Three‐dimensional analysis of jaw kinematic alterations in patients with chronic TMD – disc displacement with reduction

The study investigated whether chronic TMD patients with disc displacement with reduction (DDR), performing non‐assisted maximum jaw movements, presented any changes in their mandibular kinematics with respect to an age‐matched control group. Moreover, it was examined whether jaw kinematics and a valid clinic measure of oro‐facial functional status have significant associations. Maximum mouth opening, mandible protrusion and bilateral laterotrusions were performed by 20 patients (18 women, 2 men; age, 18–34 years) and 20 healthy controls (17 women, 3 men; age, 20–31 years). The three‐dimensional coordinates of their mandibular interincisor and condylar reference points were recorded by means of an optoelectronic motion analyser and were used to quantitatively assess their range of motion, velocity, symmetry and synchrony. Three functional indices (opening–closing, mandibular rototranslation, laterotrusion – right and left – and protrusion) were devised to summarise subject's overall performance, and their correlation with the outcome of a clinical protocol, the oro‐facial myofunctional evaluation with scores (OMES), was investigated. TMD patients were able to reach maximum excursions of jaw movements comparable to healthy subjects’ performances. However, their opening and closing mandibular movements were characterised by remarkable asynchrony of condylar translation. They had also reduced jaw closing velocity and asymmetric laterotrusions. The functional indices proved to well summarise the global condition of jaw kinematics, highlighting the presence of alterations in TMD‐DDR patients, and were linearly correlated with the oro‐facial functional status. The jaw kinematic alterations seem to reflect both oro‐facial motor behaviour adaptation and a DDR‐related articular impairment.     

Analysis of rotation centers of various mandibular closures

Wax interocclusal records of five subjects made during three types of mandibular closing movement at various degrees of jaw opening were successively placed between mandibular and maxillary casts that were mounted on an articulator. Recording pins inserted into the lateral sides of the casts were used to record the amount of movements. The rotation centers were then calculated and the following results were obtained. (1) For the terminal hinge closure in which the mandible was guided by the chinpoint, no statistically constant rotation center was observed. (2) For the most retruded closure of the mandible in which each subject was asked to make the most retruded position by his own effort, a constant rotation center was found in two of five subjects. (3) For habitual closure of the mandible no constant rotation center was observed, and where the interocclusal distance was less than 1 mm the mandible seemed to close perpendicular to the occlusal plane.     

健康人髁突运动中心前伸和大张口轨迹特征的研究

目的 探讨髁突参考点选择不同对髁突运动轨迹形态的影响。方法 利用自行开发的髁突运动中心轨迹显示分析系统，分别以运动中心，终末绞链轴点作为参考点，研究30名健康人下颌前伸和大张口时髁突运动的矢状面轨迹。结果 运动中心位于终末绞链轴点的前上方，二者轨迹不同。健康人的髁突运动中心大张口迹轨，为一斜向前下方的平滑曲线，形态稳定，没有轨迹异常特征出现且左右侧对称，大张口运动轨迹起止点连线距离与前伸运动轨迹起止点连线距离的比值大于1．5。而终末绞链轴点大张口轨迹左右侧不对称，形态不稳定，会出现不规则形状，大张口运动轨起止点连线距离与前伸运动轨迹起止点连线距离的比值较小。结论 对于同一健康个体，运动中心轨迹较终末绞链轴点轨迹更恒定。     

Distortion of mandibular kinesthesia induced by vibration of human jaw muscles.

Kinesthetic experience accompanying vibration of human jaw muscles was investigated in 12 healthy subjects. Vibration of the masseter muscle with the jaw in a 20-mm opened position caused the subjects either to underestimate jaw closing effects or to experience jaw opening movements depending on whether the mandible was free to move or kept in a constant position. During vibration of the depressor muscles with the mandible in its rest position the subjects underestimated an opening movement, but fixation of the mandible caused no illusions of movement. All kinesthetic illusions perceived during vibration corresponded to elongation of the muscles under study beyond their actual length. Distortion of kinesthesia was independent of the amplitude and frequency of vibration and it persisted during anesthesia of the temporomandibular joints and loading of the mandible. It can be concluded that jaw muscle receptors may contribute to mandibular kinesthesia.     

