Abstract
Botulinum toxin type A (BoNT-A), a potent neurotoxin, is increasingly used to treat myogenic temporomandibular disorders (TMDs); however, the interplay between muscle atrophy and pain relief remains incompletely understood. This pilot study investigated how masseter and temporalis muscle thickness and pain intensity change over 12 weeks following BoNT-A injections in 15 patients (mean age 51.42 years) with myogenic TMD. Muscle thickness was measured via ultrasonography across multiple anatomical positions under both clenching and resting conditions at baseline and at 2, 4, 8, and 12 weeks post-injection. Significant thinning of both muscles occurred within 2 weeks, lasting until 12 weeks, but became less pronounced after the first month. Pain intensity showed parallel decreases, most notably early on, but these reductions were not consistently statistically significant. Correlation analyses revealed no strong persistent association between muscle thickness and pain except for a moderately positive correlation in the anterior temporalis at two weeks (r = 0.61, p = 0.04). BoNT-A induces rapid masticatory muscle atrophy and modest pain relief; however, these outcomes do not coincide. Pain relief was observed earlier than the full development of muscle atrophy and should be considered during TMD pain management.