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A Comparative Study of Contact Angles of Four Different Root Canal Sealers
Basic Research—Technology
A Comparative Study of Contact Angles of Four Different Root Canal Sealers Evangelos G. Kontakiotis, DDS, PhD,* Giorgos N. Tzanetakis, DDS,† and Alexios L. Loizides, DDS, MSc‡ Abstract The present in vitro study was conducted with the aim of evaluating and comparing the contact angles of three different types of root canal sealers—Roth 801, AH26, and RSA RoekoSeal—with the contact angle of a newly developed silicone-based root canal filling material (Gutta-Flow) on dentin and gutta-percha surfaces at two different time periods. The contact angles were determined mathematically by measuring software and were calculated from base width and height of the droplet meniscus of each sealer. Under the conditions of this study, Roth 801 and AH26 recorded lower values of contact angles when root dentin surface was used as the substrate. RSA RoekoSeal and Gutta-Flow seem to spread similarly on dentin and gutta-percha surfaces, although the contact angles of these silicone-based sealers were found to be significantly higher than the contact angles of Roth 801 and AH26 sealers. According to these findings, it can be concluded that conventional root canal sealers (Roth 801 and AH26) may passively have the potential for better wettability of dentin and gutta-percha surfaces than that of siliconebased sealers (RSA RoekoSeal and Gutta-Flow). This fact means that Roth 801 and AH26 may have a better spreading capacity under clinical conditions on the root canal walls and gutta-percha surfaces. Application of a sufficient load during lateral or vertical compaction seems to be needed for RSA RoekoSeal and Gutta-Flow to satisfactorily wet gutta-percha and dentin under clinical conditions. (J Endod 2007;33:299 –302)
Key Words Contact angle, root canal sealers, wetting behavior
*Assistant Professor, †Postgraduate student, ‡Endodontist, Department of Endodontics, Dental School, University of Athens, Greece. Addrress requests for reprints to E. G. Kontakiotis, Dental School, University of Athens, Antheon 2 Ano Patisia, 11143 Athens, Greece. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.11.016
T
he attainment of an airtight seal in a root canal system is very important for the long-term success of endodontic treatment (1–3). During the obturation of a root canal system with gutta-percha, root canal sealer performs several functions to attain and maintain this seal (4). These functions concern the filling of root canal wall irregularities such as apical ramifications and deltas as well as spaces where the primary root canal filling material failed to reach. In addition, the sealer acts as a binding agent between root canal walls and the main filling material (5, 6), and thus the interface between either sealer and gutta-percha or sealer and dentin is of prime clinical importance. The physicochemical properties of a root canal sealer may characterize its clinical behavior during and after obturation of the root canal system (7–9). Among these properties are satisfactory wetting and adequate flow rate (8, 10). Wetting means that an interface contact is being formed between a liquid and a solid with a simultaneous expulsion of air. The tendency of a liquid to spread on a solid surface is expressed with the formation of a contact angle (11). Contact angle measurements provide a better understanding of the interactions between solids and liquids. These interactions play a key role in understanding not only material wettability, but also wetting, spreading, and adsorption of liquids. In vitro testing of physical properties is a basic prerequisite for the introduction of a new material in clinical endodontic practice (12). Gutta-Flow is a newly established silicone-based root canal filling material (Coltene/Whaledent, Langenau, Germany), recently introduced for use in endodontics. It seems that Gutta-Flow is classified as a type II material, intended to be used with or without core material or other sealer (4). Gutta-Flow is a modification of the RSA RoekoSeal (Roeko Dental Products, Langenau, Germany) and, according to the company, it contains very small gutta-percha particles with a size of ⬍30 m and sealer in its mass. The manufacturer claims an improved seal because of the increased flowability and the fact that the material expands slightly on setting, although until now no leakage study has yet been published about Gutta-Flow in the literature. It has also been established that Gutta-Flow can be used alone to fill the root canal with only one main gutta-percha cone in place. Furthermore, it was shown that this material has an adequate adaptability to root canal walls (13). However, the wetting behavior of this new material has not yet been tested by an in vitro study. The purpose of the present study was to evaluate and compare the contact angles of three different types of root canal sealers with respect to the contact angle of a newly developed silicon-based root canal filling material (Gutta-Flow) without the application of any load on dentin and gutta-percha surfaces at two different time periods.
