To correlate the immediate skeletal and occlusal pattern changes with the electromyographic (EMG) activity of anterior temporalis and superficial masseter muscles following rapid maxillary expansion (RME).

The study included 12 patients aged 10–15 years (mean, 12.5 ± 1.45 years) who underwent RME therapy using a standardised protocol. EMG of superficial masseter and anterior temporalis and T-scans were taken before appliance fixation (T0), immediately after the appliance fixation (T1), three weeks of expansion (T2), and three months post-expansion (T3). Changes in the occlusal pattern and muscle activity following rapid palatal expansion were measured using the Friedman analysis of variance (ANOVA) test and correlated using Pearson's correlation coefficient.

The occlusal pattern changes following RME are significant at molars, i.e., the P-Value for right side molars is significant, i.e., P = 0.042, and non-significant at premolars. The changes in EMG activity of superficial masseter and anterior temporalis over three months following RME, i.e.(P > 0.05), were non-significant.

The muscular activity of the masseter and temporalis muscles following RME increases transiently, then decreases toward baseline due to neuromuscular adaptation. The muscular activity changes of the masseter and temporalis are weak and negatively correlated to the occlusal pattern changes following rapid maxillary expansion.