Changes in the masticatory cycle following treatment of posterior unilateral crossbite in children

In a previous study, we established that young children with unilateral pos terior crossbite have a longer mandibular ramus and more superiorly and pos teriorly positioned condyles on the crossbite side. In this study, we evalu ated chewing cycle shape and duration in 14 of the patients before treatmen t, and we looked for changes in cycle shape and duration 6 months after tre atment with rapid palatal expansion. Mandibular kinematics was recorded whi le chewing gum using an optoelectric recording system at 100 Hz. Subjects w ere asked to chew normally for 20 cycles, chew on the crossbite side only f or 20 cycles; and chew on the noncrossbite side only for 20 cycles. A speci al computer program selected the 10 most representative cycles from each se ries and computed an average duration and an average maximum excursion alon g 3 orthogonal axes. Multilevel linear models were used to generate an 8th- order polynomial describing average cycle shape and to test for statistical ly significant differences in shape between the patients and the controls a nd between the patients before and after treatment. Before treatment, the p atients chewed more slowly than did the controls. Treatment shortened their cycle duration to equal control values. Before treatment, the patients als o had larger maximum excursions than did the controls and exhibited a rever se-sequence cycle shape when chewing on the crossbite side. Treatment did n ot alter the patients' abnormal cycle shape: These results suggest that som e features of the masticatory kinematics respond to orthodontic treatment a lone, but others do not.