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 path pattern during mastication of chewing gum with regard to gender difference

PurposeTo clarify the masticatory path patterns of the mandibular incisal point during mastication of softened chewing gum with regard to gender difference.MethodsOne hundred healthy subjects (50 males and 50 females) were asked to chew softened chewing gum on one side at a time (right side and left side) and the movement of the mandibular incisal point was recorded using MKG K6I. After a catalog of path patterns was made, the movement path was classified into one of the pattern groups, and then the frequency of each pattern was investigated.ResultsA catalog of path patterns consisting of the three types of opening path (op1, linear or concave path; op2, path toward the chewing side after toward the non-working side; op3, convex path) and two types of closing path (cl1, convex path; cl2, concave path) was made. The movement path was classified into one of seven patterns, with six patterns being from the catalog and a final extra pattern in which the opening and closing paths crossed. The most common pattern among the subjects was Pattern I, followed by Patterns III, II, IV, V, VII, and VI, in that order. The majority of cases, 149 (74.5%) of 200 cases, showed either Pattern I (op1 and cl1) or Pattern III (op2 and cl1). There was no significant difference between the two genders in the frequency of each pattern.ConclusionThe movement path could be classified into seven patterns and no gender-related difference was found in the frequency of each pattern.     

Masticatory muscles. Part III. Biomechanics of the masticatory muscles

The masticatory muscles are able to produce forces. These forces may cause movements of the lower jaw. Furthermore, they can be applied by the teeth for the generation of bite or chewing forces. During these kind of processes the temporomandibular joints will be loaded also. The interaction between forces and movements in the masticatory system is complex but obeys the relatively simple laws of mechanics. By application of these laws the development of joint loading, force patterns and movements during masticatory function and dysfunction can be understood. This is illustrated by a few examples of both statical and dynamical masticatory performance.     

Biomechanics of the human temporomandibular joint during chewing

Experimental data on the loading of the human temporomandibular joint during chewing are scarce. Coincidence of the opening and closing chewing strokes of the condyles probably indicates compression in the joint during chewing. Using this indication, we studied the loading of the joint during chewing and chopping of a latex-packed food bolus on the left or right side of the mouth. Mandibular movements of ten healthy subjects were recorded. Distances traveled by the condylar kinematic centers were normalized with respect to the distances traveled during maximum opening. We judged coincidence of the opening and closing condylar movement traces without knowing their origin. When subjects chewed, the ipsilateral condyles traveled shorter distances than did the contralateral condyles. During chewing and chopping, all contralateral condyles showed a coincident movement pattern, while a significantly smaller number of ipsilateral condyles did. These results suggest that the ipsilateral joints were less heavily loaded during chewing and chopping than were the contralateral joints.     

Post-operative optimization of gum-chewing kinematics in a prognathic patient

Smooth jaw movements during gum chewing, which are defined as those driven by optimally smooth patterns of temporal change in acceleration/deceleration, have been quantified in subjects with acceptable occlusions. This paper reports a case in which significant improvement of the smoothness of masticatory jaw movement was observed following surgical-orthodontic treatment. A patient, who demonstrated a mandibular prognathism, underwent the treatment. The irregularity in acceleration/deceleration of jaw closing movement during gum chewing was quantified by the movement jerk-cost, where the jerk is rate of change in movement acceleration/deceleration. The normalized jerk-costs and results of maximum-smoothness model simulation were compared between jaw movements at pre- and post-treatment stages. The correction of mandibular prognathism and crossbite allowed the patient to close the jaw with wider lateral excursion. Furthermore, smoothness of the jaw closing movements increased significantly and the velocity profile was characterized as similar to that predicted by the kinematic model after treatment. These findings for achievement of 'functional occlusion' that allows the patient to perform smooth and economical jaw closing movements during chewing demonstrate necessity of orthodontic treatment of mandibular prognathism to improve jaw motor function.     

