|Year : 2016 | Volume
| Issue : 4 | Page : 221-225
Influence of different types of co-solvents on the bonding abilities of one step self-etching adhesives: An Ex vivo Study
Suruchi Chaudhary1, Rajiv Bali1, Abhishek Tayal2
1 Department of Conservative Dentistry and Endodontics, BRS Dental College and Hospital, Panchkula, Haryana, India
2 Department of Prosthodontics, BRS Dental College and Hospital, Panchkula, Haryana, India
|Date of Web Publication||27-Dec-2016|
H. No. 2001, Sector-21, Panchkula, Haryana
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the tensile bond strength of three one step self-etch adhesives: Adper easy Bond, G-Bond, Tetric N bond self etch to dentin which contained ethanol and water, acetone and water and only water as a solvent respectively. Materials and Methods: Freshly extracted intact sixty permanent molars were collected for the study. To standardize the depth of cavity, 1.5 mm hole was drilled in the deepest part of the central fossa. All the teeth were ground and polished to expose the flat dentinal surface. All the teeth were embedded in the autopolymerising acrylic resin in separate moulds and were divided into three equal groups of twenty teeth each. Group 1: Twenty samples restored with composite and Adper easy one as bonding agent. Group 2: Twenty samples restored with composite and G-Bond as bonding agent. Group 3: Twenty samples restored with composite and Tetric N Bond as bonding agent. A wire loop was placed over the predesigned locationin the composite held with the split brass mold. Tensile loading was done using UTM and statistical analysis was done using one step ANOVA and Tukey's HSD test. Results: The mean bond strengths of ethanol containing, acetone containing and water containing adhesives were 12.57 MPa, 10.16 MPa and 11.46 MPa. Conclusion: Comparison of contemporary adhesives in this ex-vivo study revealed that in self-etch adhesives, the type of solvent may be one of the factors that affects the bond strength. The adhesives containing ethanol based solvent showed better bonding than acetone and water based self etch adhesives.
Keywords: Self-etch adhesive, solvent, tensile bond strength
|How to cite this article:|
Chaudhary S, Bali R, Tayal A. Influence of different types of co-solvents on the bonding abilities of one step self-etching adhesives: An Ex vivo Study. Indian J Dent Sci 2016;8:221-5
|How to cite this URL:|
Chaudhary S, Bali R, Tayal A. Influence of different types of co-solvents on the bonding abilities of one step self-etching adhesives: An Ex vivo Study. Indian J Dent Sci [serial online] 2016 [cited 2020 Oct 20];8:221-5. Available from: http://www.ijds.in/text.asp?2016/8/4/221/196818
| Introduction|| |
The adhesive dentistry is an area of clinical practice where the technology of the adhesives and the techniques that are being developed to use with them are continuously changing. Therefore, it is an area of research that withdraws much attention. Effective adhesion to enamel has been reached with relative ease and has repeatedly proven to be a durable and reliable clinical procedure for routine applications in modern adhesive restorative dentistry.
Conversely, adhesion to dentin is not as reliable as adhesion to enamel. Thus, justifying a great number of studies in this area, including this article. Currently, self-etch approach is introduced for bonding and used widely as there is no longer need of an etch and rinse phase. However, independent to the approach chosen, bond to dentin is usually critical because of the morphologic, histologic, and compositional differences between the two substrates, i.e., enamel and dentin.,
One of the greatest challenges in adhesion is related to the need of dentin being slightly moist before being properly bonded. When demineralized dentin matrix is air-dried, it may collapse up to 65% in volume. During dehydration, collagen fibrils are brought into closer contact, facilitating a variety of weak molecular associations between polypeptide chains that stabilize the structure of dry dentin and make it stiffer. This shrinkage phenomenon reduces the interfibrillar spaces that serve as diffusion channels for resin infiltration and ultimately compromises the bonding of adhesive systems to dentin. One way to overcome the shrinkage problem is to rewet the dentin surface with water before bonding so as to maintain the surface in the moist state. Water is an essential component of dentin matrix to prevent the collapse of the collagen network after etch step. However, excessive moisture could decrease the content of adhesive monomeric components within the collagen network and possibly interfere with their polymerization, which would result in a lower cross-linking density of the formed hybrid layer.
