Application of computer-assisted techniques in osseous genioplasty / 中华整形外科杂志

Objective@#To discuss the efficacy of computer aided design (CAD) and computer aided manufacturing (CAM) in the treatment of microgenia by osseous genioplasty.@*Methods@#From July 2015 to January 2018, 17 cases (Male, n=5, Female, n=12), aged from 17 to 32 years, with the meanage of 24 years, were enrolled. All patients had microgenia, and underwent osseous genioplasty. Computed tomography (CT) was performed preoperatively and 7-10 days postoperatively for all cases. Based on preoperative CT data, CAD was applied to make individualized surgical plan, surgery simulation, todetermine the movement of mentum. CAM was used to prefabricate the individualized surgical templates and transfer the CAD into intraoperative guidance. The registration of CAD and postoperative CT were performed to evaluate the surgical accuracy.@*Results@#All patients were satisfied with the surgical outcomes. The deformity of microgenia was significantly corrected. The Pg error was (0.24±0.08) mm, and the Me error was (0.15±0.17) mm.@*Conclusions@#The application of CAD increases the accuracy of surgical planning, and CAM provides areliable guidance with individualized template. Anoptimal surgical outcome can be achieved.

Establishment of three-dimensional mirror image plane of hemifacial microsomia: a new method / 中华整形外科杂志

Objective@#To discuss the establishment of three-dimensional mirror image plane ofhemifacial microsomia.@*Methods@#32 cases of hemifacial microsomia from Jan. 2006 to Jan. 2017 were collected in our hospital. CT scanning was performed for all patients. Then, the deformity characteristics were summarized through three steps: 3D reconstruction, mirror and discrepancy analysis.@*Results@#After statistical analysis, the stability of these three points was good. Clinical result showed that the patient′s appearance was greatly improved.@*Conclusions@#Using these three points to determine the mirror image plane is helpful to analyze the patient's facial features and facilitate the surgical design.

Surgery-first approach for Angle class Ⅲ malocclusion: clinical retrospective analysis of 185 cases / 中华整形外科杂志

Objective@#The purpose of this study was to explore the surgery-first approach in sequential combined orthodontic-orthognathic treatment to shorten total treatment duration and improve the clinical outcome.@*Methods@#This study included 185 patients with Angle classⅢ malocclusion. The patients were divided into 3 different types according to cephalometry analyses and facial features. ①Type Ⅰ: mandibular prognathism or asymmetry mandibular prognathism; ②Type Ⅱ: mandibular prognathism and maxillary retrusion; ③ Type Ⅲ: mild Angle′s Class Ⅲ malocclusion, cross bite in anterior teeth, or normal overlap and overbite relation with midfacial hypoplasia. All of patients received surgery first approach therapy. The surgical procedures were chosen according to different malformation types. Type Ⅰ was treated with the sagittal split ramus osteotomy (SSRO). Type Ⅱ was treated by Le Fort Ⅰmaxillary osteotomy combined with SSRO. Type Ⅲ underwent anterior subapical osteotomy combined pyriform aperture augmentation with biomaterials as well as maxillary anterior orthodontics. All patients received postoperative rapid orthodontic treatment for 6-12 month after 2 weeks of operation. Using the straight arch wire techniques and the class Ⅲ intermaxillary traction, we removed the overcrowding upper and lower teeth, the compensatory axial tilt of teeth, and the deviation of the dental arch and maintained the neutral relationship of the molar. The mandible Hawley retaining devices were used during the maintaining stage.@*Results@#The cases in study acquired satisfactory clinical outcome, which included the shortened overall treatment duration, the significantly improved facial features, the corrected occlusion relationship, and the restored function of mastication and temporomandibular joint. There were some complications as follows: intraoperative fracture (6 cases, 3.24%), the inferior alveolar nerve bundle injury (2 cases, 1.1%), and temporary open-bite that diminished by inter-maxillary elastic distraction one month after operation (19 cases, 10%). All cases in this study accepted postoperative orthodontic treatment. Follow-up time ranged from 6 months to 5 years. The cephalometric analysis results of 126 cases who had complete image data and over 6 months of follow-up showed that hard and soft tissue indexes were restored to normal range after combined orthognathic-orthodontic treatment. The stability of the maxillary and occlusive relationship of SFA(surgery-first approach) was similar to that of the COS(conventional orthodontics-first system) [relapse ratio=(T2-T1)/(T1-T0)×100%]. Over six months of follow-up , SNB and ANB showed that the average relapse ratio were 22% and 19.8%, whereas the relapse angle are less than 2°.@*Conclusions@#The Surgery-first approach could be used to treat most patients with Angle skeletal Class Ⅲ malocclusion, but the indications and the surgical procedures should be noticed and chosen.

