). Among the differential genes involved in the pathway, 28 were upregulated and 5 were downregulated in group A, 12 were upregulated and 4 were downregulated in group B, and 12 were upregulated and 1 was downregulated in group C (P <0.05). The most significant GO items included "response to lipopolysaccharide", "inflammatory response", "positive regulation of NF-κB transcription factor activity", "positive regulation of NF-κB import into nucleus" and "response to hypoxia"(P <0.001). qRT-PCR results showed no significant difference in TNF-α mRNA expression in group C compared with that in group D, TNF-α was upregulated in both groups A and B (P <0.01), and mRNA expression decreased in the following order: group A > group B > group C (P <0.05). Compared with group D, the expression levels of prostaglandin-endoperoxide synthase 2 (PTGS2) and interleukin-6 ( IL-6) in groups A, B and C were significantly upregulated (P <0.05), but the expression levels of PTGS2 and IL-6 in group A were lower than those in group B (P < 0.05). @*Conclusion@#The TNF signaling pathway is activated in the early stage of orthodontic tooth movement in rats with periodontitis. The pathway products participate in many biological processes and play an important role in the inflammatory response and bone absorption.