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Evaluation of a calcium silicate-based cement as a root reinforcement material for endodontically treated maxillary anterior teeth
RESEARCH AND EDUCATION
Evaluation of a calcium silicate-based cement as a root reinforcement material for endodontically treated maxillary anterior teeth Peter M. Di Fiore, DDS, MS,a Adrian Reyes, DDS,b Samuel O. Dorn, DDS,c Stanley G. Cron, MSPH,d and Joe C. Ontiveros, DDS, MSe The objectives for restoring ABSTRACT endodontically treated teeth Statement of problem. Fractures of endodontically treated teeth have been attributed to weakare to maintain their structural ened tooth structure caused by root canal enlargement and post preparation. integrity and retain them as Purpose. The purpose of this in vitro study was to evaluate the fracture resistance of roots filled fully functional units in the with either gutta percha, composite resin (LuxaCore Dual), or calcium silicate-based cement dentition.1 During endodontic (Biodentine). instrumentation, root canals Material and methods. One hundred twenty freshly extracted, human, permanent maxillary are cleaned and shaped in a anterior teeth were sorted by type and assigned to 1 of 4 groups (n=30). The teeth in group NT manner that respects their were not endodontically treated and served as the control. The teeth in groups GP, LC, and, BD were morphology without altering accessed and instrumented to size 40/06. In group GP, the root canals were completely filled with or weakening their roots.2 gutta percha. In groups LC and BD, only the apical 5-mm portion of the root canals was filled with Endodontically treated teeth gutta percha, and the remaining portion of the root canals was filled with (LuxaCore Dual) in group LC and with (Biodentine) in group BD. Fracture resistance (kN) was assessed at the middle portion of often require the placement of each root, using a 3-point bending test with a universal testing machine exerting a compressive a post and core for crown load on a loading pin at a crosshead speed of 0.5 mm/min until fracture occurred. One-way 3 restoration. Fractures of ANOVA was used to compare the mean root fracture resistance among the 4 groups (a=.05). endodontically treated teeth Results. The mean ± SD fracture loads were 2.13 ±0.53 kN for group NT, 1.97 ± 0.60 kN for group have been attributed to weakGP, 2.18 ±0.71 kN for group LC, and 2.22 ±0.54 kN for group BD. No statistically significant differened tooth structure caused by ences were found among the 4 groups (P>.05). endodontic and restorative Conclusions. The roots of endodontically treated maxillary anterior permanent incisors filled with procedures.4 Occlusal stresses gutta percha, Biodentine, or LuxaCore Dual had resistance to fracture similar to that of teeth that and reduced mechanical were not endodontically treated. (J Prosthet Dent 2015;-:---) properties of endodontically treated teeth may also teeth had a significant effect on stress distribution and contribute to fatigue-induced root fractures.5 An invesfracture resistance.6 Removal of excessive dentin during tigation using 3-dimensional finite analysis found that root canal instrumentation and preparation for dowels the amount of remaining coronal dentin and the type of and posts can result in the loss of root strength and an post and crown used to restore endodontically treated
Supported by a research grant from the American Association of Endodontists Foundation. a Professor, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. b Resident, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. c Professor and Program Director, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. d Statistician, Center for Nursing Research, University of Texas, School of Dentistry, Houston, Tex. e Associate Professor, Department of Restorative Dentistry and Prosthodontics, University of Texas, School of Dentistry, Houston, Tex.
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Clinical Implications Biodentine and LuxaCore Dual appear to be appropriate root reinforcement materials for maxillary anterior permanent teeth. Endodontically treated teeth with root canals prepared to a size of 40/06 and filled with gutta percha may not necessarily need root reinforcement.
increased susceptibility to root fracture.7-11 Therefore, the preservation of tooth structure is essential in preventing root fractures in endodontically treated teeth.8,10,11 The resistance to fracture of endodontically treated roots is also influenced by the presence and strength of the root canal obturation material and the bond strength between the material and root canal dentin.11 Roots with empty root canals were more susceptible to fracture than filled roots, whereas roots reinforced with a suitable intracanal materials maintained fracture resistance.11 Several studies have investigated the fracture resistance of endodontically treated extracted human teeth with roots with cemented fiber posts with resin based materials.12-14 These studies concluded that the modulus of elasticity of fiber posts influenced fracture resistance,12 that fiber post-supported cores improved fracture resistance,13 and that fiber posts prevented catastrophic fractures.14 Trope et al8 compared the resistance to fracture of endodontically treated maxillary central incisors reinforced with different types of materials and concluded that post space preparation weakened roots and that post placement did not necessarily strengthen roots. However, acid etching of root canal dentin before filling the post space with a bonded composite resin significantly increased root fracture resistance. Trabert et al9 tested the resistance to fracture of endodontically treated maxillary central incisors reinforced with large and small diameter posts and found that extensive preparation of root canals and placement of large diameter posts significantly reduced root fracture resistance. Reeh et al10 compared the effect of endodontic and restorative procedures on the overall stiffness of extracted maxillary second premolars and demonstrated that endodontic procedures reduced tooth stiffness by 5%, whereas restorative procedures, such as mesio-occlusal distal coronal cavity preparations, reduced stiffness by 60%. Sornkul et al11 tested the fracture resistance of single-rooted mandibular premolar roots with and without endodontic treatment and post restoration and showed that the roots of untreated premolars had a greater resistance to fracture than roots with any mode of post restoration, demonstrating that preserving tooth structure was the most important factor for fracture resistance. Zamin et al15 and Zandbiglari et al16 evaluated the fracture susceptibility of THE JOURNAL OF PROSTHETIC DENTISTRY
