JOURNAL OF ENDODONTICS Copyright © 2002 by The American Association of Endodontists
Printed in U.S.A. VOL. 28, NO. 3, MARCH 2002
Effect of Er:YAG Laser on Adhesion of Root Canal Sealers Manoel D. Sousa-Neto, DDS, PhD, Melissa A. Marchesan, DDS, Jesus D. Pe´cora, DDS, PhD, Aldo Brugnera Junior, DDS, MSc, Yara T.C. Silva-Sousa, DDS, PhD, and Paulo C. Saquy, DDS, PhD
Adhesion is the capacity of a root canal sealer to stick to the root canal walls, hold gutta-percha cones together, and hold these cones to dentin. White et al. (2) and Kennedy et al. (3) reported that smear layer is a negative factor in root canal sealing, because this organic and inorganic material adheres easily to the root canal wall, reducing the adhesion of sealers. This smear layer may prevent penetration of the sealer into the dentinal canaliculi, thus impeding the mechanical interlock of the sealer to the canal wall. In endodontic therapy, EDTA has been used to remove smear layer (4). Recently, the laser has shown a great capacity for smear layer removal from root canal walls, especially the Er:YAG laser (5). This study evaluated the effect of Er:YAG laser, applied to human dentin in vitro, on the adhesion of Grossman, Endomethasone, N-Rickert, and Sealer 26 root canal sealers.
This in vitro study evaluated the effect of Er:YAG laser on adhesion to human dentin of Grossman, Endomethasone, N-Rickert, and Sealer 26 root canal sealers. The crowns of 40 human molars were cut on the occlusal side until a flat dentin surface was obtained. The teeth were divided into two groups: group 1, no laser application; and group 2, irradiation with Er:YAG laser (KaVo Key Laser 2; 11 mm focal distance, perpendicular to the dentin surface, 4 Hz frequency, 200 mJ energy, 62 J total energy and 313 pulses, 1-min application time, and 2.25 W power). Five samples were tested for each sealer and each group. An Instron universal testing machine was used for the adhesion test. Sealer 26 showed the best adhesion both with and without laser application (p < 0.01). Grossman and N-Rickert sealers had intermediate values, and Endomethasone had the worst adhesion. Application of Er:YAG laser did not alter the adhesion of Grossman, N-Rickert, or Endomethasone sealers. However, laser application increased the adhesion of Sealer 26. The epoxy resin-based root canal sealer (Sealer 26) adhered better to dentin prepared with and without Er:YAG laser than the zinc oxide/eugenol-based sealers (Endomethasone, N-Rickert, and Grossman).
MATERIALS AND METHODS Forty extracted human maxillary and mandibular molars with intact crowns were kept in 0.1% thymol at 9°C until use. The crowns were cut on the occlusal side with 1212 KG-Sorensen diamond drills (KG-Sorensen; Barveri, SP, Brazil) until a flat dentin surface was obtained, and the teeth were fixed by their roots into a resin block. The teeth were divided into two groups: group 1, no laser application; and group 2, irradiation with Er:YAG laser (4 Hz frequency, 200 mJ energy, 62 J total energy, 2.25 W power; KaVo Key Laser 2, KaVo Key; Warthausen, Germany) The laser was applied perpendicular 11 mm from the dentin surface by using 313 pulses per minute with a universal handpiece (2051) and a beam diameter of 2 mm. Five samples were tested for each sealer and each group. The surfaces were washed for 1 min with running distilled and deionized water and dried with air. Four root canal sealers were used: Sealer 26 (Dentsply, Petro´polis, RS, Brazil), N-Ricket (Inodon, Porto Alegre, RS, Brazil), Endomethasone (Septodont, Saint-Maur, France), and Grossman (FORP-USP, Ribeira˜o Preto, SP, Brazil). Endomethasone was studied because this sealer is frequently used in Brazil, even though it is prohibited in several other countries. Sealer 26 is composed of powder and resin, whereas the other three sealers are composed of powder and liquid. Powder/liquid or powder/resin ratio and setting time of each sealer were determined before the test of adhesion, using the method proposed by Sousa-Neto et al. (6, 7) (Table 1).
