Effect of food size on the movement of the mandibular first molars and condyles during deliberate unilateral mastication in humans

To date, the effect of food size on the movement of the mandibular first molars and condyles during chewing has not been fully examined due to methodological problems. The purpose of the present study was to examine the previously unknown effect of food size on masticatory jaw movement. Using a face bow, light-emitting diodes, and optical cameras, we recorded, in 16 young adults with good occlusion, mandibular movement for the first 10 strokes during the unilateral chewing of similarly shaped hard gummy jellies weighing 5 g and 10 g, respectively. The chewing cycle time for the 10-g jelly was significantly longer than that for the 5-g jelly. The jaw-closing and -opening maximum velocities, gapes at the maximum velocities, and maximum gape were significantly faster and larger when 10-g gummy jellies were chewed, compared with results with 5-g jellies, at the mandibular first molar on the chewing side and the condyle on the non-chewing side. With the exception of the velocity, similar tendencies were observed at the molar on the non-chewing side. However, such significant differences were not detected at the condyle on the chewing side. The mandibular first molar on the chewing side was that most affected by food size, and the mean value of the maximum gape coincided approximately with the height of each jelly. These results suggest that humans chew hard coherent food such that the mandibular teeth that come into contact with the food open to a height equivalent to that of the food bolus, and that the changes in movement of the other parts of the mandible are minimized, ensuring efficient mastication.     

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.     

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.     

Extraction treatment of a Class II division 2 malocclusion with mandibular posterior discrepancy and changes in stomatognathic function

This case report describes the successful extraction treatment of a Class II division 2 malocclusion with mandibular posterior discrepancy and a congenitally missing maxillary lateral incisor on the left side. The posterior space in the mandibular arch was small, and the mandibular second molars were impacted, with distal tipping. The discrepancies in the maxillary and mandibular arches were resolved by extraction of the maxillary lateral incisor on the right side and the mandibular second premolars on both sides. The mesial movement of the mandibular first molars occurred appropriately, with the second molars moving into an upright position. A lip bumper was used with a preadjusted edgewise appliance in the maxillary dentition to reinforce molar anchorage and labial movement of the retroclined incisors. Despite the extraction treatment, a deep bite could be corrected without aggravation as a result of the lip bumper and utility arch in the mandibular dentition. Thus, an Angle Class I molar relationship and an ideal overbite were achieved. The occlusal contact area and masticatory muscle activities during maximum clenching increased after treatment. The maximum closing velocity and the maximum gape during chewing increased, and the chewing pattern changed from the chopping to grinding type. The findings in the present case suggest that the correction of a deep bite might be effective for improving stomatognathic function.     

Influence of posterior dental arch length on brain activity during chewing in patients with mandibular distal extension removable partial dentures

It is well known that shortened dental arch decreases masticatory function. However, its potential to change brain activity during mastication is unknown. The present study investigates the effect of a shortened posterior dental arch with mandibular removable partial dentures (RPDs) on brain activity during gum chewing. Eleven subjects with missing mandibular molars (mean age, 66·1 years) on both sides received experimental RPDs with interchangeable artificial molars in a crossover trial design. Brain activity during gum chewing with RPDs containing (full dental arch) and lacking artificial molars (shortened dental arch) was measured using functional magnetic resonance imaging. Additionally, masticatory function was evaluated for each dental arch type. Food comminuting and mixing ability and the perceived chewing ability were significantly lower in subjects with a shortened dental arch than those with a full dental arch (P < 0·05). Brain activation during gum chewing with the full dental arch occurred in the middle frontal gyrus, primary sensorimotor cortex extending to the pre‐central gyrus, supplementary motor area, putamen, insula and cerebellum. However, middle frontal gyrus activation was not observed during gum chewing with the shortened dental arch. These results suggest that shortened dental arch affects human brain activity in the middle frontal gyrus during gum chewing, and the decreased middle frontal gyrus activation may be associated with decreased masticatory function.     

