Provisional crowns - Temporary post crowns - Long-term temporization.
A high percentage of endodontically treated teeth receive a coronal coverage cast restoration, as the rate of clinical success is significantly improved for posterior teeth treated in this manner (Sorensen & Martinoff 1984). It has also been reported that approximately 19% of vital teeth restored with full-coverage cast restorations demonstrate radiographic evidence of periradicular disease (Saunders & Saunders 1998). Consequently, many teeth restored with coronal-coverage cast restorations may present for either endodontic treatment or re-treatment. Endodontic treatment can be completed through an access cavity gained in a well-fitted good quality cast restoration (Beach et al. 1996). However, when the existing restoration is of an unacceptable quality, secondary caries is present around its margins or doubts arise about the remaining tooth structure under the restoration, removal of the permanent crown and its replacement with a provisional restoration is mandatory. According to Shillingburg et al. (1997), a temporary restoration must provide pulp protection, positional stability, occlusal function, ease of cleaning, biologically acceptable margins, strength, retention and aesthetics. Little is mentioned in the literature about the importance of microleakage of provisional restorations and their relation to endodontic treatment. Marginal accuracy of the provisional restoration is an important factor in determining its sealing ability. The amount of cement exposed to oral fluids, which depends on the marginal gap, may be related to cement dissolution. A provisional crown made by the indirect technique with a properly selected material provides superior marginal accuracy compared to a crown made by the direct technique (Crispin et al. 1980). Temporary cement sealability is another factor which should be accounted for. In one comparative study of the marginal leakage of six temporary cements, it was found that all the materials tested demonstrated different degrees of microleakage. Zinc phosphate cement and cavity base compound had the best sealing properties (Baldissara et al. 1998). For these reasons, it is essential to remove caries from the remaining tooth structure after the removal of the defective crown and an appropriate sealing material can be used to replace this loss. The access cavity through the core must be temporized between the appointments. The provisional crown should be used for as a short a period as possible and if left for longer period must be checked frequently to replace the temporary cement. Temporary post crowns.
A temporary post crown may be necessary for temporizing broken down teeth, especially when a custom-made cast post and core is planned. Temporary post crowns can be constructed using an aluminum temporary Parapost1 (Whaledent, Mahwah, NJ, USA) combined with polycarbonate temporary crowns and a self-curing acrylic polymer. Alternatively a methacrylate resin crown can be made directly in the mouth using an impression or external surface form. Both techniques are widely used and can provide a good aesthetic result and acceptable margins (Gegauff & Holloway 2001). When microleakage of a temporary post crown cemented with a ZOE temporary cement was compared to microleakage of a cast post and core and a prefabricated post and composite core, it was found that the temporary post crowns leaked significantly more than the permanent types (Fox&Gutteridge1997). A recent in vitro study compared prefabricated posts cemented permanently with zinc oxyphosphate and temporarily with Temp Bond (Sybron Kerr Corp., Orange, CA, USA), and found the temporary posts leaked to a similar degree to the positive controls: there was significantly less leakage amongst the permanently cemented posts (Demarchi & Sato 2002). Clearly, temporary flluting cements such as Temp Bond cannot be expected to provide a perfect marginal seal, and the material sealing ability deteriorates with time (Mashet al.1991). In addition, unlike other temporary crowns, temporary post crowns are often used in teeth with minimal remaining coronal tooth structure, which in turn does not provide adequate contact of the temporary restoration with the axial walls of the remaining core. For these reasons, it is recommended to restore the tooth immediately after obturation with a prefabricated post and core system to minimize microleakage and resultant canal re-contamination (Fox & Gutteridge 1997). If a custom-made cast post and core is selected, the temporary post crown should be left in place for as short time as possible (Fox & Gutteridge 1997). A provisional removable partial denture may also be used as an alternative. With this method, it is unlikely that the coronal seal will be disturbed between appointments (Messer & Wilson1996). Temporization for internal bleaching (walking bleach).
Sodium perborate mixed with water or 35% hydrogen peroxide (Superoxol) is commonly used in the walking bleach technique (Freccia et al. 1982, Rotstein et al. 1991, 1993). A protective cement barrier is placed over the obturation material, especially if Superoxol is used. Polycarboxylate, zinc phosphate, glass-ionomer, IRM or Cavit at least 2 mm thick are recommended (Rotstein & Walton 2002). Sodium perborate as an oxidiser decomposes into sodium metaborate and hydrogen peroxide, releasing nascent oxygen (Naoum2000).The gas release may increase the pressure inside the pulp chamber resulting in loosening or displacement of the temporary restoration. After insertion, the bleaching paste should be removed from the cavity walls and the access is temporized with a suitable material. Cavit and Coltosol used with sufficient bulk can provide a better seal when compared to composite resin materials, ZOE and zinc phosphate cement (Rutledge & Montgomery 1990, Waite et al.1998, Hosoya et al. 2000). Long-term temporization.
Some clinical situations such as apexification or root resorption may require long-term temporization. A permanent- type restoration can be used in these instances. Glass-ionomer cement can be considered an appropriate materialas its sealability for longer periods of time is well documented (Bobotis et al.1989, Lim1990, Barthel et al. 1999). Composite resins are another alternative, but it is preferable to seal the canal opening with another temporary material before placement of composite, to allow relative ease of access and to prevent accidental loss of composite material into the root canal. For severely broken down posterior teeth, pin-retained amalgam restorations can be used for long-term temporization.