Materials and Methods The sealers tested in this study were Roth 801 (Roth International, Chicago, IL, USA), AH26 silver free (Dentsply De Trey GmbH, Konstanz, Germany), RSA RoekoSeal (Roeko, Langenau, Germany), and Gutta-Flow (Coltene/Whaledent). All root canal sealers and Gutta-Flow were prepared according to the manufacturers’ instructions immediately before measurements as follows: 1. RSA RoekoSeal was mixed automatically with its mixing tip. 2. Gutta-Flow was prepared by vibrating the capsules for 30 seconds on a vibration device (Silamat S5, Ivoclar Vivadent, Bendererstrasse, Lichtenstein). 3. AH26 and Roth 801 were prepared manually on a glass plate with a spatula, according to manufacturer’s instructions for each sealer, respectively.
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Basic Research—Technology Contact angle measurements were carried out on two types of substrates: (1) dentin disks (2 mm thick) and (2) gutta-percha surfaces. Forty extracted intact fresh and caries-free mandibular molars were used for the preparation in an equal number of dentin disks. The extracted teeth were rinsed thoroughly under running tap water and then placed in 10% formalin until use. After storage, the teeth were cross-sectioned to expose the dentin of the root canal surface. The dentin disks were prepared with the use of a diamond disk (Komet; Brasseler GmbH, Lemgo, Germany) under running water. Polish paper no. 0.5 was used to reduce the roughness of dentin surfaces. Ultrasonic vibrations were applied to clean the dentin disks from any extra-organic components in distilled water for 5 minutes, after which the dentin specimens were placed in an incubator at 37°C to dry for the same period of time (5 minutes). The samples were carried directly from the incubator and placed into the measuring device (Fig. 1A). Two glass plates and thermoplasticized gutta-percha (Easyflow, Endodent, Duarte, CA, USA) were used to prepare 40 gutta-percha flat smooth surfaces. The specimens (dentin disks, gutta-percha surfaces) were positioned one by one on a flat glass surface in the measuring device. Controlled (0.1 mL) volume droplets of each sealer were placed onto ten dentin disks and onto ten gutta-percha surfaces. The volume of each sealer was controlled by means of a micropipette (Eppendorf Reference, adjustable-volume, Eppendorf AG, Hamburg, Germany). This micropipette could be manually maneuvered through a tiny hole on the top of the measuring device. Each specimen was photographed (contra lighted) twice, at 5 and 60 minutes, after positioning of the
droplets. The experiments were performed under standard conditions of temperature and relative humidity. The temperature was kept constant to within 1°C with the aid of a thermostat. Images of the droplets of each sealer (Fig. 1B) were digitalized by a scanner. After that, both base width (b) and height (h) of the droplet meniscus were measured by SigmaScan Pro V 5.0.0 Software (1987– 1999 SPSS, Inc., Leesburg, FL, USA). The contact angles were calculated according to the equation: a ⫽ 2 arc(cos 2h/b) (14, 15). One-way analysis of variance (ANOVA), followed by Bonferroni test of multiple comparisons, was used to investigate differences of the distributional properties of gutta-percha and dentin with respect to various root canal sealers and vice versa, at 5 and 60 minutes, respectively. All tests were two sided and the level of significance was set at 5%.
Results The mean values and standard deviations of contact angles for each sealer on dentin disks and gutta-percha surfaces for the two observation periods (5 minutes and 1 hour) are shown in Tables 1a and 1b, respectively. Statistically significant higher values were recorded for AH26 and Roth 801 on gutta-percha with respect to dentin after 5 minutes (p ⬍ 0.0001). On the contrary, RSA RoekoSeal recorded significantly higher values on dentin, whereas the values of Gutta-Flow did not differ significantly after 5 minutes between dentin and gutta-percha (p ⫽ 0.146). After 1 hour, AH26 and Roth 801 continued recording significantly higher values on gutta-percha compared to dentin (p ⫽
Figure 1. (A) Schematic illustration of the measuring device. (1) thermometer [23°C, 38% humidity, (2) micropipette, (3) flat glass plate, (4) dentin disk or gutta-percha surface, (5) meniscus of the sealer droplet (6) pressure gauge, (7) photographic camera, (8) light source. (B) Representative images of the droplet meniscus of each sealer on gutta-percha and dentin surfaces.