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teeth whose root canals were prepared with large and small tapered endodontic instruments. Both of these investigations found that root canals prepared with large tapered instruments significantly weakened roots, especially in the cervical third of the root, compared with root canals prepared with small tapered instruments. Lang et al17 investigated the influence of endodontic and restorative procedures on extracted maxillary incisors at different stages of treatment (access cavity preparation, root canal instrumentation, and post preparation) and found that deformation on loading increased as more tooth structure was removed after each treatment stage. A variety of intracanal materials have been used to reinforce the roots of endodontically treated teeth and can be divided into 2 main types, prefabricated and custom fabricated posts that are either cemented or adhesively bonded in root canals.18 However, these posts require root canal enlargement to an appropriate size for post insertion, necessitating the removal of intracanal dentin.18 Although both prefabricated metal and fiber posts can be used for root reinforcement,19,20 adhesive bonding of composite resin materials, which require little or no removal of intracanal dentin, have been used to reinforce the roots of endodontically treated teeth, especially in those with compromised root thickness and have been shown to increase root fracture resistance.8,11-13 Additionally, composite resin filled root canals substantially increased root fracture resistance compared with gutta percha-filled root canals and unfilled root canals.8,11 However, the physical properties of composite resin do not mimic the physical properties of dentin.21-23 Polymerization shrinkage is an inherent property of composite resins, which can result in resin debonding at the dentin interface and may affect its reinforcing properties.24,25 As a consequence, shrinkage and bond failure may be possible drawbacks of composite resins as root reinforcing materials.24,25 Biodentin (Septodont) is a recently developed biocompatible calcium silicate-based cement material composed of tricalcium silicate, calcium carbonate, zirconium oxide, calcium chloride and polycarboxylate. Its applications include replacing lost coronal dentin, forming a core structure, and repairing root perforations.26,27 An ideal intracanal root reinforcing material should have similar physical properties to those of dentin.18 This calcium silicate-based cement and human dentin share similar physical properties.26,27 The modulus of elasticity of the cement, being similar to dentin, would allow for stress distribution in endodontically treated roots during function and could reduce the chance of fracture.1,26,27 This concept was tested in an in vitro investigation that used experimental dentin posts to reinforce the roots of endodontically treated anterior teeth and found that the fracture resistance under static loading was highest for posts made of dentin compared with glass fiber or carbon Di Fiore et al
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fiber posts.20 The purpose of this study was to evaluate and compare the root fracture resistance of endodontically treated teeth with root canals filled with gutta percha, composite resin (LuxaCore Dual; Kerr Corp), or calcium silicate-based cement (Biodentine; Septodent). MATERIAL AND METHODS This research was approved by the Institutional Review Board of the University, Health Science Center, School of Dentistry, where this study was conducted. Human, freshly extracted fully developed permanent maxillary anterior teeth were collected and disinfected in accordance with the policy and protocol of the School of Dentistry. The teeth were placed in a holding solution of 0.5% sodium hypochlorite immediately after extraction, immersed in 10% formalin solution for a period of 2 weeks for disinfection, and then stored in physiological saline solution until use. The teeth were inspected for any defects (abrasions, caries, cracks, crazes, erosions, fractures, or resorptions) using a surgical microscope (Global Surgical Microscope; Global Surgical) at ×5 magnification. A digital periapical radiograph of each tooth was also made to aid in identifying defects. Teeth with any defects were excluded from the study. To ensure the use of roots with comparable dimensions, the mesial distal (MD) and facial palatal (FP) dimensions of the roots were measured at middle root level with a digital caliper (Digital Caliper; Mitutoyo). A total of 120 teeth were sorted by type and divided into 4 groups (group NT, group GP, group LC, and group BD) of 30 teeth each. Table 1 shows mean ±SD, MD, and FP dimensions of the roots for each group. The teeth in group NT were not treated, served as the control, and were kept in physiological saline solution. The teeth in groups GP, LC, and BD had a standard endodontic access prepared on the lingual surface of their crowns. A no. 10 stainless steel hand file (FlexoFile; Dentsply Maillefer) was inserted in the orifice of the root canal until observed to be flush with the apical foramen, and its length was measured from the incisal reference point. Working length (WL) was established by subtracting 1 mm from this length. A #15 stainless steel hand file (FlexoFile; Dentsply Maillefer) was inserted into the root canal to the WL to establish a glide path. The root canals were enlarged to a master apical file (MAF) size of 40/06 with nickel titanium rotary instruments (ProFile; Dentsply Intl) in a crown down manner to WL. During instrumentation, the root canals were irrigated with 6% NaOCl and 17% EDTA. A 10mL plastic syringe with a 27-gauge side-vented needle was used to deliver the irrigating solutions into the canal. The teeth were stored in physiological saline solution immediately after completion of root canal instrumentation. Di Fiore et al
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Table 1. Mean ±standard deviations of root dimensions Mean Facial-Lingual Dimension
Mean Mesial-Distal Dimension
Negative control group NT
7.18 ±0.99 mm
5.23 ±0.71 mm
Gutta percha group GP
7.16 ±0.80 mm
5.12 ±0.55 mm
LuxaCore dual group LC
7.16 ±0.89 mm
5.23 ±0.73 mm
Biodentine group BD
7.24 ±0.92 mm
5.08 ±0.65 mm
Group
The root canals of the teeth in group GP were filled with gutta percha (Gutta Percha Cones; Brasseler USA) and resin-based sealer (AH Plus; Dentsply Intl) using the continuous wave obturation technique to the level of the cementoenamel junction. The access cavities were etched for 15 seconds with 35% phosphoric acid (UltraEtch; Ultradent Products Inc), rinsed with water, and dried with coarse paper points. Bonding agent (Optibond Solo Plus; Kerr Corp) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The access cavities were filled flush to the lingual surface of the crowns with composite resin (PermaFlo; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The apical 5 millimeters of the root canals of the teeth in group LC were filled with gutta percha as previously described, and the remaining unfilled root canals and access cavities were etched for 15 seconds with 35% phosphoric acid (Ultra-Etch; Ultradent Products Inc), rinsed with water, and dried with course paper points. Bonding agent (Optibond Solo Plus; Kerr Corp) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The remaining root canals and access cavities were then filled to the level of the lingual surface of the crowns with composite resin (LuxaCore Dual; Kerr Corp) using a microsyringe and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The apical 5 millimeters of the root canals of the teeth in group BD were filled with gutta percha as previously described, and the remaining unfilled root canals and access cavities were rinsed with water and dried with coarse paper points. A calcium silicate-based cement (Biodentine; Septodent) was prepared according to the manufacturer’s instructions and placed into the canals in small increments using material carriers (MTA Carriers; Vista Dental), followed by compaction of each increment of Biodentine (Biodentine; Septodent) using ISO sized endodontic pluggers (Endo Pluggers; Dentsply Maillefer). The filling procedure was repeated until THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 2. Mean ±SD root fracture resistance Group
Number Mean ±SD Root Fracture Resistance (kN)
Negative control group NT
30
2.13 ±0.53
Gutta percha group GP
25
1.97 ±0.60
LuxaCore dual group LC
30
2.18 ±0.71
Biodentine group BD
26
2.22 ±0.54
Figure 1. Radiographs of root-filled teeth. A, Gutta percha. B, Composite resin. C, Calcium silicate-based cement.
