The restoration of endodontically treated teeth is significantly influenced by the condition of the underlying core. When minimal loss of dental structure has occurred, an amalgam, composite, or glass-ionomer cement buildup should be selected to restore the core. In patients who have experienced extensive loss of coronal tooth structure due to access preparation for the endodontic treatment, preexisting restorations, tooth fracture, or dental caries, coronoradicular stabilization is required to provide retention for the restoration.1-4 While post and core combinations are commonly utilized to restore extensive structure loss, the efficacy of posts to reinforce endodontically treated teeth remains a widely debated topic.5,6 Various studies have demonstrated that the placement of a post does not necessarily reinforce the endodontically treated tooth, but instead serves only as an attachment apparatus for prosthetic treatment.7,8 The purpose of a post is to support the overlying core, which consequently replaces the missing coronal tooth structure.7,9
Post and Core Prerequisites
For the successful restoration of endodontically treated teeth using currently available post and core systems, several aspects (eg, ferrule design, passivity, shape, length) should be considered prior to treatment.
The ferrule is the quantity of remaining tooth structure that surrounds the crown or root of a tooth. The resistance to fracture of endodontically treated teeth is largely dependent on the strength provided by the bulk of the ferrule.7,10,11 In order to ensure long-term post and core permanence beneath the crown restoration, a 1 mm to 2 mm ferrule extension to the tooth structure is required.12,13
Several studies have demonstrated that post passiveness within the root canal is a prerequisite for the prevention of root fracture. When luting cast post and core units, passive insertion is exhibited by the absence of a cement line between the metal post and the remaining tooth structure. In an optimal clinical situation, intraoral stresses would be uniformly distributed, and any cement line would indicate incomplete insertion into the canal with subsequent localized stress in specific root areas.
Greater retention is offered by parallel-sided posts in comparison to tapered posts.14,15 It has also been demonstrated that the parallel-sided shape necessitates the removal of less tooth structure during the preparation of the post space. In addition, the parallel-sided shape offers greater stress distribution properties than the tapered version while causing less irreversible damage upon failure. The principal disadvantage is that in preparing the root for placement of a parallel-sided post, a greater risk of root perforation exists due to root anatomy. The utilization of a cylindrical bur that is slightly tapered at the apex can significantly reduce the risk of perforation during root canal preparation.
The standard post is generally two thirds of the canal length. While longer posts offer greater retention and more optimal stress distribution than shorter ones, the additional canal preparation required increases the risk of root perforation and risks disturbing the apical endodontic seal (4 mm to 5 mm).16,17
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Conventional Post and Core Systems
The superior physical properties of metal posts provide numerous clinical benefits.18-20 Over time, however, custom-fabricated base metal alloy posts and stainless steel prefabricated posts release corrosive products (eg, iron, chromium, nickel, and silver) that result in discoloration and increase the potential of fracture.21,22 This phenomenon is virtually nonexistent in instances where posts with adequate biocompatibility (ie, titanium posts and cast gold-platinum alloy dowels) are utilized.21
When prosthetic treatment is required in anterior teeth, the use of all-ceramic full-coverage restorations may be warranted due to their extraordinary aesthetics, translucence, and vitality (as long as the substructure is not chromatically compromised). Unfortunately, the use of a metallic-cast post and core or a prefabricated post with an amalgam core does not allow adequate light transmission through the restoration. In these circumstances, an aesthetic core is indicated to optimize the definitive result.
Composite materials can also be utilized to reconstruct the core in an aesthetic manner. When a large degree of dental structure is missing, however, a post is essential for support of the restoration. Although titanium posts have been widely utilized to achieve this objective, carbon fiber posts in conjunction with composite core buildups could be a valid alternative.22 Due to its epoxy resin matrix, the cylindrical carbon fiber post can bond either to the composite cement used for passive insertion into the canal or to the self-polymerizing composite material selected for coronal reconstruction. Since the carbon fiber and composite core materials exhibit a modulus of elasticity very similar to that of dentin, a homogeneous tooth-post-restoration integral unit is subsequently created. In order to reduce stress on the tooth, several reports have advocated the use of posts with a modulus of elasticity similar to that of the natural root structure.23,24 Additional studies have debated the use of carbon fiber posts and composite cores in comparison to ceramic crown material, which has a higher modulus of elasticity than the post and core.25 These investigations have concluded that microscopic movements of the post and core material caused by flexure can result in cement failure, core breakdown, and the eventual disintegration of the entire restorative complex.25,26
Aesthetic concerns can be successfully eliminated through the use of a cast post and core fabricated with dentin porcelain and supported by a specific design of metal substructure (Figures 1-2-3). Saturated dentin porcelain is subsequently used to build up the core and to establish the color of the prepared tooth. The ceramic portion of the core is supported by a metal post that features two metal extensions that are interproximally oriented at their widest surface. This arrangement allows sufficient support to the ceramic material and permits proper light penetration. Use of a ceramic core provides several advantages, including improved light transmission, suitable coloration, and an improved overall aesthetic appearance. This modality is used by the author in the presence of thick periodontal tissue and a low lip line, as the color of the root does not influence the aesthetic result in either instance (Figures 4-5-6-7).
