Fabricating Fiber-Reinforced Composite Posts

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The prosthetic treatment of seriously damaged, endodontically-treated teeth often requires an endodontic post as an additional retention element for buildup with crown restoration. In addition to metal-based posts and zirconia-based ceramic posts, fiber-reinforced composite posts have recently become the center of interest for dentists and science.
In the past, it was commonly accepted, to some extent, that teeth would become brittle after root canal treatment with an increased risk of fracture. Historically, it was alleged that the strengthening effect of endodontic posts would compensate for any weaknesses caused by the endodontic treatment done. Today, we know that the mechanical properties of tooth substance are not significantly altered by proper endodontic treatment.1,2 Any weakening of endodontically treated teeth is rather the result of additional carious or traumatic destruction, pre-existing loss of tooth substance through the endodontic cavity/trepanation access, and the preparation of the root canals.3,4 Further tooth substance removing measures, such as unnecessary and expansive preparations of the canals and post bed drillings for endodontic posts, additionally weaken the tooth. The bottom line is that the strength of endodontically treated teeth cannot be increased through endodontic posts. On the contrary, weakening (and/or an increase in clinical failure) of the teeth with endodontic posts has been established.

Indications for Endodontic Posts
The creation of reliable resistance and retention form for the definitive restoration, while preserving the maximum amount of healthy tooth structure possible, should be the aim when creating coronal buildups in endodontically treated teeth.5 With modern dental materials using adhesive techniques, the use of endodontic posts can now be avoided in many cases. In cases with an insufficient amount of remaining coronal tooth structure, composite resin adhesive bonding techniques offer the possibility of creating additional retention for the core buildup. The answer to the question of whether an endodontic post is necessary, thus, depends on the degree of destruction of the clinical crown:
• Teeth with a minimal amount of destruction can be prepared using an adhesively bonded direct composite resin buildup for the prosthetic restoration.
• With a medium amount of destruction, a buildup with post anchoring can likewise be avoided in many cases, thanks to the adhesive bonding technique.
• With an extensive amount of destruction of the clinical crown, an endodontic post should be used to create reliable retention of the core buildup.
Note: for those interested, more exact information on this topic can be taken from the shared scientific opinion of the German Scientific Association of Dentistry (DGZMK), German Association of Prosthodontics and Dental Materials (DGZPW), and the German Association of Conservative Dentistry (DGZ) in Aufbau endodontisch behandelter Zähne (“Buildup of Endodonically Treated Teeth”) (2003).

Requirements of Endodontic Posts
The fundamental requirements of endodontic posts include, among other things: high tensile strength, high fatigue resistance to occlusal and shear loading, and stress-free distribution of the forces affecting the tooth root; excellent accuracy of fit, biocompatibility, and electrochemical innocuity are also essential. Unnecessarily weakening the tooth root through increased substance loss should be avoided by selecting a suitable post form (shape).6
For therapy of aesthetically challenging situations these days, all-ceramic crowns and bridges fabricated from translucent ceramic are widely used, especially in the anterior and premolar regions. These are comparable to natural teeth with respect to their light-conducting properties. The expectations of the optical properties of endodontic posts are rising in response to the demand for aesthetic restorations in teeth that have undergone root canal therapy. Unaesthetic effects, originating from the endodontic post shining through and metal or black carbon fiber posts construction, cannot be reconciled with high expectations of aesthetic results.5
In addition to metal posts, which can be subdivided into active posts (with screw threads) and passive designs, up-to-date metal-free systems made from high-strength zirconium oxide ceramic and fiber-reinforced composites are now available.6 In addition to the unfavorable optical properties, the disadvantages of metal posts include: high rigidity (high E modulus) with resulting concomitant risk of arising hypercritical stress peaks (with active posts foremost from the thread outward) and the problem of corrosion. All-ceramic posts made from zirconium oxide are indeed almost tooth-colored; however, these represent an increased risk in the occurrence of stress peaks. This is due to extremely hard and inelastic materials (E modulus, ca. 200 GPa) that are not in harmony (from a biomechanical perspective) with the relatively elastic dentine (E modulus, ca. 18 to 20 GPa) of the tooth root, resulting in an increased risk for root fractures. In addition, in most cases involving postoperative complications, the zirconium oxide posts cannot be removed without considerable and irreparable damage to the tooth root due to their considerable hardness.