Rotational head motion concurrent to rhythmical mandibular opening movements

We have previously demonstrated the existence of a functional-rhythmical coupling between the head and the mandible using maxillary and mandibular incisal tracking points. However, that data did not provide information neither on the movement of the head as a whole nor on the location of its instantaneous centre of rotation. Thus, the objective of the present study was to determine whether the head undergoes a rotational motion during mouth opening and to locate its putative instantaneous centre of rotation. The same 6 d.f. (degree of freedom) measuring device employed in our previous studies was used again to analyse data from five male adults (age range: 26-29 years old) chosen as subjects. Concomitant head and mandibular movements were assessed in the sagittal plane by allocating several reference points in the head (upper incisor, cranial base, occipital and parietal points) and a mandibular incisor point during maximal mouth open-close movements. Then, the magnitude and inclination of the vectors of motion in each reference point during the opening phase were calculated. The instantaneous centre of rotation was defined as the point showing the least amount of motion in a determined area around each head reference point. The mandibular incisal point and the maxillary incisal point showed concomitant movements; that is, during opening the mandibular point moved downwards and the maxillary incisor point upwards. Making a large jaw opening movement caused an inferior-anterior displacement in the O point, a posterior-inferior displacement of the P point, and an anterior-superior displacement in the C point in all subjects. During jaw closing all points followed a trajectory opposite to that described above. In other words, during opening the head moved clockwise and counter-clockwise during closing, at least in the sagittal plane of the subjects' left side. These results suggest that the head undergoes a rotation-like sagittal movement during mouth opening whose rotation centre seems to be located above the cranial base point, which was set close to the centre of mass of the head. However, its location varies according to the magnitude of mouth opening.     

Distortion of mandibular kinesthesia induced by vibration of human jaw muscles

abstract — Kinesthetic experience accompanying vibration of human jaw muscles was investigated in 12 healthy subjects. Vibration of the masseter muscle with the jaw in a 20mm opened position caused the subjects either to underestimate jaw closing effects or to experience jaw opening movements depending on whether the mandible was free to move or kept in a constant position. During vibration of the depressor muscles with the mandible in its rest position the subjects underestimated an opening movement, but fixation of the mandible caused no illusions of movement. All kinesthetic illusions perceived during vibration corresponded to elongation of the muscles under study beyond their actual length. Distortion of kinesthesia was independent of the amplitude and frequency of vibration and it persisted during anesthesia of the temporomandibular joints and loading of the mandible. It can be concluded that jaw muscle receptors may contribute to mandibular kinesthesia.     

下颌前突患者下颌支矢状劈开截骨术后髁突运动轨迹的改变

目的:研究双侧下颌支矢状劈开截骨术对下颌前突患者髁突运动轨迹的影响。方法:采用ARCUSdigma下颌三维运动轨迹描记仪,以髁突运动中心为参考点,研究30例正常受试者、14例下颌前突患者手术前后开口、前伸和左右侧向髁突运动的轨迹。用SPSSV11.0统计软件包进行配对t检验和成组t检验。结果:下颌前突患者术前、术后、正常组左侧髁突的运动轨迹与右侧基本相同,左侧髁突与右侧的开口、前伸和侧方运动范围无显著性差异(P>0.05)。术前组与正常组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均小于正常组(P<0.05);术后与正常组髁突运动轨迹接近,术后开口、前伸和侧方运动范围与正常组无统计学差异;术前与术后组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均显著小于术后组(P<0.05)。结论:下颌前突患者手术后,随着术后正畸治疗及咬合自我调整,建立了正常的咬合引导关系,使下颌功能运动趋向正常。     

Recording of the retruded position of the mandible in patients with mandibular dysfunction.

The precision (reproducibility) of active and passive recordings of the retruded position of the mandible was studied by two examiners on 10 patients with mandibular dysfunction symptoms. The position of the mandible was recorded with an intra-oral graphic method, before and after treatment of the symptoms. The precision of the recording was highest when the retruded position was recorded by passive hinge movement and lowest when it was recorded by active hinge movement and when recording habitual closure. Both systematical and accidental errors tended to be somewhat larger among these patients than that previously found among individuals without signs or symptoms of mandibular dysfunction. The accidental errors in antero-posterior and medio-lateral directions were the same fo both examiners and of the same magnitude before and after treatment of the symptoms. Both examiners recorded the retruded position on the average 0.20 mm more posterior after treatment than before. The results showed that because of its good reproducibility the retruded position of the mandible can be recommended as a reference position in functional analysis of occlusion and for jaw recordings also in patients with TMJ muscle-pain dysfunction symptoms. During the recording the conventional technique with passive hinge movement and a posterior pressure should be used.     

