Bite registration is a crucial factor in the design and construction of a functional appliance. The construction bite determines the degree of activation built into the appliance, aiming to reposition the mandible to improve the jaw relationship. The degree of activation should stretch the muscles of mastication sufficiently to provide a positive proprioceptive response. At the same time, activation must be within the physiological range of activity of the muscles of mastication and the ligamentous attachments of the temporomandibular joint. Bite registration should achieve a balance between these factors by providing the degree of mandibular protrusion required to achieve the optimum functional stimulus of growth.