Fiber-Reinforced Composite Endodontic Posts
Fiber-reinforced composite posts consist of a resin matrix, in which structural reinforcing carbon fibers or quartz/glass fibers are embedded. Black carbon fiber-reinforced composite posts are, on the one hand, poorly suited for combination with translucent all-ceramic restorations due to their unaesthetic optical properties. On the other hand, carbon fiber posts also have unfavorable biomechanical properties (significantly higher E modulus, ca. 120 GPa) in comparison to the nearly tooth-colored quartz fiber and glass fiber posts.
The quality of fiber-reinforced composite posts, which are now offered by a large number of manufacturers, can vary greatly because the manufacturing process determines the quality. The highest quality is provided by ensuring for the most even distribution of the fiber in the organic matrix possible, optimally dense fibers, a high degree of polymerization of the organic components, and a homogeneous post structure absent of blisters and inclusions.7 After polymerization, the blanks are brought into their final form through a milling process. There are different post geometries, which also exhibit considerable differences in surface quality due to variations in the milling processes.
Endodontic posts fabricated from quartz fiber- or glass fiber-reinforced composite have favorable biomechanical properties. They feature high strength and, at the same time, exhibit elasticity characteristics that are similar to dentine.8 This minimizes the risk of root fractures caused by stress peaks induced by loading and shear forces through the most stress-free distribution possible of these arising forces in the tooth root. The even load distribution is supported through the friction-locked bond between post and tooth substance, due to adhesively bonding the fiber post in the root canal with composite cement. The adhesive bond, however, appears to be inferior to the radicular dentine due to the structural differences in comparison to coronal dentine sections.9,10
The favorable optical properties of tooth-colored fiber posts (glass and quartz fiber), which are consistent with natural teeth in their ability to conduct light, facilitate the goal of high quality and aesthetic restorations when they are combined with all-ceramic materials. The posts can be processed in one time-saving surgery visit that eliminates the dental laboratory steps, due to the direct technique in combination with an adhesive composite buildup. This technique is also a procedure that is gentle to the tooth substance: thin dentine walls are stabilized by the plastic buildup composite and the composite resin cement. Moreover, the areas underneath can be saved and maintained as additional retentive areas for the plastic buildup composite restoration.11
The rare failures of fiber posts are either due to loss of adhesion or a fracture of the post. Catastrophic post failure, which leads to a fracture in the tooth root, is less likely in contrast to posts made from rigid metal or zirconium oxide materials.12 Contrary to tooth-colored posts made from zirconium oxide, posts made from fiber-reinforced composite can be removed from the root canal, if the need arises, without serious complications that often arise when excavation is done with a rotating instrument.
The following case report will demonstrate the clinical steps involved in the utilization of a fiber-reinforced composite endodontic post in a maxillary central incisor and the subsequent treatment with an all-ceramic crown.

CASE REPORT
Diagnosis and Treatment Plan

Figure 1. Preoperative photo: note the unsightly existing crown on tooth No. 8. Figure 2. Periapical radiograph: an endodontically treated tooth with a metal post.

A 38-year-old patient presented with the desire to replace an unsightly crown on the right central incisor (tooth No. 8) and to have a veneer placed on the left central incisor (tooth No. 9) (Figure 1). The PFM crown on the No 8 was much too short and the dentin core was extremely discolored and dark. The tooth reacted unremarkably to percussion and did not display any irritation to the cryogenic spray in the sensitivity test. An endodontically treated tooth with a metal post in the root and a normal periapical region was exhibited in the periapical radiograph (Figure 2). Other than a large, mesial, provisional composite buildup, tooth No. 9 was clinically and radiographically unremarkable.
After presenting and explaining the treatment alternatives, a decision was reached to remove the crown on tooth No. 8 with an attempt to take out the metal post. Subsequent insertion of an adhesively bonded, fiber-reinforced composite endodontic post and fabrication of a zirconium oxide all-ceramic crown were planned. An all-ceramic veneer for tooth No. 9 was also planned.

