MICROSCOPY RESEARCH AND TECHNIQUE 78:489–494 (2015)
Influence of Double Application Technique on the Bonding Effectiveness of Self-Etch Adhesive Systems RAJNI NAGPAL,1 PALLAVI SHARMA,1* NAVEEN MANUJA,2 SHASHI PRABHA TYAGI,1 UDAI PRATAP SINGH,1 SHIPRA SINGH,1 AND PAYAL SINGH1 1
Department of Conservative Dentistry & Endodontics, Kothiwal Denta L College & Research Centre, Moradabad, Uttar Pradesh, India 2 Department of Pediatric Dentistry, Kothiwal Dental College & Research Centre, Moradabad, Uttar Pradesh, India
KEY WORDS
double-application; single-step self-etch adhesives; microleakage; resin-dentin interfacial micromorphology
ABSTRACT Aim: To evaluate and compare the effect of double-application of single-step self-etch adhesives using microleakage study and to analyze the dentin–adhesive interfacial micromorphology. Methods: In total, 72 extracted human premolars were divided into three groups for different self-etch adhesives (G Bond, GC [GB], Optibond, Kerr [OB], and Xeno V Plus, Dentsply [XV]). Class V cavities were prepared. Each group was further divided into two subgroups (n 5 10) according to the placement technique of the adhesive, using the singleapplication [subgroup (a)] or double-application method [subgroup (b)]. Resin composite (Z 250, 3M ESPE, St. Paul, MN) was used to restore the cavities and light cured for 40 s. Twenty samples from each group were subjected to microleakage study. Two samples from both the subgroups of the three adhesives were used for scanning electron microscopic examination of the resin–dentin interfacial ultrastructure. Dye leakage scores were subjected to statistical analysis using Kruskal–Wallis and Mann–Whitney U-tests at significance level of P < 0.05. Results: GB depicted significantly more microleakage which was significantly greater than OB and XV. The double application led to significant decrease in microleakage of GB with no significant effect on the microleakage scores of other two all-in-one adhesives, that is OB and XV. Conclusion: Double application of all-in-one self-etch adhesives improves the marginal sealing ability in dentin although it appears to be product dependent. Microsc. Res. Tech. 78:489–494, 2015. V 2015 Wiley Periodicals, Inc. C
INTRODUCTION Trend toward the simplification of bonding procedures and overcoming the problem of inconsistent adhesion to dentin have led to the introduction of selfetch adhesives. The self-etch systems have been categorized as two-step and one-step adhesives. Furthermore, these one-step self-etch adhesives have been subclassified as strong, moderate (intermediary strong), and mild, based on their pH value (Van Meerbeek et al., 2003). One-step self-etch adhesives combine all the components of an adhesive system (etchant, primer, and bonding agent) into a single solution with a single-application (SA) step (Van Landuyt et al., 2005). With this approach, the rinsing and drying phase is eliminated, which does not only reduce clinical application time, but also significantly decreases technique sensitivity (Tay and Pashley, 2001; Van Meerbeek et al., 2001). In addition, the simultaneous impregnation of the exposed collagen matrix with resin up to the same depth of demineralization eliminates the risk of incomplete resin infiltration (Van Landuyt et al., 2005). Unfortunately, it seems that this simplicity relates to the extent of efficacy (Reis et al., 2007) as controversies over the performance of these adhesives with regard to their bonding potential have also been C V
2015 WILEY PERIODICALS, INC.
reported (Batra et al., 2014; Chersoni et al., 2004; De Munck et al., 2003; Inoue et al., 2001; Ishikawa et al., 2007; Manuja and Nagpal, 2012b; Nagpal et al., 2011). The poor bonding performance of one-step self-etch adhesives reported in dentin may be attributed to different factors (Hegde and Bhandary, 2008). The etching pattern is not well defined as that provided by phosphoric acid (Manuja et al., 2012a; Miguez et al., 2003; Moura et al., 2006; Perdigao and Geraldeli, 2003). These products create very thin coatings, leading to oxygen inhibition, resulting in a suboptimal polymerization. They are prone to phase separation as the solvent evaporates from the solution and they behave as semi-permeable membranes after polymerization (Albuquerque et al., 2008). These adhesives are extremely hydrophilic as they contain high concentrations of both ionic and hydrophilic monomers (Miyazaki et al., 2000). Such hydrophilicity renders these *Correspondence to: Pallavi Sharma, Department of Conservative Dentistry & Endodontics, Kothiwal Dental College & Research Centre, Moradabad, Uttar Pradesh, India. E-mail: [email protected] REVIEW EDITOR: Prof. Alberto Diaspro Received 2 February 2015; accepted in revised form 7 March 2015 Abbreviations: DA, double application; GB, G bond; OB, optibond; SA, single application; SEM, scanning electron microscope; XV, Xeno V Plus DOI 10.1002/jemt.22499 Published online 10 April 2015 in Wiley Online Library (wileyonlinelibrary.com).
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R. NAGPAL ET AL TABLE 1. Manufacturers, compositions, and application procedures of the tested self-etch adhesives Application procedure
Adhesive/manufacturer
Composition
SA
DA
GB (GC, Tokyo, Japan)
4-MET,UDMA, TEGDMA methacrylic acid ester, acetone, water, fumed silica fillers, photoinitiator GPDM, HEMA, mono- and difunctional methacrylate monomers, ethanol, acetone, and water as solvents, camphorquinone photoinitiators, nanofillers, and fluoride-releasing fillers Bifunctional acrylate, acidic acrylate, functionalized phosphoric acid ester, water, tertiary butanol, initiator, stabilizer
1. Application of one coat of adhesive (5–10 s) 2. Gentle air stream (5 s) 3. Light activation (10 s–600 mW/cm2) 4. Composite placement curing (40 s) 1. Application of one coat of adhesive (20 s) 2. Gentle air stream (10 s) 3. Light activation (10 s–600 mW/cm2) 4. Composite placement curing (40 s)
1. Steps 1–2 from (SA) 2. Repeat Steps 1–2 3. Step 3 4. Step 4 1. Steps 1–2 from (SA) 2. Repeat Steps 1–2 3. Step 3 4. Step 4
1. Application of one thick coat of adhesive under pressure 2. Gently agitate the adhesive for 20 s 3. Gentle air stream (5 s) 4. Light activation (10 s–600 mW/cm2) 5. Composite placement curing (40 s)
1. Steps 1–3 from (SA)
OB all-in-one (Kerr, Orange, CA)
XV (Dentsply DeTrey, Konstanz, Germany)
2. Repeat Steps 1–3 3. Step 4 4. Step 5
Abbreviations: Bis-GMA, bisphenol-A diglycidyl methacrylate; HEMA, 2-hydroxyethyl methacrylate; MDP, 10-methacryloyloxydecyl dihydrogen phosphate; TEGDMA, triethylene glycol dimethacrylate; 4-MET, 4-methacryloyloxy–ethyl trimellitic phosphate; UDMA, urethane dimethacrylate.
