MICROSCOPY RESEARCH AND TECHNIQUE 77:282–288 (2014)
Effects of Er:YAG Laser on Bond Strength of Self-etching Adhesives to Caries-Affected Dentin ALP ERDIN KOYUTURK,1* BILAL OZMEN,1 MURAT CORTCU,1 UGUR TOKAY,1 GUL TOSUN,2 AND MUSTAFA ERHAN SARI1 1 2
Department of Pediatric Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Kurupelit 55139, Samsun, Turkey Department of Pediatric Dentistry, Faculty of Dentistry, Selcuk University, Selcuklu, Konya, Turkey
KEY WORDS
tensile strength; caries; primary teeth; Er:YAG lasers; dentin-bonding agents
ABSTRACT The erbium:yttrium–aluminum–garnet (Er:YAG) laser may be effective the bond strength of adhesive systems on dentine surfaces, the chemical composition and aggressiveness of adhesive systems in clinical practice. The purpose of this study was to evaluate the effects of the Er:YAG laser system with the bonding ability of two different self-etching adhesives to caries-affected dentine in primary molars. Ninety mid-coronal flat dentine surfaces obtained from sound and caries-affected human primary dentine were treated with an Er:YAG laser or a bur. The prepared surfaces were restored with an adhesive system (Xeno V; Clearfil S3) and a compomer (Dyract Extra). The restored teeth were sectioned with a low-speed saw and 162 samples were obtained. The bond strength of the adhesive systems was tested using the microtensile test method. The data were statistically analyzed. A restored tooth in each group was processed for scanning electron microscopy evaluation. The values of the highest bond strength were obtained from the Clearfil S3-Er:YAG laser-sound dentine group in all groups. (24.57 6 7.27 MPa) (P > 0.05). The values of the lowest bond strength were obtained from the Xeno V-Er:YAG laser-sound dentine group in all groups (11.01 6 3.89 MPa). It was determined that the Clearfil S3 increased the bond strength on the surface applied with Er:YAG laser according to the Xeno V. Microsc. Res. Tech. 77:282–288, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Primary teeth have been presumed to be similar to permanent teeth according to their mechanical properties. However, some studies have suggested that the primary dentine may differ from permanent dentine due to the different degrees of mineralization (Hosoya et al., 2000). It has also been reported that adhesive restorative materials have a lower bonding strength to primary teeth as opposed to (relatively) permanent dentine (Bordin-Aykroyd et al., 1992). Furthermore, this observation is assumed to be linked to degree of mineralization. But a limited number of studies have been conducted on the mechanical properties of primary dentine (Hosoya et al., 2000; Mahoney et al., 2000). Carious dentine is typically identified as consisting of infected and affected layers. While the cariesinfected dentine layers are removed, the cariesaffected dentine layer is generally not removed during treatment (Yoshiyama et al., 2002). Thus, a large area of the cavity floor that was prepared for adhesive restoration is composed of caries-affected dentine. The characteristic features of caries-affected dentine are different from those of normal dentine. Caries-affected dentine is softer than normal dentine because it is partially demineralized (Marshall et al., 2001). Most tubules of caries-affected dentine are also obturated by mineral crystals, but they are bacteria free (Nakajima et al., 2000). There has been increasing relationship between bonding and caries-affected dentin with C V
2014 WILEY PERIODICALS, INC.
adhesive systems (Arrais et al., 2004). When the size of the primary teeth is considered, the caries-affected dentine area has increased importance. To identify the caries-affected dentine may use visual examination, sharp excavator, and staining with caries detector dye without doing histology. Self-etching adhesive systems have been used to simplify adhesive procedures and decrease technical sensitivity (Kenshima et al., 2005). Hydrophilic one-step selfetching adhesive system is one solution that includes etching, priming, and bonding procedures (Pashley et al., 2002). The self-etching adhesive systems facilitate the etching and priming of the dentine at the same time without rinsing and the smear plugs are merged into the resin tags (Pashley et al., 2002; Tay and Pashley, 2001). For pediatric patients, unable to tolerate the treatment process as adults, self-etching adhesives can be used to reduce the treatment steps. Different techniques have been used in the dentistry industry as alternatives to high-speed bur (Cozean et al., 1997; Krause et al., 2008). The use of laser irradiation has been widely studied and applied for that purpose, due to its precise and effective ability to *Correspondence to: Alp Erdin Koyuturk; Department of Pediatric Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey. E-mail: [email protected] Received 29 October 2013; accepted in revised form 16 January 2014 REVIEW EDITOR: Dr. Chuanbin Mao DOI 10.1002/jemt.22340 Published online 30 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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TABLE 1. Dentine bonding systems used in this study Product name 3
Clearfil S Bond
Kuraray, Osaka, Japan
Xeno V Bond
Dentsply, Konstanz, Germany
a
Compositiona
Application
10-MDP, Bis-GMA, HEMA, DMA, camphorquinone, ethanol, water, silanated colloidal silica
Apply adhesive to entire surface with a disposable brush tip; leave in place for 20 s; dry the entire surface sufficiently by air-drying with high pressure for more than 10 s while spreading the bond layer thinly; light cure for 20 s. Apply adhesive to entire surface with a disposable brush tip; leave in place for 20 s; dry the entire surface sufficiently by air-drying with high pressure for more than 5 s while spreading the bond layer thinly; light cure for 10 s.
Manufacturer
10-MDP, 10-Methacryloyloxydecyl dimethacrylate.