Replacing a Failed Endodontic Post
Tom M. Limoli, Jr
With the clinical case report, as presented by Dr. Manhart, the use of code D3346 for endodontic retreatment would be clearly inappropriate. Tooth No. 8 suffered from a simple post rather than complete endodontic failure in that he left 4 mm of root filling material from the original apical seal.
In order to accurately submit a benefit claim, the doctor must provide an original date of completion for any root canal therapy on a particular tooth if a core buildup on that tooth is to be supported by either a cast or prefabricated post. The third-party payers may also request a dated radiograph of the completed root canal as well as a diagnostic photograph confirming that which is not seen in the radiograph.
The removal of the original metal post would accurately be coded as D2955 in that endodontic retreatment was not necessary. The construction of the core on the fiber-reinforced composite post is a necessary prerequisite to the final restoration identified in the article as being a zirconium oxide all-ceramic crown.
A post is simply a dowel that is placed in the instrumented canal to retain the core buildup. The CDT does not furnish a coded procedure for the individual post, per se. Therefore, using a post without a buildup of the anatomical core does not justify the use of code D2954.
Table. Replacement Endodontic Post Codes and Fees
Code Description Low Medium High National Average National RV
D2740 Crown—porcelain/ceramic substrate $749 $1,008 $1,454 $1,173 25.50
D2954 Prefabricated post and core in addition to crown $211 $280 $367 $302 6.57
D2955 Post removal (not in conjunction with endodontic therapy) $150 $260 $345 $238 5.17

CDT-2011/2012 copyright American Dental Association. All rights reserved. Fee data copyright Limoli and Associates/Atlanta Dental Consultants. This data represents 100% of the 90th percentile. The relative value is based upon the national average and not the individual columns of broad-based data. The abbreviated code numbers and descriptors are not intended to be a comprehensive listing. Customized fee schedule analysis for your individual office is available for a charge from Limoli and Associates/Atlanta Dental Consultants at (800) 344-2633 or limoli.com.

Clinical Treatment Steps
After the crown was removed from tooth No. 8, the existing build-up material was carefully removed and the coronal portion of the metal endodontic post exposed (Figure 3). The post still exhibited good retention, so an attempt was made to destroy the integrity of the cement with ultrasonic energy (Figure 4), in order to remove the post without a bur and/or other instrumentation, which can often endanger the precious remaining root structure (caveat: longitudinal fracture). After a short time, the post loosened and was easily removed from the canal (Figure 5).

Figure 3. After removal of the existing PFM crown, the old build-up material was removed. Figure 4. The integrity of the cement layer was broken with ultrasonic energy for an atraumatic removal of the old post.

A fiber-reinforced composite post (Rebilda Post [VOCO GmbH]) that would be adhesively bonded into place was chosen. After placing a retraction cord and selecting the appropriate post diameter, the post preparation was carried out with a depth-marked precision drill (Figure 6). The penetration depth was already preset by the length/ extent of the old metal post in this special case. The length of the post drilling should usually allow that a minimum of 4 mm of endodontic root filling material remains, in order to ensure an adequate apical seal.
Figure 7 shows the try-in of the fiber-reinforced post with the maximum coronal diameter (2.0 mm) possible. The fiber-reinforced post was inserted into the cavity and the fit verified. Rebilda Post glass fiber-reinforced composite posts are available in 3 sizes (coronal diameter: 1.2 mm, 1.5 mm, and 2.0 mm) and all have a cylindrical-conical design. The tapered anatomical shape of the tooth root in the apical region is reflected in the design (conical shape) of the post. This permits an anatomically influenced preparation design that is more conservative than those required for straight parallel-walled post systems.
To prepare for the adhesive cementation procedure, the dental assistant cleaned the post with alcohol, dried it with air and then applied silane (Ceramic Bond [VOCO GmbH]). The task of disinfecting the post preparation was carried out concurrently (according to the manufacturer’s instructions) with 3% NaOCl (Figure 8). Next, the prepared canal was flushed with water (Figure 9) and then dried with paper points (Figure 10).

