Three-dimensional computed tomography evaluation of craniofacial characteristics according to lateral deviation of chin

Acceptable esthetic limits for maxillary dental midline shift and mandibular asymmetry: Who notices what and how much?

INTRODUCTION

This study aimed to evaluate maxillary dental midline shifts and mandibular asymmetries created in different amounts and directions on photographs taken from 7 different angles by different groups and to determine acceptable esthetic limits.

METHODS

Photographs of a female model in a social smile position were taken from 7 different angles (0° [frontal], 15°, 30°, and 45° on the right and left sides) and digitally modified for maxillary dental and mandibular midline deviations at specified degrees using Adobe Photoshop. To enable participants to evaluate the photographs sequentially, the photographs were transformed into videos using Adobe Premiere Pro software. The videos were rated by 188 participants (48 orthodontists; 49 dentists; 45 esthetic, plastic, and reconstructive surgeons; and 46 laypersons) using the visual analog scale (VAS) in a survey. An analysis of variance test was used to compare VAS scores among raters, and the Bonferroni test was used to compare VAS scores among the groups.

RESULTS

The threshold for the acceptability of maxillary dental midline shifts was 2 mm for orthodontists; dentists; and esthetic, plastic, and reconstructive surgeons but 4 mm for laypersons. Although laypersons were unable to perceive changes in mandibular asymmetry between 0°-6°, the threshold was 3° for other groups. For participants in which mandibular asymmetries and maxillary dental midline shifts were in opposite directions, the threshold for all groups was 6°. For participants in which lower jaw asymmetries and maxillary dental midline shifts were in the same direction, the threshold value for orthodontists was 6°. Other groups could not perceive variables related to asymmetry.

CONCLUSIONS

More sensitive esthetic assessments can be made by evaluating smile esthetics from different angles. Mandibular asymmetries are considered more esthetically acceptable than maxillary dental midline shifts. In mandibular asymmetry and maxillary dental midline shifts, deviations in the same direction are more esthetically acceptable than deviations in opposite directions. Orthodontists are able to notice small changes in mandibular asymmetry.

Establishment of the mid-sagittal reference plane for three-dimensional assessment of facial asymmetry: a systematic review : Establishment of the mid-sagittal reference plane: a systematic review

OBJECTIVE

To systematically review the literature for mid-sagittal plane establishment approaches to identify the most effective method for constructing the mid-sagittal plane for the evaluation of facial asymmetry.

MATERIALS AND METHODS

Six electronic databases (PubMed, Medline (via Ovid), EMBASE (via Ovid), Cochrane Library, Web of Science, and Scopus) and grey literature were searched for the studies that computed the mid-sagittal reference plane three-dimensionally, using a combination of MeSH terms and keywords. The methodological quality and the level of evidence for the included studies were analyzed using QUADAS-2 and GRADE, respectively.

RESULTS

The preliminary search yielded 6746 records, of which 42 articles that met the predefined inclusion criteria were included in the final analysis. All the included articles reported the construction of the mid-sagittal reference plane (MSP) using varied methods. The risk of bias and concerns regarding the applicability of the included studies were judged to be 'low'. The level of evidence was determined to be 'low' for the effectiveness of the technique and 'moderate' for the ease of clinical applicability.

CONCLUSION

Despite methodological heterogeneity, this review substantiates the comparable efficacy of cephalometric and morphometric MSP construction methods. A fully automated morphometric MSP holds promise as a viable option for routine clinical use. Nevertheless, future prospective studies with an emphasis on the impact, accuracy, and clinical applicability of MSP construction techniques in cases of facial asymmetry are required.

CLINICAL RELEVANCE

The present review will assist clinicians in selecting the most suitable method for MSP construction, leading to improved treatment planning and ultimately more favorable treatment outcomes.

Three-Dimensional Analysis of the Cranial Base Structure in Patients with Facial Asymmetry

Facial asymmetry is often seen in patients with skeletal mandibular prognathism and is associated with deformities in the maxillofacial and head regions. The maxillofacial deviation is three-dimensional and affects not only the lateral deviation of the mandible and midface, but also the cranium. This study conducted a three-dimensional morphological evaluation of the cranial base morphology of patients with skeletal mandibular prognathism (ANB < 0°, Wits < 0 mm) with the aim of examining the relationship between deformities of the head region and facial asymmetry. Data obtained from computed tomography conducted during the initial examination of patients with and without skeletal mandibular prognathism with facial asymmetry were used. Differences in the position of structures present in the cranial base were measured, and the association between cranial deformities and mandibular deviation was assessed. The middle cranial base area and the lateral deviation of the mandibular fossa were significantly larger in patients with facial asymmetry compared to those without facial asymmetry. In addition, a correlation between the amount of mandibular deviation and the area of the anterior cranial base was identified in patients with significant cranial deformity (p = 0.012). Given the identified association between the structure of the head region and facial asymmetry, further studies are needed to determine the factors implicated in the growth process.

Aesthetic Genioplasty Based on Strategic Categorization

BACKGROUND

Genioplasty is a popular procedure used for lower facial contour correction. Various osteotomy techniques enable us to perform advancement, setback, reduction, or narrowing procedures. Computed tomographic images facilitate preoperative planning in detail. The authors used a novel planning method based on strategic categorization. The analytic results are described.

