Liwei Xiao

To assess the relationship between mandibular ramus morphology and lower third molar impaction among patients with Class II malocclusion using CBCT. A retrospective study included 536 patients with Class II malocclusion, classified into normally erupted (n = 84), impacted (n = 359), and absent third molar groups (n = 93). Mandibular ramus dimensions, including height, widths, condyle to gonion length, retromolar space, coronoid process length, and gonial angle, were measured using CBCT-derived 2D and 3D images. Third molar impaction was classified using the Pell&Gregory and Winter systems. The third molar position differed significantly between groups across Pell and Gregory, ABC, and Winter classifications, with P = 0.0001. Impacted molars were mainly Class II or III, position C, and mesioangular or horizontal (57.1%, 32.9%, 52.44%, 46.2%, 36.5%, respectively). Gender distribution showed no significant difference. Retromolar space was significantly reduced in the mean value in the impacted group at 5.77 ± 2.63 mm compared with the normal group at 14.49 ± 3.79 mm and the without-molar group at 13.95 ± 2.90 mm. Condyle to gonion length and ramus height showed no significant differences in 2D or 3D sagittal measurements but were significantly reduced in the impacted group on 3D volumetric analysis with P = 0.022 and P = 0.002. Maximum ramus width differed significantly across groups. Significant differences were observed between 2D and 3D measurement methods. Third molar impaction in Class II patients is mainly associated with reduced retromolar space and subtle mandibular volumetric deficiencies. 3D CBCT offers a more comprehensive assessment than 2D imaging, while linear and angular parameters show minimal clinical relevance.

Yinyin Zhang ; Liwei Xiao ; Xinyue Cao ; Yunting Zeng . Korean J Orthod 2025;55:337-48. https://doi.org/10.4041/kjod24.148

Objective The purpose of this study was to three-dimensionally evaluate the relationship between the degree of bilateral impacted mandibular third molar (IM3M) angulation and the mandibular dental arch parameters in normal skeletal and dental malocclusion patients. Materials and methods In this retrospective cross-sectional comparative study, 120 adult subjects’ cone-beam computed tomography (CBCT) images were three-dimensionally analyzed. The sample included 120 adults aged 20–30 years, with a gender distribution of 51 male and 69 female participants. The sample was divided into 100 adults with bilateral IM3M (study group) and 20 adults with normal bilateral erupted M3M (control group). The study group was sub-divided into three groups according to the degree of IM3M buccolingual angulation (BL°): group A, < 12° on the center of the ridge (N = 30), group B, 12–24° off-center of the ridge (N = 40), group C, > 24° off-center of the ridge (N = 30). The study group was also sub-divided into two groups according to IM3M mesiodistal angulation (MD°): group 1 from 10 to 45° (N = 36), group 2 > 45° (N = 64). Comparison within and between groups was performed using one-way ANOVA followed by Tukey’s post hoc test. The correlation between IM3M, BL, and MD angulation and the mandibular arch parameter was calculated using Pearson’s correlation coefficient. Results Statistically significant differences (P < 0.001) were found between the IM3M BL° and anterior teeth inclination, arch length (AL), and inter-second molar width (inter 2^nd MW) as well as between the IM3M MD° with anterior crowding and the arch length (P < 0.001). A significant positive correlation was found between IM3M BL° and anterior teeth inclination and between IM3M MD° and anterior teeth crowding and inter 2^nd MW. A significant negative correlation was observed between IM3M BL° and inter 1^st MW and 2^nd MW. Conclusion The degree of buccolingual and mesiodistal angulation of the impacted mandibular third molars was related with mandibular dentoalveolar changes. Increased buccolingual angulation is generally associated with increased anterior teeth inclination and decreased 1^st and 2^nd inter-molar width. The increase in mesiodistal angulations was generally related with increased anterior teeth crowding and 2^nd inter-molar width. Clinical relevance Assessment of the relationship between the impacted mandibular third molars and the degree of arch discrepancy, and the position of mandibular incisors in the three planes of space might help in the decision-making process for the extraction of the impacted third molars in adult patients.

Objectives: The purpose of this study was to three-dimensionally evaluate the relationship between the degree of bilateral impacted mandibular third molars (IM3M) angulation and the mandibular dental arch parameters in normal skeletal and dental malocclusion patients. Materials and Methods: In this retrospective cross-sectional comparative study, 120 adult subjects’ cone beam computed tomography (CBCT) images were three-dimensionally analyzed. The sample was divided into four groups according to degree of M3M buccolingual angulation (BL°); Group A 24° off center of the ridge (N=30), and Group D (control group with normal erupted bilateral M3M).The study subjects were further also divided into three groups according to IM3M mesiodistal angulation (MD°); Group 1 from10° to 45°, Group 2> 45° and Group 3 (control group with normal erupted bilateral M3M, 0 -10°). Comparison within and between groups were performed using One-way ANOVA followed by Tukey's post hoc test, respectively. Correlation between IM3M, BL and MD angulation and mandibular arch parameter was calculated using Pearson's correlation coefficient. Results: Statistically significant differences (P < .001) were founded between the IM3M BL° and anterior teeth inclination, arch length (AL) and inter second molar width (inter 2^nd MW) as well as between the IM3M MD° with anterior crowding and the arch length (P < .001). Significant positive correlation was founded between IM3M BL° and anterior teeth inclination, and between IM3M MD° and anterior teeth crowding and inter 2nd MW. Significant negative correlation was observed between IM3M BL° and inter 1^st MW and 2^nd MW. Conclusion: The degree of buccolingual and mesiodistal angulation of the impacted mandibular third molars was associated with mandibular dentoalveolar changes. The increase in buccolingual angulation is associated with increase of anterior teeth inclination, and the decrease of 1^st and 2^nd inter-molars width. The increase in mesiodistal angulations was associated with increase in anterior teeth crowding and 2^nd inter-molars width. Clinical relevance: Assessment of the relationship between the impacted mandibular third molars and the degree of arch discrepancy, and the position of mandibular incisors in the three planes of space might help in the decision-making process for extraction of the impacted third molars in adult patients.

