Motion of the human mandibular condyle during mastication

It has been reported that loading to the mandible during closing movement makes the condylar path move more in the superior direction than that during the free closing movement. In this study, the hypothesis was tested that the displacement of the condyle on the chewing side is greater in the direction of the mandibular fossa than that on the non-chewing side. Using a six-degrees-of-freedom jaw movement recording system, we recorded condylar motion in 12 healthy adults without TMD, during the chewing of a large hard gummy jelly. The maximum displacements at the condyle on the chewing side from the maximum intercuspation (CO) position were significantly larger in the superior and medial directions at the initial stage and in the posterior direction at all stages (0.5 mm, 0.5 mm, and 0.6 mm, respectively) than those on the non-chewing side (0.0 mm, 0.1 mm, and 0.1 mm, respectively). This suggests that, in healthy adults, the condyles at CO are located in a position such that excessive load is not applied to the temporomandibular joint when there are the aforementioned displacements.     

A comparison and validation of amorphous sensor condylar movement analysis to MRI diagnosis of anterior disc displacement

This study compared temporomandibular joint condylar movements in a sample of six patients with clinically normal joints, with those of nine patients with joints diagnosed by magnetic resonance imaging (MRI) to have anterior disc displacement with reduction (ADD). The aim of this study was to compare and validate the use of the amorphous sensor to MRI diagnosis in condylar movement analysis. The measuring device consisted of an amorphous sensor and a small magnet. Condylar and jaw movements were recorded simultaneously over the course of 10 open-close cycles. Maximum velocity of condylar movement during the opening phase in the ADD joints was significantly higher than the normal joints. The degree of jaw opening at the turning point of condylar movement in the ADD joints was significantly larger than the normal joints. The diagnostic sensitivity and specificity of the maximum velocity of condylar movement during the opening phase was 75.0 and 75.0%, respectively, while those of the degree of jaw opening at the turning point of condylar movement were 91.7 and 91.7%, respectively. These results suggest that the analysis of condylar movement, employing the amorphous sensor may be a reliable method for diagnosis of ADD.     

偏颌畸形下颌开闭口运动特征的研究

目的 研究发育性偏颌畸形患者下领开闭口运动的特点，探讨偏颌畸形对下颌运动功能的影响。方法 采用下颌运动轨迹描记仪(Sirognathograph,SGG)采集28例偏颌畸形者及41例咬合正常者最大开闭口运动的三维方向时间—位移信号，比较两组受试者下颌运动轨迹的形态、开闭口运动的位移及速度等参数的差异。结果 偏颌畸形患者开闭口运动轨迹在冠状面内主要分布在患侧，下颌向患侧移动的幅度明显大于向健侧移动的幅度，开口运动中下颌偏离中轴的程度较闭口运动时明显。偏颌者下颌开闭口运动三维空间内的位移、速度比正常咬合者大。结论 偏颌患者下颌运动处于能量消耗较高的状态，下颌运动功能的异常可能影响口颌系统的功能。     

下颌偏斜患者颜面与颈背部肌肌电研究

目的 探讨下颌偏斜对咀嚼机、颈、肩背部肌肌电的影响。方法 采用K6－Ⅰ系统对15例正常咬合者及12例下颌偏斜患者在最大开闭口运动、咀嚼运动、颈肩背部肌运动时咬肌、二腹肌、胸锁乳突肌与斜方肌的表面肌电进行采集分析，比较两组受试者双侧对应肌肌电平均幅值的对称性。结果 ①下合同功能性运动时颈背部肌有肌电活动；颈背部运动时咀嚼肌也有相应的肌电增强。②开闭口运动与咀嚼运动时患者组双侧咬肌、二腹肌、胸锁乳突肌肌电平均幅值的对称性明显差于正常咬合组；双侧斜方肌对称性在颈肩部运动时两组间差异显著。③正常咬合组三种运动时对应肌肌电幅值无显著性差异；患者组咀嚼运动时双侧二腹肌及颈肩部运动时双侧胸锁乳突肌、二腹肌肌电幅值有明显差异。结论 下颌偏斜影响咀嚼肌、颈肩背部肌肌电的对称性并可能导致头颈、双肩姿势的偏斜。     

