Ch12.qxd 10/10/03 11:55 AM Page 111 Occlusion and removable 12 prosthodontics R. Jagger – Occlusal analysis Synopsis – Clinical stages Occlusal considerations for removable – Onlay dentures prostheses are essentially the same as for • Complete dentures fixed restorations. – Occlusion for complete dentures The approach to establishing occlusion for – Occlusal vertical dimension removable partial dentures is usually – Artificial teeth conformative. Partial dentures should not – Balanced occlusion transmit excessive forces to supporting – Lingualised occlusion tissues nor interfere with any contacts in – Occlusion and patient satisfaction intercuspal position or in functional – Clinical stages movements. Occasionally a reconstructive approach using onlays is used. Occlusion for complete dentures has three significant differences: Good occlusal practice for removable dentures is very similar to that described for fixed prostheses. • The absence of natural teeth in edentulous Partial dentures should not transmit excessive forces to patients may present significant difficulties supporting tissues nor interfere in intercuspal position or in determining an acceptable occlusal in functional movements. The occlusal form is usually vertical dimension. conformative with the natural teeth. Occasionally a • Complete denture occlusion is always a reconstructive approach using onlays is used. Occlusion reorganised occlusion. for complete dentures, however, has three significant • Absence of teeth produces problems of differences: denture stability (resistance to displacement by lateral forces), particularly • The absence of natural teeth in edentulous patients of the mandibular complete denture. The may present significant difficulties in determining an stability of complete dentures is optimised acceptable occlusal vertical dimension (OVD). by a balanced occlusion/articulation. • Complete denture occlusion is always a ‘reorganised’ occlusion. This chapter provides an overview of •Absence of teeth produces problems of denture occlusion for partial and complete removable stability (resistance to displacement by lateral forces), prostheses, including discussion of both particularly of the mandibular complete denture. The clinical and laboratory procedures. stability of complete dentures is optimised by a balanced occlusion. Key points PARTIAL DENTURES • Partial dentures Occlusion: conformative/reorganised – Occlusion: conformative/reorganised approaches The usual goal of partial denture treatment (in respect of –Treatment planning for partial dentures the occlusion) is to position the artificial teeth so that there is even contact and maximum intercuspation (MI) in the 111 Ch12.qxd 10/10/03 11:55 AM Page 112 SECTION 3 CLINICAL PRACTICE AND THE OCCLUSION intercuspal position (ICP). For more extensive partial Insertion – occlusal correction dentures, such as bilateral distal extension saddle dentures, the aim might also be to achieve a balanced occlusion. Minor interferences are often present, as in complete Occasionally, instead of this conformative approach a dentures, due to previous clinical or laboratory errors. reorganised approach is used when onlays or an onlay The dentures must be adjusted so that the natural teeth appliance covers some or all of the occluding surfaces of meet in precisely the same way both with and without the the dental arch. dentures in place. Often chairside adjustment by selective grinding is sufficient. Marks produced by articulating paper must be Treatment planning for partial dentures interpreted with caution, by visual confirmation and by When replacing missing teeth, it is of evident importance asking the patient for his or her perception of how the that treatment is based on a comprehensive treatment teeth contact. The patient should be asked whether the plan. The treatment plan must be derived from a careful teeth contact evenly or meet on one side first. If aware of history, examination and the use of appropriate special a premature contact, can the patient feel which tooth or investigations. For the partially dentate patient, special teeth meet first. Again, this information must be used investigations include radiographs, tooth vitality tests with caution. and usually articulated, surveyed study casts. The When maxillary and mandibular dentures are being treatment plan for the partially dentate patient must inserted, each denture must be checked and corrected include a detailed design of any prosthesis. separately. A final correction is done with both dentures in place. Very occasionally the occlusal errors are so large that Occlusal analysis chairside correction is not possible. In these cases, the During the treatment-planning phase it is important to artificial teeth causing the interferences should be