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Basic Research—Technology TABLE 1a. Mean values and standard deviations (SDs) of contact angles of each sealer on dentin surface after 5 minutes and 1 hour, respectively Dentin 5 minutes AH26 Roth 801 RSA Roekoseal Gutta-Flow 1 hour AH26 Roth 801 RSA Roekoseal Gutta-Flow
Mean
SD
Minimum
Maximum
14.54 11.05 83.72 45.14
1.57 1.13 0.15 7.52
12.45 9.09 88.44 28.96
18.26 12.53 88.90 58.26
8.51 9.23 41.64 38.75
0.73 1.74 2.83 6.93
7.89 6.78 37.48 28.18
9.73 19.49 46.55 47.23
TABLE 1b. Mean values and standard deviations (SDs) of contact angles of each sealer on gutta-percha surface after 5 minutes and 1 hour, respectively Gutta-percha (GP) 5 minutes AH26 Roth 801 RSA Roekoseal Gutta-Flow 1 hour AH26 Roth 801 RSA Roekoseal Gutta-Flow
Mean
SD
Minimum
Maximum
18.23 16.03 45.54 45.54
1.45 1.58 5.53 5.58
15.57 13.09 36.58 36.58
19.64 17.84 52.13 52.13
12.61 11.65 43.34 37.30
1.19 1.83 5.86 3.11
7.91 8.34 33.57 33.69
12.34 13.26 48.47 43.43
0.003 and p ⫽ 0.004, respectively). However, RSA RoekoSeal did not demonstrate any statistically significant difference after 1 hour between gutta-percha and dentin (p ⫽ 0.418), whereas Gutta-Flow continued not to differ between gutta-percha and dentin (p ⫽ 0.313). The multiple comparisons (Bonferroni test) after 5 minutes and 1 hour revealed that AH26 and Roth 801 exhibit significantly lower values than those of RSA RoekoSeal and Gutta-Flow (p ⬍ 0.0001) on guttapercha. Moreover, after 1 hour Gutta-Flow showed significantly lower values than RSA RoekoSeal on the gutta-percha surface (p ⫽ 0.0022). On dentin, AH26 and Roth 801 again exhibited significantly lower values than RSA RoekoSeal and Gutta-Flow after 5 minutes and 1 hour, respectively (p ⬍ 0.0001). Furthermore, after 5 minutes, Gutta-Flow had significantly lower values than RSA RoekoSeal (p ⬍ 0.0001). On the contrary, the values of Gutta-Flow and RSA RoekoSeal on dentin surfaces did not differ significantly after 1 hour (p ⫽ 0.999). The diagram of Fig. 2 schematically shows the wetting levels of each sealer on guttapercha and dentin for the two observation periods.
Discussion Reliability of the experimental procedure followed in the present study was tested in previous studies and found to be particularly high (14). The main advantage is that measurements can be done using very small quantities of liquid. In the present study, all measurements were carried out on very small specimens using controlled volume (0.1 mL) of each sealer. This was done because any volumetric change could affect the value of contact angle (16, 17). Also, the entire experimental procedure was performed under standard environmental conditions because the surface tension coefficient of liquids is influenced by temperature change and humidity (18). Roth 801 and AH26 were found to wet dentin better than guttapercha for the two observation periods. Based on these results, it appears that the surface free energy of dentin is relatively high compared
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to that of gutta-percha. Accordingly, it can be substantiated that the surface energy forces of dentin overcome the forces of surface tension of these sealers with respect to the surface energy forces of gutta-percha. On the contrary, RSA RoekoSeal did not spread satisfactorily on dentin with respect to gutta-percha after 5 minutes, although after 1 hour no significant differences were observed between gutta-percha and dentin. In this case, the surface roughness of dentin and the initial incomplete wetting of RSA RoekoSeal seem to play a more significant role. On the other hand, Gutta-Flow was found to spread similarly on dentin and gutta-percha for the two observation periods. The addition of very small particles of gutta-percha in its mass appears to improve the wetting of the material compared to RSA RoekoSeal. In the second part of the study, statistically significant differences were found between silicone-based sealers (RSA RoekoSeal and GuttaFlow) and conventional root canal sealers (AH26 and Roth 801). Conventional sealers documented generally lower contact angles than those of silicone-based sealers on dentin and gutta-percha after 5 and 60 minutes, respectively. This finding was obtained perhaps as a result of the different syntheses of each sealer. Synthesis is a basic factor that influences critical surface tension (19). The presence of silicone produces possibly high surface tension forces, thus making the spreading of these materials more difficult. However, Gutta-Flow seems to have a better spreading capacity than that of RSA RoekoSeal initially, possibly because of the presence of very small gutta-percha particles. RSA RoekoSeal at first demonstrated difficulty in satisfactorily wetting the substrates and generally it had a delayed wetting behavior. In the present