Effects of positions of experimental premature contacts on jaw function

The effects of different positions of experimental premature contacts on the jaw function were investigated on 6 subjects. The metal castings of 100-microns thickness were fabricated to make experimental premature contacts on each of 4 mandibular posterior teeth (from the first premolar to the second molar on the preferable masticatory side). The EMG activity of the masseter, anterior and posterior temporal muscles during maximum clenching and gum chewing as well as the mandibular movement during gum chewing were evaluated. The experimental premature contacts reduced the muscle activity, especially on the contralateral side during maximum clenching. As the premature contact was moved more posteriorly, the following results were observed. 1. The activity of the posterior temporal muscle was decreased on the ipsilateral side while it increased on the contralateral side during maximum clenching in many subjects. 2. The duration of the occlusion phase during the ipsilateral chewing was shortened in many subjects. 3. During ipsilateral chewing, a larger muscle activity was produced during the closing phase and the muscle activity produced during the occlusion phase was the least on the first molar. 4. In any chewing side, the closing and opening paths tended to go toward the chewing side.     

Masticatory mandibular movements for different foods textures related to onomatopoetic words

This study aimed to investigate the effects of different sensory-evaluated food textures on masticatory movements, and to identify meaningful factors that correspond to different food textures. Masticatory movements of three healthy subjects were evaluated with a jaw movement tracking device using five different test foods: almond, hard and light rice crackers, apple, and chewing gum. The movements of the incisor point, working and non-working condyle and the entire mandible at the occlusal phase in the horizontal plane were analyzed. For harder foods, the incisor entered the intercuspal position from a rear and lateral, the working condyle showed anterior and noticeable medial movements as the entire mandible translated posteriorly and medially. For soft foods, the incisor movements were nearly coincidental with the lateral border movements, and the mandible rotated towards the inner side near the working condyle. Although the overall paths of the mandibular movements are individually different, it appeared that jaw movement at the final closure is particular to the food texture. From the standpoint of mandibular movements, it is suggested that masticatory movements during the occlusal phase in the horizontal plane is useful for revealing the relationship between mandibular movements and food textures that were evaluated with onomatopoetic words.     

Masticatory jaw movement optimization after introduction of occlusal interference

Summary How ‘control’ characteristics of masticatory jaw movement, such as skilfulness of the movement, change after alteration in occlusion remains uncertain. For each of 10 healthy adults with good occlusion, an occlusal interference with artificial ‘tooth‐cusp’ was introduced to the crown of the upper molar tooth on the non‐working side of unilateral chewing. Mandibular incisor‐point movements were then recorded by a 3D tracking device. The introduction of the occlusal interference induced a remarkable increase in the normalized jerk‐cost (NJC), prolonged duration of the decelerative phase and lowered peak velocity for jaw closing movement during chewing. Overall, the NJC and velocity profile showed significant recoveries during the course of about 90 repetitive chewing cycles performed under the altered occlusal condition. These findings suggest that acute adaptive changes of jaw motion after introduction of occlusal interference might be characterized as the recovery process of movement skilfulness in terms of movement smoothness and velocity profile.     

Influence of balancing‐side occlusal interference on smoothness of working‐side condylar movement and intra‐articular space in chewing efforts

Response of temporomandibular joint (TMJ) articulation adapting to occlusal alteration has been sparsely known. For 10 healthy adults with acceptably good occlusion, an artificial occlusal interference (OI) was introduced to the lower molar on the balancing side of unilateral chewing. Subjects were asked to chew a gum on their preferred side. The chewing jaw movements with/without the OI were recorded using a video‐based optoelectronic system. The mandibular movements were generated in each individual's TMJ model reconstructed by magnetic resonance images. The smoothness of local condylar point movements towards the normal direction of the condylar surface and interarticular space on the working side was measured. Overall, the smoothness of condylar point movements in the closing phase was impaired immediately after introduction of the OI. In the intercuspal phase, the OI increased the joint space. After about 60 chewing cycles, the movement smoothness and joint space began to recover. These findings suggest that OI on the balancing side induced irregular stress field translation on the working‐side condylar surface followed by acute recovery process.     