A method of mandibular dividing / 中华整形外科杂志

Objective@#To design a method of mandibular division for plastic surgery.@*Methods@#From January 2009 to June 2017, 118 patients who underwent mandibular plastic surgery were observed, measured and analyzed. Combined with clinical experience, a new method of mandibular division was designed. The mandible was divided into right and left sides and each side was subdivided into five subunits (A, B, C, D, E). Area A is mandibular ramus upper 1/2 and mandibular coracoid area; Area B is mandibular lower 1/2 area; Area C is mandibular body area; Area D is chin area; Area E is mandibular angle.@*Results@#The mandibles of 118 patients were divided according to the new method to obtain the characteristics of mandibular deformities and guide the design of the surgical plan.@*Conclusions@#The new method of mandibular division is concise and scientific, which is in favor of the diagnosis and surgical design of plastic surgery.

Application of digital planning in goniolpasty / 中华整形外科杂志

Objective@#To design the aesthetic new gonion and osteotomy line for patients with prominent mandibular angle patients using computer-aided techniques, and to investigate the application of three-dimensional digital planning in gonioplasty.@*Methods@#From April 2016 to April 2017, 14 female patients with prominent mandibular angle underwent preoperative surgical design and surgical simulation using digital technology. Gonioplasty was performed under the guide of surgical templates, preoperative, surgical simulation and postoperative data were measured including bilateral mandibular angles, the height of ramus(Co-Go) and the length of mandibular body(Go-Me). Paired t test was used to compare the differences between surgical simulation and postoperative measurements.@*Results@#Gonioplasty was performed in 14 patients successfully, and all were satisfied with their facial outcomes. The mandibular angle was improved from 113.86°±4.11° to 124.52°±1.26° on the left side, and 114.30°±4.01° to 124.29°±1.24° on the right side respectively. The average ratio of Go-Me/Co-Go was 2.011 on both sides after operation, which was very close to surgical planning. No significant differences were found between surgical planning and postoperative measurements with respect to mandibular angle or the ratio of Go-Me/Co-Go on both sides(P>0.05). The deviations between them were 1.00°±0.68° and 0.058±0.038 on the left side, and 0.85°±0.63° and 0.072±0.053 on the right side respectively.@*Conclusions@#Computer-assisted gonioplasty could improve the efficiency and accuracy of surgery, reduce the risk of surgical complications, and attain higher patients′ satisfaction.

Establishment of electron beam computed tomography and rapid prototyping techniques for a cranial bone defect model in goat / 中华医学美学美容杂志

Objective To establish a cranial bone defect model of goat and to study application in craniomaxillo-facial surgery.Methods Electron beam computed tomography (EBCT) scanner was used to scan goat'heads and faces in series and thin layers.Data of EBCT were input in workstation from digital inlet,and then to three-dimensional reconstruction with method of surface shadow.After final data were transformed to the files,the rapid prototyping machine was able to identify and establish the 3D model.Results The EBCT continuous thin-layer (1 mm) scanning data were passed to wave filter,falling coarse,distinguishing and collecting the outline,3D-reconstruction,curved surface reconstruction with CAD and the substance reconstruction.The final data were input into the laser rapid prototyping machine.Three-dimensional bionic cranium models were fabricated by machine in layer by layer manufacturing principle.Conclusions Establishment of the cranial bone defect model in the goat is very useful to the three-dimensional measurement,individualized reconstruction and basic and clinical research for the cranial bone defect.

