| Abstract|| |
Background: Elimination of water entrapment in hybrid layer during bonding procedure would increase bonding durability.
Aims: This study evaluated the effect of oxalate desensitizer (OX) pretreatment on bond strength of three one-bottle adhesives to ethylene-diamine tetra acetic acid (EDTA)-conditioned dentin under dry bonding.
Materials and Methods: Three adhesive systems, One-Step Plus (OS), Optibond Solo Plus (OP) and Adper Single Bond (SB) were bonded on dentin surfaces under four bonding conditions: (1) Wet-bonding on acid-etched dentin, (2) wet bonding on EDTA-conditioned dentin, (3) dry bonding on EDTA-conditioned dentin, (4) dry bonding associated with OX on the EDTA-conditioned dentin. After storage and thermo cycling, shear bond strength test was performed. Data were analyzed using two-way analysis of variance and Tukey tests.
Results: Wet bonding with EDTA or acid etching showed similar bond strength for test adhesives. Dry bonding with EDTA significantly decreased the bond strength of OS, but it had no effect on the bonding of OP and SB. OX application in the forth bonding condition, in comparison with the third condition, had a negative effect on the bond strength of OP, but not influence on OS and SB.
Conclusions: The use of an OX on EDTA-conditioned dentin compromised the bonding efficacy of OS and OP under dry bonding but compatible for SB.
Keywords: Adhesives; bond strength; dentin; dry bonding; desensitizer; ethylene-diamine tetra acetic acid-conditioning; one-bottle; oxalate; wet bonding
|How to cite this article:|
Shafiei F, Doozandeh M. Impact of oxalate desensitizer combined with ethylene-diamine tetra acetic acid-conditioning on dentin bond strength of one-bottle adhesives during dry bonding. J Conserv Dent 2013;16:252-6
|How to cite this URL:|
Shafiei F, Doozandeh M. Impact of oxalate desensitizer combined with ethylene-diamine tetra acetic acid-conditioning on dentin bond strength of one-bottle adhesives during dry bonding. J Conserv Dent [serial online] 2013 [cited 2019 Dec 15];16:252-6. Available from: http://www.jcd.org.in/text.asp?2013/16/3/252/111327
| Introduction|| |
It is well-established that achievement of high bond strength to dentin is dependent on complete penetration of resin into spaces around the collagen fibrils in demineralized dentin. In acid-etched dentin, following complete dissolution of the minerals and loss of structural support of the fibrils, interfibrillar spaces are replaced with water in a full expansion state to facilitate resin penetration and hybrid layer formation known as wet-bonding technique. , Nevertheless, this technique is sensitive and has some disadvantages. The lack of practical criteria to manage the optimal degree of wetness on dentin substrate complicates the wet bonding for clinicians. As a result, it is applied differently among operators and in instructions of the manufacturer so that over-wetting or over-drying may occur instead of ideal moisture on the dentin. 
Excess water cannot be easily evaporated due to low vapor pressure and presence of HEMA contained in many adhesives, retaining water in the bonding site; phase separation of resin components may take place. This residual water is capable of diluting the concentration of adhesive monomers, preventing monomers diffusion to the full depth of the demineralized dentin and adequate polymerization of the monomers inside the collagen network. , Subsequently, the formed porous hybrid layer is more susceptible to water degradation over time. ,,
The adverse effects of water on the adhesive interface can be minimized when the etched dentin is kept in a dry state. Dry bonding may be obtained during air drying of the cavity after rinsing by clinician to ensure the frosted etched appearance of the enamel. However, air drying the demineralized dentin leads to collapsed collagen network. As a result, resin penetration is limited to shrink and stiff matrix.  The formed sub-optimal and porous hybrid layer may account for immediate low bond strength and long-term degradation of resin-dentin bond. , Although it seems that dried etched dentin is easily obtained, in clinical situation, air blowing of the smear layer and smear plugs-free dentin for water evaporation leads to increased outward fluid flowing from the pulp.  This fluid drawing can be prevented by occlusion of the tubules.  Different studies showed the effectiveness of oxalate solution in blocking the orifice of dentinal tubules. , Therefore, it can reduce the outward flow of dentinal fluid during bonding procedure. In this way, simultaneous tubular occlusion and possible maintenance of the collagen matrix stability in the absence of water can be a beneficial approach to provide high and stable dentin bonding.
Ethylene-diamine tetra acetic acid (EDTA) is a molecule containing four carboxylic acids that function as a chelating agent at neutral pH. , Some studies reported a favorable effect of EDTA-conditioning to provide sufficient dentin bond strength. , It is capable of selectively removing hydroxyapatite, preserving the structural stability of the collagen matrix. This stability is attributed to lack of alteration of the native fibrillar structure of the collagen during dissolving the mineral phase of the dentin. , Hence, Habelitz et al.  suggested that the EDTA-conditioned dentin may be less affected by air drying due to the presence the unaltered collagen containing most of their intrafibrillar mineral.
