Medical knowledge | Dentistry » Raygot-Chai - Fracture resistance and primary failure mode of endodontically treated teeth restored with a carbon fiber reinforced resin post system in vitro

Fracture Resistance and Primary Failure Mode of Endodontically Treated Teeth Restored with a Carbon Fiber–Reinforced Resin Post System In Vitro Christophe G. Raygot, DDS, MSa John Chai, BDS, MS, MJ, DLawb Lee Jameson, DDS, MSc Purpose: This study was undertaken to characterize the fracture resistance and mode of fracture of endodontically treated incisors restored with cast post-and-core, prefabricated stainless steel post, or carbon fiber–reinforced composite post systems. Materials and Methods: Ten endodontically treated teeth restored with each technique were subjected to a compressive load delivered at a 130-degree angle to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded Results: The failure loads registered in the three groups were not significantly different. Between 70% and 80% of teeth from any of the three groups displayed fractures that were located above the simulated bone level. Conclusion: The use of

carbon fiber–reinforced composite posts did not change the fracture resistance or the failure mode of endodontically treated central incisors compared to the use of metallic posts. Int J Prosthodont 2001;14:141–145. A new carbon fiber–reinforced composite (CFC) post system (C-post, RTD)1–4 has been introduced on the market. The CFC post is made of an organomineral composite with optimal mechanical properties The reinforcement is attributed to carbon fibers of 8-µm diameter disposed in the longitudinal axis of the post. The carbon fibers represent 64% of the weight. The matrix is an epoxy resin (36%) that embeds the carbon fibers It is claimed that the compatibility between the carbon fibers and the epoxy resin ensures proper cohesion of the materials.1,2 The manufacturer claims that carbon fiber is the material of choice as a prefabricated post because of its high tensile strength and the similarity of its modulus of elasticity to that of dentin. Because carbon fiber could

adhesively bond to composite, it was claimed that when the post is used with adhesive luting agents and composite resin core materials, the system can form an adhesively retained homogenous restoration. Furthermore, with a modulus of elasticity similar to dentin, it was said that the carbon-fiber post could reduce stress concentration and thus the rate of failure. The CFC post might be a technologic breakthrough as a prefabricated post material; however, there was insufficient or contradicting published information on its fracture resistance and mode of failure. An earlier study by Purton and Payne5 reported the rigidity of CFC posts to be higher than that of stainless steel posts under transverse bending. The authors concluded that the CFC post could be more desirable because a smaller diameter of the CFC post compared to the stainless steel post would be necessary to provide the same rigidity; thereby, more tooth structure could be conserved during post preparation. Another study

revealed that the stiffness, elastic limit, and ultimate strength of two brands of zirconia posts were aPrivate Practice, Paris, France. Dean, Academic Affairs, Northwestern University Dental School, Chicago, Illinois. cDean, Northwestern University Dental School, Chicago, Illinois. b Associate Reprint requests: Dr John Chai, Northwestern University Dental School, 240 East Huron Street, Chicago, Illinois 60611. Fax: + (312) 503-0801. e-mail: jchai@nwuedu Volume 14, Number 2, 2001 141 The International Journal of Prosthodontics Carbon Fiber–Reinforced Resin Post System Raygot et al superior to a titanium-post system, which bettered a CFC-post system.6 The authors were cautious not to conclude whether a post system with better mechanical properties was more desirable. Two static load studies conducted on endodontically treated teeth restored with crowns showed that the CFC-post system was less resistant to fracture than a metallic-post system.7,8 These studies contradict a

fatigue study9,10 that showed a higher failure rate of prefabricated parallel-sided stainless steel posts and tapered cast posts compared to the CFC post. Understanding the mode of failure of various postand-core systems is of great importance to the clinician in product selection. The clinician should avoid a post system with the propensity to fail with root fractures; as such, an irreversible failure not uncommonly results in extraction. Information available indicates that the CFC post exhibits a more favorable mode of failure under a static load than a metallic post.7,8,11 Teeth restored with metallic posts showed more vertical root fractures than those restored with the CFC post.7,8 These studies, which showed the CFC post exhibiting a more favorable fracture than the metallic post, tend to confirm the low modulus of elasticity of the CFC post12 as more favorable. The mode of failure reported in these studies has to be interpreted with caution. In these studies, the failure

