|Year : 2013 | Volume
| Issue : 3 | Page : 106-113
Comparative evaluation of etch pattern, the length of resin tags, and shear bond strength of all-in-one adhesive system on intact enamel with and without phosphoric acid pre-etching: An in vitro investigation
Savitha Adiga1, Ida Ataide2, Marina Fernades2
1 Departments of Conservative Dentistry and Endodontics, The Oxford Dental College and Hospital, Bommanahalli, Bengaluru, Karnataka, India
2 Goa Dental College and Hospital, Bambolim, Goa, India
|Date of Web Publication||20-Nov-2013|
Department of Conservative Dentistry and Endodontics, The Oxford Dental College and Hospital, Bommanahalli, Hosur Road, Bengaluru - 560 068, Karnataka
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study is to compare the etch pattern, resin tag length and the shear bond strength (SBS) of all-in-one adhesive system (Clearfil S 3 bond) on intact enamel with and without phosphoric acid (PA) preetching. Materials and Methods: Freshly extracted 80 caries free cleaned sectioned crowns of upper permanent central and lateral incisors were mounted on acrylic blocks. The samples were divided into four Groups (A, B, C and D). In Group A and B the application of self-etch adhesive (SEA) was carried out without prior etching with PA and light curing performed (n = 20). In Group C and D etching was carried out with 37% PA before the application of SEA and light curing was carried out. The etch pattern, resin tag length were analyzed using scanning electron microscope and the SBS was analyzed using Instron Universal testing machine. Statistical Analysis Used: Data were analyzed with Mann-Whitney U-test using Statistical Package for Social Science version 11.5 Software. Results: The statistical analysis revealed that there was significant increase in the depth of penetration of resin tags and in the SBS of composite in Group C and D where PA pre-etching carried out in unground enamel than Group A and B (P < 0.05%). Conclusion: The results indicate that out of both treatment groups, pre-etching the intact enamel with 37% PA resulted in deeper etch pattern, formation of longer resin tags and increased SBS of the Clearfil S 3 bond to unground enamel.
Keywords: All-in-one bottle adhesive system, etch pattern, resin tags
|How to cite this article:|
Adiga S, Ataide I, Fernades M. Comparative evaluation of etch pattern, the length of resin tags, and shear bond strength of all-in-one adhesive system on intact enamel with and without phosphoric acid pre-etching: An in vitro investigation. SRM J Res Dent Sci 2013;4:106-13
|How to cite this URL:|
Adiga S, Ataide I, Fernades M. Comparative evaluation of etch pattern, the length of resin tags, and shear bond strength of all-in-one adhesive system on intact enamel with and without phosphoric acid pre-etching: An in vitro investigation. SRM J Res Dent Sci [serial online] 2013 [cited 2022 Oct 3];4:106-13. Available from: https://www.srmjrds.in/text.asp?2013/4/3/106/121634
| Introduction|| |
The general trend toward the simplifying the clinical procedure lead to the development of one-step self-etch adhesive (SEA) system following etch- and-rinse adhesive system. SEAs are composed of aqueous mixtures of acidic functional monomers, typically phosphoric acid (PA)-or carboxylic acid esters, with a pH higher than that of PA gels.  Their etching efficacy and bonding formation depends on the type of acidic monomer, pH of adhesive solution, etching time and application method. 
Among current SEAs, one and two-step adhesives exist and depending on their acidity they belong either to so-called mild or moderate (pH > 1.5) or strong SEAs (very low pH <1). 
Strong SEAs have a pH of around one, yielding ultra-morphological characteristics and etching patterns similar to those obtained with etch- and-rinse adhesives.  Conversely, mild self-etch (SE) systems have a pH of around 2 and yield only superficial demineralization normally no greater than 1 μm.  Despite the less aggressive etching pattern and shallower resin tag formation, sufficient micro-mechanical interlocking and good bond strengths may be obtained with mild SE systems. This may be the combined result of the simultaneous demineralization and resin monomer infiltration , and the remnant hydroxyapatite left attached to the collagen, which may serve as receptor for additional chemical adhesion. 
