Eur Arch Paediatr Dent DOI 10.1007/s40368-014-0149-5
ORIGINAL SCIENTIFIC ARTICLE
Comparison of microtensile bond strength of a resin composite to enamel conditioned by acid etching and Er,Cr:YSGG laser in human primary teeth B. Malekafzali • R. Fekrazad • A. Mirfasihi S. Saedi
•
Received: 15 June 2014 / Accepted: 5 September 2014 Ó European Academy of Paediatric Dentistry 2014
Abstract Aim This study was designed to compare the bond strength of composite resin restorations on the buccal surface of primary human canine after conditioning by conventional acid etching and Er,Cr:YSGG laser. Methods Twenty sound primary canines were cut buccolingually into two halves and each half was randomly placed in Er,Cr:YSGG laser or acid etch group. The samples in the acid etch group were etched with 37 % phosphoric acid for 30 s. The samples in the laser group were prepared by Er,Cr:YSGG laser. The G6-Tips and 600 lm diameter were used with a 1.5 W of power output, pulse duration of 140 ls and repetition rate of 20 Hz. The bonding agent was applied on the buccal surface of each sample and layers of resin composite were placed. The samples’ bond strengths were evaluated by a microtensile test instrument. Results The mean of microtensile bond strength was 18.55 ± 6.41 in the laser group and 24.62 ± 5.56 in acid etch group. Microtensile bond strength achieved by laser conditioning was significantly lower than microtensile bond strength achieved by the conventional acid etching. Statistics To compare the results between the acid etch and B. Malekafzali Department of Paediatric Dentistry, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran R. Fekrazad Laser Research Center in Medical Sciences (LRCMS), Periodontal Department, Dental Faculty, AJA University of Medical Sciences, Tehran, Iran A. Mirfasihi S. Saedi (&) Dental School, Shahid Beheshti University of Medical Sciences, Daneshjou Blv. Evin St, PO 1983969411 Tehran, Iran e-mail: [email protected]
laser group, the paired t test was performed (p value \ 0.001). Conclusion Conditioning enamel in primary teeth by Er,Cr:YSGG laser, cannot be used as an alternative method for acid etching and cannot substitute this conventional method. Keywords Er,Cr:YSGG laser Microtensile bond strength Enamel conditioning Primary tooth
Introduction Recently, adhesive resin composites have become an important material of choice in the restoration of primary teeth as well as permanent teeth (Krifka et al. 2008). Toothcoloured composite resins are aesthetic and the cavity preparation is a non-invasive procedure to the tooth structures (Burnett 2004; Soncini et al. 2007). The adhesion of resin to enamel is based on micromechanical retention to roughened conditioned surfaces (Jaberi Ansari et al. 2012). Since the publication of Bunocuore’s report, acid etching has been the standard protocol for conditioning the enamel (Obeidi et al. 2010; Bas¸ aran et al. 2011; Gonc¸alves et al. 2003). Conditioning the enamel for achieving a strong bond between the adhesive resin and tooth substrate is an important factor to avoid risk of marginal microleakage and pulpal inflammation responses following polymerisation shrinkage of the composite and it increases the restoration durability (Sungurtekin and Oztas 2010; Sasaki et al. 2008; Jaberi Ansari et al. 2012). The structural differences between primary and permanent teeth, such as more frequent occurrence of thicker layers of prismless enamel in primary teeth, are believed to affect the resin retention and etching efficiency in primary
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teeth (Agostini et al. 2001; Nordenvall et al. 1980). Decalcifying the enamel leaves the decalcified sites susceptible to acid attack and reduces the caries resistance (Wen et al. 2014; Sagir et al. 2013; Sungurtekin and Oztas 2010; Firat et al. 2012). Concerning the fact that primary teeth have lower content of calcium phosphate than permanent teeth, resulting in a lower degree of mineralisation, primary teeth are more susceptible to dissolution (De Menezes Oliveira et al. 2010). These issues have led researchers to study alternative methods in conditioning the enamel. Laser, as an alternative method for conventional acid etching, is painless and it produces less noise and vibration, which provides the patient with more comfort (Sungurtekin and Oztas 2010; Us¸ u¨mez et al. 2002; Lorenzo et al. 2012). It has been reported that laser treatment modifies the calcium-to-phosphate ratio and reduces the carbonate-tophosphate ratio as well. As a result, the surface etched by laser is more stable and less acid soluble (Sungurtekin and Oztas 2010; Us¸ u¨mez et al. 2002). The bactericidal effect of laser irradiation is also known as an advantage of using lasers to conditioning dental hard tissues (Lorenzo et al. 2012). Erbium lasers are high output lasers, consisting of Er:Yag and Er,Cr:YSGG which are used for conditioning dental hard tissues without damaging the pulp (Bas¸ aran et al. 2011). The investigators have reported rough and micro-irregular surfaces similar to acid-etched ones after conditioning with Erbium lasers (Us¸ u¨mez et al. 2002). Erbium lasers ablate the enamel via a thermomechanical procedure, by emitting the wavelength of 2.6–3 lm, which is the peak wavelength of absorption for water and hydroxyapatite (Berk et al. 2008). The energy absorption results in the evaporation of water, the important component of tooth tissues. The water vapours trapped in hydroxyapatite crystals produce microexplosions and tiny particles from the surface will be removed and yield a rough and uneven surface ideal for adhesion (Obeidi et al. 2010; Sagir et al. 2013). The energy level required for this thermomechanical ablation process in primary enamel may be influenced according to the different composition and structure of primary and permanent enamel, mainly due to the higher content of water in primary enamel (Olivi and Genovese 2011; Al-Batayneh et al. 2014). Erbium lasers in adhesive dentistry were mainly operated in cavity preparation (Hossain et al. 2002; Kohara et al. 2002; Al-Batayneh et al. 2014; Yamada et al. 2002) and conditioning of occlusal pit and fissures for application of fissure sealants (Borsatto et al. 2004, 2007; Sungurtekin and Oztas 2010) and there are limited studies concentrating on laser conditioning of enamel for composite resin restorations in primary teeth (Wanderley et al. 2005). In addition, these studies reported controversial results concerning
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microleakage and bond strength of resins to laser-prepared enamel in primary teeth. Therefore, the following study was designed to compare the microtensile bond strength of adhesive resin composite restorations to buccal surfaces of primary canines conditioned by 37 % phosphoric acid etching or Er,Cr:YSGG laser irradiation.
