Changes in masticatory mandibular movements in growing individuals: a six-year follow-up

The pattern of mandibular movement during chewing is influenced by several central and peripheral factors. The aim of the present study was to determine whether changes in masticatory function, characterized by mandibular velocity and displacement, occurred during individuals' normal growth. Forty-seven children, 9-15 years of age, were followed over a 6-year period. All had an Angle Class I occlusion with no obvious orthodontic problems. Oral motor function with respect to mandibular displacement, duration, and velocity was monitored 3-dimensionally with an opto-electronic method. The chewing cycle was divided into an opening, closing, and occlusal phase. Total body height was measured. During the follow-up period, all masticatory variables except the 3-dimensional opening distance showed significant changes. The total chewing cycle duration, the opening and occlusal time of the chewing cycle, and the 3-dimensional closing distance increased during the growth period, while the closing time of the chewing cycle, the 2-dimensional lateral and vertical distances and both the opening and closing velocity decreased. The children who grew proportionally most in height during the 6-year period, i.e. the youngest children in the group studied, showed a significantly larger decrease in the opening velocity. From this study it becomes evident that the variables of the chewing cycle undergo a continuous process of change during growth. This is possibly a reflection of anatomical changes, maturation of the central nervous system, and altered functional demands.     

Characteristics of masticatory mandibular movements and velocity in growing individuals and young adults

Studies of the development of mastication in the normal growing individual have received little attention in the literature. The aim of this study was to determine whether changes in oral motor function occurred during growth. Ninety healthy individuals with normal occlusion were divided into six groups of males and females, 9-10, 13-15, and 20-22 years of age. Oral motor function, with respect to mandibular displacement and velocity, was monitored with an opto-electronic method. The results revealed that the total duration of the masticatory cycle was not influenced by age or gender. However, the time distribution between the different phases was found to be influenced by the age factor, causing a longer opening time and a shorter closing time in the adults. In mastication, both mandibular displacement and the mandibular velocity in closing were less in females. A reduction of the masticatory opening velocity and an increase in closing velocity were observed with increasing age. Physiological maturation of the masticatory system due to central and peripheral changes and functional adjustments due to changes in dentition and skeletal growth may be the underlying reasons for our findings.     

Adaptive changes of masticatory movement characteristics after rehabilitation with osseointegrated fixed prostheses in the edentulous jaw: a 10-year follow-up study.

The aim of this study was to assess possible adaptive changes in the masticatory rhythmical pattern after insertion of an osseointegrated fixed denture. Registrations of masticatory cycle duration, mandibular velocity, and displacement were performed before and 2 months and 10 years after rehabilitation. No major changes except for a decreased occlusal level phase had occurred regarding cycle duration over the years. However, a significantly higher mandibular velocity and greater displacement were recorded 2 months after rehabilitation. This trend was further established in the long term. Temporal timing of rhythmical chewing seems to be relatively consistent, suggesting that the central pattern generator driving output over time is constant.     

Characteristics of mandibular masticatory movement in young and elderly dentate subjects

Dimensions and velocity of mandibular movement are important variables in the evaluation of masticatory and speech patterns. However, little information is available concerning elderly dentates and their oral motor function and behavior. Double recordings of a chewing period, from start to swallowing, were performed in 14 elderly (mean age, 80 years) and 30 young (mean age, 26 years) dentate subjects chewing crispbread. Three-dimensional records of mandibular movements were obtained by means of the Selspot movement analysis system, which monitors infrared light pulses from light-emitting diodes attached to the test subject. There was no difference in the duration of the total chewing cycle between the two groups. Mandibular velocity was significantly lower in the elderly group, in both the opening and the closing phases. Despite great inter-individual variations, significantly smaller mean vertical displacements of the mandible were found in the elderly than in the younger group. The lateral component in the vertical opening movement was similar for both the elderly and younger subjects. The similar chewing rates in the two groups might imply that the function of the central pattern generator was unaffected by old age. Aging was, however, associated with reduction of vertical mandibular displacement and velocity.     

Effects of intense chewing on some parameters of masticatory function.

This study recorded the influence of 30 minutes of intense chewing on the masticatory function in 17 healthy subjects. Functional recordings of mandibular movements and velocity, measurements of masticatory efficiency, maximal occlusal force, and occlusal force endurance time were performed before and after functional stimulation and finally in a 2- to 5-day follow-up registration. After intense chewing, a substantially decreased masticatory cycle and occlusal level phase duration were recorded. No major mandibular displacements or changes in velocity were recorded. Masticatory efficiency and maximal occlusal force in the incisal region diminished after 30 minutes of intense chewing. Occlusal force endurance time was also lowered after intense chewing. The measurements were close to their original values at the follow-up. Intense chewing had various short-term effects on masticatory function, including a significant reduction of masticatory efficiency, maximal occlusal force, occlusal force endurance, and masticatory cycle duration.     

