Morphological Changes of the Mandibular Angle After Orthognathic Surgery with Class III Deformity in East Asia.

The aims of this study were to analyze the morphological changes of the mandibular angle after orthognathic surgery for mandibular setback and investigate related factors. This retrospective study included patients from January 2017 to December 2021 diagnosed with skeletal class III deformity who underwent BSSRO (Group I) or bimaxillary surgery (Group II). Preoperative (T0), within 1 month postoperatively (T1), and 6 months postoperatively (T2) CT scans were collected from 61 patients to three-dimensionally analyze the proximal segment displacement, the linear and angular changes of the mandibular angle. The gonion points moved posteriorly and laterally (P < 0.001), while the inferior movement was not significant (P = 1.000, P = 0.274). The intergonial width increased by 3.32 ± 1.87 mm and 2.34 ± 1.77 mm as revealed by T2 CTs, respectively, in Group I and Group II. Mandibular angle decreased in both groups and by 1.41 ± 2.95° in Group I and 1.37 ± 3.41° in Group II. The increase in intergonial width between T1 and T0 was negatively correlated with the preoperative mandibular angle (P = 0.003) and positively correlated with the transverse outward movement of the proximal segment (P < 0.001). After surgery, the intergonial width increased and the inferior and posterior border of the proximal segment flared outward. The changes in intergonial width and mandibular angle were mainly related to the rotation of the proximal segment, which has a certain impact on the aesthetics of the lower face. Therefore, controlling the position of the proximal segment is of vital importance to lessen the changes in the mandibular angle area.Level of Evidence III. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Evaluation of Different Fixation Methods Combinations After L-Shaped Osteotomy Reduction Malarplasty: An In Vitro Biomechanical Study.

BACKGROUND: This in vitro study compared the stability of different fixation method combinations for the zygomatic complex after simulated L-shaped osteotomy reduction malarplasty, a common facial contouring surgery in East Asia with high postoperative complications due to poor fixation methods. MATERIALS AND METHODS: The study used 108 zygoma replicas with various fixation methods combinations in the zygomatic body (L-shaped plate with short wing on zygoma and on the maxilla, two bicortical screws, one bicortical screw with L-shaped plate, square plate, and rectangular plate) and zygomatic arch (Mortise-Tenon structure, 3-hole plate, and Mortise-Tenon structure plus short screw). The failure force under incremental load was applied through the Instron tensile machine to a well-stabilized model using a rubber band simulating the masseter muscle and recorded the increasing force digitally. ANOVA test was used for comparison between recorded values (P < 0.05). RESULTS: The results showed that the most stable combination was a six-hole rectangular plate and a Mortise-Tenon structure plus one short screw (358.55 ± 51.64 N/mm2). The results also indicated that the placement vector of the fixation methods around the L-shaped osteotomy and the use of the two-bridge fixation method were important factors in enhancing the stability of the zygomatic complex. CONCLUSION: The study suggested that surgeons should choose appropriate fixation methods based on these factors to reduce postoperative complications and improve surgical outcomes. NO LEVEL ASSIGNED: This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Stability of different fixation methods after reduction malarplasty under average and maximum masticatory forces: a finite element analysis.

BACKGROUND: Although titanium plates/screws are effective fixation methods (FM) after L-shaped osteotomy reduction malarplasty (LORM), the ideal FM remains controversial. This first finite element analysis (FEA) aimed to study the effect of various zygomatic body/zygomatic arch FM combinations and their placement vectors on the zygoma complex stability after virtual LORM under the effect of both average (150 N/mm2) and maximum (750 N/mm2) forces and three-dimensional (3D) mapping of stress and strain parameters distribution over the zygomatic bone, fixation methods, and total model. RESULTS: The fixation methods about the short-arm of the L-shaped osteotomy showed lower stress, strain, and displacement values than those across the long-arm osteotomy site. Combined with any zygomatic arch fixation methods (ZAFm), the two bicortical screws group (2LS) on the zygomatic body osteotomy site resulted in smaller displacements and the lowest zygoma bone stress and displacement when combined with Mortice-Tenon structure (MT) as zygomatic arch fixation method. Applied forces caused statistically significant differences in zygomatic bone stress (P < 0.001 and P = 0.001) and displacement (P = 0.001 and P = 0.002). CONCLUSION: All FMs both on the zygomatic body and zygomatic arch provide adequate zygomatic complex stability after LORM. The 2LS group showed better resistance than rectangular plate (RP) and square plate (SP) with lower stress concentrations. The L-shaped plate with short-wing on the maxilla (LPwM) is more stable than having the short-wing on the zygoma bone (LPwZ). Future prospective clinical studies are required to validate the current findings.

