Influence of Oral Splints on Masseter Motor Unit Recruitment Behaviour

Objective: Therapeutic effects on musculoskeletal pain are lately attributed to intramuscular reorganisation of motor unit (MU) activity unloading injured MUs. Oral splints might evoke similar effects. Should this be the case for masticatory muscles, the prerequisite is a local differential activation at the level of MUs. The goal of this experimental study was to investigate the influence of small changes of the vertical and horizontal jaw relation on the recruitment behaviour of masseter MUs. Method: 20 healthy subjects (10 female) were involved in the experimental study (mean age: 24.7±2.5 years). An intraoral force-measuring system enabled the subjects to perform feedback-controlled submaximum bite-force tasks in three different vertical and horizontal jaw relations, comparable with positional changes induced by oral splints. The electromyographic (EMG) activity of the right masseter was registered with intramuscular bipolar wire electrodes in three different muscle regions. The...