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Basic Research—Technology

Comparison of the Efficacy of Three Chelating Agents in Smear Layer Removal Sedigheh Khedmat, DDS, MSc, and Noushin Shokouhinejad, DDS, MSc Abstract The purpose of this study was to compare the efficacy of SmearClear (Sybron Endo, Orange, CA), 17% EDTA, and 10% citric acid in smear layer removal. Forty-eight extracted single-rooted human teeth were randomly divided into 4 groups (n  12) and instrumented using Mtwo nickel-titanium rotary instruments. Each canal was subsequently irrigated with one of the following solutions: 5.25% NaOCl (control), SmearClear, 17% EDTA, or 10% citric acid. After that, all the specimens were subjected to irrigation with 5.25% NaOCl. The teeth were then processed for scanning electron microscopy (SEM), and the removal of the smear layer was examined in the coronal, middle, and apical thirds. The results showed that there were no significant differences in the efficacy of three chelating agents at all levels of the root canals. The comparison of three one thirds in each group showed no significant difference in the SmearClear and EDTA groups. However, the efficacy of citric acid was significantly less in the apical third compared with the coronal and middle thirds of the canals. In conclusion, the protocol used in this study was not efficient to completely remove the smear layer especially in the apical third of the canal. (J Endod 2008;34:599 – 602)

Key Words Chelating agents, citric acid, EDTA, smear layer, SmearClear

From the Department of Endodontics, School of Dentistry/ Dental Research Center, Medical Sciences/University of Tehran, Tehran, Iran. Supported by Tehran University of Medical Sciences & Health Services, Tehran, Iran (grant no 132/8543). Address requests for reprints to Dr Noushin Shokouhinejad, Department of Endodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Ghods Ave, Enghelab St, Tehran, Iran. E-mail address: shokouhinejad@yahoo.com. 0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2008.02.023

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tudies have shown that mechanical instrumentation of the root canals leaves a smear layer covering the dentinal walls (1, 2). This layer contains inorganic and organic materials (1). Despite the controversy over keeping or maintaining the smear layer, it has been demonstrated that the smear layer itself may be infected and may protect the bacteria within the dentinal tubules (3). The smear layer has also been shown to hinder the penetration of intracanal disinfectants (4) and sealers (5) into dentinal tubules and has the potential of compromising the seal of the root canal filling (6, 7). For effective removal of both organic and inorganic components of the smear layer, combined application of NaOCl and a chelating agent, such as EDTA, is recommended (8 –10). It has been reported that the smear layer was completely removed by 17% EDTA for 1 minute followed by 5% NaOCl (11). On the other hand, the application of EDTA for more than 1 minute (10 –13) and in volume more than 1 mL (10, 12, 13) has been reported to be associated with dentinal erosion. Crumpton et al. (14) showed that the smear layer was efficiently removed using 1 mL of 17% EDTA for 1 minute followed by 3 mL of 5.25% NaOCl as final irrigants. Citric acid may also be used for the smear layer removal. Concentrations ranging from 1% to 50% have been investigated (15–20). Wayman et al. (17) showed that the use of 10% citric acid and 2.5% NaOCl is a very effective approach for the smear layer removal. Di Lenarda et al. (21) reported no or a negligible difference in smear layer removal obtained by citric acid and EDTA. SmearClear (Sybron Endo, Orange, CA) is a product recently introduced for removing the smear layer. It is a 17% EDTA solution including a cationic (cetrimide) and an anionic surfactant. The only published study to date comparing SmearClear with EDTA in removing the smear layer in the apical and middle thirds of the root canal showed that the surfactants within the SmearClear did not improve its efficiency (22). This study aimed to compare the efficacy of SmearClear, 17% EDTA, and 10% citric acid in combination with 5.25% sodium hypochlorite as final irrigants in the removal of the smear layer in the coronal, middle, and apical thirds of the instrumented root canal.

