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Ethanol-wet bonding technique: Clinical versus laboratory findings Eunice Kuhn a , Patrícia Farhat b , Ana Paula Teitelbaum b , Alexandra Mena-Serrano c , Alessandro D. Loguercio a , Alessandra Reis a,∗ , David H. Pashley d a
Department of Restorative Dentistry, State University of Ponta Grossa, Rua Carlos Cavalcanti, 4748, Bloco M, Sala 64A – Uvaranas, Ponta Grossa, Paraná, Brazil b School of Dentistry, CESCAGE (Cenro de Ensino Superior dos Campos Gerais), Rua Tomazina S.N – Olarias, Ponta Grossa, Paraná, Brazil c Department of Restorative Dentistry, Universidad de las Americas, Av. de los Granados E12-41, Pichincha, Quito, Ecuador d Department of Oral Biology, Medical College of Georgia, School of Dentistry, 1120 15th Street, CL2112, Augusta, GA, USA
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. This study evaluated the microtensile bond strength (TBS) and nanoleakage (NL)
Received 25 August 2014
of dentin bonded interfaces produced with ethanol-wet and water-wet bonding protocols
Received in revised form
under clinical and laboratory conditions.
18 November 2014
Methods. The sample was composed of forty primary second molars in advanced exfoliation
Accepted 26 May 2015
process. Occlusal cavities were prepared leaving a flat dentin surface on the pulpal floor.
Available online xxx
In half of the teeth, the water-wet protocol was followed using a three-step etch-and-rinse
Keywords:
70%, 80%, 95% and 3 × 100%), 15 s each for the ethanol-bonding protocol. An experimental
Ethanol-wet bonding
hydrophobic primer was used, followed by the neat adhesive application. Resin build-ups
In vivo
were prepared, stored for 24 h, sectioned into sticks and tested in tensile mode (0.5 mm/min).
adhesive. In the other half, dentin was dehydrated with ascending ethanol solutions (50%,
In vitro
NL was performed for all groups. The TBS and NL data were submitted to two-way ANOVA
Nanoleakage
and Kruskall–Wallis tests, respectively (˛ = 0.05).
Microtensile bond strength
Results. Under clinical conditions, the highest TBS was observed for the water-wet bonding while under the laboratory setting, the highest TBS was obtained for the ethanol-wet bonding. Increased NL was observed in the water-wet bonding groups irrespective of the bonding condition. Significance. The immediate benefits of the ethanol-bonding observed in the laboratory setting was not confirmed when the same protocol was performed in vivo. However, as reduced nanoleakage was seen in adhesive interfaces produced with the ethanol-wet bonding technique, suggests that the hybrid layer may be more resistant to degradation. © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
∗
Corresponding author. E-mail address: reis [email protected] (A. Reis).
http://dx.doi.org/10.1016/j.dental.2015.05.010 0109-5641/© 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kuhn E, et al. Ethanol-wet bonding technique: Clinical versus laboratory findings. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.05.010
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1.
Introduction
Early generations of dental adhesives were relatively hydrophobic, and dry substrates were required for bonding. However, drying acid-etched dentin causes collapse of the collagen meshwork that prevented resin infiltration. As a consequence, the resulting dentin bond strengths were very low [1]. Modifications of adhesive formulations, by the inclusion of more hydrophilic monomers and acidic resin monomers, made adhesive solutions more compatible with moist dentin, which, in turn, yielded significant improvements in the immediate bonding effectiveness of most adhesive systems [2,3]. The potential problems associated with incorporation of hydrophilic formulations are well known [1]. Increased water sorption [4–6] rapid deterioration of mechanical properties of the adhesive layer [4,7] as well as increased permeability of the adhesive interface [8,9] that jeopardize the longevity of resin–dentin bonds after short- and long-term periods under in vivo and in vitro investigations [10–17]. In an attempt to solve these problems, some studies attempted to make acid-etched dentin more hydrophobic [18–20]. The strategy involved the replacement of water within the demineralized collagen matrix with ascending concentrations of ethanol, allowing the latter to penetrate the collagen matrix without causing additional shrinkage of the interfibrillar spaces, in the so-called ethanol-wet bonding technique [20]. Although dentin bonding with hydrophobic resins using the ethanol-wet bonding technique has shown encouraging results in terms of resin–dentin bond stability [18,21,22] the protocol is time consuming and technique-sensitive [23]. Additionally, a complete replacement of water by ethanol may not be feasible under clinical conditions due to the constant presence of an outward physiological dentinal fluid coming up from the dental pulp. Although the ethanolwet bonding technique was conceived to be a bonding philosophy rather than a bonding technique, due to its clinical difficulties, the understanding of the behavior of this technique in a clinical setting may complement what has been reported in laboratory studies and it may be a major contribution to the adhesive dentistry. So far, to the extent of the authors’ knowledge no study has attempted to investigate the ethanol-wet bonding protocol in an in vivo setting. Therefore, the aim of the present study was to compare the resin–dentin bond strength and nanoleakage of dentin-bonded interfaces produced with ethanol- and water-wet bonding protocols under clinical and laboratory conditions. The following null hypotheses were tested: (1) there are no differences in the resin–dentin bond strength and nanoleakage produced by an etch-and-rinse adhesive system bonded with the ethanol-wet and water-wet protocols; (2) there are no differences in the resin–dentin bond strength and nanoleakage produced by an etch-andrinse adhesive system bonded under clinical or laboratory conditions.
2.
Materials and methods
2.1. Specimen preparation for the clinical and laboratory experiments The present investigation was approved by the local Ethics Committee under protocol number 24/2009. For the clinical experiment, clinical and radiographic examination of approximately 100 patients ranging from 10 to 12 years old were performed in order to find 20 patients to take part in this study. These patients were required to have an incipient caries lesion in the primary second molar (up to the upper 1/3 of the dentin in the interproximal radiograph) and be in need of restorative treatment in the same hemi-arch, so that patients would necessarily receive anesthesia and rubber dam isolation. All teeth selected were at an advanced stage of physiological root resorption and mobility, indicating advanced physiological exfoliation process. The fact that these teeth have been used as source of stem cells was evidence of their pulp vitality [24,25]. For the laboratory evaluation, 20 recently exfoliated primary second molars free of caries or having an incipient caries lesion were used. Teeth were stored in saline solution at 4 ◦ C for up to 3 months before the in vitro experiment.
2.2.
