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.
Figure 17-1 Posterior occlusion of a maxillary complete denture opposing a Class I mandibular removable partial denture. The stability of the maxillary complete denture can be promoted by developing balanced occlusion as shown.
Figure 17-2 Bilateral distal extension mandibular removable partial denture opposed by natural dentition in the maxillary arch. Working contacts are achieved, balancing contacts are purposefully avoided because they would not enhance the stability of the restoration, and protrusive balance is avoided in favor of an acceptable appearance and a favorable occlusal plane.
Figure 17-3 Opposing Class I partially edentulous arches arranged to allow working side contacts of opposing posterior teeth with balancing contact arranged to minimize tipping of the maxillary removable partial denture and to broadly distribute forces accruing to its supporting structures (abutments and residual ridges).
Figure 17-4 When occlusion is developed for a Class II removable partial denture (maxillary or mandibular), only working side contacts are necessary, as the cross-arch framework stability gained from tooth engagement provides resistance to movement. Balancing side contacts do not enhance stability beyond that provided by the contralateral teeth.
Figure 17-5 Mandibular posterior teeth should not be arranged distal to the upward incline (ascending ramus) of the residual ridge. The molar tooth has been placed just anterior to a mark on the cast land area designating the beginning incline.
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.
Figure 17-6 The posterior teeth in this distal extension with a narrower buccal-lingual width than the original teeth have been selected, and they are placed relative to the primary support (buccal shelf) to distribute the functional load to the most anatomically favorable location in a manner that reduces leverage effects.
Figure 17-7 A, Maxillary molar occluded in a normal horizontal relationship to the opposing molar. B, The resultant position is lateral to the supporting crest of the residual ridge. This position is functionally unfavorable because of the potentially unstable leverage effects; however, stability can be improved by arranging simultaneous working and balancing contacts in the occlusal scheme.
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.
The first method is used when sufficient opposing teeth remain in contact to make the existing jaw relationship obvious, or when only a few teeth are to be replaced on short denture bases and no evidence of occlusal abnormalities is found. With this method, opposing casts may be occluded by hand. The occluded casts should be held in apposition with rigid supports attached with sticky wax to the bases of the casts until they are securely mounted in the articulator.
At best, this method can only perpetuate the existing occlusal vertical dimension and any existing occlusal disharmony present between the natural dentition. Occlusal analysis and the correction of any existing occlusal disharmony should precede the acceptance of such a jaw relation record. The limitations of such a method should be obvious. Yet, such a jaw relation record is better than an inaccurate interocclusal record between the remaining natural teeth. Unless a record is made that does not influence the closing path of the mandible because of its bulk and/or the consistency of the recording medium, direct apposition of opposing casts at least eliminates the possibility that the patient may have a faulty jaw relationship.
A second method, which is a modification of the first, is used when sufficient natural teeth remain to support the removable partial denture (Kennedy Class III or IV) but the relation of opposing natural teeth does not permit the occluding of casts by hand. In such situations, jaw relations must be established as for fixed restorations with some type of interocclusal/>