Materials and methods Ethical approval Ethical approval for this study was obtained from the ‘‘Institutional Ethical Committee’’ of Shahid Beheshti Dental Research Center, Tehran, Iran. Cases of primary canine extraction for orthodontic reasons were selected and parents were informed about the research procedure. Written consents were obtained. Sample preparation Twenty sound primary canines extracted for orthodontic reasons were rinsed and cleansed from blood and soft tissues. The samples were disinfected in 0.5 % chloramines T solution for one week (Jaberi Ansari et al. 2012). The teeth were stored in distilled water and the water content was changed weekly to prevent further contaminations (Berk et al. 2008). The samples were cut buccolingually into two equal halves with a thin diamond bur. The halves were centrically embedded in acrylic resin blocks. The groups designed in this study were Group 1: Conditioned with 37 % phosphoric acid gel (ScotchbondTM etchant delivery system, 3 M ESPE, St Paul, USA) for 30 s. Group 2: Conditioned by Er,Cr:YSGG laser (Waterlase, Biolase Technology Inc, San Clemente, CA, USA), G6Tips with 600 lm diameter with 55 % water and 65 % air spray, water spray 12 ml/min, wavelength 2,780 nm, pulse duration 140 ls, power 1.5 watt, energy 75 mJ/pulse, repetition rate 20 Hz, total energy delivered 15 J, speed of movement 1 mm/s. Each half-tooth sample was randomly placed in one specific group and the second half of the samples was placed in the other group to have 20 study samples in each group. In Group 1, the acid was applied on each tooth surface for 30 s and washed with water spray for 20 s at a distance of 1 cm. The teeth were dried with air to observe the chalky white enamel. In group B, 3 9 3 mm2 of enamel was irradiated for 10 s at a distance of 1–2 mm in vertical
Eur Arch Paediatr Dent
and horizontal patterns to establish an even irradiation of the surface until chalky white enamel was seen. After etching each sample, the bonding agent (Single Bond, 3 M ESPE Dental Products, USA) was applied on the plastic Nelaton matrix and light cured for 20 s. The resin composite Z100 (3 M ESPE, St Paul, USA) was placed in the Nelaton matrix in 2 mm layers and each layer was cured with LED curing light device (Mectron, Starlight pro GAC, Italy) for 40 s, at a distance of 2 mm, with the light intensity of 300 W/cm2, which was checked previously by radiometry.
Table 1 Descriptive statistical values of lTBS (MPa) Mean
Standard deviation
Median
Min
Max
Group A
24.62
5.56
25.05
14.43
33.97
Group B
18.55
6.41
17.54
10.75
32.69
Bond strength test A predictable and standardised test, micro-tensile bond strength (lTBS) test was used in this study to compare the tensile bond strength in laser and acid etch group. After the composite was cured, the matrix was separated with a surgical blade. The samples in both groups were sectioned by Accustom-50 (Struers, Denmark) in the proper dimensions for Microtensile Tester instrument (Bisco, USA). The length and width of each section were measured by a digital calliper and the bonding area (A) was derived by multiplying the width and length of each sample. The tensile bond strength test was performed on the samples by Microtensile Tester Instrument (Bisco, USA). The force applied at the fracture point(F) was recorded for each sample and inserting it in the following formula the microtensile bond strength (P) of each sample was derived: PðMPaÞ ¼
FðNÞ : Aðmm2 Þ
Statistical analysis All the values were calculated as mean ± standard deviation using SPSS software version 17.0 (SPSS Inc, Chicago, USA). The Paired t test was used to compare the results of lTBS in group 1 with the results in group 2.
Results Table 1 presents the descriptive statistical values of lTBS in both groups. The mean of lTBS in the acid etch group was 24.62 MPa with the standard deviation of 5.56. The maximum lTBS in this group was 33.97 MPa and the minimum lTBS was 14.43 MPa. In the laser group, the mean of lTBS values obtained was 18.55 MPa with the standard deviation of 6.41. The maximum lTBS reported in this group was 32.69 MPa and the minimum lTBS in this group was 10.75 MPa.
Fig. 1 Comparison of lTBS in laser and acid etch group
The Paired t test used for comparison of lTBS values between two groups showed a significant difference between the acid etch and laser group (p value \ 0.0001). The lTBS values in the laser group were significantly lower than the acid etch group with a greater standard deviation. Figure 1 compares the bond strength obtained in both groups and reveals the higher values in acid etch group. The distribution of lTBS in both groups are demonstrated in Fig. 2. Comparing these figures reveals that higher bond strengths are more frequent in the acid etch group.
