A working-side change to lateral tooth guidance increases lateral pterygoid muscle activity

Abstract

The inferior head of lateral pterygoid (IHLP) is thought to play a critical role in the generation and control of lateral jaw movements. The aim was to test the hypothesis that a change to the lateral tooth guidance (working-side occlusal alteration, OA) results in a significant change in the electromyographic (EMG) activity of the IHLP during standardised lateral jaw movements (laterotrusion) tracked by a jaw-tracking system. Ten trials of right laterotrusion were repeated under: control 1 (before occlusal alteration), OA (after occlusal alteration placement), and control 2 (after occlusal alteration removal) conditions in 14 subjects while recording left IHLP, bilateral anterior and posterior temporalis, masseter and submandibular muscles. IHLP activity was significantly (p<0.05) increased with the occlusal alteration during the outgoing (movement from intercuspal position to approximately 5mm right) and return phases of laterotrusion. The other muscles demonstrated no change or a significant decrease in activity. These findings suggest that a change to the occlusion on the working-side in the form of a steeper guidance necessitates an increase in IHLP activity to move the mandible down the steeper guidance. It must be emphasised that these data cannot be used as justification for occlusal therapy.