Search

The purpose of this study was to test the null hypothesis that molar movement during gum chewing in children with primary dentition is as smooth as in adults. Twenty-two healthy children with primary dentition and 23 healthy adult females participated in this study. Mandibular movement during gum chewing was recorded using an optoelectronic analysis system with six degrees-of-freedom at 100 Hz, and 10 cycles were selected for analysis. Normalized jerk cost (NJC) at the incisors and working and balancing molars were calculated in each phase (i.e., opening, closing and occlusal level phases) for each chewing cycle. The NJC of the working side molar in children was larger than in adults in both the opening and occlusal phases. Inter-individual variances of the NJC in each phase in children and adults were smaller than corresponding intra-individual variances, except for the NJC during the occlusal phase of adults for the working and balancing side molars. The inter- and intra-individual variances of the NJC during the closing phase were the smallest in each phase for both children and adults. This indicates that the jaw movements of children with primary dentition are more variable, less smooth, and faster than that of adults. more...

The purpose of this study was to clarify the characteristics of permanent and primary tooth-crown inclinations. Landmark points from cephalograms and dental casts of two groups; 23 women (mean 20.3 +/- 3.3 years) and 11 girls (mean 5.2 +/- 0.1 years) were digitized, and the coordinates were integrated and transformed to a standardized plane. The 3-dimensional crown inclinations were projected on the sagittal plane, and the angles between the tooth vectors and the FH plane were calculated. An independent-group t-test was used to test for group differences of each tooth inclination, and correlation coefficients were generated for the inclination angles among the permanent and primary teeth. Most maxillary tooth-crown inclinations showed significant age-related differences, while only the second premolar and primary second molar differed significantly in the mandible. The maxillary molars were parallel to the corresponding mandibular molars and correlated with each other, but the primary molars were not. Significant correlations were found between inclinations of most permanent teeth, but not the primary teeth. Maxillary tooth-crown inclinations change during growth, but tooth-crown inclinations of the mandibular teeth do not. more...

This cross-sectional study tested the reproducibility of a simple button-pulling system for measuring lip-closing strength in normal preschool children and compared their strength to that of normal adults. The sample consisted of 348 preschool children and 123 adults. Lip-closing strength was measured by inserting a button, fastened to a piece of string, into the vestibule between the incisors and lips with minimal mouth opening. The string was attached to a digital tension gauge and was pulled parallel to the floor. Maximum tension, with three repetitions, was recorded at the instant that the button was pulled out of the mouth. Multilevel statistical models were used to evaluate any differences in contractive muscle strength between age groups and between the genders. The strength in children increased significantly from three years to five years (p<0.01). Gender-related differences were found in adults but not in preschool children. Inter-individual variation at each age was larger than intra-individual variation. Measurement of lip-closing strength by button pulling is highly reproducible in children and has potential clinical and research applications. more...

Anterior crossbite (ACB) malocclusions are frequent; however, its characteristic functional features have not been fully described. The purpose of this study was to determine the characteristics of habitual mandibular open-close motion in children with ACB of their primary dentition. Two groups of children were selected for study; 17 with ACB (eight boys and nine girls; four years one month to seven years one month) and 19 with normal occlusion (eight boys and 11 girls; four years six months to six years seven months). The motion was recorded using an optoelectronic analysis system with six degrees-of-freedom. Mandibular incisor and condylar motion were analyzed by measuring their three-dimensional ranges and trajectories. Also estimated incisor and condylar pathways of the two groups were compared. Patients with ACB opened wider with more anterior-posterior condylar translation and more mandibular rotation. Although between-subject (inter-individual) variance of all variables in children with ACB was larger, they had less within-subject variance at the condyles. These results indicate that open-close mandibular motion in children with ACB is completely different from that of children with normal occlusion. The different motions might be related to morphological differences between the two groups. more...

This study was undertaken to characterize jaw motion during mastication in children with primary dentition and to compare jaw motion with that in adults. The means and the variances of the traditional parameters for the chewing cycle, i.e., duration, excursive ranges and 3-D distances of travel at the lower incisor, molars and condyles were analyzed and compared in 23 children and 25 female adults. The duration of opening in children was significantly shorter than that of adults. Significant differences between children and adults were observed in lateral and vertical excursion of the incisor, lateral excursion at the molars, and vertical excursion at the condyles. Many of these measurements had larger between-subject and between-cycle variances in children than adults, suggesting that chewing motion in children has not yet matured. The results of this study indicate that chewing motion in children is different from that of adults. more...

The purpose of this study was to determine whether the development of masseter muscle activity at mandibular rest position is characteristic for different angle classifications. The sample consisted of 64 boys and 108 girls, aged ten to 18. Electromyographic (EMG) activity from the right and left masseter muscles was recorded using an EMG scanner. First or second order polynomials were used to separately model the age-related changes in resting muscle activity of each gender and Angle's classification. The EMG activity of Class I boys and girls were expressed in positive second order polynomials. The EMG activities of Class II and Class III subjects were expressed in first order polynomials, and the EMG levels in Class III subjects were lower than in Class II subjects. These results indicated that development of resting activity levels might distinguish and characterize the anteroposterior mandibular position relative to craniofacial region. more...