adhesives very permeable and denies their ability to hermetically seal dentin surfaces. This water sorption plasticizes polymers and lowers their mechanical properties (Bastioli et al., 1990). Although hydrophobic dimethacrylates are added to all-in-one adhesives to produce stronger crosslinked polymer networks, the hydrophilic monomers tend to cluster together before polymerization to create hydrophilic domains (Eliades et al., 2001; Spencer and Wang, 2002) and microscopic water-filled channels called water trees (Ferrari and Tay, 2003; Tay et al., 2002). Several authors have reported that self-etch adhesive systems did not improve bonding effectiveness to dentin in spite of their purported reduction in technique sensitivity (Manuja et al., 2012c; Tay and Pashley, 2003; Toledano et al., 2001). Infiltration of adhesives into the dentin and the thickness of the adhesive layer are directly correlated to rheological and chemical characteristics (Albuquerque et al., 2008; Moszner et al., 2005), but they could also be influenced by the mode of application (Belli et al., 2011). To offset the limitations of self-etching adhesives, altered bonding protocols that increase resin–dentin bond quality were suggested (Pashley et al., 2002; Toledano et al., 2007). Among the different clinical approaches are the use of an additional layer of hydrophobic resin agent (King et al., 2005), multiple-layer application of additional coats of adhesive (Erhardt et al., 2009; Hashimoto et al., 2004; Ito et al., 2005; Pashley et al., 2002; Wei et al., 2009), enhanced solvent evaporation (Van Landuyt et al., 2005), use of collagen crosslinkers and matrix metalloproteinase inhibitors (Nagpal et al., 2013, 2014; Sharma et al., 2015; Verma et al., 2013), and prolonged curing-time intervals (Breschi et al., 2007; Cadenaro et al., 2005; Erhardt et al., 2009). It has been reported that double application (DA) of onestep self-etch adhesives may result in a more uniform infiltration of the adhesive into smear layer-covered dentin if a one-step self-etch adhesive is applied in two layers (Pashley et al., 2002). Different studies have reported the effect of additional application of one-step self-etch adhesives to dentin. However, most of these studies have been
performed on flat surfaces which do not take into account the influence of C-factor on bonding. Thus, the objective of this study was to evaluate the influence of DA technique on the bonding effectiveness of self-etch and to observe the morphological characteristics of the resin–dentin interface after such treatment under scanning electron microscope (SEM). The null hypothesis tested was that the DA of adhesives on the prepared dentin surface will not affect the microleakage of onestep self-etch adhesives. MATERIALS AND METHODS This study was performed on 72 intact caries-free human premolars extracted for orthodontic purpose. After debridement and disinfection in 1% of thymol solution, teeth were stored in distilled water until use. Buccal Class V cavities centered on the cementoenamel junction were prepared with 3-mm mesiodistal width, 3 mm occlusogingival dimensions, and 1.5 mm depth, using ISO 012 straight fissure diamond point (Dentsply Detrey, USA) in an air–water-cooled highspeed handpiece. The bur was changed after every five preparations. The gingival margins on dentin were maintained as butt joint. The teeth were randomly divided into six groups according to three one-step selfetch adhesives used: G Bond (GB) (GC, Tokyo, Japan), optibond (OB) (Kerr, Orange, CA, USA), and Xeno V Plus (XV) (Dentsply DeTrey, Konstanz, Germany) and two application modes (Table 1). Group 1a; GB-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of GB application according to the manufacturer’s directions. Group 1b; GB-DA: The GB adhesive applied as in Group 1, followed by DA of self-etch adhesive. Group 2a; OB-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of OB application according to the manufacturer’s directions. Group 2b; OB-DA: The OB adhesive applied as in Group 1, followed by DA of self-etch adhesive. Microscopy Research and Technique
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TABLE 2. Mean score for dye penetration of all the three self-etch adhesives Adhesives and application modes Mean microleakage score GB Group 1a; GB-SA Group 1b; GB-DA OB Group 2a; OB-SA Group 2b; OB-DA XV Group 3a; XV-SA Group 3b; XV-DA
2.6 1.6 1.6 1.4 1.4 1.0
TABLE 3. Intergroup comparisons using Mann–Whitney U-test Group comparison
P-values
Groups 1a and 1b Groups 1a and 2a Groups 1a and 3a Groups 1b and 2b Groups 1b and 3b Groups 2a and 2b Groups 2a and 3a Groups 2b and 3b Groups 3a and 3b
0.023a 0.023a 0.011a 0.639 0.203 0.639 0.639 0.431 0.431
a
Statistically significant difference between the two groups at a significance level of P < 0.05.
Group 3a; XV-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of XV application according to the manufacturer’s directions. Group 3b; XV-DA: The XV adhesive applied as in Group 1, followed by DA of self-etch adhesive. The cavities were bulk filled with resin composite (Z 250, 3M ESPE, St. Paul, MN), light cured using Spectrum 800 (Dentsply, Caulk, Milford, DE) for 40 s at 600 mW/cm2 and polished. The restored teeth in each group were thermocycled for 500 cycles at 5 and 55 C with 30 s of dwell time. For microleakage test, 10 samples from each group were coated with two layers of sticky wax, leaving a 1-mm window around the cavity margins. All the samples were then immersed in freshly prepared 2% methylene blue dye for 48 h. The teeth were then rinsed with water, the sticky wax was removed, and the teeth were left to air dry at room temperature for 24 h. After drying the samples at room temperature, the teeth were sectioned longitudinally in a buccolingual direction with the help of diamond disk by a cut through the center of the restoration. Dye penetration at the tooth–restoration interface was assessed by a stereomicroscope (Olympus 2.5X) at a magnification of 103. The following ranking systems were used to score the degree of dye penetration (Nagpal et al., 2007; Silveira et al., 2006). Dye leakage score 0 1 2 3
Criteria for Scoring No evidence of microleakage Dye penetration up to half the cavity depth Dye penetration of more than half the cavity depth Dye penetration along the axial wall
SEM Evaluation The restored samples were sectioned mesiodistally, and polished with wet 210 grit SiC paper. Acid–base Microscopy Research and Technique
Fig. 1. a: SEM view showing generalized gap at resin–dentin interface after bonding with GB using SA technique (Group 1a; GB-SA). b: SEM view showing improved interfacial seal after bonding with GB using DA technique (Group 1b; GB-DA).