Simplified adhesives that combine the (SE) primer with the adhesive resin were developed to create one-step SEAs or so-called "all-in-one" adhesives. The simplified bonding procedure, reduction of chair side time, reduced technique sensitivity and in addition to supposed chemical bonding, are alternative features of SEAs. ,,] However, in these adhesives SE primer and a hydrophobic resin are combined into a single application, yielding highly hydrophilic polymers that are much more permeable to water movement after polymerization.  Their acidic functional monomers create highly hydrophilic interfacial structures making them more susceptible to water sorption and hydrolytic degradation. 
The shallower etching pattern and reduced micro-mechanical retention has been reported to be a concern with mild SEAs , especially when bonding to unprepared enamel , perhaps jeopardizing the strength of the resin-enamel interface. Studies have also shown that bonding to the ground versus unprepared enamel yields similar bond strengths of SEAs.  Since the evidence in the subject remains controversial, manufacturers often recommend a preliminary PA etching step prior to the application of mild SEAs to improve the bond strength to enamel. ,
Morphological analysis of enamel surface treated with SE primers have shown not very demineralized surfaces when compared with other areas that were predominantly un-etched. ,, In an attempt to improve the bonding of SE systems to enamel, surface pre-treatments, increase in acidic monomer concentration, increase of etching time as well as different application methods have been recommended. ,,
The present in vitro study aimed to evaluate and to compare the effects of pre-etching with 37% PA on etch pattern, resin tag length and shear bond strength (SBS) of one-step SEA (7 th generation) Clearfil tri-S (S 3 ) (Kuraray, Japan, Medical Inc.) to intact enamel surface [Figure 1].
|Figure 1: Materials used-Clearfil S3 bond, Clearfil AP-X composite resin, eco-etch 37% phosphoric acid etching gel|
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| Materials and Methods|| |
A total of 80 freshly extracted, single rooted, well-formed human maxillary central and lateral incisors with intact enamel were cleaned, polished and are sectioned at the level of cementoenamel junction. The sectioned crowns were stored in distilled water until use. All the crowns were individually mounted in auto-polymerizing resin filled cylindrical poly vinyl chloride pipes, with labial surface exposed.
The teeth were randomly divided into four groups (n = 20). Two groups were taken for bonding with SEA without pre-etching with PA; other two were taken for SEA with pre-etching with PA. The prepared teeth in each group were bonded as follows.
Group A and B: SEA without PA
Clearfil S 3 bond (SEA) was used without pre-etching with 37% PA. The enamel surface was rinsed with water, air-dried and then the Clearfil S 3 bond was applied on mid labial intact enamel surface as per manufacturer's instructions and left for 20 s, dried with air for 5 s and then light-cured for 10 s (QHL75 curing unit/450 mW/cm 2 ).
Group C and D: SEA with PA
Clearfil S 3 bond (SEA) used with pre-etching with 37% PA. The enamel surface was etched for 15 s with 37% PA gel, then rinsed for 15 s and gently air-dried. Clearfil S 3 bond was applied to the enamel surface as per manufacturer's instructions.
Then the samples from Group A and C were used for resin tag evaluation. Samples from Group B and D were used for bond strength assessment.
nonePlacement of composite and resin tag evaluation in Group A and Group C
After curing of the adhesive system, Clearfil AP-X composite resin material (Kuraray Japan) was placed incrementally over the bonded labial surface of approximately 2 mm thickness and light cured for 60 s. Then, each sample was longitudinally cut into three sections of approximately 1 mm in thickness in the labio-lingual direction in hard tissue microtome (LEICA, SP-1600), [Figure 2]a and b. All specimens are cleaned in distilled water with ultrasonic agitation for 30 min and gently air-dried. Middle third section from each specimen were mounted on aluminum stubs and gold sputtered (SPI sputter coater) [Figure 3] and examined under scanning electron microscopy (SEM) (JEOL-5800 LV, Ltd., Tokyo, Japan), for the evaluation of resin tags. Microphotographs of the samples were made at ×1000 and ×3500 for each enamel surface in the center of the samples to standardize the microscopic observations. The maximum resin tag length of each sample was measured with a digital caliper using INCA software (ETAS).
