Changes in active mouth opening following a single treatment of latent myofascial trigger points in the masseter muscle involving post-isometric relaxation or strain/counterstrain

The aim of this study was to compare the immediate effect, on active mouth opening, following a single treatment of latent myofascial trigger points (MTrPs) in the masseter muscle involving a muscle energy technique, i.e. post-isometric relaxation, and the strain/counterstrain technique. Ninety subjects, 42 men and 48 women, aged 19–44 years old, participated in this study. Subjects underwent a screening process to establish the presence of MTrPs in the masseter muscle as described by Simons et al. Subjects were divided randomly into three groups: group A which was treated with a post-isometric relaxation technique, group B treated with the strain/counterstrain technique, and group C as control group. The outcome measure was the maximum active mouth opening. It was assessed pre-treatment and 5 min post-treatment by an assessor blinded to the treatment allocation of the subject. Within-group changes showed a significant improvement in active mouth opening following application of the post-isometric relaxation technique (P<0.001P<0.001), but not following application of strain/counterstrain (P=0.08P=0.08). The control group did not show any change (P<0.1P<0.1). Pre–post-effect sizes were large in the post-isometric relaxation group (d=1.46d=1.46), small to medium in the strain/counterstrain group (d=0.32d=0.32) and small in the control group (d=0.01d=0.01). Differences were found between the post-isometric relaxation group and both the strain/counterstrain and control groups (P<0.001P<0.001), but not between these two latter groups (P=0.8P=0.8). Our results suggest that the post-isometric relaxation technique might be employed in the management of latent MTrPs in the masseter muscle in order to improve the maximum mouth opening.