Root Fracture Resistance (kN)
3.5 3
2.18 2.13
1.97
2.22
2.5 2 1.5 1 0.5 0 Untreated
Gutta Percha
Luxa Core
Biodentine
Figure 3. Means ±standard deviations of root fracture resistance.
Figure 2. Three-point bending test fixture and loading pin.
the calcium silicate-based cement (Biodentine; Septodent) reached a level approximately 3 mm below the lingual surface of the crown. The unfilled portions of the access openings were etched for 15 seconds with 35% phosphoric acid (Ultra-Etch; Ultradent Products Inc), rinsed with water, and dried with coarse paper points. Bonding agent (Optibond Solo Plus; Kerr) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The access openings were filled flush to the lingual surface of the crowns with composite resin (PermaFlo; Ultradent Products Inc) and light polymerized (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The filled teeth were radiographed to ensure complete filling of the root canals (Fig. 1). Immediately after completion of the root canal and access cavity filling, the teeth in each of the treatment groups were placed in 100% humidity at 37 C for at least 72 hours to allow THE JOURNAL OF PROSTHETIC DENTISTRY
the root filling and root reinforcement materials to completely set before testing. The root fracture resistance of each tooth was evaluated by using a custom 3-point bending test fixture and loading pin with a universal testing machine (Instron Testing Machine; Instron) and materials testing software (Bluehill Software; Instron) (Fig. 2). The 3-point bending test fixture had a span length of 10 mm between the 2 lower support points. Each tooth was placed on the test fixture, with the facial root surface facing down and supported by the 2 test fixture support points. The tooth contact surfaces on the fixture support points was visually verified to make sure that the 2 support points made contact only on root surfaces. A loading pin attached to the universal testing machine (Instron Testing Machine; Instron) and centered between the 2 support points was used to apply the third vertically oriented load on the root. (Fig. 2) at a crosshead speed of 0.5 mm/min until root fracture occurred. The test was aborted if the tooth slipped or rotated during application of the load. The root fracture resistance of each tooth was the load measured in kilonewtons at the point of root fracture, which was recorded and plotted on a graph using materials testing software (Bluehill Software; Instron). Available resources allowed the use of 120 teeth (30 per group). Based on this sample size, a 1-way univariate analysis of variance (ANOVA) would have sufficient power to detect a medium effect size of (f=.31). Statistical analysis was performed with software (SPSS v20; IBM Corp). One-way ANOVA was used to analyze and Di Fiore et al
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Figure 4. Typical root fracture patterns. A, Single root fracture. B, Double root fracture.
compare the mean root fracture resistance among the 4 groups. Post hoc comparisons among groups were performed with Tukey multiple comparisons (a=.05). RESULTS Mean values for the root fracture resistance of each group are presented in Table 2 and illustrated in Figure 3. The mean ±SD root fracture resistance values for each group were 2.13 ±0.53 kN for group NT (n=30), 1.97 ±0.60 kN for group GP (n=25), 2.18 ±0.71 kN for group LC (n=30), and 2.22 ±0.54 kN for group BD (n=26). Some teeth in groups GP and BD were excluded from the results because of slipping or rotating on the test fixture during application of the load. The data did not violate the assumption of normality, with absolute values for both skewness and kurtosis <1. The results of the 1-way ANOVA indicated no statistically significant difference in load among the groups (F (3, 107)=.891, P=.449). The Tukey multiple comparisons test confirmed no statistically significant differences (P>.05) among any of the groups. DISCUSSION This study compared root fracture resistance values of endodontically treated maxillary anteriorpermanent teeth, root filled with gutta percha, composite resin, or calcium silicate-based cement. The study design specifically tested the ability of these 3 materials, placed in the middle portion of the root canal, to resist root fracture by using a customized 3-point bending test fixture. Untreated maxillary anterior teeth served as the control. This study found no statistically significant difference in the mean root fracture resistance among the 4 groups. All of the procedures were performed by 1 operator (A.R.) to ensure consistency in preparation and testing. The custom made 3-point bending fixture was designed so that the tooth would be in contact with the 2 fixture support points on root surfaces only. Loads were directed with the loading pin exactly at the midpoint of the roots between the 2 fixture support points of the 3-point bending test fixture. This exerted the load precisely to the middle portion of the roots filled with either gutta percha, composite resin, or calcium silicate-based cement, where fracture resistance was specifically Di Fiore et al
tested, without any influence of the apical or coronal structural elements of the tooth (Fig. 2). The distribution of tooth types was consistent for each group: group NT (19 canines, 5 central, and 6 lateral incisors); group GP had 16 canines, 5 central and 4 lateral incisors; group LC (18 canines, 5 central, and 7 lateral incisors), and group BD had 17 canines, 7 central, and 2 lateral incisors. Measurements of the roots made at middle root level showed consistency in mean root dimensions amongst the groups (Table 1). Although effort was made to have consistency in each group, some variations were present in root dimensions and shapes within the groups, which could have influenced the results. This was a limitation of the study, since root dentin thickness has been shown to significantly influence root strength when subjected to various types of loading conditions.5 Two typical patterns of root fracture were commonly observed in all groups (Fig. 4). The first fracture pattern that occurred was a single horizontally or obliquely directed fracture that occurred at the point where the loading pin was in contact with the root, resulting in the tooth splitting into 2 separate pieces (Fig. 4A). The second fracture pattern was 2 separate horizontal or oblique fractures that occurred on each side of the loading pin, resulting in the tooth splitting into 3 pieces (Fig. 4B). Close inspection of the fractured pieces from the GP group and LC group revealed areas where separation and debonding of the materials from the dentin occurred (Fig. 5). However, in most of the fractured tooth pieces inspected from the Biodentine group, there were no areas of material de-bonding from dentin, and the Biodentine material often appeared to fracture along the same plane as the surrounding dentin (Fig. 6). The teeth with root canals filled with gutta percha and those filled with root-reinforcing materials (LuxaCore Dual or Biodentine) showed statistically similar root fracture resistance values compared with the untreated teeth (Fig. 3). This finding was not in agreement with the study of Sornkul et al,11 in which teeth with untreated root canals showed greater root fracture resistance than teeth with treated root canals. The root canals of the endodontically treated teeth in this study were all prepared to a standard MAF instrument size of 40/06, which would be considered appropriate for root canal preparation of maxillary anterior teeth. Of the 3 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 5. Root fracture with material debonding from dentin. A, Gutta percha. B, LuxaCore.
