Nondeviated Side Research Articles

Three-dimensional computed tomography analysis of mandibular morphology in patients with facial asymmetry and mandibular retrognathism.

The purpose of this study was to analyze the morphologic features of skeletal units in the mandibles of patients with facial asymmetry and mandibular retrognathism using cone-beam computed tomography. The subjects consisted of 50 adults with facial asymmetry and mandibular retrognathism, divided intothe symmetry group (n=25) and the asymmetry group (n=25) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with cone beam computed tomography. Landmarks were designated on the reconstructed 3-dimensional images. Linear and volumetric measurements were made on the mandibles. In the asymmetry group, the lengths of condylar, body, and coronoid units were shorter, and condylar width was narrower on the deviated side than on the nondeviated side (P<0.01). The lengths of angular and chin units were not significantly different between the deviated and nondeviated sides (P>0.05). Hemimandibular, ramal, and body volumes were less on the deviated side than on the nondeviated side (P<0.01). Condylar, body, and coronoid units contribute to mandibular asymmetry in patients with facial asymmetry and mandibular retrognathism.

Does two-dimensional vs. three-dimensional surgical simulation produce better surgical outcomes among patients with class III facial asymmetry?

The aim of this study was to compare the outcomes of traditional two-dimensional planning (2DP) and three-dimensional surgical simulation (3DS) in the surgical correction of skeletal class III with facial asymmetry. This retrospective cohort study included 37 consecutive adult Taiwanese patients. Preoperative and postoperative three-dimensional cephalometric measurements were obtained from cone beam computed tomography scans. The outcome variables were the differences in preoperative and postoperative linear and angular measurements and the differences between the two groups after surgery. When the surgical result was compared between the 2DP and 3DS groups, significant differences were found for four cephalometric variables: the distance from gonion on the non-deviated side to the midsagittal plane (MSP), mid-gonion to the MSP, upper first molar on the non-deviated side to the Frankfort horizontal plane, and the yaw angle. In the 3DS group, mandibular symmetry was achieved because the centre between the bilateral gonions was improved, and because there was no significant difference in the horizontal gonion (Go to the MSP) between the deviated and non-deviated sides after surgery. 3DS provides all the necessary information for planned surgical movements for the correction of facial asymmetry; it should be considered during surgical planning to improve surgical outcomes, particularly the achievement of bilateral mandibular contour symmetry.

Cone-beam computed tomography analysis of transverse dental compensation in patients with skeletal Class III malocclusion and facial asymmetry.

ObjectiveThe purpose of this study was to analyze the transverse dental compensation in reference to the maxillary and mandibular basal bones using cone-beam computed tomography (CBCT) and evaluate the correlations between transverse dental compensation and skeletal asymmetry variables in patients with skeletal Class III malocclusion and facial asymmetry.MethodsThirty patients with skeletal Class I (control group; 15 men, 15 women) and 30 patients with skeletal Class III with menton deviation (asymmetry group; 16 men, 14 women) were included. Skeletal and dental measurements were acquired from reconstructed CBCT images using OnDemand3D 1.0 software. All measurements were compared between groups and between the deviated and nondeviated sides of the asymmetry group. Correlation coefficients for the association between skeletal and dental measurements were calculated.ResultsDifferences in the ramus inclination (p < 0.001), maxillary canine and first molar inclinations (p < 0.001), and distances from the canine and first molar cusp tips to the midmaxillary or midmandibular planes (p < 0.01) between the right and left sides were significantly greater in the asymmetry group than in the control group. In the asymmetry group, the ramus inclination difference (p < 0.05) and mandibular canting (p < 0.05) were correlated with the amount of menton deviation. In addition, dental measurements were positively correlated with the amount of menton deviation (p < 0.05).ConclusionsTransverse dental compensation was correlated with the maxillary and mandibular asymmetry patterns. These results would be helpful in understanding the pattern of transverse dental compensation and planning surgical procedure for patients with skeletal Class III malocclusion and facial asymmetry.

