An orthodontic appliance may include an outer shell having a plurality of cavities shaped to receive the patient's teeth and generate one or more of a force or a torque in response to the appliance being worn on the patient's teeth. The orthodontic appliance may also include an inner structure having a stiffness different than a stiffness of the outer shell. The inner structure can be positioned on an inner surface of the outer shell in order to distribute the one or more of a force or a torque to at least one tooth received within the plurality of cavities.