Based on the above-mentioned points, the interfering effect of water with bonding performance of the simplified etch-and-rinse (one-bottle) adhesives may be prevented by the combination of EDTA-conditioning and occluding effect of oxalate desensitizers during dry bonding without compromising bonding efficacy. Therefore, the aim of this study was to evaluate whether this combination produces the adhesive bond strength similar to that made using conventional wet bonding on acid-etched dentin.
| Materials and Methods|| |
One-hundred and twenty extracted sound human third molars were used in the current study. The teeth were stored in 1% chloramines T solution for 2 weeks, and then in distilled water at 4°C before use. After removing the roots, the teeth were fixed in cold-curing acrylic resin. The midcoronal dentin surfaces were exposed by removing the occlusal enamel with a diamond saw (Letiz, 1600, Germany) under running water. The flat dentin surfaces were polished with silicon carbide paper to standardize the smear layer. The specimens were randomly divided into 12 groups of 10 teeth each. In the first four groups, One-Step Plus (OS) was used and Optibond Solo Plus (OP) was applied in the other four groups. In the remaining four groups, Adper Single Bond (SB) was used.
The bonding procedures were performed as follows: In the control groups 1, 5, and 9 (wet/acid), after phosphoric acid etching for 15 s and rinsing, the dentin surfaces were gently air dried for 5 s while leaving the moist dentin. Then, OS, OP, and SB were applied according to the manufacturer's instructions, respectively [Table 1].
In the experimental groups 2, 6, and 10 (wet/EDTA), the dentin surfaces were conditioned with 0.1 M EDTA solution (pH 7.4, MERCK Co., Germany) for 60 s instead of using the phosphoric acid etching. The remaining bonding procedures were performed as in respective control groups.
In the experimental groups 3, 7, and 11 (dry/EDTA), EDTA conditioning and bonding procedures were performed similar to the previous respective groups, with the exception of dry bonding. After rinsing, the conditioned surfaces were extensively air dried for 30 s with oil-free compressed air. In control, wet/EDTA, and dry/EDTA groups, we had removed the pulp tissue prior to preparing the specimens for bonding procedure.
In the experimental groups 4, 8, and 12 (dry/EDTA + OX), the bonding procedures were performed similarly to the previous respective groups, only an OX (BisBlock, Bisco) was added to bonding procedures. After EDTA conditioning and rinsing, OX was applied and dwelled onto the dentin surfaces for 30 s; then, the surfaces were rinsed for 60 s and dry bonding was performed.
After curing the adhesives for 20 s at 600 mW/cm 2 with a light curing unit (VIP Junior, Bisco, Schaumburg, IL, USA), a resin composite (Z250) was placed on the cured adhesive using a cylindrical split mold with a height of 2.5 mm and surface diameter of 2 mm. Two increments of 1 mm and 1.5 mm were applied and separately cured for 40 s.
After 24 h water storage and thermocycling (1000 times), bond strength test was performed. Shear bond strength (SBS) was measured with a universal testing machine (Instron Z020, Zwick, Roell, Germany). A knife-edge shearing rod at a cross head speed of 1 mm/min was applied to load the specimens until fracture and bond strength in MPa was recorded. The data were analyzed using two-way analysis of variance (ANOVA) and Tukey's Honestly Significant Differences (HSD) HSD post-hoc tests for pair-wise comparisons at a significance level of 0.05.
After testing, the fracture modes were evaluated under a stereomicroscope (Ziess) at ×10 and classified according to the predominant mode of fractures as adhesive, cohesive in dentin, cohesive in composite and mixed, a combination of adhesive and cohesive [Table 2].
| Results|| |
The mean bond strength and standard deviations of the 12 groups are presented in [Table 2], and the results of two-way ANOVA are shown in [Table 3]. The use of EDTA instead of phosphoric acid did not alter SBS of the three used adhesives. When dry bonding by EDTA, OS showed significantly lower SBS than those of wet bonding by phosphoric acid or EDTA (P < 0.0001) while both OP and SB revealed similar SBS in the three bonding conditions (P = 0.91).
By adding the OX treatment to the dry bonding by EDTA, a significant reduction in SBS was observed for OP (P < 0.0001), but not for OS and SB (P > 0.05). SBS of OS in dry bonding with or without OX was similar, being significantly lower than wet bonding with phosphoric acid etching (P < 0.05). Only SB had comparable bond strength in four bonding conditions (P > 0.05). The pair-wise comparisons of four bonding conditions for each adhesive (OS and OP) are summarized in [Table 4].
|Table 4: Results of pair-wise comparisons of four bonding conditions was performed by Tukey HSD test for each of two adhesives|
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Fracture analysis revealed that most of the fractures of groups 3 and 4 (OS in dry bonding with EDTA conditioning with or without OX) and group 8 (OP with OX) were adhesive mode. In other groups, all four modes of fractures were observed.
| Discussion|| |
In the current study, three one-bottle adhesives with different solvent content (acetone and water/ethanol) and pH were used under four bonding conditions. EDTA-conditioning and acid etching revealed similar bond strengths under wet bonding for these adhesives. This finding is similar to the results of previous studies. ,,,, EDTA can remove the smear layer and mildly demineralize the dentin. The thin EDTA-demineralized collagen matrix contains intrafibrillar mineral, preserving its spongy and stable state, and hence may improve resin infiltration. ,,, The resultant more homogenous hybrid layer may be strong and could produce a high bond strength due to possible chemical interaction between acidic/functional monomers with calcium in residual mineral within the collagen fibrils. , This phenomenon is referred as 3-phase hybridization instead of 2-phase one. The latter usually occurs in the resin bonded to acid-etched dentin. 
