Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles

Abstract

This study examined changes in masticatory function after botulinum toxin type A (BTX-A) injection using objective and subjective tests during 12weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M-T group) were injected. Forty subjects were assigned into two groups; M group (n=20) and the M-T group (n=20). The Meditoxin(®) was used as BTX-A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4weeks and gradually recovered with time. Compared with the pre-injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4weeks after the injection (P<0·05). When the results between M group and M-T group were compared, scores of VAS and FIA were significantly different 4weeks after the injection (P<0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX-A injection into the masticatory muscle after 4 and 8weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12weeks. Furthermore, after 8weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.