Basic Research—Technology

Similar Influence of Stabilized Alkaline and Neutral Sodium Hypochlorite Solutions on the Fracture Resistance of Root Canal–treated Bovine Teeth Erick Miranda Souza, DDS, MS, PhD,* Amanda Martins Calixto, DDS,† Camila Nara e Lima, DDS,† Fernanda Geraldo Pappen, DDS, MS, PhD,‡ and Gustavo De-Deus, DDS, MS, PhD§ Abstract Introduction: Stabilizing sodium hypochlorite (NaOCl) at an alkaline pH is proposed to increase solution stability and tissue dissolution ability; however, a reduction on the flexural strength of dentin discs has been found to be a side effect. This study sought to determine whether a stabilized alkaline NaOCl reduces the fracture resistance of root canal–treated bovine teeth after root canal preparation compared with a neutral solution counterpart. Methods: The 4 anterior incisors were removed from 20 mandibular bovine jaws, and each 1 was randomly assigned to 1 of 4 groups (20 teeth each). Teeth were prepared with a sequence of 6 K-type files. The following experimental groups received a different irrigation regimen: G1: distilled water (negative control), G2: 5% NaOCl at a pH of 7.2, and G3: 5% NaOCl at a pH of 12.8; in the positive control group (G4), teeth remained untreated. The time of contact and volume of solution were carefully standardized. After bone and periodontal ligament simulation, teeth were subjected to a fracture resistance test. Results: A significant difference was observed among the 4 groups tested (analysis of variance, P < .05). The 5% NaOCl groups (G2 and G3) presented significantly lower resistance to fracture than the control (G1 and G4) (Tukey test, P < .05). Both NaOCl solutions similarly reduced the fracture resistance at approximately 30% (Tukey test, P > .05). No differences were observed between positive and negative control groups (Tukey test, P > .05). Conclusions: Stabilized alkaline and neutral NaOCl solutions similarly reduced the fracture resistance of root canal–treated bovine teeth by about 30%. (J Endod 2014;-:1–4)

Key Words Alkaline NaOCl, bovine teeth, fracture resistance of endodontically treated teeth

T

he use of sodium hypochlorite (NaOCl) solutions largely remains the mainstream approach for root canal disinfection because of the unique tissue proteolysis capacity and microbial suppression by NaOCl (1, 2). These essential properties of NaOCl solutions are predominantly influenced by the amount of available chlorine (3, 4). In NaOCl solutions, chlorine can take different chemical forms depending on the solution’s pH. At an alkaline pH, the predominant form is hypochlorite (ClO ), whereas at a neutral pH the hypochlorous acid form predominates (5). The latter is considered to be more bactericidal than hypochlorite (6); thus, it seems appropriate to adjust the pH of NaOCl to a neutral level with the purpose of increasing its antimicrobial effectiveness (7). However, at a pH of 7.5, NaOCl was found to be unstable, which causes a severe reduction in its shelf life (7, 8), preventing the neutralized solution from being marketed on a regular basis. In addition, the drop in hypochlorite ion renders neutralized NaOCl more cytotoxic (8) and less effective in dissolving organic tissue (9) because the cleaning effectiveness of NaOCl solutions is related to the presence of ClO (8, 10, 11). Therefore, all NaOCl solutions available for clinical use are alkaline. Albeit alkaline, NaOCl solutions rapidly show a drop in pH when active chlorine is consumed during interaction with tissues and microorganisms (3, 5, 9), which, in turn, result in a severe decline in the solution’s ability to dissolve organic tissue (9). Recently, the effect of adding an alkali with the aim of maintaining the stability of the solution and preserving its capacity to dissolve organic tissue has been investigated (9). Some available household bleach and dental-marketed NaOCl solutions are currently adding alkali to provide stabilization and to increase the shelf life of NaOCl (12), while also claiming a superior proteolytic effect. Unquestionably, tissue proteolysis encompasses a pivotal feature of NaOCl because either vital or necrotic tissue remnants may became a potential source for root canal reinfection in cases of incomplete canal disinfection or leakage. Nonetheless, the proteolytic action of NaOCl also negatively impacts on dentin, causing the depletion of its components of organic nature (13). This highly undesired NaOCl side effect irreversibly changes the dentin framework, causing a dry weight reduction by 14% (14). Therefore, the occurrence of physical and mechanical changes in dentin disks, such as microcrack formation and the reduction in flexural strength, microhardness, and modulus of elasticity after NaOCl use is not a surprise (14–23). Following a cause-effect rationale, the increase in the proteolytic effect triggered by a stabilized alkaline NaOCl solution (8–10) may intensify the side effect on the organic scaffold of dentin, ultimately leading to the undesired end result of root weakening