study, the contact angle was measured using not only the liquid of the sealer (20) but also all the mixed sealer paste. This is because the wetting behavior and specifically the contact angle could be different between the liquid part and the mixed sealer paste. The measurement times chosen in the present study (5 and 60 minutes) represent the time of beginning and completion of root canal obturation, respectively. Furthermore, the measurement of a single static contact angle to characterize the interaction between liquid and solid is thought to be inadequate. For any given solid–liquid interaction there is a range of contact angles that may be found. These angles fall within a range with advanced angles approaching a maximum value and receded angles approaching a minimum value (21, 22). At this point, it should be mentioned that, according to the manufacturers, the setting times of RSA RoekoSeal and Gutta-Flow are 50 and 10 minutes, respectively. This fact means that both these sealers were set at the time of second measurements. From the above, it can be concluded that the value of contact angle for RSA RoekoSeal and Gutta-Flow at 60 minutes is the final minimum value that can be attained from these materials. Dentin disks were vibrated in an ultrasonic device for 5 minutes and then placed in an incubator at 37°C. This was done to remove all extra-organic components and to dry the specimens, respectively. Drying of the specimens was done to simulate the clinical condition. The time of 5 minutes was kept constant because water in the reaction with proteins in the acquired dentin may influence the results (14). Moreover, an extended period of dehydration can appreciably affect the contact angles for each sealer (23). In addition, the surfaces of dentin disks were free from any chemical treatment because it was previously reported that some irrigants (such as EDTA) can influence the dentin surface energy and the critical surface tension (20). Contact angle measurement is a useful indicator of wetting behavior of any liquid tested (24). This angle is formed by a liquid at the three-phase boundary where a liquid, gas, and solid intersect. Low contact angle values indicate that the liquid (such as a sealer) wets well, whereas high values indicate poor wetting. If the value of contact angle is ⬍90° the liquid (sealer) wet the substrate; if it is ⬎90° it is said to be non-wetting. A zero contact angle represents complete wetting (25).
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Figure 2. Diagram of wetting levels for each sealer on gutta-percha and dentin after 5 minutes and 1 hour, respectively.
The lower the contact angle, the faster the liquid will spread on substrates (dentin and gutta-percha surfaces) (26). The surface tension of liquid, the surface free energy of solid, the homogeneity of the solid surface, the surface contamination, and the surface roughness are the five main factors that affect the contact angle between a liquid and a solid surface (27). Under the circumstances of the present in vitro study, conventional sealers were found to wet dentin and gutta-percha better than siliconebased sealers. These results were obtained without the application of any load to the materials tested. Under the lateral compaction pressure during the obturation of a root canal system, these materials may behave in different ways. However, during the obturation using Gutta-Flow no lateral compaction pressure is applied except the pressure during vertical compaction at the end of the obturation. It seems that Gutta-Flow needs to be vertically compacted very thoroughly to flow adequately in small areas inside the root canal system. Nevertheless, contact angle is only one of the physical properties that characterize the clinical behavior of a sealer. Many other physical properties of this new material (flow, viscosity, film thickness) should be investigated in the future so that more safe and thorough conclusions can be obtained.
References 1. Strindberg LZ. The dependence of the results of pulp therapy on certain factors. An analytic study based on radiographic and clinical follow-up examinations (Thesis). Acta Odontol Scand 1956;Suppl 21:14. 2. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;11:723– 44. 3. Sjögren U, Hägglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498 –504. 4. Himel TV, McSpadden TJ, Goodis EH. Instruments, materials and devices. In: Cohen S, Hargreaves MK, eds. Pathways of the pulp, 9th ed. St. Louis: Mosby, 2006:265–71. 5. Wennberg A, Orstavik D. Adhesion of root canal sealers to bovine dentine and guttapercha. Int Endod J 1990;23:13–9. 6. Lee KW, Williams MC, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta-percha. J Endod 2002;28:684 – 8. 7. McElroy DL. Physical properties of root canal filling materials. J Am Dent Assoc 1955;50:433– 40.