Improvement in jaw motion following treatment of unilateral crossbite in a child with primary dentition: a case report

This case report examines jaw motion during both habitual opening-closing and gum chewing in a young (3 years, 10 months) patient with unilateral crossbite at the primary dentition stage. Jaw motion was measured three times: 1. before treatment; 2. after active treatment; and 3. after retention. The abnormal habitual open-close pathway seen prior to treatment was improved after retention. Prior to treatment, movement of the affected-side condyle preceded movement of the non-affected-side condyle during opening. After retention, the movement of the condyles was better coordinated. The chopping type chewing pattern, with less lateral movement, before treatment changed to a more grinding type pattern on the affected side after activation. This study suggests that the prescribed treatment effectively improved both the patient's morphology and function. However, neither the open-close pathways nor the chewing patterns were completely normal after retention. The results in this case suggest that early treatment of functional unilateral crossbite can be effective.     

Relationship between condylar and incisor point displacement during habitual maximum open-close movements

SUMMARY The relationship between condylar movements and incisor point movements during habitual maximum open-close movements were studied in 10 healthy male and 10 healthy female subjects. Jaw movements were recorded by means of an opto-electronic jaw movement recording system, OKAS-3D, capable of recording the six degrees of freedom at a sample frequency of 300 Hz. The lower jaw position of the lateral pole of the condyles was found by means of palpation. In order to analyse the movements, the opening and closing path of the incisor point were divided into ten equal intervals and the corresponding condylar displacement in each interval was calculated. A displacement index was obtained by normalizing the condylar displacement with respect to the maximum condylar displacement. Due to the normalization, the displacement index is not sensitive to possible errors in the location of the lateral condylar point. A clear condylar displacement was already recorded in the first movement interval, right at the start of opening (average displacement index in the first opening interval was significantly greater than zero, P < 0.0005). The condylar displacements in the start and the end interval of opening and closing were smaller than in the intermediate movement intervals ( P < 0.00005).     

Influence of maximum bite force on jaw movement during gummy jelly mastication

It is known that maximum bite force has various influences on chewing function; however, there have not been studies in which the relationships between maximum bite force and masticatory jaw movement have been clarified. The aim of this study was to investigate the effect of maximum bite force on masticatory jaw movement in subjects with normal occlusion. Thirty young adults (22 men and 8 women; mean age, 22·6 years) with good occlusion were divided into two groups based on whether they had a relatively high or low maximum bite force according to the median. The maximum bite force was determined according to the Dental Prescale System using pressure‐sensitive sheets. Jaw movement during mastication of hard gummy jelly (each 5·5 g) on the preferred chewing side was recorded using a six degrees of freedom jaw movement recording system. The motion of the lower incisal point of the mandible was computed, and the mean values of 10 cycles (cycles 2–11) were calculated. A masticatory performance test was conducted using gummy jelly. Subjects with a lower maximum bite force showed increased maximum lateral amplitude, closing distance, width and closing angle; wider masticatory jaw movement; and significantly lower masticatory performance. However, no differences in the maximum vertical or maximum anteroposterior amplitudes were observed between the groups. Although other factors, such as individual morphology, may influence masticatory jaw movement, our results suggest that subjects with a lower maximum bite force show increased lateral jaw motion during mastication.     

Trajectories of condylar points during working-side excursive movements of the mandible

STATEMENT OF PROBLEM: Trajectories of different condylar points provide different interpretations of condylar movement during open-close jaw movements. Movement of the working-side condyle is often assessed clinically by recording the trajectory of a single arbitrary condylar point. PURPOSE: This study examined the effect of the differences in condylar point location on condylar point movement trajectories during a working-side movement. METHODS: Different points exhibited different trajectories during a single working-side movement in each of 44 subjects. RESULTS: Up to 40% of a point's displacement could be attributed simply to the location of the point. CONCLUSIONS: Interpretation of condylar movement on the working side within a subject depends on the point chosen.     

Trajectories of condylar points during nonworking side and protrusive movements of the mandible.

