Clinical Examination Reliability of SP6 Acupuncture Point in the Masseter

Objectives: Application of 1kg force is generally recommended for masticatory muscle palpation. But in the masseter there is an acupuncture point called SP6. It is located on the deepest central part of the muscle, which responds with dull ache under stimulus. The aim of this study was to compare the pain threshold under pressure between ST6 point and an upper anterior point on the masseter muscle.
Methods: 25 consecutively selected healthy adults participated: 11 males (mean age=19.27±1.19) and 14 females (mean age=20,5±1.06). Adults undergoing orthopedic treatment with pharmacotherapy, edentulous or partially edentulous were excluded. Social networks and visual displays were used to advertise and recruit participants at the Faculty of Dentistry at Universidad del Desarrollo. People who responded and attended were informed, consented and subsequently examined according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) to determine if participants fulfilled our inclusion criteria. Participants were seated in an orthostatic position. A randomly chosen masseter muscle for each participant was tested using a pressure algometer (Somedic®). An increasing load was applied over the ST6 acupuncture point and over the upper anterior point of the chosen masseter. The order of sites at which forces were applied was also randomly determined. Participants were instructed to press the algometer device when they felt pain (unpleasant sensation) to stop the stimulus. Once the algometer’s counter was stopped data were recorded. T-test for independent samples was used.
Results: The average pain threshold on the masseter’s SP6 acupuncture point under pressure was 139.52 ± 23.53 and 158.44 ± 21.46 on the upper anterior point (p-value = 0.000).
Conclusions: The pain threshold on the masseter’s ST6 acupuncture point under pressure was lower than the pain threshold in the upper anterior point. The masseter’s examination protocol under pressure should be re-evaluated.