Discussion The studies investigating the efficiency of lasers in adhesive dentistry concentrate on microleakage and bond strength tests (Olivi and Genovese 2011). To evaluate laser efficiency in adhesive dentistry cavity preparations and occlusal pit and fissure conditioning were performed on primary teeth. In addition, as far as we are aware the bond strength of composite resin restoration to primary enamel was evaluated in one study (Wanderley et al. 2005). The microleakage of composite resin restorations in cavities prepared by laser was compared to acid-etched bur cut cavities (Hossain et al. 2002; Kohara et al. 2002; Yamada et al. 2002; Al-Batayneh et al. 2014). Other experiments evaluated the bond strength and microleakage of fissure sealants applied in occlusal pits and fissures after laser treatment in primary molars (Borsatto et al. 2004, 2007;
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Fig. 2 Distribution of lTBS in acid etch group
Sungurtekin and Oztas, 2010). There are confusing reports on the efficiency of lasers. Whilst some of these studies reported favourable results (Hossain et al. 2002; Kohara et al. 2002; Yamada et al. 2002; Wanderley et al. 2005; AlBatayneh et al. 2014), the other studies reported lower bond strengths (Borsatto et al. 2007) and higher scores of microleakage (Borsatto et al. 2004; Sungurtekin and Oztas 2010) when using lasers. Wanderley and colleagues (2005) reported a lower shear bond strength of composite resin to acid-etched enamel compared to bonding of composite resins to enamel conditioned by Er:YAG laser prior to acid etching when 60 mJ/2 Hz and 80 mJ/2 Hz laser irradiations were used. However, when pretreating the enamel with 100 mJ/2 Hz, no significant difference was reported. Sungurtekin and Oztas (2010) performed a microleakage test to evaluate the marginal integrity of fissure sealants in primary molars. Acid etching was compared to Er,Cr:YSGG laser irradiation in this study. The parameters of laser were set to 20 Hz, 140–200 ls and 2.5 or 3.5 W according to the study group. The results of this study revealed a lower microleakage in acid etch group than laser conditioning with 2.5 and 3.5 W power. Borsatto et al. (2004, 2007) reported higher tensile bond strength of fissure sealant in primary teeth after conditioning enamel with both acid etching and Er:YAG laser (Defocused mode, Repetition Rate: 2 Hz, 1.5 ml/min). The lowest bond strength was reported when conditioning enamel with laser irradiation. In a second study by the same authors, the microleakage of fissure sealants followed by Er:YAG laser conditioning (Wavelength 2.9 lm,
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Energy 120 mJ, Repetition Rate 4 Hz, water spray 5 ml/ min) and acid etching were compared and it was demonstrated that acid etching prior to laser must not be eliminated. The experiments assessing tensile and microtensile bond strengths in permanent teeth mainly reported lower bond strengths in laser groups. Firat et al. (2012) evaluated the microtensile bond strength of composite restorations in human permanent molar after applying different pulse durations of Er:YAG laser alone and in combination with acid etching and concluded that acid etching improved the bond strength. In another study comparing laser cut and bur cut enamel and dentine in permanent molars, De Munck and colleagues (2002) declared that microtensile bond strength of a total etch adhesive to enamel prepared by Er:YAG laser was improved after acid etching. An increase in tensile bond strength was also reported by Sasaki et al. (2008) when using the combination of acid etching and Er:YAG in third human molars. The lowest tensile bond strength was reported for the laser group in this study. Gonc¸alves et al. (2003) also declared that using Er:YAG laser with 80 mJ associated with acid etching at 1, 2, 3 and 4 Hz frequencies did not improve the tensile bond strength in permanent teeth. The results presented herein primary enamel conditioning with laser are in accordance with these studies. Despite the results of the previous studies, some studies on the shear bond strength of orthodontic brackets have reported different results. Hosseini et al. (2012) indicated higher shear bond strengths of brackets to enamel in premolars when using Er:YAG with 1 and 1.5 W power than acid etching. Basaran et al. (2007) also reported that the mean shear bond strength of orthodontic brackets, when enamel is conditioned by 1 and 2 W Er,Cr:YSGG laser irradiation, is comparable to acid etching. Comparing the shear bond strength of a dual-cure resin composite with different power outputs of Er,Cr:YSGG, Bas¸ aran et al. (2011) reported comparable results to acid etching when using 1.5 and 1.75 W laser irradiation for 15 s in permanent incisors. In addition, Sag˘ir et al. (2013) showed that Er:Yag laser irradiation of premolars with medium-short pulse mode and quantum-square pulse mode can be used as an alternative to acid etching by measuring the shear bond strength. According to Olivi and Genovese (2011), repetition rate of 10–20–50 Hz, power output of 0.65–3.7 W and energy level of 65–75 mJ are recommended parameters for enamel conditioning before acid etching in primary teeth using Er,Cr:YSGG laser. Er,Cr:YSGG laser used in the current study is proven to have no thermal effects on the pulpal tissue and is approved by Food and Drug Administration (FDA). The parameters used in this study (power output of 1.5 W and 75 mJ/pulse, pulse duration of 140 ls and the
Eur Arch Paediatr Dent