Tooth preparation and restorative procedures
In each tooth, one standardized occlusal cavity was prepared under local anesthesia without vasoconstrictor (3% mepivacaine solution, Mepisv, Nova DFL, Rio de Janeiro, RJ, Brazil) and rubber dam isolation, using a cylindrical diamond bur (#1092, KG Sorensen, São Paulo, Brazil) under watercooling. Each diamond bur was used in four preparations and then discarded. The cavities were prepared in order to achieve: 1 – the largest possible dimensions, which averaged 7 mm wide, 6 mm long and 2 mm deep; 2 – completely flat cavity floor dentin; 3 – complete enamel cavo-surface margins. The specimens were randomly divided into two groups, according to the bonding technique: water-wet (n = 10 teeth) and ethanol-wet bonding techniques (n = 10 teeth). Due to the cavity dimensions, the bonding was performed in deep dentin. For the water-wet bonding technique, preparations were total-etched with 35% phosphoric acid gel for 15 s, followed by water rinsing (15 s). Two coats of the Scotchbond MultiPurpose primer (Adper Scotchbond Multi-Purpose Plus – 3M ESPE, St. Paul, MN, batch number # 0804002271; Table 1) were applied to visibly moist demineralized dentin according to the manufacturer’s directions. After briefly air-drying for 10 s, Scotchbond Multi-Purpose Adhesive was applied and light cured for 10 s. After acid-etching, dentin in the ethanol-wet bonding group was treated with a series of increasing ethanol concentrations: 50%, 70%, 80%, 95% and three 100% ethanol applications for 15 s each following a chemical dehydration protocol [22]. Dehydration procedures were meticulously performed to ensure that the dentin surface was always
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Table 1 – Composition and application mode of the adhesive system used in this study. Adhesive system brand Adper Scotchbond MultiPurpose Plus
Component 1: Etchant 35% phosphoric acid Component 2: Scotchbond Multi-Purpose primer (HEMA, polyalkenoic acid polymer, water). Component 3: Scotchbond Multi-Purpose adhesive (Bis-GMA, HEMA, tertiary amines, photo-initiator)
immersed in a liquid phase by keeping it visibly moist prior to the application of the subsequent solution. Two consecutive coats of the experimental hydrophobic primer were applied to ethanol-saturated dentin. The experimental primer solution was prepared by diluting the Scotchbond Multi Purpose Adhesive (Table 1) with 50 wt% absolute ethanol. This procedure was performed to produce a water-free bonding resin with similar composition of the hydrophilic adhesive employed in the water-wet protocol. Excess ethanol solvent was evaporated with a gentle air stream for 10 s. Then, a layer of the neat Scotchbond MultiPurpose Adhesive was applied and spread over the primed surface and light cured for 10 s. Preparations from both groups were restored with a microhybrid composite resin (shade EA2; Opallis – FGM Dental Products, Joinville, SC, Brazil; batch number # 160708) in three increments. Each increment was light-cured for 20 s. All lightcuring procedures were performed for 10 s using a Radii LED light-curing unit (SDI Limited, Bayswater, Victoria, Australia) with an output intensity of 800 mW/cm2 . Within 20 min after completion of the bonding procedures, teeth were extracted, immersed in distilled water (pH 7), and kept in a moist environment for 24 h at 37 ◦ C before being prepared for the microtensile bond test and nanoleakage analysis. All operative and restorative procedures reported for the clinical experimental was repeated under laboratory conditions in the extracted teeth.
2.3.
Modified adhesive used for the ethanol-wet bonding
Original adhesive used for the water-wet bonding protocol
Microtensile bond strength test (TBS)
Bonded teeth from both experiments were longitudinally sectioned in both “x” and “y” directions across the bonded interface with a diamond saw in an ISOMET 1000 machine (Buehler, Lake Bluff, IL, USA), under water cooling at 300 rpm to obtain bonded sticks with a cross-sectional area of approximately 0.8 mm2 . Individual bonded sticks were attached to a device (Odeme Biotechnology, Joac¸aba, SC, Brazil) for microtensile testing, with cyanoacrylate resin (Super Bonder, Locitec, São Paulo, SP, Brazil), so that tensile forces acted perpendicularly to the dentin/adhesive interface. Specimens were subjected to a tensile force in a universal testing machine (Kratos, São Paulo, SP, Brazil) at a crosshead speed of 0.5 mm/min. The failure modes were evaluated at 400× magnification (HMV-2, Shimadzu, Tokyo, Japan) and classified as cohesive in dentin (CD) or composite resin (CR) (failure exclusively within dentin or resin composite), adhesive (A, adhesive failure, restricted to the resin–dentin interface without partial cohesive failure of the neighboring substrates) and mixed (M, adhesive failure
Component 1: Etchant 35% phosphoric acid Component 2: Scotchbond Multi-Purpose adhesive diluted in 50 wt% ethanol (Bis-GMA, HEMA, tertiary amines, photo-initiator and ethanol) Component 3: Scotchbond Multi-Purpose adhesive (Bis-GMA, HEMA, tertiary amines, photo-initiator)
along with partial cohesive failure of the neighboring substrates). The number of specimens that showed premature failure was also recorded.
2.4.
Nanoleakage analysis
One resin–dentin bonded stick of each tooth, randomly selected and not tested under tensile forces, was prepared for nanoleakage evaluation. These bonded sticks were immersed in ammoniacal silver nitrate for 24 h [26] and the silver impregnated specimens were rinsed thoroughly in distilled water and placed in a photo-developing solution for 8 h under a fluorescent light. The adhesive interfaces were polished with descending grits of SiC papers (1000; 1200; 1500; 2000 and 2500) and 1 and 0.25 m diamond paste (Erios Prod. Odont. Ltda, São Paulo, SP, Brazil) using a polishing cloth. Specimens were ultrasonically cleaned and left in a desiccator for 24 h at room temperature. Specimens were then mounted on stubs and sputter-coated with a 10-nm gold layer to be analyzed by scanning electron microscopy (SEM) (JSM 6360LV, Jeol Ltd., Tokyo, Japan) using a backscattered detector. A representative image per tooth were obtained at 600× magnification by a blinded operator, not aware of the experimental conditions under investigation, and the amount of silver nitrate impregnation along the adhesive interface was evaluated by scoring nanoleakage interfacial [27] expression by two calibrated observers as reported in Table 2. Disagreements between observers were resolved by consensus.
2.5.