statistically significant difference in root fracture resistance when compared with untreated teeth. A calcium silicate-based cement may be a suitable material for root reinforcement. Further studies are indicated on the performance of calcium silicate-based cements as a root reinforcement material for endodontically treated teeth. REFERENCES
Figure 6. Biodentine root fracture without debonding from dentin.
treatment groups, endodontically treated teeth with gutta percha root canal filling had the lowest mean root fracture resistance (Fig. 3). However, since no significant differences were found in the root fracture resistance of untreated teeth and endodontically treated teeth with gutta percha root canal fillings, teeth treated in this manner may not necessarily need root reinforcement. Another explanation for the finding of no significant difference among the 3 treatment groups could be that the reinforcing potential of the materials was not fully realized in root canals prepared to a 40/06 instrument size and that instrumentation to a larger size may have caused greater differences in fracture resistance. The root fracture resistance values reported in the present study are large compared with those found in other studies.7,8,20 This difference was most probably due to the short span 3-point bending fixture and loading pin testing device used in this study, which produced a gradual compressive load at 0.5 mm/min until root fracture occurred (Fig. 2). For this reason, the results obtained in this study are not directly comparable with those obtained in other studies which used a single oblique compressive force applied to the coronal lingual surfaces of mounted teeth.7,8,20 CONCLUSIONS Within the limitations of this in vitro study, the root reinforcement materials evaluated did not produce a THE JOURNAL OF PROSTHETIC DENTISTRY
1. Schwartz RS, Robbins JW. Post placement and restoration of endodontically treated teeth: a literature review. J Endod 2004;30:289-301. 2. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96. 3. Baraban DJ. A simplified method for making posts and cores. J Prosthet Dent 1970;24:287-97. 4. Kishen A. Mechanisms and risk factors for fracture predilection in endodontically treated teeth. Endodontic Topics 2006;13:57-83. 5. Tang W, Wu Y, Smales RJ. Identifying and reducing risks for potential fractures in endodontically treated teeth. J Endod 2010;36:609-17. 6. Verissimo C, Simamoto Júnior PC, Soares CJ, Noritomi PY, Santos-Filho PC. Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors. J Prosthet Dent 2014;111:234-46. 7. 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. 8. Trope M, Maltz DO, Tronstad L. Resistance to fracture of restored endodontically treated teeth. Endod Dent Traumatol 1985;1:108-11. 9. Trabert KC, Caput AA, Abou-Rass M. Tooth fractureda comparison of endodontic and restorative treatments. J Endod 1978;4:341-5. 10. Reeh ES, Messer HH, Douglas WH. Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod 1989;15:512-6. 11. Sornkul E, Stannard JG. Strength of roots before and after endodontic treatment and restoration. J Endod 1992;18:440-3. 12. 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. 13. Scotti N, Rota R, Scansetti M, Paolino DS, Chiandussi G, Pasqualini D, et al. Influence of adhesive techniques on fracture resistance of endodontically treated premolars with various residual wall thicknesses. J Prosthet Dent 2013;110:376-82. 14. Franco EB, Lins do Valle A, Pompéia Fraga de Almeida AL, Rubo JH, Pereira JR. Fracture resistance of endodontically treated teeth restored with glass fiber posts of different lengths. J Prosthet Dent 2014;111:30-4. 15. Zamin C, Silva-Sousa YT, Souza-Gabriel AE, Messias DF, Sousa-Neto MD. Fracture susceptibility of endodontically treated teeth. Dent Traumatol 2012;28:282-6. 16. Zandbiglari T, Davids H, Schafer E. Influence of instrument taper on the resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:126-31. 17. Lang H, Korkmaz Y, Schneider K, Raab WH. Impact of endodontic treatments on the rigidity of the root. J Dent Res 2006;85:364-8. 18. Cheung W. A review of the management of endodontically treated teeth. Post, core and the final restoration. J Am Dent Assoc 2005;136:611-9. 19. Giovani AR, Vansan LP, de Sousa Neto MD, Paulino SM. In vitro fracture resistance of glass-fiber and cast metal posts with different lengths. J Prosthet Dent 2009;101:183-8. 20. Ambica K, Mahendran K, Talwar S, Verma M, Padmini G, Periasamy R. Comparative evaluation of fracture resistance under static and fatigue loading of endodontically treated teeth restored with carbon fiber posts, glass fiber posts, and an experimental dentin post system: an in vitro study. J Endod 2013;39:96-100.
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21. Kinney JH, Marshall SJ, Marshall GW. The mechanical properties of human dentin: a critical review and re-evaluation of the dental literature. Crit Rev Oral Biol Med 2003;14:13-29. 22. Craig RG, Peyton FA. Elastic and mechanical properties of human dentin. J Dent Res 1958;37:710-8. 23. Fuentes V, Toledano M, Osorio R, Carvalho RM. Microhardness of superficial and deep sound human dentin. J Biomed Mater Res 2003;66:850-3. 24. Schneider LFJ, Cavalcante LM, Silikas N. Shrinkage stresses generated during resin- composite applications: A review. J Dent Biomech 2010;1:1-14. 25. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach. J Endod 2005;31:584-9. 26. Jeffries SR. Bioactive and biomimetic restorative materials: a comprehensive review. Part I. J Esthet Restor Dent 2014;26:14-26.
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27. Jeffries SR. Bioactive and biomimetic restorative materials: A comprehensive review. Part II. J Esthet Restor Dent 2014;26:27-39.
Corresponding author: Dr Peter M. Di Fiore Department of Endodontics University of Texas, School of Dentistry 7500 Cambridge St. Ste. 6400 Houston, TX 77054 Email: [email protected] Copyright © 2015 by the Editorial Council for The Journal of Prosthetic Dentistry.
