Bruxism is an oral habit consisting of involuntary non-functional gnashing, clenching, grinding of teeth and is a very common condition in the general population. Various treatment modalities such as occlusal splints, pharmacologic agent and cognitive-behavioral therapy have been investigated for the management of bruxism, but none is reported to be fully effective. Recently locally injected botulinum toxin has been used in various movement disorders, but its usefulness and objective effects on nocturnal bruxism have not been evaluated using objective measures such as polysomnography. Moreover, there is no systematic study about which site is most appropriate for injection to obtain maximal effects.