treatment (6 N HCl for 30 s followed by 4% NaOCl for 10 min) was done, and the samples were dehydrated in ascending ethanol concentration (50, 75, and 95% for 20 min each and 100% for 1 h), and then transferred to a critical point dryer for 30 min. All 12 specimens were then gold sputter coated and the surfaces were examined under a SEM (Leo 435 VP Cambridge, United Kingdom). Statistical Analysis Dye leakage scores obtained were subjected to statistical analysis using Kruskal–Wallis and Mann– Whitney U-tests (SPSS Base 15.0 software) at a significance level of P < 0.05. RESULTS Sealing Ability Table 2 lists the mean scores of microleakage for GB, OB, and XV and Table 3 summarizes the intergroup comparisons using Mann–Whitney U-test and corresponding P-values. When used according to the manufacturer’s instructions in SA mode, GB depicted maximum microleakage which was significantly
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Fig. 2. a: SEM view showing generalized gap at resin–dentin interface after bonding with OB using SA technique (Group 2a; OB-SA). b: SEM view showing perfect interfacial seal after bonding with OB using DA technique (Group 2b; OB-DA).
Fig. 3. a: SEM view showing generalized gap at resin–dentin interface after bonding with XV using SA technique (Group 3a; XV-SA). b: SEM view showing perfect interfacial seal after bonding with XV using DA technique (Group 3b; XV-DA).
greater than OB and XV. The double-layer application of adhesive systems led to significant decrease in microleakage with GB self-etch adhesive (Groups 1a and 1b; P 5 0.023). However, DA had no significant effect on the microleakage scores of both the other allin-one adhesives, that is OB and XV.
adhesive bonding (Kantona and Winkler, 1994; Kidd, 1976; Manuja et al., 2011; Yoshikawa et al., 1999). The results of the present investigation led to the rejection of the null hypotheses as the use of a DA technique significantly improved marginal sealing for GB although improved marginal adaptation after DA was observed for all the self-etch adhesive systems regardless of the acetone-based (GB), ethanol-based (XV), or ethanol- and acetone-based (OB) nature of the adhesives. This was also observed by Hashimoto et al. (2006). Several mechanisms could account for the better performance of DA. As the first layer of the adhesive begins to etch the dentin substrate, it might become rapidly buffered by the hydroxyapatite (Camps and Pashley, 2000), so that the additional layers of unpolymerized acidic monomers may improve the etching ability of these adhesives by increasing the concentration of acidic reagents. Simultaneously to this process, more impregnation of resin might occur by additional supply of adhesive resin as hypothesized by Ito et al. (2005) and the increased thickness of the adhesive layer, which is known to reduce polymerization stress and improve the marginal seal (Choi et al., 2000).
Scanning Electron Microscope SEM observations of the resin–dentin interface are shown in Figures 1–3. All the self-etch adhesives when applied according to the manufacturer’s directions showed the presence of interfacial gap at the dentinal surface with little or no resin tag formation. The maximum interfacial gap was evident with GB. After double-layer application of these adhesives, reduction in interfacial gap was observed for all the adhesives. DISCUSSION The problem encountered with adhesive restorative procedures is the impaired marginal seal and to ensure outstanding marginal adaptation of an adhesive restoration, some restorative aspects must be considered, such as preparation design, composite shrinkage, and
Microscopy Research and Technique
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SA of the adhesive has the effect of a strong etchant although the infiltration of resin to demineralized dentin may not be sufficient. In the second application, the additional supply of adhesive resin may improve the infiltration of resin monomers into the intertubular demineralized dentin. Two of the one-step self-etching adhesives are 2hydroxyethyl methacrylate (HEMA)-free: GB and XV. The HEMA monomer is commonly added to the bonding agents and improves the stability of adhesive solutions that contain hydrophobic and hydrophilic components. In this study, GB presented significantly more microleakage as compared to other two adhesives. GB is a HEMA-free, acetone/water-based mild one-step self-etch adhesive containing a high percentage of acetone (40%). Acetone being more volatile than ethanol does not form an azeotrope with water, and hence it may not promote water evaporation when compared to ethanol-based adhesives, resulting in a low water/solvent evaporation ratio (Cho and Dickens, 2004). Lower polymerization efficiency owing to residual-free water and phase separation of its components (owing to a lack of HEMA) may result in marginal gap along the tooth–adhesive junction (Van Landuyt et al., 2007; Van Meerbeek et al., 2003; Zheng et al., 2001). This can partly explain the increased microleakage after the dye penetration test. Similarly, XV is also a HEMA-free water-based unfilled adhesive with t-butanol solvent and contains functionalized phosphoric acid esters. The presence of t-butanol in XV may plays the role of HEMA and in addition may help in eliminating the high water contents present by lowering the water vapor pressure by the formation of azeotrope (Yoshida et al., 2004). Both XV and OB depicted similar leakage scores significantly lesser than GB. This may be attributed to the fact that XV and OB have similar acidity levels, which should cause similar demineralization patterns. They are known as moderately strong self-etch adhesives; unlike strong self and total-etch adhesives, they create only a submicron hybrid layer (Tay et al., 1999). In addition to micromechanical interlocking through hybridization, specific functional monomers of these adhesives may interact chemically with residual hydroxyapatite crystals that remain available in the submicron hybrid layer (Inoue et al., 2001; Tay et al., 1999). Glycerol phosphate dimethacrylate (GPDM) adhesive monomer and filled adhesive technologies coupled with OB unique ternary solvent system provide excellent adhesion to all dental substrates. Although the tested adhesives have similar mechanisms of adhesion, HEMA-containing OB adhesive depicted lower microleakage scores and this justifies the presence of HEMA to prevent organic phase separations from the water-based composition. Several mechanisms may account for the superior performance of OB. The longer adhesive application time (40 s) recommended by the manufacturer may improve the etching ability of OB by increasing the exposure time of acidic reagents. Chemical composition of OB also differs from that of the other adhesives. This adhesive uses a ternary solvent system (water, acetone, and ethanol) that, according to the product’s technical bulletin, provides effective etching, enhanced material Microscopy Research and Technique
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stability, and a uniform adhesive layer. Functional acidic monomers of these adhesives also differ: OB uses GPDM as the functional monomer, OB adhesive contains nanofillers; the previous reports (Deliperi et al., 2007; Fortin and Swift, 1994) found that the collagen fibril network filters out most nanofillers, holding them at the hybrid layer surface where they act as an intermediate shock absorber. Reduced microleakage scores have been reported for filled adhesives (Deliperi et al., 2003, 2007; Fortin and Swift, 1994). These differences in chemical composition may have helped create a thicker, more homogeneous resin layer above the hybrid layer using OB, which may have improved resistance to microleakage. In addition, under the conditions of this study, the DA of this adhesive over the cured OB and XV adhesives did not reduce the microleakage scores in comparison with the application according to the manufacturers’ directions. Thus, lower leakage values can be obtained with OB and XV adhesives applied according to the manufacturers’ directions; it is not necessary to consider the alternative modes of application.