THE JOURNAL OF PROSTHETIC DENTISTRY
Evaluation of a calcium silicate-based cement as a root reinforcement material for endodontically treated maxillary anterior teeth Peter M. Di Fiore, DDS, MS,a Adrian Reyes, DDS,b Samuel O. Dorn, DDS,c Stanley G. Cron, MSPH,d and Joe C. Ontiveros, DDS, MSe The objectives for restoring ABSTRACT endodontically treated teeth Statement of problem. Fractures of endodontically treated teeth have been attributed to weakare to maintain their structural ened tooth structure caused by root canal enlargement and post preparation. integrity and retain them as Purpose. The purpose of this in vitro study was to evaluate the fracture resistance of roots filled fully functional units in the with either gutta percha, composite resin (LuxaCore Dual), or calcium silicate-based cement dentition.1 During endodontic (Biodentine). instrumentation, root canals Material and methods. One hundred twenty freshly extracted, human, permanent maxillary are cleaned and shaped in a anterior teeth were sorted by type and assigned to 1 of 4 groups (n=30). The teeth in group NT manner that respects their were not endodontically treated and served as the control. The teeth in groups GP, LC, and, BD were morphology without altering accessed and instrumented to size 40/06. In group GP, the root canals were completely filled with or weakening their roots.2 gutta percha. In groups LC and BD, only the apical 5-mm portion of the root canals was filled with Endodontically treated teeth gutta percha, and the remaining portion of the root canals was filled with (LuxaCore Dual) in group LC and with (Biodentine) in group BD. Fracture resistance (kN) was assessed at the middle portion of often require the placement of each root, using a 3-point bending test with a universal testing machine exerting a compressive a post and core for crown load on a loading pin at a crosshead speed of 0.5 mm/min until fracture occurred. One-way 3 restoration. Fractures of ANOVA was used to compare the mean root fracture resistance among the 4 groups (a=.05). endodontically treated teeth Results. The mean ± SD fracture loads were 2.13 ±0.53 kN for group NT, 1.97 ± 0.60 kN for group have been attributed to weakGP, 2.18 ±0.71 kN for group LC, and 2.22 ±0.54 kN for group BD. No statistically significant differened tooth structure caused by ences were found among the 4 groups (P>.05). endodontic and restorative Conclusions. The roots of endodontically treated maxillary anterior permanent incisors filled with procedures.4 Occlusal stresses gutta percha, Biodentine, or LuxaCore Dual had resistance to fracture similar to that of teeth that and reduced mechanical were not endodontically treated. (J Prosthet Dent 2015;-:---) properties of endodontically treated teeth may also teeth had a significant effect on stress distribution and contribute to fatigue-induced root fractures.5 An invesfracture resistance.6 Removal of excessive dentin during tigation using 3-dimensional finite analysis found that root canal instrumentation and preparation for dowels the amount of remaining coronal dentin and the type of and posts can result in the loss of root strength and an post and crown used to restore endodontically treated
Supported by a research grant from the American Association of Endodontists Foundation. a Professor, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. b Resident, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. c Professor and Program Director, Department of Endodontics, University of Texas, School of Dentistry, Houston, Tex. d Statistician, Center for Nursing Research, University of Texas, School of Dentistry, Houston, Tex. e Associate Professor, Department of Restorative Dentistry and Prosthodontics, University of Texas, School of Dentistry, Houston, Tex.
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Clinical Implications Biodentine and LuxaCore Dual appear to be appropriate root reinforcement materials for maxillary anterior permanent teeth. Endodontically treated teeth with root canals prepared to a size of 40/06 and filled with gutta percha may not necessarily need root reinforcement.
increased susceptibility to root fracture.7-11 Therefore, the preservation of tooth structure is essential in preventing root fractures in endodontically treated teeth.8,10,11 The resistance to fracture of endodontically treated roots is also influenced by the presence and strength of the root canal obturation material and the bond strength between the material and root canal dentin.11 Roots with empty root canals were more susceptible to fracture than filled roots, whereas roots reinforced with a suitable intracanal materials maintained fracture resistance.11 Several studies have investigated the fracture resistance of endodontically treated extracted human teeth with roots with cemented fiber posts with resin based materials.12-14 These studies concluded that the modulus of elasticity of fiber posts influenced fracture resistance,12 that fiber post-supported cores improved fracture resistance,13 and that fiber posts prevented catastrophic fractures.14 Trope et al8 compared the resistance to fracture of endodontically treated maxillary central incisors reinforced with different types of materials and concluded that post space preparation weakened roots and that post placement did not necessarily strengthen roots. However, acid etching of root canal dentin before filling the post space with a bonded composite resin significantly increased root fracture resistance. Trabert et al9 tested the resistance to fracture of endodontically treated maxillary central incisors reinforced with large and small diameter posts and found that extensive preparation of root canals and placement of large diameter posts significantly reduced root fracture resistance. Reeh et al10 compared the effect of endodontic and restorative procedures on the overall stiffness of extracted maxillary second premolars and demonstrated that endodontic procedures reduced tooth stiffness by 5%, whereas restorative procedures, such as mesio-occlusal distal coronal cavity preparations, reduced stiffness by 60%. Sornkul et al11 tested the fracture resistance of single-rooted mandibular premolar roots with and without endodontic treatment and post restoration and showed that the roots of untreated premolars had a greater resistance to fracture than roots with any mode of post restoration, demonstrating that preserving tooth structure was the most important factor for fracture resistance. Zamin et al15 and Zandbiglari et al16 evaluated the fracture susceptibility of THE JOURNAL OF PROSTHETIC DENTISTRY
