Rupert E. Hall
Unique, made by Rupert E. Hall
Rupert Hall left no known documentation related to this instrument, so its intent can only be surmised. According to its design, it can be concluded that it was a prototype based on Hall's "conical" theory. The basic premise of the "conical" theory is that geometric solution to mandibular movement is that the mandible rotates around a central axial point located in the region of the external occipital protuberance. In other words, Hall believed that the maxillary teeth conformed to a segment of an arc of an 8 inch cone.
The posterior control consists of a 45 degree guide plate with a center slot and 3 set screws attached to the lower member. On the upper member is a central ball with lateral rods that allow the ball to travel and rotate within the slot. The two upper and one lower set screws can fix the ball and rod assembly at any position along the plate. The controlling mechanism is the incisal pin and guide. The unique incisal guide consists of three sections, each with fixed lateral wings of different degrees, the highest being 45 degrees but with a straight protrusive path.
Dr. Edgar N. Starcke's articles in the Journal of Prosthodontics have more information on the history of articulators.