Aesthetic Post and Core Systems
The inherent color of the metal post and core or carbon fiber can cause a gray-blue discoloration and shadowing in the cervical aspects of the root. Since this effect can result in an aesthetic compromise of the maxillary dentition, it must be considered prior to the selection of a restorative system. As the transmission of light by the underlying translucent root structure is partially responsible for the color of the healthy gingival tissues, these concerns must be addressed - particularly when treating a patient with thin periodontal tissues and a high lip line - in order to achieve optimal aesthetics.
In the presence of discolored endodontically treated teeth, the discoloration must be treated prior to the selection of a post and core fabrication technique. The internal bleaching of endodontically treated teeth with relatively intact crowns offers a relatively high degree of reliability and permanence. Since the chemicals utilized for chairside bleaching can result in external root resorption, systems that utilize 35% hydrogen peroxide and sodium perborate should be used in place of procedures that use hydrogen peroxide alone. Once bleaching has been performed, two to three weeks should elapse prior to positioning the post and core in order to allow all traces of residual hydrogen peroxide to disappear.27,28 The normal transillumination of gingival tissue should be preserved by using a material that allows light transmission in a manner similar to that of a natural tooth, which avoids shadowing in the root and gingival areas. Several "white" materials with excellent strength properties have recently been developed for this purpose.
Due to the high resistance values achieved by contemporary ceramic materials, the use of aluminous ceramic is indicated not only for the fabrication of crown and fixed partial denture restorations, but for post and core restorations when the post is of sufficient width (Figures 8-9-10-11-12-13-14). Prefabricated zirconia posts exhibit favorable mechanical properties (eg, flexural strength and fracture toughness) that rival those of metal-ceramic restorations.25,29 Direct techniques, which use a zirconia post with a composite core, can be employed when a minimum of one third of the clinical crown is present. In this process, the surface of the zirconium-oxide post is abraded, a chemical silanization treatment is applied, and the post is cemented with an adhesive procedure. A composite material is then built up to serve as a core. As with all composite structures, those made with zirconia posts - despite the use of enhanced bonding agents - can experience a shrinkage gap between the tooth structure and the core material that may result in microleakage beneath the crown restoration.25,26 In addition, a less than ideal bond strength appears to exist between the zirconia and composite materials.30
Zirconium posts are primarily used by the author for the indirect restoration of compromised teeth (Figure 15), This process involves a leucite-reinforced ceramic material for the fabrication of the core buildup over the post. An impression is taken with a suitable impression material, and the core pattern is waxed to the zirconium post (Figure 16), invested, burned out, and pressed using a glass-ceramic material. This material contains Zr 02 crystals, which possess a coefficient of thermal expansion compatible with that of zirconium (Figure 17).31 The zirconium post is covered in the coronal and root areas, which form a single unit that can be etched and silaned in order to allow a more predictable bond strength between the final post and core and the resin cement (Figure 18).
An increased emphasis on aesthetic considerations has resulted in the development of contemporary restorative systems for the coronal aspects and roots of endodontically treated teeth. While the absence of adequate dental structure complicates the restoration of endodontically treated teeth, the effective utilization of contemporary materials and techniques can render a definitive result that satisfies the aesthetic criteria of the patient and the functional criteria of the clinician.
* Special lecturer, Department of Prosthodontics, Louisiana State University, New Orleans, Louisiana; private practice, Pesaro and Milano, Italy.
† Private practice, Pesaro, Italy.
‡ Private practice, Ancona, Italy.
- Cohen S, Burns R. Pathways of the Pulp. 4th ed. St. Louis, MO: Mosby; 1987:640-684.
- Shillingburg HT, Hobo S, Whitsett LD, et al. Fundametals of Fixed Prosthodontics. 2nd ed. Carol Stream, IL: Quintessence Publishing; 1981:147-159.
- Shillingburg HT, Kessler JC. Restoration of the Endodontically Treated Tooth. Carol Stream, IL: Quintessence Publishing; 1982:13-203.