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8. Siqueira JF Jr, Favieri A, Gahyva SM, Moraes SR, Lima KC, Lopes HP. Antimicrobial activity and flow rate of newer and established root canal sealers. J Endod 2000;26:274 –7. 9. McMichen FR, Pearson G, Rahbaran S, Gulabivala K. A comparative study of selected physical properties of five root-canal sealers. Int Endod J 2003;36:629 –35. 10. Weisman MI. A study of the flow rate of ten root canal sealers. Oral Surg Oral Med Oral Pathol 1970;29:255– 61. 11. Huntsberger JR. Surface energy, wetting and adhesion. Adhesion 1981;12:3–12. 12. Heuer AM, Miserendino JL. Instruments and materials. In: Cohen S, Burns RC, eds. Pathways of the pulp, 4th ed. St. Louis: Mosby, 1987:421– 4. 13. ElAyouti A, Achleithner C, Lost C, Weiger R. Homogeneity and adaptation of a new gutta-percha paste to root canal walls. J Endod 2005;31:687–90. 14. De Jong HP, Van Pelt AWJ, Arends J. Contact angle measurements on human enamel—an in vitro study of influence of pellicle and storage period. J Dent Res 1982;61:11–3. 15. Dumitrascu N, Borcia C. Determining the contact angle between liquids and cylindrical surfaces. J Colloid Interface Sci 2006;294:418 –22. 16. Good RJ, Koo MN. The effect of drop size on contact angle. J Colloid Interface Sci 1979;71:283. 17. Vafaei S, Podowski MZ. Analysis of the relationship between liquid droplet size and contact angle. Adv Colloid Interface Sci 2005;113:133– 46. 18. Newmann AW. Contact angles and their temperature dependence. Adv Colloid Interface Sci 1974;4:105–91. 19. Ozcelik B, Tasman F, Ogan C. A comparison of the surface tension of calcium hydroxide mixed with different vehicles. J Endod 2000;26:500 –2. 20. Nakashima K, Terata R. Effect of pH modified EDTA solution to the properties of dentin. J Endod 2004;30:47–9. 21. Extrand CW, Kumagai Y. An experimental study of contact angle hysteresis. J Colloid Interface Sci 1997;191:378 – 83. 22. Lam CN, Wu R, Li D, Hair ML, Neumann AW. Study of the advancing and receding contact angles: liquid sorption as a cause of contact angle hysteresis. Adv Colloid Interface Sci 2002;96:169 –91. 23. Rosales JI, Marshall GW, Marshall SJ, et al. Acid-etching and hydration influence on dentin roughness and wettability. J Dent Res 1999;78:1554 –9. 24. Donskoi AA, Shashkina MA, Zaikov GE. Contact angle, wettability and adhesion, vol. 3. Philadelphia, PA: Coronet Books, 2003. 25. Extrand CW. Contact angles and their hysteresis as a measure of liquid-solid adhesion. Langmuir 2004;20:4017–21. 26. Basrani B, Ghanem A, Tjaderhane L. Physical and chemical properties of chlorhexidine and calcium hydroxide-containing medications. J Endod 2004;30: 413–7. 27. Johnson RE Jr, Dettre RH. Wettability and contact angles. In: Matijevic E, ed. Surface and colloid science, vol. 2. New York: Wiley–Interscience 1969:85–153.
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A Comparative Study of Contact Angles of Four Different Root Canal Sealers Evangelos G. Kontakiotis, DDS, PhD,* Giorgos N. Tzanetakis, DDS,† and Alexios L. Loizides, DDS, MSc‡ Abstract The present in vitro study was conducted with the aim of evaluating and comparing the contact angles of three different types of root canal sealers—Roth 801, AH26, and RSA RoekoSeal—with the contact angle of a newly developed silicone-based root canal filling material (Gutta-Flow) on dentin and gutta-percha surfaces at two different time periods. The contact angles were determined mathematically by measuring software and were calculated from base width and height of the droplet meniscus of each sealer. Under the conditions of this study, Roth 801 and AH26 recorded lower values of contact angles when root dentin surface was used as the substrate. RSA RoekoSeal and Gutta-Flow seem to spread similarly on dentin and gutta-percha surfaces, although the contact angles of these silicone-based sealers were found to be significantly higher than the contact angles of Roth 801 and AH26 sealers. According to these findings, it can be concluded that conventional root canal sealers (Roth 801 and AH26) may passively have the potential for better wettability of dentin and gutta-percha surfaces than that of siliconebased sealers (RSA RoekoSeal and Gutta-Flow). This fact means that Roth 801 and AH26 may have a better spreading capacity under clinical conditions on the root canal walls and gutta-percha surfaces. Application of a sufficient load during lateral or vertical compaction seems to be needed for RSA RoekoSeal and Gutta-Flow to satisfactorily wet gutta-percha and dentin under clinical conditions. (J Endod 2007;33:299 –302)
Key Words Contact angle, root canal sealers, wetting behavior
*Assistant Professor, †Postgraduate student, ‡Endodontist, Department of Endodontics, Dental School, University of Athens, Greece. Addrress requests for reprints to E. G. Kontakiotis, Dental School, University of Athens, Antheon 2 Ano Patisia, 11143 Athens, Greece. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.11.016
T