dihydrogen
phosphate;
Bifunctional acrylates, Acrylic acid, Tert-butyl alcohol, Phosphoric acid ester, Acidic acrylate, Phosphine oxide photoinitiator
Bis-GMA,
Bisphenol-A
eliminate carious tissue while avoiding the removal of sound tooth substrate, thus resulting in a more conservative cavity design. The erbium:yttrium–aluminum–garnet (Er:YAG) lasers have an advantage thermomechanical ablation that like etching hard tissues, a rough structure in dental tissue. Consequently, the primary indication for these systems is the preparation of cavities for restorations (Hossain et al., 2002). Though many kinds of laser systems have been developed that can cut dental hard tissues efficiently, erbium lasers have been shown to be the most promising laser equipment. In 1997, the US Food and Drug Administration accepted that the Er:YAG laser is an effective and safe technique to use on intraoral hard tissues (Cozean et al., 1997). Various laboratory research and clinical studies have demonstrated that the Er:YAG laser was effectively ablated hard dental tissue, with the minimum of injury to pulp, and surrounding structures. The 2.94 lm wavelength emission coincides with the main absorption peaks of water and hydroxyapatite, thus resulting in good absorption of erbium laser in all biological tissues, including enamel, dentine, and cementum (Corona et al., 2003). Erbium lasers have several advantages: microfractures are prevented, vibration is decreased, and patient discomfort originating from voice and pressure is eased. As laser-plugged dentine tubules aid the migration of microorganisms, postoperative sensitivity is abolished. However, recent research has shown that lasing of enamel and dentin may result in surface and subsurface alterations that have negative effects on both adhesion and seal (De Moor and Delme, 2010). Few studies in the literature evaluate the effects of lasers on caries-affected dentine. The purpose of this study was to examine the effects of lasers on the bond strength to caries-affected dentine of two self-etch adhesives. The hypothesis tested was that the Er:YAG laser will be affect the bond strength of adhesive systems on dentine surfaces. MATERIALS AND METHODS Ninety extracted human primary molars with coronal carious lesions, stored in 0.1% isotonic saline at 4 C, were used in this study. Soft and infected tissue were cleaned from the teeth and placed in isotonic saline before the experiment began. The enamel occlusal surface was wet-ground perpendicular to the long Microscopy Research and Technique
diglycidylemethacrylate;
HEMA,
hydroxyethylmethacrylate;
DMA,
axis of the tooth with 320-grit silicon carbide (SiC) abrasive paper to expose a flat dentine surface with carious lesion. Both caries-affected and sound dentine surfaces were mid-coronally prepared on the tooth. To remove caries dentine, grinding was performed using 320-grit silicon carbide abrasive papers under running water using the combined criteria of visual examination, a sharp excavator, and staining with a caries detector solution (Kuraray, Osaka, Japan). Relatively soft, dark-red-stained dentine was classified as cariesinfected dentine, while discolored, harder dentine that was stained pink was classified as caries-affected. Yellow, hard dentine was classified as sound dentine. The flat dentine surfaces of the teeth were then polished with 600, 800, and 1000 grit silicon carbide papers on an abrasive machine (Phoenix Beta, Buehler, Germany) under running water before bonding the procedure. Laser and Bur Treatments All dentine surfaces prepared using a round bur (Edenta AG.) in a contra-angle speed-reducing hand piece (400 rpm), and an Er:YAG laser with a wavelength of 2,940 lm (Fotona AT Fidelis Plus III, Ljubljana, Slovenia) was given its final form. The laser operating parameters used for all of the treatment groups (using the free-running emission mode) were as follows: 200 mJ per pulse, 20 Hz, power of 4.0 W, and 100 ls pulse duration. A sapphire tip with a diameter of 1.3 mm and a length of 8 mm was used. The coaxial water spray feature of the hand piece was set to ‘on’. A contact tip was also used. Bonding Procedures The line of the caries-affected dentine area was marked with a waterproof pen before the application of the adhesive system. Following the application of the adhesives to the prepared surfaces according to the manufacturers’ instructions (Table 1), the respective compomer (Dyract Extra, Dentsply, Konstanz, Germany) of bonding agents were built up incrementally in three to four layers to a height of 4–5 mm. Bonding agents and compomer resins were cured with a halogen curing light (Lunar curing light, Benlioglu Dental, Ankara, Turkey) according to the stipulated curing time, where light intensity was at least 400 mW/cm2. Specimens were then stored in distilled water at 37 C
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for 24 h. The teeth were longitudinally sectioned perpendicular to the bonded interface to produce several rectangular bonded sticks with the cross-sectional area approximately 1 mm2 with a low-speed saw (Isomet 1000, Buehler, Lake Bluff, IL). The caries-affected dentine sticks were first prepared from the level marked with the waterproof pen. ‘I’ shaped longitudinal cuts were obtained with the top half consisting of composite and the bottom half consisting of dentine from each tooth (Fig. 1). Microtensile Bond Strength Test Each stick was carefully examined in a dissecting microscope (320) to ensure that the test site was homogeneous with regard to caries-affected dentine (Olympus SZ 4045 TRPR, Tokyo, Japan). The crosssectional area and remaining dentine thickness were measured using a digital calliper (Mitutoyo, Tokyo, Japan) (Table 2). For microtensile bond testing, the sticks were fixed to the microtensile bond testing apparatus and a test machine (Harvard Apparatus Co., Dover, MA). Tensile forces were applied to the resin– dentine interface at a crosshead speed of 1 mm/min until failure occurred. To determine the tensile bond strengths, the maximum load (N) was recorded and converted to megapascals (MPa). Fracture Type Analysis After tensile testing, the fracture samples were collected and stored in distilled water for 24 h. The samples were classified as follows: Adhesive failure: The failure at the interface was between compomer and dentine.
Mixed failure: The failure was partially adhesive and partially cohesive compomer fractures and/or dentine fracture. Cohesive failure: The failure was in the compomer or dentine. Scanning Electron Microscopy Evaluation The second aim of this study was to observe the micromorphology of the interface between the adhesives and sound and caries-affected dentine. Four additional primary molar teeth with occlusal dentine caries for per group were used to evaluate the morphology of the interface by scanning electron microscopy (SEM). The teeth were prepared using the same previouslymentioned methods. The compomers were bonded to the prepared dentin surfaces using bonding agents according to the manufacturers’ instructions. The bonded specimens were longitudinally sectioned perpendicular to the bonded interface. The cut surfaces were fixed in a 10% formaldehyde solution for 24 h, ground with 600 grit silicon carbide abrasive paper, and highly polished with a diamond paste 6-3-1-1/4 mm (Struers, Copenhagen, Denmark). Then, the specimens were immersed in 10% phosphoric acid solution for 3–5 s, rinsed with distilled water, and treated for 5 min with 5% sodium hypochlorite solution and again rinsed thoroughly with distilled water. After drying at room temperature (27 C), the specimens were coated with Polaron Sc500 Sputter Coater (VG Microtech, Tokyo, Japan) and examined under SEM (JSM-5600, JEOL, Tokyo, Japan) at an accelerating voltage of 20 kV(Tosun et al., 2008). Statistical Analysis Statistical analysis was performed using a one-way ANOVA and Tukey test (P < 0.05). Differences between the groups in terms of failure type was performed using a Kruskal Wallis-H test (P < 0.05). RESULTS The micro tensile bond strengths to dentine varied from 3.05 MPa for the one-step self-etch adhesive Xeno V bond to 37.95 MPa for Clearfil S3 bond. The highest bond strength rates were obtained from both cariesaffected and sound primary dentine in the Clearfil S3 bond groups used Er:YAG laser (19.30 6 6.12 and 24.57 6 7.27 MPa). However, there was no statistically difference (P > 0.05). There was no difference among groups in the Xeno V sound and caries-affected primary dentine, laser and bur (P > 0.05) (Table 3). No statistical differences were seen among the remaining dentine thickness in the groups (P > 0.05) (Table 2).