From the *Department of Dentistry II, Federal University of Maranh~ao, S~ao Luis, Brazil; †Private Practice, S~ao Luis, Brazil; ‡Department of Endodontics, Federal University of Pelotas, Pelotas, Brazil; and §Department of Endodontics, Grande Rio University, Rio de Janeiro, Brazil. Address requests for reprints to Prof Erick Miranda Souza, Av dos Holandeses, Cond Sports Garden, ap 1004A–Olho D’agua, S~ao Luis, MA, Brazil 65065-180. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.02.028

JOE — Volume -, Number -, - 2014

Root Canal–treated Bovine Teeth

1

Basic Research—Technology (9, 13, 23). In fact, stabilized alkaline NaOCl induced a severe decrease in the elastic modulus and flexure strength of dentin discs compared with a nonstabilized counterpart (9). Because weakened roots may significantly impact tooth survival, the effect of stabilized alkaline NaOCl over fracture resistance should be investigated. We aimed to evaluate whether the use of a stabilized alkaline NaOCl solution influences the strength of root canal–treated bovine teeth compared with a neutral NaOCl solution counterpart. The null hypothesis is that NaOCl solutions at 2 different pH levels do not influence the fracture resistance of bovine teeth.

Materials and Methods Sample Size Calculation An analysis of variance (ANOVA) fixed-effects model (F family, G*Power 3.1.1 for Windows, Heinrich-Heine-Universit€at D€usseldorf, Germany) was used to set the ideal sample size. Based on a pilot study, the effect size was determined at 0.58; an alpha-type error = 0.05 and power b = 0.95 were input. The results indicated a minimum total sample size of 56 teeth and a critical F of 2.79 for the ANOVA evaluation. Sample Selection and Preparation Twenty mandibular bovine jaws from cattles similar in age were selected to provide the 4 anterior incisors. Animals were slaughtered for feeding purposes, and the jaws were donated to this study. With the aim of providing anatomic matching among the groups, each selected incisor was randomly assigned to 1 of 4 groups, resulting in 20 teeth per group and a total sample size of 80 teeth. For each jaw, the 4 incisors were measured at a level 8 mm from the apex to ensure roots display a 8–10 mm diameter. Root diameters lower or lager than the established parameters results in the exclusion of the cow. After extraction, teeth were stored in saline until use. All teeth were cross-sectioned at levels of 8 mm coronally and 12 mm apically to the cement/enamel junction by means of a lowspeed saw (VC-50 Precision Diamond Saw; Leco, Miami, FL) under copious water cooling resulting in samples with lengths of 20 mm. The pulpal tissue was removed with Hedstr€oen files (Dentsply Maillefer, Ballaigues, Switzerland). Preparation and Characterization of Irrigating Solutions Freshly prepared technical-grade NaOCl solutions were obtained from a pharmacy (Special Farma, S~ao Luis, Brazil). A 2-mol/L NaOH solution was mixed with a standard 10% NaOCl solution to obtain an NaOH-stabilized alkaline 5% NaOCl solution (9). The neutral solution was acquired by mixing a standard 10% NaOCl solution with 1% sodium bicarbonate (NaHCO3) (24). The available chlorine of the solutions was certified using a standard iodine/thiosulfate titration method immediately before and after the experiments (20 days later). Before and after the experiment, the pH of the solutions was verified using a calibrated pH electrode (Model 6.0210.100; Metrohm, Herisau, Switzerland). The pH of NaOH-stabilized NaOCl was also determined after 40 minutes of contact with a bovine root canal to confirm that the stabilization was effective (9). All root canal preparations were performed in a controlled room temperature. Root Canal Instrumentation and Irrigation The apical portion of each tooth was sealed off with wax, preventing any irrigation liquid from being extruded from the large apical opening created after apical sectioning. Groups G1–G3 received different irrigation regimes as follows: G1: distilled water (negative control), G2: 5% sodium hypochlorite with a pH of 7.2, and G3: 5% NaOCl 2

Souza et al.