Statistical analysis
We based our sample size calculation on a previous study [28]. In order to detect a significant difference of 8 MPa between means, with an average standard deviation of 6 MPa, at a power of 80% and a level of significance of 5%, ten teeth were required per experimental condition. The TBS values of all sticks from the same tooth were averaged for statistical purposes. The bonded sticks that showed
Table 2 – Classification of nanoleakage scores according to Saboia et al. [27]. Score 0 1 2 3 4
% of adhesive interface showing nanoleakage No nanoleakage 25% with nanoleakage 25 ≤ 50% with nanoleakage 50 ≤ 75% with nanoleakage >75% with nanoleakage
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Table 3 – Means and standard deviations of resin–dentin bond strength values (MPa) for the experimental conditions with and without the inclusion of premature failures in the tooth mean. Without inclusion of PF*
Clinical Laboratory ∗ ∗∗
With inclusion of PF**
Water-wet
Ethanol-wet
Water-wet
33.0 (6.8)A 27.5 (6.3)A,B
23.9 (6.3)B 34.4 (9.5)A
31.0 (8.0)a 25.1 (6.5)a,b
Ethanol-wet 21.0 (4.0)b 31.5 (8.1)a
Different uppercase letters indicate statistically different means (p < 0.05). Different lowercase letters indicate statistically different means between groups (p < 0.05). PF – premature failures.
Table 4 – Number of specimens according to the fracture pattern modea of the resin–dentin beams for all experimental conditions. Bonding condition
Clinical Laboratory a
Water bonding
Ethanol bonding
Ad
Mi
Cd
Cc
PF
Ad
Mi
Cd
Cc
PF
12 14
35 30
5 2
3 9
2 3
15 12
35 30
10 11
7 4
6 6
Number of sticks with adhesive (Ad) or mixed (Mi) fracture mode, cohesive failure in dentin (Cd) or composite (Cc) and premature failures (PF).
cohesive failures either in dentin or composite resin were not included in the tooth mean. With regard to premature failures, two statistical analyses were performed, with and without the inclusion of premature failures in the tooth mean. We assigned a value of zero to the premature failures. The Kolmogorov–Smirnov test was performed to assess whether the data followed a normal distribution, and the Barlett’s test for equality of variances was performed to determine if the assumption of equal variances was valid. After observing the normality of the data distribution and the equality of the variances (normality; p = 0.821 and equal variance p = 0.817), the TBS (MPa) were submitted to a two-way ANOVA and Tukey’s test at ˛ = 0.05. The nanoleakage scores and the fracture modes were statistically evaluated by the Kruskall–Wallis test and pairwise comparisons were performed with the Mann–Whitney test at ˛ = 0.05.
3.
Results
The mean cross-sectional areas of the bonded sticks ranged from 0.82 to 1.03 mm2 . The mean bond strength values and their respective standard deviations are summarized in Table 3. A statistically significant interaction for the cross-product interaction bonding condition vs. adhesive technique was observed (p = 0.003 and p = 0.004 with or without the inclusion of premature failures on the average tooth bond strength). Under clinical conditions, statistically higher bond strength values were observed for the water-wet technique while under laboratory setting, the higher bond strength values were obtained for the ethanol-wet bonding approach. The fracture pattern mode of the resin–dentin bonded sticks is shown in Table 4. Most of the bond failures were adhesive and mixed irrespective of the experimental condition and no significant difference was detected among groups (p = 0.34). Table 5 depicts the data of the nanoleakage scores and representative images can be seen in Fig. 1. The Kruskall–Wallis test detected statistically differences between the medians of
nanoleakage scores at p < 0.001. Statistically higher nanoleakage was observed in the groups bonded with the water-wet technique irrespective of the bonding condition. From Fig. 1, one can observe an extensive reticular mode of silver nitrate uptake both in the hybrid and adhesive layers in the waterwet groups. Contrary to these findings, groups bonded with the ethanol-wet protocol showed only few, localized and small deposits of silver nitrate, located only in the hybrid layer.
4.
Discussion
When the micro-tensile bond strength test is used, several bonded sticks from the same tooth are produced and, therefore, they cannot be considered as experimental units [29,30]. Unfortunately, much of the literature has neglected this issue and also the amount of premature failures recorded by microtensile bond strength testing [31,32]. The correct handling of samples that failed before they could be tested is still up to debate [16,33,34]. However, it is generally accepted that premature failures cannot just be omitted as this will bias the results, yielding higher micro-tensile bond strength [16,33,34]. This is the reason why the micro-tensile bond strength was calculated in two different approaches. In the present study, both protocols were used and no difference in the final results were observed, which can be due to the few percentage of premature failures (3.5–9.5%) of this study and to the high number of teeth employed per group (n = 10). In an attempt to reduce the early degradation of the resin–dentin bonds, as mentioned in the introduction section,
Table 5 – Medians and interquartile ranges of the nanoleakage scores* for all experimental conditions. Bonding condition Clinical Laboratory ∗
Water bonding 4 (3-4)B 3 (3-4)B
Ethanol bonding 1 (1-2)A 1 (1-1)A
Different letters indicate medians statistically different (p < 0.05).
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Fig. 1 – Backscattering scanning electron micrographs of the adhesive interfaces of the experimental groups. Extensive silver nitrate deposition (white spots) could be seen in the adhesive interface produced with the water-wet bonding technique both under clinical (a) and laboratory conditions (c). Isolated silver nitrate grains can be seen in the adhesives interfaces produced with the ethanol-wet bonding technique in the clinical (b) and laboratory conditions (d).