repetition rate of 20 Hz) were all within the recommended range for enamel conditioning. The controversial results of laser studies might be due to changes of parameters in laser irradiation. The power outputs and emission modes with different wavelengths, repetition rates and pulse durations might affect the laser treated areas. This may result in various etching patterns and bond strengths (Berk et al. 2008; Firat et al. 2012; Wen et al. 2014). Er,Cr:YSGG laser can transfer a mean power output varying from 0 to 6 W. The high output irradiations of 2.5–6 are used for cutting enamel. Lower outputs are used for etching enamel (Berk et al. 2008). SEM evaluations of enamel after applying different power outputs have also revealed various etching patterns. For instance, during the SEM analysis of samples prepared by 1.5 W power Er,Cr:YSGG laser in permanent enamel a type I etching pattern was obtained, whilst type III etching pattern was obtained using 2 W power in Berk’s study (Berk et al. 2008). Berks et al. (2008) evaluation of different power outputs of Er,Cr:YSSG on shear bond strength of enamel in permanent molars revealed that the application of 1.5 and 2 W power outputs can be an alternative method for acid etching. Despite these results on shear bond strength, the laser etching with 1.5 W power in this study showed lower microtensile bond strength of laser-etched samples than acid-etched samples. Due to the higher content of water, the primary enamel conditioning is expected to require lower energy than permanent teeth (Al-Batayneh et al. 2014). However, the results of our study using 1.5 W power output setting and Sungurtekin’s study using 2.5 and 3.5 W power outputs of Er,Cr:YSGG laser were not desirable (Sungurtekin and Oztas 2010), despite the desirable results of the study by Berk et al. (2008) in permanent teeth with 1.5 and 2 W power outputs. As Sungurtekin and Oztas (2010) stated that microleakage scores in fissure sealants in conditioned primary enamel after Er,Cr:YSGG laser irradiation with 2.5 and 3.5 W power and repetition rate of 20 Hz are higher than fissure sealants placed in acid-etched enamel and concluded that laser irradiation cannot eliminate acid etching. Moreover, Krishnan et al. (2013) revealed that the shear bond strength after application of 2 W/20 Hz Er,Cr:YSGG laser irradiation was comparable to the shear bond strength after conventional acid etching in premolars. It also revealed that increasing the frequency from 10 to 20 Hz results in higher shear bond strengths with the same power output of the device (Krishnan et al. 2013).
Conclusion Microtensile bond strength values were significantly lower in a laser group than an acid etch group and the values were
not in the acceptable range for clinical application of laser. Therefore, according to results of the current study, laser etching cannot substitute the application of acid for obtaining required bond strength of resin to enamel of primary teeth. Acknowledgement This manuscript was prepared based on a postdoctoral thesis (code number: 598), in Pediatric Department, Dental School of Shahid Beheshti University of Medical Sciences under supervision of Prof. Beheshteh Malekafzali.
References Agostini FG, Kaaden C, Powers JM. Bond strength of self-etching primers to enamel and dentin of primary teeth. Pediatr Dent. 2001;23:481–6. Al-Batayneh OB, Seow WK, Walsh LJ. Assessment of Er:YAG Laser for cavity preparation in primary and permanent teeth: a scanning electron microscopy and thermographic study. Pediatr Dent. 2014;36:90–4. Basaran G, Ozer T, Berk N, Hamamci O. Etching enamel for orthodontics with an erbium, chromium:yttrium-scandium-gallium-garnet laser system. Angle Orthod. 2007;77:117–23. Bas¸ aran EG, Ayna E, Bas¸ aran G, Beydemir K. Influence of different power outputs of erbium, chromium:yttrium–scandium–galliumgarnet laser and acid etching on shear bond strengths of a dualcure resin cement to enamel. Lasers Med Sci. 2011;26:13–9. Berk N, Bas¸ aran G, Ozer T. Comparison of sandblasting, laser irradiation, and conventional acid etching for orthodontic bonding of molar tubes. Eur J Orthod. 2008;30:183–9. Borsatto MC, Corona SA, Ramos RP, et al. Microleakage at sealant/ enamel interface of primary teeth: effect of Er:YAG laser ablation of pits and fissures. J Dent Child (Chic). 2004;71:143–7. Borsatto MC, Corona SA, de Arau´jo FP, et al. Effect of Er:YAG laser on tensile bond strength of sealants in primary teeth. J Dent Child (Chic). 2007;74:104–8. Burnett LH Jr, Shinkai RS, Eduardo Cde P. Tensile bond strength of a one-bottle adhesive system to indirect composites treated with Er:YAG laser, air abrasion, or fluoridric acid. Photomed Laser Surg. 2004;22:351–6. De Menezes Oliveira MA, Torres CP, Gomes-Silva JM, et al. Microstructure and mineral composition of dental enamel of permanent and deciduous teeth. Microsc Res Tech. 2010;2010(73):572–7. De Munck J, Van Meerbeek B, Yudhira R, Lambrechts P, Vanherle G. Micro-tensile bond strength of two adhesives to Erbium:YAG-lased vs. bur-cut enamel and dentin. Eur J Oral Sci. 2002;110:322–9. Firat E, Gurgan S, Gutknecht N. Microtensile bond strength of an etch-and-rinse adhesive to enamel and dentin after Er:YAG laser pretreatment with different pulse durations. Lasers Med Sci. 2012;27:15–21. Gonc¸alves M, Corona SA, Pe´cora JD, Dibb RG. Influence of the frequency of Er:YAG laser on the bond strength of dental enamel. J Clin Laser Med Surg. 2003;21:105–8. Hossain M, Nakamura Y, Yamada Y, Murakami Y, Matsumoto K. Microleakage of composite resin restoration in cavities prepared by Er, Cr:YSGG laser irradiation and etched bur cavities in primary teeth. J Clin Pediatr Dent. 2002;26:263–8. Hosseini MH, Namvar F, Chalipa J, et al. Comparison of shear bond strength of orthodontic brackets bonded to enamel prepared By Er:YAG Laser and conventional acid-etching. J Dent (Tehran). 2012;9:20–6.
