Objective To evaluate occlusal splint type differences in patients with bruxism. Methods Seventeen controls and 51 patients were divided into three subgroups, each assigned to use a different occlusal splint (hard, soft, or semi-soft) for 3 months and assessed by ultrasonography and electromyography (EMG) before (BT) and 3 months after treatment (AT). Results EMG values in all of the occlusal splint groups were significantly lower AT than BT (p< 0.05). BT and AT EMG values in the control group did not differ. Mean muscle thicknesses in bruxism patients was greater than in controls, and the greatest muscle thickness changes occurred with the hard occlusal splint (p< 0.05). Discussion A decrease in EMG activity occurred with all three splint types and was most prominent in the hard occlusal splint group. Ultrasonographic measurements of muscle length and thickness should be used alongside EMG to measure muscle activity in bruxism patients.