CONCLUSIONS DA of adhesives significantly reduced the microleakage of GB, whereas no significant effect was observed on the microleakage of OB and XV adhesives. Thus, from the results of this study, it can be concluded that the DA of all-in-one self-etch adhesives improves the marginal sealing ability with dentin although it appears to be product dependent. REFERENCES Albuquerque M, Pegoraro M, Mattei G, Reis A, Loguercio AD. 2008. Effect of double-application or the application of a hydrophobic layer for improved efficacy of one-step self-etch systems in enamel and dentin. Oper Dent 33:564–570. Bastioli C, Romano G, Migliaresi C. 1990. Water sorption and mechanical properties of dental composites. Biomaterials 11:219– 223. Batra C, Nagpal R, Tyagi SP, Singh UP, Manuja N. 2014. In vitro bonding effectiveness of three different one-step self etch adhesives with additional enamel etching. J Investig Clin Dent 5:226–236. Belli R, Sartori N, Peruchi LD, Guimar~ aes JC, Vieira LC, Baratieri LN, Monteiro S, Jr. 2011. Effect of multiple coats of ultra-mild allin-one adhesives on bond strength to dentin covered with two different smear-layer thicknesses. J Adhes Dent 13:507–516. Breschi L, Cadenaro M, Antoniolli F, Sauro S, Biasotto M, Prati C, Tay FR, Di Lenarda R. 2007. Polymerization kinetics of dental adhesives cured with LED: Correlation between extent of conversion and permeability. Dent Mater 23:1066–1072. Cadenaro M, Antoniolli F, Sauro S, Tay FR, Di Lenarda R, Prati C, Biasotto M, Contardo L, Breschi L. 2005. Degree of conversion and permeability of dental adhesives. Eur J Oral Sci 113:525–530. Camps J, Pashley DH. 2000. Buffering action of human dentin in vitro. J Adhes Dent 2:39–50. Chersoni S, Suppa P, Grandini S, Goracci C, Monticelli F, Yiu C, Huang C, Prati C, Breschi L, Ferrari M, Pashley DH, Tay FR. 2004. In vivo and in vitro permeability of one-step self etch adhesives. J Dent Res 83:459–464. Cho BH, Dickens SH. 2004. Effects of the acetone content of single solution dentin bonding agents on the adhesive layer thickness and the microtensile bond strength. Dent Mater 20:107–115. Choi KK, Condon JR, Ferracane JL. 2000. The effects of adhesive thickness on polymerization contraction stress of composite. J Dent Res 79:812–817. Deliperi S, Bardwell DN, Papathanasiou A, Perry R. 2003. Microleakage of resin-based liner materials and condensable composites using filled and unfilled adhesives. Am J Dent 16:351–355.
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Deliperi S, Bardwell DN, Wegley C. 2007. Restoration interface microleakage using one total-etch and three self-etch adhesives. Oper Dent 32:179–184. De Munck J, Van Meerbeek B, Satoshi I, Vargas M, Yoshida Y, Armstrong S, Lambrechts P, Vanherle G. 2003. Microtensile bond strengths of one- and two-step self-etch adhesives to bur-cut enamel and dentin. Am J Dent 16:414–420. Eliades G, Vougiouklakis G, Palaghias G. 2001. Heterogeneous distribution of single-bottle adhesive monomers in the resin-dentin interdiffusion zone. Dent Mater 17:277–283. Erhardt MC, Osorio R, Pisani-Proenca J, Aguilera FS, Osorio E, Breschi L, Toledano M. 2009. Effect of double layering and prolonged application time on MTBS of water/ethanol-based self-etch adhesives to dentin. Oper Dent 34:571–577. Ferrari M, Tay FR. 2003. Technique sensitivity in bonding to vital acid-etched dentin. Oper Dent 28:3–8. Fortin D, Swift EJ, Jr, Denehy GE, Reinhardt JW. 1994. Bond strength and microleakage of current dentin adhesives. Dent Mater 10:253–258. Hashimoto M, Sano H, Yoshida E, Hori M, Kaga M, Oguchi H, Pashley DH. 2004. Effect of multiple adhesive coating on dentin bonding. Oper Dent 29:416–423. Hashimoto M, Tay FR, Svizero NR, de Gee AJ, Feilzer AJ, Sano H, et al. 2006. The effects of common errors on sealing ability of totaletch adhesives. Dent Mater 22:560–568. Hegde MN, Bhandary S. 2008. An evaluation and comparison of shear bond strength of composite resin to dentin, using newer dentin bonding agents. J Cons Dent 11:71–75. Inoue S, Vargas MA, Abe Y, Yoshida Y, Lambrechts P, Vanherle G, Sano H, Van Meerbeek B. 2001. Microtensile bond strength of eleven contemporary adhesives to dentin. J Adhes Dent 3: 237–245. Ishikawa A, Shimada Y, Foxton RM, Tagami J. 2007. Microtensile and micro-shear bond strengths of current self etch adhesives to enamel and dentin. Am J Dent 20:161–166. Ito S, Tay FR, Hashimoto M, Yoshiyama M, Saito T, Brackett WW, Waller JL, Pashley DH. 2005. Effects of multiple coating of two allin-one adhesives on dentin bonding. J Adhes Dent 7:133–141. Kantona TR, Winkler MM. 1994. Stress analysis of a bulk-filled class V lightcured composite restoration. J Dent Res 73:1470–1477. Kidd EM. 1976. Microleakage: A review. J Dent 4:199–206. King NM, Tay FR, Pashley DH, Hashimoto M, Ito S, Brackett WW, Garcıa-Godoy F, Sunico M. 2005. Conversion of one-step to twostep self-etch adhesives for improved efficacy and extended application. Am J Dent 18:126–134. Manuja N, Nagpal R. 2012b. Resin-tooth interfacial morphology and sealing ability of one-step self etch adhesives: Microleakage and SEM study. Micros Res Tech 75:903–909. Manuja N, Pandit IK, Srivastava N, Gugnani N, Nagpal R. 2011. Comparative evaluation of shear bond strength of various esthetic restorative materials to dentin: An in vitro study. J Indian Soc