threshold was determined as the point at which the specimen could no longer withstand an increase in load.7,8 This experimental design measured the load at which catastrophic failure happened, which seldom occurs clinically. Moreover, the total destruction of the specimens rendered it difficult to appreciate the primary mode of failure because numerous secondary fractures were generated in the process. Thus, it would be more appropriate to study the fracture resistance and mode of failure of a post-and-core system at its initial failure. The aim of the present study was to compare the resistance to fracture and the primary mode of failure of three post-and-core systems: CFC post–resin core, stainless steel post–composite resin core, and cast post and core. zinc oxide and eugenol sealer (Roth Dental) and obturated with a No. 40 gutta percha master cone (Dentsply-Maillefer) and three medium-fine cones using the lateral cold condensation technique. The teeth were randomly divided

into three groups of ten teeth. The first group (CFC group) was restored with CFC posts (upper shank diameter 1.4 mm, lower shank diameter 1 mm) and composite resin cores (Bis-Core, BISCO). The second group (SS group) was restored with serrated, parallel-sided stainless steel posts (1.5-mm-diameter Parapost, Whaledent) and composite resin cores (Bis-Core). The third group (cast P&C group) was restored with serrated, parallelsided posts (1.5-mm-diameter Parapost) and cores cast in a noble alloy (PG-200, Engelhart-Baker). Preparation of Coronal Tooth Structure The crown of each tooth was removed horizontally with a water spray–cooled diamond bur at high speed, creating a flat coronal surface perpendicular to the long axis at the level of the facial cementoenamel junction. The canal space was prepared 10 mm deep from the coronal surface of the root following the manufacturer’s recommendation. The root of each tooth was embedded in autopolymerizing resin contained in a plastic tube

of 30-mm diameter (Duralay, Reliance Dental) to a level 4 mm below the coronal surface. This level simulated that of the alveolar bone To ensure the vertical positioning of the tooth in the resin, the last drill used to prepare the canal space was used to orient each tooth vertically on a surveyor. The coronal dentin was prepared to a circumferential shoulder of 1-mm width and height with a mediumcoarse diamond bur (No. 835-31, Brasseler) under water-spray cooling with a high-speed handpiece mounted on a pantograph. The pantograph was a mechanical instrument constructed to allow the diamond bur to duplicate the outline of a prepared tooth. Its use ensured that all coronal preparations were similar in dimensions. The prepared specimen was thus positioned vertically with its crown margin 3 mm above the level of the acrylic resin and possessed a 10mm length of post space, a 1-mm height of coronal dentin, and a 1-mm-wide shoulder (Fig 1). Materials and Methods Fabrication of Post and Core

Thirty extracted intact human central incisors of similar dimensions, stored in physiologic saline solution, were selected. Any tooth with detectable fracture line upon transillumination was discarded. Endodontic therapy was completed for the teeth. Each tooth was instrumented up to the No. 40 K file, 1 mm short of the apex, with sodium hypochlorite irrigation. The canal was dried with a paper point and then filled with The International Journal of Prosthodontics The composite resin cores of the CFC and SS groups were syringed into the canal spaces and built up incrementally around the prefabricated posts. The post and the surface of the tooth structure in contact with the resin were previously treated with a dentin bonding agent (All-Bond 2, BISCO) according to the manufacturer’s recommendation. The core was prepared 142 Volume 14, Number 2, 2001 Raygot et al Carbon Fiber–Reinforced Resin Post System 130 degrees 130 degrees 130 degrees 3 mm 2 mm 1 mm 3 mm 8 mm Fig 1

