MICROSCOPY RESEARCH AND TECHNIQUE 77:779–784 (2014)
Micromorphology Analysis and Bond Strength of Two Adhesives to Er,Cr:YSGG Laser-Prepared vs. Bur-Prepared Fluorosed Enamel FERESHTEH SHAFIEI,1* ZAHRA JOWKAR,1 REZA FEKRAZAD,2 AND ABOLFAZL KHALAFI-NEZHAD3 1
Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran Dental Faculty, Tehran University of Medical Sciences, Laser Research Center in Medical Sciences (LRCMS), AJA University of Medical Sciences-Laser Research Center in Dentistry (LRCD), Tehran, Iran 3 Department of Internal Medicine, Shiraz University of Medical Sciences, Shiraz, Iran 2
KEY WORDS
acid etching; bond strength; Er,Cr:YSGG laser; fluorosed enamel; scanning electron microscopy
ABSTRACT Preservation of enamel during composite veneer restorations of fluorosed teeth could be achieved by conservative preparation with Erbium lasers. This study evaluated the effect of fluorosed enamel preparation with Er,Cr:YSGG vs. conventional diamond bur on the micromorphology and bond strength of a self-etch and an etch-and-rinse adhesives. Er,Cr:YSGG laser or diamond bur preparation was performed on the flattened midbuccal surfaces of 70 extracted human premolars with moderate fluorosis (according to Thylstrup and Fejerskov index, TFI 5 4–6). Adper Single Bond (SB) with acid etching for 20 or 40 s and Clearfil SE Bond (SEB) alone or with additional etching was applied in four laser groups. The same adhesive procedures were used in three bur groups except for 40 s of etching along with SB. After restoration, microshear bond strength was measured (MPa). Data were analyzed using ANOVA and Tamhane tests (a 5 0.05). Six additional specimens were differently prepared and conditioned for scanning electron microscopy evaluation. The highest and lowest bond strengths were obtained for bur-prepared/SB (39.5) and laser-prepared/SEB (16.9), respectively, with a significant difference (P 5 0.001). The different adhesive procedures used associated to two adhesives exhibited insignificantly lower bonding in laser-prepared groups compared to bur-prepared ones (P > 0.05), with the exception of additional etching/SEB, which bonded significantly higher to bur-prepared (36.4) than to laser-prepared enamel (18.7, P 5 0.04). Morphological analyses revealed a delicate etch pattern with exposed enamel prisms on laser-prepared fluorosed enamel after acid etching and less microretentive pattern after self-etching primer. The etch-and-rinse adhesive was preferred in the laser-prepared fluorosed enamel in terms of bonding performance. Microsc. Res. Tech. 77:779–784, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Despite beneficial preventive effects of fluoride on dental caries, its systemic excessive exposure during tooth development can lead to a kind of malformation named fluorosis (Aoba et al., 2002; Robinson et al., 2004). Dental fluorosis has a relatively high prevalence in many areas of the world. Epidemiological studies have reported an increase in the prevalence of fluorosis ranging (between 7.7 and 80.9% in high fluoride areas and between 2.9 and 42% in low fluoride areas (Mascarenhas et al., 2000; Pendrys, 2000).The fluorotic enamel reveals two layers: an acid resistant, highly hypermineralized surface layer and porous hypomineralized subsurface layer (Aoba et al., 2002).The pores are filled with water and enamel secretory proteins are retained because of high levels of fluoride on ameloblasts (Robinson et al., 2004; DenBesten and Thariani, 1992). Fluorosis severity has been classified based on the Thylstrup and Fejerskov index (score 0–9 for normal, mild, moderate, and severe fluorosis). The clinical appearance of fluorosis is correlated to the C V
2014 WILEY PERIODICALS, INC.
histopathologic changes in the enamel by this index (Thylstrup and Fejerskov, 1978).The various pathological changes depending on fluorosis severity are clinically accompanied with unaesthetic appearance of the fluorosed teeth or chipped enamel surface from incisal edges or cusp tips because of overextension of subsurface hypomineralization (DenBesten and Thariani, 1992; Vieira et al., 1978). Therefore, the fluorosed teeth usually need to be restored with tooth-colored materials for esthetic or functional reasons. Moderately fluorosed enamel has been shown to be caries resistant while mild and moderately fluorosed dentin is caries susceptible (Waidyasekera et al., *Correspondence to: Fereshteh Shafiei; School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. E-mail: [email protected] Received 9 February 2014; accepted in revised form 29 June 2014 REVIEW EDITOR: Dr. Chuanbin Mao Contract grant sponsor: Shiraz University of Medical Sciences; Contract grant number: 91–4700. DOI 10.1002/jemt.22399 Published online 7 July 2014 in Wiley Online Library (wileyonlinelibrary.com).
780 Material/manufacturer/batch # Adper Single Bond (Two-step etch and rinse adhesive)/ 3M ESPE, St Paul, MN, USA/N330309 Clearfil SE Bond (Two step- self etch adhesive)/ Kuraray, Osaka, Japan/01129A, 01692A
Filtek Z250 Composite resin/ 3M ESPE, St Paul, MN, USA/N386458
F. SHAFIEI ET AL. TABLE 1. The materials used in this study Composition
Application mode
Adhesive: Bis-GMA, HEMA, poly-alkenoic copolymer, water, ethanol.
Apply two coats of adhesive; gentle air-dry the surface for 5 s and light cure for 10 s.
Primer: MDP, HEMA, water, hydrophilic dimethacrylate, camphoroquinone, p-toluidine Adhesive: Bis-GMA, MDP, HEMA, hydrophobic dimethacrylate, camphoroquinone, p-toluidine, silanated colloidal silica Resin phase: Bis-GMA, UDMA, Bis-EMA, TEGDMA Filler: Zirconia, silica (0.01–3.5 mm, 75 wt%)
Apply primer and leave for 20s; dry thoroughly with mild air flow; apply bond; gentle air flow; light polymerize for 10 s
2007). So, preservation of the enamel during preparation is of major importance for restoration longevity of the teeth. Recently, laser technology has been introduced as an alternative to mechanical rotary instrument for precise and conservative tooth preparation (De Munck et al., 2002; Harashima et al., 2005). Erbium lasers especially Er,Cr:YSGG could be considered the most efficient, suitable, and safe device for esthetic restorations of preparation restricted to enamel. This laser preparation is accompanied by a water mist spray that may minimize temperatureinduced structural and chemical alterations of the irradiated enamel (Bachmann et al., 2005; Straßl et al., 2004). Surface roughening without the smear layer and exposed enamel rods on the irradiated surface seems to be receptive for adhesion (De Munck et al., 2002). Effective acid-etched enamel bonding guarantees the stability of adhesive restorations (Swift et al., 1995). Nevertheless, the etching efficacy of the acid etchant is affected by chemical composition of the enamel and etching time. Increased resistance to acid etching of the erbium-lased enamel was demonstrated because of the formation of less soluble compounds, fusion and recrystallization areas (Cardoso et al., 2008; Chimello-Sousa et al., 2006; De Munck et al., 2002). Some authors have suggested mechanical or chemical (longer acid etching) removal of this layer (Obeidi et al., 2009). On the other hand, adhesive bonding to the fluorosed enamel has been found to be rul et al., 2009; Thylstrup and problematic (Ertug Fejerskov, 1978). Different results have been reported regarding the bonding effectiveness of self-etch and etch-and-rinse adhesives to the lased-enamel (Cardoso et al., 2008; Chimello-Sousa et al., 2006; De Munck et al., 2002; Obeidi et al., 2009) and fluorosed enamel rul et al., 2009; Shida et al., 2009; Torres(Ertug Gallegos et al., 2012). However, to date there is no published study about adhesive bonding efficacy following laser preparation of the fluorosed teeth. Therefore, this in vitro study was designed to evaluate the bonding efficacy of two contemporary adhesives with and without an additional etching step/time to laserprepared fluorotic enamel using microshear bond strength test. MATERIALS AND METHODS Experimental caries-free extracted premolar teeth used in this study were collected from 20 to 35 year old patients living in fluorosis endemic areas in Iran with moderate fluorosis (TFI 5 4 to 6) (Thylstrup and Fejerskov, 1978). The patients signed informed consent
