The patient is instructed to keep the teeth together until asked to open. The record is left in place until the material has hardened. The bite registration is removed from the mouth and rinsed under running tap water. It should be inspected to ensure that all of the necessary teeth have been captured. A laboratory knife with a no. 25 blade is used to cut off all excess material on the facial and lingual sides of the prepared teeth (Fig 4-16). Any material that extends over the unprepared teeth adjacent to the preparations should be removed.
Excess thickness is removed from the upper and lower surfaces of the record (Fig 4-17). On the unprepared teeth opposing the preparation(s), enough material should be removed so that little more than the cusp tip indentations remain. Any material that reproduces edentulous ridges, gingival crevices, or the central fossae of the opposing occlusal surfaces is likely to produce incomplete seating of a cast with imperfections in those areas, so it is important to eliminate it (Fig 4-18). The overall thickness of the record should be approximately 4.0 mm, with an equal amount having been removed from its upper and lower aspects.
Fig 4-17 The excess thickness from the upper and lower surfaces of the record are removed.
Fig 4-18 All material contacting soft tissue or the central fossae of the opposing occlusal surfaces is removed.
Fig 4-19 The registration is trimmed along the facial cusps to verify complete seating of the record.
Fig 4-20 The record is placed on the mandibular cast, and complete seating is confirmed.
Fig 4-21 The maxillary cast is placed in the completed record and articulated with the mandibular cast.
Fig 4-22 The mandibular cast is mounted on the articulator using the record.
To verify seating of the casts into the record, its thickness along the facial cusps of the mandibular teeth is cut through completely using a laboratory knife with a no. 25 blade (Fig 4-19). The registration is then rinsed with a hospital-grade disinfectant before proceeding.
The record is set on the mandibular cast, and its complete seating is verified (Fig 4-20). The teeth of the maxillary cast are placed completely into the index while the teeth on the opposite side of the arch and those near the preparation(s) are articulated (Fig 4-21). The record is used to articulate the casts, and the mandibular cast is mounted on the articulator (Fig 4-22).
Fig 4-23 The patient is guided into working excursions on the right (a) and left (b) sides.
Fig 4-24 Right (a) and left (b) lateral interocclusal records are made in wax wafers.
Lateral Interocclusal Record
Lateral interocclusal records are made in the mouth for the purpose of capturing the position of the condyles in their respective fossae. These records are then used to set the condylar guides to approximate the anatomical limits of the temporomandibular joints (TMJs). This allows the maximum benefit from using an articulator, facilitating the fabrication of accurate restorations with minimal time required for intraoral adjustment when the restoration is cemented.
Because the configuration of the TMJs has a strong determining influence on the movements of the mandible, the occlusal morphology of any restoration placed in the mouth must be in harmony with the movements of the mandible to prevent the initiation of occlusal disharmony and trauma. Cusp placement, cusp height, groove direction, and groove depth are all features ultimately affected by TMJ configuration. 9
Armamentarium
Laboratory knife with no. 25 blade
Horseshoe wax wafers
Plaster bowl
Technique
The patient is guided into a CRCP closure, and the position of the mandibular midline in relation to the maxillary teeth is visually noted. The points on the maxillary teeth that would be opposite the mandibular midline if the patient moves the mandible 5.0 mm in both a right and left lateral excursion are measured and marked with a pencil (Fig 4-23). With a hand on the patient’s chin, the dentist asks the patient to open slightly. The dentist then guides the mandible approximately 5.0 mm to the right and closes it until the teeth lightly touch. The dentist explains that this procedure will be repeated with some wax between the teeth and that the patient should bite down carefully until told to stop.
Fig 4-25 The lateral interocclusal record has been trimmed before use.
A slightly warmed wax wafer (Surgident Coprwax Bite Wafer, Heraeus Kulzer) is placed against the maxillary teeth approximately 4.0 mm to the right of center. Using one hand to support the wax, the dentist guides the mandible to the right. The closure practiced previously is repeated until the teeth make indentations in the wax approximately 1.0 mm deep (Fig 4-24). The wax wafer is cooled with compressed air, removed from the mouth, and placed in a plaster bowl of cold tap water. The steps are repeated with a second wax wafer on the left side. After the wax wafer has cooled, a sharp laboratory knife is used to carefully cut off any of the wax that extends distal to the marginal ridge of the most posterior mandibular tooth on both sides of the wafer (Fig 4-25). This ensures that the wax wafer will completely seat on the mandibular cast when the articulator condylar inclination is set. The bite registrations are then rinsed with a hospital-grade disinfectant and placed in an unsealed sterilization bag until ready to be used.
References
1. Lucia VO. Centric relation: Theory and practice. J Prosthet Dent 1960;10:849–856.
2. Lucia VO. A technique for recording centric relation. J Prosthet Dent 1964;14:492–505.
3. Hobo S, Iwata T. Reproducibility of mandibular centricity in three dimensions. J Prosthet Dent 1985;53:649–654.
4. Williamson EH, Steinke RM, Morse PK, Swift TR. Centric relation: A comparison of muscle-determined position and operator guidance. Am J