The two prominent oral appliances used in treating obstructive sleep apnea differ in their designs, mid-line traction versus bilateral thrust. From a clinical perspective, it is important to know which design is superior and should be the 'treatment of choice' for improving airway function and sleep quality. These two designs differ in their protrusive mechanisms that are categorized in general under four main types: bilateral compression, bilateral thrust, midline compression and mid-line traction. Although the two designs considered in this proposal have undergone the most rigorous testing individually, well controlled 'head-to-head' trials as proposed here have not been conducted to determine their efficacy within a single test population.