Periodontitis is a progressive infectious inflammatory disease, which leads to alveolar bone resorption and loss of periodontal attachment. It is imperative for us to develop a therapeutic scaffold to repair the alveolar bone defect of periodontitis. In this study, we designed a new composite scaffold loading metformin (MET) by using the freeze-drying method, which was composed of β-tricalcium phosphate (β-TCP), chitosan (CTS) and the mesoporous silica (SBA-15). The scaffolds were expected to combine the excellent biocompatibility of CTS, the good bioactivity of β-TCP, and the anti-inflammatory properties of MET. The MET-loaded β-TCP/CTS/SBA-15 scaffolds showed improved cell adhesion, appropriate porosity and good biocompatibility in vitro. This MET composite scaffold was implanted in the alveolar bone defects area of rats with periodontitis. After 12 weeks, Micro-CT and histological analysis were performed to evaluate different degrees of healing and mineralization. Results showed that the MET-loaded β-TCP/CTS/SBA-15 scaffolds promoted alveolar bone regeneration in a rat model of periodontitis. To our knowledge, this is the first report that MET-loaded β-TCP/CTS/SBA-15 scaffolds have a positive effect on alveolar bone regeneration in periodontitis. Our findings might provide a new and promising strategy for repairing alveolar bone defects under the condition of periodontitis.

Objectives: To compare the transfer accuracy of two digital transfer trays, the three-dimensional printed (3D printed) tray and the vacuum-formed tray, in the indirect bonding of labial brackets. Materials and Methods: Ten digital dental models were constructed by oral scans using an optical scanning system. 3D printed trays and vacuum-formed trays were obtained through the 3Shape indirect bonding system and rapid prototyping technology (10 in each group). Then labial brackets were transferred to 3D printed models, and the models with final bracket positioning were scanned. Linear (mesiodistal, vertical, buccolingual) and angular (angulation, torque, rotation) transfer errors were measured using GOM Inspect software. The mean transfer errors and prevalence of clinically acceptable errors (linear errors of ≤0.5 mm and angular errors of ≤2°) of two digital trays were compared using the Mann-Whitney U -test and the Chi-square test, respectively. Results: The 3D printed tray had a lower mean mesiodistal transfer error ( P < .01) and a higher prevalence of rotation error within the limit of 2° ( P = .03) than did the vacuum-formed tray. Linear errors within 0.5 mm were higher than 90% for both groups, while torque errors within 2° were lowest at 50.9% and 52.9% for the 3D printed tray and vacuum-formed tray, respectively. Both groups had a directional bias toward the occlusal, mesial, and buccal. Conclusions: The 3D printed tray generally scored better in terms of transfer accuracy than did the vacuum-formed tray. Both types of trays had better linear control than angular control of brackets.

Objectives: To evaluate alveolar bone support around cleft-adjacent maxillary central incisors (U1) in patients with unilateral cleft lip, alveolus and palate (UCLAP) in the late mixed dentition and to investigate the correlation between the alveolar bone thickness (ABT) and tooth inclination. Materials and Methods: Cone beam computed tomography scans of 45 subjects with UCLAP (29 boys, 16 girls; mean age = 10.74 ± 1.08 years) were assessed. The distance between the cementoenamel junction (CEJ) and alveolar bone crest (AC), and the ABTs at 3 mm, 6 mm, and the apex were measured on the labial, lingual and distal surfaces of U1. The cleft and normal sides were compared using a paired t -test and Pearson's χ ² test. Pearson's correlation was used to explore the association between the ABT and tooth inclination of cleft-adjacent U1 in the labiolingual and mesiodistal dimensions. Results: The CEJ-AC distances were significantly greater in cleft-adjacent U1 ( P < .01), with more bone height reduction observed labially and distally ( P < .001). The labial, lingual, and apico-distal ABTs were decreased on the cleft side ( P < .01). A positive correlation was found between the apico-labial ABT and the labiolingual inclination ( r = 0.568, P < .01). Conclusions: Patients with UCLAP have reduced alveolar bone support around the cleft-adjacent U1, and the apico-labial ABT tends to decrease with increasing lingual tooth inclination; however, the correlation was weak.