A reproducibility method to test lip-closing strength in preschool children.

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.

Incisal paths during habitual mouth opening and closing movements of children with anterior reverse bite in the early mixed dentition.

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.

Condylar motion in children with primary dentition during lateral excursion.

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.