This study aimed to clarify the relationship between the mandibular posterior anatomic limit (MPAL) and skeletal anteroposterior and vertical skeletal patterns, with consideration of factors that may be related. In total, 230 people were included: 49 Japanese, 122 Egyptian, and 59 Korean people. The MPAL was measured at 0, 2, 4, and 6 mm from the root furcation along the sagittal and cuspal lines at the distance from the distal root of the mandibular right second molar to the mandibular cortex of the lingual bone. Eight different MPALs were evaluated using multiple regression analysis with explanatory variables for anteroposterior and vertical skeletal patterns and qualitative variables for age, sex, population, the presence of third molars, number of roots, presence of C-shaped roots, and Angle malocclusion classification. The MPAL was significantly larger as the mandibular plane angle decreased. The MPAL near the root apex was significantly larger as the A-nasion-point B angle increased, and the MPAL near the root apex measured at the cuspal line was significantly larger for C-type roots. The present study showed that a C-shaped root affected the MPAL in addition to the anteroposterior and vertical skeletal patterns.

Paired box gene 3 (PAX3) plays an important role in craniofacial development. Mutations in this gene are associated with Waardenburg syndrome, which is a condition characterized by facial anomalies such as widely spaced inner corners of the eyes. PAX3 gene polymorphisms are associated with the relative position of the nasal root (nasion), even among healthy individuals. Facial morphology has primarily been examined using three-dimensional (3D) facial scans of soft tissues, whereas studies focusing on hard tissues remain limited. Therefore, the present study aimed to analyze 3D craniofacial morphology in hard tissues using computed tomography imaging and investigate the influence of PAX3 polymorphisms on the 3D morphology of the nasal root. The analysis was conducted on three populations: 201 healthy Japanese, 74 healthy Korean, and 142 healthy Egyptian individuals. DNA was extracted from saliva samples, and the genotypes of two PAX3 single-nucleotide polymorphisms (SNPs; rs9288572 and rs7559271) were analyzed. A multiple regression analysis of the association between these SNPs and measurements related to nasal root morphology revealed a significant association between rs7559271 and the protrusion angle of the nasion. These findings suggest that PAX3 gene polymorphisms influence the morphological development of the nasal root within the normal range of hard tissues.

Objectives: This study aimed to compare the fit accuracy between retainers fabricated using conventional cold-curing resin (hereinafter referred to as “conventional retainers”) and those fabricated using three-dimensional (3D) printing based on computer-aided design/computer-aided manufacturing (CAD/CAM) technology (hereinafter referred to as “CAD/CAM retainers”). Furthermore, the study aimed to compare two different methods to evaluate the fit accuracy: the impression replica technique and the 3D triple-scan protocol. Methods: For each of the 20 working models derived from a maxillary typodont, one conventional retainer and one CAD/CAM retainer were fabricated. The fit accuracy was evaluated using the impression replica technique and the 3D triple-scan protocol. Measurements were taken at 12 points on each model, and the differences in thickness (gap) were analyzed using Wilcoxon’s signed-rank test. Moreover, the correlation between thickness and measurement site was evaluated using Spearman’s rank correlation coefficient. Results: In both evaluation methods, the CAD/CAM retainers exhibited superior fit accuracy compared to the conventional retainers. Notably, the 3D triple-scan protocol clearly demonstrated that the fit accuracy differed depending on the measurement site. Conclusions: CAD/CAM retainers demonstrated superior fit accuracy compared to conventional retainers, possibly because digital design can account for polymerization shrinkage. In the impression replica technique, the median (interquartile range) thickness for the conventional retainers was 0.169 (0.120–0.260) mm, whereas that for the CAD/CAM retainers was 0.136 (0.096–0.198) mm. The CAD/CAM retainers showed significantly smaller gap values (p < 0.001). Within the limitations of this in vitro study, CAD/CAM retainers showed significantly smaller gap values than conventional retainers, indicating improved fit accuracy. In particular, the 3D triple-scan protocol accurately captured site-specific variations in fit accuracy among the anterior, canine, and molar regions.

Background/Objectives: The local mechanical properties of periodontal supporting tissues influence their responses to orthodontic forces. This exploratory study sought to evaluate site-specific nanoindentation hardness in human root cementum and adjacent alveolar cortical bone and examine its association with cone-beam computed tomography (CBCT)- and micro-computed tomography (micro-CT)-derived relative imaging indices. Methods: Specimens from seven human cadavers were analyzed. Indentation hardness (HIT) was measured in the central and apical regions of root cementum and adjacent alveolar cortical bone. CBCT gray values and micro-CT-derived relative imaging indices were obtained from anatomically matched regions without phantom-based mineral-density calibration. Nonparametric tests, multiple linear regression analyses, and Spearman’s rank correlation analyses were performed. Results: Root cementum exhibited significantly higher HIT in the central region than in the apical region (p < 0.001). The central region and mandibular location were independently associated with higher cementum HIT. No significant regional variation or associated factors were identified for alveolar cortical bone. Neither CBCT nor micro-CT-derived indices were significantly associated with local tissue hardness. Conclusions: Human root cementum exhibits site-specific variation in hardness, unlike the adjacent alveolar cortical bone. Uncalibrated CT-derived relative imaging indices may not be significantly associated with local tissue hardness.

Background/Objectives: Multi-bracket appliances are essential in surgical orthodontic treatment, and perioperative oral management during orthognathic surgery is critical. Thorough plaque control, appropriate use of antibiotics, and shortening of operative time have been reported to be effective in preventing postoperative infections and ensuring surgical success. As highly invasive orthognathic surgery involving osteotomy may influence the postoperative oral microbiota, this study aimed to investigate the characteristics of and clarify the changes occurring in the salivary oral microbiota after orthognathic surgery. Methods: The study included 14 patients (Group S; mean age 29.3 ± 9.8 years) who underwent surgical orthodontic treatment and 15 control patients (Group C; mean age 27.1 ± 8.7 years) who received orthodontic treatment alone. Salivary samples were analyzed via 16S rRNA gene sequencing, and the relative abundances of bacteria were evaluated using the Linear Discriminant Analysis Effect Size. Results: The prevalence of Neisseria, which is associated with early biofilm formation, decreased over time in both groups. In contrast, Streptococcus exhibited an increase in prevalence. In Group S, members of Pseudomonas, the family Saccharimonadaceae, and the order Rhizobiales showed increases at 5–8 months post-surgery. Conclusions: Surgical orthodontic treatment may influence the oral microbiota and promote colonization by opportunistic pathogens. Instructions regarding oral hygiene and appropriately timed professional cleaning interventions are critical in preventing such colonization. Longitudinal monitoring of the microbiota using metagenomic analysis may be useful for future perioperative management and guidance of oral hygiene.