Comprehending the three-dimensional mandibular morphology of facial asymmetry patients with mandibular prognathism

BackgroundThe purpose of this study was to elucidate the factors that cause facial asymmetry by comparing the characteristics of the mandibular morphology in patients with mandibular prognathism with or without facial asymmetry using three-dimensional computed tomography (3D-CT).MethodsWe studied 28 mandibular prognathism patients whose menton deviated by ≥ 4 mm from the midline (FA group, n = 14) and those with a < 4-mm deviation (NA group, n = 14). DICOM data from multislice CT images were reconstructed and analysed using 3D image analysing software. Mandibular structures were assessed via linear, angular, or volumetric measurements and analysed statistically.ResultsThe lengths of the ramal and body components and condylar volume in the FA group were significantly greater on the nondeviated side than those on the deviated side. The mandibular body length of the nondeviated side in the FA group was significantly longer than that of the NA group. Other components of the FA group did not significantly differ from those of the NA group.ConclusionsImbalances in the sizes of the ramal and body components as well as the increased body length of the nondeviated side in the FA group compared with that of the NA group may contribute to facial asymmetry in patients with mandibular prognathism.

Nasal Deviation in Patients With Asymmetric Mandibular Prognathism.

This study was aimed to evaluate the nasal deviation in patients with asymmetric mandibular prognathism. Thirty-five patients with skeletal class III malocclusion were included in the study. Significant mandibular asymmetry of >4 mm menton deviation in three-dimensional (3D) reformatted cone beam computed tomography images was defined as asymmetry group (n = 20). Patients without mandibular asymmetry served as control group (n = 15). The mandibular asymmetry was evaluated pre- and postoperatively. Nasal tip was significantly shifted to the deviated side of the mandible (short side) in the asymmetry group, as compared to the control group (1.5 ± 0.9 degree, P < 0.01). Alar base angle (ABA) was significantly narrower in nondeviated side (long side) than in the deviated side in asymmetry group. However, control group showed no bilateral difference in ABA. Correction of deviated mandibular prognathism by isolated mandibular surgery resulted in change in the ABA but not the columella base position or nasal asymmetry. ABA on nondeviated side significantly decreased in proportion to the amount of transverse menton movement by surgery (r = -0.560, P < 0.01). Our results showed that mandibular chin deviation was accompanied by nasal deviation. Isolated mandibular surgery can potentially influence the alar base position on the contralateral side of deviation but not the nasal tip asymmetry. Therefore, clinicians should inform patients preoperatively of the fundamental limitation of mandibular surgery in cases with preexisting nasal asymmetry.

Evaluation of the laterality of the tissue oxygen saturation of masticatory muscles in subjects with facial asymmetry

PurposeIn subjects with facial asymmetry (FA), both morphological and functional lateralities in the masticatory muscles have been reported in literature. However, most studies evaluated masticatory muscle activity by electromyography. No report has analyzed tissue oxygen saturation (StO2) in subjects with FA. In this study, we aimed to investigate the hemodynamic laterality by measuring the bilateral masticatory muscle StO2 in subjects with FA. Materials and methodsThe subjects were divided into three groups: Group A, Class III skeletal relationship with mandibular deviation of ≥3.0mm; Group B, Class III skeletal relationship with mandibular deviation of <3.0mm; and Group C, normal skeletal relationship and occlusion. We used near-infrared spectroscopy to measure the bilateral masticatory muscle StO2 at rest, immediately after maximum clenching for 10s, and 30s after maximum clenching. We calculated the reduction rate of StO2 after maximum clenching and its recovery rate after 30s from the end of clenching, and statistically compared both sides within each group. ResultsWith regards to the reduction and recovery rates of StO2, significant difference was not found between sides in Groups B and C. However, a significant difference was observed in Group A; the reduction rate was significantly larger, and the recovery rate was significantly smaller in the side of mandibular deviation. ConclusionsHemodynamic laterality was found in the masticatory muscles between the deviated and non-deviated sides of the mandible in subjects with FA.

