Change of the thickness from skin surface to masseter muscle after botulinum toxin injection into human masseter muscle

Abstract

Botulinum toxin is widely used to treat masseter muscle hypertrophy. It affects the end of neuron to decrease acetylcholine secretion, causing muscle atrophy which leads to cure. Change of muscle thickness has been reported in many studies. However, there has been no report about change in the thickness from skin surface to masseter muscle. In this study, we aim to measure not only change of muscle thickness but also the change of thickness from skin surface to masseter muscle by using ultrasonography.

A total of 17 volunteers were enrolled in this study. 10 patients were assigned to an experimental group (injected 25 U of botulinum toxin on both masseter muscle) and 7 to a control group (injected normal saline). Thickness was measured before injection and 4 weeks, 8 weeks, 12 weeks after the injection each at rest and during maximum clenching.

Result showed that thickness from skin surface to masseter muscle did not show significant difference by time at rest (p = 0.063) and maximum contraction state (p = 0.392). There was also no significant difference between experimental group and control group at rest (p = 0.392) and during maximum clenching (p = 0.259). Muscle thickness of experimental group showed a significant difference by time. In conclusion, botulinum toxin injection only affects change in muscle thickness and does not affect thickness from skin surface to masseter muscle.