studies have tried to bond hydrophobic resin blends (such as BisGMA/TEGDMA) into acid-etched dentin after a chemical dehydration technique [19,20]. Dentin bonding performed with hydrophobic resins using ethanol-wet bonding is less susceptible to degradation [18,21] due to the fact that polymerized hydrophobic resins exhibit a five-fold reduction in water sorption when compared with polymerized hydrophilic resins [4,6,7]. The results of the laboratory experiment of this study, conducted in primary dentin, are in agreement with earlier studies, as the application of a hydrophobic resin to ethanolsaturated dentin allowed the achievement of comparable bond strengths to that obtained with contemporary hydrophilic adhesives applied to water-wet dentin [18,19,21,22]. The good performance of the ethanol-wet bonding technique in vitro is mainly attributed to the fact that a relatively homogeneous distribution of hydrophobic resins within the hybrid layer was shown to occur using two-photon laser confocal microscopy [35] and micro-Raman spectral analysis [36], a finding not observed when hydrophilic resins are applied to water-wet dentin [37,38]. Although these studies performed the bonding under simulated pulpal pressure, the outward water from this procedure did not seem to be enough to cause any detrimental effects to the bonding protocol. Under the clinical conditions of this study there was an outward fluid flow across exposed dentin in response to the low, but positive pulpal tissue pressure [39], that is completely absent in extracted teeth or not sufficiently high under simulated water pressure. In the clinical setting, the amount of outward dentinal fluid may be enough to contaminate [40,41] the bonding protocol with water as well as with other protein presented in the dentinal fluid. The repetition of this
experiment using extracted teeth under simulated water pressure could elucidate this hypothesis. This positive pulpal pressure is likely responsible for the distinctly shallower penetration of etch-and-rinse adhesives into the dentin tubules [42] and the same might occur during infiltration of hydrophobic resin to ethanol-saturated dentin. Differences between the substrate used in this study and permanent teeth should be highlighted. In this study, the bonding protocol was done in deep dentin of primary molars, near the exfoliation period. Although we have not found in the literature no study that compared the morphology of this substrate with that of permanent teeth, a earlier study published by Dr. Pashley’s group [43] reported that the density and diameter of the dentinal tubules in sound primary molars were lower than the values reported by the permanent teeth, resulting in lower permeability of the primary molars. However, we hypothesize that near the exfoliation period, this condition might be different, as primary dentin has higher permeability due to the increased vascularity of the teeth under advanced root resorption [44,45]. Whether or not the same findings would be observed in permanent teeth is yet to be addressed. Perhaps the repetition of this experimental design in premolars with indication for extraction can add information to this research field. The use of local anesthetics with vasoconstrictors can reduce the intrapulpal pressure [46] and intuitively one could hypothesize that the use of an anesthetic with vasoconstrictor, different from the one employed in this study, could prevent the outward dentinal fluid. However, previous studies have not detected significant differences in the resin–dentin bond strength values of an etch-and-rinse adhesive system applied in vivo after anesthesia with and without vasoconstrictor
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[47,48]. This probably means that even under reduced pulpal pressure an outward fluid movement may still be present and conduct more water to the hybrid layer than under 20cm water pressure of earlier in vitro studies. Thus, although contamination may not be significant under laboratory conditions this may play a role under a clinical setting, preventing the dehydration of the demineralized dentin. The fact that the bond strength values of the ethanolwet bonding group performed under clinical condition was 31% lower than that observed in the laboratory experiment requires partial rejection of the null hypothesis. These results are compatible to the in vitro findings of Sadek et al. [19] who demonstrated that partial dehydration protocols, which are probably not capable of removing all water within the demineralized matrix, yielded very low bond strengths with the hydrophobic primer version that generated the best tensile strength results with a full dehydration protocol. This means that the ethanol-wet bonding protocol is technique sensitive, in that the presence of as little as 5% water in the demineralized dentin can result in an approximate 25% decrease in tensile strength of the hydrophobic adhesive to dentin [19]. While this may not be a problem in non-vital dentin because of the use of a stepwise chemical dehydration sequence, it may be a problem under most clinical scenarios. An option would be the application of occluding dentinal tubules with calcium oxalate [41,49,50] to minimize fluid transudation prior to the use of the ethanol wet bonding protocol. Obviously, this adds an extra step to an already known complicated protocol, which reduces even more the clinical feasibility of this technique. Although lower bond strength values was observed for the ethanol-wet bonding technique, it is worth mentioning that regardless the bonding condition, minimal nanoleakage was observed in the hybrid and adhesive layers of the ethanol-wet bonding groups. These were exclusively fine, isolated silver grains that were localized at the base of the hybrid layer. Contrary to that, extensive silver nitrate deposition, with a reticular mode, could be observed in the total thickness of the hybrid layer and also within the adhesive layer in the waterwet bonding groups. There results require partial rejection of the first null hypothesis. Both modes of nanoleakage represent areas of incomplete resin infiltration and locations where remnant moisture or solvent still remained entrapped within the collagen fibrils of the demineralized dentin [51]. Although intuitively a relationship between bond strength and leakage is expected, this relationship is complex. Although both properties were designed to evaluate the bonding effectiveness of materials and/or techniques, they do not always show a good correlation [52–55], as they seem to focus on different bonding features. Bond strength data seems to predict the retention of the restorative material while nanoleakage highlights potential sites of the adhesive interface prone to hydrolytic degradation and predicts the sealing ability of the bonded interface. Significant correlation between nanoleakage and bond strength were only demonstrated when aged bond strength values were included in the correlation test [16,56,57]. The nanoleakage findings in the current study are evidence that the water-wet bonding protocol may result in adhesive interfaces that are more prone to water sorption and to the degradation by water in the polymer network [1,51]. Water
softens the polymer by swelling the network and reducing the frictional forces between the polymer chains. Thus, unreacted monomers trapped in the polymer network are released to the surroundings, creating new channels for water penetration. As a consequence, the previously resin-infiltrated collagen matrix becomes exposed and vulnerable to attack by hostderived proteolytic enzymes [3,50], which leads to reductions of bond strengths values after short- and long-term water storage [10–17]. The longevity of the resin–dentin bonds produced with the ethanol-wet bonding technique has been observed only in laboratory studies [18,19,21] and further clinical studies are needed to validate or negate the in vitro findings. Although the present study was conducted in primary dentition, it is likely that the findings of the present study may also be applicable to permanent teeth, as it was already demonstrated that similar bond strength values could be obtained in both substrates [58–63].
5.
Conclusions
The immediate benefits of the ethanol-bonding observed in the laboratory setting was not confirmed when the same protocol was performed in vivo. However the reduced silver nitrate deposition in ethanol-bonding technique interfaces may suggest superior resistance to degradation.
references
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[58] Mahdi S, Bahman S, Arghavan AB, Fatemeh M. Comparison of shear bond strength of amalgam bonded to primary and permanent dentin. J Indian Soc Pedod Prev Dent 2008;26:71–3. [59] Marquezan M, Fagundes TC, Toledano M, Navarro MF, Osorio R. Differential bonds degradation of two resin-modified glass-ionomer cements in primary and permanent teeth. J Dent 2009;37:857–64. [60] Ricci HA, Sanabe ME, Costa CA, Hebling J. Effect of chlorhexidine on bond strength of two-step etch-and-rinse adhesive systems to dentin of primary and permanent teeth. Am J Dent 2010;23:128–32. [61] Ricci HA, Sanabe ME, Costa CA, Hebling J. Bond strength of two-step etch-and-rinse adhesive systems to the dentin of primary and permanent teeth. J Clin Pediatr Dent 2010;35:163–8. [62] Soares FZ, Rocha Rde O, Raggio DP, Sadek FT, Cardoso PE. Microtensile bond strength of different adhesive systems to primary and permanent dentin. Pediatr Dent 2005;27: 457–62. [63] Yaseen SM, Subba Reddy VV. Comparative evaluation of shear bond strength of two self-etching adhesives (sixth and seventh generation) on dentin of primary and permanent teeth: an in vitro study. J Indian Soc Pedod Prev Dent 2009;27:33–8.