Upper airway asymmetry in skeletal Class III malocclusions with mandibular deviation

The purpose of this study was to investigate the relationship between bilateral differences of upper airway and mandibular morphologic patterns in subjects with skeletal Class III mandibular deviation. 47 skeletal Class III (ANB < 0°) adult patients with and without mandibular deviation were divided into 2 groups. Bilateral differences of minimum cross-sectional area, mean cross-sectional area, volume of subdivisions (nasopharynx, palatopharynx, glossopharynx, hypopharynx) were assessed paired t test. Stepwise linear regression analysis and Pearson correlation coefficients were computed between a significant pair of upper airway variables and a pair of mandibular deviation variables to examine the quantitative relationship between the upper airway asymmetry and mandibular deviation. The mean cross-sectional area and the volume of palatopharynx on the deviated side in mandibular deviated group was significantly smaller than non-deviated side. The asymmetry index of the palatopharyngeal volume showed significant correlations with CRA asymmetry (r = 0.49) and Ramus asymmetry (r = 0.54). However, in the glossopharyngeal and hypopharyngeal segment, the mandibular deviated group showed significant asymmetry, characterized by larger mean cross-sectional area and volume in deviated side. The asymmetry index of the glossopharyngeal volume and hypopharyngeal volume showed significant correlations with CRA asymmetry (r = 0.42), Me-s (r = 0.72) and Me-s (r = 0.67) respectively.

Condylar surface CT value in sagittal plane before and after sagittal split ramus osteotomy.

The purpose of this study was to evaluate the relationship between computed tomography (CT) values of the condylar surface and temporomandibular joint (TMJ) disc position in the sagittal plane before and after sagittal split ramus osteotomy (SSRO) setback surgery, retrospectively. The subjects were 75 patients (150 condyles) who underwent bilateral SSRO setback surgery. They were divided into two groups (42 symmetric patients and 33 asymmetric patients). Maximum CT values (pixel values) of five points of the condylar surface and condylar height, length, fossa height, fossa length, and ramus angle in the sagittal plane were measured preoperatively and 1year postoperatively. Disc position was classified as anterior disc displacement, anterior type, fully covered type, and posterior type, both pre- and postoperatively, using magnetic resonance imaging (MRI). Postoperative value was significantly higher than preoperative one in CT value of 135° (P=0.0199) and 180° (0.0363), in the non-deviation side in the asymmetry group. The anterior disc displacement group was significantly larger than those of some other areas pre- and postoperatively in the CT value of 0° point (P<0.05). This study suggested that CT value of the posterior site of the condylar surface could change in the non-deviation side in the asymmetry group after 1year SSRO, and the condyle with anterior displacement showed high CT value at the anterior site of the condyle before and after surgery.

Changes in condylar position after BSSRO with and without Le Fort I osteotomy via surgery-first approach in mandibular prognathism with facial asymmetry

This study aimed to evaluate changes in condylar position after bilateral sagittal split ramus osteotomy (BSSRO) with and without Le Fort I osteotomy via the surgery-first approach (SFA) in patients with facial asymmetry. Eighteen patients (36 condyles) who received surgical-orthodontic treatment using the SFA were included and divided into 2 groups depending on the extent of surgery: BSSRO-only group (n=12) and BSSRO with Le Fort I osteotomy group (n=6). Using computed tomography images taken preoperatively, immediately postoperatively, and 6months postoperatively, surgical and postoperative changes of the condylar position were analyzed 3-dimensionally. Both groups showed mainly inferolateral displacement with inward rotation immediately after surgery, and superomedial returning movement with outward rotation 6months after surgery. There was no statistical difference in time-course changes of the condylar position between the 2 groups. In comparing the deviated and nondeviated sides, the deviated side showed significantly greater amount of bodily shift and rotational movement after surgery compared with the nondeviated side in both groups. These results suggest that BSSRO via the SFA, either with or without Le Fort I osteotomy, may cause condylar displacement after surgery and that the displaced condyles return to their original position on both the deviated and the nondeviated sides.