he attainment of an airtight seal in a root canal system is very important for the long-term success of endodontic treatment (1–3). During the obturation of a root canal system with gutta-percha, root canal sealer performs several functions to attain and maintain this seal (4). These functions concern the filling of root canal wall irregularities such as apical ramifications and deltas as well as spaces where the primary root canal filling material failed to reach. In addition, the sealer acts as a binding agent between root canal walls and the main filling material (5, 6), and thus the interface between either sealer and gutta-percha or sealer and dentin is of prime clinical importance. The physicochemical properties of a root canal sealer may characterize its clinical behavior during and after obturation of the root canal system (7–9). Among these properties are satisfactory wetting and adequate flow rate (8, 10). Wetting means that an interface contact is being formed between a liquid and a solid with a simultaneous expulsion of air. The tendency of a liquid to spread on a solid surface is expressed with the formation of a contact angle (11). Contact angle measurements provide a better understanding of the interactions between solids and liquids. These interactions play a key role in understanding not only material wettability, but also wetting, spreading, and adsorption of liquids. In vitro testing of physical properties is a basic prerequisite for the introduction of a new material in clinical endodontic practice (12). Gutta-Flow is a newly established silicone-based root canal filling material (Coltene/Whaledent, Langenau, Germany), recently introduced for use in endodontics. It seems that Gutta-Flow is classified as a type II material, intended to be used with or without core material or other sealer (4). Gutta-Flow is a modification of the RSA RoekoSeal (Roeko Dental Products, Langenau, Germany) and, according to the company, it contains very small gutta-percha particles with a size of ⬍30 m and sealer in its mass. The manufacturer claims an improved seal because of the increased flowability and the fact that the material expands slightly on setting, although until now no leakage study has yet been published about Gutta-Flow in the literature. It has also been established that Gutta-Flow can be used alone to fill the root canal with only one main gutta-percha cone in place. Furthermore, it was shown that this material has an adequate adaptability to root canal walls (13). However, the wetting behavior of this new material has not yet been tested by an in vitro study. The purpose of the present study was to evaluate and compare the contact angles of three different types of root canal sealers with respect to the contact angle of a newly developed silicon-based root canal filling material (Gutta-Flow) without the application of any load on dentin and gutta-percha surfaces at two different time periods.
Materials and Methods The sealers tested in this study were Roth 801 (Roth International, Chicago, IL, USA), AH26 silver free (Dentsply De Trey GmbH, Konstanz, Germany), RSA RoekoSeal (Roeko, Langenau, Germany), and Gutta-Flow (Coltene/Whaledent). All root canal sealers and Gutta-Flow were prepared according to the manufacturers’ instructions immediately before measurements as follows: 1. RSA RoekoSeal was mixed automatically with its mixing tip. 2. Gutta-Flow was prepared by vibrating the capsules for 30 seconds on a vibration device (Silamat S5, Ivoclar Vivadent, Bendererstrasse, Lichtenstein). 3. AH26 and Roth 801 were prepared manually on a glass plate with a spatula, according to manufacturer’s instructions for each sealer, respectively.
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Basic Research—Technology Contact angle measurements were carried out on two types of substrates: (1) dentin disks (2 mm thick) and (2) gutta-percha surfaces. Forty extracted intact fresh and caries-free mandibular molars were used for the preparation in an equal number of dentin disks. The extracted teeth were rinsed thoroughly under running tap water and then placed in 10% formalin until use. After storage, the teeth were cross-sectioned to expose the dentin of the root canal surface. The dentin disks were prepared with the use of a diamond disk (Komet; Brasseler GmbH, Lemgo, Germany) under running water. Polish paper no. 0.5 was used to reduce the roughness of dentin surfaces. Ultrasonic vibrations were applied to clean the dentin disks from any extra-organic components in distilled water for 5 minutes, after which the dentin specimens were placed in an incubator at 37°C to dry for the same period of time (5 minutes). The samples were carried directly from the incubator and placed into the measuring device (Fig. 1A). Two glass plates and thermoplasticized gutta-percha (Easyflow, Endodent, Duarte, CA, USA) were used to prepare 40 gutta-percha flat smooth surfaces. The specimens (dentin disks, gutta-percha surfaces) were positioned one by one on a flat glass surface in the measuring device. Controlled (0.1 mL) volume droplets of each sealer were placed onto ten dentin disks and onto ten gutta-percha surfaces. The volume of each sealer was controlled by means of a micropipette (Eppendorf Reference, adjustable-volume, Eppendorf AG, Hamburg, Germany). This micropipette could be manually maneuvered through a tiny hole on the top of the measuring device. Each specimen was photographed (contra lighted) twice, at 5 and 60 minutes, after positioning of the
droplets. The experiments were performed under standard conditions of temperature and relative humidity. The temperature was kept constant to within 1°C with the aid of a thermostat. Images of the droplets of each sealer (Fig. 1B) were digitalized by a scanner. After that, both base width (b) and height (h) of the droplet meniscus were measured by SigmaScan Pro V 5.0.0 Software (1987– 1999 SPSS, Inc., Leesburg, FL, USA). The contact angles were calculated according to the equation: a ⫽ 2 arc(cos 2h/b) (14, 15). One-way analysis of variance (ANOVA), followed by Bonferroni test of multiple comparisons, was used to investigate differences of the distributional properties of gutta-percha and dentin with respect to various root canal sealers and vice versa, at 5 and 60 minutes, respectively. All tests were two sided and the level of significance was set at 5%.