Smoothness of human jaw movement during chewing.

Human limb movements are successfully modeled based on the assumption that the central nervous system controls the movements by maximizing movement smoothness. Movement smoothness is quantified by means of a time integral of squared jerk (jerk-cost), where jerk is defined as the rate of change in acceleration. This study was performed to investigate whether the control of human masticatory vertical jaw movements can also be explained by a minimum-jerk (maximum-smoothness) model. Based on the assumption that minimum-jerk models account for vertical jaw-opening and -closing movements during chewing, the actual time profile of the movement trajectory was simulated by the model. The simulated jerk-costs and peak velocities were compared with those obtained by actual measurements of jaw movements during chewing. Jerk-costs and peak velocities of the jaw movements during chewing were significantly correlated with those predicted by minimum-jerk models (P < 0.0001, r between 0.596 and 0.799). The minimum-jerk models predicted closing movement trajectories more accurately than opening movement trajectories (jaw opening, root-mean-square error = 1.19 mm; jaw closing, 0.52 mm, t = 4.375, P < 0.0001). The results indicated that the vertical jaw movement control during chewing was represented by the minimum-jerk control model and that the vertical jaw-closing movement is smoother than the opening movement during gum-chewing.     

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.     

Dynamic stereometry of the temporomandibular joint

Studies on jaw kinematics have provided a good understanding of the motion of the mandible in space, but are of little biomechanical relevance because they could not relate the movements to anatomic structures. This is possible by the combination of three-dimensional reconstructions of the temporomandibular joint (TMJ) anatomy with jaw motion recordings. This technique allows us to analyze the variation of the relationship between the articular surfaces, providing indirect insight into disk deformation during function and parafunction as well as TMJ loading. As far as the variation of the condyle-fossa distance is concerned, data indicated that during chewing the distance was smaller 1) on closing than on opening; 2) on the balancing than on the working side; and 3) during chewing of hard than soft food. Moreover, during a forceful static biting, the condyle-fossa distance decreased more on the contralateral, i.e. on the balancing side than on the working side. The decrease was related to the degree of clenching force. These results support the content that both condyles are loaded during chewing and the balancing side joint more than the working one. Biomechanically, the development of osteoarthrosis is more likely related to the magnitude and frequency of stresses applied on the cartilage. Joint movements produce tractional forces that may cause shear stresses contributing to cartilage wear and fatigue. Tractional forces are the result of frictional forces caused by the cartilage surface rubbing and of plowing forces caused by the translation of a stress-field through the cartilage matrix, as the intra-articular space changes during motion. Translation of the stress-field in mediolateral direction seems to be particularly important for the integrity of the TMJ disk because of its anisotropic properties. Dynamic stereometry showed that stress-fields translate in mediolateral direction during opening/closing, protrusion and laterotrusion, and that their translatory velocity varies intraindividually and with the rate of the condylar movement. Furthermore, the results seem to indicate that the lateral area of the TMJ disk is more often exposed to shear stresses caused by stress-field translation than the medial one. In conclusion, dynamic stereometry provides a good visualization of the movement of the condyles in the respective fossae. This helps improving our understanding for the complexity of condylar movements. The technique may also contribute to ameliorate our knowledge of TMJ biomechanics and therefore of the etiology of degenerative joint diseases and possibly also of internal derangement.     

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。     

A Computerized System to Study Masticatory Function

This article describes a system that allows for simultaneous analysis of subjects' mandibular movements and electromyographic activity during chewing. The authors examined clockwise and counterclockwise movements separately, using the following parameters for the opening and closing strokes at 20 different degrees of jaw separation: 1. Number of times the movement occurred.