Materials and Methods Forty-eight freshly extracted human teeth with straight single root canals stored in 0.1% thymol were selected for this study. The teeth were decoronated to standardized root length of 12 mm and randomly divided into 4 groups (n  12). The working lengths were measured by deducting 1 mm from lengths recorded when tips of #10 or #15 K-files (Dentsply Maillefer, Tulsa, OK) were visible at the apical foramina. The specimens were prepared using Mtwo Ni-Ti rotary instruments (VDW, Munich, Germany). Five instruments were used at the working length in each canal according to the manufacturer’s instructions in the following sequence: (1) size 10, .04 taper; (2) size 15, .05 taper; (3) size 20, .06 taper; (4) size 25, .06 taper; and (5) size 30, .05 taper. Each instrument was only used for the preparation of five teeth. After using each file and before proceeding to the next, canals were irrigated with 2 mL of 5.25% NaOCl (Vista Dental Products, Racine, WI). After instrumentation, all teeth underwent final irrigation as follows: (1) control group, 1mL of 5.25% NaOCl for 1 minute followed by 3 mL of 5.25% NaOCl; (2) SmearClear group, 1 mL of SmearClear for 1 minute followed by 3 mL of 5.25% NaOCl; (3) EDTA group, 1 mL of 17% EDTA (Pulpdent, Watertown, MA) for 1 minute followed by 3 mL of 5.25% NaOCl; and (4) citric acid group, 1 mL of 10% citric acid (Merck KGaA, Darmstadt, Germany) for 1 minute followed by 3 mL of 5.25% NaOCl.

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Basic Research—Technology TABLE 1. Mean Smear Scores ( SD) and Statistical Comparison of the Remaining Smear Layer among the Coronal, Middle, and Apical Thirds of the Canals in Each Group Coronal third scores

Group

Control (n  10) SmearClear (n  12) 17% EDTA (n  12) 10% citric acid (n  12)

Mean

1

2

3

0 4 8 9

0 8 4 3

10 0 0 0

3.00 1.6 0.4 1.3 0.4 1.3 0.6

Middle third scores 1

2

3

0 4 8 7

0 8 3 4

10 0 1 1

The solutions were introduced into the canals by means of a 30-G needle, which penetrated to within 1 to 2 mm from the working length. Then, the root canals were irrigated with 5 mL of distilled water and dried with paper points. Finally, two longitudinal grooves were prepared on the buccal and lingual surfaces of each root using a diamond disc without penetration into the canal. The roots were then split into two halves with a chisel. For each root, the half containing the most visible part of the apex was conserved and coded. The coded specimens were then mounted on metallic stubs, gold sputtered, and examined by a scanning electron microscope (DSM 940 A; Carl Zeiss, Oberkochen, Germany). After general survey of the canal wall, 12 scanning electron microscopy photomicrographs were taken at magnifications of 1,000 and 2,000 at the coronal (10 mm to apex), middle (6 mm to apex), and apical (2 mm to apex) thirds of each specimen. Some areas were also observed at a higher magnification (5,000). The amount of smear layer remained on the surface of the root canal or in the dentinal tubules was scored according to the following criteria (10): 1  no smear layer: no smear layer was detected on the surface of the root canals and all tubules were clean and open; 2 

Mean

3.00 1.6 0.4 1.4 0.6 1.5 0.6

Apical third scores 1

2

3

0 3 5 1

0 6 7 9

10 3 0 2

Mean

p value

3.00 2 0.7 1.5 0.5 2.0 0.5

1 0.3 0.4 0.0

moderate smear layer: no smear layer was observed on the surface of the root canal, but tubules contained debris; and 3  heavy smear layer: the smear layer covered the root canal surface and the tubules. Approximately 600 scanning electron microscopy photomicrographs were scored by an endodontist who was unaware of the coding system to exclude observer bias. Evaluation was repeated twice for the first 20 specimens to ensure intraexaminer consistency. Data were analyzed using Kruskal-Wallis and Mann-Whitney U tests; p values were computed and compared with the p  0.05 level.

