Visualization of mandibular movement relative to the maxilla during mastication in mice: integration of kinematic analysis and reconstruction of a three-dimensional model of the maxillofacial structure.

BACKGROUND: Mastication is one of the most fundamental functions for the conservation of human life. To clarify the pathogenetic mechanism of various oral dysfunctions, the demand for devices for evaluating stomatognathic function has been increasing. The aim of the present study was to develop a system to reconstruct and visualize 3-dimensional (3D) mandibular movements relative to the maxilla, including dynamic transition of occlusal contacts between the upper and lower dentitions during mastication in mice. METHODS: First, mandibular movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, 3D models of maxillofacial structure were reconstructed from micro-computed tomography images. Movement trajectories of anatomical landmark points on the mandible were then reproduced by integrating the kinematic data of mandibular movements with the anatomical data of maxillofacial structures. Lastly, 3D surface images of the upper dentition with the surrounding maxillofacial structures were transferred to each of the motion capture images to reproduce mandibular movements relative to the maxilla. We also performed electromyography (EMG) of masticatory muscles associated with mandibular movements. RESULTS: The developed system could reproduce the 3D movement trajectories of arbitrary points on the mandible, such as incisor, molars and condylar points with high accuracy and could visualize dynamic transitions of occlusal contacts between upper and lower teeth associated with mandibular movements. CONCLUSIONS: The proposed system has potential to elucidate the mechanisms underlying motor coordination of masticatory muscles and to clarify their roles during mastication by taking advantage of the capability to record EMG data synchronously with mandibular movements. Such insights will enhance our understanding of the pathogenesis and diagnosis of oral motor disorders by allowing comparisons between normal mice and genetically modified mice with oral behavioral dysfunctions.

Promoting factors of physical and mental development in early infancy: a comparison of preterm delivery/low birth weight infants and term infants.

OBJECTIVE: The aim of this study was to assess correlations between various factors and the physical and mental development of 4-month-old infants using a multi-faceted evaluation approach. METHODS: A total of 1,402 self-administered questionnaires were distributed to consenting mothers of infants who had undergone a 4-month health checkup in Hiroshima prefecture, Japan. The questionnaires included items from the Japan Child and Family Research Institute Child Rearing Support Questionnaire and the KIDS type A test. Of the 421 completed questionnaires on mother-child pairs that were returned, 318 met the inclusion criteria and were eligible for further analysis. RESULTS: Comparison between infants in a preterm delivery or low birth weight (LBW) group (preterm and/or LBW group; n = 31) and a term delivery appropriate-weight for date (AFD) infant group (term AFD group; n =287) revealed that the preterm and/or LBW group had significantly higher mother child-rearing anxiety and difficult baby scores, along with significantly lower infant development and motor skill scores. Within the term AFD group, infants of primiparous mothers had significantly higher scores for motor skill and sociability with adults than those of multiparous mothers. Language comprehension scores were significantly higher in infants that were exclusively breast-fed than those formula-fed or combined breast-fed and formula-fed. Verbalization scores of infants whose mothers worked were significantly higher than those of infants whose mothers did not work. Infants with siblings aged <4 years exhibited significantly lower scores for motor skills, verbalization, and sociability with adults than infants without siblings or with siblings aged at least 5 years. In particular, we found that a mother's child-rearing anxiety was related to many areas of infant development. CONCLUSIONS: Evaluating the absence or presence of such factors and conducting preventive treatment could promote healthy infant development.