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/dema
Ethanol-wet bonding technique: Clinical versus laboratory findings Eunice Kuhn a , Patrícia Farhat b , Ana Paula Teitelbaum b , Alexandra Mena-Serrano c , Alessandro D. Loguercio a , Alessandra Reis a,∗ , David H. Pashley d a
Department of Restorative Dentistry, State University of Ponta Grossa, Rua Carlos Cavalcanti, 4748, Bloco M, Sala 64A – Uvaranas, Ponta Grossa, Paraná, Brazil b School of Dentistry, CESCAGE (Cenro de Ensino Superior dos Campos Gerais), Rua Tomazina S.N – Olarias, Ponta Grossa, Paraná, Brazil c Department of Restorative Dentistry, Universidad de las Americas, Av. de los Granados E12-41, Pichincha, Quito, Ecuador d Department of Oral Biology, Medical College of Georgia, School of Dentistry, 1120 15th Street, CL2112, Augusta, GA, USA
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. This study evaluated the microtensile bond strength (TBS) and nanoleakage (NL)
Received 25 August 2014
of dentin bonded interfaces produced with ethanol-wet and water-wet bonding protocols
Received in revised form
under clinical and laboratory conditions.
18 November 2014
Methods. The sample was composed of forty primary second molars in advanced exfoliation
Accepted 26 May 2015
process. Occlusal cavities were prepared leaving a flat dentin surface on the pulpal floor.
Available online xxx
In half of the teeth, the water-wet protocol was followed using a three-step etch-and-rinse
Keywords:
70%, 80%, 95% and 3 × 100%), 15 s each for the ethanol-bonding protocol. An experimental
Ethanol-wet bonding
hydrophobic primer was used, followed by the neat adhesive application. Resin build-ups
In vivo
were prepared, stored for 24 h, sectioned into sticks and tested in tensile mode (0.5 mm/min).
adhesive. In the other half, dentin was dehydrated with ascending ethanol solutions (50%,
In vitro
NL was performed for all groups. The TBS and NL data were submitted to two-way ANOVA
Nanoleakage
and Kruskall–Wallis tests, respectively (˛ = 0.05).
Microtensile bond strength
Results. Under clinical conditions, the highest TBS was observed for the water-wet bonding while under the laboratory setting, the highest TBS was obtained for the ethanol-wet bonding. Increased NL was observed in the water-wet bonding groups irrespective of the bonding condition. Significance. The immediate benefits of the ethanol-bonding observed in the laboratory setting was not confirmed when the same protocol was performed in vivo. However, as reduced nanoleakage was seen in adhesive interfaces produced with the ethanol-wet bonding technique, suggests that the hybrid layer may be more resistant to degradation. © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
∗
Corresponding author. E-mail address: reis [email protected] (A. Reis).
http://dx.doi.org/10.1016/j.dental.2015.05.010 0109-5641/© 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
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1.
Introduction
Early generations of dental adhesives were relatively hydrophobic, and dry substrates were required for bonding. However, drying acid-etched dentin causes collapse of the collagen meshwork that prevented resin infiltration. As a consequence, the resulting dentin bond strengths were very low [1]. Modifications of adhesive formulations, by the inclusion of more hydrophilic monomers and acidic resin monomers, made adhesive solutions more compatible with moist dentin, which, in turn, yielded significant improvements in the immediate bonding effectiveness of most adhesive systems [2,3]. The potential problems associated with incorporation of hydrophilic formulations are well known [1]. Increased water sorption [4–6] rapid deterioration of mechanical properties of the adhesive layer [4,7] as well as increased permeability of the adhesive interface [8,9] that jeopardize the longevity of resin–dentin bonds after short- and long-term periods under in vivo and in vitro investigations [10–17]. In an attempt to solve these problems, some studies attempted to make acid-etched dentin more hydrophobic [18–20]. The strategy involved the replacement of water within the demineralized collagen matrix with ascending concentrations of ethanol, allowing the latter to penetrate the collagen matrix without causing additional shrinkage of the interfibrillar spaces, in the so-called ethanol-wet bonding technique [20]. Although dentin bonding with hydrophobic resins using the ethanol-wet bonding technique has shown encouraging results in terms of resin–dentin bond stability [18,21,22] the protocol is time consuming and technique-sensitive [23]. Additionally, a complete replacement of water by ethanol may not be feasible under clinical conditions due to the constant presence of an outward physiological dentinal fluid coming up from the dental pulp. Although the ethanolwet bonding technique was conceived to be a bonding philosophy rather than a bonding technique, due to its clinical difficulties, the understanding of the behavior of this technique in a clinical setting may complement what has been reported in laboratory studies and it may be a major contribution to the adhesive dentistry. So far, to the extent of the authors’ knowledge no study has attempted to investigate the ethanol-wet bonding protocol in an in vivo setting. Therefore, the aim of the present study was to compare the resin–dentin bond strength and nanoleakage of dentin-bonded interfaces produced with ethanol- and water-wet bonding protocols under clinical and laboratory conditions. The following null hypotheses were tested: (1) there are no differences in the resin–dentin bond strength and nanoleakage produced by an etch-and-rinse adhesive system bonded with the ethanol-wet and water-wet protocols; (2) there are no differences in the resin–dentin bond strength and nanoleakage produced by an etch-andrinse adhesive system bonded under clinical or laboratory conditions.
2.
