Repeated Botulinum Toxin Type A Injections on Intramuscular Fat Accumulation in Individuals With Sleep Bruxism.

Botulinum toxin type A (BoNT-A) is commonly used for the management of sleep bruxism, yet concerns persist regarding its long-term effects on muscle structure, including the possibility of intramuscular fat accumulation in the masseter muscle. This prospective longitudinal study follows adults with probable sleep bruxism who receive bilateral BoNT-A injections at six-month intervals. Ultrasound imaging is performed immediately before each injection, resulting in four injection cycles and five standardized ultrasound assessments.

Intramuscular fat percentage is quantified from B-mode images at rest and during maximum voluntary contraction using binary segmentation techniques. By examining changes over repeated treatment cycles, the study evaluates whether BoNT-A leads to progressive fat infiltration or instead demonstrates a stable or adaptive pattern. Findings will help clarify the structural safety of long-term BoNT-A use in non-spastic masticatory muscles and guide clinical decision-making for ongoing bruxism management.

Inclusion criteria

• Adults aged 18 years or older.
• Clinical diagnosis of probable sleep bruxism according to the international consensus criteria proposed by Lobbezoo et al.
• Indication for BoNT-A injection in the masseter muscle due to bruxism-related pain or muscle hypertrophy.
• Willingness to undergo repeated BoNT-A injections at six-month intervals.
• Willingness to participate in ultrasonographic evaluations at each follow-up visit.

Exclusion criteria

• Presence of neurological or neuromuscular disorders affecting the masticatory muscles (e.g., dystonia, myasthenia gravis).
• History of orofacial trauma, temporomandibular joint dysfunction, or maxillofacial surgery.
• Systemic diseases that may affect neuromuscular transmission or muscle metabolism.
• Use of medications known to interfere with neuromuscular function, including aminoglycoside antibiotics or corticosteroids.