Filtek Z250 composite resin was applied in 0.5-mm layer and light cured for 40 s
form which was approved by the local ethics committee for research. The teeth were stored in 0.5% chloramine solution at 4 C and used within three months after extraction. After removing the roots from the crowns, 0.5 mm depth orientation grooves were prepared on the midbuccal surfaces of the teeth. They were then mounted in an acrylic resin with their buccal surfaces upward and parallel to the base of the resin block. The buccal surfaces were grounded using 320-grit silicon carbide papers under water cooling in order to obtain a standardized flat enamel surface. The absence of exposed dentin on the enamel surfaces was checked using a stereomicroscope (Carl Ziess, Oberkochen, Germany). The bonded area was defined using an adhesive tape with a punched hole over the center of flattened surface. Seventy specimens were randomly divided into seven groups according to the adhesive protocol and preparation type. For the laser-prepared groups (1–4), an Er,Cr:YSGG laser (Waterlase, Biolase Technology, San Clemente, CA, USA) was used with the following parameters: wavelength of 2.78 mm, pulse duration of 140 ms, repetition rate of 20 Hz, G-6 tip with 600 mm in diameter, power of 5 W, energy per pulse of 275 mJ, 80% water, and 90% air spray. The specimens were irradiated at a 90 angle in noncontact and focused mode with a distance of 1 mm away from the laser tip for 7 s in a scanning movement on a surface area with 2 mm diameter. An even ablated surface was obtained. In groups 1 and 2, the enamel surfaces were etched with 37% phosphoric acid (3M ESPE, St Paul, MN, USA) for 20 and 40 s, respectively. After rinsing and gently air drying for 5 s, Adper Single Bond (SB,3M ESPE) was applied according to manufacturer ’s instructions (Table 1). In group 3, Clearfil SE Bond (SEB, Kuraray, Okayama, Japan) was applied (Table 1). In group 4, the surfaces were acid etched for 30 s, rinsed, and then dried for 30s. Then, Clearfil SE Bond was used similar to group 3. In burprepared groups (5–7), the enamel surface was flattened by medium-grit fissure diamond bur (#10061, Dia. Tessin, Gordevio, Switzerland) under air water spray. The bur was replaced for every five uses. The adhesive procedures were the same as that described for groups 1, 3 and 4, respectively. Prior to light curing of the adhesives, translucent polyvinyl chloride microtubes (0.7 mm in diameter and 0.5 mm in height) were placed on the bonding surfaces and subsequently filled with Z250 composite (3M ESPE, St Paul, MN, USA). Light curing was done using a light curing unit (VIP Junior, Bisco, Schaumburg, IL, USA) at 600 mW/cm2. The specimens were stored in distilled water at 37 C Microscopy Research and Technique
MICROMORPHOLOGY ANALYSIS AND BOND STRENGTH OF TWO ADHESIVES
781
TABLE 2. Mean microshear bond strength (MPa) to fluorosed enamel (n 5 10) 6 standard deviation and failure mode Group 1 2 3 4 5 6 7
Enamel preparation/ adhesive procedure
Mean 6 SD (MPa)
Failure mode (A/C/M)
Er,Cr:YSGG/20s E1SB Er,Cr:YSGG/40s E1SB Er,Cr:YSGG/SEB Er,Cr:YSGG/30s E1SEB Bur/20s E1SB Bur/SEB Bur/30s E1SEB
26.3 6 6.7ABC 28.7 6 7.1ABC 16.9 6 4.2B 18.7 6 5.1B 39.5 6 8.8A 31.7 6 9.3AB 36.4 6 9.8.1AC
2/1/7 1/2/7 4/1/5 4/2/4 1/0/9 3/1/6 1/1/8
Data with the same superscript are not statistically significantly different. A, adhesive; C, cohesive; M, mixed; E,: acid etching; SB, adper single bond; SEB, clearfil SE bond.
for 24 hours and then mounted onto a jig attached to a universal testing machine (Instron, Z020. Zwick Roell, Germany). The microshear bond strength was measured at a cross head speed 1 mm/min. The obtained data were statistically analyzed using one-way analysis of variance (ANOVA) and multiple comparisons were performed using Tamhane post-hoc tests (a 5 0.05). The failure mode was determined using a stereomicroscope (Carl Ziess Inc) at 203 magnification according to the following categories: (A) adhesive failure within the adhesive interfacial zone; (B) cohesive in the composite or in enamel; and (C), mixed adhesive failure and cohesive failure. Morphological Evaluation Using Scanning Electron Microscope Six additional specimens were differently prepared and conditioned: bur with etching or self-etching primer, laser with 20 or 40 s etching, self-etching primer, and 30 s etching 1 self-etching primer) in the same manner as that of bonding testing. The specimens were dehydrated, gold sputter coated, and examined under a scanning electron microscope (SEM) (KYKY, EM 3200, China). RESULTS Mean microshear bond strength (mSBS) and standard deviation (MPa) for the seven groups are shown in Table 2. According to the results of ANOVA test, there was a significant difference among the groups (P < 0.001). Despite higher mSBS obtained in the burprepared groups compared to those of laser-prepared ones with two adhesives with and without an additional etching step or time, these differences were not statistically significant (P > 0.05). The additional etching for SEB in two preparation types and an additional etching time for SB in laser groups revealed no effect on mSBS (P 5 1). However, the former in the bur group (group7) had a higher mSBS (36.4) than that in the laser group (18.7, P 5 0.04). Among the groups, the highest mSBS was obtained in group 5 (bur-prepared/ SB, 39.5) that yielded significant differences with group 3 (laser/SEB,16.9) and group 4 (laser/etching1 SEB,18.7) (P 5 0.001 and 0.002, respectively). Fracture analysis revealed that most of the failure (>50%) of all groups were mixed, except for groups 3 and 4 in which 50% or less failures were mixed. SEM images of burprepared fluorosed enamel treated with acid etching and self-etching primer are presented in Figures 1a and 1b. Figures 2a–2d show the laser-prepared Microscopy Research and Technique
Fig. 1. SEM images of bur-prepared fluorosed enamel: (a) acid etched, prominent etch pattern with very rough surface; and (b) treated with self-etching primer, less microretentive surface (35003). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
fluorosed enamel treated with acid etching for 20 and 40 s, self-etching primer, and etching for 30 s 1 selfetching primer, respectively. DISCUSSION With increasing prevalence of fluorosis in many areas of the world and widespread use of laser ablation, achieving high bond strength of adhesive materials on laser-prepared fluorosed enamel is a critical factor in the success of esthetic restorations of the fluorosed teeth. The fluorotic teeth used in this study were premolars obtained from 20 to 40 year old patients living in fluorosis-endemic regions (southern province) in Iran with a prevalence range from 67% to 80% (Ramezani et al., 2004). This specific tooth type and the age group minimized the effect of these factors on the fluoride content and consequent enamel bond strength rul et al., 2009). The (Ateyah and Akpata, 2000; Ertug used teeth classified as TFI score 4–6 (moderate fluorosis) exhibited chalky white appearance and distinct pitting area on the enamel surface. In higher TFI score, considerable parts of the surface enamel are lost (Fejerskov et al., 1990; Torres-Gallegos et al., 2012). In