Materials and methods
2.1. Specimen preparation for the clinical and laboratory experiments The present investigation was approved by the local Ethics Committee under protocol number 24/2009. For the clinical experiment, clinical and radiographic examination of approximately 100 patients ranging from 10 to 12 years old were performed in order to find 20 patients to take part in this study. These patients were required to have an incipient caries lesion in the primary second molar (up to the upper 1/3 of the dentin in the interproximal radiograph) and be in need of restorative treatment in the same hemi-arch, so that patients would necessarily receive anesthesia and rubber dam isolation. All teeth selected were at an advanced stage of physiological root resorption and mobility, indicating advanced physiological exfoliation process. The fact that these teeth have been used as source of stem cells was evidence of their pulp vitality [24,25]. For the laboratory evaluation, 20 recently exfoliated primary second molars free of caries or having an incipient caries lesion were used. Teeth were stored in saline solution at 4 ◦ C for up to 3 months before the in vitro experiment.
2.2.
Tooth preparation and restorative procedures
In each tooth, one standardized occlusal cavity was prepared under local anesthesia without vasoconstrictor (3% mepivacaine solution, Mepisv, Nova DFL, Rio de Janeiro, RJ, Brazil) and rubber dam isolation, using a cylindrical diamond bur (#1092, KG Sorensen, São Paulo, Brazil) under watercooling. Each diamond bur was used in four preparations and then discarded. The cavities were prepared in order to achieve: 1 – the largest possible dimensions, which averaged 7 mm wide, 6 mm long and 2 mm deep; 2 – completely flat cavity floor dentin; 3 – complete enamel cavo-surface margins. The specimens were randomly divided into two groups, according to the bonding technique: water-wet (n = 10 teeth) and ethanol-wet bonding techniques (n = 10 teeth). Due to the cavity dimensions, the bonding was performed in deep dentin. For the water-wet bonding technique, preparations were total-etched with 35% phosphoric acid gel for 15 s, followed by water rinsing (15 s). Two coats of the Scotchbond MultiPurpose primer (Adper Scotchbond Multi-Purpose Plus – 3M ESPE, St. Paul, MN, batch number # 0804002271; Table 1) were applied to visibly moist demineralized dentin according to the manufacturer’s directions. After briefly air-drying for 10 s, Scotchbond Multi-Purpose Adhesive was applied and light cured for 10 s. After acid-etching, dentin in the ethanol-wet bonding group was treated with a series of increasing ethanol concentrations: 50%, 70%, 80%, 95% and three 100% ethanol applications for 15 s each following a chemical dehydration protocol [22]. Dehydration procedures were meticulously performed to ensure that the dentin surface was always
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Table 1 – Composition and application mode of the adhesive system used in this study. Adhesive system brand Adper Scotchbond MultiPurpose Plus
Component 1: Etchant 35% phosphoric acid Component 2: Scotchbond Multi-Purpose primer (HEMA, polyalkenoic acid polymer, water). Component 3: Scotchbond Multi-Purpose adhesive (Bis-GMA, HEMA, tertiary amines, photo-initiator)
immersed in a liquid phase by keeping it visibly moist prior to the application of the subsequent solution. Two consecutive coats of the experimental hydrophobic primer were applied to ethanol-saturated dentin. The experimental primer solution was prepared by diluting the Scotchbond Multi Purpose Adhesive (Table 1) with 50 wt% absolute ethanol. This procedure was performed to produce a water-free bonding resin with similar composition of the hydrophilic adhesive employed in the water-wet protocol. Excess ethanol solvent was evaporated with a gentle air stream for 10 s. Then, a layer of the neat Scotchbond MultiPurpose Adhesive was applied and spread over the primed surface and light cured for 10 s. Preparations from both groups were restored with a microhybrid composite resin (shade EA2; Opallis – FGM Dental Products, Joinville, SC, Brazil; batch number # 160708) in three increments. Each increment was light-cured for 20 s. All lightcuring procedures were performed for 10 s using a Radii LED light-curing unit (SDI Limited, Bayswater, Victoria, Australia) with an output intensity of 800 mW/cm2 . Within 20 min after completion of the bonding procedures, teeth were extracted, immersed in distilled water (pH 7), and kept in a moist environment for 24 h at 37 ◦ C before being prepared for the microtensile bond test and nanoleakage analysis. All operative and restorative procedures reported for the clinical experimental was repeated under laboratory conditions in the extracted teeth.
2.3.
Modified adhesive used for the ethanol-wet bonding
Original adhesive used for the water-wet bonding protocol
Microtensile bond strength test (TBS)
Bonded teeth from both experiments were longitudinally sectioned in both “x” and “y” directions across the bonded interface with a diamond saw in an ISOMET 1000 machine (Buehler, Lake Bluff, IL, USA), under water cooling at 300 rpm to obtain bonded sticks with a cross-sectional area of approximately 0.8 mm2 . Individual bonded sticks were attached to a device (Odeme Biotechnology, Joac¸aba, SC, Brazil) for microtensile testing, with cyanoacrylate resin (Super Bonder, Locitec, São Paulo, SP, Brazil), so that tensile forces acted perpendicularly to the dentin/adhesive interface. Specimens were subjected to a tensile force in a universal testing machine (Kratos, São Paulo, SP, Brazil) at a crosshead speed of 0.5 mm/min. The failure modes were evaluated at 400× magnification (HMV-2, Shimadzu, Tokyo, Japan) and classified as cohesive in dentin (CD) or composite resin (CR) (failure exclusively within dentin or resin composite), adhesive (A, adhesive failure, restricted to the resin–dentin interface without partial cohesive failure of the neighboring substrates) and mixed (M, adhesive failure
Component 1: Etchant 35% phosphoric acid Component 2: Scotchbond Multi-Purpose adhesive diluted in 50 wt% ethanol (Bis-GMA, HEMA, tertiary amines, photo-initiator and ethanol) Component 3: Scotchbond Multi-Purpose adhesive (Bis-GMA, HEMA, tertiary amines, photo-initiator)
along with partial cohesive failure of the neighboring substrates). The number of specimens that showed premature failure was also recorded.
2.4.
Nanoleakage analysis
One resin–dentin bonded stick of each tooth, randomly selected and not tested under tensile forces, was prepared for nanoleakage evaluation. These bonded sticks were immersed in ammoniacal silver nitrate for 24 h [26] and the silver impregnated specimens were rinsed thoroughly in distilled water and placed in a photo-developing solution for 8 h under a fluorescent light. The adhesive interfaces were polished with descending grits of SiC papers (1000; 1200; 1500; 2000 and 2500) and 1 and 0.25 m diamond paste (Erios Prod. Odont. Ltda, São Paulo, SP, Brazil) using a polishing cloth. Specimens were ultrasonically cleaned and left in a desiccator for 24 h at room temperature. Specimens were then mounted on stubs and sputter-coated with a 10-nm gold layer to be analyzed by scanning electron microscopy (SEM) (JSM 6360LV, Jeol Ltd., Tokyo, Japan) using a backscattered detector. A representative image per tooth were obtained at 600× magnification by a blinded operator, not aware of the experimental conditions under investigation, and the amount of silver nitrate impregnation along the adhesive interface was evaluated by scoring nanoleakage interfacial [27] expression by two calibrated observers as reported in Table 2. Disagreements between observers were resolved by consensus.