Fig. 1. The caries-affected dentin and sound dentin stick.
TABLE 2. Descriptive statistics of the remaining dentine thickness (mm) of the dentin groups Dentine type Sound dentine
Caries-affected dentine
Preparation type Bur Laser Bur Laser Bur Laser Bur Laser
Bonding system 3
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Mean (mm)
SD (mm)
SE (mm)
Min. (mm)
Max. (mm)
21 21 20 20 19 20 20 21
2.81 2.46 2.85 2.64 2.45 2.53 2.87 2.62
0.30 0.39 0.38 0.28 0.41 0.63 0.48 0.29
0.07 0.08 0.08 0.06 0.09 0.14 0.10 0.07
2.20 1.40 2.15 2.20 1.68 1.58 1.99 2.15
3.30 3.02 3.52 3.12 3.07 3.80 3.74 2.96
P > 0.05; SD, standard deviation; SE, standard error; N, number; Min, minimum level of bond strength; Max, maximum level of bond strength.
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TABLE 3. Descriptive statistics of the mean micro tensile bond strength (MPa) of the dentin groups Dentine type Sound dentine
Caries-affected dentine
Preparation type
Bonding system 3
Bur Laser Bur Laser Bur Laser Bur Laser
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Mean 6 SD (MPa)
SE
Min.
Max.
21 21 20 20 19 20 20 21
20.32 6 7.54 ab 24.57 6 7.27a 12.10 6 4.80c 11.02 6 3.90 c 15.51 6 5.49 bc 19.30 6 6.12 ab 12.40 6 5.04c 13.12 6 4.33 c
1.65 1.58 1.07 0.87 1.25 1.36 1.12 0.95
11.63 12.84 3.05 6.60 7.26 9.12 6.47 4.52
35.83 37.95 22.08 20.54 29.14 31.31 21.47 20.27
There is no statistical difference between same letters in same column (P < 0.05), SD, standard deviation; SE, standard error; N, number; Min, minimum level of bond strength; Max, maximum level of bond strength.
TABLE 4. Failure mode distribution (%) in each group Fracture types Dentine type Sound dentine
Caries-affected dentine
Preparation type Bur Laser Bur Laser Bur Laser Bur Laser
Bonding system 3
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Adhesive
Mix
Cohesive
21 21 20 20 19 20 20 21
21 (100%) 21 (100%) 15 (75%) 15 (75%) 18 (94%) 17 (85%) 18 (90%) 18 (85%)
0 0 5 (25%) 5 (25%) 1 (6%) 3(15%) 2 (10%) 3 (15%)
0 0 0 0 0 0 0 0
There is no statistical difference in all groups (P > 0.05).
Table 4 summarizes the failure patterns of the specimens to both caries-affected and sound dentine. The most common fracture type was adhesive fracture. There was no cohesive failure in any of the groups (P > 0.05). In terms of adhesive failure, Clearfil S3 bond showed this failure pattern for both lasers and burs groups on sound dentine (100%). With Xeno V, adhesive failure percentage was 75% for both lasers and burs groups on sound dentine. With Clearfil S3 and Xeno V bond, adhesive failure was approximately 90% for both lasers and burs groups on caries-affected dentine. SEM Observation SEM of the resin–dentine interface showed that the hybrid layer thickness of the Clearfil S3 bond in sound and caries-affected dentine applied with Er:YAG laser and bur was approximately 2–3 mm (Fig. 2). In the Xeno V bond group, the thickness hybrid layer was approximately 2–3 mm in sound and caries-affected dentine applied with Er:YAG laser and bur (Fig. 3). The resin tags were seen in the two bonding groups. No gaps were seen between compomer and dentine surfaces for all test groups. DISCUSSION A few studies on primary teeth have compared the bond strength between caries-affected dentine and sound dentine (Hosoya et al., 2006; Tosun et al., 2008). To our knowledge, no studies have evaluated the effects of lasers on primary teeth caries-affected dentine. Therefore, the purpose of this in vitro study was to evaluate the bond strength between caries-affected dentine and sound dentine using lasers and burs. Although Clearfil S3 bond showed good results in the sound primary dentine, Xeno V bond didn’t show good results in either groups (sound and carriesMicroscopy Research and Technique
affected dentine). There was a difference between the Clearfil S3 and the XenoV adhesive in bonding to these. Clearfil S3 adhesive also has higher tensile bond strengths than the XenoV adhesive. We must reject the first null hypothesis. In this study, when the Er:YAG laser was used in both dentine types, the bond strengths of adhesive systems were not differences in sound and caries-affected primary dentine groups. Thus, we must accept the second null hypothesis. Self-etch adhesives are a promising development in the adhesive dentistry, especially in terms of reduction of the necessary application steps and the possibility of a chemical interaction with hydroxyapatite-coated collagen fibers. At the same time, better polymerization of the adhesive layer is achieved as the formation of the oxygen-inhibited layer in the adhesive is prevented and, as a result, higher microtensile bond strength is obtained (Nikaido et al., 2008). It is also believed that the application of a self-etch adhesive system has the advantage of reducing postoperative sensitivity in comparison with a conventional etch-and-rinse adhesive system. However, several potential problems may affect bonding efficacy when self-etch adhesives are used on caries-affected dentine. Caries-affected dentine is softer than normal dentine because it is partially demineralized (Tosun et al., 2008). Carious intertubular dentine exhibits a higher degree of porosity than sound intertubular dentine, due to the loss of minerals. Tay and Pashley (2001) reported that self-etch adhesives differed in their aggressiveness. Therefore, they are classified into three categories, according to acidity: mild, moderate, and aggressive. Self-etch adhesive whose pH is lower than 1.5 are called aggressive selfetch adhesives. This high acidity results in rather deep demineralization effects .On the other hand, self-etch adhesives, which have a pH higher than 1.5 are categorized as mild or moderate. “Mild” self-etch systems,
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Fig. 2. Scanning electron micrographs of the resin/dentin interface of the polished cross-sectional dentin bonded with Clearfil S3 bond. (a) bur-sound dentin, (b) bur-caries-affected dentin, (c) Er:YAG lasersound dentin, (d) Er:YAG laser-caries-affected dentin. R, resin adhesive; H, hybrid layer; D, dentin (20 kV, X2500, scale bar: 10 lm).