782
F. SHAFIEI ET AL.
Fig. 2. SEM images of Er,Cr:YSGG-prepared fluorosed enamel: (a) 20 s acid-etched, a delicate etch pattern with rough surface, visible enamel prisms and microcracks between them; (b) 40 s acid-etched, the same appearance of 20 s etching; (c) self-etching primed, a shal-
low etch pattern; and (d) acid-etched and then self-etching primed, a more retentive pattern with longitudinal exposure of enamel prisms and microcracks between them (35003). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
the current study, 0.3 mm of the enamel surface of the fluorosed teeth was removed to simulate clinical condition of tooth preparation for composite veneer restorations. This grinding also provided a flat surface to be bonded on the enamel for shear testing (Ateyah and Akpata, 2000; Ermis et al., 2007). In addition, bond strength measurement of the adhesives to uncut enamel might be difficult because of the weak nature of the fluorosed enamel (Ermis et al., 2007). Microshear bond strength testing used in this study could be more representative of the clinical situation in which composite veneer is bonded on the fluorosed enamel. There is no necessity for specimen preparation, preventing micro-crack formation at the adhesive interface (Shida et al., 2009). Using an ultra-small bonding area could overcome nonuniformity of stress distribution at the interface occurring in conventional shear test. However, the higher bond strength values were obtained (Weerasinghe et al., 2005). As different elastic modulus of composites could influence the bond strength (Shafiei and Memarpour, 2009; Shafiei et al., 2009), the same composite (Z250) was used in all the groups of this study. According to our findings, enamel preparation with laser revealed insignificantly lower result than that of
bur preparation in terms of bond strength for two etchand-rinse and self-etch adhesives. This insignificant difference may indicate that larger sample sizes were required. A number of authors have demonstrated a lower bond strength of some adhesives to the lasednormal enamel compared to the bur-cut one. This reduced strength had been attributed to a more mineralized and stable enamel surface along with fusion and obliterated enamel micropores (Cardoso et al., 2008; Chimello-Sousa et al., 2006; Delfino et al., 2006; De Munck et al., 2002). Nevertheless, these alterations may result in less susceptibility of adhesive interface to hydrolytic degradation (Amaral et al., 2010). In the current study, despite observation of microcrack formation on the lased enamel, a unique and delicate etch pattern was seen in nonmelted etched lased-enamel. This retentive rough surface may explain insignificant reduced bond strength of etch-and-rinse adhesive obtained for the lased group in comparison with the bur group. The resin penetration into the microcrack may reinforce the lased enamel. The positive effect of phosphoric acid etching associated with etch-and-rinse adhesives was confirmed by some authors (De Munck et al., 2002; Dunn et al., 2005; Jaberi Ansari et al., Microscopy Research and Technique
MICROMORPHOLOGY ANALYSIS AND BOND STRENGTH OF TWO ADHESIVES
2012). The lack of significant difference between the bond strength of an etch-and-rinse adhesive to the laser-prepared and bur-prepared normal enamel was previously reported (Amaral et al., 2010; Jaberi Ansari et al., 2012). Obeidi et al. (2009; 2010) demonstrated significant and insignificant improvement of bond strength with increasing etching time to 40 s of the lased-enamel in two recent studies. However, this procedure exhibited no additionally beneficial effect on the fluorosed enamel used in this study. Although some authors have suggested increasing etching time for bonding to fluorosed enamel (AlSugair and Akpata, 1999), others reported no significant difference in the bond strengths to fluorotic and normal enamel with different etching times (Ateyah and Akpata, 2000). A number of authors stated that grinding the enamel surface to flatten the enamel surface for shear testing leads to removal of 200 mm hypermineralized surface layer (Ateyah and Akpata, 2000; Weerasinghe et al., 2005). This surface layer was also removed in all of the enamel specimens used in this study with abrading/grinding. According to De Munck et al., (2002) preparation of a flat surface using laser is almost impossible. Therefore, a standardized flat enamel surface was obtained prior to laser irradiation in all bond strength studies. After the grinding, the enamel structure involved in laser or bur preparation and adhesive bonding could not be determined. A thickness of about 50 mm was reported for the subsurface porous enamel with a TFI score of 4 (Thylstrup and Fejerskov, 1978). In higher scores, this layer extended toward the inner enamel (Aoba et al., 2002). Chemical surface analysis is necessary in this regard. Two adhesives used in this study, SEB and SB, exhibited comparable bond strength on the burprepared fluorosed enamel. This finding is consistent with the previous study (Ermis et al., 2007).This similarity might be attributed to the removal of hypermineralized surface layer on the ground enamel. Especially, enamel grinding might be a critical factor for efficient bonding of mild self-etch adhesives (Ermis et al., 2007). This explanation could be relevant to laser-prepared groups that revealed no significant difference between bonding performance of the two adhesives used. Moreover, although laser preparation compared with the bur one resulted in a lower bonding of SEB to the fluorosed enamel, this difference was not significant. This result is in agreement with those of a previous study (De Munck et al., 2002) and a recent study on normal enamel (Adebayo et al., 2012). However, the significantly lower bond strength of SEB to the lased-normal enamel compared to that of the bur-cut one was found by Cardoso et al. (2008). Despite shallow and less retentive etching pattern created by the mild self-etch adhesive, its MDP content could contribute to the bonding effectiveness of SEB on smear layer-free surface following laser ablation of the enamel (Cardoso et al., 2008). Increased calcium of lased-enamel composition may reinforce the chemical bonding of MDP to the surface calcium (Hossain et al., 2003). In addition to structural alterations of the lased-enamel, the compositional characteristics of adhesives might also play an important role in the enamel bonding ability. Considering low etching Microscopy Research and Technique
783
efficacy of self-etch adhesives and their questionable bonding ability to the enamel, some authors recommended acid etching prior to the adhesives (Rotta et al., 2007; Van Meerbeek et al., 2011). Weerasinghe et al. (2005) reported that an additional acid etching on the ground enamel significantly improved the bond strength of SEB to moderate and severe fluorosed enamel. The results of the present study showed that the additional etching had no significant effect on bonding to laser- and bur-prepared moderate fluorosed enamel. Moreover, the etching associated to SEB resulted in a significantly higher bonding to the burprepared surface than the lased one. Removal of calcium from the etched surface and remaining water and HEMA contents of the primer into deep etched zone may account for the obtained result. Those remaining components may limit the penetration of Bis-GMA and dimethacrylate components of the adhesive part of SEB. It should be taken into account that in addition to the etching potential of self-etch adhesives, cohesive strength of the adhesive layer may be an important factor in the attainment of adequate bond strength to the enamel (Pashley and Tay., 2001). The different results reported in the literature on bonding efficacy of adhesives on laser-irradiated enamel might be attributed to variations in parameter settings of irradiation, laser devices, testing methods, type, and compositions of the adhesive and chemical/ structural composition of the irradiated tissue (normal enamel vs. fluorosed enamel). According to a bond durability study conducted by Amaral et al. (2010), bond strength to the erbium laser-prepared normal enamel was not affected by different periods of water storage and thermocycling. Further studies should investigate long-term bonding stability of different adhesives to the laser-prepared enamel in the fluorosed teeth. Chemical analysis of different layers of the fluorosed enamel could lead to our understanding about the interaction of laser with different compositional layers of the enamel. CONCLUSIONS Within the limitations of the current study, it might be concluded that for two adhesives with or without additional etching step/time, laser preparation of the moderate fluorosed enamel resulted in a lower bond strength compared to that of bur preparation; however, this reduction was not statistically significant. An etch-and-rinse adhesive in the bur group revealed the highest bond strength that was significantly higher than that of the self-etch adhesive (with or without etching) in the laser group. Therefore, an etch-andrinse adhesive (20 or 40 s etching) was preferred in the laser-prepared fluorosed enamel in terms of bond strength. ACKNOWLEDGMENTS This research was supported by the Vice-chancellery for research of Shiraz University of Medical Sciences as a thesis for the MSc degree of Dr Z Jowkar in Operative Dentistry. The authors thank Dr M. Vossoughi from the Dental Research Development Center, for statistical analysis and Dr N. Shokrpour at Centre for Development of Clinical Research of Nemazee Hospital for editorial assistance.
