Dental Articulators

An articulator is a mechanical hinged device used in dentistry to which plaster casts of the maxillary (upper) and mandibular (lower) jaw are fixed, reproducing some or all the movements of the mandible in relation to the maxilla. The human maxilla is fixed and the scope of movement of the mandible (and therefore the dentition) is dictated by the position and movements of the bilateral temperomandibular joints, which sit in the glenoid fossae in the base of the skull. The temperomandibular joints are not a simple hinge but rotate and translate forward when the mouth is opened.

source ~ wikipedia