in general, have a pH of about 2 and demineralize dentin only up to a depth of 1lm (De Munck et al., 2003; Tosun et al., 2008). In this study, two all-in one selfetch adhesives were used. One of them was moderate and the other mild. The pHs of them were given as follows: Xeno V (pH < 2), and Clearfil S3 Bond (pH 5 2.7). The results of this study showed that mild self-etch adhesive Clearfil S3 bond exposed better bond strength values than moderate self-etch adhesive Xeno V. It has been reported in previous study that the adhesion of resin to caries-affected dentine was inferior to that of normal dentine due to weaker collagen and/or weaker resin (Nakajima et al., 2005). Generally, the mode of adhesion for systems that remove the smear layer is principally founded on the combined effect of micromechanical interlocking of resin molecules into an exposed dentine collagen fibril network (the hybrid zone), together with resin-tag development into the opened dentine tubules. Penetration of resin in terms of the resin-impregnated dentine layer and resin tags for caries-affected dentine was noted to be less than sound dentine. Some previous studies have reported different microtensile bond strength (lTBS) values when using Er:YAG laser for cavity preparation (Flury et al., 2012; Manhaes et al., 2005). Bertrand et al. (2006) conclude that either bur or Er:YAG laser used dentine were equally receptive to adhesion. Using the Er:YAG laser in this study, the best value of microtensile bond strength was obtained from Clearfil S3 bond and sound primary tooth dentine (Bertrand et al., 2006).
In the current study, the microtensile bond strength testing was used because of the possibility of performing the analysis in an area of approximately 1 mm2. A small area was used to minimize potential defects and increase adhesion values. Although the microtensile test was an effective method in terms of its accuracy in small areas, it is time consuming and difficult to conduct for specimen preparation, especially for primary teeth (Shimada et al., 2002). The technique eliminates most of the cohesive resin or dentine fractures seen in more traditional tensile strength test procedures (Shono et al., 1999). With this method, several studies have indicated that the resin bond strength depends upon both the type of dentine (caries-affected or normal) and the adhesive systems used (Sengun et al., 2002; Yoshiyama et al., 2000). Yoshiyama et al. (2000) measured the bond strength of two resin bonding systems to sound and caries-affected dentine. They obtained lower bond strengths to caries-affected dentine than to normal dentine. Similarly, Say et al. (2005) indicate that bond strengths to sound dentine with photo- and dual-cure adhesives using total- and self-etch techniques were significantly higher than those to caries-affected dentine. However, Yoshiyama et al. (2000) and Say et al. (2005) used the permanent teeth in their study. During their study using primary teeth, Nakornchai et al. (2005) found that the self-etching adhesive demonstrated no statistical difference in bond strength between sound and caries-affected dentine. Scholtanus et al. (2010) used one of the three tested adhesives: Microscopy Research and Technique
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Fig. 3. Scanning electron micrographs of the resin/dentin interface of the polished cross-sectional dentin bonded with Xeno V. (a) bur-sound dentin, (b) bur-caries-affected dentin, (c) Er:YAG laser-sound dentin, (d) Er:YAG laser-caries-affected dentin. R, resin adhesive; H, hybrid layer; D, dentin (20 kV, X2500, scale bar: 10 lm).
Adper Scotchbond 1 XT (3M ESPE), 2-step etch-andrinse adhesives, Clearfil S3 bond (Kuraray), a 1-step self-etching or all-in-one adhesive, and Clearfil S3 bond (Kuraray), a 2-step self-etching adhesive. No significant differences in bond strength values to normal dentine were found between the three adhesives. Adper Scotchbond 1 XT and Clearfil S3 bond showed significantly lower bond strength values to cariesaffected dentine. Bond strength values to normal and caries-affected dentine for Clearfil S3 bond were not significantly different (Scholtanus et al., 2010). In this study, adhesive systems showed different tensile bond strengths according to different dentine substrates. One-step self-etch adhesive Clearfil S3 bond strength in the sound primary dentine achieved better results than the caries-affected primary dentine. However, there was no difference among groups when the Xeno V was used.
Er:YAG laser-applied dentinal surfaces can be observed higher adhesive values. When Laser and Clearfil S3 bond applied together, both sound dentin and caries-affected dentin yielded better results. SEM of resin–dentin interface with Clearfil S3 bond is better than the Xeno V bond in terms of resin tags and hybrid layer. Therefore, Er:YAG laser may be an important tool, and the chemical composition, and aggressiveness of adhesive systems seems to be the key to this technology becoming more efficient. ACKNOWLEDGMENTS We thank Dr. Soner C¸ankaya for statistical analysis and Mah-ya dental shop for their support of this project. REFERENCES
CONCLUSIONS Within the limitations of this in vitro study, lTBS values may change because of teeth dentin structure. Microscopy Research and Technique
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Marshall GW, Habelitz S, Gallagher R, Balooch M, Balooch G, Marshall SJ. 2001. Nanomechanical properties of hydrated carious human dentin. J Dent Res 80:1768–1771. Nakajima M, Kitasako Y, Okuda M, Foxton RM, Tagami J. 2005. Elemental distributions and microtensile bond strength of the adhesive interface to normal and caries-affected dentin. J Biomed Mater Res B Appl Biomater 72:268–275. Nakajima M, Sano H, Urabe I, Tagami J, Pashley DH. 2000. Bond strengths of single-bottle dentin adhesives to caries-affected dentin. Oper Dent 25:2–10. Nakornchai S, Harnirattisai C, Surarit R, Thiradilok S. 2005. Microtensile bond strength of a total-etching versus self-etching adhesive to caries-affected and intact dentin in primary teeth. J Am Dent Assoc 136:477–483. Nikaido T, Kitasako Y, Burrow MF, Umino A, Maruoka R, Ikeda M, Tagami J. 2008. Effect of resin coating on dentin bond durability of a resin cement over 1 year. Am J Dent 21:64–68. Pashley EL, Agee KA, Pashley DH, Tay FR. 2002. Effects of one versus two applications of an unfilled, all-in-one adhesive on dentine bonding. J Dent 30:83–90. Say EC, Nakajima M, Senawongse P, Soyman M, Ozer F, Tagami J. 2005. Bonding to sound vs caries-affected dentin using photo- and dual-cure adhesives. Oper Dent 30:90–98. Scholtanus JD, Purwanta K, Dogan N, Kleverlaan CJ, Feilzer AJ. 2010. Microtensile bond strength of three simplified adhesive systems to caries-affected dentin. J Adhes Dent 12:273–278. Sengun A, Unlu N, Ozer F, OztUrk B. 2002. Bond strength of five current adhesives to caries-affected dentin. J Oral Rehabil 29:777– 781. Shimada Y, Yamaguchi S, Tagami J. 2002. Micro-shear bond strength of dual-cured resin cement to glass ceramics. Dent Mater 18:380– 388. Shono Y, Ogawa T, Terashita M, Carvalho RM, Pashley EL, Pashley DH. 1999. Regional measurement of resin-dentin bonding as an array. J Dent Res 78:699–705. Tay FR, Pashley DH. 2001. Aggressiveness of contemporary selfetching systems. I: Depth of penetration beyond dentin smear layers. Dent Mater 17:296–308. Tosun G, Koyuturk AE, Sener Y, Sengun A. 2008. Bond strength of two total-etching bonding systems on caries-affected and sound primary teeth dentin. Int J Paediatr Dent 18:62–69. Yoshiyama M, Tay FR, Doi J, Nishitani Y, Yamada T, Itou K, Carvalho RM, Nakajima M, Pashley DH. 2002. Bonding of selfetch and total-etch adhesives to carious dentin. J Dent Res 81: 556–560. Yoshiyama M, Urayama A, Kimochi T, Matsuo T, Pashley DH. 2000. Comparison of conventional vs self-etching adhesive bonds to caries-affected dentin. Oper Dent 25:163–169.
