Objective This study investigates the effects of using a twin inclined plane device (TIPD) on the remolding and ultrastructure variation of mandibular condyle in growing rats. Materials and Methods Forty-eight male Wistar rats (six weeks old, body weight of approximately 190–210 g) were divided into experimental group (wearing appliance, n = 32) and control group (no appliance, n = 16). Samples were collected on days 3, 14, 30, and 60. The immunohistochemical analysis for vascular endothelial growth factor (VEGF) and type II collagen was carried out. Tartrate-resistant acid phosphatase (TRAP) reaction was performed to evaluate the osteoclastic activity. Three-dimensional morphometric images were reconstructed for morphometric analysis by microcomputed tomography (micro-CT). The ultrastructure of the condylar surface was observed by scanning electron microscopy (SEM). Results The expression of VEGF significantly increased, while the expression of type II collagen decreased in the experimental group at days 30 and 60. Furthermore, the enhanced osteoclast activity was observed under the subchondral bone, which was highest at day 30, and decreased to the lowest at day 60 in the experimental group. In addition, adaptive subchondral bone remolding in the posterior part of the condyle was observed at day 60 in the experimental group, and the SEM revealed the ultrastructure variations after installation of the TIPD. However, these changes began to reverse after 30 days. Conclusion Condylar tissue changes point to the osteoclastic activity in the posterior region of the condyle. These adaptive changes point to bone resorption in the posterior condyle. Type II collagen and VEGF contribute to the MCC remolding induced by the TIPD. The ultrastructural changes in the posterior condylar area in response to mechanical stresses are recoverable at the initial stage.

Objectives To investigate the prevalence and severity of external apical root resorption (EARR) volumetrically with clear aligner therapy using cone-beam computed tomography (CBCT) as well as determine the possible risk factors and develop a prediction model for EARR. Materials and Methods In this retrospective study, 320 incisors from 40 Class II patients treated with aligners (Invisalign) were included in this study. CBCT images were obtained at pretreatment (T0) and posttreatment (T1). Root volume was calculated by three-dimensional reconstruction of CBCT images, and apical tooth movement was measured from superimposed CBCT images. Changes in root volume were compared using paired t-tests, and the relationship between root volume loss and potential risk factors was analyzed by multiple linear regression. Results All of the measured incisors showed root volume loss, with an average of 11.48 ± 6.70 mm3, and the prevalence of severe resorption was 0.625%. The prediction model for EARR included variables of posttreatment sagittal root position (SRP), extraction, tooth type, and apical intrusion and extrusion displacements, with an R2 of 0.51. Age, sex, duration, pretreatment SRP, attachment, advancement, and retraction movements were excluded from the model. Conclusions Most incisors showed mild to moderate resorption during aligner treatment; only a minimal percentage showed severe resorption. Posttreatment SRP (which showed the highest association with EARR), extraction, tooth type, and apical intrusion and extrusion displacements were risk factors for EARR.

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Summary Objective This study investigated the expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the compression area during orthodontic relapse in rat molars. Materials and methods Thirty Wistar rats (6 weeks old) underwent orthodontic tooth movement (OTM) of the left first maxillary molar for 21 days, followed by removal of the force device. The contralateral maxillary molar served as a control with no mechanical force stimuli. Animals were sacrificed at 0, 1, 3, 7, and 14 days of relapse after force withdrawal. Tooth relapse and alveolar bone parameters were measured using microcomputed tomography (micro-CT). Maxilla sections were obtained for haematoxylin and eosin (HE), immunohistochemical staining [EMMPRIN, nuclear factor kappa B ligand (RANKL) and vascular endothelial growth factor (VEGF)] and tartrate-resistant acid phosphatase (TRAP). Correlation analyses were then performed. Results After force removal, nearly 79.88% of the total relapse occurred within the initial 3 days. The number of osteoclasts clearly increased while the alveolar bone density decreased on the pressure side on Day 3 of relapse. Moreover, the EMMPRIN expression level significantly increased on Day 1, peaked up on Day 3 and decreased on Days 7 and 14. Statistically, a strong positive correlation was found between EMMRPIN expression and the osteoclast number and RANKL and VEGF expression. Conclusion EMMPRIN was highly expressed on the pressure side during the orthodontic tooth relapse, which could be involved in osteoclastogenesis and alveolar bone resorption in association with RANKL and VEGF expression.

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