METHODS

This retrospective study reviewed 208 patients who underwent genioplasty procedures for facial contouring from October of 2015 to April of 2020. During preoperative evaluation of the mandible, the operative procedure selected was one of three types: (1) horizontal segment osteotomy, (2) vertical and horizontal segment osteotomy, and (3) bone graft after repositioning. Adequate osteotomies were followed by rigid fixation using a titanium plate and screws. The follow-up period ranged from 8 to 24 months (average, 17 months). The results were assessed based on medical records, photographs, and facial bone computed tomographic images.

RESULTS

Overall, the patients were satisfied with the outcomes and had responder-based improvement in lower facial contour and balance. Chin point deviations were noted in 176 cases; left-side deviation ( n = 135) was more frequent than right-side deviation ( n = 41). Strategic osteotomies based on precise measurements led to correction of asymmetries. Temporary partial sensory losses reported in 12 cases resolved within an average of 6 months after surgery.

CONCLUSIONS

Each patient's chief complaint and bony structures should be carefully evaluated before genioplasty procedures are performed. During the operation, meticulous osteotomy, precise movement, and rigid fixation are necessary. The strategic process used for genioplasty resulted in aesthetic balance and predictable outcomes.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

The Vectra M3 3-dimensional digital stereophotogrammetry system: A reliable technique for detecting chin asymmetry

Purpose

The aim of this study was to evaluate the reliability of the Vectra M3 (3D Imaging System; Canfield Scientific, Parsippany, NJ, USA) in detecting chin asymmetry, and to assess whether the automatic markerless tracking function is reliable compared to manually plotting landmarks.

Materials and Methods

Twenty subjects (18 females and 2 males) with a mean age of 42.5±10.5 years were included. Three-dimensional image acquisition was carried out on all subjects with simulated chin deviation in 4 stages (1-4 mm). The images were analyzed by 2 independent observers through manually plotting landmarks and by Vectra software auto-tracking mode. Repeated-measures analysis of variance and the Tukey post-hoc test were performed to evaluate the differences in mean measurements between the 2 operators and the software for measuring chin deviation in 4 stages. The intraclass correlation coefficient (ICC) was calculated to estimate the intra- and inter-examiner reliability.

Results

No significant difference was found between the accuracy of manually plotting landmarks between observers 1 and 2 and the auto-tracking mode (P=0.783 and P=0.999, respectively). The mean difference in detecting the degree of deviation according to the stage was <0.5 mm for all landmarks.

Conclusion

The auto-tracking mode could be considered as reliable as manually plotted landmarks in detecting small chin deviations with the Vectra® M3. The effect on the soft tissue when constructing a known dental movement yielded a small overestimation of the soft tissue movement compared to the dental movement (mean value<0.5 mm), which can be considered clinically non-significant.

Prevalence of mandibular asymmetry in different skeletal sagittal patterns

OBJECTIVES

To analyze the prevalence of mandibular asymmetry in skeletal sagittal malocclusions.

MATERIALS AND METHODS

PubMed/MEDLINE, EMBASE, LILACS, Web of Science, Scopus, LIVIVO and gray literature (OpenGrey, ProQuest, and Google Scholar) were electronically searched. Two independent investigators selected the eligible studies, and assessed risk of bias and certainty of evidence (GRADE). One reviewer independently extracted the data and the second reviewer checked this information. Any disagreement between the reviewers in each phase was resolved by discussion between them and/or involved a third reviewer for final decision.

RESULTS

Electronic search identified 5,132 studies, and 5 observational studies were included. Risk of bias was low in two studies, moderate in one, and high in two. The studies showed high heterogeneity. Mandibular asymmetry ranged from 17.43% to 72.95% in overall samples. Horizontal chin deviation showed a prevalence of 17.66% to 55.6% asymmetry in Class I malocclusions, and 68.98% in vertical asymmetry index. In Class II patients, prevalence of mandibular asymmetry varied from 10% to 25.5% in horizontal chin deviation, and 71.7% in vertical asymmetry index. The Class III sample showed a prevalence of mandibular asymmetry ranging from 22.93% to 78% in horizontal chin deviation and 80.4% in vertical asymmetry index. Patients seeking orthodontic or orthognathic surgery treatment showed greater prevalence of mandibular asymmetry.

CONCLUSIONS

Skeletal Class III malocclusion showed the greatest prevalence of mandibular asymmetry. Mandibular vertical asymmetry showed a marked prevalence in all malocclusions. However, conclusions should be interpreted with caution due to use of convenience samples and low-quality study outcomes.

Effect of Botulinum Toxin Injection on Asymmetric Lower Face with Chin Deviation

The purpose of this study was to compare the efficacy of botulinum toxin (BoNT) in masseter muscle reduction depending on the amount of chin deviation. Exploring distinctive effects of BoNT relative to the characteristics of facial asymmetry will aid in planning and predicting treatment outcomes. Sixteen adult volunteers were classified into two groups according to the degree of menton deviation observed in posteroanterior cephalograms. Eight had a menton deviation of 3 mm or more and the other eight had less than 3 mm. A total of 25 Units of BoNT was injected into the unilateral masseter muscle of the prominent side for each participant. Changes in the volume and bulkiest height of the lower face on each side were measured with a 3D laser scan at four time points: before and 4, 8, and 12 weeks after the injection. Two-way mixed ANOVA was employed for analyses. The volume and bulkiest height of the injected side decreased over time in both types of asymmetry, with significant differences at each time point. The reductions in the volume and bulkiest height were significantly greater in subjects without chin deviation. The reductions in the volume and bulkiest height of the lower face using BoNT are more effective for subjects without chin deviation.