Malfunctioning brainstem autonomic neurons responsible for muscular control of the upper airway are the cause of the inappropriate collapse of the muscular walls and obstructions (apneas) of the upper airway while asleep. The cause of these sick neurons is unknown. Rather than obesity causing sleep apnea, it's the sleep apnea which causes obesity, which in turn worsens the sleep apnea. No matter how much weight loss, no matter what oral appliance, no matter what surgical procedures are done, sleep apnea will still be there, because the neurological disease remains unchanged. Until a cause and cure of this neurological disease is found, you will always have to use CPAP (or have a tracheostomy) to prevent the adverse consequences of sleep apnea.