Bite force in children with unilateral crossbite before and after orthodontic treatment. A prospective longitudinal study.

In this prospective, longitudinal study, bite force was examined in children with a unilateral posterior crossbite before (stage 1), immediately after orthodontic treatment (stage 2), and after retention (stage 3). The sample comprised 19 (7 girls, 12 boys) children aged 7-11 years. The children were treated according to conventional practice, with an expansion plate (seven subjects) or a quadhelix appliance (12 subjects). Unilateral bite force was measured at the first molars by means of a standardized method. Statistical analysis was undertaken using Shapiro-Wilks W- and t-tests, and analysis of variance. There was no significant difference in bite force regarding age, gender, appliance, or side, i.e. right or left molar region. However, during stage 2 the bite force was significantly lower ipsilaterally to the crossbite than contralaterally (P<0.05). In general, the bite force was systematically lower than reference values, but the mean bite force (P<0.05) and the bite force on the ipsilateral side (P<0.01) increased significantly from stage 2 to stage 3. The bite force level was reduced immediately after treatment, but increased again after retention and approached the bite force level in children with neutral occlusion. The fluctuation in bite force level during orthodontic treatment may be due to transient changes in occlusal support, periodontal mechanoreceptors, and jaw elevator muscle reflexes.