The Hall “Triplex” is likely the final version of the “Universal” Articulator” based on the positional concept of articulator design. (Please see the Hall “Universal” Articulator for basic details of the technique.) Although its construction and materials are of high quality, it is not certain what company manufactured the “Triplex.”
The “Triplex” is also a hinge type articulator; however the hinge mechanism is unique in that it is designed to be released for freedom of movement upon a 45-degree incline. Disk-shaped locks are rolled down to hold the hinge rod in centric position. The reason that the hinge is designed in this manner is to convert the articulator into a grinding machine using the incisal pin. For milling purposes, the incisal pin is secured in a special rotary attachment with a pulley and offset hole to affect an elliptical motion of the pin. Other incisal guides are available: a 45-degree cone and a cup for custom developed guidance. The Hall “Triplex” as well as the Hall “Universal” represents departures in principle from the usual positional articulators (See the Stansbery “ Dental Orient ” and “ Triplex” , both in the collection.) In the “Triplex”, the mandibular cast is changed in relation to the maxillary by moving the cast itself and not the articulator. The articulator remains fixed, and serves only as a means to establish and maintain static relations of the casts to one another according to the plaster records.
Dr. Edgar N. Starcke's articles in the Journal of Prosthodontics have more information on the history of articulators.