Bruxism is a common problem defined by the involuntary grinding or clenching of teeth. This study aimed to compare the treatment outcomes of Botulinum toxin type A (BTX/A) injections into the masseter and lateral pterygoid muscles with injections into the masseter muscle only in patients with bruxism.

Thirty patients with bruxism aged 18–45 years were randomly divided into two groups. Group 1: Bilateral BTX/A injections in the masseter and lateral pterygoid muscle. Group 2: bilateral BTX/A injections in the masseter muscle only. Electromyography (EMG) of the muscles was measured before treatment (t0) and two weeks after treatment (t1). The bruxism questionnaire has four close-ended questions. Patients' answers were recorded five times: t0, t1, six weeks after (t2), three months after (t3), and six months after (t4).

Regarding the bruxism questionnaire scores, group 1 was not superior to group 2 ( p > 0.05), and there was an improvement over time ( p < 0.05). Both groups were equally effective in improving the EMG scores in the masseter muscle ( p > 0.05). However, group 1 outperformed group 2 in improving the lateral pterygoid muscle EMG scores ( p < 0.05). indicating that injection of BTX/A in the lateral pterygoid muscle could benefit patients with bruxism.

The bruxism scores were notably decreased when BTX/A was administered to the masseter muscle alone or in conjunction with the lateral pterygoid muscle. It suggests hyperactivity in the lateral pterygoid muscle may occur when the BTX/A is solely injected into the masseter muscle.