Neuromuscular Adaptation After Orthognathic Surgery

Stability of single-jaw vs two-jaw surgery following the correction of skeletal class III malocclusion: A systematic review and meta-analysis

This review aims to compare the stability of sagittal skeletal and overjet anteroposterior correction of skeletal class III malocclusion in single-jaw and two-jaw orthognathic procedures. An unrestricted comprehensive electronic search was undertaken on Embase, Cochrane's CENTRAL, Web of Science, Medline, Scopus and LILACs databases up to October 2020. The bibliographies of relevant studies, ongoing, unpublished and grey literature were screened. Two independent reviewers performed study selection, bias assessment and data extraction; a third reviewer mediated inconsistencies. Randomized clinical trials, prospective cohort, retrospective cohort and series with a minimum of 1 year follow-up were eligible for inclusion. Additional subgroup analyses were undertaken. The generated effects were scored using the GRADE approach. Nine articles met the inclusion criteria and eight studies were subsequently analysed quantitatively. No significant difference in sagittal stability at the ANB angle, A-point or B-point on a short-term was detected. However, a statistically significant difference, indicating a greater short-term relapse in overjet with mandibular setbacks alone, was found (MD: -0.40 mm; 95% CI -0.77 to -0.04; I² : 0%; P = .03). Long-term follow-up (≥5 years) revealed a statistically non-significant difference in stability of sagittal skeletal and overjet corrections. Within the limitations of this review, both procedures seem to offer comparable skeletal and overjet stability outcomes; however, further high-quality research is required to confirm these findings.

Early and long-term changes in the muscles of the mandible following orthognathic surgery

OBJECTIVES

The aim of the present study is to evaluate the early and long-term postoperative dimensional changes of the muscles of the mandible in patients with orthognathic surgery for class II and class III malocclusions by using ultrasonography (US).

MATERIAL AND METHODS

Twenty-six patients who underwent bimaxillary orthognathic surgery for class II or class III malocclusions (14 and 12 patients, respectively) were ultrasonographically examined. The length, width, and cross-sectional area of the masseter and suprahyoid muscles were measured at three different time points: T₀ (preoperatively), T₁ (early postoperatively at 1 month after the surgery), and T₂ (late postoperatively at 9 months). A repeated measures ANOVA was used to calculate statistically significant dimensional changes of the mandibular muscles.

RESULTS

Statistically significant dimensional changes were found postoperatively in class II malocclusion patients only. The digastric muscle showed higher values for the length and lower values for the width (p < .05) at T₁. The geniohyoid muscles were higher in length at T₁ and lower in cross-sectional area (CSA) (p < .05) at T₂. A decreased measured length and an increased measured width were found in case of the mylohyoid muscle (p < .05) at T₂. The early and long-term postoperative dimensional changes of the masseter muscle were not statistically significant.

CONCLUSIONS

The mandibular muscles showed a variable adaptive response to the orthognathic surgery. US should be considered for the long-term follow-up of muscular dimensional changes in class II malocclusion patients.

CLINICAL RELEVANCE

From a clinical perspective, US is a reliable, non-invasive, and widely available method, which allows monitoring the postoperative muscular changes occurring in class II malocclusion patients.

Skeletal relapse following sagittal split ramus osteotomy advancement

BACKGROUND

Sagittal split ramus osteotomy (SSRO) is an accepted and standard procedure to address mandibular corpus deficiency. The relapse following the mandibular advancement has a negative impact both on clinician and patient.

PURPOSE

To analyse the hard tissue changes and to investigate relapse following SSRO advancement procedure.

MATERIALS AND METHODS

A retrospective review of 21 patients treated by bilateral SSRO advancement at our institute was conducted. Lateral cephalograms obtained at pre-treatment (T1), pre-surgery (T2), 2 months (T3) and 2 years post-surgery (T4) were evaluated by an independent investigator. The data T2-T3 revealed immediate postoperative changes, and T3-T4 revealed skeletal relapse following surgery after 2 years.

RESULTS

Twelve females and nine males with age ranging from 16 to 24 years underwent mandibular advancement. The mean follow-up period was 2 years 7 months ± 4 months. The mean mandibular advancement at pogonion was 5.1 ± 1.25 mm with significant improvement in SNB, ANB, CoGn, maxillo-mandibular differential and SN:GoPg ratio following surgery. Comparison of the outcomes following surgery revealed that the mean relapse at pogonion was 0.2 ± 0.44 mm. B point, mandibular corpus length, anterior and posterior facial height remained stable with no significant relapse following mandibular advancement.

CONCLUSION

Sagittal split ramus osteotomy within the range of mandibular advancement is a stable procedure.

