The relationship between frontal facial morphology and occlusal force in orthodontic patients with temporomandibular disorder

The aim of this study was to investigate the relation between frontal craniofacial morphology and the distribution of occlusal force in orthodontic patients with and without TMD. Experimental data were obtained from 45 female orthodontic patients (TMD-free group: 22 subjects; TMD group: 23 subjects) using the pressure-sensitive sheet. The following results were obtained: (1) There were significant differences in the gonial angle width and the mandibular deviation of the postero-anterior cephalogram between the two groups. (2) There were significant differences in occlusal force, occlusal contact area and average occlusal pressure between the two groups. (3) On the relation between the frontal craniofacial morphology and the occlusal data, the asymmetry indices of occlusal force and occlusal contact area showed significant positive correlations to the mandibular deviation and the ratios of maxillary and gonial angle widths in the TMD group. The TMD-free group showed the smaller mandibular deviation and the smaller asymmetry indices of occlusal force and occlusal contact area than those in the TMD group. It could be concluded that orthodontic patients with TMD may have not only the morphological disharmony but also the imbalance of occlusal force.     

Changes in stomatognathic function induced by orthognathic surgery in patients with mandibular prognathism.

PURPOSE: This study was designed to investigate the changes in stomatognathic function through orthognathic treatment in patients with mandibular prognathism. PATIENTS AND METHODS: Thirty-six patients with mandibular prognathism were tested and compared with 30 healthy controls with normal occlusion. For each subject, the occlusal contact area and occlusal force were measured during maximum voluntary clenching (MVC). Activities of the masseter and temporalis muscles were recorded during MVC and voluntary gum chewing. Jaw movement was analyzed during chewing on the left and right sides. For the analyses, 2 parameters, asymmetry index (AI) and error index (EI), were established to further investigate the nature of masticatory function. AI was used to evaluate the bilateral balance of masticatory muscle activity, and EI indicates the rate of abnormal jaw movement pattern. RESULTS: In patients with mandibular prognathism, the occlusal contact area and maximum bite force decreased before surgery, and increased after surgery. The masseter and temporal muscle activities also decreased before surgery, but showed no substantial increase even after surgery. The occlusal and muscle efficiency exhibited significantly smaller values in the patient group than in the controls, irrespective of treatment stages. The AI decreased after surgery. The EI decreased significantly after surgery, but was still significantly greater in the patient group than in the controls. CONCLUSIONS: It is suggested that masticatory muscles in the patients with mandibular prognathism may adapt to the new environment achieved with surgically corrected dentofacial structure, although the activities remain at lower levels as compared with the controls.     

骨性Ⅲ类偏颌患者髁突与(牙合)平面特征的CBCT研究

目的 利用锥形束CT(CBCT)测量分析骨性Ⅲ类偏颌患者髁突及(牙合)平面特征。方法 选取符合纳入标准的骨性Ⅲ类成年患者40例,所有个体按照颏下点偏离正中矢状面距离进行分组,分别测量各组左右两侧(牙合)平面角、髁突位置及形态,并对数据进行统计学分析。结果 骨性Ⅲ类偏颌患者的偏侧与对侧相比,(牙合)平面角、关节前间隙、关节上间隙、关节外间隙及髁突内外径差异有统计学意义(P<0.05),偏侧关节后位所占比例较大,下颌骨偏移量与偏侧髁突前间隙及对侧(牙合)平面角均呈正相关(P<0.01)。骨性Ⅲ类非偏颌患者的左右两侧(牙合)平面角、髁突位置及形态指标之间差异均无统计学意义(P>0.05),关节以前位、中位为主。结论 骨性Ⅲ类偏颌患者左右两侧(牙合)平面角、髁突位置及形态不对称,偏侧(牙合)平面角及髁突内外径较小,髁突向后下内方移位,且偏颌程度与(牙合)平面角及髁突位置之间存在相关性。     

