Fracture Resistance of Endodontically Treated Roots with Oval Canals Restored with Oval and Circular Posts ganay, DDS,† Bu gra G€ uler, DDS,* I_ smail Uzun, DDS, PhD,* Hakan Arslan, DDS, PhD,† Ezgi Do ‡ Cang€ ul Keskin, DDS,* and Ismail Davut C ¸ apar, DDS, PhD Abstract Introduction: The aim of the present study was to evaluate the effects of post space preparations with circular and oval post drills and the placement of oval and circular posts on the fracture strength of roots with oval canals. Methods: Seventy mandibular premolars with oval root canals were decoronated. Fourteen teeth were used as a control group (group 1), and the root canals of the remaining teeth were prepared up to size #30. The root canals were filled, and the samples were randomly divided into 4 experimental groups as follows: post space preparation with circular-shaped drills (group 2), post space preparation with ovalshaped drills (group 3), circular post placement (group 4), and oval post placement (group 5). A fracture strength test was performed on each specimen, and the data were statistically evaluated using 1-way analysis of variance and Tukey post hoc tests. Results: The fracture strengths of the circular posts–placed group were higher than those of the oval post–placed group (P < .001). The post space preparation using ovalshaped drills significantly decreased the fracture strength of the roots compared with the control group (P < .001). Conclusions: Within the limitations of the present study, oval posts did not provide a higher fracture resistance to endodontically treated roots with oval canals compared with circular posts. Therefore, clinicians should be aware that oval posts are similar to circular posts in terms of enhancing the fracture resistance of roots with oval canals. (J Endod 2015;-:1–5)
Key Words Endodontically treated tooth, fiber post, fracture strength, oval fiber post
nsufficient coronal structure of a tooth because of serious damage by decay and/or traumatic dental injury commonly requires the placement of a post system inside the root canal after adequate endodontic treatment to provide a retentive medium for core and coronal restoration (1). Practitioners frequently use prefabricated or custom posts made of metal, which increases the risk for unfavorable vertical root fracture because of their elastic modulus being above the dentin (2). However, fiberreinforced composite posts have elastic properties similar to those of dentin, which makes fractures restorable (2–5). Moreover, this type of post eradicates the corrosion problems associated with metal posts (6). These properties of fiberreinforced composite posts makes them advantageous in restoring endodontically treated teeth (7). Cement thickness is 1 of the main factors affecting the retention of post systems (8). Uzunoglu et al (8) evaluated the effect of 2 different post space diameters and related resin cement film thicknesses on the bond strength of fiber posts and found that increases in post space diameter significantly reduced the bond strength of fiber posts to root dentin for both groups. Similarly, Gomes et al (9) evaluated the effect of resin cement thickness on the bond strength and gap formation of fiber posts bonded to root dentin, and they reported that a lower resin cement thickness resulted in better fiber post adhesion (ie, higher bond strength and less gap formation). Effective bonding can contribute to reducing stress generated on the root canal walls, thereby strengthening the remaining tooth structure and decreasing the risk of fracture (10, 11). Another issue affecting the stress distribution is the post type. Okada et al (12) found that fiber posts showed a lower stress value when compared with metallic posts (titanium and stainless steel). Various adhesion strategies for fiber-reinforced composite posts have been used in root canals, and etch-and-rinse adhesives in combination with dual-cure resin cements were found to give the most reliable results (13). However, the use of simplified adhesives, such as etch-and-rinse 2-step and single-step self-etch adhesives, simplifies the handling. As far as resin cements are concerned, conventional dual-cured resin cements require prior application of adhesive systems. However, self-adhesive cements do not require any surface treatment of the root canals. They are easier to handle and have a clinically effective bond strength (14). The chemical reaction between phosphate methacrylates in self-adhesive cements and hydroxyapatite in dentin provides bonding (15). Endodontically treated roots are more susceptible to fracture because of their weakened structure. Endodontic treatment procedures, including access cavity preparation, root canal instrumentation, irrigation, post space preparation, and obturation, could be considered as possible predisposing factors (16–20). Recently, oval posts with their oval-shaped ultrasonic drills (Ellipson Tip; RTD/Satelec, Merignac, France)
From the*Department of Endodontics, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey; †Department of Endodontics, Faculty of Dentistry, Atat€urk University, Erzurum, Turkey; and ‡Department of Endodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkey. Address requests for reprints to Dr Hakan Arslan, Department of Endodontics, Faculty of Dentistry, Atat€urk University, Erzurum, 25640, Turkey. E-mail address: [email protected]
0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.11.009
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Fracture Resistance after Oval or Round Post Placement
Basic Research—Technology have been introduced for use in teeth with oval root canals. The manufacturer claims that this system results in fewer root fractures (21). The aim of the present study was to evaluate the effect of post space preparations with circular and oval post drills and the placement of oval and circular posts on the fracture strength of roots with oval canals. The null hypothesis was that there are no significant differences in fracture strength among the groups.
