Mandibular skeletal posterior anatomic limit for molar distalization in patients with Class III malocclusion with different vertical facial patterns.

OBJECTIVE: The aim of this study was to compare the differences in mandibular posterior anatomic limit (MPAL) distances stratified by vertical patterns in patients with skeletal Class III malocclusion by using cone-beam computed tomography (CBCT). METHODS: CBCT images of 48 patients with skeletal Class III malocclusion (mean age, 22.8 ± 3.1 years) categorized according to the vertical patterns (hypodivergent, normodivergent, and hyperdivergent; n = 16 per group) were analyzed. While parallel to the posterior occlusal line, the shortest linear distances from the distal root of the mandibular second molar to the inner cortex of the mandibular body were measured at depths of 4, 6, and 8 mm from the cementoenamel junction. MPAL distances were compared between the three groups, and their correlations were analyzed. RESULTS: The mean ages, sex distribution, asymmetry, and crowding in the three groups showed no significant differences. MPAL distance was significantly longer in male (3.8 ± 2.6 mm) than in female (1.8 ± 1.2 mm) at the 8-mm root level. At all root levels, MPAL distances were significantly different in the hypodivergent and hyperdivergent groups (p < 0.001) and between the normodivergent and hyperdivergent groups (p < 0.01). MPAL distances were the shortest in the hyperdivergent group. The mandibular plane angle highly correlated with MPAL distances at all root levels (p < 0.01). CONCLUSIONS: MPAL distances were the shortest in patients with hyperdivergent patterns and showed a decreasing tendency as the mandibular plane angle increased. MPAL distances were significantly shorter (~3.16 mm) at the 8-mm root level.

Evaluation of the stability of maxillary expansion using cone-beam computed tomography after segmental Le Fort I osteotomy in adult patients with skeletal Class III malocclusion.

OBJECTIVE: The aim of this study is to quantitatively evaluate the stability of the skeletal and dental widths using cone-beam computed tomography (CBCT) after segmental Le Fort I osteotomy in adult patients with skeletal Class III malocclusion requiring maxillary expansion. METHODS: In total, 25 and 36 patients with skeletal Class III malocclusion underwent Le Fort I osteotomy (control group) and segmental Le Fort I osteotomy (experimental group), respectively. Coronal CBCT images were used to measure the dental and skeletal widths before (T1) and after (T2) surgery and at the end of treatment (T3). The correlation between the extent of surgery and the amount of relapse in the experimental group was also determined. RESULTS: In the control group, the dental width exhibited a significant decrease of 0.70 ± 1.28 mm between T3 and T2. In the experimental group, dental and skeletal expansion of 1.83 ± 1.66 and 2.55 ± 1.94 mm, respectively, was observed between T2 and T1. The mean changes in the dental and skeletal widths between T3 and T2 were -1.41 ± 1.98 and -0.67 ± 0.72 mm, respectively. There was a weak correlation between the amount of skeletal expansion during segmental Le Fort I osteotomy and the amount of postoperative skeletal relapse in the experimental group. CONCLUSIONS: Maxillary expansion via segmental Le Fort I osteotomy showed good stability, with a skeletal relapse rate of 26.3% over approximately 12 months. Our results suggest that a greater amount of expansion requires greater efforts for the prevention of relapse.

Three-dimensional assessment of upper lip positional changes according to simulated maxillary anterior tooth movements by white light scanning.

OBJECTIVE: Esthetic improvements during orthodontic treatment are achieved by changes in positions of the lips and surrounding soft tissues. Facial soft-tissue movement has already been two-dimensionally evaluated by cephalometry. In this study, we aimed to three-dimensionally assess positional changes of the adult upper lip according to simulated maxillary anterior tooth movements by white light scanning. METHODS: We measured changes in three-dimensional coordinates of labial landmarks in relation to maxillary incisor movements of normal adults simulated with films of varying thickness by using a white light scanner. RESULTS: With increasing protraction, the upper lip moved forward and significantly upward. Labial movement was limited by the surrounding soft tissues. The extent of movement above the vermilion border was slightly less than half that of the teeth, showing strong correlation. Most changes were concentrated in the depression above the upper vermilion border. Labial movement toward the nose was reduced significantly. CONCLUSIONS: After adequately controlling several variables and using white light scanning with high reproducibility and accuracy, the coefficient of determination showed moderate values (0.40-0.77) and significant changes could be determined. This method would be useful to predict soft-tissue positional changes according to tooth movements.

Three-dimensional symmetry and parallelism of the skeletal and soft-tissue poria in patients with facial asymmetry.