颞下颌关节盘可复性前移位患者咬合接触特征的研究

目的观察颞下颌关节盘可复性前移位患者的咬合接触特征并比较其与正常人的差异。方法采用T-ScanⅡ咬合分析系统记录30名颞下颌关节盘可复性前移位患者和30名正常人于牙尖交错位和后退接触位时的咬合接触信息并进行统计分析。结果颞下颌关节盘可复性前移位患者在牙尖交错位可出现力中心较大的偏移、两侧接触点不平衡、两侧力不对称、弹响侧接触点数目多于非弹响侧;在后退接触位颞下颌关节盘可复性前移位患者双侧接触点数目有显著差异,单侧接触者显著增多。结论颞下颌关节盘可复性前移位患者咬合接触情况与正常人有显著的差异,提示咬合因素与颞下颌关节盘可复性前移位有密切的关系。     

第一磨牙缺失不同修复方法的咬合接触特征研究

目的 针对单个第一磨牙缺失的病例,研究种植及可摘局部义齿（RPD）种不同修复方法所恢复的牙列咬合接触特征。方法 选择15名单个第一磨牙缺失的患者作为实验组,15名正常牙列人群作为对照组,其中,实验组每位患者同时进行种植及RPD修复,应用TeeTester咬合分析仪,测试对照组和实验组在未修复、RPD修复及种植义齿修复后3种状态下分别做正中咬合及咀嚼运动,分析其咬合接触特征(总咬合力、总接触面积、不平衡指数、单次咀嚼循环时间,OT/DT比值),并进行统计学分析。结果 患者做正中咬合时,在总咬合力、总接触面积、不平衡指数方面,患者未修复时分别为（48.76±12.82）kg,（317.59±58.47）mm2,（24.78±7.40）,行RPD修复时分别为（54.36±10.59）kg,（355.81±77.43）mm2,（18.29±8.42）,行种植修复时分别为（61.94±12.36）kg,（398.17±83.86）mm2,（17.80±6.69）;患者咀嚼运动时在总咬合力、总接触面积、不平衡指数、单次咀嚼循环时间及T0/Td方面,患者行种植修复时分别为（52.14±16.53）kg,（348.08±81.76）mm2,（15.69±9.16）,（0.4072±0.10）s,（1.718±0.26）。统计学分析表明,RPD、种植义齿修复和对照组的部分咬合接触特征结果无显著性差异,但与未修复前结果有显著性差异。单次咀嚼循环时间及T0/Td在各组间均无显著性差异。结论 在恢复咬合力及咬合接触面积方面,种植义齿优于RPD,较接近天然牙列,并明显优于不修复。正中咬合时全牙列的总咬合力及总接触面积明显大于咀嚼运动时,但不平衡指数无明显统计学差异。     

Bite force, occlusal contact area and masticatory efficiency before and after orthognathic surgical correction of mandibular prognathism

The purpose of this study was to evaluate bite force, occlusal contact area and masticatory efficiency before and after sagittal split ramus osteotomy in 27 patients with mandibular prognathism, in comparison with 27 control subjects with normal occlusion. Bite force and occlusal contact area were simultaneously measured with a computerized occlusal analysis system, the Dental Prescale system. Masticatory efficiency was estimated by a low-adhesive colour-developing chewing-gum system. The data were collected at initial medical consultation, immediately before surgery, and at 6 weeks, 3 months, 6 months, 1 year and more than 2 years after surgery. Both bite force and occlusal contact area of the patients before surgery were significantly less than those of the controls. Although all three parameters had improved after orthognathic surgery, the bite force and occlusal contact area did not reach the values of the controls within 2 years postoperatively; masticatory efficiency at 2 years after surgery drew near to control levels. Bite force correlated with occlusal contact area in the patients postoperatively, whereas masticatory efficiency did not correlate with either of the other two parameters. These results suggest that further adjustment of occlusion and mechanical advantage should be considered before the end of treatment.     

Relationship between the morphologies of the masseter muscle and the ramus and occlusal force in patients with mandibular prognathism.