784
F. SHAFIEI ET AL.
REFERENCES Adebayo OA, Burrow MF, Tyas MJ, Palamara J. 2012. Effect of tooth surface preparation on the bonding of self-etching primer adhesives. Oper Dent 37:137–149. Al-Sugair MH, Akpata ES. 1999. Effect of fluorosis on etching of human enamel. J Oral Rehabil 26:521–528. Amaral FL, Colucci V, Souza-Gabriel AE, Chinelatti MA, Palma-Dibb RG, Corona SA. 2010. Bond durability in erbium:yttrium-aluminum-garnet laser-irradiated enamel. Lasers Med Sci 25:155–163. Aoba T, Fejerskov O. 2002. Dental fluorosis: chemistry and biology. Crit Rev Oral Biol Med 13:155–170. Ateyah N, Akpata E. 2000. Factors affecting shear bond strength of composite resin to fluorosed human enamel. Oper Dent 25:216– 222. Bachmann L, Diebolder R, Hibst R, Zezell DM. 2005. Changes in chemical composition and collagen structure of dentine tissue after erbium laser irradiation. Spectrochim Acta A Mol Biomol Spectrosc 61:2634–2639. Cardoso MV, De Munck J, Coutinho E, Ermis RB, Van Landuyt K, de Carvalho RC, Van Meerbeek B. 2008. Influence of Er,Cr:YSGG laser treatment on microtensile bond strength of adhesives to enamel. Oper Dent 33:448–455. Chimello-Sousa DT, de Souza AE, Chinelatti MA, P ecora JD, PalmaDibb RG, Milori Corona SA. 2006. Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel. J Dent 34:245–251. Delfino CS, Souza-Zaroni WC, Corona SA, Palma-Dibb RG. 2006. Microtensile bond strength of composite resin to human enamel prepared using erbium: Yttrium aluminum garnet laser. J Biomed Mater Res A 80:475–479. De Munck J, Van Meerbeek B, Yudhira R, Lambrechts P, Vanherle G. 2002. Micro-tensile bond strength of two adhesives to Erbium: YAG-lased vs. bur-cut enamel and dentin. Eur J Oral Sci 110:322– 329. DenBesten PK, Thariani H. 1992. Biological mechanisms of fluorosis and level and timing of systemic exposure to fluoride with respect to fluorosis. J Dent Res 71:1238–1243. Dunn WJ, Davis JT, Bush AC. 2005. Shear bond strength and SEM evaluation of composite bonded to Er:YAG laser-prepared dentin and enamel. Dent Mater 21:616–624. Ermis RB, De Munck J, Cardoso MV, Coutinho E, Van Landuyt KL, Poitevin A, Lambrechts P, Van Meerbeek B. 2007. Bonding to ground versus unground enamel in fluorosed teeth. Dent Mater 23: 1250–1255. Ertu grul F, T€ urk€ un M, T€ urk€ un LS, Toman M, Cal E. 2009. Bond strength of different dentin bonding systems to fluorotic enamel. J Adhes Dent 11:299–303. Fejerskov O, Manji F, Baelum V. 1990. The nature and mechanisms of dental fluorosis in man. J Dent Res (Spec No):692–700. Harashima T, Kinoshita J, Kimura Y, Brugnera A, Zanin F, Pecora JD, Matsumoto K. 2005. Morphological comparative study on ablation of dental hard tissues at cavity preparation by Er:YAG and Er,Cr:YSGG lasers. Photomed Laser Surg 23:52–55. Hossain M, Nakamura Y, Tamaki Y, Yamada Y, Murakami Y, Matsumoto K. 2003. Atomic analysis and knoop hardness measurement of the cavity floor prepared by Er,Cr:YSGG laser irradiation in vitro. J Oral Rehabil 30:515–521. Jaberi Ansari Z, Fekrazad R, Feizi S, Younessian F, Kalhori KA, Gutknecht N. 2012. 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 27:761–765.
Mascarenhas AK. 2000. Risk factors for dental fluorosis: a review of the recent literature. Pediatr Dent 22:269–277. Obeidi A, McCracken MS, Liu PR, Litaker MS, Beck P, Rahemtulla F. 2009. Enhancement of bonding to enamel and dentin prepared by Er,Cr:YSGG laser. Lasers Surg Med 41:454–462. Obeidi A, Liu PR, Ramp LC, Beck P, Gutknecht N. 2010. Acid-etch interval and shear bond strength of Er,Cr:YSGG laser-prepared enamel and dentin. Lasers Med Sci 25:363–369. Pashley DH, Tay FR. 2001. Aggressiveness of contemporary selfetching adhesives. Part II: etching effects on unground enamel. Dent Mater 17:430–444. Pendrys DG. 2000. Risk of enamel fluorosis in non-fluoridated and optimally fluoridated populations: considerations for the dental professional. J Am Dent Assoc 131:746–755. Ramezani GH, Valaei N, Eikani H. 2004. Prevalence of DMFT and fluorosis in the students of Dayer city (Iran). J Indian Soc Pedod Prev Dent 22:49–53. Robinson C, Connell S, Kirkham J, Brookes SJ, Shore RC, Smith AM. 2004. The effect of fluoride on the developingtooth. Caries Res 38: 268–276. Rotta M, Bresciani P, Moura SK, Grande RH, Hilgert LA, Baratieri LN, Loguercio AD, Reis A. 2007. Effects of phosphoric acid pretreatment and substitution of bonding resin on bonding effectiveness of self-etching systems to enamel. J Adhes Dent 9:537–545. Shafiei F, Memarpour M. 2009. Effect of repeated use on dentin bond strength of two adhesive systems: All-in-one and one-bottle. Indian J Dent Res 20:180–184. Shafiei F, Saffarpour A, Moradmand M, Alavi AA. 2009. Effect of light activation mode on the incompatibility between one-bottle adhesives and light-cured composites: An in vitro shear bond strength study. Oper Dent 34:558–564. Shida K, Kitasako Y, Burrow MF, Tagami J. 2009. Micro-shear bond strengths and etching efficacy of a two-step self-etching adhesive system to fluorosed and non-fluorosed enamel. Eur J Oral Sci 117: 182–186. € Straßl M, Ublacker B, B€ acker A, Beer F, Moritz A, Wintner E. 2004. Comparison of the emission characteristics of three erbium laser systems. A physical case report. J Oral Laser Appl 4:263–270. Swift EJ Jr, Perdig~ ao J, Heymann HO.1995. Bonding to enamel and dentin: a brief history and state of the art. Quintessence Int 26:95– 110. Thylstrup A, Fejerskov O. 1978. Clinical appearance of dental fluorosis in permanent teeth in relation to histologic changes. Community Dent Oral Epidemiol 6:315–328. Torres-Gallegos I, A Martinez-Casta~ non G, Loyola-Rodriguez JP, Pati~ no-Marin N, Encinas A, Ruiz F, Anusavice K. 2012. Effectiveness of bonding resin-based composite to healthy and fluorotic enamel using total-etch and two self-etch adhesive systems. Dent Mater J 31:1021–1027. Van Meerbeek B, Yoshihara K, Yoshida Y, Mine A, De Munck J, Van Landuyt KL. 2011. State of the art of self-etch adhesives. Dent Mater 27:17–28. Vieira AP, Hancock R, Limeback H, Maia R, Grynpas MD. 1978. Is fluoride concentration in dentin and enamel a good indicator of dental fluorosis? J Dent Res 83:76–80. Waidyasekera PG, Nikaido T, Weerasinghe DD, Wettasinghe KA, Tagami J. 2007. Caries susceptibility of human fluorosed enamel and dentine. J Dent 35:343–349. Weerasinghe DS, Nikaido T, Wettasinghe KA, Abayakoon JB, Tagami J. 2005. Micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel. J Dent 33:419–426.
