Temporization of an access cavity within a restoration.
The literature is replete with both in vitro and in vivo studies evaluating the sealing ability of endodontic temporary restorative materials in intact teeth. However, many teeth requiring endodontic therapy have large permanent coronal restorations of acceptable quality. Few studies have tested the sealing ability of temporary restorative materials in such situations. Paiet al. (1999) found that dye leakage at the interface between an amalgam restoration and IRM, Caviton and a double seal of Caviton and IRM temporary restorations was less than the leakage between the temporary materials and tooth cavity walls. In another in vitro study, access cavities were prepared entirely in amalgam restorations and temporized with Cavit, Cavit-G, TERM, zinc phosphate cement, polycarboxylate cement, glass-ionomer cement and IRM. Apart from zinc phosphate and polycarboxylate cements, all the tested materials provided a seal that was as leak-proof a s the control teeth which had class I preparations restored with amalgam alone (Turner et al. 1990). Also, it has been demonstrated that access cavities prepared through composite resin restorations and temporized with ZOE or Cavit showed less leakage when compared to access cavities prepared in amalgam restorations and temporized with these two materials (Orahood et al. 1986). In vivo, Beach et al. (1996) showed that both Cavit and IRM could effectively seal access cavities in an IRM temporary restoration, amalgam fillings and gold or porcelain fused to metal crowns.
From these studies, its is reasonable to conclude that access cavities prepared in coronal restorations and temporized with an appropriate temporary filling material can provide as good a seal as that provided by the primary restoration. Nevertheless, these studies were conducted in vitro and may not reflect the actual clinical situation of an aged primary restoration which has been in function for many years. That is why when the temporary restoration is in contact with the tooth structure apical to the primary restoration-tooth interface amore predictable seal can be expected. When doubts arise about the quality and seal provided by the primary restoration, removal of the entire restoration and its replacement with a temporary restorative material is justified (Melton et al.1990) (Table 3).
Table 3. Summary of in vitro and in vivo studies on leakage of temporary endodontic materials in access cavities within coronal restorations.Clinical recommendations.
During material placement, the chamber and cavity walls should be dry. The use of a thin layer of cotton wool over canal orifices is a controversial step during temporization. The advantage is the ease of removal of the temporary restoration without running the risk of unnecessary removal of intact tooth structure or even worse, perforating the floor of the pulp chamber. Placement of a cotton layer can also preclude the accidental blockage of the canal by small fragments of the temporary filling displaced into the canal. The technique was recommended in occlusal cavities by Messer & Wilson (1996) and used in in vivo studies (Krakow et al. 1977, Lamers et al.1980). In another in vivo study, Sjogren et al. (1991) used a sterile foam pellet under the temporary filling without compromising the seal for an extended period of time of up to 5 weeks. However, the use of a cotton layer can introduce complications which may seriously compromise the intended seal. First, it may significantly reduce the thickness of the temporary restoration to increase leakage. Second, it may compromise the stability of the restoration by acting as a cushion allowing displacement during masticatory loading. Third, it could compromise the adaptation of the temporary cement during placement. Fourth, fibres of the cotton pellet may inadvertently adhere to the cavity walls and serve as a wick. Finally, there is an increased risk of leakage through exposed lateral canals (Webber et al.1978, Orahood et al. 1986, Bishop & Briggs 1995). Based on the above, the following empiric recommendations can be made. A small-sized pellet that covers the canal orifice but avoids the flfloor of the pulp chamber, or a thin and well-adapted cotton layer to cover the floor of the chamber may be used. A small sterile and well-adapted piece of polytetrafluoroethylene tape can also be used as a mechanical barrier under the temporary restoration (Stean 1993). The importance of having as much bulk and thickness as possible of the temporary restoration cannot be overstated. The material can be inserted in increments with good condensation into the access cavity to obtain adequate adaptation to cavity walls. The margins should be carefully finished and the occlusion adjusted. Careful removal of the temporary restoration with rotary instruments or the use of ultrasonically energised tips may preclude possible complications (Bishop & Briggs1995).
After completion of endodontic treatment guttapercha should be cut back to within the canal orifices and an intermediary restoration (coronal barrier) placed to protect it. For a variety of reasons, the placement of a permanent coronal restoration may be delayed. It is generally accepted that the sealing quality of the available endodontic temporary restorative materials deteriorates with time (Lamers et al.1980). Few studies have investigated microleakage of temporary restorations placed after root-canal preparation and obturation. Imura et al. in an in vitro study showed that gutta-percha stopping, IRM and Cavit all permitted bacterial penetration of obturated canals. The average times for broth contamination in access cavities closed with gutta-percha, IRM and Cavit were 7.8, 12.9 and 9.8 days, respectively (Imura et al. 1997). Safavi et al. in an in vivo study observed greater endodontic treatment success in teeth restored with permanent restorations within 2 months of completion of root-canal therapy than teeth with temporary restorations. However, the difference did not reach significance (Safavi et al.1987). Due to the possible disintegration of the temporary restorations with time and the potential for canal contamination, it is recommended to restore teeth after endodontic treatment with an immediate definitive coronal restoration after canal obturation.