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Eur Arch Paediatr Dent Jaberi Ansari Z, Fekrazad R, Feizi S, et al. The effect of an Er, Cr:YSGG laser on the micro-shear bond strength of composite to the enamel and dentin of human permanent teeth. Lasers Med Sci. 2012;2012(27):761–5. Kohara EK, Hossain M, Kimura Y, et al. Morphological and microleakage studies of the cavities prepared by Er:YAG laser irradiation in primary teeth. J Clin Laser Med Surg. 2002;20:141–7. Krifka S, Bo¨rzso¨nyi A, Koch A, et al. Bond strength of adhesive systems to dentin and enamel–human vs bovine primary teeth in vitro. Dent Mater. 2008;24:888–94. Krishnan K, Kumaran NK, Iyer VH, Rajasigamani K. Laser etched vs conventional etched enamel: effect on shear bond strength of orthodontic brackets. Int J Laser Dent. 2013;3:1–6. Lorenzo MC, Portillo M, Albaladejo A, et al. Effect of ultrashort laser microstructuring of enamel and dentin surfaces on bond strengths in orthodontics and conservative dentistry. Photonics Laser Med. 2012;1:171–82. Nordenvall KJ, Bra¨nnstro¨m M, Malmgren O. Etching of deciduous teeth and young and old permanent teeth a comparison between 15 and 60 seconds of etching. Am J Orthod. 1980;78:99–108. Obeidi A, Liu PR, Ramp LC, Beck P, Gutknecht N. Acid-etch interval and shear bond strength of Er, Cr:YSGG laser-prepared enamel and dentin. Lasers Med Sci. 2010;25:363–9. Olivi G, Genovese MD. Laser restorative dentistry in children and adolescents. Eur Arch Paediatr Dent. 2011;12:68–78. Sag˘ır S, Usumez A, Ademci E, Usumez S. Effect of enamel laser irradiation at different pulse settings on shear bond strength of orthodontic brackets. Angle Orthod. 2013;83:973–80.
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Sasaki LH, Lobo PD, Moriyama Y, et al. Tensile bond strength and SEM analysis of enamel etched with Er:YAG laser and phosphoric acid: a comparative study in vitro. Braz Dent J. 2008;19:57–61. Soncini JA, Maserejian NN, Trachtenberg F, Tavares M, Hayes C. The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth: findings from the New England Children’s Amalgam Trial. J Am Dent Assoc. 2007;138:763–72. Sungurtekin E, Oztas¸ N. The effect of erbium, chromium:yttrium– scandium–gallium-garnet laser etching on marginal integrity of a resin-based fissure sealant in primary teeth. Lasers Med Sci. 2010;25:841–7. Us¸ u¨mez S, Orhan M, Us¸ u¨mez A. Laser etching of enamel for direct bonding with an Er, Cr:YSGG hydrokinetic laser system. Am J Orthod Dentofacial Orthop. 2002;122:649–56. Wanderley RL, Monghini EM, Pecora JD, Palma-Dibb RG, Borsatto MC. Shear bond strength to enamel of primary teeth irradiated with varying Er:YAG laser energies and SEM examination of the surface morphology: an in vitro study. Photomed Laser Surg. 2005;23:260–7. Wen X, Zhang L, Liu R, et al. Effects of pulsed Nd:YAG laser on tensile bond strength and caries resistance of human enamel. Oper Dent. 2014;39:273–82. Yamada Y, Hossain M, Nakamura Y, Murakami Y, Matsumoto K. Microleakage of composite resin restoration in cavities prepared by Er:YAG laser irradiation in primary teeth. Eur J Paediatr Dent. 2002;3:39–45.
ORIGINAL SCIENTIFIC ARTICLE
Comparison of microtensile bond strength of a resin composite to enamel conditioned by acid etching and Er,Cr:YSGG laser in human primary teeth B. Malekafzali • R. Fekrazad • A. Mirfasihi S. Saedi
•
Received: 15 June 2014 / Accepted: 5 September 2014 Ó European Academy of Paediatric Dentistry 2014
Abstract Aim This study was designed to compare the bond strength of composite resin restorations on the buccal surface of primary human canine after conditioning by conventional acid etching and Er,Cr:YSGG laser. Methods Twenty sound primary canines were cut buccolingually into two halves and each half was randomly placed in Er,Cr:YSGG laser or acid etch group. The samples in the acid etch group were etched with 37 % phosphoric acid for 30 s. The samples in the laser group were prepared by Er,Cr:YSGG laser. The G6-Tips and 600 lm diameter were used with a 1.5 W of power output, pulse duration of 140 ls and repetition rate of 20 Hz. The bonding agent was applied on the buccal surface of each sample and layers of resin composite were placed. The samples’ bond strengths were evaluated by a microtensile test instrument. Results The mean of microtensile bond strength was 18.55 ± 6.41 in the laser group and 24.62 ± 5.56 in acid etch group. Microtensile bond strength achieved by laser conditioning was significantly lower than microtensile bond strength achieved by the conventional acid etching. Statistics To compare the results between the acid etch and B. Malekafzali Department of Paediatric Dentistry, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran R. Fekrazad Laser Research Center in Medical Sciences (LRCMS), Periodontal Department, Dental Faculty, AJA University of Medical Sciences, Tehran, Iran A. Mirfasihi S. Saedi (&) Dental School, Shahid Beheshti University of Medical Sciences, Daneshjou Blv. Evin St, PO 1983969411 Tehran, Iran e-mail: [email protected]
laser group, the paired t test was performed (p value \ 0.001). Conclusion Conditioning enamel in primary teeth by Er,Cr:YSGG laser, cannot be used as an alternative method for acid etching and cannot substitute this conventional method. Keywords Er,Cr:YSGG laser Microtensile bond strength Enamel conditioning Primary tooth
Introduction Recently, adhesive resin composites have become an important material of choice in the restoration of primary teeth as well as permanent teeth (Krifka et al. 2008). Toothcoloured composite resins are aesthetic and the cavity preparation is a non-invasive procedure to the tooth structures (Burnett 2004; Soncini et al. 2007). The adhesion of resin to enamel is based on micromechanical retention to roughened conditioned surfaces (Jaberi Ansari et al. 2012). Since the publication of Bunocuore’s report, acid etching has been the standard protocol for conditioning the enamel (Obeidi et al. 2010; Bas¸ aran et al. 2011; Gonc¸alves et al. 2003). Conditioning the enamel for achieving a strong bond between the adhesive resin and tooth substrate is an important factor to avoid risk of marginal microleakage and pulpal inflammation responses following polymerisation shrinkage of the composite and it increases the restoration durability (Sungurtekin and Oztas 2010; Sasaki et al. 2008; Jaberi Ansari et al. 2012). The structural differences between primary and permanent teeth, such as more frequent occurrence of thicker layers of prismless enamel in primary teeth, are believed to affect the resin retention and etching efficiency in primary
