17: Occlusal Relationships for Removable Partial Dentures

CHAPTER 17 Occlusal Relationships for Removable Partial Dentures

The fourth phase* in the treatment of patients with removable partial dentures is the establishment of a functional and harmonious occlusion. Occlusal harmony between a removable partial denture and the remaining natural teeth is a major factor in the preservation of the health of their surrounding structures. In the treatment of patients with complete dentures, the inclination of the condyle path is the only factor not within the control of the dentist. All other factors may be altered to obtain occlusal balance and harmony in eccentric positions to conform to a particular concept and philosophy of occlusion.

Balanced occlusion is desirable with complete dentures because unbalanced occlusal stresses may cause instability of the dentures and trauma to the supporting structures. These stresses can reach a point that causes movement of the denture bases. In removable partial dentures, however, because of the attachment of the removable partial denture to the abutment teeth, occlusal stresses can be transmitted directly to the abutment teeth and other supporting structures, resulting in sustained stresses that may be more damaging than those transient stresses found in complete dentures. Failure to provide and maintain adequate occlusion on the removable partial denture is primarily a result of (1) lack of support for the denture base, (2) the fallacy of establishing occlusion to a single static jaw relation record, and (3) an unacceptable occlusal plane.

In establishing occlusion on a removable partial denture, the influence of the remaining natural teeth is usually such that the occlusal forms of the teeth on the removable partial denture must be made to conform to an already established occlusal pattern. Occlusal adjustment or restoration may have altered this pattern. However, the pattern present at the time the removable partial denture is made dictates the occlusion on the removable partial denture. The only exceptions are those in which an opposing complete denture can be made to function harmoniously with the removable partial denture, or in which only anterior teeth remain in both arches and the incisal relationship can be made so that tooth contacts do not disturb denture stability or retention. In these situations, jaw relation records and the arrangement of the teeth may proceed in the same manner as with complete dentures, and the same general principles apply.

With all other types of removable partial dentures, the remaining teeth dictate the occlusion. The dentist should strive for planned contacts in centric occlusion and no interferences in lateral excursions. Although a functional relationship of the removable partial denture to the natural dentition sometimes may be adjusted satisfactorily in the mouth, extraoral adjustment is often easier for both dentist and patient, is more accurate, and can be accomplished in a more comprehensive manner.

Establishment of a satisfactory occlusion for the removable partial denture patient should include the following: (1) analysis of the existing occlusion; (2) correction of existing occlusal disharmony; (3) recording of centric relation or an adjusted centric occlusion; (4) harmonizing of eccentric jaw movements for a functional eccentric occlusion; and (5) correction of occlusal discrepancies created by the fit of the framework and during processing of the removable partial denture.

Desirable Occlusal Contact Relationships for Removable Partial Dentures

The following occlusal arrangements are recommended to develop a harmonious occlusal relationship among removable partial dentures and to enhance stability of the removable partial dentures:

3. Bilateral balanced occlusion in eccentric positions should be formulated when a maxillary complete denture (Figure 17-1) opposes the removable partial denture. This is accomplished primarily to promote the stability of the complete denture. However, simultaneous contacts in a protrusive relationship do not receive priority over appearance, phonetics, and/or a favorable occlusal plane.
4. Working side contacts should be obtained for the mandibular distal extension denture (Figure 17-2). These contacts should occur simultaneously with working side contacts of the natural teeth to distribute the stress over the greatest possible area. Masticatory function of the denture is improved by such an arrangement.
5. Simultaneous working and balancing contacts should be formulated for the maxillary bilateral distal extension removable partial denture whenever possible (Figure 17-3). Such an arrangement will compensate in part for the unfavorable position the maxillary artificial teeth must occupy in relation to the residual ridge, which is usually lateral to the crest of the ridge. However, this desirable relationship often must be compromised when the patient’s anterior teeth have an excessively steep vertical overlap with little or no horizontal overlap. Even in this situation, working side contacts can be obtained without resorting to excessively steep cuspal inclinations.
6. Only working contacts need to be formulated for the maxillary or mandibular unilateral distal extension removable partial denture (Figure 17-4). Balancing side contacts would not enhance the stability of the denture because it is entirely tooth supported by the framework on the balancing side.

A harmonious relationship of opposing occlusal and incisal surfaces alone is not adequate to ensure stability of distal extension removable partial dentures. In addition, the relationship of the teeth to the residual ridges must be considered. Bilateral eccentric contact of the mandibular distal extension removable partial denture need not be formulated to stabilize the denture. The buccal cusps, however, must be favorably placed to direct stress toward the buccal shelf, which is the primary support area in the mandibular arch. In such positions, the denture is not subjected to excessive tilting forces (Figure 17-6). On the other hand, the artificial teeth of the bilateral, distal extension, maxillary removable partial denture often must be placed lateral to the crest of the residual ridge (Figure 17-7). Such an unfavorable position can cause tipping of the denture, which is restrained only by direct retainer action on the balancing side. To enhance the stability of the denture, it seems logical to provide simultaneous working and balancing contacts in these situations if possible.

Methods for Establishing Occlusal Relationships

Five methods of establishing interocclusal relations for removable partial dentures will be briefly described. Before any of these is described, it is necessary that the use of a facebow mounting of the maxillary cast and pertinent factors in removable partial denture occlusion be considered. The technique for applying the facebow has been described briefly in Chapter 12.

Although a hinge axis mounting may be desirable for complete oral rehabilitation procedures, any of the common types of facebow will facilitate mounting of the maxillary cast in relation to the condylar axis in the articulating instrument with reasonable accuracy and are acceptable for a removable partial denture. As was suggested in Chapter 12, it is still better that the plane of occlusion be related to the axis-orbital plane. Because the dominant factor in removable partial denture occlusion is the remaining natural teeth and their proprioceptive influence on occlusion, a comparable radius at the oriented plane of occlusion in an acceptable instrument will allow reasonably valid mandibular movements to be reproduced.

Semiadjustable articulators can simulate but not duplicate jaw movement. Realization of the limitations of a specific instrument and knowledge of the procedures that can overcome these limitations are necessary if an adequate occlusion is to be created.

The recording of occlusal relationships for the partially edentulous arch may vary from the simple apposition of opposing casts (by occluding sufficient remaining natural teeth) to the recording of jaw relations in the same manner as for a completely edentulous patient. As long as some natural teeth remain in contact, however, the cuspal influence that those teeth will have on functional jaw movements dictates the placement of the artificial teeth and the occlusal scheme.

The horizontal jaw relation (planned intercuspal position or centric relation) in which the restoration is to be fabricated should have been determined during diagnosis and treatment planning. Mouth preparations also should have been accomplished in keeping with this determination, including occlusal adjustment of the natural dentition, if such was indicated. Therefore one of the following conditions should exist: (1) centric relation and planned intercuspal position coincide with no evidence of occlusal pathologic conditions, therefore the decision should be to fabricate the restoration in centric relation; (2) centric relation and the planned intercuspal position do not coincide, but the planned intercuspal position is clearly defined and the decision has been made to fabricate the restoration in the planned intercuspal position; (3) centric relation and the planned intercuspal position do not coincide and the intercuspal position is not clearly defined, therefore the decision should be made to fabricate the restoration in centric relation; and (4) posterior teeth are not present in one or both arches, and the denture will be fabricated in centric relation.

Occlusal relationships may be established by using the most appropriate of the following methods to fit a particular partially edentulous situation.

Jan 17, 2015 | Posted by in Prosthodontics | Comments Off on 17: Occlusal Relationships for Removable Partial Dentures
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