Comparison of changes in the transverse dental axis between patients with skeletal Class III malocclusion and facial asymmetry treated by orthognathic surgery with and without presurgical orthodontic treatment

ObjectiveTo evaluate transverse skeletal and dental changes, including those in the buccolingual dental axis, between patients with skeletal Class III malocclusion and facial asymmetry after bilateral intraoral vertical ramus osteotomy with and without presurgical orthodontic treatment.MethodsThis retrospective study included 29 patients with skeletal Class III malocclusion and facial asymmetry including menton deviation > 4 mm from the midsagittal plane. To evaluate changes in transverse skeletal and dental variables (i.e., buccolingual inclination of the upper and lower canines and first molars), the data for 16 patients who underwent conventional orthognathic surgery (CS) were compared with those for 13 patients who underwent preorthodontic orthognathic surgery (POGS), using three-dimensional computed tomography at initial examination, 1 month before surgery, and at 7 days and 1 year after surgery.ResultsThe 1-year postsurgical examination revealed no significant changes in the postoperative transverse dental axis in the CS group. In the POGS group, the upper first molar inclined lingually on both sides (deviated side, −1.8° ± 2.8°, p = 0.044; nondeviated side, −3.7° ± 3.3°, p = 0.001) and the lower canine inclined lingually on the nondeviated side (4.0° ± 5.4°, p = 0.022) during postsurgical orthodontic treatment. There were no significant differences in the skeletal and dental variables between the two groups at 1 year after surgery.ConclusionsPOGS may be a clinically acceptable alternative to CS as a treatment to achieve stable transverse axes of the dentition in both arches in patients with skeletal Class III malocclusion and facial asymmetry.

Comparison of the computed tomography values of the bone fragment gap after sagittal split ramus osteotomy in mandibular prognathism with and without asymmetry

The purpose of this study was to compare computed tomography (CT) Hounsfield unit values of bone fragment gaps after sagittal split ramus osteotomy (SSRO) in patients with and without asymmetry, and to evaluate differences between the deviated and non-deviated sides in asymmetric patients. Thirty-two patients who underwent a bilateral SSRO were included in this retrospective study. Patients were divided into symmetric and asymmetric groups by cephalometric analysis. CT values of the bone fragment gap were measured at 1 week and at 1 year after surgery. There were significant differences between CT values obtained at 1 week and at 1 year after surgery for all measurement points. However, there were no significant differences in CT values between symmetric and asymmetric patients at either 1 week or 1 year after surgery. Among asymmetric patients, there were no significant differences between the deviated and non-deviated sides at 1 week or 1 year after surgery. This study showed ossification of the bone fragments and adaptation to change the mandible form in patients with and without asymmetry following SSRO.

Morphologic Analysis of the Temporomandibular Joint Between Patients With Facial Asymmetry and Asymptomatic Subjects by 2D and 3D Evaluation: A Preliminary Study.

Signs and symptoms of temporomandibular joint (TMJ) dysfunction are commonly found in patients with facial asymmetry. Previous studies on the TMJ position have been limited to 2-dimensional (2D) radiographs, computed tomography (CT), or cone-beam computed tomography (CBCT). The purpose of this study was to compare the differences of TMJ position by using 2D CBCT and 3D model measurement methods. In addition, the differences of TMJ positions between patients with facial asymmetry and asymptomatic subjects were investigated.We prospectively recruited 5 patients (cases, mean age, 24.8 ± 2.9 years) diagnosed with facial asymmetry and 5 asymptomatic subjects (controls, mean age, 26 ± 1.2 years). The TMJ spaces, condylar and ramus angles were assessed by using 2D and 3D methods. The 3D models of mandible, maxilla, and teeth were reconstructed with the 3D image software. The variables in each group were assessed by t-test and the level of significance was 0.05.There was a significant difference in the horizontal condylar angle (HCA), coronal condylar angle (CCA), sagittal ramus angle (SRA), medial joint space (MJS), lateral joint space (LJS), superior joint space (SJS), and anterior joint space (AJS) measured in the 2D CBCT and in the 3D models (P < 0.05). The case group had significantly smaller SJS compared to the controls on both nondeviation side (P = 0.009) and deviation side (P = 0.004). In the case group, the nondeviation SRA was significantly larger than the deviation side (P = 0.009). There was no significant difference in the coronal condylar width (CCW) in either group. In addition, the anterior disc displacement (ADD) was more likely to occur on the deviated side in the case group.In conclusion, the 3D measurement method is more accurate and effective for clinicians to investigate the morphology of TMJ than the 2D method.