Pedod Prev Dent 29:7–13. Manuja N, Nagpal R, Pandit IK. 2012a. Dental adhesion: Mechanism, techniques and durability. J Clin Pediatr Dent 36:223–234. Manuja N, Nagpal R, Chaudhary S. 2012c. Bonding efficacy of onestep self adhesives: Effect of additional enamel etching and hydrophobic layer application. J Dent Child 79:3–8. Miguez PA, Castro PS, Nunes MF, Walter R, Pereira PN. 2003. Effect of acid etching on enamel bond of two self-etching systems. J Adhes Dent 5:107–112. Miyazaki M, Sato M, Onose H. 2000. Durability of enamel bond strength of simplified bonding systems. Oper Dent 25:75–80. Moszner N, Salz U, Zimmermann J. 2005. Chemical aspects of selfetching enamel-dentin adhesives: A systematic review. Dent Mater 21:895–910. Moura SK, Pelizzaro A, Dal Bianco K, de Goes MF, Loguercio AD, Reis A, Grande RH. 2006. Does the acidity of self-etching primers affect bond strength and surface morphology of enamel? J Adhes Dent 8:75–83. Nagpal R, Tewari S, Gupta R. 2007. Effect of various surface treatments on the microleakage and ultrastructure of resin-tooth interface. Oper Dent 32:16–23. Nagpal R, Manuja N, Tyagi SP, Singh UP. 2011. In vitro bonding effectiveness of self-etch adhesives with different application
techniques: A microleakage and scanning electron microscopic study. J Conserv Dent 14:258–263. Nagpal R, Manuja N, Pandit IK. 2013. Effect of proanthocyanidin treatment on the bonding effectiveness of adhesive restorations in pulp chamber. J Clin Pediatr Dent 38:49–53. Nagpal R, Manuja N, Pandit IK. 2014. Adhesive bonding to pulp chamber dentin after different irrigation regimens. J Investig Clin Dent 1:1–4. Pashley EL, Agee KA, Pashley DH, Tay FR. 2002. Effect of one versus two applications of an unfilled, all-in-one adhesive on dentin bonding. J Dent 30:83–90. Perdig~ ao J, Geraldeli S. 2003. Bonding characteristics of self-etching adhesives to intact versus prepared enamel. J Esthet Restor Dent 15:32–41. Reis AF, Bedran-Russo AK, Giannini M, Pereira PN. 2007. Interfacial ultramorphology of single step adhesives: Nanoleakage as a function of time. J Oral Rehab 34:213–221. Sharma P, Nagpal R, Tyagi SP, Singh UP, Manuja N. 2015. Adhesion to pulp chamber dentin: Effect of ethanol-wet bonding technique and proanthocyanidins application. Saudi Endod J 5:38–45. Silveira de Ara ujo C, Incerti da Silva T, Ogliari FA, Meireles SS, Piva E, Demarco FF. 2006. Microleakage of seven adhesive systems in enamel and dentin. J Contemp Dent Pract 7:26–33. Spencer P, Wang Y. 2002. Adhesive phase separation at the dentin interface under wet bonding conditions. J Biomed Mater Res 62: 447–456. Tay FR, Pashley DH. 2001. Aggressiveness of contemporary selfetching systems 1: Depth of penetration beyond dentin smear layer. J Dent 17:296–308. Tay FR, Pashley DH. 2003. Water treeing—A potential mechanism for degradation of dentin adhesives. Am J Dent 16:6–12. Tay FR, Moulding KM, Pashley DH. 1999. Distribution of nanofillers from a simplified-step adhesive in acid-conditioned dentin. J Adhes Dent 1:103–117. Tay FR, Pashley DH, Yoshiyama M. 2002. Two modes of nanoleakage expression in single-step adhesives. J Dent Res 81:472–476. Toledano M, Osorio R, de Leonardi G, Rosales-Leal JI, Ceballos L, Cabrerizo-Vilchez MA. 2001. Influence of self etching primer on the resin adhesion to enamel and dentin. Am J Dent 14:205–210. Toledano M, Proenc¸a JP, Erhardt MCG, Osorio E, Aguilera FS, Osorio R, Tay FR. 2007. Increases in dentin-bond strength if doubling application time of an acetone-containing one-step adhesive. Oper Dent 32:133–137. Van Landuyt KL, De Munck J, Snauwaert J, Coutinho E, Poitevin A, Yoshida Y, Inoue S, Peumans M, Suzuki K, Lambrechts P, Van Meerbeek B. 2005. Monomer-solvent phase separation in one-step self-etch adhesives. J Dent Res 84:183–187. Van Landuyt KL, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, Coutinho E, Suzuki K, Lambrechts P, Van Meerbeek B. 2007. Systematic review of the chemical composition of contemporary dental adhesives. Biomaterials 28:3757–3785. Van Meerbeek B, Vargas M, Inoue S, Yoshiday Y, Peumans M, Lambrechts P, Vanherle G. 2001. Adhesives and cements to promote preservation dentistry. Oper Dent 26: S119–S144. Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, Van Landuyt K, Lambrechts P, Vanherle G. 2003. Buonocore memorial lecture. Adhesion to enamel and dentin: Current status and future challenges. Oper Dent 28:215–235. Verma R, Singh UP, Tyagi SP, Nagpal R, Manuja N. 2013. Long term bonding effectiveness of simplified etch-and-rinse adhesive to dentin after different surface pre-treatments. J Conserv Dent 16:367–370. Wei S, Shimada Y, Sadr A, Tagami J. 2009. Effect of double-application of three single-step self-etch adhesives on dentin bonding and mechanical properties of resin-dentin area. Oper Dent 34:716–724. Yoshida Y, Nagakane K, Fukuda R, Nakayama Y, Okazaki M, Shintani H, Inoue S, Tagawa Y, Suzuki K, De Munck J, Van Meerbeek B. 2004. Comparative study on adhesive performance of functional monomers. J Dent Res 83:454–458. Yoshikawa T, Sano H, Burrow MF, Tagami J, Pashley DH. 1999. Effect of dentin depth and cavity configuration on bond strength. J Dent Res 78:898–905. Zheng L, Pereira PN, Nakajima M, Sano H, Tagami J. 2001. Relationship between adhesive thickness and microtensile bond strength. Oper Dent 26:97–104.