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teeth (Agostini et al. 2001; Nordenvall et al. 1980). Decalcifying the enamel leaves the decalcified sites susceptible to acid attack and reduces the caries resistance (Wen et al. 2014; Sagir et al. 2013; Sungurtekin and Oztas 2010; Firat et al. 2012). Concerning the fact that primary teeth have lower content of calcium phosphate than permanent teeth, resulting in a lower degree of mineralisation, primary teeth are more susceptible to dissolution (De Menezes Oliveira et al. 2010). These issues have led researchers to study alternative methods in conditioning the enamel. Laser, as an alternative method for conventional acid etching, is painless and it produces less noise and vibration, which provides the patient with more comfort (Sungurtekin and Oztas 2010; Us¸ u¨mez et al. 2002; Lorenzo et al. 2012). It has been reported that laser treatment modifies the calcium-to-phosphate ratio and reduces the carbonate-tophosphate ratio as well. As a result, the surface etched by laser is more stable and less acid soluble (Sungurtekin and Oztas 2010; Us¸ u¨mez et al. 2002). The bactericidal effect of laser irradiation is also known as an advantage of using lasers to conditioning dental hard tissues (Lorenzo et al. 2012). Erbium lasers are high output lasers, consisting of Er:Yag and Er,Cr:YSGG which are used for conditioning dental hard tissues without damaging the pulp (Bas¸ aran et al. 2011). The investigators have reported rough and micro-irregular surfaces similar to acid-etched ones after conditioning with Erbium lasers (Us¸ u¨mez et al. 2002). Erbium lasers ablate the enamel via a thermomechanical procedure, by emitting the wavelength of 2.6–3 lm, which is the peak wavelength of absorption for water and hydroxyapatite (Berk et al. 2008). The energy absorption results in the evaporation of water, the important component of tooth tissues. The water vapours trapped in hydroxyapatite crystals produce microexplosions and tiny particles from the surface will be removed and yield a rough and uneven surface ideal for adhesion (Obeidi et al. 2010; Sagir et al. 2013). The energy level required for this thermomechanical ablation process in primary enamel may be influenced according to the different composition and structure of primary and permanent enamel, mainly due to the higher content of water in primary enamel (Olivi and Genovese 2011; Al-Batayneh et al. 2014). Erbium lasers in adhesive dentistry were mainly operated in cavity preparation (Hossain et al. 2002; Kohara et al. 2002; Al-Batayneh et al. 2014; Yamada et al. 2002) and conditioning of occlusal pit and fissures for application of fissure sealants (Borsatto et al. 2004, 2007; Sungurtekin and Oztas 2010) and there are limited studies concentrating on laser conditioning of enamel for composite resin restorations in primary teeth (Wanderley et al. 2005). In addition, these studies reported controversial results concerning
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microleakage and bond strength of resins to laser-prepared enamel in primary teeth. Therefore, the following study was designed to compare the microtensile bond strength of adhesive resin composite restorations to buccal surfaces of primary canines conditioned by 37 % phosphoric acid etching or Er,Cr:YSGG laser irradiation.
Materials and methods Ethical approval Ethical approval for this study was obtained from the ‘‘Institutional Ethical Committee’’ of Shahid Beheshti Dental Research Center, Tehran, Iran. Cases of primary canine extraction for orthodontic reasons were selected and parents were informed about the research procedure. Written consents were obtained. Sample preparation Twenty sound primary canines extracted for orthodontic reasons were rinsed and cleansed from blood and soft tissues. The samples were disinfected in 0.5 % chloramines T solution for one week (Jaberi Ansari et al. 2012). The teeth were stored in distilled water and the water content was changed weekly to prevent further contaminations (Berk et al. 2008). The samples were cut buccolingually into two equal halves with a thin diamond bur. The halves were centrically embedded in acrylic resin blocks. The groups designed in this study were Group 1: Conditioned with 37 % phosphoric acid gel (ScotchbondTM etchant delivery system, 3 M ESPE, St Paul, USA) for 30 s. Group 2: Conditioned by Er,Cr:YSGG laser (Waterlase, Biolase Technology Inc, San Clemente, CA, USA), G6Tips with 600 lm diameter with 55 % water and 65 % air spray, water spray 12 ml/min, wavelength 2,780 nm, pulse duration 140 ls, power 1.5 watt, energy 75 mJ/pulse, repetition rate 20 Hz, total energy delivered 15 J, speed of movement 1 mm/s. Each half-tooth sample was randomly placed in one specific group and the second half of the samples was placed in the other group to have 20 study samples in each group. In Group 1, the acid was applied on each tooth surface for 30 s and washed with water spray for 20 s at a distance of 1 cm. The teeth were dried with air to observe the chalky white enamel. In group B, 3 9 3 mm2 of enamel was irradiated for 10 s at a distance of 1–2 mm in vertical
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and horizontal patterns to establish an even irradiation of the surface until chalky white enamel was seen. After etching each sample, the bonding agent (Single Bond, 3 M ESPE Dental Products, USA) was applied on the plastic Nelaton matrix and light cured for 20 s. The resin composite Z100 (3 M ESPE, St Paul, USA) was placed in the Nelaton matrix in 2 mm layers and each layer was cured with LED curing light device (Mectron, Starlight pro GAC, Italy) for 40 s, at a distance of 2 mm, with the light intensity of 300 W/cm2, which was checked previously by radiometry.