Embedded tooth specimen. (Note: actual core preparation followed principles of two-plane reduction and gently rounded incisal reduction.) Fig 2 to the dimensions specified in Fig 1 after allowing 5 minutes for the completion of polymerization. For the cast P&C group, resin post-and-core patterns were built up with a serrated, parallel-sided burnout post and an autopolymerizing resin (Duralay), and prepared to the dimensions specified in Fig 1. The patterns were invested, burnt out, and cast in a noble alloy. Cementation of the cast post was accomplished in the same fashion as the posts of the previous groups. Testing Procedure All specimens were stored in distilled water for 24 hours prior to the mechanical testing. Compressive load was applied with a universal load-testing machine (Instron) to the teeth at a cross-head speed of 25.4 mm per minute A device was made to allow loading of each tooth at an angle of 130 degrees to its long axis7,13 (Fig 2). The testing apparatus was

connected to a calibrated drive chart, which plotted force against the time curve during the test procedure. All data were recorded from the first fracture point that was represented on the paper chart by the first drop of the load. The load-testing machine was interrupted immediately after the drop of load. Waiting for complete destruction of the crown post-and-core system would interfere with the final result when investigating the modes of fracture. One-way analysis of variance (ANOVA) was used to compare the fracture load among the three groups. To investigate the mode of failure, the teeth were immersed in black ink (Pelikan Drawing Ink A) for 12 hours to allow penetration into the tooth. The teeth were sectioned in the mesiodistal plane with a carborundum disk (National Keystone) and examined for dye penetration.13 The location of the fracture and the Fabrication of Crowns The crowns were directly fabricated on the preparations (Fig 1). Two coats of die spacer (PDQ, Whip Mix)

were applied on the preparation. A waxing jig was used to standardize the location of a flat surface to contact the rod connected to the load cell on the testing machine (Fig 2). The loading surface was positioned on the palatal surface of each crown, oriented at 130 degrees from the long axis and 6 mm above the margin of the restoration. The completed crowns were sprued, invested, and then cast in a noble alloy (PG 200). The crowns were cemented onto the teeth with zinc phosphate cement under finger pressure for 10 minutes.13 Volume 14, Number 2, 2001 Specimen is placed onto the load-testing machine. 143 The International Journal of Prosthodontics Carbon Fiber–Reinforced Resin Post System Raygot et al failing interface were observed and compared between groups. Tooth fracture was classified as either favorable or unfavorable according to its location. Fracture above the resin was considered to be favorable. Fracture below the resin level was considered unfavorable manner,

changes in the material and design of postand-core systems became more evident.16,17 This experiment demonstrated no statistical differences in fracture resistance of central incisors restored with three systems of post and core: the CFC post–composite core, the parallel-sided post–composite core, and the cast parallel-sided post and core. Examination of the samples revealed no differences in the mode of failure between the three groups. These results contradict those of two other studies7,8 In both studies, the authors found that the post-core and crown system with metallic posts was more resistant to fracture than the CFC-post system. They also found that the mode of failure of the system using metallic posts was less favorable, that is, the failures involved more tooth structure These observations were not noted in the current study most probably because of the difference in experimental design. In the present study, the load of the sample was stopped as soon as the initial drop

in the load was detected. The procedure characterized the fracture resistance of the post-and-core system at initial failure and allowed an evaluation of its failure mode. The evaluation of the primary failure mode of a post-and-core system is important for future product development to improve the performance of the system. For example, a post-and-core system characterized by post fracture as the initial failure mode would require improvement in the mechanical strength of the post. Studies that report failure resistance and the mode of failure of postand-core systems after catastrophic failure of the specimen are less likely to isolate the primary failure mode Dean et al18 reported similar fracture resistance of anterior teeth restored with CFC posts–composite cores and metallic posts–composite cores. However, the study revealed that 50% of failures of the metallic posts involved root fractures, whereas no root fractures were found with the CFC posts. This differed from the