Place of sagittal split osteotomy in mandibular surgery

With the development of craniofacial surgery, today sagittal split mandibular osteotomies are frequently used for the treatment of mandibular deformities with modifications and different fixation techniques. In clinics, 57 patients are evaluated in this study. Of these patients, 35 were male, 22 were female, and their ages were between 17 and 47 years (on average, it was 23 years). Thirty-seven of these patients were treated with bilateral sagittal split mandibular osteotomy (SSMO), 12 of them with unilateral SSMO, 6 of them with bilateral SSMO + Le Fort I osteotomy, and 2 of them with bilateral SSMO + Le Fort II osteotomy. Orthodontic treatment modalities were performed for 8 patients preoperatively and to all of the patients postoperatively. All patients were examined with cephalometric analysis preoperatively and postoperatively. Internal and external distractors were applied for 14 patients. Rigid fixation with plates and screws was done for 21 patients. Fixation with screws for 5 patients, fixation with wires for 3 patients, and intermaxillary fixation for 8 patients were performed. Patients were followed up on average 13 months (6-22 months). In 1 patient, infection on the osteotomy line and recurrency developed. Sensory area of the alveolar nerve became normal in 10 to 16 weeks usually, but in 3 patients, sensory loss developed at this region. Complaints of temporomandibular joint dysfunction developed in 1 patient at the third postoperative month. When the clinical use was determined, we observed that SSMO could give satisfactory results in selected patients with mandibular deformities. Dental structures are important in relation to the postoperative occlusion and masticatory functions, for this reason, we think that postoperative orthodontic treatment will be useful for these patients.

Alteration of the mandibular plane during sagittal split advancement: Short- and long-term stability

OBJECTIVES

We investigated predictors of long- and short-term stability of surgical mandibular advancements with bilateral sagittal split osteotomy (BSSO).

STUDY DESIGN

Class II patients (n = 127) received mandibular advancement through BSSO with either rigid internal fixation or wire osteosynthesis. We used multiple linear regression analysis to assess the association of predictor variables with post-treatment horizontal and vertical B-point movement through 2 years.

RESULTS

Counterclockwise rotation of the mandibular plane angulation (MPA) was associated with greater horizontal and vertical relapse at all time periods except 8 weeks. Wire osteosynthesis, larger advancements, younger age, and genioplasty were significantly associated with relapse.

CONCLUSIONS

Surgically closing the MPA is associated with late horizontal and vertical relapse, whereas fixation type is related to early B-point movement. Large advancements with forward and upward repositioning of the mandible, genioplasty, and young age also play a role in relapse after BSSO.

Condylar change after upward and forward rotation of the maxillomandibular complex

Tomographic radiographs of 44 healthy temporomandibular joints in 22 patients undergoing large upward and forward rotations of the maxillomandibular complex were evaluated. Immediate postsurgery results showed decreases in all areas of the joint space. Long-term results showed a decrease in the superior and posterior regions, 14.8% and 19.7%, with no significant change anteriorly. Simple and multiple regression analysis did not show any relationship with age, gender, or degree of change in the decrease of the occlusal plane angle, to the temporomandibular joint changes described. Some condylar remodeling was noted.

Effect of mandibular setback surgery on occlusal force

PURPOSE

This study investigated the effect of mandibular setback surgery on occlusal force and evaluated the extent to which postsurgical changes in such force can be explained by the type of operation, the duration of maxillo-mandibular fixation (MMF), and the changes in the mechanical advantage of the jaw musculature.

MATERIALS AND METHODS

Maximal molar bite force was measured before surgery and at MMF removal, and 3, 6, and 12 months thereafter in 26 patients with mandibular prognothism. To correlate bite force and skeletal change, the cephalometric tracings were measured, tabulated, and statistically analyzed.

RESULTS

Mean bite force was 13.7 kg before surgery, 7.6 kg at MMF removal, 14.2 kg at 3 months, 19.7 kg at 6 months, and 26.1 kg at 12 months post-surgery. The bite force was positively correlated with the surgical change in mandibular plane angle and mandibular body length. The recovery of bite force was significantly affected by the type of operation and duration of MMF.

CONCLUSIONS

To hasten recovery and increase bite force after orthognathic surgery, long periods of MMF and injury to the masticatory muscles should be avoided.

Stability of orthognathic surgery: a review of rigid fixation

The use of rigid fixation with orthognathic surgery was greeted by both excitement and healthy concern when it began to find its way into the literature approximately 10 years ago. The purpose of this paper is to review the literature and make comments based on the experience of the senior author on whether one of the early premises was true. Has rigid fixation improved stability with orthognathic surgery? The authors chose to examine mandibular advancements treated with a bilateral sagittal split osteotomy and maxillary osteotomies treated with a Le Fort I osteotomy. When compared to wire osteosynthesis, rigid fixation has improved stability; however, the individual move associated with the osteotomy must be considered. In some cases, auxiliary techniques should be used to ensure stability. Condylar resorption with mandibular advancement continues to be an area of concern.