- Malone WFP, Koth DL, Cavazos E, et al. Tylman's Theory and Practice of Fixed Prosthodontics. 8th ed. St. Louis, MO: Ishiyaku EuroAmerica Inc.; 1989:410-415.
- Guzy GE, Nicholls JI. In vitro comparison on intact endodontically treated teeth with and without endo-post reinforcement. J Prosthet Dent 1979;42(1):39-44.
- Rud J, Omnell KA. Root fractures due to corrosion. Diagnostic aspects. Scand J Dent Res 1970;78(5):397-403.
- Sorensen JA, Martinoff JT. Intracoronal reinforcement and coronal coverage: A study of endodontically treated teeth. J Prosthet Dent 1984;51(6):780-784.
- Sorensen JA, Martinoff JT. Clinically significant factors in dowel design. J Prosthet Dent 1984;52(1):28-35.
- Caputo AA, Standlee JP. Biomechanics in Clinical Dentistry. Carol Stream, IL: Quintessence Publishing; 1987:185-186.
- Trabert CK, Caputo AA, Abou Ross M. Tooth fracture - A comparison of endodontic and restorative treatments. J Endod 1978;4(11):341-345.
- Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs. cast-gold dowel-cores. J Prosthet Dent 1977;38(5):507-514.
- Gelfand M, Goldman M, Sunderman EJ. Effects of complete veneer crowns on the compressive strength of endodontically treated teeth. J Prosthet Dent 1984;52:635-638.
- Libman WJ, Nicholls JI. Load fatigue of teeth restored with cast posts and cores and complete crowns. Int J Prosthodont 1995;8(2):155-161.
- Kurer HG, Combe EC, Grant AA. Factors influencing the retention of dowels. J Prosthet Dent 1997;38:515-525.
- Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensile and torsional forces. J Prosthet Dent 1979;41:159-162.
- Zmener O. Effect of dowel preparation on the apical seal of endodontically treated teeth. J Endod 1980;6(8):687-690.
- Mattison GD, Delivanis PD, Thacker RW Jr, Hassell KJ. Effect of post preparation on the apical seal. J Prosthet Dent 1984;51(6):785-789.
- Wirz J, Christ R. In vitro study of the occurrence of screw and pin corrosion in dental prosthesis structures. SSO Schweiz Monatsschr Zahnheilkd 1982;92(5):408-428.
- Eliasson S, Bergström J, Sanda A. Periodontal bone levels of teeth with posts. A radiographic study. J Clin Periodontol 1995;22(11):850-853.
- Duret B, Reynaud M, Duret F. New concept of coronoradicular reconstruction: The Composipost (1). Chir Dent France 1990;60(540):131-141.
- Engelman MJ, Sorensen JA, Avera SP, Lew D. Effect of luting agents on corrosion resistance of metal posts. J Dent Res 1990;69(Abstract No. 913):223.
- Arvidson K, Wroblewski R. Migration of metallic ions from screwposts into dentin and surrounding tissues. Scand J Dent Res 1978;86(3):200-205.
- Assif D, Oren E, Marshak BL, Aviv I. Photoelastic analysis of stress transfer by endodontically treated teeth to the supporting structure using different restorative techniques. J Prosthet Dent 1993;69:36-40.
- King PA, Setchell DJ. An in vitro evaluation of a prototype CPRC prefabricated post developed for the restoration of pulpless teeth. J Oral Rehabil 1990;17(6):599-609.
- Sorensen JA, Mito WT. Rational and clinical technique for esthetic restoration of endodontically treated teeth with the Cosmopost and IPS Empress Post System. Quint Dent Technol 1998;81-90.
- Hormati AA, Denehy GE. Microleakage of pin-retained amalgam and composite resin bases. J Prosthet Dent 1980;44(5):526-530.
- Dishman MV, Covey DA, Baughan LW. The effects of peroxide bleaching on composite to enamel bond strength. Dent Mater 1994;10(1):33-36.
- Barkhordar RA, Kempler D, Plesh O. Effect of nonvital bleaching on microleakage of resin composite restorations. Quint Int 1997;28(5):341-344.
- Meyenberg HK, Lüthy H, Schärer P. Zirconia posts: A new all-ceramic concept for nonvital abutment teeth. J Esthet Dent 1995;7(2):73-80.
- Dietschi D, Romelli M, Goretti A. Adaptation of adhesive posts and cores to dentin after fatigue testing. Int J Prosthodont 1997;10(6):498-507.
- Schweiger M, Frank M, Cramer von Clausbruch S, et al. Mechanical properties of a pressed ceramic core to a zirconia post. Quint Dent Technol 1998;21:71-77.