present study, which revealed that the failure modes of the two systems were not different. Dean et al’s observation is in agreement with two previously discussed reports7,8 that revealed a higher likelihood of metallic posts being associated with more drastic tooth fractures. This observation can again be explained by the method of characterizing initial failure in the current study in contrast to the characterization of catastrophic failures in the other studies.7,8 It may be suggested that catastrophic failures of metallic post systems tend to involve more root fractures compared to the CFC-post system. However, the clinically more meaningful method of characterizing initial failure did not reveal any advantage of the CFC-post system. Encouraging clinical results have been reported with the use of the CFC posts. A clinical study of 236 CFC posts for a period of 2 to 3 years did not reveal any failures because of fracture of the CFC post.19 However, Results The fracture resistance

of two specimens, one each from the CFC and the cast P&C groups, were not recorded properly because of a malfunction of the chart recording. Nevertheless, these two specimens were adequate to be included in the mode of failure analysis. The mean fracture resistance of the cast P&C group, at 374 ± 104 N, was higher than those of the CFC (307 ± 33 N) and stainless steel (305 ± 47 N) post groups. However, one-way ANOVA did not show any significant differences in fracture resistance among the groups (P > 0.05) Adhesive failures were noted for all specimens at the crown margin and between the post/core and tooth material. For all specimens, there were no failures discovered at the junction between the post and the core, nor was any failure observed cohesively within the restorative materials. All specimens failed with tooth fracture. Between 70% and 80% of the teeth from any of the three groups displayed favorable failures, that is, the fractures were located above the resin.

Discussion The purpose of a post-and-core system is to provide retention for the crown. The design as well as the material of the post can affect the fracture resistance of the post-core and crown restoration.14,15 The intent of this study was to compare the resistance to fracture and the mode of failure of three post-and-core systems. The amount of tooth structure is a significant factor in determining the fracture resistance of an endodontically treated tooth. It has been shown that endodontically treated teeth restored with posts and cores of different materials and designs tend to exhibit similar fracture resistance when abundant tooth structure remains. 13 Conversely, the strength of endodontically treated teeth with a minimal amount of coronal tooth structure depends heavily on the postand-core material and design. The present study simulated a realistic clinical condition of a reduced amount of tooth structure with a 1-mm height of coronal dentin. With such a design, the

compressive load was largely borne by the post and core. In this The International Journal of Prosthodontics 144 Volume 14, Number 2, 2001 Raygot et al Carbon Fiber–Reinforced Resin Post System longer successful clinical trials will be necessary for the full endorsement of the CFC post in light of the finding that the mechanical properties of the CFC post can be severely affected by water storage and thermocycling.20 7. Sidoli GE, King PA, Setchell DJ An in vitro evaluation of a carbon fiber-based post and core system. J Prosthet Dent 1997;78:5–9 8. Martinez-Insua A, Silva LD, Rilo B, Santana U Comparison of the fracture resistances of pulpless teeth restored with a cast post and core or carbon-fiber post with a composite core. J Prosthet Dent 1998;80:527–532. 9. Isidor F, Brøndum K Intermittent loading of teeth with tapered, individually cast or prefabricated, parallel-sided posts. Int J Prosthodont 1992;5:257–261. 10. Isidor F, Ödman P, Brøndum K Intermittent

loading of teeth restored using prefabricated carbon fiber posts Int J Prosthodont 1996;9:131–136. 11. King PA, Setchell DJ An in vitro evaluation of a prototype CFRC prefabricated post developed for the restoration of pulpless teeth. J Oral Rehabil 1990;17:599–609 12. Craig RG Restorative Dental Materials, ed 9 St Louis: Mosby, 1985:384–449. 13. Guzy GE, Nicholls JI In vitro comparison of intact endodontically treated teeth with and without endo-post reinforcement J Prosthet Dent 1979;42:39–44. 14. Sorensen JA, Martinoff JT Intracoronal reinforcement and coronal coverages: A study of endodontically treated teeth J Prosthet Dent 1984;51:780–784. 15. Trabert KC, Caputo AA, Abou-Ross M Tooth fractureA comparison of endodontic and restorative treatments J Endod 1978;4:341–345. 16. Libman WJ, Nicholls JI Load fatigue of teeth restored with cast posts and cores and complete crowns. Int J Prosthodont 1995;8:155–161 17. Sorensen JA, Engelman MJ Ferrule design and fracture