Figure 5. The carefully removed metal post. Figure 6. The post preparation was done with a length-marked standard post drill.
Figure 7. The fiberglass-reinforced composite post (Rebilda Post [VOCO GmbH]) was tried in the root preparation. The assistant then cleaned the post with alcohol, dried it, and applied silane to it (Ceramic Bond [VOCO GmbH]). Figure 8. The root canal was flushed with NaOCI solution.
Figure 9. The post preparation was rinsed with water. Figure 10. The prepared canal was dried with paper points.
Figure 11. A clear matrix was placed, followed by adhesive pretreatment of the post preparation and residual tooth structure with a self-etching dual-cured adhesive resin (Futurabond DC [VOCO GmbH]). Figure 12. Excess adhesive was removed with a paper point.

A clear matrix band was placed on the tooth to help properly shape the buildup. A self-etching dual-cured adhesive, Futurabond DC (VOCO GmbH), was rubbed into remaining tooth substance and in the entire post canal for 20 seconds with a small endodontic microbrush (Figure 11). Then, the solvent was gently evaporated with oil-free air and excess adhesive was removed from the post preparation with the assistance of a paper point (Figure 12). Immediately after this, a low viscosity dual-cured composite resin core build-up material (Rebilda DC [VOCO GmbH]) was applied into the preparation with a QuickMix (VOCO GmbH) syringe using a slender application tip. The syringe tip was inserted to the deepest point in the prepared post canal and the build-up composite was continuously injected while slowly withdrawing the tip. The tip was watched carefully to be sure that the opening was always immersed in the luting composite. This type of “immersion filling” ensures that there are no air bubbles in the cement layer, which also results in maximum adhesion to the canal wall and increased post-to-tooth integrity. The excess cement that escaped from the coronal opening of the post preparation was simply left to incorporate into the buildup. The coronal composite buildup was created with the same application syringe after the post was inserted (Figure 13). The composite was subsequently polymerized with the curing light for 40 seconds (Figure 14). After removing the matrix, tooth No. 8 was immediately prepared for a zirconium oxide all-ceramic crown (Figure 15). A band of dentin edge was clearly discernable in the preparation cervical to the composite buildup. The dentine border serves as a ferrule, which should be a minimum of 2 mm wide circumferentially in the ideal case. When circularly surrounded by the definitive crown, this creates a ferrule effect that protects the integrity of the remaining root structure and increases the strength of the post-core assembly and the expected longevity for the definitive restoration. Tooth No. 9 was then prepared for a ceramic veneer (Figure 15). A temporary was fabricated from the preoperative impressions and placed with temporary cement (Figure 16). The adhesively cemented fiber-reinforced composite post was clearly discernible on a postoperative periapical radiograph (Figure 17).
Figure 18 shows the aesthetic results achieved for the patient.

Figure 13. The post was luted into place and the core buildup was created using a low viscosity dual-cured composite resin (Rebilda DC [VOCO GmbH]). Figure 14. The composite resin was polymerized with light for 40 seconds.
Figure 15. The completed preparations for a zirconium oxide crown on tooth No. 8 and an all-ceramic veneer on tooth No. 9. Figure 16. The provisional restorations were fabricated from a preoperative impression and cemented temporarily into place.
Figure 17. Postoperative periapical radiograph. Figure 18. The completed case. Note the markedly improved aesthetics.