顔面非対称を伴う不正咬合症例における下顎頭の三次元形態学的特徴

The aim of the present study was to clarify morphological differences in mandibular condyles between deviated and non-deviated sides and the spatial position of the mandible on craniomaxillary complex in a three-dimensional manner in facial asymmetry cases. A virtual reality model reconstructed from 30 patients with facial asymmetry was used in this study. The virtual reality model was segmented into two components, craniomaxillary complex and mandible, and two coordinate systems, global and local, were established in two segmented components for each of the two components. As geometric features of these virtualized models, the position and attitude of the mandible relative to the craniomaxillary complex, which represent the degree of facial asymmetry, and the angle and length of the condylar long axis, which represent the condylar morphology, were extracted. Condylar morphology was compared between the deviated and non-deviated sides. Furthermore, correlations between degrees of facial asymmetry and differences in condylar morphology between the deviated and non-deviated sides were examined. The results were as follows: (1) the length of the condylar long axis on the deviated side was significantly smaller than that on the non-deviated side; (2) the difference in the length of the condylar long axis increased with an increase of lateral deviation of the mandible; (3) the angle of the condylar axis on a Md axial plane on the deviated side was significantly larger than that on the non-deviated side; and (4) the difference in angle of the condylar long axis tended to increase with an increase of relative attitude of the mandible toward craniomaxillary complex on the axial plane. The results obtained from the 3D analysis method for which a reference coordinate system was established in the mandible itself indicated close relationships between bilateral morphological differences in the condyles and facial asymmetry.

Clinical application of a 3-dimensional morphometric apparatus for diagnosis and treatment of a Class III patient with facial asymmetry: A pilot study

This article demonstrated the usefulness of a non-contact 3-dimensional (3D) morphometric apparatus in orthodontic diagnosis and treatment evaluation. A female patient, 23 years 6 months of age, had a Class III malocclusion with mandibular deviation. The 3D images taken by a 3D morphometric apparatus figured out her protrusive chin of 6mm on the deviation side compared to the non-deviation side, and showed a possibility of orthognathic surgery. Before starting of orthodontic treatment, a diagnostic splint was used for 2 months to determine her proper mandibular position. The 3D images retaken for quantitative evaluation showed decrease of the mandibular protrusion by approximately 3mm, and improvement of facial asymmetry. Then, we decided to treat the patient without orthognathic surgery. After 18 months of active orthodontic treatment with miniscrew anchorage, the mandibular deviation was improved and an acceptable occlusion was achieved. The 3D images at posttreatment demonstrated significant decrease of chin protrusion on the deviation side, and improvement of facial asymmetry. In conclusion, a 3D morphometric apparatus could provide quantitative data of facial asymmetry and chin protrusion and contributed decision making process of treatment planning in a patient with facial asymmetry.

Three-dimensional analysis of molar compensation in patients with facial asymmetry and mandibular prognathism.

To evaluate the characteristic transverse dental compensations in patients with facial asymmetry and mandibular prognathism and to compare features of dental compensations between two types of mandibular asymmetry using 3-dimensional (3D) cone-beam computed tomography (CBCT). Seventy-eight adult patients with skeletal Class I (control group; n = 33; 19 men and 14 women) or skeletal Class III with facial asymmetry (experimental group; n = 45; 23 men and 22 women) were included. The experimental group was subdivided into two groups according to the type of mandibular asymmetry: translation type (T-type; n = 20) and roll type (R-type; n = 19). CBCT images were acquired before orthodontic treatment and 3D analyses were performed. The transverse dental distance was significantly different between the two groups only at the palatal root apex of the maxillary first molar (P < .05). In the experimental group, the first molar axes were compensated significantly on both arches except the maxillary nondeviated side. The vertical molar heights were different between the two groups only on the maxillary arch (P < .001). The R-type showed greater mandibular ramal length difference and menton deviation than the T-type (P < .001). In the R-type, transverse compensation of the maxillary first molars was more obvious than with the T-type, which resulted in canting in the maxillary occlusal plane. Mandibular asymmetry with prognathism showed a characteristic transverse dental compensation pattern. The mandibular asymmetry type influenced the amount and direction of molar compensation on the maxillary arch.