with a pH of 12.8. In the positive control group (G4), teeth remained untreated. To ensure irrigated groups (G1–G3) received the same volume of irrigation, root canals were instrumented using a sequence of 6 hand K-files (Dentsply Maillefer), which were selected after determining the first instrument to bind at 1 mm from the apical opening. After each hand file, 5 mL irrigation solution was delivered into the root canal using a 27-G endodontic needle (NaviTip; Ultradent Products, South Jordan, UT) reaching 3 mm from the apex. A constant rate of 1 mL/min was achieved using a VATEA peristaltic pump (ReDent Nova, Ra’anana, Israel). After irrigation, the root canals remained filled with the solution, and the subsequent instrument was used to prepare the root canal using a step-back technique. Each instrument was used for 2 minutes. Considering the number of instruments used (6), the total period that root canal dentin remained in contact with the solutions was 26 minutes. The extruded solution was aspirated adjacently to the coronal opening to make sure that any solution was drawn off the external root surface. All teeth received a final irrigation with 10 mL distilled water for 5 minutes, removing any solution remnants from the root canal. Furthermore, root canals were dried with paper points and stored at 37 C with 100% humidity until the strength tests were performed.

Simulation of the Periodontal Support Apparatus Teeth were firstly immersed in melted wax (Horus; Herpo Produtos Dentarios, Petropolis, RJ, Brazil) up to 2.0 mm below the cementoenamel junction to create a 0.2- to 0.3-mm-thick wax layer covering the root. Furthermore, a polystyrene resin (Cristal, Piracicaba, Brazil) was used to embed the roots in polyvinyl chloride cylinders (a 21-mm diameter and 25-mm high). After the resin was set, the teeth were withdrawn from the polyvinyl chloride cylinders, and the wax removed from root surface and resin cylinder ‘‘sockets’’ using a warm water flush for 2 seconds. A polyether impression material (Impregum Soft; 3 M/ESPE, Seefeld, Germany) was delivered to the cylinder hole using a syringe. The samples were immediately reinserted into the respective cylinder socket, and any excess of impression material was removed, finally resulting in a simulated periodontal ligament of 0.2–0.3 mm (25). Fracture Strength Test All specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min by means of a servo-hydraulic universal testing machine (EMIC DL2000; EMIC Equipamentos e Sistemas de Ensaio Ltda, S~ao Jose dos Pinhais, Brazil) until fracture. The specimen was fixed to an apparatus that allowed a 45 angle formation with the EMIC loading tip, simulating a traumatic shock on the middle third of the crowns from a buccal-lingual direction. The ultimate load required to fracture the specimens was recorded in newtons. Statistical Analysis Raw data adhesion to Gaussian distribution and homogeneity of the variance were studied a priori (Shapiro-Wilk and Levene tests). Because both assumptions were confirmed (P > .05), 1-way ANOVA followed by the Tukey Honest Significant Difference post hoc test were selected to verify the effect of the solution in the fracture strength of bovine teeth. The a-type error was set to 0.05. Results Table 1 displays the mean and standard deviations of the tested groups. One-way ANOVA indicated a significant difference between the groups (P < .05). The negative control group (distilled water) behaved similarly to positive controls because no significant change JOE — Volume -, Number -, - 2014

Basic Research—Technology TABLE 1. Mean and Standard Deviations (SD) of the Ultimate Fracture Strength (Newtons) of the Groups Tested Groups

Mean

Positive control Negative control (distilled water) pH = 7.2, 5% NaOCl Stabilized pH = 12.8, 5% NaOCl

a

103.13 105.88a 79.85b 74.09b

SD 24.42 28.13 18.34 18.25

Different letters indicate significant differences at P < .05 (Tukey HSD).

in resistance to fracture was observed (Tukey HSD, P > .05). However, both NaOCl groups (G2 and G3) significantly reduced the fracture resistance of bovine teeth by approximately 30% compared with controls (Tukey HSD, P < .05). The 5% NaOCl group with a stabilized pH of 12.8 (G3) presented a similar influence in the fracture resistance as the 5% NaOCl group with a pH of 7.2 (G2) (Tukey HSD, P > .05).