Microscopy Research and Technique
Effects of Er:YAG Laser on Bond Strength of Self-etching Adhesives to Caries-Affected Dentin ALP ERDIN KOYUTURK,1* BILAL OZMEN,1 MURAT CORTCU,1 UGUR TOKAY,1 GUL TOSUN,2 AND MUSTAFA ERHAN SARI1 1 2
Department of Pediatric Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Kurupelit 55139, Samsun, Turkey Department of Pediatric Dentistry, Faculty of Dentistry, Selcuk University, Selcuklu, Konya, Turkey
KEY WORDS
tensile strength; caries; primary teeth; Er:YAG lasers; dentin-bonding agents
ABSTRACT The erbium:yttrium–aluminum–garnet (Er:YAG) laser may be effective the bond strength of adhesive systems on dentine surfaces, the chemical composition and aggressiveness of adhesive systems in clinical practice. The purpose of this study was to evaluate the effects of the Er:YAG laser system with the bonding ability of two different self-etching adhesives to caries-affected dentine in primary molars. Ninety mid-coronal flat dentine surfaces obtained from sound and caries-affected human primary dentine were treated with an Er:YAG laser or a bur. The prepared surfaces were restored with an adhesive system (Xeno V; Clearfil S3) and a compomer (Dyract Extra). The restored teeth were sectioned with a low-speed saw and 162 samples were obtained. The bond strength of the adhesive systems was tested using the microtensile test method. The data were statistically analyzed. A restored tooth in each group was processed for scanning electron microscopy evaluation. The values of the highest bond strength were obtained from the Clearfil S3-Er:YAG laser-sound dentine group in all groups. (24.57 6 7.27 MPa) (P > 0.05). The values of the lowest bond strength were obtained from the Xeno V-Er:YAG laser-sound dentine group in all groups (11.01 6 3.89 MPa). It was determined that the Clearfil S3 increased the bond strength on the surface applied with Er:YAG laser according to the Xeno V. Microsc. Res. Tech. 77:282–288, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Primary teeth have been presumed to be similar to permanent teeth according to their mechanical properties. However, some studies have suggested that the primary dentine may differ from permanent dentine due to the different degrees of mineralization (Hosoya et al., 2000). It has also been reported that adhesive restorative materials have a lower bonding strength to primary teeth as opposed to (relatively) permanent dentine (Bordin-Aykroyd et al., 1992). Furthermore, this observation is assumed to be linked to degree of mineralization. But a limited number of studies have been conducted on the mechanical properties of primary dentine (Hosoya et al., 2000; Mahoney et al., 2000). Carious dentine is typically identified as consisting of infected and affected layers. While the cariesinfected dentine layers are removed, the cariesaffected dentine layer is generally not removed during treatment (Yoshiyama et al., 2002). Thus, a large area of the cavity floor that was prepared for adhesive restoration is composed of caries-affected dentine. The characteristic features of caries-affected dentine are different from those of normal dentine. Caries-affected dentine is softer than normal dentine because it is partially demineralized (Marshall et al., 2001). Most tubules of caries-affected dentine are also obturated by mineral crystals, but they are bacteria free (Nakajima et al., 2000). There has been increasing relationship between bonding and caries-affected dentin with C V
2014 WILEY PERIODICALS, INC.
adhesive systems (Arrais et al., 2004). When the size of the primary teeth is considered, the caries-affected dentine area has increased importance. To identify the caries-affected dentine may use visual examination, sharp excavator, and staining with caries detector dye without doing histology. Self-etching adhesive systems have been used to simplify adhesive procedures and decrease technical sensitivity (Kenshima et al., 2005). Hydrophilic one-step selfetching adhesive system is one solution that includes etching, priming, and bonding procedures (Pashley et al., 2002). The self-etching adhesive systems facilitate the etching and priming of the dentine at the same time without rinsing and the smear plugs are merged into the resin tags (Pashley et al., 2002; Tay and Pashley, 2001). For pediatric patients, unable to tolerate the treatment process as adults, self-etching adhesives can be used to reduce the treatment steps. Different techniques have been used in the dentistry industry as alternatives to high-speed bur (Cozean et al., 1997; Krause et al., 2008). The use of laser irradiation has been widely studied and applied for that purpose, due to its precise and effective ability to *Correspondence to: Alp Erdin Koyuturk; Department of Pediatric Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey. E-mail: [email protected] Received 29 October 2013; accepted in revised form 16 January 2014 REVIEW EDITOR: Dr. Chuanbin Mao DOI 10.1002/jemt.22340 Published online 30 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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TABLE 1. Dentine bonding systems used in this study Product name 3
Clearfil S Bond
Kuraray, Osaka, Japan
Xeno V Bond
Dentsply, Konstanz, Germany
a
Compositiona
Application
10-MDP, Bis-GMA, HEMA, DMA, camphorquinone, ethanol, water, silanated colloidal silica
Apply adhesive to entire surface with a disposable brush tip; leave in place for 20 s; dry the entire surface sufficiently by air-drying with high pressure for more than 10 s while spreading the bond layer thinly; light cure for 20 s. Apply adhesive to entire surface with a disposable brush tip; leave in place for 20 s; dry the entire surface sufficiently by air-drying with high pressure for more than 5 s while spreading the bond layer thinly; light cure for 10 s.