Water, acetone, and ethanol are commonly used solvents in the majority of current bonding systems which are responsible for either carrying excess water out or infiltrating resin monomers into interfibrillar dentin. Benefits offered by solvents rely on their properties of improving substrate wetting, aiding to impede the collagen fibrils collapse or to stiffen them. However, the degree of wetness that is ideal for resin-dentin bonding varies widely among the different adhesive systems and depends on the incorporated solvents.
Thus, the current study evaluated the role of different co-solvents on the tensile bond strengths of self-etch adhesive systems applied to dentin. The null hypothesis was that the type of solvent would not have an influence on the bond strength of the self-etch adhesive to dentin.
| Materials and Methods|| |
Materials used in the study are shown in [Table 1].
Sixty intact caries free mandibular permanent molars were collected for the study. After the extraction, the teeth were cleaned of debris and blood in the running water. The teeth were then stored in the normal saline. During sample preparation, to depth holes 1.5 mm were drilled in the deepest part of the central fossa of each tooth with the help of round diamond bur. All the teeth were ground until the drilled hole depth to expose the flat dentinal surface. This was followed by polishing of the flat dentinal surfaces with 600 grit silicon carbide paper to produce a uniform smear layer. The teeth were then placed on the glass slab with the flat dentinal surfaces facing the glass slab and stabilized at the periphery with the wax sheet. Rectangular aluminum molds of dimension 2.5 × 2 × 2.5 inches were placed in the position over the wax sheet bearing the teeth. A thin mix of auto polymerizing acrylic resin was placed in the molds. A punch hole tape with the diameter of 3 mm was placed over the occlusal surface. The molds were then randomly divided into three main groups of 20 samples each.
Group 1: Samples were restored with Adper Easy Bond (3M ESPE, St Paul, MN, USA) and composite Filtek Z 350XT (3M ESPE, St Paul, MN, USA): Using an applicator tip, it was applied on the dentinal surface, left undisturbed for 20 s and dried with a strong blast of air for 5 s.
Group 2: Samples were restored with G-Bond (GC Corp, Tokyo, Japan) and composite FiltekZ350XT (3M ESPE, St Paul, MN, USA): Using an applicator tip, it was applied on the dentinal surface, left undisturbed for 10 s and dried with a strong blast of air for 5 s.
Group 3: Samples were restored with Tetric N Bond Self-Etch (Ivoclar Vivadent, Liechtenstein) and composite Filtek Z350XT (3M ESPE, St Paul, MN, USA): Using an applicator tip, it was applied as a thick layer on the dentinal surface and brushed in for 30 s. The excess amount of self-etch adhesive was dispersed with a strong blast of air stream and was further light cured for 10 s.
All the bonded specimens were placed in the distilled water and kept in the incubator at 37°C. A split brass mold of diameter 3 mm and height 5 mm was used to form and hold the restorative resin onto the dentin surface. The resin composite Filtek Z 350XT was condensed into the mold in three equal increments. After the placement of the first increment, a stainless steel wire loop was placed so that the composite stabilized it perpendicular to the surface and each increment was light-cured for 20 s. The bonded specimens were placed in the incubator for 24 h.
Equipment for testing
Twenty-four hours after bonding, the specimens were removed from the incubator and tested in tensile mode in Universal Testing Machine (Llyod's Machine, CIPET, Amritsar) at the speed of 1 mm/min.
