The severity of obstructive sleep apnea is categorized in three different levels depends on how many breathing disorder symptoms are develop per an hour during asleep: mild (AHI= 5-15), moderate (AHI= 16-30), severe (AHI= >30).

If a patient is diagnosed as a mild to moderate sleep apnea or moderately high OSA, Oral Appliance is very effective.  However, if any patient is diagnosed as a very severe sleep apnea: AHI= 50, 60, 70, 80...), oral appliance may ot effective because the jaw has limited forward movement to open the airway, and CPAP may have compliance problem because of intolerance to high air pressure through the nose.  

Combination Therapy is utilizing good parts from both Oral Appliance therapy and CPAP therapy. Oral appliance increases volume of the airway by repositioning the jaw forward and CPAP provides low pressured positive air, which is tolerable to patients. 

Combination therapy is very effective for severe obstructive sleep apnea patients, and considered as an ultimate therapy modality for sleep-related breathing disorders.