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teeth whose root canals were prepared with large and small tapered endodontic instruments. Both of these investigations found that root canals prepared with large tapered instruments significantly weakened roots, especially in the cervical third of the root, compared with root canals prepared with small tapered instruments. Lang et al17 investigated the influence of endodontic and restorative procedures on extracted maxillary incisors at different stages of treatment (access cavity preparation, root canal instrumentation, and post preparation) and found that deformation on loading increased as more tooth structure was removed after each treatment stage. A variety of intracanal materials have been used to reinforce the roots of endodontically treated teeth and can be divided into 2 main types, prefabricated and custom fabricated posts that are either cemented or adhesively bonded in root canals.18 However, these posts require root canal enlargement to an appropriate size for post insertion, necessitating the removal of intracanal dentin.18 Although both prefabricated metal and fiber posts can be used for root reinforcement,19,20 adhesive bonding of composite resin materials, which require little or no removal of intracanal dentin, have been used to reinforce the roots of endodontically treated teeth, especially in those with compromised root thickness and have been shown to increase root fracture resistance.8,11-13 Additionally, composite resin filled root canals substantially increased root fracture resistance compared with gutta percha-filled root canals and unfilled root canals.8,11 However, the physical properties of composite resin do not mimic the physical properties of dentin.21-23 Polymerization shrinkage is an inherent property of composite resins, which can result in resin debonding at the dentin interface and may affect its reinforcing properties.24,25 As a consequence, shrinkage and bond failure may be possible drawbacks of composite resins as root reinforcing materials.24,25 Biodentin (Septodont) is a recently developed biocompatible calcium silicate-based cement material composed of tricalcium silicate, calcium carbonate, zirconium oxide, calcium chloride and polycarboxylate. Its applications include replacing lost coronal dentin, forming a core structure, and repairing root perforations.26,27 An ideal intracanal root reinforcing material should have similar physical properties to those of dentin.18 This calcium silicate-based cement and human dentin share similar physical properties.26,27 The modulus of elasticity of the cement, being similar to dentin, would allow for stress distribution in endodontically treated roots during function and could reduce the chance of fracture.1,26,27 This concept was tested in an in vitro investigation that used experimental dentin posts to reinforce the roots of endodontically treated anterior teeth and found that the fracture resistance under static loading was highest for posts made of dentin compared with glass fiber or carbon Di Fiore et al
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fiber posts.20 The purpose of this study was to evaluate and compare the root fracture resistance of endodontically treated teeth with root canals filled with gutta percha, composite resin (LuxaCore Dual; Kerr Corp), or calcium silicate-based cement (Biodentine; Septodent). MATERIAL AND METHODS This research was approved by the Institutional Review Board of the University, Health Science Center, School of Dentistry, where this study was conducted. Human, freshly extracted fully developed permanent maxillary anterior teeth were collected and disinfected in accordance with the policy and protocol of the School of Dentistry. The teeth were placed in a holding solution of 0.5% sodium hypochlorite immediately after extraction, immersed in 10% formalin solution for a period of 2 weeks for disinfection, and then stored in physiological saline solution until use. The teeth were inspected for any defects (abrasions, caries, cracks, crazes, erosions, fractures, or resorptions) using a surgical microscope (Global Surgical Microscope; Global Surgical) at ×5 magnification. A digital periapical radiograph of each tooth was also made to aid in identifying defects. Teeth with any defects were excluded from the study. To ensure the use of roots with comparable dimensions, the mesial distal (MD) and facial palatal (FP) dimensions of the roots were measured at middle root level with a digital caliper (Digital Caliper; Mitutoyo). A total of 120 teeth were sorted by type and divided into 4 groups (group NT, group GP, group LC, and group BD) of 30 teeth each. Table 1 shows mean ±SD, MD, and FP dimensions of the roots for each group. The teeth in group NT were not treated, served as the control, and were kept in physiological saline solution. The teeth in groups GP, LC, and BD had a standard endodontic access prepared on the lingual surface of their crowns. A no. 10 stainless steel hand file (FlexoFile; Dentsply Maillefer) was inserted in the orifice of the root canal until observed to be flush with the apical foramen, and its length was measured from the incisal reference point. Working length (WL) was established by subtracting 1 mm from this length. A #15 stainless steel hand file (FlexoFile; Dentsply Maillefer) was inserted into the root canal to the WL to establish a glide path. The root canals were enlarged to a master apical file (MAF) size of 40/06 with nickel titanium rotary instruments (ProFile; Dentsply Intl) in a crown down manner to WL. During instrumentation, the root canals were irrigated with 6% NaOCl and 17% EDTA. A 10mL plastic syringe with a 27-gauge side-vented needle was used to deliver the irrigating solutions into the canal. The teeth were stored in physiological saline solution immediately after completion of root canal instrumentation. Di Fiore et al
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Table 1. Mean ±standard deviations of root dimensions Mean Facial-Lingual Dimension
Mean Mesial-Distal Dimension
Negative control group NT
7.18 ±0.99 mm
5.23 ±0.71 mm
Gutta percha group GP
7.16 ±0.80 mm
5.12 ±0.55 mm
LuxaCore dual group LC
7.16 ±0.89 mm
5.23 ±0.73 mm
Biodentine group BD
7.24 ±0.92 mm
5.08 ±0.65 mm
Group
The root canals of the teeth in group GP were filled with gutta percha (Gutta Percha Cones; Brasseler USA) and resin-based sealer (AH Plus; Dentsply Intl) using the continuous wave obturation technique to the level of the cementoenamel junction. The access cavities were etched for 15 seconds with 35% phosphoric acid (UltraEtch; Ultradent Products Inc), rinsed with water, and dried with coarse paper points. Bonding agent (Optibond Solo Plus; Kerr Corp) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The access cavities were filled flush to the lingual surface of the crowns with composite resin (PermaFlo; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The apical 5 millimeters of the root canals of the teeth in group LC were filled with gutta percha as previously described, and the remaining unfilled root canals and access cavities were etched for 15 seconds with 35% phosphoric acid (Ultra-Etch; Ultradent Products Inc), rinsed with water, and dried with course paper points. Bonding agent (Optibond Solo Plus; Kerr Corp) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The remaining root canals and access cavities were then filled to the level of the lingual surface of the crowns with composite resin (LuxaCore Dual; Kerr Corp) using a microsyringe and light polymerized with (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The apical 5 millimeters of the root canals of the teeth in group BD were filled with gutta percha as previously described, and the remaining unfilled root canals and access cavities were rinsed with water and dried with coarse paper points. A calcium silicate-based cement (Biodentine; Septodent) was prepared according to the manufacturer’s instructions and placed into the canals in small increments using material carriers (MTA Carriers; Vista Dental), followed by compaction of each increment of Biodentine (Biodentine; Septodent) using ISO sized endodontic pluggers (Endo Pluggers; Dentsply Maillefer). The filling procedure was repeated until THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 2. Mean ±SD root fracture resistance Group
Number Mean ±SD Root Fracture Resistance (kN)
Negative control group NT
30
2.13 ±0.53
Gutta percha group GP
25
1.97 ±0.60
LuxaCore dual group LC
30
2.18 ±0.71
Biodentine group BD
26
2.22 ±0.54
Figure 1. Radiographs of root-filled teeth. A, Gutta percha. B, Composite resin. C, Calcium silicate-based cement.