Tensile bond strength measurement
For the tensile bond strength measurement, the wire protruding out of the composite cylinder was gripped into the superior cross head, and the aluminum mold was held in the inferior cross head of the universal testing machine. Tensile loading was done until the dislodgement of the composite cylinder from the dentinal surface occurred. The results of the tensile bond strength testing were tabulated in the value of force (Newton, N) and were later converted into Mpa by dividing the load with the surface area of the specimen.
| Results|| |
The bond strength measured for Group 1 was highest 12.57 MPa, followed by the mean tensile bond strength obtained for Group 3 which was 11.46 MPa and least for Group 2 which was 10.16 MPa as shown in [Table 2]. Post hoc comparisons were carried using Tukey's Honest significant difference (HSD) test with the statistical significance set at α = 0.01. The intergroup comparison of various groups revealed statistically highly significant differences (P < 0.01) as shown in [Table 3]. The mean differences (I − J) for Group (1 − 2) was 2.4075, for Group (1 − 3) was 1.1125, and for Group (3 − 2) was 1.2950, which was more than the Tukey's HSD value 0.6577 thus all the results were statistically significant.
|Table 3: Intergroup comparisons of tensile bond strength in Mpa of different groups|
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| Discussion|| |
The concept of adhesive restoration has been essentially the most noteworthy development in ever progressing science. Thus, during the evolution of dentin bonding agents, attempts were made to ease out the technique and achieve good bonding with enamel and dentin. In this process, the recent development is combining etchant, primer and bonding agent in one component to form “self-etch adhesives.” These self-etching adhesives can be used to etch both ground enamel and dentin simultaneously, and they bond equally well to superficial and deep dentin. Ideally, the adhesives should be formulations based on hydrophobic monomers with high molecular weight, without additives such as solvents and water. However, due to the necessity for the adhesive to penetrate into micro porosities of the dentin, substrate inherently wet, hydrophilic resinous diluents and solvents were incorporated into the adhesive. For the liquid to be spread uniformly over a solid surface, the surface tensile of liquid must be less than the energy free surface of the substrate. The low viscosity of primers and/or adhesive resins can be partly achieved by dissolution of the monomers in a solvent which will improve its ability of diffusion into the micro-retentive tooth surface. Further, it has been observed that the interfibrillar spaces between collagen contain hydrogel composed of proteoglycans which may interfere with the comonomer infiltration during bonding. Therefore, solvents are used in these dentin bonding agents to replace water in dentin collagen network and to enable adhesive monomers to penetrate into this network.
During the cavity preparation, decalcification of enamel and dentin and removal of the smear layer occurs, both of which are ionic processes. Calcium ions are chelated by acidic monomers, and parts of collagen fibers are solubilized or hybridized. For these ionic processes, water is required, and therefore, self-etching adhesives or primers are generally water based. However, excess water could decrease the content of the adhesive's monomeric components within the collagen network and probably interfere with their polymerization, which would then result in a lower cross-linking density of the formed hybrid layer. Thus, co-solvents like ethanol are added to self-etching adhesives, which form an azeotropic mixture with water and thus accelerate the surface dehydration by means of air syringe drying.
Further, it has been studied that the ability of solvent to maintain the demineralized dentin collagen matrix is essential for the bonding procedure. In fact, studies have shown that high values of bond strength to dentin, were obtained after the development of hydrophilic monomers and their association with organic solvents.,
The study was planned to be conducted in vitro as it can help to evaluate the effect of single variable while keeping the other variables constant. The results of tensile bond strength measurement of three groups were tabulated and compared, and the statistical analysis was done using one step ANOVA test and post hoc Tukey HSD test. The results showed that the Group 1 with tensile bond strength of 12.57 MPa performed better than the other two groups Group 2 with bond strength of 10.16 MPa and Group 3 with bond strength of 11.46 MPa. Adper Easy bond showed higher tensile bond strength than G-Bond and Tetric N bond Self-etch and the result was statistically significant (P < 0.01). This result could be attributed to the composition of these dentin bonding adhesives.