Materials and Methods A total of 70 single-rooted, freshly extracted, noncarious human mandibular premolar teeth with similar dimensions were used for this study. The reason for extraction was not related to the study. To disinfect the teeth, they were immersed in 0.5% Chloramine-T solution (Merck, Darmstadt, Germany) for 48 hours, and soft tissue and calculus were mechanically removed from the root surfaces using a periodontal scaler. The specimens were radiographed in both the buccolingual and mesiodistal directions, and they were classified as oval if the buccolingual diameter of the root was 1.6 times greater its mesiodistal diameter at a level of 5 mm from the root apex (22). The exclusion criteria were as follows: teeth with more than a single root canal, previous root canal treatment, internal/external resorption, immature root apices, caries/cracks/fractures on the root surface, or a root canal curvature of more than 10 . The teeth were stored in distilled water at room temperature until use. The samples were decoronated to obtain a standardized length of 15 mm. Fourteen samples served as a control group, and the remaining samples were prepared as follows: a #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was moved down into the root canal until the file was just visible, the length of the file was recorded, and the working length was determined as 1 mm less than this length. Root canal shaping procedures were performed by using ProTaper rotary instruments (Dentsply Maillefer) up to an apical preparation with size #30 (F3). One milliliter of 2.5% NaOCl was used between instrument changes. The final irrigation protocol was performed using 5 mL 17% EDTA for 1 minute and 5 mL 2.5% NaOCl followed by 5 mL distilled water. The root canals were dried and filled with AH Plus sealer (Dentsply DeTrey, Konstanz, Germany) and gutta-percha (Dentsply Maillefer) using the cold lateral compaction technique. The 56 experimental samples were then divided into 4 groups (n = 14).
Group 5 Post space preparation was performed as in group 3. An oval fiber post was seated (diameter of the tip of the fiber = 0.6 mm, thickness = 1.1 mm, width = 1.8 mm) (Ellipson Posts, RTD/Satelec). The experimental design is summarized in Figure 1. In the experimental groups, the root canal filling material was removed using a heated plugger (size 2; VDW GmbH, Munich, Germany) before post space preparation. A 10-mm-deep post space preparation was performed, and the posts were cemented into the post spaces by using a selfadhesive resin luting agent (RelyX Unicem; 3M ESPE, Seefeld, Germany) according to the manufacturer’s instructions. After the posts were separated above the roots, the samples were stored in distilled water for 1 day at 37 C. The samples were then mounted in the acrylic resin (Imicryl, Konya, Turkey), exposing 5 mm of the coronal part. The fracture strength test was performed by using a universal testing machine (Instron Corp, Norwood, MA) at a constant crosshead speed of 1 mm/min. The force at which fracture occurred in each sample was recorded in newtons. Statistical analysis was performed using 1-way analysis of variance and Tukey post hoc tests for the fracture strength data (P = .05) with SPSS software (SPSS Inc, Chicago, IL). The failure type was recorded and classified as favorable (would allow repair) or catastrophic (nonrestorable). The favorable failure type was located at the cervical third, whereas catastrophic failure was located at the middle or apical thirds. The direction of the failure was also recorded as buccolingual, mesiodistal, or mesiolingual.
Group 1 (Control Group) Root canals were not instrumented, and post space preparation and post placement were not performed. Group 2 The post space preparation was performed using a circularshaped drill (size #2, 1.55 mm) (Unicore; Ultradent, Salt Lake City, UT). Post placement was not performed. Group 3 Post space preparation was performed using an oval-shaped, ultrasonic drill (Ellipson Tip) mounted in a Suprasson handpiece (Satelec/ Acteon, Merignac, France). Post placement was not performed. Group 4 Post space preparation was performed as in group 2. A circular fiber post (size #2, 1.55 mm) (Unicore posts size 2, Ultradent) was seated to the full depth by using finger pressure.
Uzun et al.