OBJECTIVE: The purpose of this study was to examine the symmetry and parallelism of the skeletal and soft-tissue poria by three-dimensional (3D) computed tomographic (CT) imaging. METHODS: The locations of the bilateral skeletal and soft-tissue poria in 29 patients with facial asymmetry (asymmetric group) and 29 patients without facial asymmetry (symmetric group) were measured in 3D reconstructed models of CT images by using a 3D coordinate system. The mean intergroup differences in the anteroposterior and vertical angular deviations of the poria and their anteroposterior and vertical parallelism were statistically analyzed. RESULTS: The symmetric and asymmetric groups showed significant anteroposterior angular differences in both the skeletal and the soft-tissue poria (p = 0.007 and 0.037, respectively; Mann-Whitney U-test). No significant differences in the anteroposterior and vertical parallelism of the poria were noted (p ≤ 0.05; Wilcoxon signed-rank test). CONCLUSIONS: In general, the skeletal poria are parallel to the soft-tissue poria. However, patients with facial asymmetry tend to have asymmetric poria.

Soft-tissue thickness of South Korean adults with normal facial profiles.

OBJECTIVE: To standardize the facial soft-tissue characteristics of South Korean adults according to gender by measuring the soft-tissue thickness of young men and women with normal facial profiles by using three-dimensional (3D) reconstructed models. METHODS: Computed tomographic images of 22 men aged 20 - 27 years and 18 women aged 20 - 26 years with normal facial profiles were obtained. The hard and soft tissues were three-dimensionally reconstructed by using Mimics software. The soft-tissue thickness was measured from the underlying bony surface at bilateral (frontal eminence, supraorbital, suborbital, inferior malar, lateral orbit, zygomatic arch, supraglenoid, gonion, supraM2, occlusal line, and subM2) and midline (supraglabella, glabella, nasion, rhinion, mid-philtrum, supradentale, infradentale, supramentale, mental eminence, and menton) landmarks. RESULTS: The men showed significantly thicker soft tissue at the supraglabella, nasion, rhinion, mid-philtrum, supradentale, and supraglenoid points. In the women, the soft tissue was significantly thicker at the lateral orbit, inferior malar, and gonion points. CONCLUSIONS: The soft-tissue thickness in different facial areas varies according to gender. Orthodontists should use a different therapeutic approach for each gender.

Assessing soft-tissue characteristics of facial asymmetry with photographs.

INTRODUCTION: Precise diagnosis and treatment of facial asymmetry are important in orthodontics. The aims of this study were to determine the soft-tissue characteristics of patients perceived to have severe asymmetry requiring treatment and the soft-tissue factors affecting the subjective assessment of facial asymmetry. METHODS: In the first part of this study, 5 observers examined 1000 photographs of patients receiving orthodontic treatment and selected 100 for further assessment. These photographs showed 50 patients who were considered to have little or moderate asymmetry and 50 who were considered to have severe asymmetry. A pilot study was performed to select the reference photographs representing the most symmetric (score of 0) and the most asymmetric (score of 100). A panel of 9 orthodontists then rated the facial asymmetry of the 100 patients on a 100-mm visual analog scale. The scale was divided into 3 equal regions. Region 1 included patients with the least facial asymmetry; according to the orthodontists, these patients did not require treatment. Region 2 included patients with moderate facial asymmetry who did not require treatment. Region 3 included patients with the most facial asymmetry who did require treatment. RESULTS: One-way analysis of variance showed that lip canting, chin deviation, body inclination difference, and gonial angle difference had significant differences between the groups. Chin deviation and gonial angle difference were significant factors affecting the assessment of facial asymmetry, according to stepwise linear regression analysis. CONCLUSIONS: These results will help in the diagnosis and treatment planning for patients with asymmetry.

Skeletal changes of maxillary protraction in patients exhibiting skeletal class III malocclusion: a comparison of three skeletal maturation groups.

This cephalometric study evaluated skeletal and dentoalveolar changes produced by rapid maxillary expansion and facial mask therapy in 85 subjects exhibiting a Class III malocclusion with a retruded maxilla. The skeletal maturity of individual patients was assessed on the basis of Fishman's skeletal maturity indicator (SMI), using hand-wrist radiographs at the initiation of treatment, to determine the relationship between the effect of maxillary protraction and skeletal age. Patients were divided into three groups: prepubertal growth peak group (SMI 1-3), pubertal growth peak group (SMI 4-7), and postpubertal growth peak group (SMI 8-11). The major findings of this cephalometric study were as follows: (1) there was no difference in the effects of maxillary advancement after maxillary protraction between the prepubertal growth peak and the pubertal growth peak group, but there was a decrease in the postpubertal growth peak group; (2) in the postpubertal growth peak group, there was a decrease in maxillary skeletal advancement, whereas the dentoalveolar effect was increased; (3) the posteroinferior rotation of mandible, the increase of lower facial height, and the eruption of maxillary molars showed no correlation with skeletal age. The results of our study emphasize the importance of performing a biologic evaluation of skeletal maturity and pubertal growth peak in individual patients in the diagnosis and treatment planning of Class III malocclusions.