THRESHOLD PROPERTIES OF LATERAL PTERYGOID MOTOR UNITS IN CLINICAL PAIN

Talal H. Salame PhD*

ABSTRACT

TMD-related chronic pain is a major health problem that affects the contemporary society and could cause severe economical, social and personal problems. Chronic TMD pain is associated with parafunctional activity of different masticatory muscles. The Lateral pterygoid (LP) muscle has been frequently implicated in TMD and a number of studies have suggested that its activity is different between asymptomatic individuals and patients with TMDs. A disturbance to the normal role of the muscle in the control or stabilisation of the temporomandibular joint was suggested as possible cause. Other theories, including muscle hyperactivity, muscle hypoactivity and poor coordination between the Inferior Head and the Superior Head of the Lateral Pterygoid (IHLP and SHLP), have also been proposed. The IHLP was proven to be a heterogeneous muscle due to its Single Motor Units (SMUs) distribution. However, none of the studies have tested its heterogeneity in TMDs. The aim of this study is to investigate the effect of clinical TMD pain on the activity of the IHLP during standardised horizontal jaw movement, with special reference to the relation between CT-verified location of recording electrodes and the threshold values of SMU, to test the heterogeneity of the IHLP already proposed in previous studies.

Keywords: Orofacial pain, Muscle activity, Lateral pterygoid muscle, IHLP, TMD, EMG.