2. Mean displacement values.

3. Actual velocity.

4. Velocity values on the three coordinates X, Y, and Z.

A plotter was used for a graphic analysis of the movements. The system recorded electromyographic activity from both masseters with a two-channel electromyograph. (However, the system can record up to eight channels at once.) After the data was collected, the mean electrical activity for each degree of jaw separation during opening and closing was calculated. The system used for this study seems to be a reliable and comprehensive means of assessing masticatory activity in function and dysfunction.     

Masticatory muscle activity and hyoid bone behavior during cyclic jaw movements in man. A synchronized electromyographic and videofluorographic study

Synchronized electromyography (EMG) and videofluorography were used to relate the EMG activity from the suprahyoid and masseter muscles and the movement of the hyoid bone to different phases of the jaw open-close-clench cycle. The subjects investigated comprised 19 adult males with normal dentofacial appearances. Five subjects were excluded from the analyses because of a uniform suprahyoid EMG pattern during cyclic jaw movements. The results from the remaining fourteen subjects revealed that mandibular opening was preceded by suprahyoid EMG activity and movement of the hyoid bone in an upward-forward direction. During jaw opening and the first half of the jaw-open phase, EMG activity was registered exclusively from the suprahyoid muscles. The hyoid bone was moved downward-backward during jaw opening. Mandibular closing was preceded by masseter EMG activity and movement of the hyoid bone in a further downward-backward direction. During jaw closing the hyoid bone moved upward and forward. Discrete EMG bursts from the suprahyoid muscles were occasionally registered simultaneously with the masseter EMG activity during jaw closing. No absolute reciprocity existed between suprahyoid and masseter muscle activity during cyclic jaw movements. A period of no EMG activity from either the suprahyoid muscle group or the masseter muscle was noted during the jaw-open phase and the occlusal phase.     

Chewing Movements in Near Ideal Occlusion With and Without TM Symptoms

Orthodontic models hand-articulated into maximum intercuspation of 720 untreated subjects were evaluated by 17 criteria for grading an ideal anatomic occlusion including good dental interdigitation and alignments. Of the 720 subjects screened, the best 17 subjects were divided into three groups that contained 11 near ideal occlusions scored with 92–98%, three lower evaluated occlusions scored with 86–88% and three near ideal occlusions with TM signs or symptoms scored with 90–94%, Border and chewing movements were recorded using incisor tracking instrument (Visitrainer, model 3). Border movements in asymptomatic subjects demonstrated a well-defined intercuspal position, smooth and equal lateral excursions, and straight opening/closing movements. However, one subject with pain of right joint recorded an inconsistent intercuspal position, restricted excursions and a deviated path corresponding to a reciprocal click in opening/closing movements. Chewing movements in asymptomatic subjects with near ideal occlusion demonstrated either no or a lower rate of opening gliding tooth contact along the lateral border movement on non-working side, and a higher rate of closing gliding tooth contact along border movement on the working side. Chewing movements in symptomatic subjects with near ideal occlusion showed opening and closing without gliding along the lateral excursions, and closing point was inconsistent with maximum intercuspal position in the pain subject. In examining these near ideal occlusion subjects, the different characteristic chewing and border movements were defined for subjects with and without TM symptoms, respectively. Asymptomatic subjects with near ideal occlusion and lower evaluated occlusion showed almost the same chewing function. The goal of orthodontic treatment might be anatomic ideal occlusion with good chewing and border movements indicated in this study.     

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.     