Chewing patterns before and after treatment with completè maxillary and bilateral distal-extension mandibular removable partial dentures

Prosthodontic rehabilitation with complete maxillary dentures and mandibular bilateral distal-extension removable partial dentures did not change the general masticatory function to any great extent. However, the velocity of the mandible was increased, especially in the opening phase, and so was the mandibular displacement. The latter seems to be the cause for a long closing duration. The chewing cycle became more even and teardrop shaped, and the prosthodontic rehabilitation also resulted in a decrease of the number of chewing cycles. The Selspot system offers a possibility to study adaptation to prosthodontic treatment objectively by measurements of time and movement.     

Jaw movements'' in young adult men during chewing

Jaw movements of a selected group of subjects were studied by clinical observation, examination of wax occlusal records and mounted casts, photoelectric mandibulography, and oscilloscopic tracings. Subjects were found to have substantially consistent and reproducible patterns of jaw movement during empty and functional chewing exercises. However, the individual patterns could not be predicted from analysis of occlusal status.Mean values of (1) the chewing cycle time, (2) the pause at centric occlusion, (3) maximum opening, (4) maximum movement to the right and left of the midline, and (5) maximum jaw point velocity while opening, closing, and moving to the right and left were obtained for 22 subjects chewing a single peanut on the right and the left sides. Great diversity in chewing patterns was observed, but in general, individual subjects exhibited specific and repetitive patterns.All subjects exhibited a pause in centric occlusion at the end of a closing masticatory stroke. A substantially constant jaw point velocity was observed for most of a chewing cycle when the open-close, close-open, left-right, and right-left components of jaw movements were analyzed separately.     

Mandibular movement and velocity in relation to state of dentition and age

Parameters of mastication, such as mandibular displacement, velocity and chewing cycle duration, were investigated in relation to age and rehabilitation with complete dentures. Two groups of elderly subjects (mean age 80 years), one with natural dentition and the other with complete dentures, and one group of young dentate adults (mean age 26 years) participated. Three-dimensional records of masticatory mandibular movements were obtained using the Selspot movement analysis system. There were no differences in the duration of the total or individual components of a chewing cycle, except for the closing phase, which was significantly longer in the complete denture group. Mandibular closing velocity was significantly lower in the two groups of elderly subjects than in the group of young adults. There was a high degree of inter-individual variation in mandibular displacement in all groups, but the mean vertical amplitude was smaller in the elderly groups compared to the group of young adults. For many of the parameters the variation was significantly greater in the groups of elderly subjects than in the younger group. Ageing thus appeared to have a more important effect than the state of the dentition on the parameters studied.     

A comparative study of mastication between complete denture wearers and dentate subjects.

A computer system was used for simultaneously collecting and processing mandibular movements and the myoelectric activities of the masticatory muscles of 15 dentate subjects and 11 complete denture wearers. The displacement, velocity, cycle of mandibular movements, and the muscular mean potentials were indices in observing mastication. A good complete denture should perform with physiologic characteristics, and restore masticatory function and oral health. The kinetic energy from the velocities of lateral and vertical directions can serve for the chewing and comminution of food, but lateral comminution may affect denture retention. The mean myoelectrical potentials of the mandibular elevator muscles of complete denture wearers tend to increase at the opening phase; however, the potentials decrease at the closing phase.     

Effect of masticatory muscle fatigue on cranio-vertical head posture and rest position of the mandible

The aim of this study was to investigate whether induced fatigue of the masticatory muscles had any influence on the head posture, and whether this influence is related to the rest position and the movement characteristics of the mandible. The sample consisted of 13 female individuals, aged 23–34 yr. For the evaluation of possible changes in the natural cranio-vertical head posture, standardized facial profile photographs were used. Photographs were also used for the study of the facial characteristics. The freeway space and the opening and closing velocity of the mandibular displacement, as well as the duration of the masticatory cycles, were monitored with an optoelectronic method. A controlled dynamic fatigue was induced by a specially constructed spring-loaded device placed in the premolar region. No significant changes in the mean cranio-vertical postural position of the head were found during the various recording stages, while the freeway space was found to increase significantly after the fatigue test. No significant differences were observed concerning the average values of the mandibular movement characteristics. The analysis of the associations between the individual changes showed an increase in the freeway space after the fatigue test in the subjects which exhibited an increase in the duration of the masticatory cycle in that period. No significant associations could be found between the changes in the head posture and the mandibular movement characteristics. Also, no significant correlation could be found between the facial type of the subjects and the variables studied.     

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.     