Microscopy Research and Technique
Influence of Double Application Technique on the Bonding Effectiveness of Self-Etch Adhesive Systems RAJNI NAGPAL,1 PALLAVI SHARMA,1* NAVEEN MANUJA,2 SHASHI PRABHA TYAGI,1 UDAI PRATAP SINGH,1 SHIPRA SINGH,1 AND PAYAL SINGH1 1
Department of Conservative Dentistry & Endodontics, Kothiwal Denta L College & Research Centre, Moradabad, Uttar Pradesh, India 2 Department of Pediatric Dentistry, Kothiwal Dental College & Research Centre, Moradabad, Uttar Pradesh, India
KEY WORDS
double-application; single-step self-etch adhesives; microleakage; resin-dentin interfacial micromorphology
ABSTRACT Aim: To evaluate and compare the effect of double-application of single-step self-etch adhesives using microleakage study and to analyze the dentin–adhesive interfacial micromorphology. Methods: In total, 72 extracted human premolars were divided into three groups for different self-etch adhesives (G Bond, GC [GB], Optibond, Kerr [OB], and Xeno V Plus, Dentsply [XV]). Class V cavities were prepared. Each group was further divided into two subgroups (n 5 10) according to the placement technique of the adhesive, using the singleapplication [subgroup (a)] or double-application method [subgroup (b)]. Resin composite (Z 250, 3M ESPE, St. Paul, MN) was used to restore the cavities and light cured for 40 s. Twenty samples from each group were subjected to microleakage study. Two samples from both the subgroups of the three adhesives were used for scanning electron microscopic examination of the resin–dentin interfacial ultrastructure. Dye leakage scores were subjected to statistical analysis using Kruskal–Wallis and Mann–Whitney U-tests at significance level of P < 0.05. Results: GB depicted significantly more microleakage which was significantly greater than OB and XV. The double application led to significant decrease in microleakage of GB with no significant effect on the microleakage scores of other two all-in-one adhesives, that is OB and XV. Conclusion: Double application of all-in-one self-etch adhesives improves the marginal sealing ability in dentin although it appears to be product dependent. Microsc. Res. Tech. 78:489–494, 2015. V 2015 Wiley Periodicals, Inc. C
INTRODUCTION Trend toward the simplification of bonding procedures and overcoming the problem of inconsistent adhesion to dentin have led to the introduction of selfetch adhesives. The self-etch systems have been categorized as two-step and one-step adhesives. Furthermore, these one-step self-etch adhesives have been subclassified as strong, moderate (intermediary strong), and mild, based on their pH value (Van Meerbeek et al., 2003). One-step self-etch adhesives combine all the components of an adhesive system (etchant, primer, and bonding agent) into a single solution with a single-application (SA) step (Van Landuyt et al., 2005). With this approach, the rinsing and drying phase is eliminated, which does not only reduce clinical application time, but also significantly decreases technique sensitivity (Tay and Pashley, 2001; Van Meerbeek et al., 2001). In addition, the simultaneous impregnation of the exposed collagen matrix with resin up to the same depth of demineralization eliminates the risk of incomplete resin infiltration (Van Landuyt et al., 2005). Unfortunately, it seems that this simplicity relates to the extent of efficacy (Reis et al., 2007) as controversies over the performance of these adhesives with regard to their bonding potential have also been C V
2015 WILEY PERIODICALS, INC.
reported (Batra et al., 2014; Chersoni et al., 2004; De Munck et al., 2003; Inoue et al., 2001; Ishikawa et al., 2007; Manuja and Nagpal, 2012b; Nagpal et al., 2011). The poor bonding performance of one-step self-etch adhesives reported in dentin may be attributed to different factors (Hegde and Bhandary, 2008). The etching pattern is not well defined as that provided by phosphoric acid (Manuja et al., 2012a; Miguez et al., 2003; Moura et al., 2006; Perdigao and Geraldeli, 2003). These products create very thin coatings, leading to oxygen inhibition, resulting in a suboptimal polymerization. They are prone to phase separation as the solvent evaporates from the solution and they behave as semi-permeable membranes after polymerization (Albuquerque et al., 2008). These adhesives are extremely hydrophilic as they contain high concentrations of both ionic and hydrophilic monomers (Miyazaki et al., 2000). Such hydrophilicity renders these *Correspondence to: Pallavi Sharma, Department of Conservative Dentistry & Endodontics, Kothiwal Dental College & Research Centre, Moradabad, Uttar Pradesh, India. E-mail: [email protected] REVIEW EDITOR: Prof. Alberto Diaspro Received 2 February 2015; accepted in revised form 7 March 2015 Abbreviations: DA, double application; GB, G bond; OB, optibond; SA, single application; SEM, scanning electron microscope; XV, Xeno V Plus DOI 10.1002/jemt.22499 Published online 10 April 2015 in Wiley Online Library (wileyonlinelibrary.com).
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R. NAGPAL ET AL TABLE 1. Manufacturers, compositions, and application procedures of the tested self-etch adhesives Application procedure
Adhesive/manufacturer
Composition
SA
DA
GB (GC, Tokyo, Japan)
4-MET,UDMA, TEGDMA methacrylic acid ester, acetone, water, fumed silica fillers, photoinitiator GPDM, HEMA, mono- and difunctional methacrylate monomers, ethanol, acetone, and water as solvents, camphorquinone photoinitiators, nanofillers, and fluoride-releasing fillers Bifunctional acrylate, acidic acrylate, functionalized phosphoric acid ester, water, tertiary butanol, initiator, stabilizer
1. Application of one coat of adhesive (5–10 s) 2. Gentle air stream (5 s) 3. Light activation (10 s–600 mW/cm2) 4. Composite placement curing (40 s) 1. Application of one coat of adhesive (20 s) 2. Gentle air stream (10 s) 3. Light activation (10 s–600 mW/cm2) 4. Composite placement curing (40 s)
1. Steps 1–2 from (SA) 2. Repeat Steps 1–2 3. Step 3 4. Step 4 1. Steps 1–2 from (SA) 2. Repeat Steps 1–2 3. Step 3 4. Step 4
1. Application of one thick coat of adhesive under pressure 2. Gently agitate the adhesive for 20 s 3. Gentle air stream (5 s) 4. Light activation (10 s–600 mW/cm2) 5. Composite placement curing (40 s)
1. Steps 1–3 from (SA)
OB all-in-one (Kerr, Orange, CA)
XV (Dentsply DeTrey, Konstanz, Germany)
2. Repeat Steps 1–3 3. Step 4 4. Step 5
Abbreviations: Bis-GMA, bisphenol-A diglycidyl methacrylate; HEMA, 2-hydroxyethyl methacrylate; MDP, 10-methacryloyloxydecyl dihydrogen phosphate; TEGDMA, triethylene glycol dimethacrylate; 4-MET, 4-methacryloyloxy–ethyl trimellitic phosphate; UDMA, urethane dimethacrylate.