Results Two specimens in control group were excluded from the study because the canals were perforated by disc during preparation for SEM evaluation. The results for smear layer scores in each group are presented in Table 1. The examination of the surface of root canal walls in control group showed the presence of a heavy smear layer throughout the entire length of the root canals (Fig. 1A). Most samples of SmearClear group showed

Figure 1. Scanning electron microscopy photomicrographs of the root canal walls after final irrigation (original magnification 2,000). (A) The smear layer on the middle third of a root canal in control group. (B) The smear layer was removed from the coronal third of a root canal in the SmearClear group, but dentinal tubules contained debris (a moderate smear layer). (C) Complete removal of the smear layer from the middle third of a root canal in 17% EDTA group. All dentinal tubules are clean and open. (D) The smear layer has removed from the apical surface of a root canal in 10% citric acid group, but dentinal tubules contained debris (a moderate smear layer).

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Basic Research—Technology moderate smear layer on the coronal, middle, and apical thirds (Fig. 1B). In EDTA and citric acid groups, no smear layer was detected on the surface of most samples in the coronal and middle thirds, but a moderate smear layer was observed in the apical third of most roots in these two groups (Figs. 1C and D). The comparison of the four groups showed that the canal walls in the SmearClear, EDTA, and citric acid groups were significantly cleaner than in control group (p ! 0.001). The comparison of remaining smear layer showed no significant differences in the efficacy of SmearClear, EDTA and citric acid in smear layer removal at the coronal (p  0.110), middle (p  0.191) and apical (p  0.147) thirds of the root canals. Comparison of three one thirds of the canals in each group showed no statistically significant difference in SmearClear, EDTA, and control groups (Table 1). But in the citric acid group, the efficacy of the chelating agent was significantly less in the apical third of the samples compared with the coronal (p  0.007) and middle (p  0.039) thirds.

decalcifying ability (15, 18). However, another study did not show any relation between decalcifying ability of these solutions and their efficiency in smear layer removal (34). EDTA is an effective chelating agent for the removal of the smear layer. However, the erosion of dentinal tubules caused by the application of EDTA over 1 minute and in a volume more than 1 mL has been reported (10 –13). Crumpton et al. (14) showed that the smear layer was efficiently removed with a final rinse of 1 mL of 17% EDTA for 1 minute followed by 3 mL of 5.25% NaOCl. But the present study showed that this protocol was not efficient to completely remove the smear layer, especially in the apical third. Murray et al. (35) also showed that the smear layer was not completely removed from all of the instrumented root canals by using %17 EDTA according to this protocol. Consequently, it is important to use other methods, such as ultrasonic devices, for improving the efficiency of low-volume chelating agents used for a short application time (22).

Discussion

Based on the results of this study, the application of 1 mL of SmearClear, 17% EDTA, and 10% citric acid for 1 minute followed by 3 mL of 5.25%NaOCl was not sufficient to completely remove the smear layer, especially in the apical third. The addition of surfactants to EDTA in SmearClear did not result in better smear layer removal compared with EDTA alone.

Conclusion The relevant literature shows a wide variety of irrigation times and volumes of irrigants in removing the smear layer. To minimize destructive effects on dentin reported by some investigators (10 –13), we used a low volume (1 mL) of chelating agents for a short application time (1 minute). The significant difference between control and the other groups is in accordance with other studies that have shown that NaOCl is not effective in removing the smear layer (10, 12, 23–25). The current study showed that the process of smear layer removal was more efficient in the coronal and middle thirds than in the apical third of the canals. This finding is in agreement with the results of various studies that have shown an effective cleaning action in the coronal and middle thirds of the canals even when different irrigation times and volumes of solutions were investigated (9, 10, 26, 27). A larger canal diameter in the coronal and middle thirds exposes the dentin to a higher volume of irrigants, allowing a better flow of the solution and, hence, further improving the efficiency of smear layer removal (10, 27). SmearClear is a 17% EDTA solution with two additional surfactants. Abou-Rass and Patonai (28) confirmed that reduction of surface tension of endodontic solutions improved their flow into narrow root canals. Therefore, it may be speculated that the addition of two surfactants to EDTA should improve its penetration ability into narrow apical region of the root canal. However, the present study showed that the surfactants in SmearClear did not improve its efficacy in smear layer removal compared with the surfactant-free EDTA. This result is in agreement with the findings of Lui et al. (22) who used 5 mL of SmearClear for 1 minute followed by 5 mL of 1% NaOCl as final irrigants. Also, other studies have shown that the reduction of surface tension of endodontic chelators did not improve their calcium chelating ability (18, 29). The results of smear layer removal with 10% citric acid compared with 17% EDTA in this study are in agreement with those studies that reported a minor or no difference in smear layer removal with citric acid and EDTA (20, 21, 30 –32). In the current study, 1 mL of 10% citric acid was used for 1 minute. The significant difference between the apical third and the two other thirds of the root canals in citric acid group may be related to the volume and/or application time of citric acid. It seems the application of higher volumes of citric acid over 1 minute improves its efficacy in removing the smear layer. Accordingly, Sterrett et al. (33) showed that the effect of 10% citric acid on dentin demineralization was time dependent at 1, 2, and 3 minutes. Some investigators have reported that the application of 10% citric acid for more than 1 minute and in a volume more than 1 mL was more effective than 17% EDTA in terms of JOE — Volume 34, Number 5, May 2008

