In some embodiments, a system for improving a user's breathing includes a mask configured to be positioned on a user's face to deliver gas to the user, a first oral appliance arch configured to be worn in the user's mouth on the user's mandibular dentition, a first tension element coupled to the first oral appliance arch, an adjustment device coupled to the mask, and a control system. The adjustment device is configured to receive the first tension element and to adjust the position of the first tension element to adjust the forward position of the first oral appliance arch, such that the when the mask is positioned on the user's face and the first oral appliance arch is worn on a user's mandibular dentition, the forward position of the user's mandible is adjusted.