Aesthetic Posts and Cores
Subir Banerji and Shamir B. Mehta
Restoration of the endodontically treated tooth can prove highly challenging, particularly where there has been a copious loss of coronal tooth tissue. Under such circumstances there is often a need to place a post (commonly referred to as a dowel) in the root canal chamber. The function of a post is primarily to retain a core, which will in turn provide support for the definitive restoration. A post will also provide protection to the remaining tooth structure by distributing occlusal stresses to the root along the post.
It is difficult to define the precise indications for a post. Historically, where there may have been less than half of the coronal volume remaining, the prescription of a post would have been given due consideration.1 Where possible, however, the placement of a post should be avoided, as it may cause further weakening of the tooth, there may be risks of iatrogenic damage (including inadvertent perforations and disturbance of the apical seal), it may render access to the root canal system difficult (should root canal re-treatment or post replacement be required) and further financial costs will be encountered when planning a post and core restoration.
There are a large variety of post and core systems in today’s marketplace. They may be classified in accordance with their shape (tapered versus parallel), their composition (metallic versus non-metallic) and their method of fabrication (direct versus indirect).
Traditionally, the use of parallel-sided metal posts has commonly been advocated. However, the potential risks of root fracture (on account of a marked difference in the modulus of elasticity between root dentine and the post material, of up to and more than 13-fold) is a significant drawback.2 The use of metallic posts is also associated with the risk of corrosion, the need for further tooth preparation to provide retention form, an alteration of the optical properties of the overlying restoration, concomitant darkening of the gingival margin (especially in patients with thin gingival biotypes in the aesthetic zone), as well as difficulties with removal.
In more recent times, the use of posts fabricated in ceramic (zirconia) or composite (based on epoxy resin) has become popular, providing an aesthetic alternative. While bio-compatible, zirconia posts have a similar modulus of elasticity to stainless steel. Therefore, root fractures may be a more likely occurrence, as may endodontic failure, as a provisional post-retained restoration may be required (with an increased risk of bacterial ingress by the process of micro-leakage).
Fibre-reinforced resin posts have gained in popularity over the past few years. They have the potential to offer a number of advantages, which include:
- Reduced risk of root fracture (lower modulus of elasticity compared to metallic posts)
- Potential to chemically bond to resin-based luting agent, to form a ‘monoblock’
- Ease of retrieval
- Direct technique (reduced costs and less need for laboratory-fabricated post and core), with lower risks of micro-leakage as a provisional restoration will not be required.