PURPOSE: The purpose of this study was to examine the relationship between the morphologies of the masseter muscle and the ramus and occlusal force in patients with mandibular prognathism. PATIENTS AND METHODS: The study group consisted of 71 patients with mandibular prognathism. They were divided into 2 groups, consisting of prognathism with or without symmetry, determined by frontal cephalogram analysis. All patients underwent 3-dimensional (3D) computed tomography (CT) and occlusal force was recorded with pressure-sensitive sheets. RESULTS: In the cross-sectional area of masseter muscle, there were no significant differences between the right and left sides in the symmetry and asymmetry groups. In occlusal force, there was no significant difference between the symmetry and asymmetry groups. Occlusal force was not significantly correlated to the cross-sectional area of the ramus, but it was significantly positively correlated to the cross-sectional area of the masseter muscle (P < .05). CONCLUSION: Occlusal force was associated with the ipsilateral cross-sectional area of masseter muscle in patients with prognathism; however, it was not associated significantly with the degree of mandibular deviation.     

Relationship between occlusal curvatures and mandibular deviation in orthodontic patients with temporomandibular disorders

The aim of this study was to investigate the relationships between occlusal curvature (OC) and frontal craniofacial morphology in patients with and without temporomandibular disorders (TMD), using frontal cephalograms and a sophisticated measuring device (XYZAX S400A). Thirty-seven female orthodontic patients (mean age 24.0 years) were divided into a TMD group (n = 25) and no-TMD group (n = 12). In the TMD group, the lateral OCs of the mandibular second premolar, and first and second molars were significantly deeper on the deviated side than on the non-deviated side, and the anteroposterior OCs of the mandibular second premolar and first molar were also significantly shallower on the deviated side. In the no-TMD group, however, there were no significant differences in OCs between deviated and non-deviated sides. The differences between right and left lateral OCs in the mandibular second premolar and first and second molars, as well as the anteroposterior OCs in the mandibular first and second molars, showed significant correlations with mandibular deviation in the TMD group. On the other hand, in the no-TMD group, there was no significant correlation between OCs and mandibular deviation. The above results suggest that OCs might try to compensate for mandibular deviation in patients with TMD.     

Size and orientation of masticatory muscles in patients with mandibular laterognathism

Size measurements of jaw muscles reflect their force capabilities and correlate with facial morphology. Using MRI, we examined the size and orientation of jaw muscles in patients with mandibular laterognathism in comparison with a control group. We hypothesized that the muscles of the deviated side would be smaller than those of the non-deviated side, and that the muscles of both sides would be smaller than in controls. In patients, a comparison of deviated and non-deviated sides showed, in orientation, differences for masseter and medial pterygoid muscles, but, in size, differences only for the masseter muscle. Nevertheless, muscle sizes in patients were much smaller than in controls. Lateral displacement of the mandible can explain the orientation differences, but not the smaller muscle size, in patients. It is possible that the laterodeviation initiates an adaptive process in the entire jaw system, resulting in extensive atrophy of the jaw muscles.     

