| Part one:The anatomic study of normal adult female mandibular angle with multi-slice spiral CTObjective:Through the normal mandibular angle of 60 cases of adult women undergone 16-slice spiral CT volume scanning and three dimensional reconstruction, to analyze the anatomical characteristics of the mandibular angle in general, the mandibular cortical bone in different place and the anatomic characteristic of neural tube, and to provide anatomical basis for surgery of narrow the mandibular angle.Methods:60 cases healthy adult female (120 sides) were included in this study. The patients ranged in age from 20 to 43 years (mean age 27.1 years). The patients ranged in height from 152 to 183 centimeter with a mean height of 166.5 centimeter. the patients ranged in weight from 40 to 95 kilogram with a mean weight of 57.3 kilogram. All patients have no history of mandibular trauma or operation. Use of, GE Light speed 16 multi-slice spiral CT machine, conventional cross-sectional scanning was performed, the scanning baseline was vertical to the longitudinal section of the body corresponding to MC line. Scan range including a complete mandible, slice thickness 0.625 mm, no interval volume scan. Tube voltage 120 kV, tube current 260 mAs. Bone algorithm reconstruction was performed. The raw data were imported into ADW4.2 workstation, volume reconstruction (VR), MPR reconstruction were performed, window width 2000 Hounsfield unit, window level 500 Hounsfield unit.Three dimensional reconstruction, including volume reconstruction (VR) and multi planar reconstruction (MPR). To get the standard coronal plane, sagittal plane and arbitrary angles sagittal and coronal plane images, by adjusting the different axes can get all the facets of the reorganization of the image.Through volume reconstruction, we can observe the whole general anatomical characteristics of the mandibular angle.On VR image a straight line was drawn through the occlusal plane with the back edge of the mandible as a point of intersection of A; Through the mental foramen to draw a parallel line with the inferior margin of mandible parallel the back edge of and intersect with the mandible to the intersection point of B; Through the front edge of mandibular ramus mandible to do the vertical of the inferior margin of mandible and the intersection point as a point C; Through the mental foramen to do a vertical with the inferior margin of mandible, intersecting at the point of D. The AB segment defined as posterior margin of mandible, BC segment defined as angle of mandible area and CD segment defined as inferior border of mandible. In the VR image positioning, each section were measured five points. MPR images automatically match, on MPR measured the thickness of the cortical bone at five points correspond to the inner plate, outer plate and edge, respectively. In this group we measured 60 cases of 120 lateral mandibular cortical bone thickness. SPSS10.0 statistical software were used to process the data, calculation of mean, standard deviation and coefficient of variation, bilateral mandibular cortical bone thickness did two independent samples t test. P<0.05 was considered statistically significant difference.MPR reconstruction of the mandibular nerve canal measured from the mandible in different locations outside the board and the distance between the lower edge of the measured data were analyzed statistically.Result:1. The general morphology of mandibular angle The connection mode of the lower edge of mandible and post-edge have four types:single-angle turn-based (11.67%), biangle turn-based (8.33%), angel transition form (73.33%), anterior-posterior project type (6.67%); The position relation of angle of mandible with the axial plane of the mandible have three types:extraversion (11.67%), neutral (70.00%), enstrophe (18.33%).2. Cortical bone thickness of the mandibular angle areaThe exterior, interior and marginal cortical bone thickness of the left posterior border of mandible are 2.12±0.29mm,2.89±0.35mm,4.40±0.66mm; The exterior, interior and marginal cortical bone thickness of the left angle of mandible are 2.13±0.35 mm,2.91±0.35 mm,5.76±1.22 mm; The exterior, interior and marginal cortical bone thickness of the left inferior border of mandible are 2.18±0.41mm,3.01±0.42mm,4.29±0.68mm.The exterior, interior and marginal cortical bone thickness of the right posterior border of mandible are 2.14±0.25 mm,2.73±0.29mm,4.19±0.60mm; The exterior, interior and marginal cortical bone thickness of the right angle of mandible are 2.24±0.24mm,2.76±0.32mm, 5.65±1.09mm; The exterior, interior and marginal cortical bone thickness of the right inferior border of mandible are 2.40±0.39mm,2.98±0.42mm, 4.14±0.64mm. bilateral exterior cortical bone thickness of the posterior border of mandible (PE:t=4.882, P=0.000; PM:t=2.974, P=0.004), exterior cortical bone thickness of the angle of mandible (AI:t=3.394, P=0.001; AE:t=4.217, P=0.000), and interior cortical bone thickness of the inferior border of mandible (Ⅱ:t=6.540, P<0.05) have statistically significant, other part have not statistically significant.3. The measure of the mandibular neural tubeThe distance of the neural tube to the outer edge of the mandibular jaw in the third molar level is the minimum (left 4.20±1.05; right 4.27±1.00); The maximum distance between the first two molars (left 5.73±1.40 mm; right 5.58±1.38 mm); The distance of the neural tube to the lower edge of the mandibular jaw in the third molar level is the maximum (left 8.50±2.09 mm; right 8.82±2.42 mm), the smallest distance is between the First molar and second molar (left 6.98±0.72mm; right 6.87±0.91 mm)Conclusions:1. Multi-slice spiral CT can three-dimensional observed the posterior edge of the mandible, mandibular angle, the lower edge of shape in vivo, preoperative evaluation