Figure 1. A schematic presentation of the procedures. Group 1: noninstrumented, group 2: post space preparation using a circular drill, group 3: post space preparation using an oval drill, group 4: circular post placement, and group 5: oval post placement. Loading was performed at 1 mm/min.
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Basic Research—Technology TABLE 1. Fracture Strength Details of the Groups (Newtons) Failure type, n (%) Groups Control group Post space preparation using circular drill Post space preparation using oval drill Circular post placement Oval post placement
Direction, n (%)
Minimum Maximum Favorable Catastrophic
2 (14.2) 3 (21.4)a
12 (85.8) 11 (78.6)a
4 (28.5) 3 (21.4)a
10 (71.6) 11 (78.6)a
14 (100) 9 (64)
0 (0) 5 (36)
0 (0) 0 (0)
13 (92.8) 12 (85.8)
0 (0) 2 (14.2)
1 (7.2) 0 (0)
BL, buccolingual; MD, mesiodistal; ML, mesiolingual; SD, standard deviation. Different letters show statistically significant differences between the groups (P < .05).
Results The mean fracture strengths for different groups are shown in Table 1. The post space preparation using an oval-shaped drill significantly decreased the fracture resistance of the roots compared with the control group (P < .001). However, there was no significant differences in fracture strength between the control group and the post space preparation using circular-shaped drills (P > .05). Both the circular and oval post placements significantly increased the fracture strength of the roots compared with the control group (P < .001), and the fracture strengths of the circular post–placed group were higher than those of the oval post–placed group (P < .001). The modes of failure are listed in Table 1. Catastrophic failure was the most frequent type of failure in all groups (Figs. 2 and 3). There were no significant differences among the groups in terms of failure type (P > .05), and the most fracture lines were in the buccolingual direction.
Discussion Endodontically treated roots are susceptible to fracture because of their weakened structure. Thus, 1 of the goals of root canal treatment is to reinforce the endodontically treated root. Oval post systems have been popular in recent years to obtain retention in teeth with oval root canals. Coniglio et al (23) found that teeth treated with oval posts had lower cement thicknesses than those treated with circular posts. Furthermore, Er et al (24) suggested that oval fiber posts are preferable to circular fiber posts in ovalshaped canals given the stress distribution at the post-dentin interface. Despite these advantages of oval posts, there are no available data on the effects of post space preparation using oval-shaped drills and oval post placements on the fracture resistance of endodontically treated roots. Therefore, the present study aimed to compare the effects of post space preparations with circular and oval post drills and
the placement of oval and circular posts with a noninstrumented group on the fracture strength of roots with oval canals. Because there were significant differences between these groups, the null hypothesis is rejected. The main finding of this study is that circular or oval post placement increased the fracture strength of the endodontically treated roots compared with the control group. Torres-Sanchez et al (25) compared the fracture strength of endodontically treated teeth restored with glass fiber–reinforced or cast gold posts and cores cemented with 3 cements, and they concluded that the use of a glass fiber–reinforced post increased the fracture resistance of the endodontically treated teeth. This increased fracture resistance could be caused by the fact that resin-based materials are able to preserve and reinforce the remaining tooth structures (26). Conversely, Sagsen et al (27) concluded that titanium posts and fiber posts were found to have no reinforcing effect on endodontically treated roots. This finding is not in line with those of the present study. In the study by Sagsen et al (27), the root canals of the specimens were enlarged, filled, and used as a control group. The conflicting results might be caused by the fact that we did not instrument or fill the roots in the control group. Also, in the study by Sagsen et al (27), the lack of significant effect of fiber post placement on the reinforcement of the roots might be because of the use of a resin-based root canal sealer in the control group. Krastl et al (28) found that oval posts did not increase the fracture resistance of root canal–treated premolars with oval-shaped root canals compared with circular posts, which was similar to our findings. According to the results of the present study, both circular and oval posts enhanced the fracture strength of teeth with oval-shaped root canals. The most likely reason to explain this finding might be the reduced fracture strength after the use of oval post drills. The results of the present study reveal that post space preparation using circular and oval-shaped ultrasonic drills reduces
Figure 2. Failure types according to the groups. The favorable failure type was located at the cervical third; on the other hand, the catastrophic failure type was located at the middle or apical thirds.
