CHAPTER 21 Relining and Rebasing the Removable Partial Denture
Differentiation between relining and rebasing the removable partial denture has been discussed previously in Chapter 1. Briefly, relining is the resurfacing of the tissue of a denture base with new material to make it fit the underlying tissue more accurately. Rebasing is the replacement of the entire denture base with new material. The artificial teeth may need to be replaced in a rebase procedure. Relining removable partial dentures is a common occurrence in many dental practices; however, rebasing is not indicated as often.
In either situation, a new impression is necessary and uses the existing denture base with modifications (Figure 21-1) as an impression tray for a closed-mouth or an open-mouth impression procedure. One of several types of impression materials may be used, such as metallic oxide impression paste, rubber-base or silicone elastomers, tissue conditioning materials, or mouth-temperature wax. With a tooth-supported prosthesis, the impression method (open- or closed-mouth) is not as critical. In deciding between a closed-mouth and an open-mouth impression method for relining a distal extension removable partial denture, a major consideration is the resiliency of the mucosa covering the residual ridge. As with secondary impression techniques, a firm mucosal foundation can likely accommodate a closed-mouth functional impression technique or an open-mouth selective pressure technique. However, when the mucosa is easily displaced, the open-mouth selective pressure technique is preferable. Both techniques should guard against framework movement during the impression procedure.
Figure 21-1 Use of an existing Kennedy Class I removable partial denture base as a tray during a reline impression. The selective pressure impression philosophy requires space for the impression material that is greater over the ridge crest (secondary stress bearing area) than at the buccal shelf region (primary stress bearing area). A pear-shaped laboratory bur is used to provide general relief (0.5 to 1.0 mm) of the denture base, with additional relief (1.0 mm) obtained over the ridge crest with a #8 round straight shank laboratory bur. Care must be taken to ensure that the tissue surface is relieved of all undercuts that could cause cast fracture when one is recovering the cast from the impression.
Before relining or rebasing is undertaken, the oral tissue must be returned to an acceptable state of health (Figure 21-2). For more information, refer to the Chapter 13 discussion about conditioning abused and irritated tissue.
Figure 21-2 Kennedy Class I modification 1 arch with a removable partial denture that requires relining. Tissue abuse evident at the left buccal shelf region must be corrected before the reline impression is made. Management requires a period of function without the prosthesis or relief of the prosthesis in the affected region along with placement of a tissue resilient liner in an effort to reduce the traumatic effects of pressure.
When total abutment support is available, but for one reason or another a removable partial denture has been the restoration of choice, and support for that restoration is derived entirely from the abutment teeth at each end of each edentulous span. This support may be effective through the use of occlusal rests, boxlike internal rests, internal attachments, or supporting ledges on abutment restorations. Except for intrusion of abutment teeth under functional stress, the supporting abutments prevent settling of the restoration toward the tissue of the residual ridge. Tissue changes that occur beneath tooth-supported denture bases do not affect the support of the denture; therefore relining or rebasing is usually done for reasons that include (1) unhygienic conditions and the trapping of debris between the denture base and the residual ridge; (2) an unsightly condition that results from the space that has developed; or (3) patient discomfort associated with lack of tissue contact that arises from open spaces between the denture base and the tissue. Anteriorly, loss of support beneath a denture base may lead to some denture movement, despite occlusal support and direct retainers located posteriorly. Rebasing would be the treatment of choice if the artificial teeth are to be replaced or rearranged, or if the denture base needs to be replaced for esthetic reasons, or because it has become defective.
To accomplish relining or rebasing, the original denture base must have been made of a resin material that can be relined or replaced. Commonly, tooth-supported removable partial denture bases are made of metal as part of the cast framework. These generally cannot be satisfactorily relined, although they sometimes may be altered by drastic grinding to provide mechanical retention for the attachment of an entirely new resin base, or some of the new resin bonding agent may be used. Ordinarily, a metal base, with its several advantages, is not used in a tooth-supported area in which early tissue changes are anticipated. A metal base should not be used after recent extractions or other surgery, or for a long span when relining is anticipated to provide secondary tissue support. A distal extension metal base ordinarily is used only when a removable partial denture is made over tissue that has become conditioned to supporting a previous denture base.
Because the tooth-supported denture base cannot be depressed beyond its terminal position with the occlusal rests seated and the teeth in occlusion, and because it cannot rotate about a fulcrum, a closed-mouth impression method is used. Virtually any impression material may be used, provided sufficient space is allowed beneath the denture base to permit the excess material to flow to the borders—where it may be turned by the bordering tissue, or, as in the palate, may be allowed to escape through venting holes without undue displacement of the underlying tissue. The qualities of each type of impression material must be kept in mind when the material to be used is selected. Ordinarily, an impression material is used that will record the anatomic form of the oral tissue.
A word of caution should be mentioned when a tooth-supported resin base is relined with autopolymerizing resin as an intraoral procedure. When one or more relatively short spans are to be relined, making an impression for relining purposes necessitates that the denture be flasked and processed. The possibilities that the vertical dimension of occlusion may be increased and that the denture may be distorted during laboratory procedures must be weighed against the disadvantages of using a direct-reline material. Fortunately, these materials are constantly improved with greater predictability and color stability. The possibility that the original denture base will become crazed or distorted by the action of the activated monomer is minimal when the base is made of modern cross-linked resin. However, caution should be exercised to ensure that the older types of resin bases are compatible when one is relining with direct-reline resins.
When relining in the mouth with a resin reline material is done with an appropriate technique, the results can be highly satisfactory, with complete bonding to the existing denture base, good color stability, permanence, and accuracy. The procedure for applying a direct reline of an existing resin ba/>