The influence of orthodontic and orthopaedic therapy on mandibular motion

Orthodontic functional appliances for the correction of Class II malocclusions work by both dental and orthopaedic effects on the mandible. In asymmetrical Class II malocclusions, unilateral appliances can be used to effect correction on the affected side. Very little is known about the effect of functional appliances on mandibular kinematics in general, and to date, no data has been found on the effect of a unilateral functional appliance on mandible movement. Ten subjects were recruited for the study, five in a group with a bilateral fixed FORSUS® fatigue resistant appliance, and five with a unilateral FORSUS appliance. Three participants in the bilateral group were lost to the study, leaving seven participants in total. Where possible, jaw movement recordings were taken pre-treatment, pre-FORSUS appliance placement (ie, after fixed appliances had been placed), pos-FORSUS removal, and post-treatment. Recordings were done using a 12-camera opto-electric Eagle system that monitored movement of the lower jaw relative to the cranium by tracking reflective markers. The mandible markers were mounted on a splint that rigidly fixed to the lower jaw. Participants were requested to do two open-close movements, protrusion movement and both left and right lateral excursion movements. Data were processed using a Butterworth filter and standardized to 100 data points The data were exported to a spreadsheet, where maximum opening, protrusion and for the unilateral group, rotation around the vertical axis was assessed. Descriptive statistical analysis was used to assess the recordings. There was individual variation in the recordings, but results showed that the use of a unilateral FORSUS appliance does not appear to alter either open-close, protrusion or rotation. Assessment of bilateral FORSUS was made difficult with only two participants completing the study, with both showing individual variation on both measures of open-close and protrusion. In this group particularly, treatment effects may have confounded the recordings. The placement of fixed appliances did not influence mandibular kinematics, and there appeared to be little difference between repeat open-close recordings within any particular recording session. In conclusion, the results indicate that a unilateral fixed FORSUS appliance does not alter jaw function either during or post-orthodontic treatment. Further research is indicated with both unilateral and bilateral FORSUS appliances, especially with regards to mandibular kinematic with the appliance in situ