Manufacturer
10-MDP, 10-Methacryloyloxydecyl dimethacrylate.
dihydrogen
phosphate;
Bifunctional acrylates, Acrylic acid, Tert-butyl alcohol, Phosphoric acid ester, Acidic acrylate, Phosphine oxide photoinitiator
Bis-GMA,
Bisphenol-A
eliminate carious tissue while avoiding the removal of sound tooth substrate, thus resulting in a more conservative cavity design. The erbium:yttrium–aluminum–garnet (Er:YAG) lasers have an advantage thermomechanical ablation that like etching hard tissues, a rough structure in dental tissue. Consequently, the primary indication for these systems is the preparation of cavities for restorations (Hossain et al., 2002). Though many kinds of laser systems have been developed that can cut dental hard tissues efficiently, erbium lasers have been shown to be the most promising laser equipment. In 1997, the US Food and Drug Administration accepted that the Er:YAG laser is an effective and safe technique to use on intraoral hard tissues (Cozean et al., 1997). Various laboratory research and clinical studies have demonstrated that the Er:YAG laser was effectively ablated hard dental tissue, with the minimum of injury to pulp, and surrounding structures. The 2.94 lm wavelength emission coincides with the main absorption peaks of water and hydroxyapatite, thus resulting in good absorption of erbium laser in all biological tissues, including enamel, dentine, and cementum (Corona et al., 2003). Erbium lasers have several advantages: microfractures are prevented, vibration is decreased, and patient discomfort originating from voice and pressure is eased. As laser-plugged dentine tubules aid the migration of microorganisms, postoperative sensitivity is abolished. However, recent research has shown that lasing of enamel and dentin may result in surface and subsurface alterations that have negative effects on both adhesion and seal (De Moor and Delme, 2010). Few studies in the literature evaluate the effects of lasers on caries-affected dentine. The purpose of this study was to examine the effects of lasers on the bond strength to caries-affected dentine of two self-etch adhesives. The hypothesis tested was that the Er:YAG laser will be affect the bond strength of adhesive systems on dentine surfaces. MATERIALS AND METHODS Ninety extracted human primary molars with coronal carious lesions, stored in 0.1% isotonic saline at 4 C, were used in this study. Soft and infected tissue were cleaned from the teeth and placed in isotonic saline before the experiment began. The enamel occlusal surface was wet-ground perpendicular to the long Microscopy Research and Technique
diglycidylemethacrylate;
HEMA,
hydroxyethylmethacrylate;
DMA,
axis of the tooth with 320-grit silicon carbide (SiC) abrasive paper to expose a flat dentine surface with carious lesion. Both caries-affected and sound dentine surfaces were mid-coronally prepared on the tooth. To remove caries dentine, grinding was performed using 320-grit silicon carbide abrasive papers under running water using the combined criteria of visual examination, a sharp excavator, and staining with a caries detector solution (Kuraray, Osaka, Japan). Relatively soft, dark-red-stained dentine was classified as cariesinfected dentine, while discolored, harder dentine that was stained pink was classified as caries-affected. Yellow, hard dentine was classified as sound dentine. The flat dentine surfaces of the teeth were then polished with 600, 800, and 1000 grit silicon carbide papers on an abrasive machine (Phoenix Beta, Buehler, Germany) under running water before bonding the procedure. Laser and Bur Treatments All dentine surfaces prepared using a round bur (Edenta AG.) in a contra-angle speed-reducing hand piece (400 rpm), and an Er:YAG laser with a wavelength of 2,940 lm (Fotona AT Fidelis Plus III, Ljubljana, Slovenia) was given its final form. The laser operating parameters used for all of the treatment groups (using the free-running emission mode) were as follows: 200 mJ per pulse, 20 Hz, power of 4.0 W, and 100 ls pulse duration. A sapphire tip with a diameter of 1.3 mm and a length of 8 mm was used. The coaxial water spray feature of the hand piece was set to ‘on’. A contact tip was also used. Bonding Procedures The line of the caries-affected dentine area was marked with a waterproof pen before the application of the adhesive system. Following the application of the adhesives to the prepared surfaces according to the manufacturers’ instructions (Table 1), the respective compomer (Dyract Extra, Dentsply, Konstanz, Germany) of bonding agents were built up incrementally in three to four layers to a height of 4–5 mm. Bonding agents and compomer resins were cured with a halogen curing light (Lunar curing light, Benlioglu Dental, Ankara, Turkey) according to the stipulated curing time, where light intensity was at least 400 mW/cm2. Specimens were then stored in distilled water at 37 C
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for 24 h. The teeth were longitudinally sectioned perpendicular to the bonded interface to produce several rectangular bonded sticks with the cross-sectional area approximately 1 mm2 with a low-speed saw (Isomet 1000, Buehler, Lake Bluff, IL). The caries-affected dentine sticks were first prepared from the level marked with the waterproof pen. ‘I’ shaped longitudinal cuts were obtained with the top half consisting of composite and the bottom half consisting of dentine from each tooth (Fig. 1). Microtensile Bond Strength Test Each stick was carefully examined in a dissecting microscope (320) to ensure that the test site was homogeneous with regard to caries-affected dentine (Olympus SZ 4045 TRPR, Tokyo, Japan). The crosssectional area and remaining dentine thickness were measured using a digital calliper (Mitutoyo, Tokyo, Japan) (Table 2). For microtensile bond testing, the sticks were fixed to the microtensile bond testing apparatus and a test machine (Harvard Apparatus Co., Dover, MA). Tensile forces were applied to the resin– dentine interface at a crosshead speed of 1 mm/min until failure occurred. To determine the tensile bond strengths, the maximum load (N) was recorded and converted to megapascals (MPa). Fracture Type Analysis After tensile testing, the fracture samples were collected and stored in distilled water for 24 h. The samples were classified as follows: Adhesive failure: The failure at the interface was between compomer and dentine.