Microscopy Research and Technique
Micromorphology Analysis and Bond Strength of Two Adhesives to Er,Cr:YSGG Laser-Prepared vs. Bur-Prepared Fluorosed Enamel FERESHTEH SHAFIEI,1* ZAHRA JOWKAR,1 REZA FEKRAZAD,2 AND ABOLFAZL KHALAFI-NEZHAD3 1
Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran Dental Faculty, Tehran University of Medical Sciences, Laser Research Center in Medical Sciences (LRCMS), AJA University of Medical Sciences-Laser Research Center in Dentistry (LRCD), Tehran, Iran 3 Department of Internal Medicine, Shiraz University of Medical Sciences, Shiraz, Iran 2
KEY WORDS
acid etching; bond strength; Er,Cr:YSGG laser; fluorosed enamel; scanning electron microscopy
ABSTRACT Preservation of enamel during composite veneer restorations of fluorosed teeth could be achieved by conservative preparation with Erbium lasers. This study evaluated the effect of fluorosed enamel preparation with Er,Cr:YSGG vs. conventional diamond bur on the micromorphology and bond strength of a self-etch and an etch-and-rinse adhesives. Er,Cr:YSGG laser or diamond bur preparation was performed on the flattened midbuccal surfaces of 70 extracted human premolars with moderate fluorosis (according to Thylstrup and Fejerskov index, TFI 5 4–6). Adper Single Bond (SB) with acid etching for 20 or 40 s and Clearfil SE Bond (SEB) alone or with additional etching was applied in four laser groups. The same adhesive procedures were used in three bur groups except for 40 s of etching along with SB. After restoration, microshear bond strength was measured (MPa). Data were analyzed using ANOVA and Tamhane tests (a 5 0.05). Six additional specimens were differently prepared and conditioned for scanning electron microscopy evaluation. The highest and lowest bond strengths were obtained for bur-prepared/SB (39.5) and laser-prepared/SEB (16.9), respectively, with a significant difference (P 5 0.001). The different adhesive procedures used associated to two adhesives exhibited insignificantly lower bonding in laser-prepared groups compared to bur-prepared ones (P > 0.05), with the exception of additional etching/SEB, which bonded significantly higher to bur-prepared (36.4) than to laser-prepared enamel (18.7, P 5 0.04). Morphological analyses revealed a delicate etch pattern with exposed enamel prisms on laser-prepared fluorosed enamel after acid etching and less microretentive pattern after self-etching primer. The etch-and-rinse adhesive was preferred in the laser-prepared fluorosed enamel in terms of bonding performance. Microsc. Res. Tech. 77:779–784, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Despite beneficial preventive effects of fluoride on dental caries, its systemic excessive exposure during tooth development can lead to a kind of malformation named fluorosis (Aoba et al., 2002; Robinson et al., 2004). Dental fluorosis has a relatively high prevalence in many areas of the world. Epidemiological studies have reported an increase in the prevalence of fluorosis ranging (between 7.7 and 80.9% in high fluoride areas and between 2.9 and 42% in low fluoride areas (Mascarenhas et al., 2000; Pendrys, 2000).The fluorotic enamel reveals two layers: an acid resistant, highly hypermineralized surface layer and porous hypomineralized subsurface layer (Aoba et al., 2002).The pores are filled with water and enamel secretory proteins are retained because of high levels of fluoride on ameloblasts (Robinson et al., 2004; DenBesten and Thariani, 1992). Fluorosis severity has been classified based on the Thylstrup and Fejerskov index (score 0–9 for normal, mild, moderate, and severe fluorosis). The clinical appearance of fluorosis is correlated to the C V
2014 WILEY PERIODICALS, INC.
histopathologic changes in the enamel by this index (Thylstrup and Fejerskov, 1978).The various pathological changes depending on fluorosis severity are clinically accompanied with unaesthetic appearance of the fluorosed teeth or chipped enamel surface from incisal edges or cusp tips because of overextension of subsurface hypomineralization (DenBesten and Thariani, 1992; Vieira et al., 1978). Therefore, the fluorosed teeth usually need to be restored with tooth-colored materials for esthetic or functional reasons. Moderately fluorosed enamel has been shown to be caries resistant while mild and moderately fluorosed dentin is caries susceptible (Waidyasekera et al., *Correspondence to: Fereshteh Shafiei; School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. E-mail: [email protected] Received 9 February 2014; accepted in revised form 29 June 2014 REVIEW EDITOR: Dr. Chuanbin Mao Contract grant sponsor: Shiraz University of Medical Sciences; Contract grant number: 91–4700. DOI 10.1002/jemt.22399 Published online 7 July 2014 in Wiley Online Library (wileyonlinelibrary.com).
780 Material/manufacturer/batch # Adper Single Bond (Two-step etch and rinse adhesive)/ 3M ESPE, St Paul, MN, USA/N330309 Clearfil SE Bond (Two step- self etch adhesive)/ Kuraray, Osaka, Japan/01129A, 01692A
Filtek Z250 Composite resin/ 3M ESPE, St Paul, MN, USA/N386458
F. SHAFIEI ET AL. TABLE 1. The materials used in this study Composition
Application mode
Adhesive: Bis-GMA, HEMA, poly-alkenoic copolymer, water, ethanol.
Apply two coats of adhesive; gentle air-dry the surface for 5 s and light cure for 10 s.
Primer: MDP, HEMA, water, hydrophilic dimethacrylate, camphoroquinone, p-toluidine Adhesive: Bis-GMA, MDP, HEMA, hydrophobic dimethacrylate, camphoroquinone, p-toluidine, silanated colloidal silica Resin phase: Bis-GMA, UDMA, Bis-EMA, TEGDMA Filler: Zirconia, silica (0.01–3.5 mm, 75 wt%)
Apply primer and leave for 20s; dry thoroughly with mild air flow; apply bond; gentle air flow; light polymerize for 10 s
2007). So, preservation of the enamel during preparation is of major importance for restoration longevity of the teeth. Recently, laser technology has been introduced as an alternative to mechanical rotary instrument for precise and conservative tooth preparation (De Munck et al., 2002; Harashima et al., 2005). Erbium lasers especially Er,Cr:YSGG could be considered the most efficient, suitable, and safe device for esthetic restorations of preparation restricted to enamel. This laser preparation is accompanied by a water mist spray that may minimize temperatureinduced structural and chemical alterations of the irradiated enamel (Bachmann et al., 2005; Straßl et al., 2004). Surface roughening without the smear layer and exposed enamel rods on the irradiated surface seems to be receptive for adhesion (De Munck et al., 2002). Effective acid-etched enamel bonding guarantees the stability of adhesive restorations (Swift et al., 1995). Nevertheless, the etching efficacy of the acid etchant is affected by chemical composition of the enamel and etching time. Increased resistance to acid etching of the erbium-lased enamel was demonstrated because of the formation of less soluble compounds, fusion and recrystallization areas (Cardoso et al., 2008; Chimello-Sousa et al., 2006; De Munck et al., 2002). Some authors have suggested mechanical or chemical (longer acid etching) removal of this layer (Obeidi et al., 2009). On the other hand, adhesive bonding to the fluorosed enamel has been found to be rul et al., 2009; Thylstrup and problematic (Ertug Fejerskov, 1978). Different results have been reported regarding the bonding effectiveness of self-etch and etch-and-rinse adhesives to the lased-enamel (Cardoso et al., 2008; Chimello-Sousa et al., 2006; De Munck et al., 2002; Obeidi et al., 2009) and fluorosed enamel rul et al., 2009; Shida et al., 2009; Torres(Ertug Gallegos et al., 2012). However, to date there is no published study about adhesive bonding efficacy following laser preparation of the fluorosed teeth. Therefore, this in vitro study was designed to evaluate the bonding efficacy of two contemporary adhesives with and without an additional etching step/time to laserprepared fluorotic enamel using microshear bond strength test. MATERIALS AND METHODS Experimental caries-free extracted premolar teeth used in this study were collected from 20 to 35 year old patients living in fluorosis endemic areas in Iran with moderate fluorosis (TFI 5 4 to 6) (Thylstrup and Fejerskov, 1978). The patients signed informed consent
