Muscle weakness after repeated injection of botulinum toxin type A evaluated according to bite force measurement of human masseter muscle.
BACKGROUND
Botulinum toxin type A (BTX-A) has been applied successfully to treat masseteric hypertrophy, but it can cause muscle weakness.


OBJECTIVE
To measure the change in maximum bite force (MBF) after BTX-A injection into the human masseter muscle and to evaluate the influence of a booster (repeated) injection.


METHODS
Thirty volunteers completed 18-week follow-up, and MBF was measured. At 18 weeks after the first injection, a booster injection was given to 14 patients, and they were followed up until 18 weeks from the booster injection.


RESULTS
Mean MBF was approximately 20% lower at 2 weeks than before the injection, and it recovered gradually after 4 weeks to return to the preinjection level at 12 weeks. MBF differed significantly between before the injection and at 2, 4, and 8 weeks after the injection (p<.05). In the booster injection group (n=14), MBF was markedly lower at 6 weeks (p<.05), and it recovered gradually in 12 weeks.


CONCLUSIONS
MBF was significantly lower after booster injection of BTX-A into the human masseter muscle, but it gradually recovered in a predictable pattern, and the degree of discomfort experienced by the subjects had little effect on normal mastication.
Kim
Ki Seo
KS
Temporomandibular Joint and Orofacial Pain Clinic, Department of Oral Medicine, School of Dentistry, Yonsei University, Seoul, Korea.
Byun
Young Sub
YS
Kim
Yong Jeong
YJ
Kim
Seong Taek
ST
D000328:Adult; D001732:Bite Force; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000188:drug therapy; D007273:Injections, Intramuscular; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects* / Q000473:pathology; D018908:Muscle Weakness / Q000139:chemically induced*; D009465:Neuromuscular Agents / Q000008:administration & dosage / Q000494:pharmacology*
D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A