References 1. McComb D, Smith DC. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endod 1975;1:238 – 42. 2. Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod 1984;10:477– 83. 3. Torabinejad M, Handysides R, Khademi AA, Bakland LK. Clinical implications of the smear layer in endodontics: a review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:658 – 66. 4. Örstavik D, Haapasalo M. Disinfection by endodontic irrigants and dressings of experimentally infected dentinal tubules. Endod Dent Traumatol 1990;6: 142–9. 5. White RR, Goldman M, Lin PS. The influence of the smeared layer upon dentinal tubule penetration by plastic filling materials. J Endod 1984;10:558 – 62. 6. Economides N, Liolios E, Kolokuris I, Beltes P. Long-term evaluation of the influence of smear layer removal on the sealing ability of different sealers. J Endod 1999;25:123–5. 7. Shahravan A, Haghdoost AA, Adl A, Rahimi H, Shadifar F. Effect of smear layer on sealing ability of canal obturation: a systematic review and meta-analysis. J Endod 2007;33:96 –105. 8. Yamada R, Aramas A, Goldman M, Lin PS. A scanning electron microscope comparison of a high volume final flush with several irrigating solutions. Part 3. J Endod 1983;9:137– 42. 9. Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endod 1987;13:147–57. 10. Torabinejad M, Khademi AA, Babagoli J, et al. A new solution for the removal of the smear layer. J Endod 2003;29:170 –5. 11. Calt S, Serper A. Time-dependent effects of EDTA on dentin structures. J Endod 2002;28:17–9. 12. Torabinejad M, Cho Y, Khademi AA, Bakland LK, Shabahang S. The effect of various concentrations of sodium hypochlorite on the ability of MTAD to remove the smear layer. J Endod 2003;29:233–9. 13. Tay FR, Gutmann JL, Pashley DH. Microporous, demineralized collagen matrices in intact radicular dentin created by commonly used calcium-depleting endodontic irrigants. J Endod 2007;33:1086 –90. 14. Crumpton BJ, Goodell GG, McClanahan SB. Effects on smear layer and debris removal with varying volumes of 17% REDTA after rotary instrumentation. J Endod 2005;31:536 – 8. 15. Machado-Silveiro LF, González-López S, González-Rodríguez MP. Decalcification of root canal dentine by citric acid, EDTA and sodium citrate. Int Endod J 2004;37:365–9. 16. Baumgartner JC, Brown CM, Mader CL, Peters DD, Shulman JD. A scanning electron microscopic evaluation of root canal debridement using saline, sodium hypochlorite, and citric acid. J Endod 1984;10:525–31.