Discussion Together with the loss of tooth substance (26), chemical-induced changes over dentin are largely considered the main reasons for a reduction in the stiffness of root canal–treated teeth (23). Microhardness, elastic modulus, and flexural strength are some mechanical properties of dentin that are highly modified by treatment with NaOCl (23). Changes in microhardness, for instance, disclose modifications in both organic and inorganic parts of dentin, whereas a reduction in elastics modulus and flexural strength may potentially turn dentin brittle (23). The NaOCl strong oxidant effect adversely reacts with the dentin, causing a remarkable depletion of its organic framework (13). This organic constituent, composing about 22 wt% (13), is mainly constituted by type I collagen and proteoglycans (27). The collagen matrix forms the major component and organizes itself into a fibrillar frame around peritubular dentin, whereas proteoglycans connect 1 or more glycosaminoglycan chains and are responsible for regulating water content and intratubular permeability (28, 29). Overall, the deleterious effects of NaOCl solutions on the collagen and proteoglycan matrix might result in dentin contraction, induce an increase in stress concentration and crack propagation, and ultimately contribute to the significant reduction in the fracture strength (13). Moreover, the nonspecific proteolytic action of NaOCl is also capable of affecting carbonate ions (30), an inorganic reinforcing phase that also influences dentin mechanical properties (31). These known effects of NaOCl over dentin are certainly reasons for the reduction in root toughness, which was observed in the NaOCl-treated groups. Therefore, the null hypothesis presented here is rejected. However, bearing in mind the reported superior proteolytic effect of alkalized NaOCl solutions (8–10), the disclosure that the stabilized alkaline 5% NaOCl solution significantly reduced the fracture resistance of bovine teeth to the same level as the theoretically less proteolytic neutral NaOCl (P > .05) is surprising. Even though neutral NaOCl solutions are currently not marketed as endodontic irrigants, a pH level of 7.2 has been selected to confirm the hypothesis that a reduction in the pH level would be beneficial by decreasing the proteolytic side effect on the organic part of dentin, which could minimize root weakening. However, both pH solutions similarly reduced the fracture resistance of bovine roots to about 30%, which is in contrast with a previous report that found an intensification of the negative effect by stabilized NaOCl solution over flexure strength and elastic modulus of dentin (9). The present outcome might be interpreted as the interplay of various factors including the remarkable differences in the nature of the present study setup compared with flexural strength and elastic modulus investigation JOE — Volume -, Number -, - 2014

designs. In the latter, dentin discs are usually submerged into the irrigant, leading to the discs being affected by the solution from all sides. Also, the volume of irrigant to dentin ratio is inversed in this assay because in clinical reality the amount of solution is small compared with the extent of root dentin (9). In the close to clinical scenario used here, the solution only affected the inner root canal surface. Gravitational forces also push the solution in a perpendicular direction in relation to the dentinal tubules, which certainly influences its spreadability into dentin. Penetration into dentinal tubules by syringe-driven NaOCl is, indeed, very limited (32). Thus, mimicking the clinical scenario, the superior proteolytic effect over dentin by stabilized NaOCl appeared not to affect root dentin stiffness in the same magnitude as previously reported using dentin bar designs (9). Another factor accounting for this outcome is the role of the total contact time of NaOCl with dentin. Both the proteolytic and antimicrobial effects of NaOCl solution are known to be strongly time dependent (5). The same can be expected for the deleterious effects on dentin. Microcracks, for instance, were markedly visible over dentin surface after 6 hours of immersion in a 5% NaOCl solution (13), and flexural strength and elastic modulus of dentin were reduced after a minimum of 24 minutes–2 hours of contact with NaOCl (23). The 26-minute average contact time used in this study, which was selected to mimic a multifile instrumentation approach, might have been insufficient to make the stronger oxidant and proteolytic effect over root toughness by the NaOH-stabilized alkaline NaOCl prominent. A decrease in the pH level as ClO is consumed (33) could also be hypothesized as an explanation for the similar results between NaOCl solutions. Jungbluth et al (9) were unable to find any pH reduction after 30 minutes of contact with dentin discs, which might be explained by the fact that NaOH maintains high pH levels despite the consumption of available chlorine. Here, after 40 minutes of contact of NaOH-stabilized solution with the roots, no drop in pH was observed. Because various factors could affect the tissue dissolution ability of NaOCl solutions, such as the concentration of available chlorine, temperature, and time of contact (5), efforts were made to keep these constant during the experiment. Considering the unreliable concentrations of chlorine in household bleach and dental NaOCl irrigants (9), technical-grade NaOCl solutions were ordered from a pharmacy in order to a priori guarantee the amount of available chlorine content; this was confirmed by solution titrations before and after experiments. The temperature of the room was also controlled to avoid any interference with the proteolytic action of solutions. Surprisingly, the instrumentation-only group (positive control) did not display any lowering impact on the root strength as largely observed in other previous studies on human tooth (26). A speculative explanation could be hypothesized because of the natural morphologic differences between bovine and human teeth. Bovine incisors present thicker dentinal walls (3–4 mm) compared with human roots (1–3 mm). After canal instrumentation of human root, the dentin loss possibly has a superior impact on overall tooth resistance compared with bovine teeth in which the thicker dentinal walls would be less impacted by the dentin removed after instrumentation. However, the lack of studies on the effect of root canal instrumentation in bovine teeth prevents a further confirmation of this speculative hypothesis. The use of bovine teeth could be regarded as a limitation. However, some similarities between bovine and human teeth can be viewed as positive for this study, such as the similar modulus of elasticity and tensile strength (34) and the number and distribution of dentinal tubules (35–37), which potentially influence the ability of dentin to resist loading. Also, the possibility to easily standardize bovine teeth among groups according to age is advantageous. In addition, using a splitmouth design is depicted as an experimental improvement. These