Experimental jaw-muscle pain has a differential effect on different jaw movement tasks

AIMS: To determine the effects of experimental jaw-muscle pain on jaw movements. METHODS: Mandibular mid-incisor point was tracked in 22 asymptomatic subjects during standardized (at 2.2 mm/s) protrusion, contralateral excursion, and open jaw movements, as well as free, right-sided chewing and chewing standardized for timing (900 ms/cycle). Tonic infusion of 4.5% hypertonic saline into the right masseter muscle maintained pain intensity between 30 and 60 mm on a 100-mm visual analog scale. Subjects performed tasks in 3 sessions on the same experimental day: control condition (baseline trials), test condition 1 (during hypertonic or 0.9% isotonic saline infusion), and test condition 2 (during isotonic or hypertonic saline infusion). RESULTS: In comparison with control, there were no significant effects of hypertonic saline infusion on amplitude or velocity for protrusion or contralateral jaw movements or on velocity for jaw opening. Jaw-opening amplitude was significantly smaller in comparison with control during hypertonic, but not isotonic, saline infusion. During free but not standardized chewing, subjects chewed faster and exhibited larger amplitude gapes during hypertonic and isotonic infusion in comparison with control. Therefore, it was unlikely that pain had an effect on the kinematic parameters of jaw movement during free chewing. Qualitatively, individual subject data revealed considerable variability in the effects of hypertonic saline on movement parameters, which suggests that the effect of pain on jaw movement may not be uniform between individuals. CONCLUSIONS: The data indicate that the effect of pain on jaw movement may vary with the task performed.     

Jaw movements in patients with a history of pain: an exploratory study

The aims were to determine whether individuals with a past history of pain exhibit (i) altered jaw movement (e.g. reduced amplitude, increased jaw movement variability) in comparison with matched asymptomatic controls, and (ii) correlations between psychological measures (e.g. catastrophising) and altered jaw movement variables. Sixteen participants with a history of trigeminal neuropathic pain (TNP) and 15 age‐ and gender‐matched healthy controls had jaw movements recorded during open/close, free gum chewing and chewing at standardised rates. All completed the Pain Catastrophising Scale (PCS), the Pain Self‐Efficacy Questionnaire (PSEQ), and the Depression, Anxiety and Stress Scales (DASS). Velocity and amplitude for open/close and chewing, as well as variability, bias and mean square error for open/close jaw movements were compared between groups. Spearman's rank correlation coefficient was used to relate kinematic variables with psychological variables. Statistical significance: P < 0·05. There were no significant differences in mean jaw velocity and amplitude between the TNP and control groups during the open/close jaw movements or free or standardised chewing. In comparison with control, the TNP participants exhibited significantly greater variability, bias and/or mean square error during slow and/or fast opening, and significantly greater variance in velocity and/or amplitude during free and standardised chewing. There were significant negative correlations between PCS scores and velocity and/or amplitude of free and/or standardised chewing. This exploratory study suggests that individuals with a history of pain have altered patterns of jaw movements in comparison with asymptomatic control participants and that catastrophising may play a role in the manifestation of these altered jaw movements.     

Analysis of temporal variation in human masticatory cycles during gum chewing

ObjectiveThe study investigated modulation of fast and slow opening (FO, SO) and closing (FC, SC) chewing cycle phases using gum-chewing sequences in humans.DesignTwenty-two healthy adult subjects participated by chewing gum for at least 20 s on the right side and at least 20 s on the left side while jaw movements were tracked with a 3D motion analysis system. Jaw movement data were digitized, and chewing cycle phases were identified and analysed for all chewing cycles in a complete sequence.ResultsAll four chewing cycle phase durations were more variant than total cycle durations, a result found in other non-human primates. Significant negative correlations existed between the opening phases, SO and FO, and between the closing phases, SC and FC; however, there was less consistency in terms of which phases were negatively correlated both between subjects, and between chewing sides within subjects, compared with results reported in other species.ConclusionsThe coordination of intra-cycle phases appears to be flexible and to follow complex rules during gum-chewing in humans. Alternatively, the observed intra-cycle phase relationships could simply reflect: (1) variation in jaw kinematics due to variation in how gum was handled by the tongue on a chew-by-chew basis in our experimental design or (2) by variation due to data sampling noise and/or how phases were defined and identified.