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.