The role of ephrinB2-EphB4 signalling in bone remodelling during orthodontic tooth movement.

OBJECTIVE: The aim of this study was to investigate the role of ephrinB2-EphB4 signalling in alveolar bone remodelling on the tension side during orthodontic tooth movement (OTM). MATERIALS AND METHODS: An OTM model was established on sixty 8-week-old male Wistar rats. They were randomly divided into the experimental group and the control group. The animals in the experimental group were administrated with subcutaneous injection of EphB4 inhibitor NVP-BHG712 every other day, whereas the control group received only the vehicle. Samples containing the maxillary first molar and the surrounding bone were collected after 0, 3, 7, 14 and 21 days of tooth movement. RESULTS: EphrinB2-EphB4 signalling was actively expressed on the tension side during tooth movement. Micro-CT analysis showed the distance of tooth movement in the experimental group was significantly greater than that of the control group (P < .05) with significantly increased trabecular separation (Tb. Sp) and decreased trabecular number (Tb. N) from day 14 to day 21. The number of osteoclasts significantly increased in the experimental group compared with the control group after 3 and 7 days of tooth movement (P < .05). The expressions of alkaline phosphatase (ALP) and osteopontin (OPN) were significantly reduced by inhibition of EphB4 (P < .05). CONCLUSION: The inhibition of EphB4 suppressed bone formation and enhanced bone resorption activities on the tension side of tooth movement. The ephrinB2-EphB4 signalling might play an important role in alveolar bone remodelling during OTM.

Risk factors for maxillary impacted canine-linked severe lateral incisor root resorption: A cone-beam computed tomography study.

INTRODUCTION: Impacted maxillary canine-linked severe lateral incisor root resorption (SIRRc) is rare, but it greatly influences the survival of the affected teeth. Our study was designed to investigate the risk factors for SIRRc. METHODS: Eighty-two patients with SIRRc and 81 patients with impacted maxillary canines but without SIRRc were included and evaluated by cone-beam computed tomography in software programs by 1 examiner (H.W.). Age, sex, positions, and dental follicles and angular inclinations of impacted canines were measured in this study. Binary logistic regression was used to analyze the risk factors for SIRRc. RESULTS: SIRRc was highly related to sex, vertical and mesiodistal position, dental follicles sizes of canines, and intersection angles in 3 dimensions. The regression analysis showed female sex, dental follicles between 1 mm and 3 mm, mesial third and apical third position, vertical angle smaller than 30°, and the relative angle between 30° and 60° were significant risk factors for SIRRc. CONCLUSIONS: Early diagnosis and treatment for SIRRc are imperative, especially in Asian patients that are female with apically and mesially positioned canines as well as wider dental follicles. Vertical angles and relative angles of impacted canines should also be noticed.

Palatal expansion and relapse in rats: A histologic and immunohistochemical study.

INTRODUCTION: Rapid palatal expansion is an effective intervention for correcting transverse maxillary deficiency in growing patients. However, relapse after treatment is often observed, and the mechanisms of tissue remodeling during expansion and relapse remain unclear. This study aimed to gain insight into such a mechanism. METHODS: A total of 24 5-week-old male Wistar rats were randomly divided into either the expansion or sham device (control) group. Each rat underwent 7 days of expansion and 7 days of relapse. The width of the dental arch, palatal bone, and suture, as well as the angle of the teeth, were measured. Tissue remodeling in the midpalatal suture was examined using microcomputed tomography and histologic and immunohistochemical analyses. RESULTS: The mechanical expansion force caused an increase in arch width, which relapsed after the removal of force. Bilateral tilting of the teeth and midpalatal suture expansion contributed to the widening of the maxillary arch, and only the relapse of the palatal bone width was observed. Histochemical staining showed that suture tissue remodeling was activated by mechanical force in the expansion group and reverted to the level of the control group after relapse. Immunohistochemistry staining revealed that the expression of cathepsin K, osteocalcin, and collagen type I was higher in the expansion group than that in the control group on day 7; however, the difference dissipated by day 14. CONCLUSIONS: The expansion force stimulated osteogenic activity in the midpalatal suture area. After removal of the expansion force, tissue remodeling went back to the normal level.

Effects of estrogen on root repair after orthodontically induced root resorption in ovariectomized rats.

INTRODUCTION: This study aimed to investigate the effects of estrogen on root repair after orthodontically induced root resorption. METHODS: Seventy-two 6-week-old female Wistar rats were randomly divided into 3 groups: ovariectomy only (OVX), ovariectomy plus estradiol injection (OVX + E2), and sham operation (control). E2 was administrated to all the experimental animals after the establishment of the root repair model. One-way analysis of variance with the Tukey post-hoc test was used to analyze the experimental results. RESULTS: Micro-computed tomography and hematoxylin and eosin staining showed that the total volumes of resorption lacunae were significantly smaller in the control and OVX + E2 groups than those in the OVX group. Alkaline phosphatase and tartrate-resistant acid phosphatase stainings suggested that the cementoblastic activities and the amount of new cementum formation were inhibited while the activities of osteoclasts were obvious in the OVX group. The immunohistochemistry stainings revealed that the osteoprotegerin to receptor activator of nuclear factor-кB ligand ratio and the phosphorylated extracellular signal-regulated kinases to extracellular signal-regulated kinases ratio of the control and OVX + E2 groups were significantly greater than those of the OVX group. CONCLUSIONS: These findings demonstrated that estrogen administration might be a solution to reduce orthodontically induced root resorption through the activation of extracellular signal-regulated kinase-1/2 pathway and enhancement of cementogenesis.