STATEMENT OF PROBLEM: During lateral excursive and protrusive jaw movements, condylar points are distant from any instantaneous rotational center. Therefore, it is likely that different condylar points would follow similar trajectories during these movements. PURPOSE: This study evaluated the effect of changes in condylar point location on trajectories of condylar points on the nonworking side and during a protrusive jaw movement and compared these changes with the effects described for open-close and working-side condylar movements in the same group of subjects. METHODS: The movements of 5 clinically determined condylar points were recorded in 44 subjects during a contralateral excursion and during protrusion (7 radiographically determined condylar points in 2 subjects). RESULTS: During any single jaw movement, the trajectory of each condylar point was similar in form and dimension to the other condylar points within that subject. CONCLUSION: Changes in condylar point location had little effect on the trajectories of condylar points on the nonworking side and during protrusive jaw movement.     

Influence of changing the chewing region on mandibular movement

Background:  In the shortened dental arch condition, little is known of how patients adapt their jaw function during mastication to the new oral environment. This study aimed to investigate the changes in mandibular movements when the chewing region was changed from the first molar to the first premolar.
Methods:  Thirty clinical residents with natural dentitions were recruited. The subjects were asked to chew a piece of beef jerky using either the first molar or the first premolar on the preferred chewing side. Three-dimensional trajectories of lower incisors and both condyles were analysed using a jaw movement tracking device with six degrees of freedom during the period between the onset and offset of electromyographic bursts from the masseter and anterior temporal muscles.
Results:  The closing angle of the lower incisors for first premolar chewing was narrower in comparison with that for first molar chewing (p < 0.05). The lengths of the condylar trajectories and the maximum velocities of the condylar movement for first premolar chewing were smaller and slower, respectively, in comparison with those for first molar chewing (both sides; p < 0.01).
Conclusions:  The mandibular movement during mastication might be changed to adapt the premolar chewing because of a loss of posterior occlusal supports.     

Functional magnetic resonance imaging of temporomandibular joint disorders

Fifty-eight temporomandibular joints (TMJs) from 40 patients with TMJ-related symptoms were examined by means of magnetic resonance scans with modified gradient echo sequences and a special double coil. This technique yielded a good spatial resolution of the intra-articular soft tissues, especially the articular disc and the bone structure of the TMJ. In combination with an incremental jaw opener, the disc-condyle complex was analysed in various closed and open mouth positions, depending on the clinical examination. Open mouth movement with differentiation of disc-condyle rotational and translation movement was demonstrated. Disturbances of TMJ motion showed interrupted condylar translation combined with mandibular deviation during open mouth movement (n = 8/58). Early phases of internal derangement of the TMJ with partial anterior disc displacement with (n = 12/58) or without (n = 2/58) reduction, total anterior disc displacement without reduction (n = 10/58), disc deformation (n = 10/58), disc adhesion (n = 2/58), condylar hypermobility (n = 6/58), condylar displacement (n = 8/58), and late phases of internal derangement of the TMJ with osteoarthrosis (n = 14/58) were clearly identified. Bilateral TMJ disorder was found in 72.5 per cent of the patients. By using motion-adapted, semi-dynamic magnetic resonance imaging (MRI), it is possible to improve the understanding of the complexity of TMJ movements.     

Movement of the lateral and medial poles of the working condyle during mastication in patients with unilateral posterior crossbite.

Patients with unilateral posterior crossbite often show reverse sequential jaw movement patterns on the frontal view during mastication on the crossbite side. Recent studies show that such patients are prone to suffer from temporomandibular joint (TMJ) disc displacement, particularly the lateral portion. The purpose of this study was to examine the movement of the lateral and medial poles of the working condyle during mastication in such patients. Subjects were 12 consecutive patients with unilateral posterior crossbites and without TMJ disc displacements and 12 normal subjects. An optoelectronic jaw-tracking system with 6 degrees of freedom was used to record the motion of the lateral and medial poles of the working condyle during mastication of standardized hard, gummy jelly. The data from the first 10 cycles were analyzed. The lateral and medial poles of the condyle on the crossbite side moved more in the medial direction and less in the lateral direction during mastication in the crossbite patients than the condyle in the normal subjects. The lateral pole of the working condyle moved more in the posterior and inferior directions and less in the anterior direction than the medial pole in all subjects. These results suggest that these condylar movements in patients with unilateral posterior crossbites might be related to the susceptibility to TMJ disc displacement, particularly the lateral portion.     

