material is removed from the bite fork, which is then placed in a sealed sterilization bag and submitted for steam sterilization.
Fig 5-24 The upper member of the articulator is placed on the condyles (a) and lowered against the support bar (b).
Fig 5-25 The centric latch is engaged to lock the upper member of the articulator in the correct position.
Fit 5-26 The maxillary cast has been mounted on the articulator with the transfer base and transfer assembly removed.
Mounting the mandibular cast
The incisal guide pin is replaced in the upper frame of the articulator with the rounded end down and set at a 2-mm opening. (The second mark above the circumferential line of the pin is aligned with the top edge of the bushing.) The centric latch is snapped closed at the rear center of the articulator (see Fig 5-25). The upper frame of the articulator (with maxillary cast attached) is placed upside down on the laboratory bench with the incisal guide pin extending over the front edge of the bench. The centric relation interocclusal record is set on the maxillary cast. The teeth should seat completely into the depressions in the record.
The mandibular cast is now positioned in the interocclusal record, and it is confirmed that the teeth are fully seated. The maxillary and mandibular casts should not contact at any location. The mandibular cast is removed and soaked, tooth side up, in a plaster bowl for approximately 2 minutes. There should not be enough water in the bowl to cover the teeth.
After the cast has soaked, it is reseated into the record. Mounting stone is mixed to the consistency of thick cream, and a golf ball–sized mound of stone is placed on the bottom of the cast. A small portion of stone is applied to the mounting plate on the lower frame, and the lower frame is hinged down into the soft stone until contact is made between the incisal guide pin and the incisal guide block. The mandibular cast is held to steady it in the interocclusal record until the mounting stone has set (Fig 5-27). The centric latch is rechecked to be sure it has remained closed.
Fig 5-27 The mandibular cast is steadied by hand while the mounting stone sets.
Fig 5-28 The condylar inclination is set at 0 degrees.
Fig 5-29 The lateral translation controls are set at maximum opening.
These features are checked:
Each condylar element should be against the posterior and superior walls of its condylar guide.
The maxillary and mandibular casts should be completely seated in the interocclusal record.
The mounting stone should be engaged in the undercuts on both the base of the cast and on the mounting plate.
The mounting stone is allowed to set completely. Then the mounting accuracy is confirmed by opening the articulator, removing the interocclusal record, and raising the incisal guide pin 2.5 cm (1 inch). A 5-cm (2-inch) strip of no. 10 red-inked silk ribbon is placed between the posterior teeth on both sides, and the teeth are lightly tapped with the condyles retruded. This will leave red dots at centric relation position, as mentioned in chapter 4.
The pieces of 28-gauge green wax are removed from the storage cup and carefully placed over the maxillary cast. If the red dots show through the perforations in the wax, the accuracy of the mounting procedure has been confirmed. If they do not show through, the procedure should be rechecked and the error corrected.
Both casts are removed, with their respective mounting plates, from the articulator. More mounting stone is mixed, and all voids between the casts and mounting plates are filled. The mounting stone is smoothed over using a finger to give it a neat appearance. There must be no stone on the surface of the mounting plate that contacts the articulator frame. The neatness of the casts (or lack thereof) is interpreted by the technician and the patient as an indicator of how much the dentist cares about the work that he or she is doing.
Setting condylar guidance
The medial pair of clamp thumbscrews on the top or backside of the upper frame of the articulator are loosened slightly. Both condylar guides are set at 0 degrees (Fig 5-28). The lateral translation clamp screws on the forward aspect of each condylar guide are loosened, and the immediate lateral translation controls are set at their most open position (Fig 5-29). The incisal guide pin is raised so that it will not touch the plastic incisal stop in any position.
The upper frame, with cast attached, is inverted, and the right lateral interocclusal record is seated on the teeth of the maxillary cast. The teeth should seat completely in the wax indentations. The upper frame 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 gently positioned in the indentations of the wax record. They must be seated completely. The articulator is supported in this position with one hand on the right side. The left condylar element will have moved downward, forward, and inward. It is not touching the condylar guide at any point (Fig 5-30).
Fig 5-30 With the right lateral interocclusal record in place, the left condyle does not contact the superior wall (a) or the medial wall (b) of the guide.
Fig 5-31 The condylar inclination is increased until the condyle contacts the superior wall of the guide.
Fig 5-32 The medial wall of the guide is moved (a) until it contacts the condyle (b).
The inclination of the left guide is set by releasing its clamp screw. The guide is rotated inferiorly until the superior wall again touches the condylar element (Fig 5-31). The holding screw is tightened. Mandibular lateral translation is accommodated by releasing the lateral translation clamp screw and sliding the lateral translation guide laterally until it touches the medial surface of the condylar element (Fig 5-32). The clamp screw is retightened. The right condylar guidance is set by using the record for the left lateral excursion and repeating these steps.
Once the lateral interocclusal records have been made for the diagnostic mounting and the articulator has been set, the data is recorded on the patient’s information card. On the patient’s casts, the correct articulator settings for each side are marked. For example, a condylar inclination of 40 degrees and a lateral translation of 0.3 mm would be