The instantaneous center of rotation has been used to describe sagittal plane kinematics of mandibular opening and closing. Although, lateral excursions are also important because the closing pathways of masticatory movements frequently coincide with those of lateral excursions with occlusal contacts, there are no similar descriptions of mandibular lateral excursions. To compensate for this deficiency, lateral excursions of 20 women were recorded in this study. Reference points around each subject's mandible were tracked in three dimensions for each 0.1 mm interval of 3-D distance traveled by the incisor during the first 6.0 mm of lateral excursion. ICR was represented by the point that traveled the least 3-D curvilinear distance during each interval. To describe the entire series of intervals, a lateral excursion center was represented by the point with the smallest 3-D curvilinear distance throughout the excursive movement. In the results of this study, lateral excursions can be described as rotation around a single fixed lateral excursion center that is located close to the intercondylar axis, but 22 mm posterior to the initial position of the working side condyle. more...

In order to provide standard values for craniofacial growth of normal children, we evaluated the growth changes of skeletal and soft tissue cephalometric landmarks from lateral cephalograms of 180 Japanese children. They were divided into three groups: primary dentition, mixed dentition, and permanent dentition. Specific skeletal angles and distances showed significant gender differences with increasing age. The only significant soft tissue gender difference was nose height in the oldest group. Upper pharynx dimension and nose height differed significantly among the groups in both genders. Positions of both the upper and lower lip changed significantly between the intermediate and oldest groups of both genders. Nasolabial angle did not change significantly with growth. The results of this study should be useful for predicting craniofacial growth and development or determining the effect of orthodontic treatment. more...

The purpose of this study was to investigate the relationship between incisor and condyle movement during protrusion in children with primary dentition. Subjects were categorized into two age groups. A primary dentition group consisted of 20 children, and a permanent dentition group consisted of 25 women. The occlusion and TMJ in both groups were normal, with no history of orthodontic treatment. Three orthogonal excursive ranges, linear distance and curvilinear distance of the incisal and condylar points; sagittal angle of condylar rotation; and correlations between incisor and condyle distances during protrusion were estimated by using multilevel statistical models. Protrusion in children with primary dentition was characterized by: 1. significantly smaller superior-inferior ranges for incisal and condylar points in children than in adults; 2. strong positive correlations between incisor and condylar anterior-posterior ranges and linear distances, a pattern similar to that in adults. more...

The purpose of this study was to investigate whether the pathways of habitual mouth opening and closing in children with anterior reverse bite in the early mixed dentition differed from those of children with normal occlusion. The two subject groups for this study were composed of ten children with anterior reverse bite (reverse bite group) and twelve children with normal occlusion (normal occlusion group), respectively. These movements were measured by an optoelectronic analyzing system with six degrees of freedom. Movements of the incisal point were projected on the sagittal plane to characterize the paths, and sagittal angles between the incisal path and the horizontal plane were calculated and compared. Opening and closing sagittal angles in the reverse bite group were almost equal over the entire pathway, indicating that the pathways of habitual mouth opening and closing were similar. In contrast, all opening and closing sagittal angles in the normal occlusion group were different, especially close to maximum intercuspation, indicating that their pathway of habitual mouth opening differed from their mouth closing pathway. In conclusion, children with anterior reverse bite in the early mixed dentition have different patterns of habitual mouth opening and closing movements than children with normal occlusion. more...

Normal development of primary and mixed dentition is indispensable for establishing a healthy mandibular function of the permanent dentition. Because condylar movements are crucial for mandibular function, extensive studies have been reported. However, most of these studies have dealt with mandibular functions in adults, and there is less known about children with primary dentition. The purpose of this study was to clarify the condylar movements during lateral excursions in children with primary dentition and compare these movements with those of adults from the viewpoint of functional development. With use of an optoelectronic recording system with six degrees of freedom, the lateral excursions of 24 children and 20 young women, with sound dentition, were recorded at 100 Hz. The results show that the balancing side condyle of the children had a significantly smaller vertical excursion and a significantly larger anteroposterior excursion than that of adults, indicating the shallower and more anteriorly directed movements of the entire mandible during lateral excursions in children with primary dentition. more...

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

Translation and rotation of the mandible during habitual mouth opening movements were studied in 13 children with skeletal-based anterior reverse bite (reverse bite group) and in 13 children with normal occlusion (normal occlusion group) whose dental stage was the primary dentition. Movements were recorded by an opto-electronic movement-analyzing system that could measure mandibular movements with six degrees of freedom. Inferior translation of the mandible was analyzed at the left primary central incisor, both of the primary canines, and both of the primary second molars. Anterior translation of the mandible was analyzed at both of the condyles. Rotation of the mandible was measured in the sagittal plane. The results showed that the associations between the translation and rotation of the mandible during habitual mouth opening in the reverse bite group differed from those in the normal occlusion group. The reverse bite group had greater anterior translation of both of the condylar points than did the normal occlusion group. No significant differences were found in the inferior translation or rotation of the mandible between the two groups. more...