Characteristics of the gum chewing occlusal phase in children with primary dentition

Understanding of the growth and development of mandibular function is indispensable to the diagnosis of functional disturbances during childhood. The purpose of this study was to clarify the characteristics of the occlusal phase during gum chewing in children with primary dentition. Chewing motion at the working molar of 14 children with primary dentition and 28 female adults was recorded optoelectrically, and the frontal and sagittal angles of their closing and following opening strokes were measured and compared. In children the closing strokes were entered more vertically and anteriorly than in adults, and the opening strokes shifted to the non-working side in adults but moved to the working side in children. The degree of variance also differed between the two groups; the variance of the frontal angle was larger than that of sagittal angle in adults, but the opposite was true in children. These results suggested that the chewing pattern in children during the occlusal phase is distinctly different from adults and the chewing movement in children is not always less stable than in adults.     

正常(牙合)青年(牙合)平面与咀嚼运动轨迹的相关性分析

目的 分析个别正常(牙合)青年(牙合)平面与咀嚼运动轨迹特征的相关性,以期为临床定位(牙合)平面提供参考.方法 收集43名个别正常(牙合)青年志愿者,拍摄头颅侧位X线片,测量耠平面倾斜度(OP-CP);记录下颌中切牙切点的左右侧咀嚼运动轨迹,测量矢状面垂直向最大位移(V)、矢状面水平向前后最大位移之和(P+A)、冠状面水平向左右侧方位移之和(L+R)以及(牙合)平面与咀嚼运动轨迹的夹角,对(牙合)平面倾斜度(OP-CP)与V、(P+A)、(L+R)以及(牙合)平面与咀嚼运动轨迹的夹角进行Pearson线性相关分析.结果 OP-CP为(2.1±3.8)°.V为(20.22±4.28)mm,(P+A)为(11.42±2.45)mm,(L+R)为(8.62±1.52)mm.OP-CP与(L+R)呈负相关,相关系数r为-0.39(P<0.05).矢状面(牙合)平面与牙尖交错位及其附近的咀嚼运动开闭口轨迹近似垂直;OP-CP与咀嚼运动轨迹(牙合)期阶段2.0 mm、(牙合)外期上段的(牙合)平面-闭口轨迹角呈正相关(P<0.05);咀嚼轴角平均为(66.50±7.98)°,与OP-CP不相关(P>0.05).结论 矢状面(牙合)平面倾斜度与咀嚼运动轨迹有一定相关性.(牙合)平面对咀嚼运动(牙合)期闭合轨迹的影响较明显.     

Computer-based assessment of habitual mastication

A computer-based system to assess mandibular movements and EMG masseter and temporal muscle activity during habitual mastication was applied to 12 healthy subjects and the chewing performance was tested with a standardized bolus of crisp bread. A Siemens Sirognatograph instrument was used to record mandibular movements while EMG signals were recorded with surface silver-silver electrodes. Software provided data of single chewing cycles in space and versus time, of mean mandibular displacement during opening and closing, mean velocity, and EMG activity. Clockwise and counterclockwise cycles were computed separately. The data obtained allow the following conclusions: Habitual mastication is a rhythmic event with different envelopes of motion that alternate characteristically in each subject. Each chewing cycle accomplishes several tasks but, depending on its envelope, is probably more oriented to a specific performance. A mean chewing cycle can be constructed for each individual. Its pattern depends on the distribution of different envelopes of motion that alternate during the masticatory sequence. During closure, a prevalently isotonic and a prevalently isometric phase of muscle contraction can be distinguished. Mean movement and EMG data for the whole group are not distributed at random, but according to a typical pattern. The system seems to be finalized to a well-balanced function and distribution of loads.     

Temporo-mandibular joint kinetics and chewing cycles in children. A 3-year follow-up

Summary. Objectives. To report the temporo‐mandibular joint (TMJ) kinetics and masticatory function in healthy children. Design. Temporo‐mandibular joint palpation and electrognathographic registrations of chewing cycles were repeated for 3 years in order to evaluate changes. Setting. Healthy children without systemic pathologies, decayed cavities and previous dental treatment. Sample and methods. Electrognathographic (EGN) registration of masticatory cycles and TMJ palpation were carried out on 52 patients (mean age: 5 years 8 months, range: 5 years 1 month, 6 years 8 months), by two university researchers, once a year for 3 consecutive years. TMJ palpation, differentiated TMJ synchronism (simultaneous bilateral opening movement) and TMJ asynchronism (not simultaneous bilateral opening movement), TMJ subluxation and click were observed. Electrognathographic registrations differentiated normal and abnormal jaw chewing cycles, and narrow and large cycles. Results. Temporo‐mandibular joint asynchronism was evident in 34 of 52 patients in the primary dentition, in 42 of 52 patients after the eruption of the first permanent molar, and in 31 of 52 patients after the eruption of the permanent incisors. TMJ subluxation increased during the full period of observation. Three temporomandibular clicks appeared after the eruption of the permanent incisors. Altered mastication was not always associated with TMJ disorders. Conclusions. In children, normal chewing cycles can coexist with occlusal discrepancies, cranio‐facial growth and TMJ alterations.     

