Apparatus and methods for adjustably retaining an oral appliance to an abutment assembly are disclosed. In one variation, a securement apparatus can comprise a sleeve having a sleeve frame and a number of locking flaps. The sleeve can define a lumen therethrough for positioning upon an abutment assembly. The locking flaps can have varying length dimensions and can project radially inward or outward relative to the sleeve frame. The outward flaps can lock against surface features defined along an inner surface of a coping coupled to the oral appliance and the inward flaps can lock against surface features defined along a portion of the abutment assembly. The sleeve can release the oral appliance from the abutment assembly when the locking flaps of the sleeve are actuated by an actuation unit.