Year : 2009 | Volume
: 27 | Issue : 1 | Page : 33--38
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
SM Yaseen1, VV Subba Reddy2,
1 Department of Pedodontics and Preventive Dentistry, KBH Dental College, Nashik, India
2 Department of Pedodontics and Preventive dentistry, College of Dental Sciences, Davangere, India
S M Yaseen
Department of Pedodontics and Preventive Dentistry, KBH Dental College, Panchavati, Nashik
Aim: The present study was undertaken to compare and evaluate shear bond strength of two self-etching adhesives (sixth and seventh generation) on dentin of primary and permanent teeth. Materials and Methods: Flat dentin surface of 64 human anterior teeth (32 primary and 32 permanent) divided into four groups of 16 each. Groups A and C were treated with Contax (sixth generation), while groups B and D were treated with Clearfil S3 (seventh generation). A teflon mold was used to build the composite (Filtek Z-350) cylinders on the dentinal surface of all the specimens. Shear bond strength was tested for all the specimens with an Instron Universal Testing Machine. Data were statistically analyzed using one-way ANOVA for multiple group comparison, followed by student«SQ»s unpaired «SQ»t«SQ» test for group-wise comparison. Results: There was no statistically significant difference in shear bond strength among the study groups except that primary teeth bonded with Contax exhibited significantly lesser shear bond strength than permanent teeth bonded with Clearfil S3. Conclusion: This study revealed that Clearfil S3 could be of greater advantage in pediatric dentistry than Contax because of its fewer steps and better shear bond strength in dentin of both primary and permanent teeth.
|How to cite this article:|
Yaseen S M, Subba Reddy V V. 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;27:33-38
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Yaseen S M, Subba Reddy V V. 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 [serial online] 2009 [cited 2020 Aug 13 ];27:33-38
Available from: http://www.jisppd.com/text.asp?2009/27/1/33/50814
During the past twenty years, significant improvements have been made in the field of dentin adhesives. A key breakthrough occurred in 1979 when Fusayama et al , showed that good dentin adhesion could be achieved in vivo by acid etching the dentin before an unfilled resin was placed on the dentin surface. However, because of concerns that acid etching of dentin could damage pulp, it took until the early 1990s before dentin bonding agent was placed in order to optimize the bond strength.
Dentin bonding agents used during the early 90s are still in use and are often referred to as a fourth generation of dentin adhesives. These adhesives consist of a separate etchant, often a 30-40% phosphoric acid solution, a separate primer, and a separate bonding resin. Primer is a hydrophilic monomer dissolved in solvent such as acetone, ethanol, or water. The bonding resin consists of the same monomer system as used in the composite which consists of three steps (etching, priming, and adhesive placement) needed for placing these adhesives. Dentists thought the fourth generation of dentin adhesives as complex and time consuming to use, and demanded simpler solutions. The first simplification was the fifth generation of bonding agents, systems in which the primer and the adhesive were mixed together and supplied as a single system. These systems though gained popularity results did not suggest that these fifth generation systems performed as well as fourth generation of dentin adhesives. However, fifth generation dentin adhesives showed that dentists wanted simpler adhesive systems. As a consequence, systems even simpler to use were developed. Two such systems evolved, one consisting of an acidic primer and a bonding resin referred to as a sixth generation adhesive, and another in which the etchant, primer, and adhesive are combined into one single delivery system marketed as seventh generation of adhesive systems.
New dental adhesives are continuously being developed and the newer self-etching adhesives are marketed as being as less technique sensitive, less time consuming, and as effective as older total-etch adhesives. Studies evaluating shear bond strength of self-etching adhesive have shown inconclusive results on permanent dentin and few studies have evaluated their effectiveness on primary dentin.
The advantages of the self-etching system include complete infiltration of the bonding agent into the demineralized dentin and a reduced number of clinical procedural steps.
The self-etching system is attractive in pediatric dentistry because of its 'fewer steps' and 'less time' than does the total-etching system
In the last few years, due to increased use of composite resins for esthetic restorations, not only in anterior teeth but also in posterior teeth because of their enhanced resistance to the masticatory forces, the dentin/restoration interface has become of great interest. Extensive studies are being carried out in the three research fields, viz, microleakage evaluation, bond strength tests, and micromorphology analysis, by several researchers.
Laboratory in vitro tests play a very important role in providing the necessary information regarding the efficacy of new products in a short period of time and lesser cost, whereas clinical evaluations would provide information only after a long period of use. ,,
Materials and Methods
Sixty four freshly extracted sound human anterior teeth were used in the study, of which 32 were primary and 32 permanent. The samples were thoroughly cleaned and stored in deionized distilled water.
In the test group, the teeth were divided into four groups:
Group A: Sixteen primary teeth bonded using sixth generation bonding agent (Contax)
Group B: Sixteen permanent teeth bonded using sixth generation bonding agent (Contax)
Group C: Sixteen primary teeth bonded using seventh generation bonding agent (Clearfil S3)
Group D: Sixteen permanent teeth bonded using seventh generation bonding agent (Clearfil S3).
