(4) The completion of the maxillary occlusion rim follows the same procedure as described for the mandibular occlusion rim (E, fig 5-18).

d. Increasing Rim Height. In a few instances, the two rims (18 mm. and 22 mm.) are not high enough to allow the distal ends of the casts to touch when they are placed together. In these cases, the height of the rims is increased by adding single thicknesses of baseplate wax alternately to each occlusion rim until there is at least a 2 mm space between the distal ends of the master casts when they are placed together.

5-15. Stabilization of Occlusion Rims

a. Metallic Oxide Impression Paste (fig 5-19). Stabilization of occlusion rims with metallic oxide impression paste is done as follows.

are

(1) Undercuts on the master cast blocked out with wet asbestos or modeling clay.

(2) Tin foil is adapted to the master cast. A piece of .001 thickness is cut large enough to extend from the midline of the master cast over onto the land area at the side, front, and rear of the cast. A thin layer of petrolatum is applied to the master cast to hold the tin foil in place (A, fig 5-19). The tin foil is burnished to the ridge then lingually over the palate, and facially into the peripheral groove and over the edge of the cast. A piece of cotton roll makes an effective

burnisher and will not tear the tin foil if used carefully. A second piece of tin foil is cut and the same procedure is repeated for the other side of the cast overlapping the first piece at the midline (B, fig 5-19).

(3) Metallic oxide impression paste is mixed according to the manufacturer's directions and is spread evenly over the tissue surface of the occlusion rim (C, fig 5-19). The occlusion rim is placed on the tin foil on the master cast and seated firmly under hand pressure (D, fig 5-19).

(4) After the paste has hardened, the occlusion rim is removed and the loose edges of the tin foil are trimmed and smoothed (E and F, fig 5-19).

b. Polysulfide Base Impression Material. Polysulfide base impression material can be used to stabilize occlusion rims in the same way as metallic oxide impression material, with two differences. Using the polysulfide base impression material, the cast is painted with separating material instead of using tin foil. Secondly, the tissue surface of the occlusion rim must be painted with rubber cement so that the impression material will adhere to it.

c. Autopolymerizing Acrylic Resin. If an occlusion rim is fabricated by using autopolymerizing acrylic resin, no further stabilization is required. For this technique see paragraph 5–56 (2).

5-16. General

a. At this stage in the fabrication of complete dentures, the size of the occlusion rims is approximately equivalent to the amount of space to be occupied by the finished dentures. The denture teeth will be arranged on the occlusion rims. The master casts can be mounted or attached to an articulator (para 5-18) so that the fabrication of the denture or dentures can proceed in the dental laboratory. The articulator should do two things. It should duplicate the relationship between the patient's maxillae and mandible when they are closed together and it should reproduce the movement of the mandible during incising and chewing.

b. There are many types of articulators. All satisfy the first requirement, in a above, but the degree to which they can meet the second requirement depends upon varying refinements in their design. Unless the articulator can be adjusted to conform to the patient's range of chewing movements, and unless the denture teeth are arranged to conform to these movements, the maxillary and mandibular denture teeth will come together differently in the mouth than they do on the articulator.

c. This section describes the measurements and recordings a dental officer makes with each complete denture patient. Then the dental prosthetic specialist transfers them to the articulator so that the master casts can be mounted in the same relationship as are the patient's jaws.

d. The proper use of these measurements and recordings requires the dental prosthetic specialist to understand the antomy of the temporomandibular joint, the events which occur in the masticatory cycles, and the three types of articulators available for use in the dental laboratory.

5-17. Masticatory Cycles

a. Chewing (fig 5-20). The basic chewing movement of the mandible may be described as:

(1) Diagonally downward, forward, and sideward toward the working side (chewing side) as the mouth is opened.

(2) Diagonally upward and backward into the working position.

(3) Complete closure with the inclined planes of the teeth making maximum contact on both sides (centric occlusion).

(4) Return to rest position. (Unless the teeth are actively engaged in chewing, there is a slight space between the occlusal surfaces of the

maxillary and mandibular teeth.) When the mandible is at rest, both condyles are positioned posteriorly in the mandibular (glenoid) fossae. In a left working relation, the right condyle rotates and slides down, forward, and to the left. The left condyle rotates counterclockwise as viewed from above and also shifts laterally to some extent. As it returns to complete the chewing movement, the right condyle travels backward and sideward as the teeth grind the food. The left condyle rotates clockwise and shifts slightly sideward. Both condyles return to their most posterior position in the mandibular (glenoid) fossae.

6

Figure 5-20. Basic chewing movement.

b. Incising (Biting) (fig 5-21). The basic incising movement of the mandible may be described as:

(1) Downward and slightly forward in the midline as the mouth is opened.

(2) Forward and upward until the incisal edges of the mandibular anterior teeth touch those of the maxillary anterior teeth (protrusive position).

(3) Upward and backward to complete closure (centric occlusion).

(4) Return to rest position. When the mandible is at rest, the condyles are in a posterior position in the mandibular (glenoid) fossae. At the start of a protrusive movement, both condyles move slightly forward and down. The condyles then move to their most forward positions on the articular eminences. To complete the movement,

An articulator is a mechanical device representing the temporomandibular joints and the jaws to which maxillary and mandibular casts may be attached. It is used for convenience in setting denture teeth and in perfecting occlusal relationships during the fabrication of prosthodontic restorations. There are two types of articulators, nonadjustable and adjustable.

5-19. Nonadjustable Articulators

a. Plain Line Articulator (fig 5-22). The plain line articulator is the simplest of the three types used in the Army dental service. It is inexpensive, ruggedly constructed, and practically maintenance-free when given reasonable care. It is small and easy to handle and store. This type of articulator has a simple, hinge-type opening and closing movement and lateral and protrusive movements of the average mandible. Since it cannot faithfully reproduce all movements of the patient's mandible, it is best suited for simple fixed partial denture restorations.

b. Fixed Guide Articulator (fig 5-23). The fixed guide articulator is better able to reproduce lateral and protrusive movements of the average

Figure 5-22. Nonadjustable articulator, plain line. mandible. Although it is better suited for complete denture fabrication than the plain line articulator, its use is limited to those patients whose mandibular movements fit the instrument. 5-20. Adjustable Articulators

Adjustable articulators are the most complicated type. They can be adjusted to come closest to duplicating not only the movements of the mandible but also the inclination of the angles of those movements. They are precision instruments which require accurate and careful use.

a. Hanau, Model H2. The standard articulator used in the military dental service is the Hanau, Model H2. It has two basic parts, the movable upper member and the stationary lower member, which is the base of the articulator. (This differs from the situation in the patient's mouth where the mandible moves and the maxillae are stationary. At first this may present a problem in orientation to the dental prosthetic specialist who must remember that the difference does exist.) The component parts of the articulator are as follows:

(1) Incisal pin. The incisal pin is the metal rod at the center front of the articulator. It fits into a hole in the upper member and is held in position by a set screw maintaining a selected amount of opening between the members of the articulator. Unless the dental officer directs otherwise, the flattened top end of the pin is always set flush with the top surface of the upper member. The lower end of the pin is tapered and rests on the incisal guide table of the lower member.