Fundamentals of Fixed Prosthodontics. James C. Kessler
is placed between the posterior teeth on both sides. The teeth are tapped together lightly with the condyles against the posterior wall of the condylar guide, leaving red dots that represent the contacts at centric relation position, as described in chapter 4.
The pieces of 28-gauge green wax that have been stored in a cup are retrieved and lightly placed on the teeth of the maxillary cast. The accuracy of the mounting is confirmed if the red dots are visible through the perforations in the wax. If they are not visible, the procedure should be rechecked and the error corrected.
The casts and their mounting plates are removed from the articulator. Additional mounting stone is mixed to fill any voids between the casts and their mounting plates. The mounting stone is smoothed with a finger to give it a neat appearance. No stone should remain on the surface of the mounting plate that will contact the articulator frame. Both the dental technician and the patient form an impression of the dentist when they see these casts on the articulator, so it is important to make sure that it is a positive one.
Setting condylar guidance
A hex driver is used to loosen the set screw on the underside of each fossa, and the medial side wall is set to a 6-degree progressive lateral translation. The lock screw on each end of the posterior aspect of the upper crossbar of the articulator is released using a hex driver, and both condylar guides are set at 0 degrees. Then the set screw is loosened on the top of each fossa as far as possible to the medial. The incisal guide pin is lifted to prevent it from touching the plastic incisal stop in any position. The centric latch is released.
The right lateral interocclusal record is seated on the maxillary cast attached to the inverted upper member of the articulator. The teeth should seat completely in the wax indentations. The upper member of the articulator is held in the left hand, and the right condylar element is placed in the right condylar guide. The teeth of the mandibular cast are seated gently but completely into the indentations of the wax record.
One hand is used on the right side of the articulator to support it in this position. The left condylar element will have moved downward, forward, and inward. It should not be touching the condylar guide at any point (Fig 5-49).
The inclination of the right protrusive condylar path is increased by rotating the fossa until the superior wall makes contact with the condylar element (Fig 5-50a). The set screw on the back of the upper crossbar is tightened with a hex driver. The immediate lateral translation is set by moving the medial wall of the fossa outward or laterally until it contacts the medial surface of the condylar element (Fig 5-50b). The set screw is retightened. The wax interocclusal record for the left lateral excursion is used to set the right condylar guidance in the same manner.
Fig 5-49 The right lateral interocclusal record causes the left condyle to move away from the superior wall (a) and the medial wall (b) of the guide.
Fig 5-50 To adjust the condylar guide, the condylar inclination is increased until the superior wall contacts the condyle (a), and the medial wall is moved into contact with the condyle (b).
After the articulator is set, the data is recorded on the patient’s information card. The articulator settings for each side are marked on the respective side of the patient’s cast. For example, a condylar inclination of 35 degrees and an immediate lateral translation of 0.6 mm would be recorded as 35/0.6. When teeth are prepared at a future time, working casts can be mounted on the articulator without making new records. The instrument can be reset using the recorded information from the diagnostic mounting.
Anterior guidance
The mounted casts are examined on the articulator. Any nonworking interferences are removed from the casts so that the articulator can move freely while the anterior teeth remain in contact. If the guidance is inadequate for any reason, it is restored to an optimum configuration with a diagnostic wax-up.
The incisal guide pin is raised so that it will be at least 1 mm off the plastic incisal guide block in all excursions (Fig 5-51). Acrylic resin or a light-cured material (Triad) may be used. If a resin is used, the surface of the guide block is moistened with monomer. A half scoop of tray resin is mixed, and, while it is still free-flowing, a small amount is placed on the incisal guide. As the polymerizing resin becomes stiffer, more is added until there is about ¼ inch of it covering the guide block (Fig 5-52). The end of the incisal guide pin and all contacting surfaces of the anterior teeth are lubricated with petrolatum. The articulator is closed so that the teeth occlude completely. The guide pin will penetrate the soft acrylic resin (Fig 5-53). The articulator is moved through all excursions repeatedly, keeping the teeth contacting at all times (Fig 5-54). The tip of the guide pin will mold the acrylic resin to record the pathway of the various movements. The movements are continued until the resin is completely polymerized. The excess is trimmed off. A record of the anterior guidance has been formed on the incisal table (Fig 5-55).
Fig 5-51 The incisal guide pin should not contact the guide block.
Fig 5-52 Acrylic resin is placed on the incisal guide.
Fig 5-53 The guide pin is allowed to close into the soft resin.
Fig 5-54 The articulator is moved through all excursions.
Fig 5-55 An anterior guidance record exists on the guide block.
Fig 5-56 The components of a Spring-Bow are (left to right) the facebow with orbital pointer and the bite fork assembly.
Fig 5-57 The vertical rod of the bite fork assembly is inserted into the bow socket. The flat side is in front, with the empty bite fork clamp to the right.
Hanau Facebow and Articulator
The Hanau Spring-Bow (Whip Mix) is an ear facebow that utilizes a one-piece spring-steel bow (Fig 5-56). It is simple in design and can be used either as a direct-mount or an indirect-mount device with the removable bite fork assembly and mounting platform.8 The technique for its use is described with the Hanau Series 184 Wide-Vue articulator (Whip Mix), an arcon semi-adjustable instrument.