Mixed failure: The failure was partially adhesive and partially cohesive compomer fractures and/or dentine fracture. Cohesive failure: The failure was in the compomer or dentine. Scanning Electron Microscopy Evaluation The second aim of this study was to observe the micromorphology of the interface between the adhesives and sound and caries-affected dentine. Four additional primary molar teeth with occlusal dentine caries for per group were used to evaluate the morphology of the interface by scanning electron microscopy (SEM). The teeth were prepared using the same previouslymentioned methods. The compomers were bonded to the prepared dentin surfaces using bonding agents according to the manufacturers’ instructions. The bonded specimens were longitudinally sectioned perpendicular to the bonded interface. The cut surfaces were fixed in a 10% formaldehyde solution for 24 h, ground with 600 grit silicon carbide abrasive paper, and highly polished with a diamond paste 6-3-1-1/4 mm (Struers, Copenhagen, Denmark). Then, the specimens were immersed in 10% phosphoric acid solution for 3–5 s, rinsed with distilled water, and treated for 5 min with 5% sodium hypochlorite solution and again rinsed thoroughly with distilled water. After drying at room temperature (27 C), the specimens were coated with Polaron Sc500 Sputter Coater (VG Microtech, Tokyo, Japan) and examined under SEM (JSM-5600, JEOL, Tokyo, Japan) at an accelerating voltage of 20 kV(Tosun et al., 2008). Statistical Analysis Statistical analysis was performed using a one-way ANOVA and Tukey test (P < 0.05). Differences between the groups in terms of failure type was performed using a Kruskal Wallis-H test (P < 0.05). RESULTS The micro tensile bond strengths to dentine varied from 3.05 MPa for the one-step self-etch adhesive Xeno V bond to 37.95 MPa for Clearfil S3 bond. The highest bond strength rates were obtained from both cariesaffected and sound primary dentine in the Clearfil S3 bond groups used Er:YAG laser (19.30 6 6.12 and 24.57 6 7.27 MPa). However, there was no statistically difference (P > 0.05). There was no difference among groups in the Xeno V sound and caries-affected primary dentine, laser and bur (P > 0.05) (Table 3). No statistical differences were seen among the remaining dentine thickness in the groups (P > 0.05) (Table 2).
Fig. 1. The caries-affected dentin and sound dentin stick.
TABLE 2. Descriptive statistics of the remaining dentine thickness (mm) of the dentin groups Dentine type Sound dentine
Caries-affected dentine
Preparation type Bur Laser Bur Laser Bur Laser Bur Laser
Bonding system 3
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Mean (mm)
SD (mm)
SE (mm)
Min. (mm)
Max. (mm)
21 21 20 20 19 20 20 21
2.81 2.46 2.85 2.64 2.45 2.53 2.87 2.62
0.30 0.39 0.38 0.28 0.41 0.63 0.48 0.29
0.07 0.08 0.08 0.06 0.09 0.14 0.10 0.07
2.20 1.40 2.15 2.20 1.68 1.58 1.99 2.15
3.30 3.02 3.52 3.12 3.07 3.80 3.74 2.96
P > 0.05; SD, standard deviation; SE, standard error; N, number; Min, minimum level of bond strength; Max, maximum level of bond strength.
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TABLE 3. Descriptive statistics of the mean micro tensile bond strength (MPa) of the dentin groups Dentine type Sound dentine
Caries-affected dentine
Preparation type
Bonding system 3
Bur Laser Bur Laser Bur Laser Bur Laser
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Mean 6 SD (MPa)
SE
Min.
Max.
21 21 20 20 19 20 20 21
20.32 6 7.54 ab 24.57 6 7.27a 12.10 6 4.80c 11.02 6 3.90 c 15.51 6 5.49 bc 19.30 6 6.12 ab 12.40 6 5.04c 13.12 6 4.33 c
1.65 1.58 1.07 0.87 1.25 1.36 1.12 0.95
11.63 12.84 3.05 6.60 7.26 9.12 6.47 4.52
35.83 37.95 22.08 20.54 29.14 31.31 21.47 20.27
There is no statistical difference between same letters in same column (P < 0.05), SD, standard deviation; SE, standard error; N, number; Min, minimum level of bond strength; Max, maximum level of bond strength.
TABLE 4. Failure mode distribution (%) in each group Fracture types Dentine type Sound dentine
Caries-affected dentine
Preparation type Bur Laser Bur Laser Bur Laser Bur Laser
Bonding system 3
Clearfil S Clearfil S3 Xeno V Xeno V Clearfil S3 Clearfil S3 Xeno V Xeno V
N
Adhesive
Mix
Cohesive
21 21 20 20 19 20 20 21
21 (100%) 21 (100%) 15 (75%) 15 (75%) 18 (94%) 17 (85%) 18 (90%) 18 (85%)
0 0 5 (25%) 5 (25%) 1 (6%) 3(15%) 2 (10%) 3 (15%)
0 0 0 0 0 0 0 0
There is no statistical difference in all groups (P > 0.05).
Table 4 summarizes the failure patterns of the specimens to both caries-affected and sound dentine. The most common fracture type was adhesive fracture. There was no cohesive failure in any of the groups (P > 0.05). In terms of adhesive failure, Clearfil S3 bond showed this failure pattern for both lasers and burs groups on sound dentine (100%). With Xeno V, adhesive failure percentage was 75% for both lasers and burs groups on sound dentine. With Clearfil S3 and Xeno V bond, adhesive failure was approximately 90% for both lasers and burs groups on caries-affected dentine. SEM Observation SEM of the resin–dentine interface showed that the hybrid layer thickness of the Clearfil S3 bond in sound and caries-affected dentine applied with Er:YAG laser and bur was approximately 2–3 mm (Fig. 2). In the Xeno V bond group, the thickness hybrid layer was approximately 2–3 mm in sound and caries-affected dentine applied with Er:YAG laser and bur (Fig. 3). The resin tags were seen in the two bonding groups. No gaps were seen between compomer and dentine surfaces for all test groups. DISCUSSION A few studies on primary teeth have compared the bond strength between caries-affected dentine and sound dentine (Hosoya et al., 2006; Tosun et al., 2008). To our knowledge, no studies have evaluated the effects of lasers on primary teeth caries-affected dentine. Therefore, the purpose of this in vitro study was to evaluate the bond strength between caries-affected dentine and sound dentine using lasers and burs. Although Clearfil S3 bond showed good results in the sound primary dentine, Xeno V bond didn’t show good results in either groups (sound and carriesMicroscopy Research and Technique
affected dentine). There was a difference between the Clearfil S3 and the XenoV adhesive in bonding to these. Clearfil S3 adhesive also has higher tensile bond strengths than the XenoV adhesive. We must reject the first null hypothesis. In this study, when the Er:YAG laser was used in both dentine types, the bond strengths of adhesive systems were not differences in sound and caries-affected primary dentine groups. Thus, we must accept the second null hypothesis. Self-etch adhesives are a promising development in the adhesive dentistry, especially in terms of reduction of the necessary application steps and the possibility of a chemical interaction with hydroxyapatite-coated collagen fibers. At the same time, better polymerization of the adhesive layer is achieved as the formation of the oxygen-inhibited layer in the adhesive is prevented and, as a result, higher microtensile bond strength is obtained (Nikaido et al., 2008). It is also believed that the application of a self-etch adhesive system has the advantage of reducing postoperative sensitivity in comparison with a conventional etch-and-rinse adhesive system. However, several potential problems may affect bonding efficacy when self-etch adhesives are used on caries-affected dentine. Caries-affected dentine is softer than normal dentine because it is partially demineralized (Tosun et al., 2008). Carious intertubular dentine exhibits a higher degree of porosity than sound intertubular dentine, due to the loss of minerals. Tay and Pashley (2001) reported that self-etch adhesives differed in their aggressiveness. Therefore, they are classified into three categories, according to acidity: mild, moderate, and aggressive. Self-etch adhesive whose pH is lower than 1.5 are called aggressive selfetch adhesives. This high acidity results in rather deep demineralization effects .On the other hand, self-etch adhesives, which have a pH higher than 1.5 are categorized as mild or moderate. “Mild” self-etch systems,
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Fig. 2. Scanning electron micrographs of the resin/dentin interface of the polished cross-sectional dentin bonded with Clearfil S3 bond. (a) bur-sound dentin, (b) bur-caries-affected dentin, (c) Er:YAG lasersound dentin, (d) Er:YAG laser-caries-affected dentin. R, resin adhesive; H, hybrid layer; D, dentin (20 kV, X2500, scale bar: 10 lm).