adhesives very permeable and denies their ability to hermetically seal dentin surfaces. This water sorption plasticizes polymers and lowers their mechanical properties (Bastioli et al., 1990). Although hydrophobic dimethacrylates are added to all-in-one adhesives to produce stronger crosslinked polymer networks, the hydrophilic monomers tend to cluster together before polymerization to create hydrophilic domains (Eliades et al., 2001; Spencer and Wang, 2002) and microscopic water-filled channels called water trees (Ferrari and Tay, 2003; Tay et al., 2002). Several authors have reported that self-etch adhesive systems did not improve bonding effectiveness to dentin in spite of their purported reduction in technique sensitivity (Manuja et al., 2012c; Tay and Pashley, 2003; Toledano et al., 2001). Infiltration of adhesives into the dentin and the thickness of the adhesive layer are directly correlated to rheological and chemical characteristics (Albuquerque et al., 2008; Moszner et al., 2005), but they could also be influenced by the mode of application (Belli et al., 2011). To offset the limitations of self-etching adhesives, altered bonding protocols that increase resin–dentin bond quality were suggested (Pashley et al., 2002; Toledano et al., 2007). Among the different clinical approaches are the use of an additional layer of hydrophobic resin agent (King et al., 2005), multiple-layer application of additional coats of adhesive (Erhardt et al., 2009; Hashimoto et al., 2004; Ito et al., 2005; Pashley et al., 2002; Wei et al., 2009), enhanced solvent evaporation (Van Landuyt et al., 2005), use of collagen crosslinkers and matrix metalloproteinase inhibitors (Nagpal et al., 2013, 2014; Sharma et al., 2015; Verma et al., 2013), and prolonged curing-time intervals (Breschi et al., 2007; Cadenaro et al., 2005; Erhardt et al., 2009). It has been reported that double application (DA) of onestep self-etch adhesives may result in a more uniform infiltration of the adhesive into smear layer-covered dentin if a one-step self-etch adhesive is applied in two layers (Pashley et al., 2002). Different studies have reported the effect of additional application of one-step self-etch adhesives to dentin. However, most of these studies have been
performed on flat surfaces which do not take into account the influence of C-factor on bonding. Thus, the objective of this study was to evaluate the influence of DA technique on the bonding effectiveness of self-etch and to observe the morphological characteristics of the resin–dentin interface after such treatment under scanning electron microscope (SEM). The null hypothesis tested was that the DA of adhesives on the prepared dentin surface will not affect the microleakage of onestep self-etch adhesives. MATERIALS AND METHODS This study was performed on 72 intact caries-free human premolars extracted for orthodontic purpose. After debridement and disinfection in 1% of thymol solution, teeth were stored in distilled water until use. Buccal Class V cavities centered on the cementoenamel junction were prepared with 3-mm mesiodistal width, 3 mm occlusogingival dimensions, and 1.5 mm depth, using ISO 012 straight fissure diamond point (Dentsply Detrey, USA) in an air–water-cooled highspeed handpiece. The bur was changed after every five preparations. The gingival margins on dentin were maintained as butt joint. The teeth were randomly divided into six groups according to three one-step selfetch adhesives used: G Bond (GB) (GC, Tokyo, Japan), optibond (OB) (Kerr, Orange, CA, USA), and Xeno V Plus (XV) (Dentsply DeTrey, Konstanz, Germany) and two application modes (Table 1). Group 1a; GB-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of GB application according to the manufacturer’s directions. Group 1b; GB-DA: The GB adhesive applied as in Group 1, followed by DA of self-etch adhesive. Group 2a; OB-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of OB application according to the manufacturer’s directions. Group 2b; OB-DA: The OB adhesive applied as in Group 1, followed by DA of self-etch adhesive. Microscopy Research and Technique
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TABLE 2. Mean score for dye penetration of all the three self-etch adhesives Adhesives and application modes Mean microleakage score GB Group 1a; GB-SA Group 1b; GB-DA OB Group 2a; OB-SA Group 2b; OB-DA XV Group 3a; XV-SA Group 3b; XV-DA
2.6 1.6 1.6 1.4 1.4 1.0
TABLE 3. Intergroup comparisons using Mann–Whitney U-test Group comparison
P-values
Groups 1a and 1b Groups 1a and 2a Groups 1a and 3a Groups 1b and 2b Groups 1b and 3b Groups 2a and 2b Groups 2a and 3a Groups 2b and 3b Groups 3a and 3b
0.023a 0.023a 0.011a 0.639 0.203 0.639 0.639 0.431 0.431
a
Statistically significant difference between the two groups at a significance level of P < 0.05.
Group 3a; XV-SA: Dentin was etched with 37% of phosphoric acid (Etchant, 3M ESPE, St. Paul, MN) for 15 s prior to SA of XV application according to the manufacturer’s directions. Group 3b; XV-DA: The XV adhesive applied as in Group 1, followed by DA of self-etch adhesive. The cavities were bulk filled with resin composite (Z 250, 3M ESPE, St. Paul, MN), light cured using Spectrum 800 (Dentsply, Caulk, Milford, DE) for 40 s at 600 mW/cm2 and polished. The restored teeth in each group were thermocycled for 500 cycles at 5 and 55 C with 30 s of dwell time. For microleakage test, 10 samples from each group were coated with two layers of sticky wax, leaving a 1-mm window around the cavity margins. All the samples were then immersed in freshly prepared 2% methylene blue dye for 48 h. The teeth were then rinsed with water, the sticky wax was removed, and the teeth were left to air dry at room temperature for 24 h. After drying the samples at room temperature, the teeth were sectioned longitudinally in a buccolingual direction with the help of diamond disk by a cut through the center of the restoration. Dye penetration at the tooth–restoration interface was assessed by a stereomicroscope (Olympus 2.5X) at a magnification of 103. The following ranking systems were used to score the degree of dye penetration (Nagpal et al., 2007; Silveira et al., 2006). Dye leakage score 0 1 2 3
Criteria for Scoring No evidence of microleakage Dye penetration up to half the cavity depth Dye penetration of more than half the cavity depth Dye penetration along the axial wall
SEM Evaluation The restored samples were sectioned mesiodistally, and polished with wet 210 grit SiC paper. Acid–base Microscopy Research and Technique
Fig. 1. a: SEM view showing generalized gap at resin–dentin interface after bonding with GB using SA technique (Group 1a; GB-SA). b: SEM view showing improved interfacial seal after bonding with GB using DA technique (Group 1b; GB-DA).
treatment (6 N HCl for 30 s followed by 4% NaOCl for 10 min) was done, and the samples were dehydrated in ascending ethanol concentration (50, 75, and 95% for 20 min each and 100% for 1 h), and then transferred to a critical point dryer for 30 min. All 12 specimens were then gold sputter coated and the surfaces were examined under a SEM (Leo 435 VP Cambridge, United Kingdom). Statistical Analysis Dye leakage scores obtained were subjected to statistical analysis using Kruskal–Wallis and Mann– Whitney U-tests (SPSS Base 15.0 software) at a significance level of P < 0.05. RESULTS Sealing Ability Table 2 lists the mean scores of microleakage for GB, OB, and XV and Table 3 summarizes the intergroup comparisons using Mann–Whitney U-test and corresponding P-values. When used according to the manufacturer’s instructions in SA mode, GB depicted maximum microleakage which was significantly
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Fig. 2. a: SEM view showing generalized gap at resin–dentin interface after bonding with OB using SA technique (Group 2a; OB-SA). b: SEM view showing perfect interfacial seal after bonding with OB using DA technique (Group 2b; OB-DA).