Relationship between Degenerative Bone Changes of Condylar Surface and Articular Disc Disorders in Symptomatic Osteoarthrosis of Temporomandibular Joints

Purpose: We investigate the relation of bone changes of the condylar surface to disc displacement and discuss the development of joint symptoms in osteoarthrosis of temporomandibular (TM) joints.Subjects and Methods: Seventy-seven patients with an image diagnosis of degenerative bone changes of the unilateral condylar surface accompanied with joint symptoms were studied. The bone changes were assessed by panoramic radiographs and classified into two groups: pathologic bone changes (PBC) including erosion, osteophyte and deformity, and adaptive bone changes (ABC) including flattening and concavity. Magnetic resonance imaging was performed on the subjective TM joints to examine the configuration and position of articular discs. A visual analogue scale was used for evaluation of joint pain.Results: Erosion and deformity showed significantly higher prevalence than the other three kinds of bone changes in the joints with anterior disc displacement without reduction (ADWoR) as compared to those with anterior disc displacement with reduction (ADWR). The cases with the vertical disc position to the condyle ranging from 60° to less than 150° were more frequent than those ranging from 0° to less than 60° in the PBC group, whereas the cases with the vertical disc position to the condyle ranging from 0° to less than 60° were more frequent than those ranging from 60° to less than 150° in the ABC group. The average degree of joint pain when chewing but not jaw opening was higher in the joints with ADWoR than in those with ADWR, and in the PBC group than in the ABC group.Conclusion: The bone changes of the condylar surface diagnosed as PBC tended to induce more advanced disc displacement and chewing pain than those diagnosed as ABC.     

A two-year kinesiographic study of mandibular movement patterns in denture wearers

Changes in functional jaw movements during a 2-year period of denture wear were investigated. The sample consisted of 27 partially edentulous subjects who were provided with an immediate complete maxillary denture and a removable partial mandibular denture. Recordings of habitual chewing of apple and empty open-close cycles were made with a mandibular kinesiograph. At the pretreatment stage, when the patients occluded on a residual anterior dentition, irregular patterns of movement were observed. After placement of the dentures, which restored posterior occlusion, the chewing and open-close patterns showed marked improvement and were characterized by significant mean decreases in sagittal and transversal range of movement. Relining of the maxillary dentures further stabilized the functional patterns. During the second year, significant reductions in vertical range of movement and lateral chewing excursions were observed, and were probably related to impaired retention of the complete upper denture.     

The influence of the leaf gauge and anterior jig on jaw muscle electromyography and condylar head displacement: a pilot study

BACKGROUND: A leaf gauge and an anterior jig may be used to assist the recording of a reproducible jaw position for restorative and prosthodontic treatment. This study investigated possible condylar displacement using an opto-electronic jaw-tracking device and a leaf gauge or anterior jig. The effect of a leaf gauge and anterior jig on jaw muscle electromyography was also examined. METHODS: Five healthy adults without symptoms of temporomandibular disorders were selected. Condylar displacement during clenching were recorded simultaneously with electromyographic activity of superior and inferior heads of the lateral pterygoid, anterior and posterior temporalis, masseter, and suprahyoid muscles. Subjects were trained to bite at maximum and half-maximum bite-force using an anterior jig incorporating a force transducer. RESULTS: No consistent condylar displacement was observed in x, y and z axes between different bite-forces although there was a trend towards superior displacement. Comparison of maximum intercuspal clench and maximum clench on a leaf gauge and an anterior jig produced significant decrease in anterior temporalis activity (p < 0.05), whilst an anterior jig with maximum clench significantly decreased posterior temporalis muscle activity. CONCLUSION: Within the limits of this pilot study, no consistent change in condylar position was identified with these appliances.     