The inferior bond strength of G-Bond and Tetric N Bond self-etch in comparison to Adper Easy one can also be contributed to absence and presence of HEMA. Adper Easy one contains HEMA which is absent in case of G-Bond and also in Tetric N Bond self-etch. The hydrophilicity of HEMA makes it an excellent adhesion-promoting monomer, and by enhancing wetting of dentin, HEMA significantly improves the bond strength. To attain high bonding strengths to dentin, it is essential for the dentin substrates to have good penetrability and diffusibility. During the bonding procedure, if the collagen network is allowed to collapse, the spaces between the collagen fibrils disappear and the adjacent fibrils come into intimate contact with each other. In the absence of water or other hydrogen forming substances, the collagen peptides may form intermolecular hydrogen bonds with the nearest neighboring collagen peptides which may contribute to the further collapse of the network by causing the shortening of the fibrils and leading to the increase in the stiffness. The addition of water and HEMA can break these intermolecular bonds with mass action thereby softening the network and allowing it to re-expand.
Further, Adper Easy one contains ethanol as a cosolvent as compared to acetone present in case of G-Bond. Ethanol is a polar solvent that will form hydrogen bonds with its solutes. Ethanol removes water from these spaces causing the hydrogel to collapse, thus enlarging the interfibrillar spaces and allowing more resin infiltration. It is speculated that the significantly higher bond strengths obtained when ethanol was used may be due to its Hansen's triple solubility parameters of the hydrogen bonds which is 19.4 (J/cm 2) 1/2 being higher than that of dried collagen 18.2 (J/cm 2) 1/2. The higher Hansen's triple solubility parameter of ethanol allows dehydration and stiffening of the matrix without allowing interpeptide H-bonding to collapse it. Acetone has a high dipole moment and forms much lower hydrogen bonds due to which it is not able to expand the shrunken demineralized collagen. Furthermore, it has a high vapor pressure of 184 mm Hg at 20°C as compared to that of ethanol (43.9 mm Hg at 20°C). As the solvent evaporates, the viscosity of the bonding system increases, which decreases the ability of the bonding system to penetrate around the exposed collagen fibers and the opened dentinal tubules producing poor and incomplete hybrid layers. Further, acetone has a boiling temperature of 56.5°C as compared to that of ethanol (78.3°C) which requires careful observation and handling of the product during bonding procedures if the optimum ratio among the components is to be maintained.
The lower bond strength of Tetric N Bond Self-Etch as compared to Adper Easy bond can also be attributed to the fact that water is present as a solvent in 20%–30% amount in Tetric N Bond Self-Etch adhesive. Water is a strongly polar solvent with a high dielectric constant, capable of dissolving ionic lattices and polar compounds its capability of forming strong hydrogen bonds. Its dissolving capacity is greatly determined by its capability of forming strong hydrogen bonds. The hydrogen bonding cohesion parameter of water is (40.4 MPa 1/2). Even if water has optimal hydrogen cohesion parameter to maintain collagen matrix as solvent, water also has many problems. The high boiling temperature and low vapor pressure of water imply that this solvent is difficult to remove from adhesive solutions after application on the tooth. This residual solvent makes the hybrid layer porous and more prone to water sorption. Tay et al. showed that excess water in the adhesive resin compromises the bond strength of adhesives due to entrapment of water blisters (“overwet phenomenon”). Thus, residuals of solvents hinder polymerization of monomers in primers and adhesives and make the hybrid layer prone for weakening over time, thus leading to lower dentinal bond strength. Furthermore, it is assumed that increasing the concentration of water beyond 20% diluted the concentration of adhesive monomers thereby lowering their inward diffusion rate.
The higher bond strength Adper Easy Bond could also be attributed to the fact that it contains polyalkenoic acid which may contribute to the bonding stability over time. This polyalkenoic acid in the presence of water forms polyalkenoate salt at the bonding interface which has a stress relaxation capacity.
| Conclusion|| |
Under the limitations of this experimental study, the following conclusions were drawn:
- Solvents play a significant role in the bond strength ability of self-etch adhesives. Thus, comparison of contemporary adhesives revealed that the constituents of the self-etch bonding agent do affect its bonding abilities, out of which type of solvent may be one of the contributing factors
- Self-etch adhesives containing ethanol as solvent showed highest tensile bond strength when compared with the other two self-etching bonding agents.
A further understanding of factors that contribute to the durability of adhesives and their bonding characteristics is needed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]