['To study the effect of Snore Guard on the genioglossus (GG) muscle activity of obstructive sleep apnea (OSA) patients.', 'Fifteen male patients with mild to severe OSA were diagnosed by overnight polysomnographic studies, and were reexamined after using Snore Guard for 2-6 months. The difference in GG muscle activity was then compared.', 'The overnight GG muscle activity decreased significantly with Snore Guard. The levels of GG muscle activity during awake quiet breath and obstructive sleep apnea were higher than in sleepstate quiet breath without Snore Guard, and significantly decreased with Snore Guard. The increase in GG muscle activity during sleepstate quiet breath with Snore Guard was not statistically significant. The fluctuating GG muscle activity without Snore Guard was effectively improved by treatment with the appliance.'] Do changes in genioglossus muscle activity in obstructive sleep apnea patients with and without snore guard?