Abstract: A mandibular-repositioning diagnostic device has an extra-oral mechanism (3) in which an apertured frame (6) and an arm (7) are attached respectively to upper- and lower-jaw trays (1,2), and the arm (7) is coupled via a ratchet-toothed strap (13) to a slider-carrier (16) retained within the frame-aperture (17). Pulling the strap (13) through a latching head (18) on the carrier (16) reduces incrementally the spacing between the arm (7) and frame (6). A ratchet-toothed strap (25) extending lengthwise of the aperture (17) from the carrier (16), is pulled through a latching head (29) on the frame (6) to draw the carrier (16), and with it the arm (7) and lower-jaw tray (2), incrementally forwards relative to the upper-jaw tray (1). The carrier (16) is movable transversely of the aperture (17) to allow lateral-movement between the patient's jaws.