of mandibular angle can be quasi-morphological characteristics of the surgical plan to provide important reference information, for mandibular angle narrowing surgery has important clinical significance.2. With Multi-slice spiral CT can precisely measure the cortical bone thickness of the back edge of the mandible, mandibular angle, the lower edge of mandibular. In the observation of bone structures at the same time can observe the soft tissue, for narrowing the mandibular angle surgery has important clinical significance. To ensure accurate implementation of the procedure, reducing operative difficulties, reduce surgical complications.3. Multi-slice spiral CT volume scanning and three-dimensional reconstruction can be a very good display of the mandibular neural tube and its traveling direction and the relationship between the surrounding structures, for mandibular surgery to say have an important clinical significance.Part two:Three-dimensional finite element analysis of mandible biomechanicsObjective:With the three-dimensional finite element method, a three-dimensional finite element model of mandible was constructed; the biomechanical characteristic variation of mandible after the mandibular angle osteotomy anaplasty by the means of partial resection surgery of mandibular bone was studied; a safety margin for the bone resection surgery of the mandibular angle osteotomy anaplasty was obtained; and an optimal balance point between the remodeling effect of the lower facial contour and the mechanical variation was observed.Method:A group of healthy young female volunteers with the well-developed craniomandibular system and the class I molar relationship was selected; the temporomandibular joint region and the mandible bone were examined through serial scan and axial tomography of the 64-slice spiral CT; the Mimics12.0 and the Ansys12.0 software were used for segmentation, smoothing processing and three-dimensional mesh generation according to the experimental requirement;with the addition of parameter setting for material mechanics and the boundary constraint design, a three-dimensional finite element model (control group) of a normal mandible with the muscle and ligament constraint for the mandible without the lower teeth was constructed. On the basis of the three-dimensional finite element model (control group), a model 1 with the resection of mandibular margin and a model 2 with the partial resection of mandible were constructed respectively (experimental group); an impact response curve was added at the corresponding point on the stress surface of the lower edge of the symphysis; the mandible stress nephogram and the dynamic stress variation nephogram of the mandible in the control group and the experimental group were calculated through the Ansys12.0 software. Three points were chosen at the mandible condyle, the mandibular body and the junction between the horizontal branch and the mandibular ramus; the stress-time load response curves of the three points were calculated through the software; and the stress data of each point with a 1ms time interval unit during the stress conduction process and the maximal stress of the points were extracted. Afterwards, the model 1 and the model 2 were introduced into the Ansys12.0 software respectively; the above solving steps were repeated; and the stress nephogram, the dynamic stress variation nephogram and the time-stress load response curve for the control group and the experimental group and the stress data of the above three points were calculated.Result:1. A three-dimensional finite element model of the normal mandible with muscle and ligament constraint, a model 1 and a model 2 were constructed.2. The stress distribution on the whole model of the mandibleThe impact stress began to spread around 1.8ms after the mentum impact and the stress mainly conducted along the external oblique direction and concentrated at the mandible condyle. After the stress on the concentration part of the anterior,internal side of the mandible condyle reached the summit of the stress 12.5ms after the impact, the stress on the mandible was in a downward status and disappeared gradually. In the whole process, the posterior edge of the mandible, the mandibular angle area and the lower edge which was close to the mandibular angle area mentioned in the former part of the study were always in a less stress state.3. The stress distribution of the mandible model 1 of the experimental groupThe stress conduction and distribution of the model were similar to the normal mandible; however, the scope and the intensity of the stress on the mandible were reduced apparently. Compared with the nephogram of the normal mandible, the color intensity of the nephogram of model 1 was weakened and the similar color area became smaller. After 11～12.5ms the addition of the impact load, the color of the surrounding area of the sigmoid incisure of mandible, coracoid process and alveolar ridge turned from less stress blue into more stress yellow when compared with the normal mandible.4. The stress distribution of the mandible model 2 of the experimental groupThe stress conduction and distribution of the model were similar to the mandible model 1; however, the scope and the intensity of the stress on the mandible were reduced furtherly. Compared with the nephogram of the normal mandible, the color intensity of the nephogram of model 1 was weakened and the similar color area became smaller. After 11～12.5ms the addition of the impact load, the yellow color intensity of the surrounding area of the moid notch of the mandible, coracoid process and alveolar ridge became stronger when compared with the mandible model 1. The result shows that the stress in this area was increased furtherly.5. The time-stress curves of the mandible condyle, the point