Table 1 Descriptive statistical values of lTBS (MPa) Mean
Standard deviation
Median
Min
Max
Group A
24.62
5.56
25.05
14.43
33.97
Group B
18.55
6.41
17.54
10.75
32.69
Bond strength test A predictable and standardised test, micro-tensile bond strength (lTBS) test was used in this study to compare the tensile bond strength in laser and acid etch group. After the composite was cured, the matrix was separated with a surgical blade. The samples in both groups were sectioned by Accustom-50 (Struers, Denmark) in the proper dimensions for Microtensile Tester instrument (Bisco, USA). The length and width of each section were measured by a digital calliper and the bonding area (A) was derived by multiplying the width and length of each sample. The tensile bond strength test was performed on the samples by Microtensile Tester Instrument (Bisco, USA). The force applied at the fracture point(F) was recorded for each sample and inserting it in the following formula the microtensile bond strength (P) of each sample was derived: PðMPaÞ ¼
FðNÞ : Aðmm2 Þ
Statistical analysis All the values were calculated as mean ± standard deviation using SPSS software version 17.0 (SPSS Inc, Chicago, USA). The Paired t test was used to compare the results of lTBS in group 1 with the results in group 2.
Results Table 1 presents the descriptive statistical values of lTBS in both groups. The mean of lTBS in the acid etch group was 24.62 MPa with the standard deviation of 5.56. The maximum lTBS in this group was 33.97 MPa and the minimum lTBS was 14.43 MPa. In the laser group, the mean of lTBS values obtained was 18.55 MPa with the standard deviation of 6.41. The maximum lTBS reported in this group was 32.69 MPa and the minimum lTBS in this group was 10.75 MPa.
Fig. 1 Comparison of lTBS in laser and acid etch group
The Paired t test used for comparison of lTBS values between two groups showed a significant difference between the acid etch and laser group (p value \ 0.0001). The lTBS values in the laser group were significantly lower than the acid etch group with a greater standard deviation. Figure 1 compares the bond strength obtained in both groups and reveals the higher values in acid etch group. The distribution of lTBS in both groups are demonstrated in Fig. 2. Comparing these figures reveals that higher bond strengths are more frequent in the acid etch group.
Discussion The studies investigating the efficiency of lasers in adhesive dentistry concentrate on microleakage and bond strength tests (Olivi and Genovese 2011). To evaluate laser efficiency in adhesive dentistry cavity preparations and occlusal pit and fissure conditioning were performed on primary teeth. In addition, as far as we are aware the bond strength of composite resin restoration to primary enamel was evaluated in one study (Wanderley et al. 2005). The microleakage of composite resin restorations in cavities prepared by laser was compared to acid-etched bur cut cavities (Hossain et al. 2002; Kohara et al. 2002; Yamada et al. 2002; Al-Batayneh et al. 2014). Other experiments evaluated the bond strength and microleakage of fissure sealants applied in occlusal pits and fissures after laser treatment in primary molars (Borsatto et al. 2004, 2007;
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Fig. 2 Distribution of lTBS in acid etch group
Sungurtekin and Oztas, 2010). There are confusing reports on the efficiency of lasers. Whilst some of these studies reported favourable results (Hossain et al. 2002; Kohara et al. 2002; Yamada et al. 2002; Wanderley et al. 2005; AlBatayneh et al. 2014), the other studies reported lower bond strengths (Borsatto et al. 2007) and higher scores of microleakage (Borsatto et al. 2004; Sungurtekin and Oztas 2010) when using lasers. Wanderley and colleagues (2005) reported a lower shear bond strength of composite resin to acid-etched enamel compared to bonding of composite resins to enamel conditioned by Er:YAG laser prior to acid etching when 60 mJ/2 Hz and 80 mJ/2 Hz laser irradiations were used. However, when pretreating the enamel with 100 mJ/2 Hz, no significant difference was reported. Sungurtekin and Oztas (2010) performed a microleakage test to evaluate the marginal integrity of fissure sealants in primary molars. Acid etching was compared to Er,Cr:YSGG laser irradiation in this study. The parameters of laser were set to 20 Hz, 140–200 ls and 2.5 or 3.5 W according to the study group. The results of this study revealed a lower microleakage in acid etch group than laser conditioning with 2.5 and 3.5 W power. Borsatto et al. (2004, 2007) reported higher tensile bond strength of fissure sealant in primary teeth after conditioning enamel with both acid etching and Er:YAG laser (Defocused mode, Repetition Rate: 2 Hz, 1.5 ml/min). The lowest bond strength was reported when conditioning enamel with laser irradiation. In a second study by the same authors, the microleakage of fissure sealants followed by Er:YAG laser conditioning (Wavelength 2.9 lm,