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Fracture Resistance after Oval or Round Post Placement
Figure 3. Representative scanning electron microscopic images. (A) Failure in the noninstrumented group, (B) failure in the circular post placement group, and (C) failure in the oval post placement group. Note that cement thickness in the oval post group was thinner than that of circular post.
the fracture strength of endodontically treated roots. However, there are no statistically significant differences in fracture strength between the control group and post space preparation using circular-shaped drills. The relatively low number of samples in the present study might be the main reason for this nonsignificant result. Coniglio et al (23) evaluated the cement thickness around oval and circular posts luted into oval post spaces and found that oval posts resulted in lower cement thicknesses than circular posts. Also, in another study by Coniglio et al (29), better adhesion was obtained with oval posts than with circular posts, and a lower resin cement thickness resulted in better fiber post adhesion and bond strength (9). This increased bond strength can contribute to the strength of the remaining tooth structure (10, 11). In the present study, however, adhesion and cement thickness were not evaluated. Despite the advantages of oval posts over circular posts, teeth treated with circular posts, which had greater cement thicknesses, had higher fracture strengths than those of oval posts according to the results of the present study. It is well established that the stress distribution can be altered by the presence of a post (30, 31). According to a recent study by Er et al (24), the oval fiber post system provides better stress distribution than the circular fiber post system in oval-shaped canals given the stress distribution at the post-dentin interface. According to the results of the present study, catastrophic failure was the most frequent type of failure in all groups, and there were no statistically significant differences between oval and round post placements. In laboratory studies, cycling loading and the aging process are important tools for the evaluation of restorative materials and techniques to replicate a clinical situation (32, 33). One limitation of the present study is that the cycling loading and aging process were not considered. In the present study, all controllable factors were standardized as much as possible; the samples in all groups were human mandibular premolar teeth, the teeth were randomly distributed to the groups, teeth with similar dimensions were selected, the root length of the specimens was standardized to 15 mm, and the root canals were enlarged and obturated using the same technique. However, the fracture strengths of specimens in the same group were quite different from each other; when extracted roots are used for evaluating strength, there may be large uncontrollable anatomic variations (34).
Conclusion Within the limitations of the present study, oval posts did not provide higher fracture resistance to endodontically treated roots with oval canals when compared with circular posts. Clinicians should be aware that oval posts are similar to circular posts in terms of enhancing the fracture resistance of roots with oval canals. Further studies should be conducted to confirm the results of the present study.
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Acknowledgments Supported in part by the Ondokuz Mayıs University Research Fund (Project No: PYO.DIS.1901.13.004). The authors deny any conflicts of interest related to this study.
References 1. Goracci C, Ferrari M. Current perspectives on post systems: a literature review. Aust Dent J 2011;56(suppl 1):77–83. 2. Chuang SF, Yaman P, Herrero A, et al. Influence of post material and length on endodontically treated incisors: an in vitro and finite element study. J Prosthet Dent 2010;104:379–88. 3. Chieruzzi M, Pagano S, Pennacchi M, et al. Compressive and flexural behaviour of fibre reinforced endodontic posts. J Dent 2012;40:968–78. 4. Martinho FC, Carvalho CAT, Oliveira LD, et al. Comparison of different dentin pretreatment protocols on the bond strength of glass fiber post using self-etching adhesive. J Endod 2014 Sep 20. pii: S0099-2399(14)00654-2, http://dx.doi.org/ 10.1016/j.joen.2014.07.018 [Epub ahead of print]. 5. Santos-Filho PC, Verıssimo C, Raposo LH, et al. Influence of ferrule, post system, and length on stress distribution of weakened root-filled teeth. J Endod 2014;40: 1874–8. 6. Kedici SP, Aksut AA, Kilicarslan MA, et al. Corrosion behaviour of dental metals and alloys in different media. J Oral Rehabil 1998;25:800–8. 7. Baba NZ, Golden G, Goodacre CJ. Nonmetallic prefabricated dowels: a review of compositions, properties, laboratory, and clinical test results. J Prosthodont 2009;18:527–36. 