The intra-articular distance within the TMJ during free and loaded closing movements

Previous studies on free opening and closing movements of the mandible have demonstrated that the opening movement traces of the condylar kinematic center (i.e., the condylar point for which the protrusive and the opening movement traces coincide) lie closer to the articular eminence than the closing traces. This indicates the presence of an intra-articular distance within the joint during free closing. Since the mandible behaves like a class III biomechanical lever, a counteracting mechanical load on the mandible during closing will press the condyle-disc complex against the articular eminence. Therefore, in this study the hypothesis was tested that the difference between opening and closing movement traces of the kinematic center is reduced when the closing movements are counteracted by a mechanical load. From 10 healthy participants, 20-second movement recordings were obtained by a six-degrees-of-freedom opto-electronic jaw movement recording system (OKAS-3D) for three types of movements: (1) free opening and closing movements, (2) free opening and loaded closing movements (i.e., the participants closed against a small or high manually applied downward-directed force to the chin), and (3) gum chewing. Off-line, the opening and closing movement traces of the kinematic center were reconstructed, and the average difference between the traces (the intra-articular distance) was calculated. The average intraarticular distance was significantly smaller during loaded closing than during free closing, whereas no significant differences were found in the intra-articular distances between the loaded situations of low and high manual loading and contralateral chewing (ANOVA and post hoc Bonferroni multiple comparisons of means test, p<0.005). In conclusion, loading of the mandible during closing movements reduces the intra-articular distance within the temporomandibular joint.     

Masticatory muscles. Part VI. Masticatory muscles and movement of the lower jaw

The movement paths of the kinematic center of the temporomandibular joint were recorded by means of a jaw movement recording system (OKAS-3D) under 3 conditions: 1. free open and close movements; 2. free opening and loaded closing movements (subjects closed against a small, manually applied, downward directed force on the chin); and 3. during chewing of chewing gum. During free jaw movements, the opening path of the kinematic center lies above the closing path. During loaded closing movements, the opening and closing paths coincide. This indicates that during opening and loaded closing, the condyle-disc complex is slightly pressed against the articular eminence. However, during free closing, there is more space between the articulating surfaces. During gum chewing, the opening and closing paths of the condyle coincide on the balancing side, on the working side they don't. Thus, the joint on the balancing side is loaded and the joint on the working side is not.     

Concomitant mandibular and head-neck movementsduring jaw opening–closing in man

To test the hypothesis of a functional relationship between the human mandibular and cranio-cervical motor systems, head-neck movements during voluntary mandibular movements were studied in 10 healthy young adults, using a wireless optoelectronic system for three-dimensional (3D) movement recording. The subjects, unaware of the underlying aim of the study, were instructed to perform maximal jaw opening–closing tasks at fast and slow speed. Movements were quantified as 3D movement amplitudes. A consistent finding in all subjects was parallel and coordinated head-neck movements during both fast and slow jaw opening–closing tasks. Jaw opening was always accompanied by head-neck extension and jaw closing by head-neck flexion. Combined movement and electromyographic recordings showed concomitant neck muscle activity during head-neck movements, indicative of an active repositioning of the head. No differences in 3D movement amplitudes could be seen with respect to speed. The head movement was 50% of the mandibular movement during jaw opening, but significantly smaller (30–40%), during the jaw closing phase. In repeated tests, the 3D movement amplitudes of the concomitant head movements were less variable during slow jaw movement and during the jaw opening phase, than during fast and jaw closing movements, suggesting speed- and phase-related differences in the mechanisms controlling the integrated mandibular and head-neck motor acts. The present results give further support to the concept of a functional trigemino-cervical coupling during jaw activities in man.     