发育性偏颌畸形对咀嚼运动的影响

目的　研究发育性偏颌畸形 (DLJD)患者咀嚼运动的特点 ,探讨偏颌畸形对咀嚼运动的影响。方法　采用下颌运动轨迹描记仪采集 35名咬合正常者及 2 8例DLJD患者左右侧咀嚼口香糖时的下颌运动信号。用配对t检验和独立样本t检验分别对咀嚼速度、幅度等特征值做组内及组间的差异显著性检验。结果　①DLJD患者左右侧咀嚼运动不对称 ,运动轨迹一致率为 6 5 8%～78 73% ,较咬合正常者 (91 93% )低 (P <0 0 1) ,其咀嚼环在冠状面内有 9例分布异常 ,7例咀嚼顺序反向。②偏颌者的下颌最大后退幅度及平均咀嚼速度显著大于对照组 (P <0 0 1) ,总位移、水平面内及咬合接触时的平均咀嚼速度也大于对照组 (P <0 0 5 )。结论　偏颌畸形使下颌咀嚼运动型及水平面内的咀嚼速度和位移异常     

可复性关节盘前移位患者的关节音特征

目的 比较青年人可复性关节盘前移位者和无颞下颌关节症状者的颞下颌关节音,探讨其关节音频谱图的特征和临床诊断价值.方法 运用BioJVA颞下颌关节振动分析仪记录21例可复性关节盘前移位患者与26例正常青年人节律性大开闭口运动中双侧颞下颌关节音;以临床诊断为标准,计算关节振动总能量,诊断可复性关节盘移位的灵敏度和特异性....     

可复性关节盘前移位患者的关节音特征

目的比较青年人可复性关节盘前移位者和无颞下颌关节症状者的颞下颌关节音,探讨其关节音频谱图的特征和临床诊断价值。方法运用BioJVA颞下颌关节振动分析仪记录21例可复性关节盘前移位患者与26例正常青年人节律性大开闭口运动中双侧颞下颌关节音;以临床诊断为标准,计算关节振动总能量,诊断可复性关节盘移位的灵敏度和特异性。结果病例组两侧颞下颌关节的振动总能量、频率小于300 Hz的振动能量、频率大于300 Hz的振动能量、频率大于300 Hz的振动能量与频率小于300 Hz的振动能量之比、峰振幅、峰频率、中间频率均明显大于对照组（P＜0.05）;病变关节随着关节盘移位程度的增加,各项关节振动参数也随之增加,振动总能量明显增加（P＜0.05）;关节振动总能量对关节盘前移位的诊断灵敏度和特异性分别为0.86和0.85。结论可复性关节盘前移位患者关节音振动的各参数明显高于正常人,不同病变阶段的关节音也不同。     

偏侧咀嚼对张闭口运动的影响

目的:分析偏侧咀嚼患者在最大张闭口运动中的下颌运动轨迹特征。方法:通过下颌运动轨迹描记检测技术,比较偏侧咀嚼和正常咀嚼人群在大张口运动中的运动轨迹,进行统计分析。结果:1)偏侧咀嚼组在大张口运动时开闭口轨迹多数分离,开口型与与双侧咀嚼组相比差异有统计学意义(P<0.05)。2)偏侧咀嚼组张闭口运动时垂直向和矢状向位移显著低于双侧咀嚼组(P<0.01)。结论:最大张闭口运动中偏侧咀嚼组开口型多数偏向工作侧,50%的人群开闭口轨迹分离,开口度减小,说明长期偏侧咀嚼会导致张闭口运动轨迹的异常。     

The electromyographic activity of the inferior part of the human lateral pterygoid muscle during clenching and chewing

The nature of activity in the two parts of the muscle is controversial. A reliable technique was developed for recording activity in its inferior part by means of an indwelling needle electrode. This part was most active during anteriorly- or contralaterally-directed intercuspal clenching, vertically-directed clenching with the jaw positioned to the contralateral side or anteriorly, and during jaw opening and least active during vertically-, ipsilaterally- or posteriorly-directed intercuspal clenching, and during vertically-directed clenches with the jaw positioned to the ipsilateral side. During chewing, activity appeared in the late intercuspal phase irrespective of the side used. It commenced earlier when chewing strokes were ipsilateral to the muscle. Activity during both ipsilateral and contralateral chewing strokes continued until maximum opening, when it ceased for the duration of the closing and crushing phases of the cycle. Thus the inferior part, with other muscles, may participate in bracing the condylar head against the articular eminence during vertical-clenching efforts involving condylar displacement, but not in the compressive or crushing phases of the cycle.