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Energy 120 mJ, Repetition Rate 4 Hz, water spray 5 ml/ min) and acid etching were compared and it was demonstrated that acid etching prior to laser must not be eliminated. The experiments assessing tensile and microtensile bond strengths in permanent teeth mainly reported lower bond strengths in laser groups. Firat et al. (2012) evaluated the microtensile bond strength of composite restorations in human permanent molar after applying different pulse durations of Er:YAG laser alone and in combination with acid etching and concluded that acid etching improved the bond strength. In another study comparing laser cut and bur cut enamel and dentine in permanent molars, De Munck and colleagues (2002) declared that microtensile bond strength of a total etch adhesive to enamel prepared by Er:YAG laser was improved after acid etching. An increase in tensile bond strength was also reported by Sasaki et al. (2008) when using the combination of acid etching and Er:YAG in third human molars. The lowest tensile bond strength was reported for the laser group in this study. Gonc¸alves et al. (2003) also declared that using Er:YAG laser with 80 mJ associated with acid etching at 1, 2, 3 and 4 Hz frequencies did not improve the tensile bond strength in permanent teeth. The results presented herein primary enamel conditioning with laser are in accordance with these studies. Despite the results of the previous studies, some studies on the shear bond strength of orthodontic brackets have reported different results. Hosseini et al. (2012) indicated higher shear bond strengths of brackets to enamel in premolars when using Er:YAG with 1 and 1.5 W power than acid etching. Basaran et al. (2007) also reported that the mean shear bond strength of orthodontic brackets, when enamel is conditioned by 1 and 2 W Er,Cr:YSGG laser irradiation, is comparable to acid etching. Comparing the shear bond strength of a dual-cure resin composite with different power outputs of Er,Cr:YSGG, Bas¸ aran et al. (2011) reported comparable results to acid etching when using 1.5 and 1.75 W laser irradiation for 15 s in permanent incisors. In addition, Sag˘ir et al. (2013) showed that Er:Yag laser irradiation of premolars with medium-short pulse mode and quantum-square pulse mode can be used as an alternative to acid etching by measuring the shear bond strength. According to Olivi and Genovese (2011), repetition rate of 10–20–50 Hz, power output of 0.65–3.7 W and energy level of 65–75 mJ are recommended parameters for enamel conditioning before acid etching in primary teeth using Er,Cr:YSGG laser. Er,Cr:YSGG laser used in the current study is proven to have no thermal effects on the pulpal tissue and is approved by Food and Drug Administration (FDA). The parameters used in this study (power output of 1.5 W and 75 mJ/pulse, pulse duration of 140 ls and the
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repetition rate of 20 Hz) were all within the recommended range for enamel conditioning. The controversial results of laser studies might be due to changes of parameters in laser irradiation. The power outputs and emission modes with different wavelengths, repetition rates and pulse durations might affect the laser treated areas. This may result in various etching patterns and bond strengths (Berk et al. 2008; Firat et al. 2012; Wen et al. 2014). Er,Cr:YSGG laser can transfer a mean power output varying from 0 to 6 W. The high output irradiations of 2.5–6 are used for cutting enamel. Lower outputs are used for etching enamel (Berk et al. 2008). SEM evaluations of enamel after applying different power outputs have also revealed various etching patterns. For instance, during the SEM analysis of samples prepared by 1.5 W power Er,Cr:YSGG laser in permanent enamel a type I etching pattern was obtained, whilst type III etching pattern was obtained using 2 W power in Berk’s study (Berk et al. 2008). Berks et al. (2008) evaluation of different power outputs of Er,Cr:YSSG on shear bond strength of enamel in permanent molars revealed that the application of 1.5 and 2 W power outputs can be an alternative method for acid etching. Despite these results on shear bond strength, the laser etching with 1.5 W power in this study showed lower microtensile bond strength of laser-etched samples than acid-etched samples. Due to the higher content of water, the primary enamel conditioning is expected to require lower energy than permanent teeth (Al-Batayneh et al. 2014). However, the results of our study using 1.5 W power output setting and Sungurtekin’s study using 2.5 and 3.5 W power outputs of Er,Cr:YSGG laser were not desirable (Sungurtekin and Oztas 2010), despite the desirable results of the study by Berk et al. (2008) in permanent teeth with 1.5 and 2 W power outputs. As Sungurtekin and Oztas (2010) stated that microleakage scores in fissure sealants in conditioned primary enamel after Er,Cr:YSGG laser irradiation with 2.5 and 3.5 W power and repetition rate of 20 Hz are higher than fissure sealants placed in acid-etched enamel and concluded that laser irradiation cannot eliminate acid etching. Moreover, Krishnan et al. (2013) revealed that the shear bond strength after application of 2 W/20 Hz Er,Cr:YSGG laser irradiation was comparable to the shear bond strength after conventional acid etching in premolars. It also revealed that increasing the frequency from 10 to 20 Hz results in higher shear bond strengths with the same power output of the device (Krishnan et al. 2013).
Conclusion Microtensile bond strength values were significantly lower in a laser group than an acid etch group and the values were
not in the acceptable range for clinical application of laser. Therefore, according to results of the current study, laser etching cannot substitute the application of acid for obtaining required bond strength of resin to enamel of primary teeth. Acknowledgement This manuscript was prepared based on a postdoctoral thesis (code number: 598), in Pediatric Department, Dental School of Shahid Beheshti University of Medical Sciences under supervision of Prof. Beheshteh Malekafzali.
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