Routine prophylactic procedure was carried out with rubber cup and aqueous slurry of pumice for all the teeth before they were treated. Samples were mounted horizontally on acrylic resin block. Teeth were cut to expose a flat dentin surface at a depth of 1.5 mm using straight fissure diamond point, where a groove marked at 1.5 mm served as standardization. Bonding agents were used as per manufacturer's instructions:
Groups A and C were bonded using Contax bonding agent (sixth generation), while Groups B and D were bonded using Clearfil S3 bonding agent (seventh generation). [Table 1]
Following application of adhesive, a teflon mold was used to build the composite resin cylinder on the dentinal surface of all the samples, measuring 2 mm in diameter and 3 mm in height, in a two-layer increment technique. Each layer was light cured for 40 seconds with a light-emitting diode light curing unit (Ellipar 3M) vertically for each increment. Additional circumferential curing of the cylinder for 60 seconds was done to ensure complete polymerization of the material. For all the specimens, the curing tip was placed as closely as possible to the composite.
After the composite buildup, the teflon matrix was removed. All the specimens were stored in deionized distilled water at 37 0 C for 24 hours in Humidor prior to testing for shear bond strength. The shear bond test was performed using a Universal Testing Machine (Instron, USA, [Figure 1]) at a cross-head speed of 1 mm per minute in a compression mode using a blade parallel to adhesive interface between adhesive (Contax/ClearfilS3] and dentin.
The values obtained were calculated in Mega Pascal (MPa) peak load at failure divided by the specimen surface area. The data so obtained were tabulated and statistically analyzed using one-way ANOVA and Student's unpaired ' t ' test.
Shear bond strength values (MPa) were calculated from peak load at failure divided by the specimen surface area. Results are expressed as mean ± SD. One-way ANOVA was used for multiple group comparisons followed by student's unpaired ' t ' test for group-wise comparisons. For all the tests, a P -value of 0.05 or less was used for statistical significance. The statistical software namely, SPSS 11.0 and Systat 8.0 were used for the analysis of the data and Microsoft Word and Excel have been used to generate graphs, tables, etc .
[Table 2] shows the comparison of the four groups regarding their range value, mean, and median values of shear bond strength in MPa.
Exclusively the mean shear bond strength and their standard deviation among the test groups.
On intercomparison between different groups there was no any statistically significant difference among different groups except between group A and group D, which showed a statistically significant mean difference with a P -value of P -value  The choice of materials is an important consideration for dental esthetic factor. The clinical success of composite restoration depends on the adhesive system that provides durable bonding of composite and dentin, effectively sealing the margins of restoration, enhancing the retention, and preventing postoperative sensitivity and microleakage.  This in vitro study measured the shear bond strength of self-etching adhesives Contax (sixth generation) and Clearfil S3 (seventh generation) to primary and permanent dentin.
The study was performed on noncarious teeth as previous studies have reported that teeth with a history of carious dentin have tubules that are less patent and the effect of acid conditioning is less than in noncarious dentin. 
Bond strength studies are quite rough categorizing tools for evaluating the efficacy of bonding materials. Several factors influence in vitro bond strength to dentin, such as the type and age of the teeth, the degree of dentin mineralization, the dentin surface being bonded, the type of bond strength test (shear or tensile), the storage media, and the environmental relative humidity  in substrates and testing conditions, these variations could be responsible for the high standard deviation and wide ranges obtained in the present study.
According to the results of this study, Clearfil S3 exhibited higher shear bond strength than Contax and permanent teeth exhibited higher shear bond strength than primary teeth, though they were statistically insignificant. However, primary teeth bonded with Contax demonstrated a significantly lesser bond strength than permanent teeth bonded with Clearfil S3 with a P -value of et al  and Courson et al ,  who reported that permanent teeth exhibited higher bond strength than primary teeth.
The probable reason for permanent teeth exhibiting higher bond strength than primary teeth could be attributed to their differences in structure and their chemical composition. Johnsen et al ,  concluded that permanent tooth dentin was more mineralized than primary tooth dentin. Courson et al ,  through neutron activation analysis and dispersive spectroscopy concluded that calcium and phosphorous concentration decreased in peritubular and intertubular dentin of primary teeth than permanent teeth which could affect the bond strength in primary tooth dentin. Moreover, he also stated that dentin from central areas of crowns of permanent teeth was found to be harder than dentin from same area of primary tooth dentin.
Koshi and Pashley  concluded that the concentration and diameter of dentinal tubules was found to be more in permanent teeth than primary, thus leading to decreased dentinal permeability in primary teeth, which could be one of the possible reason for decreased bond strength in primary teeth. Nor et al ,  stated that since the concentration of dentinal tubules is lower in primary teeth, the amount of surface moisture was found to be less, thus altering the effectiveness of the dentin conditioners, which might not be diluted readily, hence affecting the bond strength. Conversely, Burrow et al ,  concluded that the main reason for decrease in bond strength in primary teeth was the greater water content in dentin approximating pulp rather than structural variation of intertubular dentin. However, Araujo and Garcia-Godoy  demonstrated that bond strengths to dentin were not significantly altered whether the dentin was dry or wet and suggested that a shorter etching time for dentin of primary teeth might result in a thinner hybrid layer with more complete penetration of resin. Nor et al ,  demonstrated that the hybrid layer in primary teeth was comparatively thicker than in permanent teeth for the same period of conditioning but authors considered the quality of the hybrid layer to be more important than its width and rejected the hypothesis that primary tooth dentin reactivity is identical to that of permanent dentin. However, in a recent study by Burrows et al ,  demonstrated that the thickness of hybrid layer for Scotch Bond I in permanent teeth was greater than in primary teeth concluding that it could be due to the differences in the reactivity of primary tooth dentin to the acidic solutions used.