Properties of root canal sealers can be divided into the following categories: physicochemical, antimicrobial, and biological. The investigation of these properties was standardized after the publication of Specification 57 of the American Dental Association (1). This eliminated the problems caused by the lack of standardization of tests and permitted both reproducible results and more reliable comparisons of various materials and data obtained in different studies. Specification 57 recommends the following tests for the evaluation of the physical properties: working time, flow, film thickness, setting time, radiopacity, solubility, disintegration, and dimensional stability. This specification does not have any models for adhesion or infiltration tests. 185
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Journal of Endodontics
TABLE 1. Values of powder/liquid, powder/resin, and setting time obtained in 5 samples for each sealer tested
Grams powder/ 0.20 ml liquid
Setting time (min)
Endomethasone N-Rickert Grossman Sealer 26
0.68–0.80 0.78–0.90 0.94–0.98 0.22–0.30
0.73 0.85 0.95 0.26
60–63 13–16 30–35 1090–1482
61 15 32 1125
For the adhesion test, the sealers were mixed according to manufacturer instructions by using the powder/liquid or powder/ resin ratios shown in Table 1. The sealer was placed on the dentin surface with the aid of an aluminum cylinder (10 mm in height, 6 mm in diameter). The sample was placed in an incubator at 37°C with 95% relative humidity for a time that was three times the setting time of the material (Table 1). The sample was then placed in an Instron 4444 universal testing machine (Instron Corporation, Canton, MA) that was equipped with load cell, an oscillating system, and a spring adapter. The machine was calibrated at a constant speed of 1 mm/min. The tensile load was applied, and the load required to cause failure of the bond was recorded in megapascals (MPa). Data were analyzed by using ANOVA. The statistical difference level was set at p ⬍ 0.01. The Tukey test was then applied to determine which sealers were different from each other. RESULTS Sealer 26 had the best adhesion, both with and without laser application (p ⬍ 0.01). Without laser, Sealer 26 had better adhesion (0.041 ⫾ 0.0037) than Grossman (0.0117 ⫾ 0.0013) and N-Rickert (0.0119 ⫾ 0.0021) cements, which had statistically similar adhesion. Endomethasone had the least adhesion (0.0054 ⫾ 0.0012). The application of laser to the dentin surface did not influence the adhesion of Grossman (0.0121 ⫾ 0.0008), N-Rickert (0.0116 ⫾ 0.0009), and Endomethasone (0.0050 ⫾ 0.0007). However, laser application significantly increased (p ⬍ 0.01) the adhesion of Sealer 26 (0.0782 ⫾ 0.007). Thus, Sealer 26 had better adhesion with or without laser treatment. Values are the load required for separation in MPa. DISCUSSION Adhesion to the root canal wall is one of the properties that a sealing material must have. The American Dental Association did not standardize a method for the study of adhesion, because there is a lack of agreement among researchers who study this aspect. Ørstavik (8) used a universal testing machine to measure adhesion of root canal sealers. This method was also followed by Hyde (9), Wennberg and Ørstavik (10), and Sousa-Neto (11), who confirmed the uniformity and reproducibility of this machine. The values of bond strength expressed in MPa are accepted universally, which allows the comparison of results. It is important to note that an oscillating system was used between the load cell and the spring adapter in this study to avoid the application of eccentric load to the sensitive part of the load cell (11). Studies on the effect of laser are linked to laser type, power setting, distance, application time, and type of irradiated tissue (12). The laser selected for this study was Er:YAG, because this laser promotes
ablation (13) resulting in morphological changes in dentin similar to acid etching, with the removal of smear layer and collagen exposure (14). After preliminary tests, it was shown that Er:YAG laser application caused dentin surface changes similar to acid etching. In accordance with Pe´ cora et al. (15) and Visuri et al. (16), laser application on dentin surface was performed with constant water cooling, so that only a small increase in temperature of dentin occurred. The presence of rosin can explain the results for N-Rickert and Grossman sealers, because this component is responsible for adhesion by electrostatic bond of these sealers (6, 7). Thus, the morphological changes produced by laser application on dentin does not interfere with the adhesion of these sealers. Endomethasone sealer does not have rosin in its composition, therefore, the adhesion is weaker because there is no chemical bond between dentin and sealer, and little or no mechanical adhesion. The literature has shown the importance of smear layer removal (2, 3). Takeda et al. (5) reported that Er:YAG laser removed smear layer, leaving clean walls and open dentinal tubules. Pe´ cora et al. (17) observed that after Er:YAG laser application there was an increase in dentin permeability. In this study, Er:YAG laser application caused morphological changes, increasing the dentin area and forming irregularities. A sealer with epoxy resin penetrates better into the microirregularities, and because there is more cohesion between molecules, a greater mechanical interlock and better resistance to removal or separation occurs, producing increased adhesion. These changes justify the increase in adhesion of Sealer 26, which is also in agreement with Lage-Marqueˆ s and Eduardo (18), who reported that laser application increases resin adhesion to dentin. The epoxy resin sealer, differing from the other sealers, penetrates the dentinal canaliculi exposed by smear layer removal, forming tags, similar to dentinal adhesives. By using argon laser to polymerize resin in root canals, Potts and Pitrou (19) reported tag formation. We feel that when epoxy resin-based sealers are used, smear layer removal is important because it promotes greater adhesion of the sealer to the dentin. The results of this study indicate that the use of Er:YAG laser increases the adhesion of epoxy resin-based sealers to dentin. We also observed results similar to Economides et al. (20), who reported that smear layer removal caused a decrease in microleakage when epoxy resin-based sealers were used. This does not occur when zinc-eugenol-based sealers are used. Once it is clear that adhesion of sealers, such as Sealer 26, is increased after laser application to dentin, new perspectives for research on the interaction between the adhesion of sealers and apical or coronary microleakage are suggested. Drs. Sousa-Neto, Silva-Sousa, and Saquy are affiliated with the Faculty of Dentistry, UNAERP, Ribeira˜o Preto, Sa˜o Paulo, Brazil. Drs. Marchesan, Pe´cora, and Saquy are affiliated with the Faculty of Dentistry of Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brazil. Dr. Brugnera Junior is affiliated with the University Camilo Castelo Branco, Dental Association of the State of Sa˜o Paulo, Sa˜o Paulo, Brazil. Address requests for reprints to Dr.
Vol. 28, No. 3, March 2002
Er:YAG Laser and Adhesion of Root Canal Sealers
Manoel D. Sousa-Neto, R. Cav. Torquato Rizzi 1638, Apt. 43, 14020 –300 Ribeira˜ o Preto, SP, Brasil.
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