The accuracy of virtual surgical planning assisted management for L-shaped reduction malarplasty: A retrospective study.

This study aims to evaluate the accuracy of L-shaped reduction malarplasty with bone setback or resection on the zygoma and the mortice and tenon joint structure on the zygomatic arch under the guidance of virtual surgical planning (VSP). Adult patients with zygomatic protrusion or hypertrophy were enrolled and divided. L-shaped reduction malarplasty with or without bone resection and with the mortice and tenon joint structure on the zygomatic arch was conducted either by digital procedures comprising VSP and three-dimensional (3D) printing titanium templates (Group I) or by conventional methods (Group II). Positions of representative landmarks and superimposition models were analyzed by 3D cephalometry. Satisfaction rate and incidences of clinical complications were compared as well. Satisfactory reduction of zygomatic protrusion or hypertrophy was recognized among all 78 patients. Improved symmetry and great surgical accuracy were observed according to the cephalometry analyses. The bone segment movement of virtual plans and actual results in Group I were measured and showed no obvious difference for the inward movement (5.42 ± 0.98 mm vs. 5.33± 0.93 mm, P = 0.6906) and the sagittal overlap (4.77 ± 1.32 mm vs. 4.87± 1.21 mm, P = 0.7386) at the zygoma roots, along with the step length at the long-arm of the L-shaped osteotomy line (2.43 ± 1.11 mm vs. 2.39± 0.89 mm, P = 0.8665). The high resemblance between virtual plans and actual results was depicted via superimposition models. Meanwhile, a higher satisfaction rate (28 in 36, 78% vs. 20 in 42, 48%) and a lower incidence rate of complications (11 in 36, 31% vs. 21 in 42, 50%) were found in Group I. Within the limitations of the study it seems that the application of VSP in reduction malarplasty could significantly contribute to better surgical accuracy and reduced difficulties in the operation, which would be beneficial to patients with zygoma hypertrophy or prominence.

Three-dimensional analysis of zygomatic change after L-shaped reduction malarplasty with bone setback or resection.

PURPOSE: Reduction malarplasty is one of the most popular procedures for esthetic facial contouring in East Asians. The retrospective observational study aimed to analyze the association between the zygomatic change and bone setback or resection to propose quantitative guidance for L-shaped reduction malarplasty based on computed tomographic (CT) images. METHODS: A retrospective observational study was conducted on patients who underwent L-shaped reduction malarplasty with bone resection (Group I) or without bone resection (Group II). The amount of bone setback and resection was calculated. The unilateral width changes of the anterior, middle, and posterior zygomatic regions as well as zygomatic protrusion change were also evaluated. Pearson correlation analysis and linear regression analysis were used to analyze the relationship between the bone setback or resection and the zygomatic changes. RESULTS: Eighty patients who underwent L-shaped reduction malarplasty were included in this study. Significant correlation was observed between the bone setback or resection and the change of anterior, and middle zygomatic width as well as protrusion in both the two groups (P < .001). The correlation between bone setback or resection and the posterior zygomatic width change was not significant (P ＞.05). CONCLUSION: The bone setback or resection of L-shaped reduction malarplasty lead to the anterior and middle zygomatic width and zygomatic protrusion changes. Furthermore, the linear regression equation can be referenced as a guidance for a preoperative surgical plan.