Filtek Z250 composite resin was applied in 0.5-mm layer and light cured for 40 s
form which was approved by the local ethics committee for research. The teeth were stored in 0.5% chloramine solution at 4 C and used within three months after extraction. After removing the roots from the crowns, 0.5 mm depth orientation grooves were prepared on the midbuccal surfaces of the teeth. They were then mounted in an acrylic resin with their buccal surfaces upward and parallel to the base of the resin block. The buccal surfaces were grounded using 320-grit silicon carbide papers under water cooling in order to obtain a standardized flat enamel surface. The absence of exposed dentin on the enamel surfaces was checked using a stereomicroscope (Carl Ziess, Oberkochen, Germany). The bonded area was defined using an adhesive tape with a punched hole over the center of flattened surface. Seventy specimens were randomly divided into seven groups according to the adhesive protocol and preparation type. For the laser-prepared groups (1–4), an Er,Cr:YSGG laser (Waterlase, Biolase Technology, San Clemente, CA, USA) was used with the following parameters: wavelength of 2.78 mm, pulse duration of 140 ms, repetition rate of 20 Hz, G-6 tip with 600 mm in diameter, power of 5 W, energy per pulse of 275 mJ, 80% water, and 90% air spray. The specimens were irradiated at a 90 angle in noncontact and focused mode with a distance of 1 mm away from the laser tip for 7 s in a scanning movement on a surface area with 2 mm diameter. An even ablated surface was obtained. In groups 1 and 2, the enamel surfaces were etched with 37% phosphoric acid (3M ESPE, St Paul, MN, USA) for 20 and 40 s, respectively. After rinsing and gently air drying for 5 s, Adper Single Bond (SB,3M ESPE) was applied according to manufacturer ’s instructions (Table 1). In group 3, Clearfil SE Bond (SEB, Kuraray, Okayama, Japan) was applied (Table 1). In group 4, the surfaces were acid etched for 30 s, rinsed, and then dried for 30s. Then, Clearfil SE Bond was used similar to group 3. In burprepared groups (5–7), the enamel surface was flattened by medium-grit fissure diamond bur (#10061, Dia. Tessin, Gordevio, Switzerland) under air water spray. The bur was replaced for every five uses. The adhesive procedures were the same as that described for groups 1, 3 and 4, respectively. Prior to light curing of the adhesives, translucent polyvinyl chloride microtubes (0.7 mm in diameter and 0.5 mm in height) were placed on the bonding surfaces and subsequently filled with Z250 composite (3M ESPE, St Paul, MN, USA). Light curing was done using a light curing unit (VIP Junior, Bisco, Schaumburg, IL, USA) at 600 mW/cm2. The specimens were stored in distilled water at 37 C Microscopy Research and Technique
MICROMORPHOLOGY ANALYSIS AND BOND STRENGTH OF TWO ADHESIVES
781
TABLE 2. Mean microshear bond strength (MPa) to fluorosed enamel (n 5 10) 6 standard deviation and failure mode Group 1 2 3 4 5 6 7
Enamel preparation/ adhesive procedure
Mean 6 SD (MPa)
Failure mode (A/C/M)
Er,Cr:YSGG/20s E1SB Er,Cr:YSGG/40s E1SB Er,Cr:YSGG/SEB Er,Cr:YSGG/30s E1SEB Bur/20s E1SB Bur/SEB Bur/30s E1SEB
26.3 6 6.7ABC 28.7 6 7.1ABC 16.9 6 4.2B 18.7 6 5.1B 39.5 6 8.8A 31.7 6 9.3AB 36.4 6 9.8.1AC
2/1/7 1/2/7 4/1/5 4/2/4 1/0/9 3/1/6 1/1/8
Data with the same superscript are not statistically significantly different. A, adhesive; C, cohesive; M, mixed; E,: acid etching; SB, adper single bond; SEB, clearfil SE bond.
for 24 hours and then mounted onto a jig attached to a universal testing machine (Instron, Z020. Zwick Roell, Germany). The microshear bond strength was measured at a cross head speed 1 mm/min. The obtained data were statistically analyzed using one-way analysis of variance (ANOVA) and multiple comparisons were performed using Tamhane post-hoc tests (a 5 0.05). The failure mode was determined using a stereomicroscope (Carl Ziess Inc) at 203 magnification according to the following categories: (A) adhesive failure within the adhesive interfacial zone; (B) cohesive in the composite or in enamel; and (C), mixed adhesive failure and cohesive failure. Morphological Evaluation Using Scanning Electron Microscope Six additional specimens were differently prepared and conditioned: bur with etching or self-etching primer, laser with 20 or 40 s etching, self-etching primer, and 30 s etching 1 self-etching primer) in the same manner as that of bonding testing. The specimens were dehydrated, gold sputter coated, and examined under a scanning electron microscope (SEM) (KYKY, EM 3200, China). RESULTS Mean microshear bond strength (mSBS) and standard deviation (MPa) for the seven groups are shown in Table 2. According to the results of ANOVA test, there was a significant difference among the groups (P < 0.001). Despite higher mSBS obtained in the burprepared groups compared to those of laser-prepared ones with two adhesives with and without an additional etching step or time, these differences were not statistically significant (P > 0.05). The additional etching for SEB in two preparation types and an additional etching time for SB in laser groups revealed no effect on mSBS (P 5 1). However, the former in the bur group (group7) had a higher mSBS (36.4) than that in the laser group (18.7, P 5 0.04). Among the groups, the highest mSBS was obtained in group 5 (bur-prepared/ SB, 39.5) that yielded significant differences with group 3 (laser/SEB,16.9) and group 4 (laser/etching1 SEB,18.7) (P 5 0.001 and 0.002, respectively). Fracture analysis revealed that most of the failure (>50%) of all groups were mixed, except for groups 3 and 4 in which 50% or less failures were mixed. SEM images of burprepared fluorosed enamel treated with acid etching and self-etching primer are presented in Figures 1a and 1b. Figures 2a–2d show the laser-prepared Microscopy Research and Technique
Fig. 1. SEM images of bur-prepared fluorosed enamel: (a) acid etched, prominent etch pattern with very rough surface; and (b) treated with self-etching primer, less microretentive surface (35003). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
fluorosed enamel treated with acid etching for 20 and 40 s, self-etching primer, and etching for 30 s 1 selfetching primer, respectively. DISCUSSION With increasing prevalence of fluorosis in many areas of the world and widespread use of laser ablation, achieving high bond strength of adhesive materials on laser-prepared fluorosed enamel is a critical factor in the success of esthetic restorations of the fluorosed teeth. The fluorotic teeth used in this study were premolars obtained from 20 to 40 year old patients living in fluorosis-endemic regions (southern province) in Iran with a prevalence range from 67% to 80% (Ramezani et al., 2004). This specific tooth type and the age group minimized the effect of these factors on the fluoride content and consequent enamel bond strength rul et al., 2009). The (Ateyah and Akpata, 2000; Ertug used teeth classified as TFI score 4–6 (moderate fluorosis) exhibited chalky white appearance and distinct pitting area on the enamel surface. In higher TFI score, considerable parts of the surface enamel are lost (Fejerskov et al., 1990; Torres-Gallegos et al., 2012). In