Mandibular esthetics: three-dimensional measurements / 中华医学美学美容杂志

Objective To aesthetically evaluate the mandible,to position the gonion landmark of the aesthetic female with digital techniques and to establish three-dimensional mandibular measurements database of the aesthetic female.Methods 14 aesthetic volunteers were chosen by plastic surgeons and ordinary people based on the identical view of esthetic mandible.The heads were scanned by a spiral CT scanner,and the data were imported into Mimics 18.0 to generate the 3D skull images.Distance,angle and ratio measurements,which could represented the aesthetic characters of the mandible,were made on the images.All the data were transferred into the SPSS 22.0 software to perform statistical analysis.A two-tailed t test was used to compare the symmetry of bilateral mandibles.Dynamic database of aesthetic mandibles was established.The mean,standard deviation,standard error and 95％ confidence interval of data were calculated by statistical software automatically.Results The results suggested that the mean of aesthetic mandibular angle was 123.91°,and the mean of mandibular plane angle was 27.03°.The ratio between the mandibular body and ramus approximated to 2 ∶ 1,and the ratio of the distance between gonion and mental foramen to ramus was close to 1.4.Conclusions The study of mandibular esthetics contributes to positioning the new gonion accurately for patients with prominent mandibular angle and gonion reconstruction,and it can assist surgeons in surgical designing,simulating and performing.

Mandibular distraction combined with orthognathic techniques for the correction of adult hemifacial microsomia / 中华整形外科杂志

<p><b>OBJECTIVE</b>To study the combination of Mandibular distraction and orthognathic techniques for the reconstruction of adult hemifacial microsomia.</p><p><b>METHODS</b>The three-dimensional CT reconstruction data was used with Mimics for preoperation design. The osteotomy location, distraction vector, distraction distance were decided before operation with a surgical guider. At the first stage, internal distractor was implanted after ostetomy through an extra-oral approach. The distraction begun 5-7 days after operation with a frequency of 1 mm/day. After distraction, the distractor was maintained for 3-6 months. At the second stage, the distractor was removed. Le Fort I osteotomy was performed in order to correct the cross-bite and improve the facial contour. Usually, bone graft was inserted into the gap after Le Fort I osteotomy. The genioplasty was also performed if necessary.</p><p><b>RESULTS</b>9 cases of adult hemifacial microsomia with severe mandibular deviation were treated. The facial asymmetry were improved greatly. 1 patient suffered an wound infection in the maxillary region after Le Fort I osteotomy and healed uneventfully with wound irrigation.</p><p><b>CONCLUSIONS</b>Mandibular distraction combined with orthognathic surgery is an effective procedure for adult hemifacial microsomia with complicated mandibular hypoplasia.</p>

Surgical therapy of midline skull defect accompanied with frontal sinus injury / 中华整形外科杂志

<p><b>OBJECTIVE</b>To investigate the surgical therapy of midline skull defect accompanied with frontal sinus injury.</p><p><b>METHODS</b>11 cases with midline skull defect accompanied with frontal sinus injury were treated. Free temporal fascia was transplanted to close the top of frontal sinus after curettage of the frontal sinus wall. Then titanium prostheses were used to repair the skull defects at the same stage in 10 patients. 1 patient received skull defect repair at the second stage operation.</p><p><b>RESULTS</b>Good results were achieved in 10 cases. The titanium prosthesis had to be taken out in one case due to frontal sinusitis and the anastomosis of frontal sinus and nasal cavity was performed.</p><p><b>CONCLUSIONS</b>In patients with midline skull defect accompanied with frontal sinus injury, free temporal fascia could be used to close the top of frontal sinus after curettage of frontal sinus wall. If there is no infection or mild infection in frontal sinus, the skull defect repair could be performed in the same stage. If there is severe frontal sinusitis, the defect repair should be done at the second stage.</p>

Visualization of Medpor implants using surface rendering / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>The Medpor surgical implant is one of the easiest implants in clinical practice, especially in craniomaxillofacial surgery. It is often used as a bone substitute material for the repair of skull defects and facial deformities. The Medpor implant has several advantages but its use is limited because it is radiolucent in both direct radiography and conventional computed tomography, causing serious problems with visualization.</p><p><b>METHODS</b>In this study, a new technique for visualizing Medpor implants was evaluated in 10 patients who had undergone facial reconstruction using the material. Continuous volume scans were made using a 16-channel tomographic scanner and 3D reconstruction software was used to create surface renderings. The threshold values for surface renderings of the implant ranged from -70 HU to -20 HU, with bone as the default.</p><p><b>RESULTS</b>The shape of the implants and the spatial relationship between bone and implant could both be displayed.</p><p><b>CONCLUSION</b>Surface rendering can allow successful visualization of Medpor implants in the body.</p>