基于锥形束CT分析骨性Ⅲ类高角伴下颌偏斜患者髁突形态和位置的研究

目的 应用锥形束CT（CBCT）对比分析骨性Ⅲ类高角伴下颌偏斜患者与个别正常牙合患者髁突的形态和位置。方法 选取2017年9月至2019年9月于上海交通大学医学院附属第九人民医院口腔正畸科就诊的患者40例，其中骨性Ⅲ类高角伴下颌偏斜患者20例（偏斜组），个别正常牙合患者20例（对照组）。所有患者于治疗前拍摄CBCT，使用Invivo 5.0软件对CBCT影像进行三维重建及测量，并比较两组患者两侧髁突形态和位置的差异。结果 （1）偏斜组患者两侧髁突形态和位置指标测量值比较发现，在髁突形态方面，偏斜侧髁突最大轴面面积、髁突高度、髁顶高度均比非偏斜侧小，差异均有统计学意义（均P < 0.05）。在髁突位置方面，偏斜侧髁突外间隙、上间隙和后间隙比非偏斜侧小；偏斜侧髁突前间隙、内间隙及髁突外突距比非偏斜侧大，差异均有统计学意义（均P < 0.05）。（2）对照组两侧髁突形态和位置指标测量值比较，差异均无统计学意义（均P > 0.05）。（3）偏斜组两侧髁突形态和位置指标测量值分别与对照组比较发现，在髁突形态方面，偏斜组偏斜侧髁突高度比对照组大，最大轴面面积比对照组小；非偏斜侧髁突高度大于对照组，差异均有统计学意义（均P < 0.05）。在髁突位置方面，偏斜组偏斜侧髁突上间隙小于对照组，髁突内间隙、前间隙、髁突外突距及髁突与正中矢状面距大于对照组，差异均有统计学意义（均P < 0.05）。结论 骨性Ⅲ类高角伴下颌偏斜患者双侧髁突的形态和位置具有明显的不对称性，偏斜侧髁突形态较对侧小，并向后上外方向移位。骨性Ⅲ类高角伴下颌偏斜患者的髁突高度比个别正常牙合患者大。     

Changes in occlusal state of patients with mandibular prognathismafter orthognathic surgery: a pilot study

This study examined the occlusal state of patients with mandibular prognathism and compared it with that of adults with normal occlusion (controls). It also examined changes in occlusal state after orthognathic operations in these patients. The values of occlusal contact area and bite force in patients before operation were significantly lower than in controls, and occlusal pressure in patients was higher than in controls. The occlusal contact area and bite force of the patients 1 month after the operation had decreased to below preoperative values. These values 12 months after the operation had increased by 2.0 and 1.8 times in women and 1.4 and 1.4 times in men, respectively, compared with preoperative values. However, absolute values remained extremely low compared with those of controls. In contrast to the above, occlusal pressure reached its maximum value 1 month after the operation and at 12 months it was close to the value for controls.     

Occlusal contact area, occlusal pressure, bite force, and masticatory efficiency in patients with anterior disc displacement of the temporomandibular joint

The occlusal contact area, occlusal pressure, bite force, and masticatory efficiency were measured in 48 patients with anterior disc displacement (ADD) of the temporomandibular joint (TMJ). The results were compared with those of 30 normal controls without TMJ dysfunction. The values of occlusal contact area, bite force, and masticatory efficiency measured in patients with ADD were significantly smaller than those measured in the controls, although there was no difference in occlusal pressure between the two groups. The results of the measurements of 22 patients with ADD with reduction were also compared with those of 26 patients with ADD without reduction. There was no difference in any measurement between these patients subgroups. The analysis of occlusal contact area, bite force, and masticatory efficiency appeared to be useful methods in documenting the fact that masticatory function was impaired in patients with ADD of the TMJ.     

伴有颞下颌关节紊乱病的女性开患者的咬合力分析研究

目的探讨咬合因素对女性开!患者中颞下颌关节紊乱病（ TMD）发病的影响。方法选取女性开!患者102名,根据TMD的有无分为两组,伴有TMD的试验组有59名患者;不伴有TMD的对照组有43名患者。采用咬合力测试仪对两组患者进行咬合力、咬合接触面积、每一咬合接触点上的平均咬合压强和咬合重心的测试,并通过SPSS 11.0软件进行统计学分析。结果试验组的咬合力和咬合接触面积均小于对照组,两组间每一咬合接触点上的平均咬合压强和咬合重心的偏移无统计学差异。结论咬合力不足与开!女性TMD的发病有关。     