782
F. SHAFIEI ET AL.
Fig. 2. SEM images of Er,Cr:YSGG-prepared fluorosed enamel: (a) 20 s acid-etched, a delicate etch pattern with rough surface, visible enamel prisms and microcracks between them; (b) 40 s acid-etched, the same appearance of 20 s etching; (c) self-etching primed, a shal-
low etch pattern; and (d) acid-etched and then self-etching primed, a more retentive pattern with longitudinal exposure of enamel prisms and microcracks between them (35003). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
the current study, 0.3 mm of the enamel surface of the fluorosed teeth was removed to simulate clinical condition of tooth preparation for composite veneer restorations. This grinding also provided a flat surface to be bonded on the enamel for shear testing (Ateyah and Akpata, 2000; Ermis et al., 2007). In addition, bond strength measurement of the adhesives to uncut enamel might be difficult because of the weak nature of the fluorosed enamel (Ermis et al., 2007). Microshear bond strength testing used in this study could be more representative of the clinical situation in which composite veneer is bonded on the fluorosed enamel. There is no necessity for specimen preparation, preventing micro-crack formation at the adhesive interface (Shida et al., 2009). Using an ultra-small bonding area could overcome nonuniformity of stress distribution at the interface occurring in conventional shear test. However, the higher bond strength values were obtained (Weerasinghe et al., 2005). As different elastic modulus of composites could influence the bond strength (Shafiei and Memarpour, 2009; Shafiei et al., 2009), the same composite (Z250) was used in all the groups of this study. According to our findings, enamel preparation with laser revealed insignificantly lower result than that of
bur preparation in terms of bond strength for two etchand-rinse and self-etch adhesives. This insignificant difference may indicate that larger sample sizes were required. A number of authors have demonstrated a lower bond strength of some adhesives to the lasednormal enamel compared to the bur-cut one. This reduced strength had been attributed to a more mineralized and stable enamel surface along with fusion and obliterated enamel micropores (Cardoso et al., 2008; Chimello-Sousa et al., 2006; Delfino et al., 2006; De Munck et al., 2002). Nevertheless, these alterations may result in less susceptibility of adhesive interface to hydrolytic degradation (Amaral et al., 2010). In the current study, despite observation of microcrack formation on the lased enamel, a unique and delicate etch pattern was seen in nonmelted etched lased-enamel. This retentive rough surface may explain insignificant reduced bond strength of etch-and-rinse adhesive obtained for the lased group in comparison with the bur group. The resin penetration into the microcrack may reinforce the lased enamel. The positive effect of phosphoric acid etching associated with etch-and-rinse adhesives was confirmed by some authors (De Munck et al., 2002; Dunn et al., 2005; Jaberi Ansari et al., Microscopy Research and Technique
MICROMORPHOLOGY ANALYSIS AND BOND STRENGTH OF TWO ADHESIVES
2012). The lack of significant difference between the bond strength of an etch-and-rinse adhesive to the laser-prepared and bur-prepared normal enamel was previously reported (Amaral et al., 2010; Jaberi Ansari et al., 2012). Obeidi et al. (2009; 2010) demonstrated significant and insignificant improvement of bond strength with increasing etching time to 40 s of the lased-enamel in two recent studies. However, this procedure exhibited no additionally beneficial effect on the fluorosed enamel used in this study. Although some authors have suggested increasing etching time for bonding to fluorosed enamel (AlSugair and Akpata, 1999), others reported no significant difference in the bond strengths to fluorotic and normal enamel with different etching times (Ateyah and Akpata, 2000). A number of authors stated that grinding the enamel surface to flatten the enamel surface for shear testing leads to removal of 200 mm hypermineralized surface layer (Ateyah and Akpata, 2000; Weerasinghe et al., 2005). This surface layer was also removed in all of the enamel specimens used in this study with abrading/grinding. According to De Munck et al., (2002) preparation of a flat surface using laser is almost impossible. Therefore, a standardized flat enamel surface was obtained prior to laser irradiation in all bond strength studies. After the grinding, the enamel structure involved in laser or bur preparation and adhesive bonding could not be determined. A thickness of about 50 mm was reported for the subsurface porous enamel with a TFI score of 4 (Thylstrup and Fejerskov, 1978). In higher scores, this layer extended toward the inner enamel (Aoba et al., 2002). Chemical surface analysis is necessary in this regard. Two adhesives used in this study, SEB and SB, exhibited comparable bond strength on the burprepared fluorosed enamel. This finding is consistent with the previous study (Ermis et al., 2007).This similarity might be attributed to the removal of hypermineralized surface layer on the ground enamel. Especially, enamel grinding might be a critical factor for efficient bonding of mild self-etch adhesives (Ermis et al., 2007). This explanation could be relevant to laser-prepared groups that revealed no significant difference between bonding performance of the two adhesives used. Moreover, although laser preparation compared with the bur one resulted in a lower bonding of SEB to the fluorosed enamel, this difference was not significant. This result is in agreement with those of a previous study (De Munck et al., 2002) and a recent study on normal enamel (Adebayo et al., 2012). However, the significantly lower bond strength of SEB to the lased-normal enamel compared to that of the bur-cut one was found by Cardoso et al. (2008). Despite shallow and less retentive etching pattern created by the mild self-etch adhesive, its MDP content could contribute to the bonding effectiveness of SEB on smear layer-free surface following laser ablation of the enamel (Cardoso et al., 2008). Increased calcium of lased-enamel composition may reinforce the chemical bonding of MDP to the surface calcium (Hossain et al., 2003). In addition to structural alterations of the lased-enamel, the compositional characteristics of adhesives might also play an important role in the enamel bonding ability. Considering low etching Microscopy Research and Technique
783
efficacy of self-etch adhesives and their questionable bonding ability to the enamel, some authors recommended acid etching prior to the adhesives (Rotta et al., 2007; Van Meerbeek et al., 2011). Weerasinghe et al. (2005) reported that an additional acid etching on the ground enamel significantly improved the bond strength of SEB to moderate and severe fluorosed enamel. The results of the present study showed that the additional etching had no significant effect on bonding to laser- and bur-prepared moderate fluorosed enamel. Moreover, the etching associated to SEB resulted in a significantly higher bonding to the burprepared surface than the lased one. Removal of calcium from the etched surface and remaining water and HEMA contents of the primer into deep etched zone may account for the obtained result. Those remaining components may limit the penetration of Bis-GMA and dimethacrylate components of the adhesive part of SEB. It should be taken into account that in addition to the etching potential of self-etch adhesives, cohesive strength of the adhesive layer may be an important factor in the attainment of adequate bond strength to the enamel (Pashley and Tay., 2001). The different results reported in the literature on bonding efficacy of adhesives on laser-irradiated enamel might be attributed to variations in parameter settings of irradiation, laser devices, testing methods, type, and compositions of the adhesive and chemical/ structural composition of the irradiated tissue (normal enamel vs. fluorosed enamel). According to a bond durability study conducted by Amaral et al. (2010), bond strength to the erbium laser-prepared normal enamel was not affected by different periods of water storage and thermocycling. Further studies should investigate long-term bonding stability of different adhesives to the laser-prepared enamel in the fluorosed teeth. Chemical analysis of different layers of the fluorosed enamel could lead to our understanding about the interaction of laser with different compositional layers of the enamel. CONCLUSIONS Within the limitations of the current study, it might be concluded that for two adhesives with or without additional etching step/time, laser preparation of the moderate fluorosed enamel resulted in a lower bond strength compared to that of bur preparation; however, this reduction was not statistically significant. An etch-and-rinse adhesive in the bur group revealed the highest bond strength that was significantly higher than that of the self-etch adhesive (with or without etching) in the laser group. Therefore, an etch-andrinse adhesive (20 or 40 s etching) was preferred in the laser-prepared fluorosed enamel in terms of bond strength. ACKNOWLEDGMENTS This research was supported by the Vice-chancellery for research of Shiraz University of Medical Sciences as a thesis for the MSc degree of Dr Z Jowkar in Operative Dentistry. The authors thank Dr M. Vossoughi from the Dental Research Development Center, for statistical analysis and Dr N. Shokrpour at Centre for Development of Clinical Research of Nemazee Hospital for editorial assistance.