偏侧咀嚼患者下颌磨牙区种植体支抗稳定性的临床研究

目的：研究偏侧咀嚼患者正畸治疗中下颌第二前磨牙和第一磨牙间种植体支抗的稳定性。方法：2006～2012年来我科进行正畸治疗的患者中,选择具有偏侧咀嚼习惯,同时因正畸治疗需要在双侧下颌第二前磨牙和第一磨牙区种植体支抗控制的病例146例,男48例,女98例,年龄18～25岁,平均21．6岁。观察咀嚼侧和非咀嚼侧种植体支抗的稳定性,并对相关因素进行对比分析。结果：本组选择病例中半年内发生种植体支抗松动者23例,共25枚种植体,其中咀嚼侧6枚,非咀嚼侧19枚,咀嚼侧发生种植体周围炎14例,非咀嚼侧38例,对双侧局部骨密度进行测定,结果显示两侧种植体支抗脱落率、周围炎发生率及骨密度均具有显著性差异（P〈0．05）。结论：偏侧咀嚼患者非咀嚼侧种植体稳定性较差,可能与局部口腔卫生不良及骨密度相对较低有关。     

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.     

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.     

Clinical study on the relationship between chewing movements and temporomandibular joint abnormalities

Chewing movements are accomplished by the harmonious function of the stomatognathic system. Therefore, TMJs play important roles in chewing movements. Recently, significant findings on TMJ abnormalities have been obtained from many studies. However, the relationship between chewing movements and TMJ abnormalities remains unclear. The purpose of this study was to examine how TMJ abnormalities were reflected in chewing movements. Incisor point movements during chewing (chewing pattern) were investigated in 150 abnormal and 25 normal subjects using Sirognathograph Analysing System. Abnormal subjects were composed of 45 patients with anterior disk displacement with reduction (reciprocal click), 20 patients with anterior disk displacement without reduction (closed lock), 50 patients with osteoarthrosis and 35 patients with MPD syndrome. Analysis of condylar movements during chewing were also performed in 9 normal and 20 abnormal subjects. The results were as follow; 1. Subjects with TMJ abnormalities tended to show abnormal chewing patterns when chewing at their non-abnormal sides. 2. TMJ abnormality of each different type tended to show its respective characteristic chewing pattern. 1) Subjects with osteoarthrosis and reciprocal click without condylar posterior dislocation tended to show deviation of the turning point to the non-chewing side, with a convex opening path in the frontal plane and a lack of anteroposterior width in the sagittal plane. This finding was associated with the limitation in movement of the abnormal-side condyle. 2) Subjects with reciprocal click with condylar posterior dislocation tended to show a concave opening path and reversed or cross-over patterns in the frontal and horizontal planes, respectively. This finding was associated with the movement of the abnormal-side condyle in the medio-anterior direction during the initial phase of opening. 3) Subjects with closed lock without condylar posterior dislocation tended to show deviation of the turning point to the non-chewing side, with a concave opening path in the frontal plane and a lack of anteroposterior width in the sagittal plane. This finding was associated with the severe limitation in movement of the abnormal-side condyle. 4) Subjects with closed lock with condylar posterior dislocation characteristically tended to show reversed or cross-over patterns in the horizontal plane. This finding was associated with the movement of the abnormal-side condyle in the medio-anterior direction during the initial phase of opening. However, this movement was smaller than that of the reciprocal click. 3. Subjects with MPD syndrome showed chewing patterns similar to those of normal subjects. From the results, close relationships were found between chewing movements and TMJ abnormalities.     

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.     

Study of jaw movement and masticatory muscle activity during unilateral chewing with and without balancing side molar contacts

summary This research evaluated the relationship between balancing side molar contacts and chewing patterns measured with a jaw movement analyser and multi-channel electromyography (EMG) of the masticatory muscles. Nine healthy subjects with relatively normal occlusions participated in the experiment and were divided into those with balancing side molar contacts and those without. The block gum chewing task was performed on each side of the mouth for 10 s. The results showed more asymmetrical levels of jaw closing muscle activity during unilateral chewing in the group with balancing side molar contacts when compared with the group without these contacts.     

