36 Conventional Postendodontic Therapy

Root canal posts are used in the reconstruction of endodontically treated teeth that have extensive coronal defects to serve as an anchor for any build-up or for enhancing retention of the definitive restoration. However, the preparation of the root canal for the post space, and the subsequent functional load transfer via the post represent a potential risk to the integrity of the tooth root. This risk, which could, for example, lead to a vertical root fracture, should be kept as low as possible. Thus it must be kept in mind when planning postendodontic therapy that not every endodontically treated tooth must be restored using a post.

Whether a root post restoration will be required depends on the extent of the coronal defect and the expected occlusal loading (Schwartz and Robbins, 2004; Bolla et al., 2007). If the decision is made to incorporate an intracanal post, it should be constructed in such a way that the root is not excessively weakened; there will always be a trade-off between preserving the tooth substance and achieving maximum possible retention of the post.

Decisions about the design of the restoration and the materials to be used must be made on a case-by-case basis, as well as decisions about the dimensions of the root canal post and the luting agent to be used. Although the use of fiber-reinforced composite posts cemented with composite materials followed by a coronal build-up is currently very popular, the more traditional metal posts have maintained their prosthodontic value.

The goal is timely reconstruction of the endodontically treated tooth with a cusp-stabilizing definitive restoration so that the tooth is capable of withstanding functional load, and cusp fracture or bacterial microleakage is prevented (Ray and Trope, 1995). A root post is only indicated in the case of a large coronal defect and reduced strength of the dentinal walls post preparation.

It is not the post itself but rather the crown surrounding the dentin core that stabilizes the tooth—the so-called “ferrule effect”— (Isidor et al., 1999). In fact, the use of a post actually weakens the root due to additional loss of hard tissue substance, and increases the risk of perforation during final preparation. If transfer of the functional load from the post to the root results in root fatigue, the root may undergo a vertical fracture and the tooth may have to be extracted.

Therefore, passive, tapered posts, selected on the basis of the available root length and diameter, have proved most successful (Morgano, 1996; Lambjerg-Hansen and Asmussen, 1997; Nergiz et al., 2002). In contrast to the active screw-type posts, which are associated with the development of tensile forces at the end of the flank of the threads, the retention of passive posts is achieved via friction between the parallel walls of the preparation and the post surface, following cementation. Using the correctly shaped preparation instruments, tapered, passive posts can be snugly fitted against the root canal walls with a cement thickness of approximately 50 μm (Schmage et al., 2005).

As their shape conforms to the shape of the root canal, tapered posts—as opposed to cylindrical posts—can be inserted deeper within the canal. The advantage of this is that the functional load from the post can be distributed over a larger area of the root. Tapered posts must, however, be supported at their coronal end by the floor of coronal pulp cavity to avoid the “wedge effect” (Hofmann 1988). Although their retention is inferior to threaded posts, it can be markedly increased by mechanical micro-retention such as sandblasting the post surface or roughening the root canal wall, accurate fitting of the post, or chemical conditioning of the post (Nergiz et al., 1997; Sahafi et al., 2003; Schmage et al., 2006).

The retention of passive, tapered post systems has proved to be clinically adequate as long as the post length is at least as long as the crown height and a crown preparation at least 2-mm wide is made in the dentin (Smith and Schuman, 1997; Rosentritt et al., 2000). Decementation of the post build-up, and subsequent failure of the restoration, is generally the result of using a short post.

For cementing the post, fine-powder zinc oxide phosphate cement has been used successfully for decades, but composite cement is also indicated for cementing metal posts, and it provides a better seal against microleakage (Schmage />

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