2.5.
Statistical analysis
We based our sample size calculation on a previous study [28]. In order to detect a significant difference of 8 MPa between means, with an average standard deviation of 6 MPa, at a power of 80% and a level of significance of 5%, ten teeth were required per experimental condition. The TBS values of all sticks from the same tooth were averaged for statistical purposes. The bonded sticks that showed
Table 2 – Classification of nanoleakage scores according to Saboia et al. [27]. Score 0 1 2 3 4
% of adhesive interface showing nanoleakage No nanoleakage 25% with nanoleakage 25 ≤ 50% with nanoleakage 50 ≤ 75% with nanoleakage >75% with nanoleakage
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Table 3 – Means and standard deviations of resin–dentin bond strength values (MPa) for the experimental conditions with and without the inclusion of premature failures in the tooth mean. Without inclusion of PF*
Clinical Laboratory ∗ ∗∗
With inclusion of PF**
Water-wet
Ethanol-wet
Water-wet
33.0 (6.8)A 27.5 (6.3)A,B
23.9 (6.3)B 34.4 (9.5)A
31.0 (8.0)a 25.1 (6.5)a,b
Ethanol-wet 21.0 (4.0)b 31.5 (8.1)a
Different uppercase letters indicate statistically different means (p < 0.05). Different lowercase letters indicate statistically different means between groups (p < 0.05). PF – premature failures.
Table 4 – Number of specimens according to the fracture pattern modea of the resin–dentin beams for all experimental conditions. Bonding condition
Clinical Laboratory a
Water bonding
Ethanol bonding
Ad
Mi
Cd
Cc
PF
Ad
Mi
Cd
Cc
PF
12 14
35 30
5 2
3 9
2 3
15 12
35 30
10 11
7 4
6 6
Number of sticks with adhesive (Ad) or mixed (Mi) fracture mode, cohesive failure in dentin (Cd) or composite (Cc) and premature failures (PF).
cohesive failures either in dentin or composite resin were not included in the tooth mean. With regard to premature failures, two statistical analyses were performed, with and without the inclusion of premature failures in the tooth mean. We assigned a value of zero to the premature failures. The Kolmogorov–Smirnov test was performed to assess whether the data followed a normal distribution, and the Barlett’s test for equality of variances was performed to determine if the assumption of equal variances was valid. After observing the normality of the data distribution and the equality of the variances (normality; p = 0.821 and equal variance p = 0.817), the TBS (MPa) were submitted to a two-way ANOVA and Tukey’s test at ˛ = 0.05. The nanoleakage scores and the fracture modes were statistically evaluated by the Kruskall–Wallis test and pairwise comparisons were performed with the Mann–Whitney test at ˛ = 0.05.
3.
Results
The mean cross-sectional areas of the bonded sticks ranged from 0.82 to 1.03 mm2 . The mean bond strength values and their respective standard deviations are summarized in Table 3. A statistically significant interaction for the cross-product interaction bonding condition vs. adhesive technique was observed (p = 0.003 and p = 0.004 with or without the inclusion of premature failures on the average tooth bond strength). Under clinical conditions, statistically higher bond strength values were observed for the water-wet technique while under laboratory setting, the higher bond strength values were obtained for the ethanol-wet bonding approach. The fracture pattern mode of the resin–dentin bonded sticks is shown in Table 4. Most of the bond failures were adhesive and mixed irrespective of the experimental condition and no significant difference was detected among groups (p = 0.34). Table 5 depicts the data of the nanoleakage scores and representative images can be seen in Fig. 1. The Kruskall–Wallis test detected statistically differences between the medians of
nanoleakage scores at p < 0.001. Statistically higher nanoleakage was observed in the groups bonded with the water-wet technique irrespective of the bonding condition. From Fig. 1, one can observe an extensive reticular mode of silver nitrate uptake both in the hybrid and adhesive layers in the waterwet groups. Contrary to these findings, groups bonded with the ethanol-wet protocol showed only few, localized and small deposits of silver nitrate, located only in the hybrid layer.
4.
Discussion
When the micro-tensile bond strength test is used, several bonded sticks from the same tooth are produced and, therefore, they cannot be considered as experimental units [29,30]. Unfortunately, much of the literature has neglected this issue and also the amount of premature failures recorded by microtensile bond strength testing [31,32]. The correct handling of samples that failed before they could be tested is still up to debate [16,33,34]. However, it is generally accepted that premature failures cannot just be omitted as this will bias the results, yielding higher micro-tensile bond strength [16,33,34]. This is the reason why the micro-tensile bond strength was calculated in two different approaches. In the present study, both protocols were used and no difference in the final results were observed, which can be due to the few percentage of premature failures (3.5–9.5%) of this study and to the high number of teeth employed per group (n = 10). In an attempt to reduce the early degradation of the resin–dentin bonds, as mentioned in the introduction section,
Table 5 – Medians and interquartile ranges of the nanoleakage scores* for all experimental conditions. Bonding condition Clinical Laboratory ∗
Water bonding 4 (3-4)B 3 (3-4)B
Ethanol bonding 1 (1-2)A 1 (1-1)A
Different letters indicate medians statistically different (p < 0.05).
