Impact of molar teeth distalization by clear aligners on maxillary alveolar bone thickness and root resorption: a three­dimensional study.

OBJECTIVE: This study aimed to evaluate the impact of molar teeth distalization movement by clear aligners on changes in the alveolar bone thickness and orthodontically induced inflammatory root resorption (OIIRR) in maxillary molars using conebeam computed tomography (CBCT). MATERIALS AND METHODS: Three-dimensional CBCT scans of 35 adult patients (one hundred forty maxillary molars) with pre-designed selection criteria and a mean age of 24.4 ± 7.1 years were included. The measured parameters, including alveolar bone thickness for maxillary molars and root resorption (OIIRR), were analyzed using pre-and post-treatment CBCT (T0 and T1, respectively) with Invivo 6.0 software. RESULT: Post-treatment, relevant statistically significant changes included deposition of bone in the average palatal surface of the 1st molars. The reduction of bone was seen in the average buccal surface of the first molars and both surfaces of the second molars. Regarding root length after treatment, the average maxillary 1st molar roots showed significant OIIRR (p < 0.001). CONCLUSION: Clear aligner treatment could effectively reduce the incidence of alveolar bone thickness reduction and OIIRR in treating Class II malocclusions compared to conventional braces, as shown in previous studies. This research will aid in fully grasping the benefits of clear aligners.

Comprehensive three-dimensional positional and morphological assessment of the temporomandibular joint in skeletal Class II patients with mandibular retrognathism in different vertical skeletal patterns.

BACKGROUND: Only a few studies have used 3D cone-beam computed tomography (CBCT) analysis to evaluate the positional and morphological characteristics of the temporomandibular joint (TMJ) in adults with skeletal Class II. No studies have focused on the case of skeletal Class II with mandibular retrognathism in different vertical skeletal patterns. As a result, this study aimed to evaluate and compare the position and morphology of TMJ in adults with skeletal Class II with mandibular retrognathism in different vertical skeletal patterns to the position and morphology of TMJ in the normal Chinese adult population in three dimensions. METHODS: This retrospective study analyzed CBCT images of 80 adult patients. Subjects with skeletal Class II with a normal sagittal position of the maxilla and mandibular retrognathism were classified according to the mandibular angle and facial height ratio into three groups of 20 subjects each: hypodivergent, normodivergent, and hyperdivergent groups, as well as a control group of 20 subjects. The following 3D measurements of TMJ were evaluated: (1) position, parameters, and inclination of the mandibular fossa; (2) position, parameters, and inclination of the mandibular condyle; (3) condyle centralization in their respective mandibular fossae; (4) anterior, posterior, superior, and medial joint spaces; and (5) 3D volumetric measurements of the TMJ spaces. Measurements were statistically analyzed by one-way ANOVA test, followed by Tukey's post hoc test. RESULTS: Significant differences were found in the hyperdivergent and hypodivergent groups compared with the normal group in the vertical and anteroposterior mandibular fossa position, vertical condylar inclination, and condylar width and length. The hyperdivergent group showed the significantly highest condylar inclination with the midsagittal plane; anterior and superior positioning of the condyle; smallest anterior, superior, and medial joint spaces; and largest volumetric total joint space relative to the two other groups. CONCLUSIONS: The condyle-fossa position and morphology differ with various vertical facial patterns in individuals with skeletal Class II mandibular retrognathism. These differences could be considered during TMD diagnosis and orthodontic treatment.

Three-dimensional assessment of temporomandibular joint in skeletal Class I malocclusion with variable degrees of overbite and overjet.