Changes in computed tomography values of mandibular condyle and temporomandibular joint disc position after sagittal split ramus osteotomy

PurposeThe purpose of this study was to evaluate change in computed tomography (CT) value of condyle and temporomandibular joint (TMJ) disc position after sagittal split ramus osteotomy (SSRO) setback surgery, retrospectively. Subjects and methodsThe subjects were 76 patients (152 condyles) who underwent bilateral SSRO setback surgery. They were divided into 2 groups (43 symmetric patients and 33 asymmetric patients). CT values (pixel values) of 5 sites of the condyle and condylar width, length, horizontal angle were measured pre-operatively and 1 year post-operatively. Disc position was classified as anterior disc displacement, anterior type, fully covered type and posterior type, preoperatively and postoperatively using magnetic resonance imaging (MRI). ResultsIn maximum CT value at the center of the condyle, post-operative value was significantly lower than pre-operative value bilaterally (Deviation side: P = 0.0003, Non-deviation side: P = 0.0003) in asymmetry group. In minimum CT value at the center of the condyle, the post-operative value was significantly lower than the pre-operative value bilaterally (Deviation side: P = 0.0309, Non-deviation side: P = 0.0004) in the symmetry group.With regard to maximum CT value at the lateral site of the condyle in the deviation side, the value for the anterior disc displacement group was significantly larger than that of the posterior type pre-operatively (P = 0.0123). CT value of the anterior disc displacement group was significantly larger than those of some other areas pre- and post-operatively (P < 0.05). ConclusionThis study suggested that CT value of condylar bone changes after 1 year in SSRO and anterior disc displacement may partially affect the CT value of the condyle in the TMJ in mandibular prognathism patients.

Study of Condylar Asymmetry in Angle Class III Malocclusion With Mandibular Deviation

Differences in the condylar between both sides in class III cases with mandibular deviated are important for the diagnosis, treatment, and retention in this kind of patient. To detect the subtle differences, we analyzed the size, shape, and bone density with three-dimensional reconstructed technology. The symmetry group and the asymmetry group each with 20 cases were chosen according to some standards. The computed tomographic data obtained and three-dimensional model were built with SimPlant software. The distance and angle were measured in the three-dimensional model, and the bone density was measured with the SimPlant software. The differences between the separated side in each group and the difference between the 2 groups were analyzed. In the asymmetry group, some measurement projects of the bilateral condyles showed significant differences, such as the ramal height, condylar perpendicular height, the area of maximum cross section of condylar, condylar medialateral diameter, length of posterior slope, and angle of posterior slope. When the asymmetry group was compared with the symmetry group, the condyles of the asymmetry group showed more asymmetrical variations in morphology, such as the ramal height, the condylar perpendicular height, the area of maximum cross section of condylar, the medialateral diameter, the length of anterior slope, and angle of posterior slope. The bone mineral density of the condylar anterior and condylar medial point was higher in the nondeviated side, and the bone mineral density of the condylar posterior was higher in the deviated side, and no statistically significant difference was found in the symmetry group. In class III malocclusion with mandibular deviation patients, the three-dimensional morphology and bone density of condylar on the deviated side differ from the nondeviated side, which indicates the association between asymmetrical jaw function and joint remodeling.