Increased sternocleidomastoid,but not trapezius,muscle activity in response to increased chewing load

Previous findings, during chewing, that boluses of larger size and harder texture result in larger amplitudes of both mandibular and head–neck movements suggest a relationship between increased chewing load and incremental recruitment of jaw and neck muscles. The present report evaluated jaw (masseter and digastric) and neck [sternocleidomastoid (SCM) and trapezius] muscle activity during the chewing of test foods of different sizes and textures by 10 healthy subjects. Muscle activity was recorded by surface electromyography and simultaneous mandibular and head movements were recorded using an optoelectronic technique. Each subject performed continuous jaw‐opening/jaw‐closing movements whilst chewing small and large boluses of chewing gum and rubber silicone (Optosil). For jaw opening/jaw closing without a bolus, SCM activity was recorded for jaw opening concomitantly with digastric activity. During chewing, SCM activity was recorded for jaw closing concomitantly with masseter activity. Trapezius activity was present in some, but not all, cycles. For the masseter and SCM muscles, higher activity was seen with larger test foods, suggesting increased demand and recruitment of these muscles in response to an increased chewing load. This result reinforces the previous notion of a close functional connection between the jaw and the neck motor systems in jaw actions and has scientific and clinical significance for studying jaw function and dysfunction.     

A comparison of habitual jaw movements and articulator function

Inherent in adjustable articulators are errors related either to recordings from the patient or to adjustments to the instrument, or both. Furthermore, the validity of the geometric concepts on which the design of these instruments is based, stressing the dominant role of the temporomandibular joints in mandibular movements, is open to question. Microchip technology now makes it possible to view jaw movements in three dimensions while impeding physiological activity minimally. Using a kinesiograph, young dentate Swedish and Chinese adults were examined on two occasions, and the magnitude and direction of some jaw movements were recorded. The results showed that voluntary opening and closing excursions of the mandible frequently followed disparate paths and that closure from the rest position to occlusion was three-dimensional, a lateral component of movement being usual. Retruded contact position was both uncomfortable and unstable. These findings suggest that current procedures for designing and refining occlusal schemes on articulators are invalid.     

Mandibular function in children with a lateral forced bite

Open-close-clench cycles have been studied in 12 children with a lateral forced bite in order to investigate how the neuromuscular system of the mandible adapts itself in the presence of occlusal interferences. The mandibular movements were registered in a frontal plane at the central incisors with an opto-electronic registration technique. Series of 35 cycles were recorded to intercuspal position, against flat occlusal splints constructed in intercuspal raised and retruded positions, and against splints with occlusal stops in a retruded position. Average lateral displacements of the mandible during cycle series against flat occlusal splints were measured relative to cycle series to intercuspal position and relative to series against splints with occlusal stops in the retruded position. The lateral mandibular displacements were registered at maximal tooth-tooth or tooth-splint contact and at 7, 14, and 21 mm mouth-opening. It was found that the mandible in the subjects investigated is displaced to the forced bite side both during cycle series into intercuspal position as well as when occlusal contacts are eliminated by the use of flat occlusal splints.     

Functional-rhythmical coupling of head and mandibular movements

It is known that small head movements accompany the movements of the jaw during mastication; however, it is unknown whether these movements occur rhythmically and synchronously. The objective of this study was to determine whether there exists a functional coupling between the head and mandibular movements. Four healthy male adults (mean age 25.5) with normal occlusion and without TMD history were selected as subjects. Using the Trimet system, we measured tridimensionally both the movement of the head and the mandible by tracking upper and lower incisal points, respectively, during tapping movements with different opening range and frequency, then analysed the vertical component of these movements. The upper incisal point moved in opposite direction to the mandible in all tapping strokes in all subjects, during opening the head moved in a cranial direction and during closing in a caudal direction; the incidence rate for this concomitant movement was 98%, implying that the head moves periodically and rhythmically, as the mandible does. The cycle time of these coincident movements showed a correlation coefficient of 0.94. Moreover, the vertical range of head movement was within 10% of the jaw's movement. From these results we concluded that, at least during teeth tapping, the head moves in rhythmical coordination with mandibular movement.     