resistance of endodontically treated teeth. J Prosthet Dent 1990;63:529–536 18. Dean JP, Jeansonne BJ, Sarkar N In vitro evaluation of a carbon fiber post. J Endod 1998;24:807–810 19. Fredriksson M, Astback J, Pamenius M, Arvidson K A retrospective study of 236 patients with teeth restored by carbon fiberreinforced epoxy resin posts J Prosthet Dent 1998;80:151–157 20. Torbjörner A, Karlsson S, Syverud M, Hensten-Pettersen A Carbon fiber reinforced root canal posts. Mechanical and cytotoxic properties Eur J Oral Sci 1996;104:605–611 Conclusions Within the limits of the present experiment, the following conclusions can be made: • Carbon-fiber posts did not improve the fracture resistance of endodontically treated central incisors when compared to metallic posts. • The incidence of unfavorable failures of endodontically treated central incisors restored with carbon-fiber posts, stainless steel posts, and cast posts and cores was similar. References 1. 2. 3. 4. 5. 6.

Duret B, Reynaud M, Duret F. Un nouveau concept de reconstitution corono-radiculaire Le c-post (1) Chir Dent Fr 1990;540: 131–141. Duret B, Reynaud M, Duret F. Un nouveau concept de reconstitution corono-radiculaire Le c-post (2) Chir Dent Fr 1990;542: 69–77. Bolla M, Medioni E, Muller M, Rocca JP. Le systeme composipost: Etude clinique et analyse critique Inf Dent 1995;7:499–504 Medioni E, Bolla M, Nairi A, Muller M. Etude comparative, en traction, de differents Systemes de collage des tenons en fibres de carbone. Cahiers Prothese 1995;90:58–65 Purton DG, Payne JA. Comparison of carbon fiber and stainless steel root canal posts. Quintessence Int 1996;27:93–97 Amussen E, Peutzfeldt A, Heitmann T. Stiffness, elastic limit, and strength of newer types of endodontic posts. J Dent 1999;27: 275–278. Literature Abstract Influence of previous restoration of the tooth on prognosis of crowns with dowels. The aim of this retrospective study was to investigate whether the previous

type of restoration of a tooth, ie, composite restoration with screw post versus one-piece dowel crown, has an effect on the prognosis of crowns with dowels. The material consisted of 111 single crowns: 83 composite restorations with screw posts and 28 one-piece dowel crowns. All of the crowns were made by dental students and fabricated in one dental laboratory. No abutments were included in this study Only one single crown of each patient was included in the study The age of the patients (68 women and 43 men) ranged from 29 to more than 70 years. The mean follow-up time was 78 months (range 6 to 163 months) The cumulative survival was 87% for one-piece dowel crowns and 84% for composite resins with screw posts. Six root fractures, four losses of cement retention, and one tooth extraction because of caries occurred in crowns with previous composite resins with screw posts. In teeth with one-piece dowel crowns, there were two root fractures and one tooth extraction for periodontal

reasons. It was concluded that the previous restoration has no marked effect on the prognosis of crowns with dowels when studying composite resin restorations with screw posts and one-piece dowel crowns. Näpänkangas R, Salaonen MAM, Raustia AM. J Oral Rehabil 2000;27:1042–1046 References: 16 Reprints: Dr Ritva Näpänkangas, Department of Prosthodontic Dentistry and Stomatognathic Physiology, Institute of Dentistry, University of Oulu, PL 5281, FIN-90014 Oulunyliopisto, Finland. e-mail: rnapanka@cc.oulofiAW Volume 14, Number 2, 2001 145 The International Journal of Prosthodontics