Length of the occlusal glide during chewing in children with primary dentition

summary   Chewing is one of the most important functions of the mandible, but, to date, there are very few studies of this function in children. The purpose of this study was to quantify the length of the occlusal glide at the lower incisal point during gum chewing in children with primary dentition. Eleven girls with primary dentition were selected for this study. Mandibular excursions with occlusal contacts and gum chewing movement were measured using an optoelectronic system that can measure mandibular movement with six degrees-of-freedom at a sampling frequency of 100 Hz. A curved mesh diagram of incisor coordinates during mandibular excursions was established to calculate the length of the occlusal glide for each subject. The occlusal glide lengths of children were compared with previously reported results for adults. The estimated length of the occlusal glide during closing was significantly shorter in children than in adults, contrary to that during opening. This result suggests that children have a characteristic chewing pattern that differs from adults.     

Length of the occlusal glide at the lower incisal point during chewing

The purpose of this study was to estimate the length of the occlusal glide during gum chewing at the lower incisal point. Mandibular excursions with occlusal contacts in 25 females with permanent dentition were recorded using an optoelectronic system that can measure mandibular movement with 6 d.f. at a sampling frequency of 100 Hz. A curved mesh diagram of incisor coordinates during maximum mandibular excursions (CMDME) was plotted. Gum chewing movement was also measured using the same system and computer software which divided the chewing movement into cycles at each maximum opening position. Each cycle was standardized at 0.1 mm intervals from the most closed position. Finally, the distance between the CMDME and each position of the incisor during a chewing cycle was calculated. Whenever, this distance was less than 0.2 mm opposing teeth were considered to be in contact. The occlusal glide was defined as the distance travelled by the lower incisal point as the mandible moved along occlusal contacts of the CMDME. The vertical coordinates at the beginning of the occlusal glide (during closing) and at the end of occlusal glide (during opening) were also calculated. The lengths of the occlusal glide pathway averaged 1.29 mm during closing and 1.55 mm during opening, a total length of 2.84 mm. Mean vertical coordinates at the beginning and end of the glide were -0.95 and -1.12 mm from intercuspal position, respectively.     

Occlusal curvature and masticatory function

This study examined the association between masticatory movement and occlusal curvature in dentate adults. Forty-six subjects (mean age : 25.0 years) with complete permanent dentition except for their third molars participated in this study. A mandibular cast mounted on the lower member of an articulator was fixed to a three-dimensional measuring gauge (QM-Measure 353). Approximate spheres were calculated from the measurements according to the Broadrick Occlusal Plane Analyser. Subjects were asked to chew raw carrot, cheese, fish paste, boiled beef and gummy candy prepared to the size of 10 x 10 x 20 mm. Three-dimensional chewing movements of the mandibular central incisor point were measured using a Gnatho-analyzer. The Pearson correlation coefficient and multiple regression analysis were used to test the relationship between the occlusal curvature and masticatory movement. Significant correlations were found between masticatory movement and occlusal curvature in dentate adults (p < 0.01). Regression analysis found that subjects with larger occlusal curvature showed greater maximum velocity, larger vertical range and shorter cycle duration (p < 0.05). These results suggest that occlusal curvature is associated with masticatory movements.     

Jaw kinematics during mastication after unilateral fractures of the mandibular condylar process

This study compared the mandibular kinematics during mastication of patients treated for unilateral fractures of the mandibular condylar process with those of control subjects. We used a Sirognathograph (Siemens, Bensheim, Germany) to record the chewing cycles of 81 male patients with unilateral condylar process fractures while they chewed a constant bolus unilaterally on the same side as the fracture and on the opposite side. Recordings were made at 6 weeks, 6 months, 1 year, and 2 years after treatment. Similar chewing cycles were recorded for 15 male controls (Class I dental and Class I skeletal occlusion) without fractures of the condylar process. The chewing cycles of both groups were analyzed with a custom computer program, and the duration, excursive ranges, and 3-dimensional cycle shape were compared at each time interval with multilevel linear modeling statistics. Fracture patients had significantly slower chewing cycles, with significantly less maximum excursion toward the working side during the closing phase and significantly greater excursion toward the balancing side during the opening phase than the controls. The opening pathway of the incisors showed greater differences between patients and controls than the closing pathways. Differences in chewing cycle shape persisted for up to 2 years, especially when chewing was on the side opposite the fracture. Unilateral condylar process fractures produce long-lasting changes in chewing cycle duration and chewing cycle shape of adults.     

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.