Application of high-density porous polyethylene implant in chin augmentation in contour plastic surgery of low face / 中华医学美学美容杂志

Objective High-density porous polyethylene(Medpor)has been widely used in chin augmentation in recent years.The study aimed to observe the outcomes of clinical use of high-density porous polyethylene implant in chin augmentation in contour plastic surgery of low face.Methods From 2005 to 2008,149 cases of chin augmentations intraorally with Medpor implants combined with were collected.121 of them received bilateral mandibular angle osteotomy and 28 cases received bilateral mandibular angle osteotomy and bilateral malar reduction simultaneously.They wre all females aged from 17 to 46 years.The patients were followed up for 6 to 36 months(average 24 months)and photographs were taken before and after operations.Clinical outcomes were observed and analysed.Resuits 145 patients(97.3%)were satisfied with their chin and contour of low face.2 patients (1.3%)were not satisfied with the projection of their chin,and 1 of them were admitted to take out the implant and received sliding advancement genioplasty.1 patient(0.7 0A)felt the implants was too large to some extent and was admitted to modify the implant.1 patient(0.7%)received genioplasty 6months after operation because of the deviation of the implant.20 patients(13.4%)felt numbness of the lower lip which gradually disappeared 1 to 3 months postoperatively.Complications such as infection,edema and extrusion,break of the implant were not found during the following period.Conclusions Medpor is an excellent biomaterial with good biocompatibility.Simultaneously chin augmentation with Medpor combined with bilateral mandibular angle osteotomy intraorally shows a good result in contour plastic surgery of low face.

The influence on masticatory function after curved osteotomy of prominent mandibular angle / 中华整形外科杂志

<p><b>OBJECTIVE</b>To investigate the influence of mandibular curved osteotomy on masticatory function by analyzing the bite force before and after operation.</p><p><b>METHODS</b>From Jan. to Oct. 2008, 20 female cases underwent mandibular curved osteotomy. The maximal bite force in incisor area, bilateral premolar area and molar area was measured before operation and 6 months after operation.</p><p><b>RESULTS</b>The maximal bite force in incisor area, right premolar area, left premolar area, right molar area, left molar area was (11.7 +/- 3.9) kg, (23.2 +/- 1.6) kg, (30.9 +/- 2.3) kg, (35.6 +/- 4.2) kg, (38.5 +/- 3.1) kg, respectively before operation; and was (11.9 +/- 2.1) kg, (23.0 +/- 4.5) kg (31.0 +/- 1.8) kg,(35.9 +/- 3. 5) kg. (38.5 +/- 2.7) kg, respectively 6 months after operation. The postoperative maximal bite force reached the preoperative level, and even slightly above it. There was no significant difference between the measured data before operation and 6 months afterward (P > 0.05).</p><p><b>CONCLUSIONS</b>The curved osteotomy of prominent mandibular angle has no long-term effect on masticatory function.</p>

Expression of cyclin D1 in glandular tissue of pubertal mammary hypertrophy and micromastia / 中华医学美学美容杂志

Objective To investigate the expression of the cyclin D1 in pubertal mammary hypertrophy and micromastia. Methods The expression of cyclin D1 was detected by SP immunohisto-chemistry in 18 cases of pubertal mammary hypertrophy and 12 cases of micromastia. Results The expression rate of cyclin D1 within breast tissue was 83. 33 % and 16. 67 % in pubertal mammary hypertrophy and micromastia, respectively. There was significant difference between the two groups (P<0. 01). Conclusion The expression level of the cyclin D1 within breast tissue in pubertal mammary hypertrophy is higher than that in micromastia.