ground analyse the occlusion to detect any tooth alignment off. Wax can be placed on the base in those regions and problems, such as overeruption, that might prevent the CR can be rerecorded. If the denture has been returned to construction of a prosthesis with a satisfactory occlusion. the clinic with the casts, a new occlusal record can be A decision must be made as to whether any preprosthetic taken, the casts remounted and the occlusion corrected in occlusal adjustments or alterations are necessary; for the laboratory. Otherwise an overall impression should be example, the removal of any tooth cusp interferences along taken with the denture(s) in place. The impressions the arc of closure into ICP. Occlusal analysis is done both should be cast and the dentures rearticulated, reset and in the mouth and by the use of articulated study casts. retried. A detailed account of clinical occlusal analysis has been given in Chapter 5. Study casts may be articulated without an occlusal Onlay/overlay dentures record if intercuspal position is coincident with centric Whereas complete dentures always have a reorganised relation (CR) and if there are sufficient teeth to provide occlusion, partial dentures usually have a ‘conformative’ stable intercuspation of study casts. If there are insufficient occlusion. teeth, wax occlusal rims are usually used to determine Areorganised approach for partial dentures may be centric jaw relation (CR). considered: Clinical stages • to correct an overclosed occlusion • to improve the occlusion, for example when there is a Recording centric jaw relation gross discrepancy between RCP and the intercuspal position. The working casts also may be articulated without an occlusal record if centric occlusion (CO) is coincident with This approach is achieved by the use of onlays. CR and if there are sufficient teeth to provide stable ICP When a component of the partial denture extends to of the casts, If there are insufficient teeth, wax occlusal cover the greater proportion of the occlusal or incisal rims are used. The wax may be placed on shellac or surface of a tooth it is called an onlay or overlay. Onlays acrylic base plates, or more commonly on the metal may be used to cover one, many or all of the teeth in the framework. If the wax rims are to be placed on the dental arch. They may be made of acrylic resin or cast- framework it is important to ensure beforehand that the metal denture base materials. An alternative method is to framework fits accurately and does not interfere with the add acrylic resin onto retention tags in metal that has been occlusion in retruded contact position (RCP, ICP) or in cast to the fitting surface of the teeth. This has the lateral excursions. advantage that the occlusal surface may be easily adjusted. 112 Ch12.qxd 10/10/03 11:55 AM Page 113 OCCLUSION AND REMOVABLE PROSTHODONTICS 12 A B C D Fig. 12.1 A–D A mandibular partial onlay denture. The appliance replaces one of similar design that had been worn for approximately 20 years. Diagnostic or temporary onlays are usually constructed in ‘better’ dentures. Nevertheless, it is important to under- acrylic resin. stand the principles of occlusion related to removable The use of an onlay appliance to correct an overclosed prostheses in order to try to provide optimum treatment occlusion is shown in Figure 12.1. best suited to each individual. The clinician should have a Extensive coverage of teeth by occlusal onlays can clear picture of the occlusion that he or she is trying to predispose to dental caries. If clinical conditions allow, achieve for each patient. fixed restorations are the preferred treatment. Recommended occlusion for complete dentures COMPLETE DENTURES • Recommended practice is to develop maximum intercuspation of complete dentures to coincide with CR at Occlusion an acceptable OVD. Failure to achieve that can lead to intolerance, usually because of instability of the dentures In a detailed overview of the literature of occlusal or because of pain of the alveolar mucosa as a result of considerations in complete dentures, Palla (1997) noted uneven load distribution and high stress concentrations. that patients’ satisfaction with complete dentures is a • It is also recommended that a balanced occlusion (i.e. complex phenomenon and that the occlusion plays only a harmonious contacts between maxillary and mandibular minor part. Further, there is little evidence to support teeth in all excursive movements) is provided in order commonly held views on the advantages or disadvantages to help give occlusal stability. of tooth form, tooth arrangement or occlusal schemes. Patient satisfaction with dentures does not correlate Occlusal vertical dimension closely with technical quality. For example, patients with greatly decreased