8. Uzunoglu E, Turker SA, Yilmaz Z. Influence of cement type and thickness on polyfiber post adhesion. J Conserv Dent 2014;17:255–60. 9. Gomes GM, Rezende EC, Gomes OM, et al. Influence of the resin cement thickness on bond strength and gap formation of fiber posts bonded to root dentin. J Adhes Dent 2014;16:71–8. 10. Boschian Pest L, Cavalli G, Bertani P, Gagliani M. Adhesive post-endodontic restorations with fiber posts: push-out tests and SEM observations. Dent Mater 2002; 18:596–602. 11. Butz F, Lennon AM, Heydecke G, Strub JR. Survival rate and fracture strength of endodontically treated maxillary incisors with moderate defects restored with different post-and-core systems: an in vitro study. Int J Prosthodont 2001;14: 58–64. 12. Okada D, Miura H, Suzuki C, et al. Stress distribution in roots restored with different types of post systems with composite resin. Dent Mater J 2008;27:605–11. 13. Dietschi D, Duc O, Krejci I, Sadan A. Biomechanical considerations for the restoration of endodontically treated teeth: a systematic review of the literature, part II (evaluation of fatigue behavior, interfaces, and in vivo studies). Quintessence Int 2008;39:117–29. 14. Nakamura T, Wakabayashi K, Kinuta S, et al. Mechanical properties of new selfadhesive resin-based cement. J Prosthodont Res 2010;54:59–64. 15. Gerth HU, Dammaschke T, Zuchner H, Schafer E. Chemical analysis and bonding reaction of RelyX Unicem and Bifix composites—a comparative study. Dent Mater 2006;22:934–41. 16. Trope M, Ray HL Jr. Resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol 1992;73:99–102. 17. Schiavetti R, Sannino G. In vitro evaluation of ferrule effect and depth of post insertion on fracture resistance of fiber posts. Comput Math Methods Med 2012;2012: 816481. 18. Uzunoglu E, Aktemur S, Uyanik MO, et al. Effect of ethylenediaminetetraacetic acid on root fracture with respect to concentration at different time exposures. J Endod 2012;38:1110–3.
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Basic Research—Technology 19. Topcuoglu HS, Arslan H, Keles A, Koseoglu M. Fracture resistance of roots filled with three different obturation techniques. Med Oral Patol Oral Cir Bucal 2012;17: e528–32. 20. Tang W, Wu Y, Smales RJ. Identifying and reducing risks for potential fractures in endodontically treated teeth. J Endod 2010;36:609–17. 21. RTD Dental. Ellipson brochure. Avaliable at: http://www.rtddental.com/images/pdfs/ DOC5100GB00.pdf. Accessed August 4, 2014. 22. Wu MK, Kast’akova A, Wesselink PR. Quality of cold and warm gutta-percha fillings in oval canals in mandibular premolars. Int Endod J 2001;34:485–91. 23. Coniglio I, Garcia-Godoy F, Magni E, et al. Resin cement thickness in oval-shaped canals: oval vs. circular fiber posts in combination with different tips/drills for post space preparation. Am J Dent 2009;22:290–4. 24. Er O, Kilic K, Esim E, et al. Stress distribution of oval and circular fiber posts in a mandibular premolar: a three-dimensional finite element analysis. J Adv Prosthodont 2013;5:434–9. 25. Torres-Sanchez C, Montoya-Salazar V, Cordoba P, et al. Fracture resistance of endodontically treated teeth restored with glass fiber reinforced posts and cast gold post and cores cemented with three cements. J Prosthet Dent 2013;110:127–33. 26. Balkaya MC, Birdal IS. Effect of resin-based materials on fracture resistance of endodontically treated thin-walled teeth. J Prosthet Dent 2013;109:296–303.
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27. Sagsen B, Zortuk M, Ertas H, et al. In vitro fracture resistance of endodontically treated roots filled with a bonded filling material or different types of posts. J Endod 2013;39:1435–7. 28. Krastl G, Lorch H, Zitzmann NU, et al. Do oval posts improve fracture resistance of teeth with oval root canals? Dent Traumatol 2014;30:232–5. 29. Coniglio I, Carvalho CA, Magni E, et al. Post space debridement in oval-shaped canals: the use of a new ultrasonic tip with oval section. J Endod 2008;34:752–5. 30. Santos AF, Meira JB, Tanaka CB, et al. Can fiber posts increase root stresses and reduce fracture? J Dent Res 2010;89:587–91. 31. Santos-Filho PC, Castro CG, Silva GR, et al. Effects of post system and length on the strain and fracture resistance of root filled bovine teeth. Int Endod J 2008;41:493–501. 32. Heydecke G, Butz F, Strub JR. Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study. J Dent 2001;29:427–33. 33. Marchi GM, Mitsui FH, Cavalcanti AN. Effect of remaining dentine structure and thermal-mechanical aging on the fracture resistance of bovine roots with different post and core systems. Int Endod J 2008;41:969–76. 34. Teixeira FB, Teixeira EC, Thompson JY, Trope M. Fracture resistance of roots endodontically treated with a new resin filling material. J Am Dent Assoc 2004; 135:646–52.
Fracture Resistance after Oval or Round Post Placement