Occlusal splints are commonly used for the treatment of nocturnal bruxism. This study investigated the effects of hard and soft occlusal splints on nighttime muscle activity. The nocturnal muscle activity of ten participants was recorded while wearing a hard and then a soft occlusal splint. The hard occlusal splint significantly reduced muscle activity in eight of the ten participants. The soft occlusal splint significantly reduced muscle activity in only one participant while causing a statistically significant increase in muscle activity in five of the ten participants.