in general, have a pH of about 2 and demineralize dentin only up to a depth of 1lm (De Munck et al., 2003; Tosun et al., 2008). In this study, two all-in one selfetch adhesives were used. One of them was moderate and the other mild. The pHs of them were given as follows: Xeno V (pH < 2), and Clearfil S3 Bond (pH 5 2.7). The results of this study showed that mild self-etch adhesive Clearfil S3 bond exposed better bond strength values than moderate self-etch adhesive Xeno V. It has been reported in previous study that the adhesion of resin to caries-affected dentine was inferior to that of normal dentine due to weaker collagen and/or weaker resin (Nakajima et al., 2005). Generally, the mode of adhesion for systems that remove the smear layer is principally founded on the combined effect of micromechanical interlocking of resin molecules into an exposed dentine collagen fibril network (the hybrid zone), together with resin-tag development into the opened dentine tubules. Penetration of resin in terms of the resin-impregnated dentine layer and resin tags for caries-affected dentine was noted to be less than sound dentine. Some previous studies have reported different microtensile bond strength (lTBS) values when using Er:YAG laser for cavity preparation (Flury et al., 2012; Manhaes et al., 2005). Bertrand et al. (2006) conclude that either bur or Er:YAG laser used dentine were equally receptive to adhesion. Using the Er:YAG laser in this study, the best value of microtensile bond strength was obtained from Clearfil S3 bond and sound primary tooth dentine (Bertrand et al., 2006).
In the current study, the microtensile bond strength testing was used because of the possibility of performing the analysis in an area of approximately 1 mm2. A small area was used to minimize potential defects and increase adhesion values. Although the microtensile test was an effective method in terms of its accuracy in small areas, it is time consuming and difficult to conduct for specimen preparation, especially for primary teeth (Shimada et al., 2002). The technique eliminates most of the cohesive resin or dentine fractures seen in more traditional tensile strength test procedures (Shono et al., 1999). With this method, several studies have indicated that the resin bond strength depends upon both the type of dentine (caries-affected or normal) and the adhesive systems used (Sengun et al., 2002; Yoshiyama et al., 2000). Yoshiyama et al. (2000) measured the bond strength of two resin bonding systems to sound and caries-affected dentine. They obtained lower bond strengths to caries-affected dentine than to normal dentine. Similarly, Say et al. (2005) indicate that bond strengths to sound dentine with photo- and dual-cure adhesives using total- and self-etch techniques were significantly higher than those to caries-affected dentine. However, Yoshiyama et al. (2000) and Say et al. (2005) used the permanent teeth in their study. During their study using primary teeth, Nakornchai et al. (2005) found that the self-etching adhesive demonstrated no statistical difference in bond strength between sound and caries-affected dentine. Scholtanus et al. (2010) used one of the three tested adhesives: Microscopy Research and Technique
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Fig. 3. Scanning electron micrographs of the resin/dentin interface of the polished cross-sectional dentin bonded with Xeno V. (a) bur-sound dentin, (b) bur-caries-affected dentin, (c) Er:YAG laser-sound dentin, (d) Er:YAG laser-caries-affected dentin. R, resin adhesive; H, hybrid layer; D, dentin (20 kV, X2500, scale bar: 10 lm).
Adper Scotchbond 1 XT (3M ESPE), 2-step etch-andrinse adhesives, Clearfil S3 bond (Kuraray), a 1-step self-etching or all-in-one adhesive, and Clearfil S3 bond (Kuraray), a 2-step self-etching adhesive. No significant differences in bond strength values to normal dentine were found between the three adhesives. Adper Scotchbond 1 XT and Clearfil S3 bond showed significantly lower bond strength values to cariesaffected dentine. Bond strength values to normal and caries-affected dentine for Clearfil S3 bond were not significantly different (Scholtanus et al., 2010). In this study, adhesive systems showed different tensile bond strengths according to different dentine substrates. One-step self-etch adhesive Clearfil S3 bond strength in the sound primary dentine achieved better results than the caries-affected primary dentine. However, there was no difference among groups when the Xeno V was used.
Er:YAG laser-applied dentinal surfaces can be observed higher adhesive values. When Laser and Clearfil S3 bond applied together, both sound dentin and caries-affected dentin yielded better results. SEM of resin–dentin interface with Clearfil S3 bond is better than the Xeno V bond in terms of resin tags and hybrid layer. Therefore, Er:YAG laser may be an important tool, and the chemical composition, and aggressiveness of adhesive systems seems to be the key to this technology becoming more efficient. ACKNOWLEDGMENTS We thank Dr. Soner C¸ankaya for statistical analysis and Mah-ya dental shop for their support of this project. REFERENCES
CONCLUSIONS Within the limitations of this in vitro study, lTBS values may change because of teeth dentin structure. Microscopy Research and Technique
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