Patients rarely stop wearing an oral appliance due to comfort issues; it does happen, but very rarely. In fact, if an appliance is found to be effective in reducing or eliminating the problem, the likelihood of long term compliance is very high. As high as 95% according to one study published several years ago.
Keep in mind that even though oral appliances do not have as high a success rate as CPAP in the elimination of sleep apnea they are recommended as "First Line Therapy" by the American Academy of Sleep Medicine" for snoring and mild to moderate sleep apnea. The reason for this is that many studies have confirmed that a patient is much more likely to use an oral appliance, continue using it over the long term and use it for more hours each night when compared to CPAP. This would not be the case if they were difficult to wear or uncomfortable.
The patient below actually answered his phone and completed a conversation with his wife while wearing his newly made Herbst appliance. Try doing that with CPAP!
Talking on phone with wife during adjustment appointment.