Transient Anterior Open Bite Following Botulinum Neurotoxin Type A Injection Into the Muscles of Mastication: A Case Report

Botulinum neurotoxin type A (BoNT-A) is used in dentistry and orofacial medicine for conditions including myofascial pain, bruxism, and hypertrophic masticatory muscles.Although treatment is generally well tolerated, weakness of the injected muscles can alter masticatory function and, less commonly, affect occlusion.We report a patient in her 30s with refractory myofascial temporomandibular disorder (TMD) pain who developed a transient anterior open bite after repeated BoNT-A injections into the muscles of mastication.Before treatment, she had a Class I incisal relationship with normal overbite and overjet.Approximately 10 weeks after the second treatment session, which used higher masseter doses than the first session, she noticed a change in her bite and separation between her upper and lower front teeth.Examination showed a 2-3 mm anterior open bite.Panoramic radiography showed no radiographic evidence of condylar resorption.The patient was managed conservatively.Progressive improvement was first documented approximately four months after the second BoNT-A treatment session, with complete restoration of incisal contact six months after the second treatment session.The clinical course is compatible with a transient neuromuscular disturbance, although causality cannot be proven from a single case.This case emphasises the need for careful injection planning, accurate dose documentation, baseline occlusal assessment, and counselling about possible temporary changes in bite force, mastication, and occlusion.