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Dental Lab Step #3
Model Orientation and, Tooth Set Up and Articulation, and Wax Conditioning

Model Orientation Model Orientation - Suggested Quality Procedures:
  1. Determine and mark the central bearing point of the maxillary (upper) model by locating the median suture line and bisecting it (halfway between the extent of the labrial flange - adjacent to the frenum and the posterior border position) (Figure 5a).

    Figure 5a
  2. Find the ideal mounting point on the upper arm of your articulator by:
    1. Determining the inter-condylar distance on the articulator hinge (Figure 5b), line "A" on Figure 5c.

      Figure 5b
      Figure 5c
    2. Use Figure 5c to determine proper distance from the articulator hinge for the central bearing point "B" on the model for your articulator.
  3. When mounting the upper model to the articulator, be sure to place index marks in the model sufficient to ensure accurate re-mounting of the case after processing.
  4. An intra-oral tracing (gothic arch tracing) is highly recommended for predictable results and to decrease clinical occlusion problems. If the clinical professional does not provide a gothic arch tracing, clinical use of an intra-oral balancer (such as the CobleT1 Balancer) can help minimize occlusal adjustment time and lead to greater success and patient satisfaction.
  5. Casts must be centered in the articulator for best results if a face bow is not used.
1 CobleT is not a trademark of Dentsply.

Model Orientation - Quality Standards:
  1. The mounting is clean and free of plaster debris.
  2. If a semi-adjustable articulator is used, the horizontal condylar angle, Bennett angle, and incisal angle should be set according to the clinician's instructions. It is best to use a protrusive bite registration to determine the correct condylar angle. If not provided, defer to average values (30º condylar, 15º Bennett, and for incisal guidance settings, refer to the suggested "Procedures for the Arrangement and Articulation of Trubyte Anterior and Posterior Teeth", item #4087-A).
  3. Use mounting stone for maximum accuracy.
Model Orientation - Quality Failures
  1. The upper and lower ridges are significantly divergent from a parallel relationship. Note: This can occur with unusual bone resorption patterns.
  2. Inter-arch distance is insufficient to set denture teeth.
  3. Centric relation record: Upper and lower baseplates contact each other (interfering with proper centric relation) in the retro-molar/ tuberosity areas.
  4. The upper and lower models contact each other and interfere with mounting procedures.
Model Orientation Tooth Set Up - Suggested Quality Procedures:
  1. Read the prescription before starting procedure.
  2. If the clinical professional does not choose a tooth mould, select teeth of appropriate size and contour based on the patient's anatomical measurements, face form, gender, and age, if available. A "high smile line" marked on the maxillary wax rim will greatly improve the reliability of the estimate. Base the posterior teeth mould size on the remaining ridge length and anterior mould selection.
  3. Make sure the trial base plate is well adapted to the master model (Figure 6a).

    Figure 6a
  4. Set teeth according to tooth manufacturer's directions for use or clinical professional's instructions.
  5. Use minimal set-up wax to secure the teeth in position.
  6. Use baseplate wax for contouring the wax denture following natural gingival contours or according to clinical professional's instruction.
Tooth Set Up - Quality Standards:
  1. The wax is anatomically contoured (Figure 6b).

    Figure 6b
  2. The anterior tooth position matches the position and incisal length prescribed by the clinical professional or as represented in the wax occlusion rim. Use a Trubyte Alma Gauge to verify (or modify) correct anterior tooth position.
  3. The posterior occlusion is in correct contact in centric, working, and balancing relationships according to the tooth manufacturer's directions for use or according to the clinical professional's instructions (Figures below).

    centric buccal
    centric lingual

    working buccal
    working lingual

    balancing buccal
    balancing lingual
  4. Exposed surfaces of the denture teeth must be free of wax.
  5. The entire set up including the mounting and the articulator must be clean and free of extraneous wax to enhance presentation in the dental office.
Tooth Set Up - Quality Failures
  1. Teeth move during wax contouring.
  2. The wax-up does not follow natural gingival contours. Note the contrasting natural gingival countour (Figure 6c) with non-anatomical features such as the concave papilla and knife-edge margins (Figure6d).

    Figure 6c
    Figure 6d
  3. Debris from waxing units or other foreign material is present in the wax-up
  4. Thickness of wax is not to clinical professional's specifications.
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