Results The mean values and standard deviations of contact angles for each sealer on dentin disks and gutta-percha surfaces for the two observation periods (5 minutes and 1 hour) are shown in Tables 1a and 1b, respectively. Statistically significant higher values were recorded for AH26 and Roth 801 on gutta-percha with respect to dentin after 5 minutes (p ⬍ 0.0001). On the contrary, RSA RoekoSeal recorded significantly higher values on dentin, whereas the values of Gutta-Flow did not differ significantly after 5 minutes between dentin and gutta-percha (p ⫽ 0.146). After 1 hour, AH26 and Roth 801 continued recording significantly higher values on gutta-percha compared to dentin (p ⫽
Figure 1. (A) Schematic illustration of the measuring device. (1) thermometer [23°C, 38% humidity, (2) micropipette, (3) flat glass plate, (4) dentin disk or gutta-percha surface, (5) meniscus of the sealer droplet (6) pressure gauge, (7) photographic camera, (8) light source. (B) Representative images of the droplet meniscus of each sealer on gutta-percha and dentin surfaces.
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Basic Research—Technology TABLE 1a. Mean values and standard deviations (SDs) of contact angles of each sealer on dentin surface after 5 minutes and 1 hour, respectively Dentin 5 minutes AH26 Roth 801 RSA Roekoseal Gutta-Flow 1 hour AH26 Roth 801 RSA Roekoseal Gutta-Flow
Mean
SD
Minimum
Maximum
14.54 11.05 83.72 45.14
1.57 1.13 0.15 7.52
12.45 9.09 88.44 28.96
18.26 12.53 88.90 58.26
8.51 9.23 41.64 38.75
0.73 1.74 2.83 6.93
7.89 6.78 37.48 28.18
9.73 19.49 46.55 47.23
TABLE 1b. Mean values and standard deviations (SDs) of contact angles of each sealer on gutta-percha surface after 5 minutes and 1 hour, respectively Gutta-percha (GP) 5 minutes AH26 Roth 801 RSA Roekoseal Gutta-Flow 1 hour AH26 Roth 801 RSA Roekoseal Gutta-Flow
Mean
SD
Minimum
Maximum
18.23 16.03 45.54 45.54
1.45 1.58 5.53 5.58
15.57 13.09 36.58 36.58
19.64 17.84 52.13 52.13
12.61 11.65 43.34 37.30
1.19 1.83 5.86 3.11
7.91 8.34 33.57 33.69
12.34 13.26 48.47 43.43
0.003 and p ⫽ 0.004, respectively). However, RSA RoekoSeal did not demonstrate any statistically significant difference after 1 hour between gutta-percha and dentin (p ⫽ 0.418), whereas Gutta-Flow continued not to differ between gutta-percha and dentin (p ⫽ 0.313). The multiple comparisons (Bonferroni test) after 5 minutes and 1 hour revealed that AH26 and Roth 801 exhibit significantly lower values than those of RSA RoekoSeal and Gutta-Flow (p ⬍ 0.0001) on guttapercha. Moreover, after 1 hour Gutta-Flow showed significantly lower values than RSA RoekoSeal on the gutta-percha surface (p ⫽ 0.0022). On dentin, AH26 and Roth 801 again exhibited significantly lower values than RSA RoekoSeal and Gutta-Flow after 5 minutes and 1 hour, respectively (p ⬍ 0.0001). Furthermore, after 5 minutes, Gutta-Flow had significantly lower values than RSA RoekoSeal (p ⬍ 0.0001). On the contrary, the values of Gutta-Flow and RSA RoekoSeal on dentin surfaces did not differ significantly after 1 hour (p ⫽ 0.999). The diagram of Fig. 2 schematically shows the wetting levels of each sealer on guttapercha and dentin for the two observation periods.