Root Canal–treated Bovine Teeth

3

Basic Research—Technology approaches reduced the biasing role of anatomy, which is usually difficult to exclude when using human substrates. Not less important is the simulation of the periodontal apparatus that has been found to approach the in vitro setup to clinical reality by distributing the fracture pattern to radicular areas (25). The stabilization of alkaline NaOCl is seen as beneficial for helping to keep the proteolytic-driven chemical debridement active during root canal treatment. Doubt existed regarding whether the clinical use of this solution could make roots more brittle. The present results provide laboratorial evidence to minimize this concern. However, as a laboratorialbased study, extrapolations to the clinic cannot be forthright. Pondering the limitations of the present study, it can be concluded that NaOH-stabilized alkaline NaOCl solution presented the same level of influence as a neutral counterpart in the fracture resistance of root canal–treated bovine teeth.

Acknowledgments The authors deny any conflicts of interest related to this study.

References 1. Dakin HD. In the use of certain antiseptic substance in the treatment of infected wound. Br Med J 1915;2:318–20. 2. Ørstavik D, Haapasalo M. Disinfection by endodontic irrigants and dressings of experimentally infected dentinal tubules. Endod Dent Traumatol 1990;6:142–9. 3. Moorer W, Wesselink P. Factors promoting the tissue dissolving capability of sodium hypochlorite. Int Endod J 1982;15:187–96. 4. Retamozo B, Shabahang S, Johnson N, et al. Minimum contact time and concentration of sodium hypochlorite required to eliminate Enterococcus faecalis. J Endod 2010;36:520–3. 5. Zehnder M. Root canal irrigants. J Endod 2006;32:389–98. 6. Bloomfield SF, Miles GA. The antibacterial properties of sodium dichloroisocyanurate and sodium hypochlorite formulations. J Appl Bacteriol 1979;46:65–73. 7. Camps J, Pommel L, Aubut V, et al. Shelf life, dissolving action, and antibacterial activity of a neutralized 2.5% sodium hypochlorite solution. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:66–73. 8. Aubut V, Pommel L, Verhille B, et al. Biological properties of a neutralized 2.5% sodium hypochlorite solution. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:120–5. 9. Jungbluth H, Marending M, De-Deus G, et al. Stabilizing sodium hypochlorite at high pH: effects on soft tissue and dentin. J Endod 2011;37:693–6. 10. Christensen C, Mcneal SF, Eleazer P. Effect of lowering the pH of sodium hypochlorite on dissolving tissue in vitro. J Endod 2008;34:449–52. 11. Urano H, Fukuzaki S. The mode of action of sodium hypochlorite in the cleaning process. Biocontrol Sci 2005;10:21–9. 12. Clarkson R, Moule A. Sodium hypochlorite and its use as an endodontic irrigant. Aust Dent J 1998;43:250–6. 13. Lee BS, Hsieh TT, Chi DC, et al. The role of organic tissue on the punch shear strength of human dentin. J Dent 2004;32:101–7. 14. Barbosa SV, Safavi KE, Sp angberg SW. Influence of sodium hypochlorite on the permeability and structure of cervical human dentine. Int Endod J 1994;27:309–12.