Root Fracture Resistance (kN)
3.5 3
2.18 2.13
1.97
2.22
2.5 2 1.5 1 0.5 0 Untreated
Gutta Percha
Luxa Core
Biodentine
Figure 3. Means ±standard deviations of root fracture resistance.
Figure 2. Three-point bending test fixture and loading pin.
the calcium silicate-based cement (Biodentine; Septodent) reached a level approximately 3 mm below the lingual surface of the crown. The unfilled portions of the access openings were etched for 15 seconds with 35% phosphoric acid (Ultra-Etch; Ultradent Products Inc), rinsed with water, and dried with coarse paper points. Bonding agent (Optibond Solo Plus; Kerr) was applied with a brush applicator (Microbrush; Ultradent Products Inc) and light polymerized (UltraLume LED 5; Ultradent Products Inc) for 20 seconds. The access openings were filled flush to the lingual surface of the crowns with composite resin (PermaFlo; Ultradent Products Inc) and light polymerized (UltraLume LED 5; Ultradent Products Inc) for 40 seconds according to the manufacturer’s instructions. The filled teeth were radiographed to ensure complete filling of the root canals (Fig. 1). Immediately after completion of the root canal and access cavity filling, the teeth in each of the treatment groups were placed in 100% humidity at 37 C for at least 72 hours to allow THE JOURNAL OF PROSTHETIC DENTISTRY
the root filling and root reinforcement materials to completely set before testing. The root fracture resistance of each tooth was evaluated by using a custom 3-point bending test fixture and loading pin with a universal testing machine (Instron Testing Machine; Instron) and materials testing software (Bluehill Software; Instron) (Fig. 2). The 3-point bending test fixture had a span length of 10 mm between the 2 lower support points. Each tooth was placed on the test fixture, with the facial root surface facing down and supported by the 2 test fixture support points. The tooth contact surfaces on the fixture support points was visually verified to make sure that the 2 support points made contact only on root surfaces. A loading pin attached to the universal testing machine (Instron Testing Machine; Instron) and centered between the 2 support points was used to apply the third vertically oriented load on the root. (Fig. 2) at a crosshead speed of 0.5 mm/min until root fracture occurred. The test was aborted if the tooth slipped or rotated during application of the load. The root fracture resistance of each tooth was the load measured in kilonewtons at the point of root fracture, which was recorded and plotted on a graph using materials testing software (Bluehill Software; Instron). Available resources allowed the use of 120 teeth (30 per group). Based on this sample size, a 1-way univariate analysis of variance (ANOVA) would have sufficient power to detect a medium effect size of (f=.31). Statistical analysis was performed with software (SPSS v20; IBM Corp). One-way ANOVA was used to analyze and Di Fiore et al
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Figure 4. Typical root fracture patterns. A, Single root fracture. B, Double root fracture.
compare the mean root fracture resistance among the 4 groups. Post hoc comparisons among groups were performed with Tukey multiple comparisons (a=.05). RESULTS Mean values for the root fracture resistance of each group are presented in Table 2 and illustrated in Figure 3. The mean ±SD root fracture resistance values for each group were 2.13 ±0.53 kN for group NT (n=30), 1.97 ±0.60 kN for group GP (n=25), 2.18 ±0.71 kN for group LC (n=30), and 2.22 ±0.54 kN for group BD (n=26). Some teeth in groups GP and BD were excluded from the results because of slipping or rotating on the test fixture during application of the load. The data did not violate the assumption of normality, with absolute values for both skewness and kurtosis <1. The results of the 1-way ANOVA indicated no statistically significant difference in load among the groups (F (3, 107)=.891, P=.449). The Tukey multiple comparisons test confirmed no statistically significant differences (P>.05) among any of the groups. DISCUSSION This study compared root fracture resistance values of endodontically treated maxillary anteriorpermanent teeth, root filled with gutta percha, composite resin, or calcium silicate-based cement. The study design specifically tested the ability of these 3 materials, placed in the middle portion of the root canal, to resist root fracture by using a customized 3-point bending test fixture. Untreated maxillary anterior teeth served as the control. This study found no statistically significant difference in the mean root fracture resistance among the 4 groups. All of the procedures were performed by 1 operator (A.R.) to ensure consistency in preparation and testing. The custom made 3-point bending fixture was designed so that the tooth would be in contact with the 2 fixture support points on root surfaces only. Loads were directed with the loading pin exactly at the midpoint of the roots between the 2 fixture support points of the 3-point bending test fixture. This exerted the load precisely to the middle portion of the roots filled with either gutta percha, composite resin, or calcium silicate-based cement, where fracture resistance was specifically Di Fiore et al
tested, without any influence of the apical or coronal structural elements of the tooth (Fig. 2). The distribution of tooth types was consistent for each group: group NT (19 canines, 5 central, and 6 lateral incisors); group GP had 16 canines, 5 central and 4 lateral incisors; group LC (18 canines, 5 central, and 7 lateral incisors), and group BD had 17 canines, 7 central, and 2 lateral incisors. Measurements of the roots made at middle root level showed consistency in mean root dimensions amongst the groups (Table 1). Although effort was made to have consistency in each group, some variations were present in root dimensions and shapes within the groups, which could have influenced the results. This was a limitation of the study, since root dentin thickness has been shown to significantly influence root strength when subjected to various types of loading conditions.5 Two typical patterns of root fracture were commonly observed in all groups (Fig. 4). The first fracture pattern that occurred was a single horizontally or obliquely directed fracture that occurred at the point where the loading pin was in contact with the root, resulting in the tooth splitting into 2 separate pieces (Fig. 4A). The second fracture pattern was 2 separate horizontal or oblique fractures that occurred on each side of the loading pin, resulting in the tooth splitting into 3 pieces (Fig. 4B). Close inspection of the fractured pieces from the GP group and LC group revealed areas where separation and debonding of the materials from the dentin occurred (Fig. 5). However, in most of the fractured tooth pieces inspected from the Biodentine group, there were no areas of material de-bonding from dentin, and the Biodentine material often appeared to fracture along the same plane as the surrounding dentin (Fig. 6). The teeth with root canals filled with gutta percha and those filled with root-reinforcing materials (LuxaCore Dual or Biodentine) showed statistically similar root fracture resistance values compared with the untreated teeth (Fig. 3). This finding was not in agreement with the study of Sornkul et al,11 in which teeth with untreated root canals showed greater root fracture resistance than teeth with treated root canals. The root canals of the endodontically treated teeth in this study were all prepared to a standard MAF instrument size of 40/06, which would be considered appropriate for root canal preparation of maxillary anterior teeth. Of the 3 THE JOURNAL OF PROSTHETIC DENTISTRY
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Figure 5. Root fracture with material debonding from dentin. A, Gutta percha. B, LuxaCore.