Uekusa et al ,  and others in their study observed that the peritubular dentin was demineralized rapidly during acid treatment. It was thicker for primary than permanent dentin and further decrease in the available bonding substrate might occur. They also observed that acids used to condition the dentin surface removed smear layer more rapidly from primary teeth than from permanent teeth suggesting the composition of smear layer being related directly to the composition of underlying dentin which can be reasonably explained on the basis of difference in chemical composition of primary tooth dentin and permanent tooth dentin. Thus they concluded that either shorter conditioning time or use of weaker acidic solution should be considered for primary teeth. Shorter time for conditioning primary tooth dentin is indicated to promote removal of smear layer and produce a surface morphology similar to conditioned permanent tooth dentin. Thus, these reasons combined could often give possible explanation for problems that are paradigm of bonding to primary tooth dentin.
While, the other finding in this study was that Clearfil S3 (seventh generation) showed higher bond strength than Contax (sixth generation) in both primary tooth dentin and permanent tooth dentin. These results are comparable to previous studies of Maurin et al ,  who showed that the self-etching adhesives containing phenyl-P (2-methacryloyloxyethyl phenyl hydrogen phosphate) or MDP (10-methacryloxydecyl dihydrogen phosphate) exhibited good adhesion to dentin and enamel, than those self-etching adhesives which do not contain MDP.
The other probable reason for Clearfil S3 exhibiting higher bond strength could be because of the acidity of adhesives which determine the depth to which resin monomers can penetrate into dentin. If the depth of demineralization is too aggressive, that is, using very low pH adhesive, to be replaced by resin monomers, resulting in a weak zone that allows nanoleakage might be left at bottom of bonding interface.  This might be one of the reasons as Contax exhibits a lower bond strength as it possesses a low pH of 1.2 when compared to Clearfil S3 whose pH is 2.7.
Moreover, Clearfil S3 contains MDP which has been reported to have high chemical bonding potential to hydroxyapatite within a clinically reasonable application time.  Furthermore, MDP adhesive monomer molecular structure allows for decalcification and penetration into tooth structure, "creating a chemical bond to calcium" whereby, MDP chemically bonds to hydroxyapatite, as opposed to a micromechanical retention bond created using total-etch systems. Apart from this, Clearfil S3 includes a proprietary 'Molecular Dispersion Technology' enabling a two-phase liquid, hydrophilic/hydrophobic component, homogenous state at the molecular level, reportedly resulting in reduction and/or loss of water droplets at the adhesive interface and thus forming a superior bond which was lacking in Contax. Molecular Dispersion Technology not only prevents phase separation, but also improves mechanical property of hybrid layer (i.e., with two-step adhesives), only the hydrophilic monomer, a component of primer, penetrates into tooth structure creating a hybrid layer as in Contax, whereas in Clearfil S3 the hydrophilic monomer and cross-linking hydrophobic monomer are in homogeneous state and both penetrate into tooth structure, resulting in a stronger and improved hybrid layer.
The other probable reason for Contax exhibiting lesser bond strength could be because of lack of fillers, but ClearfilS3 contains high amount of nanofillers which might form a stable and higher strength bond layer. 
The type and amount of solvents, the content and percentage of monomers, and diluents in the mixture influence the bond strength. The filler load or percent mass load differs between products according to manufacturers' technology and is not well described in the adhesives' composition. Nevertheless, there is little information about the shrinkage and stiffness of these filled adhesives after polymerization. These are some of the factors that could affect the shear bond strength significantly, but is not listed by the manufacturers' since the final formulation is a proprietary secret.
However, this in vitro study needs further in vivo implementation, because this laboratory test was done using extracted teeth without regarding the pulpal pressure and presence of dentinal fluid under realistic physiological conditions, which may adversely affect dentin bonding. In extracted teeth, the collagen fibrilar network of dentin may collapse and prevent proper resin penetration in dentin. So, long-term clinical studies are required to evaluate the efficacy and durability of these self-etching bonding systems.
Within the limitations of this study conducted and results obtained, it can be concluded that:
For all treatment groups, Clearfil S3 (seventh generation) showed higher shear bond strength than Contax (sixth generation) dentin bonding systems.Permanent teeth showed higher shear bond strength than primary teeth, irrespective of bonding system.Clearfil S3 (one-bottle seventh generation] dentin bonding system permits easier and quicker application than Contax (two-bottle sixth generation), which could be a greater advantage in pediatric dentistry.
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