Interferential effect of the over-erupted third molar on chewing movement

ObjectiveTo clarify whether over-eruption of the mandibular third molar can disturb chewing movement.MethodsEighteen patients with a unilateral mandibular over-erupted third molar confirmed by both study cast observation and T-scan occlusal detection were selected from a sample of patients with complaints of temporomandibular disorder (TMD) symptoms. A unilateral gum-chewing trace was recorded separately for left and right side chewing by an electrognathography system. The average chewing pattern (ACP) was created based on segments from the recorded chewing trace to represent the chewing movement characteristics of each individual. Two factors, the TMD symptomatic side and the over-eruption side, were analysed for their effects on values of difference in the parameters (Δvalue) regarding the ACP between chewing with right and left side. Three-dimensional amplitudes of ACP and the cross point value of ACP with the vertical axis (termed the cross zero point value) which described the turning point of the chewing cycle from the balancing side to the working side, were compared between sides.ResultsThe over-eruption side had an effect on the Δvalue of the medial amplitude, the lateral amplitude, and the cross zero point (P < 0.05), but the symptomatic side didn’t (P > 0.05). When chewing on the over-eruption side, the medial amplitude was shorter, the lateral amplitude was larger, and the cross zero point value was smaller than those when chewing on the other side (P < 0.05).ConclusionThe present data indicate an effect of the over-erupted mandibular third molar on the chewing pattern while that from the symptom(s) is limited.     

Differences in masticatory function of subjects with different closing path

PurposeThe purpose of this study was to clarify whether there was a difference in the masticatory function between two masticatory path patterns: a convex closing path and a concave closing path.MethodsFor 80 healthy subjects, the masticatory function (masticatory muscular activity, mandibular movement, and masticatory performance) when chewing a gummy jelly was recorded. Out of the 160 chewing cases (80 subjects chewing on either side), 65 cases (Group I) in which the incisal point opened in a linear or concave manner toward the working side and closed in a convex manner, and 15 cases (Group II) in which the opening path was the same as that in Group I, but the closing followed a concave path, were selected. For the masticatory function, the integral values per unit time of masseter and temporal muscular activities, the gape and masticatory width, the indicators representing the stability of movement path, and the glucose extraction from chewing gummy jelly were measured and compared between the two groups.ResultsThe integral values of muscular activities and the amount of glucose extraction were significantly greater in Group I. The gape and masticatory width were not significantly different between the groups. The values of the indicators representing the stability of path were smaller in Group I than in Group II.ConclusionFrom these results, it was suggested that there was a functional difference between Group I (with a convex closing path) and Group II (with a concave closing path), and that Group I had a superior masticatory function to Group II.     

Natural course of nonreducing disc displacement of the temporomandibular joint: changes in chewing movement and masticatory efficiency.

PURPOSE: The purpose of this study was to examine changes of chewing movement and masticatory efficiency during the natural course of nonreducing disc displacement of the temporomandibular joint (TMJ). PATIENTS AND METHODS: The subjects were 15 patients who had been diagnosed with nonreducing disc displacement of the TMJ but had received no treatment. Chewing movement and masticatory efficiency were examined at the initial visit and at a mean follow-up of 21.7 months, using mandibular kinesiography and adenosine triphosphate ebteric-coated granules. As a control, 23 persons who had no current or previous TMJ symptoms were studied. RESULTS: The patients' clinical signs and symptoms tended to be alleviated during the follow-up period. In normal controls, chewing movement showed lateral excursion to the chewing side on both the right and left sides. In patients, chewing movement at the initial visit showed lateral excursion to the chewing side during chewing on the TMJ affected side, but no such deviation was noted during chewing on the TMJ unaffected side in the horizontal plane. However, chewing movement at follow-up became similar to that of controls. In patients, masticatory efficiency became better during the natural course, although that at follow-up did not always reach the control's level. CONCLUSION: In untreated patients with nonreducing disc displacement of the TMJ, chewing movement and masticatory efficiency tend to improve spontaneously.     

Temporomandibular joint articulations on working side during chewing in adult females with cross‐bite and mandibular asymmetry

Influence of mandibular asymmetry and cross‐bite on temporomandibular joint (TMJ) articulation remained unknown. This study aimed to investigate whether/how the working‐side condylar movement irregularity and articular spaces during chewing differ between patients with mandibular asymmetry/cross‐bite and control subjects. The cross‐bite group and the control group consisted of 10 adult female patients and 10 adult female subjects, respectively. They performed unilateral gum‐chewing. The mandibular movements were recorded using a video‐based opto‐electronic system. The 3D articular surface of the TMJ for each individual was reconstructed using CT/MRI data. For local condylar points, the normalised jerk cost (NJC) towards normal direction to the condylar surface, the angle between tangential velocity vector and condylar long axis and intra‐articular space were measured. Three rotatory angles at centre of the condyle were also measured. During closing and intercuspation, (i) movements of posterior portion of the deviated side condyle showed significantly less smoothness as compared with those for the non‐deviated side and control subjects, (ii) the rotations of the condyle on the deviated side induced greater intra‐articular space at posterior and lateral portions. These findings suggest that chewing on the side of mandibular deviation/cross‐bite may cause irregular movement and enlarged intra‐articular space at posterior portion of the deviated side condyle.     

