PATIENT VISIT 3

Laboratory Procedures

Arrangement of Anatomic (Cuspal) Posterior Teeth

The posterior teeth are arranged primarily for function and to a lesser extent for esthetics.

1. Esthetic criteria

The shape of the arch and the height of the occlusal plane affect posterior esthetics.  A tooth arrangement which is too wide posteriorly will give the appearance of too many teeth in the mouth.  If the teeth are arranged too far toward the tongue or palate, there will be a dark space between the cheek and the teeth when the patient talks or smiles.  Therefore, the arch width of the posterior teeth must harmonize with the width of the patient's face.  This width, in turn, is related to the width of the jaws supporting the soft tissues of the face.

The occlusal plane must be level with the incisal edges of the anterior teeth.  If it is too low, or too high, the patient will not look natural and also will have difficulty masticating.  Remember, the posterior teeth should not appear longer than the anterior teeth when the patient smiles otherwise the patient will have a reverse smile.

    

                          Acceptable Curvature                                    unacceptable reverse curvature

2. Functional criteria

The placement of posterior teeth for function may be divided into three parts, although all of these are involved as each tooth is set.  These parts are as follows: a) the height and the orientation of the occlusal plane, b) the bucco-lingual relationship of the teeth to the ridge, and c) the relationship of the teeth to their antagonists.

a. The height of the occlusal plane.
The height of the occlusal plane anteriorly is determined by the placement of the anterior teeth (Esthetic), the corners of the mouth and the dorsum of the tongue.  Posteriorly, it terminates two-thirds of the way up the retromolar pad.  The occlusal plane is located, in general, halfway between the maxillary and mandibular ridges.
Note: When the casts are related on the articulator in centric relation, and have the correct vertical dimension, two generalizations will serve as a guide to the proper division of the inter-arch distance by the teeth:
1. Teeth generally divide the inter-arch distance in half.
2. The incisal edge of the mandibular central lines on a plane which parallels the mandibular ridge crest and intersects the retromolar pad at two-thirds of its height.

b. The bucco-lingual relation of the teeth to the ridge.
The central fossa of the mandibular first molar should be over the center of the crest of the mandibular ridge.  This relationship is necessary to prevent unfavorable leverages which would cause the denture to tip and to prevent crowding of the tongue which would cause the patient to dislodge the denture.

c. The relationship of the teeth to each other.
The relationships of the teeth in maximum intercuspation are very specific.  Centric relation is equal to maximum intercuspation in complete denture patients.

1. The maxillary teeth overlap the mandibular teeth horizontally. 
2. The long axis of each maxillary tooth is distal to that of the corresponding mandibular tooth. 
3. Each tooth in both arches is opposed by two teeth, except the mandibular central incisor and the maxillary second molar.


3. Arranging the Maxillary Teeth:

a. Place the right maxillary first premolar with its long axis at right angles to the occlusal plane.  The buccal and lingual cusps are placed on the plane.

b. Place the right maxillary second premolar in like manner.  Align the buccal surfaces of the premolars and the canine with the edge of metal or plastic occlusal plane template.

c. The mesio-buccal and mesio-lingual cusps of the right maxillary first molar touch the occlusal plane.  The disto-buccal cusp is raised about 1/2 mm and the disto-lingual cusp is raised about 1/2 to 3/4 mm above the occlusal plane.

d. All of the cusps of the second molar are raised from the occlusal plane following the position of the first molar.  The mesio-buccal cusp should be about 1 mm from the occlusal plane.

e. Follow the same procedure in placing the posteriors on the opposite side.

This is an average arrangement and modifications should be made as individual conditions indicate.

4. Arranging the mandibular teeth.

a. Remove enough wax from the mandibular occlusion rim on the right side to have space for the posterior teeth.

b. Mark the land areas of the mandibular cast with a pencil to serve as a guide in tooth arrangement.  With the mandibular record base removed, place a mark on the land where the mandibular ridge turns superiorly (A).  This will represent the posterior limit for tooth arrangement( don't set teeth beyond this point).

c. With a pencil, use a ruler to mark the crest of the mandibular ridge from the base of the retromolar pad to the canine area . This will identify the crest of the mandibular ridge (B). Replace the mandibular record base and occlusion rim, and using a straight edge, extend the previous markings onto the wax rim to serve as a guide when arranging the maxillary teeth. Repeat this procedure for the other side.

d. Set the right mandibular first molar in approximately its correct position but slightly high in occlusion.  Close the articulator carefully to bring the mandibular molar into its proper position.  Guide it to the correct occlusal relation with the maxillary first molar and maxillary second premolar, making certain that the incisal guide pin remains in contact with the incisal table during all excursions.

e. Follow the same procedure in placing the right mandibular second molar and second premolar.

f. In some instances, there is not sufficient space for the mandibular first premolar.  For esthetic reasons, it is usually advisable to grind the mandibular first premolar to fit the available space rather than altering the anteriors.

j. Follow the same procedure in placing mandibular teeth on the left side.

h. Clean up the wax and prepare the denture for the try-in appointment.  Remove all wax from the teeth. Flame the wax to smooth it.  Carve the denture bases to realistically resemble the supporting structures of a person who has teeth.  Recreate gingival crevices and canine prominences in the wax.  Then flame the wax to smooth.  Stipple the tissue surface with a tooth brush or Robinson bristle brush to further simulate reality.  Psychologically, the patient is more likely to accept a natural looking, neatly waxed trial denture than a messy, poorly waxed approximation of the completed denture.