Sleep bruxism, an intensified manifestation of rhythmic masticatory muscle activity, characterized by tooth grinding or clenching during sleep, lacks a definitive physiological purpose. This paper posits that physiologically, sleep bruxism is an autonomic self-regulatory response to nighttime occurrences of tachycardia stemming from the brain experiencing microarousals during sleep. Sleep bruxism by triggering the trigeminal cardiac reflex leads to bradycardia. Rhythmic masticatory muscle activity-sleep bruxism, thereby, serves to slow the heart rate when brain microarousals cause tachycardia.