Fig. 3. a: SEM view showing generalized gap at resin–dentin interface after bonding with XV using SA technique (Group 3a; XV-SA). b: SEM view showing perfect interfacial seal after bonding with XV using DA technique (Group 3b; XV-DA).
greater than OB and XV. The double-layer application of adhesive systems led to significant decrease in microleakage with GB self-etch adhesive (Groups 1a and 1b; P 5 0.023). However, DA had no significant effect on the microleakage scores of both the other allin-one adhesives, that is OB and XV.
adhesive bonding (Kantona and Winkler, 1994; Kidd, 1976; Manuja et al., 2011; Yoshikawa et al., 1999). The results of the present investigation led to the rejection of the null hypotheses as the use of a DA technique significantly improved marginal sealing for GB although improved marginal adaptation after DA was observed for all the self-etch adhesive systems regardless of the acetone-based (GB), ethanol-based (XV), or ethanol- and acetone-based (OB) nature of the adhesives. This was also observed by Hashimoto et al. (2006). Several mechanisms could account for the better performance of DA. As the first layer of the adhesive begins to etch the dentin substrate, it might become rapidly buffered by the hydroxyapatite (Camps and Pashley, 2000), so that the additional layers of unpolymerized acidic monomers may improve the etching ability of these adhesives by increasing the concentration of acidic reagents. Simultaneously to this process, more impregnation of resin might occur by additional supply of adhesive resin as hypothesized by Ito et al. (2005) and the increased thickness of the adhesive layer, which is known to reduce polymerization stress and improve the marginal seal (Choi et al., 2000).
Scanning Electron Microscope SEM observations of the resin–dentin interface are shown in Figures 1–3. All the self-etch adhesives when applied according to the manufacturer’s directions showed the presence of interfacial gap at the dentinal surface with little or no resin tag formation. The maximum interfacial gap was evident with GB. After double-layer application of these adhesives, reduction in interfacial gap was observed for all the adhesives. DISCUSSION The problem encountered with adhesive restorative procedures is the impaired marginal seal and to ensure outstanding marginal adaptation of an adhesive restoration, some restorative aspects must be considered, such as preparation design, composite shrinkage, and
Microscopy Research and Technique
DOUBLE APPLICATION TECHNIQUE USING SELF-ETCH ADHESIVES
SA of the adhesive has the effect of a strong etchant although the infiltration of resin to demineralized dentin may not be sufficient. In the second application, the additional supply of adhesive resin may improve the infiltration of resin monomers into the intertubular demineralized dentin. Two of the one-step self-etching adhesives are 2hydroxyethyl methacrylate (HEMA)-free: GB and XV. The HEMA monomer is commonly added to the bonding agents and improves the stability of adhesive solutions that contain hydrophobic and hydrophilic components. In this study, GB presented significantly more microleakage as compared to other two adhesives. GB is a HEMA-free, acetone/water-based mild one-step self-etch adhesive containing a high percentage of acetone (40%). Acetone being more volatile than ethanol does not form an azeotrope with water, and hence it may not promote water evaporation when compared to ethanol-based adhesives, resulting in a low water/solvent evaporation ratio (Cho and Dickens, 2004). Lower polymerization efficiency owing to residual-free water and phase separation of its components (owing to a lack of HEMA) may result in marginal gap along the tooth–adhesive junction (Van Landuyt et al., 2007; Van Meerbeek et al., 2003; Zheng et al., 2001). This can partly explain the increased microleakage after the dye penetration test. Similarly, XV is also a HEMA-free water-based unfilled adhesive with t-butanol solvent and contains functionalized phosphoric acid esters. The presence of t-butanol in XV may plays the role of HEMA and in addition may help in eliminating the high water contents present by lowering the water vapor pressure by the formation of azeotrope (Yoshida et al., 2004). Both XV and OB depicted similar leakage scores significantly lesser than GB. This may be attributed to the fact that XV and OB have similar acidity levels, which should cause similar demineralization patterns. They are known as moderately strong self-etch adhesives; unlike strong self and total-etch adhesives, they create only a submicron hybrid layer (Tay et al., 1999). In addition to micromechanical interlocking through hybridization, specific functional monomers of these adhesives may interact chemically with residual hydroxyapatite crystals that remain available in the submicron hybrid layer (Inoue et al., 2001; Tay et al., 1999). Glycerol phosphate dimethacrylate (GPDM) adhesive monomer and filled adhesive technologies coupled with OB unique ternary solvent system provide excellent adhesion to all dental substrates. Although the tested adhesives have similar mechanisms of adhesion, HEMA-containing OB adhesive depicted lower microleakage scores and this justifies the presence of HEMA to prevent organic phase separations from the water-based composition. Several mechanisms may account for the superior performance of OB. The longer adhesive application time (40 s) recommended by the manufacturer may improve the etching ability of OB by increasing the exposure time of acidic reagents. Chemical composition of OB also differs from that of the other adhesives. This adhesive uses a ternary solvent system (water, acetone, and ethanol) that, according to the product’s technical bulletin, provides effective etching, enhanced material Microscopy Research and Technique
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stability, and a uniform adhesive layer. Functional acidic monomers of these adhesives also differ: OB uses GPDM as the functional monomer, OB adhesive contains nanofillers; the previous reports (Deliperi et al., 2007; Fortin and Swift, 1994) found that the collagen fibril network filters out most nanofillers, holding them at the hybrid layer surface where they act as an intermediate shock absorber. Reduced microleakage scores have been reported for filled adhesives (Deliperi et al., 2003, 2007; Fortin and Swift, 1994). These differences in chemical composition may have helped create a thicker, more homogeneous resin layer above the hybrid layer using OB, which may have improved resistance to microleakage. In addition, under the conditions of this study, the DA of this adhesive over the cured OB and XV adhesives did not reduce the microleakage scores in comparison with the application according to the manufacturers’ directions. Thus, lower leakage values can be obtained with OB and XV adhesives applied according to the manufacturers’ directions; it is not necessary to consider the alternative modes of application.
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Microscopy Research and Technique
