Background: This study aims to explore the detailed correlation between the movement of maxillary and mandibular central incisors and alveolar bone resorption in adults who had orthodontic premolar extraction treatment. Methods: A total of 63 adult patients (mean age, 24.41 years) who received orthodontic treatment with the extraction of four first premolars were included in this study. CBCT images were obtained before and after treatment. Three-dimensional evaluations of the movement of 252 central incisors (126 maxillary and 126 mandibular incisors) and alveolar bone changes were conducted. Four points were used to describe the incisor movement: C (cusp point), R (root apex point), M (mid-point of root neck), and L (labial cementoenamel junction point). The thickness of labial and palatal alveolar bone was assessed at the crestal, mid-root, and apical levels of incisors. The results were analyzed with Spearman’s correlation and multilinear regression. Results: Matching the measurements of central incisor movement and alveolar bone resorption, significant correlations could be observed. For maxillary central incisors, the labial alveolar bone resorption at the crestal level was correlated with the movement of Point L (r = 0.290, p < 0.05), and the labial alveolar bone resorption at the apical level was correlated with Point M (r = 0.387, p < 0.05). For mandibular central incisors, the labial alveolar bone resorption at the apical level was correlated with the movement of Point M (r = 0.493, p < 0.05) and R (r = 0.498, p < 0.01); the palatal alveolar bone resorption at the mid-root level with Point M (r = -0.170, p < 0.01); and the palatal alveolar bone resorption at the apical level with Point R (r = 0.177, p < 0.01). Conclusions: This study investigated the concrete correlations between central incisor movement and alveolar bone resorption in adults after orthodontic treatment with premolar extraction. It is potentially helpful for orthodontists to have a relatively accurate prediction of alveolar bone resorption based on the specific movements of central incisors and to reduce the risk of alveolar bone resorption by better adjusting the three-dimensional movement types of incisors.

Background: The objective of this study was to propose a method that combines a maxilla-based coordinate system and mandibular voxel-based superimposition for an accurate evaluation of mandibular structural and positional changes and a direct comparison between maxillary and mandibular structural changes with the same 3D vectors. Methods: Mandibular voxel-based superimposition was firstly performed to reorient the mandibles and eliminate the mandibular positional changes. Then, a maxilla-based coordinate system was constructed with four maxillary skeletal landmarks (ANS, PNS, OrL and OrR). After settling the reoriented mandibles into this coordinate system, the mandibular structural changes were accurately evaluated. To assess the accuracy and reproducibility of this method, CBCT images of a skull specimen before and after orthodontic treatment (which was simulated by rearranging the skull and the mandible) were collected. Five mandibular skeletal landmarks, three mandibular dental landmarks and two mandibular measurement planes of this skull were used to evaluate the linear and angular changes in the mandibular structures. Results: There were significant differences in the linear and angular measurements of the mandibular structures of the skull (p ˂ 0.05), which indicated mandibular positional changes after orthodontic treatment. After mandibular voxel-based superimposition, there were no significant differences in the linear and angular measurements of mandibular structures, which indicated that the mandibular positional changes were eliminated. The intraclass correlation coefficient (ICC) value of the inter- and intra-observer agreement of all measurements was 0.99. Conclusions: This method has proven advantages in terms of accuracy, reproducibility and validity; with this method, mandibular structural and positional changes can be accurately evaluated and maxillary and mandibular structural changes can be directly compared with same 3D vectors.

Rationale: Overbite control is a key factor in orthodontic treatment. In some cases, incisor intrusion is essential and could be an optimal strategy for overbite control. The aim of this article was to introduce a biomechanical system called the posterior miniscrew-assisted lever arm, which is innovative in using existing posterior miniscrews to intrude the upper incisors and to control anterior overbite while simultaneously retracting the anterior teeth. Its efficiency in incisor intrusion has been proved with 2 cases. Patient concerns: Two adult women who came for orthodontic treatment with the chief complaint of convex profile were included in this study. Diagnosis: Both patients had similar malocclusions of Class II molar relationship, anterior deep overjet, and anterior deep overbite. Interventions: Their treatment plans were to extract 4 first premolars and insert 2 maxillary posterior buccal miniscrews. After teeth aligning and leveling, en masse retraction was started in both arches. During the space-closing stage, posterior miniscrew-assisted lever arms were placed in their upper arches so as to intrude upper incisors and control the overbite. Outcomes: After respectively 4 months and 3 months of incisor intrusion, the anterior overbite was successfully reduced to the normal range in each patient. Cephalometric analysis and superimposition also confirmed the treatment effect of this biomechanical system on incisor intrusion. Lessons: The posterior miniscrew-assisted lever arm is a valuable biomechanical system for intruding incisors and controlling anterior overbite.

Background: This article studies the association between psychological status and condylar bony changes in adults and assesses psychological questionnaires as an indicator of potential condylar bony changes. It is meaningful because condylar bony changes, a severe subtype of TMD and big concern in orthodontic treatment, would likely be ignored in patients with few TMD symptoms, in which case, even with potential psychological problems (depression, somatization and anxiety) being noticed, orthodontists may underestimate the possibility or severity of condylar bony changes and thus may not perform relevant examinations. Methods: A total of 195 adults (145 female and 50 male) who consulted orthodontists and had clinical records were included in this study. Initial CBCT images taken before orthodontic treatment were used for observing their condylar bony changes, and a comprehensive questionnaire conducted by each adult to evaluate psychological status was collected. Age, sex, TMD symptom history, scores on Patient Health Questionnaire-9 (PHQ-9), PHQ-15 and Generalized Anxiety Disorder-7 (GAD-7), and condylar bony changes of these adults were recorded. Odds ratios (OR) and 95% confidence intervals (CIs) for identifying the independent risk factors associated with condylar bony changes were calculated with univariate and multivariate logistic regression analysis. The kappa statistic was used to assess intraobserver reliability of CBCT analysis. Results: The scores of PHQ-15 (OR: 2.088, 95% CI: 1.061–4.108, p < 0.05) and GAD-7 (OR: 2.133, 95% CI: 1.082–4.204, p < 0.05) were correlated with the condylar bony changes on CBCT. Besides, the probability of having condylar bony changes was positively correlated with the number of psychological problems concomitantly present in an adult (OR: 1.440, 95% CI: 1.10–1.867, p < 0.01). The intraobserver agreement value for CBCT analysis was substantial (κ = 0.732). Conclusions: This study found that positive PHQ-15 (somatization) and GAD-7 (anxiety) scores were associated with condylar bony changes in adults. Moreover, the number of psychological problems concomitantly present in an adult was positively associated with the probability of having condylar bony changes.