Correlation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of therapy

Aim: The association between periodontal status and biting force is unclear. The aim of this study was to investigate the relation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of periodontal treatment. Material and Methods: A total of 198 patients, who had entered a periodontal maintenance programme, were examined for the presence of restorations on the occlusal surface, probing pocket depth, clinical attachment loss (CAL), bleeding on probing, and mobility of teeth. Quantitative analysis of total biting force, occlusal contact area and biting pressure (defined by biting force per 1 mm² of occlusal contact area) was performed using microcapsular pressure‐sensitive sheets. Results: A multiple stepwise regression analysis showed that total biting force and occlusal contact area were positively associated with the number of present teeth and negatively associated with female gender, mean CAL and mean probing pocket depth. Biting pressure was positively associated with CAL. Conclusions: Reduced periodontal support was found to be associated with decreased total biting force and with increased biting pressure (defined as force per 1 mm² of occlusal contact area).     

Mandibular elevator muscles: physiology, action, and effect of dental occlusion

In spite of differences in embryologic origin, central nervous organization, and muscle fiber distribution, the physiology and action of mandibular elevator muscles are comparable to those of skeletal muscles of the limbs, back, and shoulder. They also share the same age-, sex-, and activity-related variations of muscular strength. With respect to pathogenesis, the type of muscular performance associated with the development of fatigue, discomfort, and pain in mandibular elevators seems to be influenced by the dental occlusion. Clinical research comparing the extent of occlusal contact in patients and controls as well as epidemiologic studies have shown reduced occlusal support to be a risk factor in the development of craniomandibular disorders. In healthy subjects with full natural dentition, occlusal support in the intercuspal position generally amounts to 12–14 pairs of contacting teeth, with predominance of contact on first and second molars. The extent of occlusal contact clearly affects electric muscle activity, bite force, jaw movements, and masticatory efficiency. Neurophysiologic evidence of receptor activity and reflex interaction with the basic motor programs of craniomandibular muscles tends to indicate that the peripheral occlusal control of the elevator muscles is provided by feedback from periodontal pressoreceptors. With stable intercuspal support, especially from posterior teeth, elevator muscles are activated strongly during biting and chewing with a high degree of force and masticatory efficiency, and with relatively short contractions, allowing for pauses. These variables of muscle contraction seem, in general, to strengthen the muscles and prevent discomfort. Therefore, occlusal stability keeps the muscles fit, and enables the masticatory system to meet its functional demands.     

Two-year follow-up of changes in bite force and occlusal contact area after intraoral vertical ramus osteotomy with and without Le Fort I osteotomy

This study was performed to examine the longitudinal changes in bite force and occlusal contact area after mandibular setback surgery via intraoral vertical ramus osteotomy (IVRO). Patients with mandibular prognathism who underwent IVRO (surgical group: 39 men and 39 women) were compared with subjects with class I skeletal and dental relationships (control group; 32 men and 35 women). The surgical group was divided into two subgroups: 1-jaw surgery (n = 30) and 2-jaw surgery (n = 48). Bite force and contact area were measured in maximum intercuspation with the Dental Prescale System before treatment, within 1 month before surgery, and at 1, 3, 6, 9, 12, and 24 months postsurgery. A linear mixed model was used to investigate the time-dependent changes and associated factors. Bite force and contact area decreased during presurgical orthodontic treatment, were minimal at 1 month postsurgery, and increased gradually thereafter. The 1-jaw and 2-jaw subgroups showed no significant differences in bite force. The time-dependent changes in bite force were significantly different according to the contact area (P < 0.05). The results of this study suggest that bite force and occlusal contact area gradually increase throughout the postsurgical evaluation period. Increasing the occlusal contact area may be essential for improving bite force after surgery.     