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Basic Research—Technology 17. Wayman BE, Kopp WM, Pinero GJ, Lazzari EP. Citric and lactic acids as root canal irrigants in vitro. J Endod 1979;5:258 – 65. 18. Scelza MF, Teixeira AM, Scelza P. Decalcifying effect of EDTA-T, 10% citric acid, and 17% EDTA on root canal dentin. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;95:234 – 6. 19. Czonstkowsky M, Wilson EG, Holstein FA. The smear layer in endodontics. Dent Clin North Am 1990;34:13–25. 20. Pérez-Heredia M, Ferrer-Luque CM, González-Rodríguez MP. The effectiveness of different acid irrigating solutions in root canal cleaning after hand and rotary instrumentation. J Endod 2006;32:993–7. 21. Di Lenarda R, Cadenaro M, Sbaizero O. Effectiveness of 1 mol L-1 citric acid and 15% EDTA irrigation on smear layer removal. Int Endod J 2000;33:46 –52. 22. Lui JN, Kuah HG, Chen NN. Effect of EDTA with and without surfactants or ultrasonics on removal of smear layer. J Endod 2007;33:472–5. 23. Garberoglio R, Becce C. Smear layer removal by root canal irrigants. A comparative scanning electron microscopic study. Oral Surg Oral Med Oral Pathol 1994; 78:359 – 67. 24. Baumgartner JC, Cuenin PR. Efficacy of several concentrations of sodium hypochlorite for root canal irrigation. J Endod 1992;18:605–12. 25. Grandini S, Balleri P, Ferrari M. Evaluation of Glyde File Prep in combination with sodium hypochlorite as a root canal irrigant. J Endod 2002;28:300 –3. 26. Abbott PV, Heijkoop PS, Cardaci SC, Hume WR, Heithersay GS. An SEM study of the effects of different irrigation sequences and ultrasonics. Int Endod J 1991;24: 308 –16.

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27. Teixeira CS, Felippe MC, Felippe WT. The effects of application time of EDTA and NaOCl on intracanal smear layer removal: an SEM analysis. Int Endod J 2005; 38:285–90. 28. Abou-Rass M, Patonai FJ Jr. The effects of decreasing surface tension on the flow of irrigating solutions in narrow root canals. Oral Surg Oral Med Oral Pathol 1982;53:524 – 6. 29. Zehnder M, Schicht O, Sener B, Schmidlin P. Reducing surface tension in endodontic chelator solutions has no effect on their ability to remove calcium from instrumented root canals. J Endod 2005;31:590 –2. 30. Goldman LB, Goldman M, Kronman JH, Lin PS. The efficacy of several irrigating solutions for endodontics: a scanning electron microscopic study. Oral Surg Oral Med Oral Pathol 1981;52:197–204. 31. Takeda FH, Harashima T, Kimura Y, Matsumoto K. A comparative study of the removal of smear layer by three endodontic irrigants and two types of laser. Int Endod J 1999;32:32–9. 32. Zehnder M, Schmidlin P, Sener B, Waltimo T. Chelation in root canal therapy reconsidered. J Endod 2005;31:817–20. 33. Sterrett JD, Bankey T, Murphy HJ. Dentin demineralization. The effects of citric acid concentration and application time. J Clin Periodontol 1993;20:366 –70. 34. Scelza MF, Pierro V, Scelza P, Pereira M. Effect of three different time periods of irrigation with EDTA-T, EDTA, and citric acid on smear layer removal. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:499 –503. 35. Murray PE, Farber RM, Namerow KN, Kuttler S, Garcia-Godoy F. Evaluation of Morinda citrifolia as an endodontic irrigant. J Endod 2008;34:66 –70.

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Basic Research—Technology

The Evaluation of Bond Strength of a Composite and a Compomer to White Mineral Trioxide Aggregate with Two Different Bonding Systems Emine ¸Sen Tunç, DDS, PhD,* Is¸ıl ¸Sarog˘lu Sönmez, DDS, PhD,† ¸Sule Bayrak, DDS, PhD,* and Türkan Eg˘ilmez, DDS* Abstract The purpose of this study was to evaluate the bond strength of a resin composite and a polyacid modified composite or “compomer” to white mineral trioxide aggregate (WMTA) with two different bonding systems (total-etch one bottle and self-etch one step). Forty specimens of WMTA were prepared and divided into four groups. In group one, Single Bond (3M/ESPE, St Paul, MN) and Z250 (3M/ESPE) were placed over WMTA. In group two, Prompt L-Pop (3M Dental Products, St Paul, MN) and Z250 were applied. In group three, Single Bond was applied with Dyract AP (Dentsply DeTrey, Konstanz, Germany), and, in group four, Prompt L-Pop was applied with Dyract AP. The shear bond strength was measured, and the fractured surfaces were examined. The results of the shear bond strength tests were analyzed by one-way analysis of variance test. The results of this study have suggested that the total-etch one-bottle adhesive system mediated a stronger bond to WMTA for both the resin composite and the compomer investigated. The placement of composite (Z250) and compomer materials (Dyract AP), used with total-etch one-bottle adhesive (Single Bond), over WMTA as final restoration may be appropriate. (J Endod 2008;34:603– 605)

