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 determi ne whether changes in masticatory function, characterized by mandibular vel ocity and displacement, occurred during individuals' normal growth. Forty-s even children, 9-15 years of age, were followed over a 6-year period. All h ad an Angle Class I occlusion with no obvious orthodontic problems. Oral mo tor function with respect to mandibular displacement, duration, and velocit y 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 variable s 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 P-dimensional late ral and vertical distances and both the opening and closing velocity decrea sed. The children who grew proportionally most in height during the 6-year period, i.e. the youngest children in the group studied, showed a significa ntly larger decrease in the opening velocity. From this study it becomes ev ident that the variables of the chewing cycle undergo a continuous process of change during growth. This is possibly a reflection of anatomical change s, maturation of the central nervous system, and altered functional demands .