Discussion Reliability of the experimental procedure followed in the present study was tested in previous studies and found to be particularly high (14). The main advantage is that measurements can be done using very small quantities of liquid. In the present study, all measurements were carried out on very small specimens using controlled volume (0.1 mL) of each sealer. This was done because any volumetric change could affect the value of contact angle (16, 17). Also, the entire experimental procedure was performed under standard environmental conditions because the surface tension coefficient of liquids is influenced by temperature change and humidity (18). Roth 801 and AH26 were found to wet dentin better than guttapercha for the two observation periods. Based on these results, it appears that the surface free energy of dentin is relatively high compared
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to that of gutta-percha. Accordingly, it can be substantiated that the surface energy forces of dentin overcome the forces of surface tension of these sealers with respect to the surface energy forces of gutta-percha. On the contrary, RSA RoekoSeal did not spread satisfactorily on dentin with respect to gutta-percha after 5 minutes, although after 1 hour no significant differences were observed between gutta-percha and dentin. In this case, the surface roughness of dentin and the initial incomplete wetting of RSA RoekoSeal seem to play a more significant role. On the other hand, Gutta-Flow was found to spread similarly on dentin and gutta-percha for the two observation periods. The addition of very small particles of gutta-percha in its mass appears to improve the wetting of the material compared to RSA RoekoSeal. In the second part of the study, statistically significant differences were found between silicone-based sealers (RSA RoekoSeal and GuttaFlow) and conventional root canal sealers (AH26 and Roth 801). Conventional sealers documented generally lower contact angles than those of silicone-based sealers on dentin and gutta-percha after 5 and 60 minutes, respectively. This finding was obtained perhaps as a result of the different syntheses of each sealer. Synthesis is a basic factor that influences critical surface tension (19). The presence of silicone produces possibly high surface tension forces, thus making the spreading of these materials more difficult. However, Gutta-Flow seems to have a better spreading capacity than that of RSA RoekoSeal initially, possibly because of the presence of very small gutta-percha particles. RSA RoekoSeal at first demonstrated difficulty in satisfactorily wetting the substrates and generally it had a delayed wetting behavior. In the present study, the contact angle was measured using not only the liquid of the sealer (20) but also all the mixed sealer paste. This is because the wetting behavior and specifically the contact angle could be different between the liquid part and the mixed sealer paste. The measurement times chosen in the present study (5 and 60 minutes) represent the time of beginning and completion of root canal obturation, respectively. Furthermore, the measurement of a single static contact angle to characterize the interaction between liquid and solid is thought to be inadequate. For any given solid–liquid interaction there is a range of contact angles that may be found. These angles fall within a range with advanced angles approaching a maximum value and receded angles approaching a minimum value (21, 22). At this point, it should be mentioned that, according to the manufacturers, the setting times of RSA RoekoSeal and Gutta-Flow are 50 and 10 minutes, respectively. This fact means that both these sealers were set at the time of second measurements. From the above, it can be concluded that the value of contact angle for RSA RoekoSeal and Gutta-Flow at 60 minutes is the final minimum value that can be attained from these materials. Dentin disks were vibrated in an ultrasonic device for 5 minutes and then placed in an incubator at 37°C. This was done to remove all extra-organic components and to dry the specimens, respectively. Drying of the specimens was done to simulate the clinical condition. The time of 5 minutes was kept constant because water in the reaction with proteins in the acquired dentin may influence the results (14). Moreover, an extended period of dehydration can appreciably affect the contact angles for each sealer (23). In addition, the surfaces of dentin disks were free from any chemical treatment because it was previously reported that some irrigants (such as EDTA) can influence the dentin surface energy and the critical surface tension (20). Contact angle measurement is a useful indicator of wetting behavior of any liquid tested (24). This angle is formed by a liquid at the three-phase boundary where a liquid, gas, and solid intersect. Low contact angle values indicate that the liquid (such as a sealer) wets well, whereas high values indicate poor wetting. If the value of contact angle is ⬍90° the liquid (sealer) wet the substrate; if it is ⬎90° it is said to be non-wetting. A zero contact angle represents complete wetting (25).
Contact Angles of Four Different Root Canal Sealers
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Figure 2. Diagram of wetting levels for each sealer on gutta-percha and dentin after 5 minutes and 1 hour, respectively.
The lower the contact angle, the faster the liquid will spread on substrates (dentin and gutta-percha surfaces) (26). The surface tension of liquid, the surface free energy of solid, the homogeneity of the solid surface, the surface contamination, and the surface roughness are the five main factors that affect the contact angle between a liquid and a solid surface (27). Under the circumstances of the present in vitro study, conventional sealers were found to wet dentin and gutta-percha better than siliconebased sealers. These results were obtained without the application of any load to the materials tested. Under the lateral compaction pressure during the obturation of a root canal system, these materials may behave in different ways. However, during the obturation using Gutta-Flow no lateral compaction pressure is applied except the pressure during vertical compaction at the end of the obturation. It seems that Gutta-Flow needs to be vertically compacted very thoroughly to flow adequately in small areas inside the root canal system. Nevertheless, contact angle is only one of the physical properties that characterize the clinical behavior of a sealer. Many other physical properties of this new material (flow, viscosity, film thickness) should be investigated in the future so that more safe and thorough conclusions can be obtained.
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