SUMMARY
Endodontic posts do not increase the strength of the remaining tooth structure in endodontically treated teeth. On the contrary, depending on the post design employed (tapered versus parallel-sided), the root can be weakened relative to the amount of tooth removed during preparation. In many cases, if there has been a high degree of damage to the clinical crown, conservative preparation for an anatomic tapered (biomimetic) post with the incorporation of a ferrule on solid tooth structure is necessary to protect the reaming root structure as well as for the long-term retention of the composite resin core and the definitive restoration. Adhesively luted endodontic posts reinforced with glass or quartz fiber lead to better homogeneous tension distribution when loaded than rigid metal or zirconium oxide ceramic posts. Fiber-reinforced posts also possess advantageous optical properties over metal or metal oxide post systems.
The clinician should realize that there are admittedly substantial differences in the mechanical loading capacity of the different fiber-reinforced endodontic posts and should be aware of such differences in order to research and select a suitable post system for use.


References

  1. Lewinstein I, Grajower R. Root dentin hardness of endodontically treated teeth. J Endod. 1981;7:421-422.
  2. Reeh ES, Messer HH, Douglas WH. Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod. 1989;15:512-516.
  3. Linn J, Messer HH. Effect of restorative procedures on the strength of endodontically treated molars. J Endod. 1994;20:479-485.
  4. Smith CT, Schuman N. Restoration of endodontically treated teeth: a guide for the restorative dentist. Quintessence Int. 1997;28:457-462.
  5. Nergiz I, Schmage P. Wurzelstifte im Wandel der Zeit. Endodontie Journal. 2004;4:10-17.
  6. Edelhoff D, Spiekermann H. Alles über moderne Stiftsysteme. Zahnärztl Mitt. 2003;93:60-66.
  7. Grandini S, Goracci C, Monticelli F, et al. Fatigue resistance and structural characteristics of fiber posts: three-point bending test and SEM evaluation. Dent Mater. 2005;21:75-82.
  8. Pfeiffer P, Schulz A, Nergiz I, et al. Yield strength of zirconia and glass fibre-reinforced posts. J Oral Rehabil. 2006;33:70-74.
  9. Kurtz JS, Perdigão J, Geraldeli S, et al. Bond strengths of tooth-colored posts, effect of sealer, dentin adhesive, and root region. Am J Dent. 2003;16(special issue):31A-36A.
  10. Mjör IA, Smith MR, Ferrari M, et al. The structure of dentine in the apical region of human teeth. Int Endod J. 2001;34:346-353.
  11. Monticelli F, Goracci C, Ferrari M. Micromorphology of the fiber post-resin core unit: a scanning electron microscopy evaluation. Dent Mater. 2004;20:176-183.
  12. Mannocci F, Ferrari M, Watson TF. Intermittent loading of teeth restored using quartz fiber, carbon-quartz fiber, and zirconium dioxide ceramic root canal posts. J Adhes Dent. 1999;1:153-158.

Dr. Manhart attended dental school of the Ludwig-Maximilians-University (LMU), Munich, and is an internationally renowned lecturer in the fields of aesthetic and restorative dentistry (composites, ceramics, aesthetic post systems, treatment planning). After graduation in 1994, he started working as a clinical dentist and scientist in the department of restorative dentistry, LMU. After conferment of the title Doctor of Medical Dentistry (PhD) in 1997, he completed a postdoc program at the University of Texas, Houston, for dental biomaterials, aesthetic dentistry, and interdisciplinary treatment planning. Dr. Manhart currently holds the position of professor in the department of restorative dentistry at the LMU Dental School. The main focus of his extensive clinical work is related to aesthetic dentistry (composite, ceramics, veneers) and the management of large, complex prosthodontic full-mouth rehabilitations. Since 1994, Dr. Manhart studies and teaches adhesive and aesthetic dentistry. He has authored more than 140 articles, one book, and several book chapters. He is principal investigator in many clinical and in vitro studies and researches the clinical longevity of dental restorations. Dr. Manhart is lecturing extensively, delivering more than 300 continuing education presentations and hands-on courses all over the world. He can be reached at manhart@manhart.com.

 

Disclosure: Dr. Manhart reports no disclosures.