Changes of masseter muscle following curved ostectomy of prominent mandibular angle: a study of real-time 3D-ultrosonography / 中华医学美学美容杂志

Objectives To investigate the changes in the masseter muscle following osteotomy of the prominent mandibular angle using real-time three-dimensional (3D) ultrasonography, and to supply guidance for resection of the mandibular angle. Methods Real-time 3D ultrasonography was applied preand post-operatively (over a 6-month follow-up period) to 10 patients who underwent curved osteotomy with the following objectives: (1) to reconstruct the morphological changes of the masseter under different conditions; (2) to assess masseter muscle volume changes, and (3) to obtain the dynamic morphological changes of masseter during mouth opening and closing. Results The reconstructed 3D images revealed that longitudinal diameters of masseter muscle decreased and angle regions changed to be arc-shaped with significant thinning 6 months after operation. The mean volume of masseter muscle was (18. 222 ±3. 028) cm36 months post-operatively, compared with the pre-operation mass of (25. 480 ± 7. 113) cm3,the statistical difference was significant (P＜0.01). Transverse and longitudinal changes of the thickest masseter muscle section 6 months post-operatively were of no statistic difference (P＞0. 01) compared with pre-operation status during mouth opening and closing motions. Conclusion A certain extent of atrophy occurs primarily in the angle region of masseter muscle after mandibular angle ostectomy. However, these changes do not significantly impair masseter muscle function. Real-time 3D ultrasonography offers a novel, safe, and convenient technique for masseter muscle reconstruction and observation of masseter muscle movement.

Changes of collagen fiber during reattaching of the musseter muscle following different curved osteotomies of prominent mandibular angle: a study in goats / 中华医学美学美容杂志

Objective To investigate the changes of the constitution and its ratio of collagen fiber in the process of masseter reattachment following different osteotomies of the prominent mandibular angle so as to offer guidance for the resection of mandibular angle. Methods Sixteen adult goats were randomized into four groups. In group A we performed unilateral curved osteotomy of the mandibular angle. In group B unilateral curved ostectomy was performed with partial masseter resection. In group C unilateral angle splitting ostectomy, while in group D unilateral dissection of the masseter muscle was conducted. The constitution and its ratio of collagen fiber in the interface were observed at 1-month, 2-month, 3-month, and 6-month after operation. Results On the changes of collagen fiber in the process of muscular reattachment, at 1-month post-operation, the constitution of collagen fiber (types Ⅰ and Ⅲ) in groups A and B were significantly different from that of control group (P<0.05). However, both groups C and D had no statistic difference from control group (P>0.05). At 2-month, 3-month and 6-month post-operation, those of all experimental groups had no statistic difference from control group. And with time, the percentage of collagen fiber type Ⅰ increased and type Ⅲ decreased gradually. Conclusion The recovery sequences of masseter muscle reattachment in this study are firstly group C, secondly group A and finally group B. It suggests that the recoveries of mastication and other oral activities are different. Group B turns out to be with a slow muscle reattachment. Thus, we recommend treating different kinds of mandibular hypertrophy with different ostectomies.

Changes of masseter muscle following curved osteotomy of mandibular angle in goats / 中华医学美学美容杂志

Objective To investigate the changes of the masseter muscle following osteotomy of the prominent mandibular angle and to provide guidance for the resection of mandibular angle. Methods Ten goats were equally divided into two groups. In group A we performed unilateral curved osteotomy of the mandibular angle, and in group B we performed unilateral dissection of the masseter muscle. The cross section area (CSA) and the sarcomere length of masseter muscle were measured beore and after operation. Results (1) Cross section area (CSA) of masseter muscle fiber in curved ostectomy group decreased at 1,2, 3 and 6 months after operation in different extent. Comparing with the control group, the difference was statistically significant (P<0.01). CSA of masseter muscle fiber in dissection group decreased 1 month postoperatively, which had significantly statistic difference with control group (P<0.01). But, they had no significant difference with control group at 2, 3, and 6 months after operation (P>0.01). (2) Sarcomere length of masseter muscle in curved ostectomy group decreased in 1 week, 1 and 2 months after operation, which had significantly statistic difference with control group (P<0.01). At 3 months after operation, sarcomere length recovered to normal. In dissection group, sarcomere length decreased in 1 week and 1 month after operation, which had significantly statistic difference with control group (P<0.01). At 2 month after operation, it recovered to normal. Conclusion Certain extent of atrophy does happen to masseter muscle after mandibular angle ostectomy. Meanwhile, these changes do not significantly impair the function of masseter muscle. According to this, we suggest a simple mandibular angle ostectomy without partial resection of masseter muscle in case of mild to morderate mandibular angle hypertrophy. Doing so, we can not only achieve the cosmetic effect but also reduce the implications.