784
F. SHAFIEI ET AL.
REFERENCES Adebayo OA, Burrow MF, Tyas MJ, Palamara J. 2012. Effect of tooth surface preparation on the bonding of self-etching primer adhesives. Oper Dent 37:137–149. Al-Sugair MH, Akpata ES. 1999. Effect of fluorosis on etching of human enamel. J Oral Rehabil 26:521–528. Amaral FL, Colucci V, Souza-Gabriel AE, Chinelatti MA, Palma-Dibb RG, Corona SA. 2010. Bond durability in erbium:yttrium-aluminum-garnet laser-irradiated enamel. Lasers Med Sci 25:155–163. Aoba T, Fejerskov O. 2002. Dental fluorosis: chemistry and biology. Crit Rev Oral Biol Med 13:155–170. Ateyah N, Akpata E. 2000. Factors affecting shear bond strength of composite resin to fluorosed human enamel. Oper Dent 25:216– 222. Bachmann L, Diebolder R, Hibst R, Zezell DM. 2005. Changes in chemical composition and collagen structure of dentine tissue after erbium laser irradiation. Spectrochim Acta A Mol Biomol Spectrosc 61:2634–2639. Cardoso MV, De Munck J, Coutinho E, Ermis RB, Van Landuyt K, de Carvalho RC, Van Meerbeek B. 2008. Influence of Er,Cr:YSGG laser treatment on microtensile bond strength of adhesives to enamel. Oper Dent 33:448–455. Chimello-Sousa DT, de Souza AE, Chinelatti MA, P ecora JD, PalmaDibb RG, Milori Corona SA. 2006. Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel. J Dent 34:245–251. Delfino CS, Souza-Zaroni WC, Corona SA, Palma-Dibb RG. 2006. Microtensile bond strength of composite resin to human enamel prepared using erbium: Yttrium aluminum garnet laser. J Biomed Mater Res A 80:475–479. De Munck J, Van Meerbeek B, Yudhira R, Lambrechts P, Vanherle G. 2002. Micro-tensile bond strength of two adhesives to Erbium: YAG-lased vs. bur-cut enamel and dentin. Eur J Oral Sci 110:322– 329. DenBesten PK, Thariani H. 1992. Biological mechanisms of fluorosis and level and timing of systemic exposure to fluoride with respect to fluorosis. J Dent Res 71:1238–1243. Dunn WJ, Davis JT, Bush AC. 2005. Shear bond strength and SEM evaluation of composite bonded to Er:YAG laser-prepared dentin and enamel. Dent Mater 21:616–624. Ermis RB, De Munck J, Cardoso MV, Coutinho E, Van Landuyt KL, Poitevin A, Lambrechts P, Van Meerbeek B. 2007. Bonding to ground versus unground enamel in fluorosed teeth. Dent Mater 23: 1250–1255. Ertu grul F, T€ urk€ un M, T€ urk€ un LS, Toman M, Cal E. 2009. Bond strength of different dentin bonding systems to fluorotic enamel. J Adhes Dent 11:299–303. Fejerskov O, Manji F, Baelum V. 1990. The nature and mechanisms of dental fluorosis in man. J Dent Res (Spec No):692–700. Harashima T, Kinoshita J, Kimura Y, Brugnera A, Zanin F, Pecora JD, Matsumoto K. 2005. Morphological comparative study on ablation of dental hard tissues at cavity preparation by Er:YAG and Er,Cr:YSGG lasers. Photomed Laser Surg 23:52–55. Hossain M, Nakamura Y, Tamaki Y, Yamada Y, Murakami Y, Matsumoto K. 2003. Atomic analysis and knoop hardness measurement of the cavity floor prepared by Er,Cr:YSGG laser irradiation in vitro. J Oral Rehabil 30:515–521. Jaberi Ansari Z, Fekrazad R, Feizi S, Younessian F, Kalhori KA, Gutknecht N. 2012. 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 27:761–765.
Mascarenhas AK. 2000. Risk factors for dental fluorosis: a review of the recent literature. Pediatr Dent 22:269–277. Obeidi A, McCracken MS, Liu PR, Litaker MS, Beck P, Rahemtulla F. 2009. Enhancement of bonding to enamel and dentin prepared by Er,Cr:YSGG laser. Lasers Surg Med 41:454–462. Obeidi A, Liu PR, Ramp LC, Beck P, Gutknecht N. 2010. Acid-etch interval and shear bond strength of Er,Cr:YSGG laser-prepared enamel and dentin. Lasers Med Sci 25:363–369. Pashley DH, Tay FR. 2001. Aggressiveness of contemporary selfetching adhesives. Part II: etching effects on unground enamel. Dent Mater 17:430–444. Pendrys DG. 2000. Risk of enamel fluorosis in non-fluoridated and optimally fluoridated populations: considerations for the dental professional. J Am Dent Assoc 131:746–755. Ramezani GH, Valaei N, Eikani H. 2004. Prevalence of DMFT and fluorosis in the students of Dayer city (Iran). J Indian Soc Pedod Prev Dent 22:49–53. Robinson C, Connell S, Kirkham J, Brookes SJ, Shore RC, Smith AM. 2004. The effect of fluoride on the developingtooth. Caries Res 38: 268–276. Rotta M, Bresciani P, Moura SK, Grande RH, Hilgert LA, Baratieri LN, Loguercio AD, Reis A. 2007. Effects of phosphoric acid pretreatment and substitution of bonding resin on bonding effectiveness of self-etching systems to enamel. J Adhes Dent 9:537–545. Shafiei F, Memarpour M. 2009. Effect of repeated use on dentin bond strength of two adhesive systems: All-in-one and one-bottle. Indian J Dent Res 20:180–184. Shafiei F, Saffarpour A, Moradmand M, Alavi AA. 2009. Effect of light activation mode on the incompatibility between one-bottle adhesives and light-cured composites: An in vitro shear bond strength study. Oper Dent 34:558–564. Shida K, Kitasako Y, Burrow MF, Tagami J. 2009. Micro-shear bond strengths and etching efficacy of a two-step self-etching adhesive system to fluorosed and non-fluorosed enamel. Eur J Oral Sci 117: 182–186. € Straßl M, Ublacker B, B€ acker A, Beer F, Moritz A, Wintner E. 2004. Comparison of the emission characteristics of three erbium laser systems. A physical case report. J Oral Laser Appl 4:263–270. Swift EJ Jr, Perdig~ ao J, Heymann HO.1995. Bonding to enamel and dentin: a brief history and state of the art. Quintessence Int 26:95– 110. Thylstrup A, Fejerskov O. 1978. Clinical appearance of dental fluorosis in permanent teeth in relation to histologic changes. Community Dent Oral Epidemiol 6:315–328. Torres-Gallegos I, A Martinez-Casta~ non G, Loyola-Rodriguez JP, Pati~ no-Marin N, Encinas A, Ruiz F, Anusavice K. 2012. Effectiveness of bonding resin-based composite to healthy and fluorotic enamel using total-etch and two self-etch adhesive systems. Dent Mater J 31:1021–1027. Van Meerbeek B, Yoshihara K, Yoshida Y, Mine A, De Munck J, Van Landuyt KL. 2011. State of the art of self-etch adhesives. Dent Mater 27:17–28. Vieira AP, Hancock R, Limeback H, Maia R, Grynpas MD. 1978. Is fluoride concentration in dentin and enamel a good indicator of dental fluorosis? J Dent Res 83:76–80. Waidyasekera PG, Nikaido T, Weerasinghe DD, Wettasinghe KA, Tagami J. 2007. Caries susceptibility of human fluorosed enamel and dentine. J Dent 35:343–349. Weerasinghe DS, Nikaido T, Wettasinghe KA, Abayakoon JB, Tagami J. 2005. Micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel. J Dent 33:419–426.
Microscopy Research and Technique