Centers of rotation during jaw movements

Anatomists consider the articulation of movable joints to be complex, involving movable instantaneous centers of rotation (ICR). However, prosthodontists often treat the temporomandibular joint (TMJ) as a model of a simple hinge. The aim of this study was to examine the case for a movable ICR during habitual opening and closing jaw movements. Young, dentate subjects were examined with a kinesiograph. Jaw movements were performed and recorded. The center of rotation of each movement pattern was identified, and its location related to the position of the TMJ. The results showed that opening and closing jaw movements were predominantly non-coincident, with a movable ICR located at a variable distance and direction from the TMJ. There was no evidence to suggest that the TMJ functioned as a simple hinge during jaw movements.     

髁突运动中心大张口轨迹与关节窝形态的关系及临床应用探讨

目的　探讨髁突运动中心大张口轨迹与关节窝形态的关系 ,对TMD患者髁突运动中心轨迹特征进行初步研究。方法　利用自行开发的髁突运动中心轨迹显示分析系统 ,分别以运动中心、终末绞链轴点作为参考点 ,观察 10名健康人和 7例临床检查怀疑盘前移位的TMD患者大张口轨迹 ,与磁共振成像得到的相应关节窝形态及关节盘位置诊断结果进行比较。结果　健康人左右侧运动中心轨迹与关节窝形态曲线重合率分别为 80 % (8/ 10 )和 90 % (9/ 10 ) ;终末绞链轴点轨迹与关节窝形态重合率均为 0 (0 / 10 )。TMD患者中 ,11侧盘前移位关节 ,除 1侧可复性盘前移位关节外 ,髁突运动中心轨迹均与正常的轨迹明显不同 ,出现各种改变 ;3侧正常盘位关节 ,髁突运动中心轨迹均与健康人的轨迹相似。结论　运动中心轨迹较终末绞链轴点个体稳定 ,可认为是较理想的研究髁突运动轨迹的参考点     

Using a Motion‐Capture System to Record Dynamic Articulation for Application in CAD/CAM Software

Purpose: One of the current limitations of computer software programs for the virtual articulation of the opposing teeth is the static nature of the intercuspal position. Currently, software programs cannot identify eccentric occlusal contacts during masticatory cyclic movements of the mandible. Materials and Methods: Chewing trajectories with six degrees of freedom (DOF) were recorded and imposed on a computer model of one subject's maxillary and mandibular teeth. The computer model was generated from a set of high‐resolution μ‐CT images. To obtain natural chewing trajectories with six DOF, an optoelectronic motion‐capturing system (VICON MX) was used. For this purpose, a special mandibular motion‐tracking appliance was developed for this subject. Results: Mandibular movements while chewing elastic and plastic food samples were recorded and reproduced with the computer model. Examples of mandibular movements at intraoral points are presented for elastic and plastic food samples. The potential of such a kinematic computer model to analyze the dynamic nature of an occlusion was demonstrated by investigating the interaction of the second molars and the direction of the biting force during a chewing cycle. Conclusions: The article described a methodology that measured mandibular movements during mastication for one subject. This produced kinematic input to 3D computer modeling for the production of a virtual dynamic articulation that is suitable for incorporation into dental CAD/CAM software.     

Influence of tooth contacts during mandibular retrusion on terminal jaw relations and EMG activity during habitual opening and closing movements]

The purpose of this study was to clarify the influence of tooth contacts during mandibular retrusion on terminal jaw relations (TJR) and the surface EMG activity during habitual opening and closing movements. The age of five healthy subjects were 25 to 28 years. The maxillary stabilization splints with steep retrusive contacts (S-SP) and with flat retrusive contacts (F-SP) were prepared for each subject who was instructed to wear S-SP for one week and then to wear F-SP for one week after an interval of two weeks without S-SP. The EMG activity of the masseter and temporal muscles and the TJR during habitual opening and closing movements using a device for recording jaw movements in 6 degrees of freedom were simultaneously measured by an intraoral central bearing device. The results were as follows: 1. The TJR recorded after wearing F-SP shifted more posteriorly than that of wearing S-SP. 2. The posterior temporal muscle activity after wearing F-SP, compared with that of wearing S-SP, resulted in a significant increase. In conclusion, the elimination of the retrusive guidance caused the predominance of posterior temporal muscle activity, and posterior displacement of the mandible.