OBJECTIVE: To three-dimensionally evaluate the position and morphology of the TMJ in skeletal Class I with variable degrees of overbite and overjet in comparison with normal peers. METHODS: Pretreatment CBCT scans of 126 adults were retrieved. Based on the severity of overjet and overbite, the sample was divided into three main groups and six subgroups (18 patients each): the first group with a normal overbite and variable overjet degree and the second group with normal overjet and variable overbite degree. These six subgroups were compared with a third control group of normal overjet and overbite. RESULTS: There were significant differences in vertical condylar position, vertical and anteroposterior condylar inclinations, condylar height, and significant posterior condylar positioning in severe deep overbite, compared with the control group. CONCLUSION: There were significant changes in the TMJ components in severe deep overbite cases. Therefore, sever deep overbite could be considered a predisposing factor for temporomandibular disorders.

Three-dimensional assessment of asymmetric mid-palatal suture expansion assisted by a customized microimplant-supported rapid palatal expander in non-growing patients: Uncontrolled Clinical Trial.

OBJECTIVES: The objective was to evaluate the magnitude, incidence and possible factors of asymmetric expansion with a customized microimplant-supported rapid palatal expander (MARPE) in non-growing patients. SETTING AND SAMPLE POPULATION: This retrospective study included a sample of 49 patients (mean age: 23.9 ± 3.9 years) treated with a customized microimplant-supported rapid palatal expander. Based on the symmetry of expansion, the sample was divided into Group S (symmetric expansion group, n = 26) and Group A (asymmetric expansion group, n = 23). METHODS: Pre- and post-treatment cone-beam computed tomography (CBCT) images were superimposed to assess skeletal change in both studied groups. Seven variables were tested: unilateral crossbite, maxillary base cant, chin deviation, the initial asymmetrical position of the mid-palatal suture, split pattern of frontomaxillary suture, Angle's classification and dental arch crowding. Paired t-test and logistic regression analyses were utilized to evaluate the possible factors behind the asymmetric expansion. RESULTS: There was a significant difference (P < .01) between the studied groups. The average expansion was 4.26 mm at the anterolateral maxillary walls (BB) and 3.83 mm at the greater palatine foramen region (GPF). The average expansion at the GPF was 90% of that at the BB. The frequency of asymmetric expansion was 46.9%. Among the seven tested variables, the presence of the initial asymmetric position of the mid-palatal suture is the only variable that showed correlation with asymmetric expansion. CONCLUSION: Initial asymmetric position of the mid-palatal suture is considered a contributing factor of skeletal asymmetric expansion following microimplant-supported rapid palatal expansion in skeletally comparable patients.

Three-dimensional morphological and positional analysis of the temporomandibular joint in adults with posterior crossbite: A cross-sectional comparative study.

OBJECTIVES: The purpose of this study was to three-dimensionally (3D) evaluate the morphological and positional features of the temporomandibular joint (TMJ) in adults with unilateral and bilateral posterior crossbite compared with aligned control subjects. MATERIALS AND METHODS: This cross-sectional comparative study analysed cone beam computed tomography (CBCT) images of 90 adult subjects' divided into three equal groups: bilateral posterior crossbite (BCG), unilateral posterior crossbite (UCG) and control group (CG). 3D measurements of the TMJ included the following: (a) position, angulation and inclination of the mandibular condyles; (b) centralisation of the condyles in their respective mandibular fossae; and (c) volumetric measurements of the TMJ spaces. Intra- and intergroup differences were identified using the paired Student's t test and an analysis of variance (ANOVA) followed by Tukey's post hoc test, respectively. RESULTS: Regarding the intra-group side-based comparisons, there were significant differences in the anterior and superior joint spaces and the anteroposterior condylar joint position in the UCG. Intergroup comparisons revealed significant differences in the vertical condylar inclination, medial condylar position, condylar width and height, and volumetric joint space between the unaffected side of the UCG and left sides of the other groups. There were significant differences in the anteroposterior condylar inclination, medial condylar position, condylar width and height, anterior, posterior, superior and volumetric joint spaces, and anteroposterior condylar joint position between the crossbite side of the UCG and the right sides of the other groups. CONCLUSION: Skeletal crossbite accompanied with characteristic morphological and positional TMJ features associated with unilateral posterior crossbite and are associated with side-specific TMJ asymmetry.