statistically significant difference in root fracture resistance when compared with untreated teeth. A calcium silicate-based cement may be a suitable material for root reinforcement. Further studies are indicated on the performance of calcium silicate-based cements as a root reinforcement material for endodontically treated teeth. REFERENCES
Figure 6. Biodentine root fracture without debonding from dentin.
treatment groups, endodontically treated teeth with gutta percha root canal filling had the lowest mean root fracture resistance (Fig. 3). However, since no significant differences were found in the root fracture resistance of untreated teeth and endodontically treated teeth with gutta percha root canal fillings, teeth treated in this manner may not necessarily need root reinforcement. Another explanation for the finding of no significant difference among the 3 treatment groups could be that the reinforcing potential of the materials was not fully realized in root canals prepared to a 40/06 instrument size and that instrumentation to a larger size may have caused greater differences in fracture resistance. The root fracture resistance values reported in the present study are large compared with those found in other studies.7,8,20 This difference was most probably due to the short span 3-point bending fixture and loading pin testing device used in this study, which produced a gradual compressive load at 0.5 mm/min until root fracture occurred (Fig. 2). For this reason, the results obtained in this study are not directly comparable with those obtained in other studies which used a single oblique compressive force applied to the coronal lingual surfaces of mounted teeth.7,8,20 CONCLUSIONS Within the limitations of this in vitro study, the root reinforcement materials evaluated did not produce a THE JOURNAL OF PROSTHETIC DENTISTRY
1. Schwartz RS, Robbins JW. Post placement and restoration of endodontically treated teeth: a literature review. J Endod 2004;30:289-301. 2. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96. 3. Baraban DJ. A simplified method for making posts and cores. J Prosthet Dent 1970;24:287-97. 4. Kishen A. Mechanisms and risk factors for fracture predilection in endodontically treated teeth. Endodontic Topics 2006;13:57-83. 5. Tang W, Wu Y, Smales RJ. Identifying and reducing risks for potential fractures in endodontically treated teeth. J Endod 2010;36:609-17. 6. Verissimo C, Simamoto Júnior PC, Soares CJ, Noritomi PY, Santos-Filho PC. Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors. J Prosthet Dent 2014;111:234-46. 7. 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. 8. Trope M, Maltz DO, Tronstad L. Resistance to fracture of restored endodontically treated teeth. Endod Dent Traumatol 1985;1:108-11. 9. Trabert KC, Caput AA, Abou-Rass M. Tooth fractureda comparison of endodontic and restorative treatments. J Endod 1978;4:341-5. 10. Reeh ES, Messer HH, Douglas WH. Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod 1989;15:512-6. 11. Sornkul E, Stannard JG. Strength of roots before and after endodontic treatment and restoration. J Endod 1992;18:440-3. 12. 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. 13. Scotti N, Rota R, Scansetti M, Paolino DS, Chiandussi G, Pasqualini D, et al. Influence of adhesive techniques on fracture resistance of endodontically treated premolars with various residual wall thicknesses. J Prosthet Dent 2013;110:376-82. 14. Franco EB, Lins do Valle A, Pompéia Fraga de Almeida AL, Rubo JH, Pereira JR. Fracture resistance of endodontically treated teeth restored with glass fiber posts of different lengths. J Prosthet Dent 2014;111:30-4. 15. Zamin C, Silva-Sousa YT, Souza-Gabriel AE, Messias DF, Sousa-Neto MD. Fracture susceptibility of endodontically treated teeth. Dent Traumatol 2012;28:282-6. 16. Zandbiglari T, Davids H, Schafer E. Influence of instrument taper on the resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:126-31. 17. Lang H, Korkmaz Y, Schneider K, Raab WH. Impact of endodontic treatments on the rigidity of the root. J Dent Res 2006;85:364-8. 18. Cheung W. A review of the management of endodontically treated teeth. Post, core and the final restoration. J Am Dent Assoc 2005;136:611-9. 19. Giovani AR, Vansan LP, de Sousa Neto MD, Paulino SM. In vitro fracture resistance of glass-fiber and cast metal posts with different lengths. J Prosthet Dent 2009;101:183-8. 20. Ambica K, Mahendran K, Talwar S, Verma M, Padmini G, Periasamy R. Comparative evaluation of fracture resistance under static and fatigue loading of endodontically treated teeth restored with carbon fiber posts, glass fiber posts, and an experimental dentin post system: an in vitro study. J Endod 2013;39:96-100.
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21. Kinney JH, Marshall SJ, Marshall GW. The mechanical properties of human dentin: a critical review and re-evaluation of the dental literature. Crit Rev Oral Biol Med 2003;14:13-29. 22. Craig RG, Peyton FA. Elastic and mechanical properties of human dentin. J Dent Res 1958;37:710-8. 23. Fuentes V, Toledano M, Osorio R, Carvalho RM. Microhardness of superficial and deep sound human dentin. J Biomed Mater Res 2003;66:850-3. 24. Schneider LFJ, Cavalcante LM, Silikas N. Shrinkage stresses generated during resin- composite applications: A review. J Dent Biomech 2010;1:1-14. 25. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach. J Endod 2005;31:584-9. 26. Jeffries SR. Bioactive and biomimetic restorative materials: a comprehensive review. Part I. J Esthet Restor Dent 2014;26:14-26.
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27. Jeffries SR. Bioactive and biomimetic restorative materials: A comprehensive review. Part II. J Esthet Restor Dent 2014;26:27-39.
Corresponding author: Dr Peter M. Di Fiore Department of Endodontics University of Texas, School of Dentistry 7500 Cambridge St. Ste. 6400 Houston, TX 77054 Email: [email protected] Copyright © 2015 by the Editorial Council for The Journal of Prosthetic Dentistry.
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