Occlusal force characteristics of masseteric muscles after intramuscular injection of botulinum toxin A(BTX - A)for treatment of temporomandibular disorder.

Our aim was to evaluate the occlusal force and therapeutic efficacy of the masseteric muscles after intramuscular injection of botulinum toxin A (BTX-A) for the treatment of patients with concurrent temporomandibular disorders (TMD) and bruxism. Thirty patients with TMD associated with bruxism were randomised into three groups (n=10 in each group), and treated by bilateral intramuscular injection of BTX-A into the masseter, placebo, or control. We used an occlusal force analysis system to collect several measures of occlusal force such as duration of biting and closing, the maximum occlusal force, and the distribution of occlusal force. The occlusal force in the intercuspid position was reduced in all three groups. There was a significant difference between the BTX-A and placebo groups (F(df=1)=8.08, p=0.01) but not between the control group and the other two(F(df=1)=4.34, p=0.047). The duration of occlusion was significantly increased in the BTX-A group after 3 months' treatment (t=4.07, p=0.003). The asymmetrical distribution of occlusal force was reduced in all three groups, but not significantly so (Levene's test F(df=2)=0.25, p=0.78,ANOVA F(df=2)=0.50, p=0.61). Treatment of TMD with BTX-A is effective in reducing the occlusal force, but psychological intervention plays an important part in treatment.