Simplified stress analysis on the temporomandibular joint in Class III patients with and without mandibular asymmetry using a rigid body spring model

Authors – Ueki K, Takeuchi N, Nakagawa K, Yamamoto E Objective – Aim of this study was to investigate the differences in stress on the temporomandibular joint (TMJ) between Class III patients with and without mandibular asymmetry using a rigid body spring model (RBSM). Design – Menton (Me), the centre point of occlusal force on the line that connected the bilateral buccal cusps of the second molars and the most lateral, superior and medial points of the condyle were plotted on frontal cephalograms, and stress on the condyles was calculated with the 2‐dimensional RBSM program of fortran . Setting and Sample Population – Eighty Japanese patients with diagnosed mandibular prognathism were divided into two groups, a symmetry group and asymmetry group on the basis of the Mx‐Md midline position. Outcome measure – The degree (force partition) of the resultant force, the direction (angulation) and displacement (X, Y) of each condyle were calculated. The horizontal displacement vector (u), the vertical displacement vector (v) and rotation angle (θ) of the mandibular body at Menton were also calculated. Results – There were significant differences between the deviated and non‐deviated sides of both groups regarding resultant force (symmetry group: p = 0.0372, asymmetry group: p = 0.0054), X (symmetry group: p < 0.0001, asymmetry group: p = 0.0001) and Y (symmetry group: p = 0.0354, asymmetry group: p = 0.0043). For angulation, there was a significant difference between the deviated and non‐deviated sides in the asymmetry group (p = 0.0095). Conclusion – The results of this study suggest that difference in stress angulation on the condyles could be associated with asymmetry in mandibular prognathism.     

[牙合]垫对牙齿重度磨耗患者口颌功能影响的临床研究

目的：研究殆垫对牙齿重度磨耗患者口颌功能的影响。方法：用殆垫恢复10例牙齿重度磨耗患者的垂直距离,分别检测治疗前、治疗后1个月、3个月、6个月的咬合平衡性、咬肌及颞肌前束的肌电幅值、颌位及殆的稳定性以及边缘运动的平滑度及对称性的变化。结果：①咬合平衡性、颌位及胎的稳定性以及边缘运动轨迹的平滑度及对称性在治疗后呈逐渐改善趋势,治疗6个月后80％的患者恢复正常;②治疗后各组的息止位肌电幅值均较治疗前显著降低（P〈0．05）,正中颌位紧咬时肌电幅值在治疗后3个月组和6个月组较治疗前显著增加（P〈O．05）。结论：通过6个月的治疗和观察,聆垫对重度磨耗患者的口颌功能的影响呈现持续改善趋势。     

Tooth axis and skeletal structures in mandibular molar vertical sections in jaw deformity with facial asymmetry using MPR images

The objective of the present study was to investigate frontal morphological asymmetry in the mandibular molar region in terms of tooth axis and skeletal structures using vertical MPR sections in jaw deformity accompanied by facial asymmetry. Subjects consisted of 15 patients with jaw deformity accompanied by facial asymmetry aged 17.4 years to 37.8 years. There were four men and eleven women. Based on X-ray computed tomography (CT) scans, DICOM viewer software was used to prepare multiplanar reconstruction (MPR) sections. The mandible was then positioned on a reference plane based on the menton and left and right gonions, and a vertical MPR section passing through the mesial root of the first mandibular molar was prepared. The following measurements were made on both the shifted and non-shifted sides: maximum buccolingual width of the mandibular body; height of the mandibular body; inclination angle of the mandibular body; degree of buccal protrusion of the mandibular body; and inclination angle of the buccolingual tooth axis of the first molar. Furthermore, degree of median deviation in the menton was measured using frontal cephalograms. Differences in morphological parameters between the shifted and non-shifted sides were assessed. Furthermore, the relationship between median deviation and asymmetry were statistically analyzed. There was no significant asymmetry in the maximum buccolingual width of the mandibular body, the height of the mandibular body or the degree of buccal protrusion of the mandibular body. However, when compared to the shifted side, the inclination angle of the buccolingual tooth axis of the first molar for the non-shifted side was significantly greater. There was a relatively strong correlation between median deviation and inclination angle of the mandibular body. The above findings clarified that, in orthognathic surgery for jaw deformity accompanied by facial asymmetry, actively improving asymmetry in the buccolingual inclination of the tooth axis of the molar region during presurgical orthodontic treatment is important in achieving favorable post-treatment occlusal stability and facial symmetry.