at the junction between the horizontal branch and the mandibular ramus and the mandibular bodyThe curve morphology of the mandible condyle, the point at the junction between the horizontal branch and the mandibular ramus and the mandibular body of each model are almost identical. However, there is difference in the summit value and the waveform before the disappearance of the stress. The maximal variation of the summit value appears at A point; two apparent rebound waves exist in mandible model 2. The rebound wave of the mandible model 1 before the disappearance of the stress at B point is not obvious; however, there is rebound wave in mandible model 2. There is no rebound wave in the mandible model before the disappearance of the stress at C point; however, the rebound wave of the mandible model 1 is not obvious; there are two apparent rebound waves in mandible model 2.6. Statistical analysis for the stress at A point of the mandible condyle, B point at the junction between the horizontal branch and the mandibular ramus and C point of the mandibular bodyWith the anova analysis, the variance of the stress at different sites of the three groups are irregular (a:F=3.174, P< 0.05; b:F=29.204, P=0.000; c:F=20.051, P=0.000); the multiple comparison among different groups is conducted through using the Dennetts method. The result shows that there is no statistical difference among three groups at A point(P> 0.05); there is statistical difference between the normal mandible group and the model 1 and the model 2 at B point (P< 0.05); there is no statistical difference between the model 1 and the model 2 at B point (P> 0.05); there is statistical difference between the normal mandible group and the model 1 at C point (P< 0.05); and there is no statistical difference between the normal mandible group and the model 2 at C point (P> 0.05).Conclusion:1. After the impact of the mandible, the stress was mainly conducted along the external oblique direction and concentrated at the mandible condyle.2. The resection of the posterior edge of the mandible,the mandibular angle and the lower edge of the mandible can cause the elevation of the stress in the surrounding area of the sigmoid incisure of mandible, coracoid process and alveolar ridge.3. The more bone was excised, the more stress was increased and the more fragile the mandible became.Part three:The clinical experience of Mandibular angle osteotomy plastic surgery and the clinical applied research of Multi-slice computed tomography on Mandibular angle osteotomy plastic surgeryObjective:Evaluation the clinical features of patients with mandibular angle osteotomy plastic surgery and the results of operation, meanwhile to observe the clinicalapplication value of multi-slice computed tomography.Methods:Since October 2007 to November 2009, Total completion 119 cases of the mandibular angle osteotomy plastic surgery, all patients underwent preoperative general examination and X-ray examination. In this group there have 119 cases, among of which there have 115 female (229 sides),4 cases men (7 sides).19 to 43 years of age and with a mean age 28.3 years. All patients maxillofacial region growth normally, occluding relation normal and have no occlusion barrier, have no sings and symptoms of temporomandibular joint disturbance syndrome, have no history of mandibular operation and trauma. The hypertrophy of mandibular angle to the main bone hypertrophy, Showed as prominent mandibular angle bone hyperplasia and Mandibular angle spacing widened. Among of which there have 25 cases undergone zygoma diminutionplasty,6 cases undergone prosthesis chin augmentation.In this group there have 21 cases have preoperative three-dimensional reconstruction and preoperative simulation, among of which there have 7 cases undergone postoperative three-dimensional reconstruction from 1 week to 12 weeks after the operation. Spiral CT scanning method and reconstruction method just like part one.To make use of Mirror system software, loading the three dimensional picture of mandible, use the stretching, panning, cutting, rotation, stitching and expanding functions of the software, based on the standards of the ministry of bone in past reported literature the following outline of the aesthetic, and made reference to the request of the patients, as well as with combined features, form a combination of factors and then simulate the effect of surgical treatment of the bone, after that make a comparison with postoperation three-dimensional reconstruction.Result:In patients with large mandibular angle with zygomatic distance of 131.2mm; the preoperation distance between mandibular angle is 116.5mm and postoperation distance is 101.8mm, Than preoperation shrunk 14.7mm. Preoperative lateral angle of the mandibular angle is 114.1°, and postoperation is 126.2°.There have 93 patients being followed up about 3 months in 119 patient's undergone operation, there have 88 cases the surgeon and patients consider significant improvement in facial contour and have satisfactory result, accounted for 73.95% of all cases.57 cases followed up about for 6 months and among of which 56 patients get satisfactory result, accounted for 47.06% of all cases.Conclusions:1. The mandibular angle osteotomy plastic surgery of the mandibular angle has a good effect, Learn more about preoperative patient characteristics of bone structure help increase the success rate of surgery and reduce the incidence of complications.2. Spiral CT in the preoperative mandibular angle osteotomy and plastic surgery can help determine the surgical plan, simulate the operation and evaluate the results of operations.3. The osteotomy line and the way of the bone process should dicided by the typing and classification of the mandibular angle.
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