Experimental study of biomechanics after mandibular outer cortex osteotomy / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the local changes of biomechanics after osteotomy of mandibular outer cortex in body and angle areas.</p><p><b>METHODS</b>Six minitype pigs at the age of 8 to 12 months were selected. The mandibular outer cortex that involves angle and part of body was removed in one side. The animals were killed 24 weeks after operation. Bone strut was taken from mandibular angle region bilaterally and sent for biomechanical test</p><p><b>RESULTS</b>There was no biomechanical difference between the two angle areas of experimental and normal sides 24 weeks after mandibular outer cortex osteotomy (maximum load P > 0.05, rigidity P > 0.05).</p><p><b>CONCLUSIONS</b>Mandibular outer cortex osteotomy had no influence on local biomechanics.</p>

Clinical research of craniofacial bone autograft using mandibular outer cortex / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To illustrate the volume changes of mandibular outer cortex after been grafted to different recipient sites of facies cranii.</p><p><b>METHODS</b>Six cases underwent onlay bone graft to the angle and body part of mandible and malar surface simultaneously by using mandibular outer cortex. Three dimensional computed tomography (3D-CT) datum of immediate postoperative and 6 months postoperative of each case were collected systematically. By true-up and dissection techniques based on 3D-CT, volume changes of bone graft at different recipient sites were observed and analyzed 6 months postoperative.</p><p><b>RESULTS</b>6 months after onlay bone grafted, bone resorption occurred. To different recipient sites, bone resorption rate was unequal. At the mandible area, bone resorption rate was 20.8% +/- 7.2%, the main site of resorption was at the lower and posterior border of mandible. At the anterior part of maxilla, bone resorption rate was 11.2% +/- 2.3%. Statistics showed significant difference of resorption rate between the two sites (P<0.05).</p><p><b>CONCLUSION</b>Bone resorption of mandibular outer cortex after onlay graft treatment is variant according to different craniofacial recipient sites. The difference of mechanical environment at variant recipient sites is considered to be an influencing factor. Quantization of bone resorption rate can guide a better clinical use.</p>

Elective neck dissection or "watchful waiting": optimal management strategy for early stage N0 tongue carcinoma using decision analysis techniques / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Although tongue cancer is a common disease of the head and neck, the choice of neck treatment between elective neck dissection and "watchful waiting" remains controversial for patients with early stage N0 oral tongue carcinoma.</p><p><b>METHODS</b>On the basis of the current state of head and neck cancers a decision analysis model was created to compare two treatment strategies for early tongue cancer. Expected value (EV) was calculated according to the literature which met the defined criteria. Sensitivity analyses were performed.</p><p><b>RESULTS</b>The results showed that the decision model favored elective neck dissection (EV = 0.87), over "watchful waiting" (EV = 0.77). One-way sensitivity analyses demonstrated that the outcome was influenced by regional recurrence, threshold value of 0.28 for the elective neck dissection group and 0.17 for the "watchful waiting" group, and a salvage rate threshold value 0.73 for the "watchful waiting" group.</p><p><b>CONCLUSIONS</b>These results suggested that elective neck dissection strategy of the neck should be applied for early stage N0 oral tongue carcinoma patients with no clinical nodal metastases. When the occult lymph node metastases rate was less than 0.17 and the salvage rate was more than 0.73, "watchful waiting" strategy would be preferable.</p>

3-dimensional CT cephalometry before and after mandibular angle osteotomy and its clinical significance / 中华整形外科杂志

<p><b>OBJECTIVE</b>To investigate the change of skeleton structure and masseter after mandibular angle osteotomy and its clinical significance in preoperative design.</p><p><b>METHODS</b>3-dimensional CT cephalometry was performed before and after surgery in 18 cases of prominent mandibular angle.</p><p><b>RESULTS</b>Pre- and post-operative data were compared. Significant differences between the pre- and post-operative data were found in the mandibular angle, the distance between mandibular angle, length of ramus, ectropion angle of mandibular angle, triangle Go-Me-Go, the thickness, width and length of masseter.</p><p><b>CONCLUSIONS</b>It indicates the skeleton structure is changed and some kind of atrophy happens in the masseter after operation. So we suggest partial resection of masseter should be unnecessary for mandibular angle osteotomy.</p>