Based on the mentioned properties of EDTA-conditioned dentin, it was speculated that this dentin is less influenced by dehydration. 
In the current study, this hypothesis was supported when OP and SB were bonded to dried EDTA-conditioned dentin, but not for OS. This difference may be attributed to various solvent types containing the adhesives. Acetone-based adhesives are more sensitive to an accurate wet bonding technique than ethanol-based ones and require greater surface wetness due to the high water-chaser effect of acetone. ,, Ethanol/water-based adhesives possess the capability of promoting re-expansion of dried collapsed matrix during the infiltration of solvated resin monomers. ,,, However, a substantial decrease of bond strength to acid-etched dentin was reported for two ethanol/water based adhesives (Excite, OP) following air drying for 10 s. 
Reis et al.  suggested that fluid flowing from the retained moist pulp tissue during dry bonding may account for insignificant reduction of bond strength of SB compared to wet bonding. However, in the study by Manso et al.  more severe dry bonding condition was performed and bond strength was significantly decreased. In the current study, the pulp tissue was removed prior to bonding procedures (except for groups with OX) similar to the latter study to eliminate the interfering effect of water permeation within the tubules; however, the bond strength of SB and OP was not altered under dry bonding on EDTA-conditioned dentin. This finding might indicate more stability of the dried dentin following EDTA-conditioning compared to acid etching.
In clinical situations, controlling the level of moisture may practically be more difficult and non-uniform wetness may exist on different regions of dentin surface. Furthermore, re-wetting capability of naturally moisture dentin may mitigate the effects of dry and wet bonding.  The references were checked and #25 was repeated and deleted. The other references numbers were corrected as made below in the text. Hence, the application of OX may be beneficial to occlude dentinal tubules, optimizing different wetness conditions; in the current study, its compatibility with the adhesives used in dry bonding with EDTA was evaluated.
The reduced permeability of acid-etched dentin was the result of precipitating calcium oxalate crystals below the demineralized dentin. , Thus, OX did not compromise the bond strength of relatively neutral etch-and-rinse adhesives (such as SB and One-Step).  Basseggio et al.  reported OX had no effect on bond strength of SB. However, in two recent studies, OX application decreased bond strength of SB, One-Step and Scotchbond Multi-Purpose, , but it had no effect on Prime and Bond NT.  In literature, the name of commercial products (all parts of each product name) is commonly started with capital letters. NT associated with Prime and Bond is the name of one commercial product. We corrected the products names in whole of the article text.
According to the results of the current study, OX had an adverse effect on bonding efficacy of OP that may be due to low pH of this adhesive. Moreover, dry bonding had a negative effect on OS contained acetone solvent. The higher number of adhesive fractures together with a decrease in bond strength in groups 3, 4 and 8 may have been caused by the lower bonding effectiveness of these bonding conditions. Therefore, only SB with a relatively high pH and the ethanol/water content exhibited the compatibility with the combination of OX treatment on the EDTA-conditioned dentin under dry bonding.
Dry bonding associated to OX pre-treatment may enhance the removal of solvents and residual water after the application of the adhesive,  and formation of resin tags.  However, dry bonding may lead to collapsed collagen matrix in the etched dentin.  Based on our results, EDTA-conditioning possibly improves resin penetration in dry bonding condition for the ethanol/water adhesive, resulting in less fibrils exposure. Nevertheless, scanning electron microscopic evaluations are needed to explain these results and actual interaction of different adhesive systems on OX treated dentin in dry and wet conditions. Moreover, EDTA treatment may extract and inactivate matrix metalloproteinase's involved in degradation of the exposed collagens.  This effect may positively influence the bonding durability of the adhesives. These long-term effects can be studied in laboratory tests with more simulating in vivo situations such as using a positive pulpal pressure and the presence of fluid flowing. Nevertheless, the need for separate enamel etching, difficult control of EDTA solution only on the dentin surfaces, and the relatively long time (60 s) needed for its application might be disadvantages in clinical practice.
| Conclusions|| |
Based on the results of this in vitro study, among the three adhesives used, only an ethanol/water based adhesive with a relatively low acidity could benefit from the association of OX pretreatment and EDTA-conditioning, in a relatively severe dry bonding technique. Both ethanol/water adhesives without OX are capable of tolerating this condition.
| Acknowledgments|| |
The authors thank the vice-chancellery of Shiraz University of Medical Sciences, for supporting the research (Grant#90-3539) and Dr. M. Vossoughi from the Dental Research Development Center for the statistical analysis, and Dr. N. Shokrpour for help with the English in the manuscript.
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Assistant Professor, Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz
Source of Support: Vice-chancellery of Shiraz University of Medical Sciences, for supporting the research (Grant#90-3539), Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4]