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Fig. 1 – Backscattering scanning electron micrographs of the adhesive interfaces of the experimental groups. Extensive silver nitrate deposition (white spots) could be seen in the adhesive interface produced with the water-wet bonding technique both under clinical (a) and laboratory conditions (c). Isolated silver nitrate grains can be seen in the adhesives interfaces produced with the ethanol-wet bonding technique in the clinical (b) and laboratory conditions (d).
studies have tried to bond hydrophobic resin blends (such as BisGMA/TEGDMA) into acid-etched dentin after a chemical dehydration technique [19,20]. Dentin bonding performed with hydrophobic resins using ethanol-wet bonding is less susceptible to degradation [18,21] due to the fact that polymerized hydrophobic resins exhibit a five-fold reduction in water sorption when compared with polymerized hydrophilic resins [4,6,7]. The results of the laboratory experiment of this study, conducted in primary dentin, are in agreement with earlier studies, as the application of a hydrophobic resin to ethanolsaturated dentin allowed the achievement of comparable bond strengths to that obtained with contemporary hydrophilic adhesives applied to water-wet dentin [18,19,21,22]. The good performance of the ethanol-wet bonding technique in vitro is mainly attributed to the fact that a relatively homogeneous distribution of hydrophobic resins within the hybrid layer was shown to occur using two-photon laser confocal microscopy [35] and micro-Raman spectral analysis [36], a finding not observed when hydrophilic resins are applied to water-wet dentin [37,38]. Although these studies performed the bonding under simulated pulpal pressure, the outward water from this procedure did not seem to be enough to cause any detrimental effects to the bonding protocol. Under the clinical conditions of this study there was an outward fluid flow across exposed dentin in response to the low, but positive pulpal tissue pressure [39], that is completely absent in extracted teeth or not sufficiently high under simulated water pressure. In the clinical setting, the amount of outward dentinal fluid may be enough to contaminate [40,41] the bonding protocol with water as well as with other protein presented in the dentinal fluid. The repetition of this
experiment using extracted teeth under simulated water pressure could elucidate this hypothesis. This positive pulpal pressure is likely responsible for the distinctly shallower penetration of etch-and-rinse adhesives into the dentin tubules [42] and the same might occur during infiltration of hydrophobic resin to ethanol-saturated dentin. Differences between the substrate used in this study and permanent teeth should be highlighted. In this study, the bonding protocol was done in deep dentin of primary molars, near the exfoliation period. Although we have not found in the literature no study that compared the morphology of this substrate with that of permanent teeth, a earlier study published by Dr. Pashley’s group [43] reported that the density and diameter of the dentinal tubules in sound primary molars were lower than the values reported by the permanent teeth, resulting in lower permeability of the primary molars. However, we hypothesize that near the exfoliation period, this condition might be different, as primary dentin has higher permeability due to the increased vascularity of the teeth under advanced root resorption [44,45]. Whether or not the same findings would be observed in permanent teeth is yet to be addressed. Perhaps the repetition of this experimental design in premolars with indication for extraction can add information to this research field. The use of local anesthetics with vasoconstrictors can reduce the intrapulpal pressure [46] and intuitively one could hypothesize that the use of an anesthetic with vasoconstrictor, different from the one employed in this study, could prevent the outward dentinal fluid. However, previous studies have not detected significant differences in the resin–dentin bond strength values of an etch-and-rinse adhesive system applied in vivo after anesthesia with and without vasoconstrictor
Please cite this article in press as: Kuhn E, et al. Ethanol-wet bonding technique: Clinical versus laboratory findings. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.05.010
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[47,48]. This probably means that even under reduced pulpal pressure an outward fluid movement may still be present and conduct more water to the hybrid layer than under 20cm water pressure of earlier in vitro studies. Thus, although contamination may not be significant under laboratory conditions this may play a role under a clinical setting, preventing the dehydration of the demineralized dentin. The fact that the bond strength values of the ethanolwet bonding group performed under clinical condition was 31% lower than that observed in the laboratory experiment requires partial rejection of the null hypothesis. These results are compatible to the in vitro findings of Sadek et al. [19] who demonstrated that partial dehydration protocols, which are probably not capable of removing all water within the demineralized matrix, yielded very low bond strengths with the hydrophobic primer version that generated the best tensile strength results with a full dehydration protocol. This means that the ethanol-wet bonding protocol is technique sensitive, in that the presence of as little as 5% water in the demineralized dentin can result in an approximate 25% decrease in tensile strength of the hydrophobic adhesive to dentin [19]. While this may not be a problem in non-vital dentin because of the use of a stepwise chemical dehydration sequence, it may be a problem under most clinical scenarios. An option would be the application of occluding dentinal tubules with calcium oxalate [41,49,50] to minimize fluid transudation prior to the use of the ethanol wet bonding protocol. Obviously, this adds an extra step to an already known complicated protocol, which reduces even more the clinical feasibility of this technique. Although lower bond strength values was observed for the ethanol-wet bonding technique, it is worth mentioning that regardless the bonding condition, minimal nanoleakage was observed in the hybrid and adhesive layers of the ethanol-wet bonding groups. These were exclusively fine, isolated silver grains that were localized at the base of the hybrid layer. Contrary to that, extensive silver nitrate deposition, with a reticular mode, could be observed in the total thickness of the hybrid layer and also within the adhesive layer in the waterwet bonding groups. There results require partial rejection of the first null hypothesis. Both modes of nanoleakage represent areas of incomplete resin infiltration and locations where remnant moisture or solvent still remained entrapped within the collagen fibrils of the demineralized dentin [51]. Although intuitively a relationship between bond strength and leakage is expected, this relationship is complex. Although both properties were designed to evaluate the bonding effectiveness of materials and/or techniques, they do not always show a good correlation [52–55], as they seem to focus on different bonding features. Bond strength data seems to predict the retention of the restorative material while nanoleakage highlights potential sites of the adhesive interface prone to hydrolytic degradation and predicts the sealing ability of the bonded interface. Significant correlation between nanoleakage and bond strength were only demonstrated when aged bond strength values were included in the correlation test [16,56,57]. The nanoleakage findings in the current study are evidence that the water-wet bonding protocol may result in adhesive interfaces that are more prone to water sorption and to the degradation by water in the polymer network [1,51]. Water
softens the polymer by swelling the network and reducing the frictional forces between the polymer chains. Thus, unreacted monomers trapped in the polymer network are released to the surroundings, creating new channels for water penetration. As a consequence, the previously resin-infiltrated collagen matrix becomes exposed and vulnerable to attack by hostderived proteolytic enzymes [3,50], which leads to reductions of bond strengths values after short- and long-term water storage [10–17]. The longevity of the resin–dentin bonds produced with the ethanol-wet bonding technique has been observed only in laboratory studies [18,19,21] and further clinical studies are needed to validate or negate the in vitro findings. Although the present study was conducted in primary dentition, it is likely that the findings of the present study may also be applicable to permanent teeth, as it was already demonstrated that similar bond strength values could be obtained in both substrates [58–63].
5.
Conclusions
The immediate benefits of the ethanol-bonding observed in the laboratory setting was not confirmed when the same protocol was performed in vivo. However the reduced silver nitrate deposition in ethanol-bonding technique interfaces may suggest superior resistance to degradation.
references
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