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.     

负荷改变对髁突软骨细胞合成蛋白多糖的影响

目的：研究负荷变化对髁突软骨细胞蛋白多糖合成的影响。方法：拔除成年家兔左下磨牙,分别于术后2周、1月和3月取双侧颞颌关节,进行阿辛兰和甲苯胺兰等组织化学染色和免疫组化染色。结果：酸性粘多糖和蛋白多糖术后量均降低,以非拔牙侧更显著,随着缺牙时间的延长这些变化而更显著。结论：异常负荷可导致软骨细胞蛋白多糖合成的减少及其构成的变化,从而使髁突纤维软骨的粘弹性降低。     

Association between masticatory performance using a colour-changeable chewing gum and jaw movement

The purpose of this study was to investigate the relationship between masticatory performance as determined using a colour-changeable chewing gum and mandibular movements. Subjects comprised 45 fully dentate adults (23 men, 22 women; mean age, 28·1 years). The gum was chewed for a specified number of chewing strokes (20, 40, 60, 80, 120 or 160 strokes) without any instructions as to chewing side. A colourimeter was used to measure L*, a* and b* values (CIE-L*a*b* colour system) for the chewed gum, then the difference between two colours in the CIE-L*a*b* colour space (ΔE) for each number of chewing strokes was calculated according to a formula. Index of masticatory performance (ΔE60) for each subject was obtained using ΔE for 20, 40, 60, 80, 120 and 160 strokes. Mandibular movements were recorded using an opto-electric system with six degrees of freedom. Twelve parameters of mandibular movements relating to amplitude, duration, velocity and angle were computed for each cycle, and mean values for 10 cycles (from cycle 11 to 20) were calculated separately. Stepwise multiple regression analysis identified maximum closing velocity and closing angle as predictors accounting for 18% of the variation in ΔE60. These results suggest that lower angles of approach to intercuspation and faster speed during closing duration are associated with colour changes in the colour-changeable chewing gum.     

Dynamic changes in bone metabolism in the rat temporomandibular joint after molar extraction using bone scintigraphy

Functional adaptation with reformation of bone tissue structure occurs after changes in mechanical stress distribution. To examine how occlusal changes affect the dynamics of bone metabolism in the mandibular condyle, bone scintigraphy of rat condyles was taken using ^99mtechnetium-methylene-diphosphonate (^99mTc-MDP) after extraction of maxillary molars resulting in unilateral loss of occlusal support. Accumulation of ^99mTc-MDP was significantly higher in the condyles on the extracted side than on the intact side 3 d after molar extraction. In addition, bone mineral density (BMD) and osteoprotegerin expression in extracted-side condyles were significantly increased while osteoclast numbers were significantly decreased when compared with intact-side condyles. These differences were not detected 28 d after molar extraction. These findings suggest that occlusal change transiently results in changes in the dynamics of bone metabolism at the mandibular condyles through the downregulation of osteoclastogenesis. These changes may be involved in functional adaptation of the temporomandibular joint.     

Tooth contact patterns and contractile activity of the elevator jaw muscles during mastication of two different types of food

The pattern of molar and canine contacts and the contractile activity of the masseter and anterior temporal muscle were studied, through integrated electromyography, during right-sided mastication of banana and apple in ten healthy male subjects. Tooth contacts occurred on both the chewing and the non-chewing side. This study does not support the clinical concept that non-chewing side contacts are necessarily detrimental to the jaw muscles and the temporomandibular joints. The activity of the elevator jaw muscles and the tooth contact patterns suggest that the mandible tilted around a sagittal axis, and rotated around a vertical axis, during the phase of elevation of a masticatory cycle.