Key Words Compomer, composite resin, shear bond strength, white mineral trioxide aggregate

From the *Department of Pediatric Dentistry, University of Ondokuz Mayıs, Samsun, Turkey; and †Department of Pediatric Dentistry, Faculty of Dentistry, University of Kırıkkale, Kırıkkale, Turkey. Address requests for reprints to Dr Is¸ıl S¸arog˘lu Sönmez, Kırıkkale U¨niversitesi, Dis¸ Hekimlig˘i Fakültesi, Pedodonti ABD, Kırıkkale, Turkey. E-mail address: isilsaroglu@yahoo.com. 0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2008.02.026

M

ineral trioxide aggregate (MTA) is a biocompatible material with numerous exciting clinical applications in endodontics (1-3). MTA is a powder consisting of fine hydrophilic particles of tricalcium aluminate, tricalcium silicate, and tricalcium oxide. It also contains small amounts of other mineral oxides, which modify its chemical and physical properties (4, 5). In the presence of moisture, MTA sets into a hard mass by forming calcium hydroxide and silicate hydrate gel (6). It is available commercially as ProRoot MTA (Dentsply; Tulsa Dental, Tulsa, OK) and has been proposed as a potential material for furcation repair, internal resorption treatment, pulpotomy procedures, and capping of pulps with reversible pulpitis (2, 4, 7–12). As the use of MTA in vital pulp therapy has gained popularity, the material that would be placed over MTA as final restoration is an important matter. The potential of restorative materials to attach to MTA is not well known. Until the initiation of this study, there were no published reports documenting the bond strength between MTA and restorative materials. The aim of this study was to measure the bond strength of a frequently used resin composite (Z250; 3M/ESPE, St Paul, MN) and a polyacid modified composite resin or “compomer” (Dyract AP; Dentsply DeTrey, Konstanz, Germany) when bonded to white MTA (WMTA) with two different bonding systems (one bottle total etch and one step self-etch).

Materials and Methods Forty specimens of WMTA (Dentsply, Tulsa Dental) were prepared by using cylindrical acryl blocks. The blocks had central hole measuring 4 mm in diameter and 2 mm in depth. WMTA was mixed according to the manufacturer’s instructions. The acrylic blocks were filled with WMTA and covered with a wet cotton pellet and temporary filling material (Cavit; ESPE America, Inc, Norristown, PA). Then, the specimens were stored at 37°C with 100% humidity for 48 hours to encourage setting. After the removal of the temporary material, the WMTA surface was not rinsed or polished. Specimens were divided into 4 groups of 10 specimens.

Group One The WMTA surface was etched for 15 seconds with 37.5% phosphoric acid etching gel (Kerr, Karlsruhe, Germany), rinsed with water for 10 seconds, and excess water was removed by blotting with absorbent paper, leaving the surface visibly moist dried. Single Bond (3M/ESPE) was then applied in 2 consecutive coats, gently air dried with oil-free compressed air from an air syringe for 5 seconds to evaporate the solvent (keeping the air syringe 2 cm from the surface), and light cured for 10 seconds. Resin composite Z250 was applied into a cylindrical shaped plastic matrix with an internal diameter of 2 mm and height of 2 mm and then light cured with a light-emitting diode light-curing unit (Elipar Freelight II, 3M ESPE) with the intensity at 1,200 mV/cm2 for 20 seconds. Group Two The WMTA surface was dried for 10 seconds (keeping the air syringe 2 cm from the surface) to ensure a dry surface. Prompt L-Pop (3M Dental Products, St Paul, MN) was applied with scrubbing for 15 seconds. Then, the surface was gently air dried with

JOE — Volume 34, Number 5, May 2008

Evaluating Bond Strength of a Composite and a Compomer to MTA

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Comparison of the Efficacy of Three Chelating Agents inf