Proximal Segment Changes After Bilateral Sagittal Split Ramus Osteotomy in Facial Asymmetry Patients

To investigate the 3-dimensional postoperative changes in the proximal segments in patients with facial asymmetry according to the anteroposterior skeletal patterns. A total of 51 patients with facial asymmetry who had undergone Le Fort I osteotomy and sagittal split ramus osteotomy (SSRO) with rigid fixation were classified according to their anteroposterior skeletal patterns. Cone-beam computed tomography (CBCT) data were obtained before (T0) and 6 months (T1) after surgery. The position, angulation, and distance of the proximal segment were measured from the CBCT superimposition. Comparing the T0 and T1 CBCT data, almost no significant differences were found in the condylar head position in any of the groups (P > .05), except for the axial condylar head position on the deviated side in the skeletal Class I group (P < .05) and the sagittal condylar head position on the deviated side in the skeletal Class III group (P < .05). However, the changes in the coronoid process and ramus down varied (P < .05), and these movements were related to changes in the ramal plane. Comparing the deviated and nondeviated sides, significant differences were found only in the skeletal Class I group (P < .05). The most influential factors affecting differences between the deviated and nondeviated sides in patients with facial asymmetry after bilateral SSRO could be the direction of the surgical movement of the distal segment of the mandible rather than its extent.

Evaluation of intra-articular distance narrowing during temporomandibular joint movement in patients with facial asymmetry using 3-dimensional computed tomography image and tracking camera system

IntroductionFunctional overloading can lead to disc displacement in the temporomandibular joint (TMJ), and a high incidence of disc displacement has been reported in patients with facial asymmetry. The aim of this study was to assess the dynamic condylar movement in patients (n = 26) with facial asymmetry using a simulation system with 3-dimensional computed tomographic images and tracking camera system. Material and methodsThe intra-articular distance (IAD) between the condyle and glenoid fossa was recorded during TMJ movement as a parameter for functional overloading and compared between Group I with severe asymmetry and Group II with mild asymmetry. ResultsThe average IAD was shorter in Group I than Group II, especially at the lowest point (P < 0.05). The ratio of IAD narrowing in Group I was significantly larger than in Group II (P < 0.05). The mean IAD were slightly smaller on the deviated side (3.41 mm) than on the nondeviated side (3.55 mm) in Group I, even though there was no statistical significance. The maximum displacement in Group I was longer than in Group II and had no significant difference between deviated side and nondeviated side. ConclusionWe suggested that the reduced IAD resulting from TMJ overloading can lead to internal derangement in severe facial asymmetry.

顔面非対称を伴う骨格性下顎前突症例の下顎骨形態の三次元計測による検討

With the exception of congenital anomalies, facial asymmetry is regarded as being caused by mandibular growth abnormalities in many cases. Conventionally, two-dimensional analysis using cephalometric X-rays is carried out to design the plan for orthognathic surgery. To improve the treatment outcome, however, it may be necessary to elucidate the factors responsible for asymmetry by performing three-dimensional analysis of the craniofacial morphology.The objective of the present study was to perform three-dimensional measurements of the mandible using three-dimensional computed tomography (3D-CT) in patients with facial asymmetry requiring orthognathic surgery, and to identify the morphological characteristics of the mandible by comparing the deviated and non-deviated sides.3D-CT images of 36 patients with facial asymmetry (≥ 4mm deviation of the mandibular midline) were analyzed using 3D planning software for orthognathic surgery. A total of 10 items were measured, including five angle measurements and five linear measurements with reference to the entire mandible, the mandibular body, or the mandibular ramus.The deviated and non-deviated sides were measured, and values were compared using the paired Student's t-test. Multi-regression analysis (step-wise selection) was also performed to evaluate the deviation of the mandibular midline and the items measured.In patients with facial asymmetry, a comparatively large mandibular ramus, mandibular body, and condylar process length were observed on the non-deviated side compared with the deviated side, with the mandibular ramus rotated anteromedially along the superior-inferior, left-right, and anterior-posterior axes. These differences between the deviated and non-deviated sides in the morphological characteristics of the mandible resulted in mandibular deviation and rotation. However, no left-right differences were observed in mandibular body height, mandibular body roll, or gonial angle. Our findings also suggested that deviation of the mandibular midline was significantly affected by mandibular ramus length, mandibular body length, and mandibular ramus pitch.