4

Souza et al.

15. Haikel Y, Gorce F, Allemann C, Voegel JC. In vitro efficiency of endodontic irrigation solutions on protein desorption. Int Endod J 1994;27:16–20. 16. Saleh AA, Ettman WN. Effect of endodontic irrigation solutions on microhardness canal dentine. J Dent 1999;27:43–6. 17. Sim TP, Knowles JC, Ng YL, et al. Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain. Int Endod J 2001;34: 120–32. 18. Grigoratos D, Knowles J, Ng YL, Gulabivala K. Effect of exposing dentine to sodium hypochlorite and calcium hydroxide on its flexural strength and elastic modulus. Int Endod J 2001;34:113–9. 19. White JK, Lacefield WR, Chavers LS, Eleazer PD. The effect of three commonly used endodontic materials on the strength and hardness of root dentin. J Endod 2002;28: 828–30. 20. Ari H, Erdemir A, Belli S. Evaluation of the effect of endodontic irrigation solutions on the microhardness and the roughness of root canal dentin. J Endod 2004;30: 792–5. 21. Santos JN, Carrilho MR, De Goes MF, et al. Effect of chemical irrigants on the bond strength of a self-etching adhesive to pulp chamber dentin. J Endod 2006;32: 1088–90. 22. Marending M, Luder HU, Brunner TJ, et al. Effect of sodium hypochlorite on human root dentine–mechanical, chemical and structural evaluation. Int Endod J 2007;40: 786–93. 23. Pascon FM, Kantovitz KR, Sacramento PA, et al. Effect of sodium hypochlorite on dentine mechanical properties. A review. J Dent 2009;37:903–8. 24. Zehnder M, Kosicki D, Luder H, et al. Tissue-dissolving capacity and antibacterial effect of buffered and unbuffered hypochlorite solutions. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:756–62. 25. Soares CS, Pizi EC, Fonseca RB, Martins LR. Influence of root embedment material and periodontal ligament simulation on fracture resistance tests. Braz Oral Res 2005;19:11–6. 26. Hood JA. Biomechanics of the intact, prepared and restored tooth: some clinical implications. Int Dent J 1991;41:25–32. 27. Butler WT. Dentin extracellular matrix and dentinogenesis. Oper Dent 1992;5: 18–23. 28. Ruoslathi E. Structure and biology of proteoglycans. Ann Rev Cell Biol 1988;4: 229–55. 29. Oyarzun A, Rathkamp H, Dreyer E. Immunohistochemical and ultrastructural evaluation of the effects of phosphoric acid etching on dentin proteoglycans. Eur J Oral Sci 2000;108:546–54. 30. Shellis RP. Structural organization of calcospherites in normal and rachitic human dentin. Arch Oral Biol 1983;28:85–95. 31. Pashley DH. Dentin: a dynamic substrate—a review. Scanning Microsc 1989;3: 161–74. 32. Paragliola R, Franco V, Fabiani C, et al. Final rinse optimization: influence of different agitation protocols. J Endod 2010;36:282–5. 33. Vollenweider M, Brunner T, Knecht S, et al. Remineralization of human dentin using ultrafine bioactive glass particles. Acta Biomater 2007;3:936–43. 34. Sano H, Ciucchi B, Matthews WG, Pashley DH. Tensile properties of mineralized and demineralized human and bovine dentin. J Dent Res 1994;73:1205–11. 35. Nakamichi I, Iwaku M, Fusayama T. Bovine teeth as possible substitutes in adhesion test. J Dent Res 1983;62:1076–81. 36. Ruse ND, Smith DC. Adhesion to bovine dentin-surface characterization. J Dent Res 1991;70:1002–8. 37. Schilke R, Lisson JA, Baub O, Geurtsen W. Comparison of the number and diameter of dentinal tubules in human and bovine dentine by scanning electron microscopic investigation. Arch Oral Biol 2000;45:355–61.

JOE — Volume -, Number -, - 2014

Similar influence of stabilized alkaline and neutral sodium hypochlorite solutions on the fracture resistance of root canal-treated bovine teeth.

Stabilizing sodium hypochlorite (NaOCl) at an alkaline pH is proposed to increase solution stability and tissue dissolution ability; however, a reduct...
150KB Sizes 0 Downloads 7 Views