Technicians are often tasked with mounting casts to Semi-Adjustable Large Frame Articulators without the aid of a Facebow registration. Over the years, techniques have evolved to do this procedure, however, in the end they are just guesses. Most of the Modern articulators are built based on the studies of Dr. William G.A. Bonwill (1833-1899), who determined that there was an average equilateral triangular measurement of 110mm between the condyles of the mandible, and the median line of the lower centrals (#24 and #25). Using this average position to place the upper and lower casts will elevate our guess to an average, but educated guess.
The Denar, Hanau and Whip Mix articulators all have mounting platforms that will help the technician to place the casts in this measured Bonwill position. The use of these Mounting Platforms is easy!
1. Secure the platform to the lower member of the articulator.
2. Align the maxillary cast in a centered position, using the positioning lines on the platform table.
3. Secure the cast using utility wax, sticky wax or hot glue.
4. Using a mounting stone or plaster, adhere the maxillary cast to the mounting plate of the upper member of the articulator.
5. When the mounting stone has hardened, remove the mounting platform from the upper cast and the lower member of the articulator.
6. Using the bite registration, relate the maxillary and the mandibular casts; hold in place with luting material.
7. Now, with the articulator inverted, adhere the lower cast to the mounting plate of the lower member of the articulator.
8. When the stone has hardened turn the articulator right side up and remove the bite registration materials.
You have now mounted the casts in the proper Bonwill position in the articulator. In this position, the use of average Protrusive Angle (condylar inclination), Immediate Side Shift (Bennett movement) and Progressive Side Shift (Bennett side shift) can be used successfully, without specific patient records provided by the clinician.