Placement of composite and bond strength measurement in Group B and Group D
Immediately, after application of adhesive to the intact enamel surface, Clearfil AP-X composite resin was bonded to the surface using the metal mold of 4 mm × 4 mm dimension [Figure 4]. The resin was built-up on this surface in two increments with 40 s curing for each increment and for an additional 20 s after removal of the mold. Then, the bonded samples were stored in distilled water at 37°C for 24 h and then they were mounted on a Universal strength testing machine [Figure 5]a. A chisel-shaped rod was aligned in close proximity to the bonded composite cylinder (post). The load was applied perpendicular to the joint between tooth surface and composite post (cylinder) at a crosshead speed of 1 mm/min, until fracture of the material occurred [Figure 5]b.
The shearing force was noted (kg F) and SBSs were determined and recorded in Mega Pascal units (MPa), which was calculated from the following equation:
Value obtained in kg × 9.81= Newton (force)
Bond strength (MPa) = Maximum load (Newton's)/surface area of the cylinder (4 mm)
| Results|| |
Etch pattern and resin tag length in Group A and Group C
The results showed [Table 1] that the mean of the resin tag length of all the 20 samples of Group A (SEA Clearfil S 3 bond without pre-etching), is 3.8 μm with a mean standard deviation of 0.61852; and in Group C resin tag length of Clearfil S 3 bond was found to increase after pre-etching, which showed the value of 16.17 μm with a mean standard deviation of 0.78070.
SEM images for samples in Group A showed shallow etch pattern with shorter resin tags [Figure 6]. SEM images for Group C samples showed deep etch pattern with longer resin tags [Figure 7].
|Table 1: Resin tag length of self-etch adhesive with and without pre-etching with PA |
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SBS between Group B and Group D
[Table 2] shows the SBS of Group B (Clearfil S 3 bond without pre-etching), which is 14.3 MPa with a mean standard deviation of 0.45018; and in Group D, bond strength of Clearfil S 3 bond was found to increase after pre-etching, which showed the value of 18.36 MPa with a mean standard deviation of 0.6727.
|Table 2: Shear bond strength of self-etch adhesive with and without pre-etching with PA |
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Statistical analysis and computation procedure were performed. Data were analyzed using statistical software "Statistical Package for Social Science." Results were represented in the form of tables and graphs.
Results were expressed using the mean for the following objective: To evaluate and to compare the resin tags and bond strength of one-step SEA on intact enamel and enamel pre-etched with PA. Once a mean and standard deviation was found between groups, inferential data was analyzed using Mann-Whitney U-test (P < 0.05).
[Table 3] illustrates the data analyzed by the Mann-Whitney U-test. This test was used to determine whether resin tag length and bond strength of SEA was significantly different from pre-etching before application of SEA. As shown in [Table 3], Z value for Groups A and C is 5.417; and Groups B and D is 5.412. P value for all groups were found to be 0.0001 (P < 0.05) which means that there is a significant difference in values between Groups A and C and between Groups B and D.
|Table 3: Statistical analysis and the calculated P value value and Z value |
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Bar diagram [Graph 1] [Additional file 1] shows the mean values between Groups A and C, which can be interpreted as resin tag length of SEA without pre-etching (Group A) showed the value of 3.8 microns; but in Group C, there was a significant increase in resin tag length of SEA after pre-etching, which showed the value of 16.17 microns. Bond strength assessment showed significant increase in bond strength of SEA Clearfil S 3 bond after pre-etching in Group D, which was about 18.36MPa as shown in bar diagram [Graph 2] [Additional file 2].
| Discussion|| |
SEAs are a promising development in adhesive dentistry, especially regarding reduction of the necessary application steps and the possibility of chemical interaction with hydroxy apatite coated collagen fibers.  However, bonding to enamel still remains critical and is controversially discussed by various authors. ,,,,,
The present study evaluated the effect of an optional etching step with 37% PA on etch pattern, resin tag length and SBS of one-step adhesive to intact enamel. Investigations revealed that the adequate bonding to intact enamel with SEAs alone cannot be achieved and will require additional PA etching for 15 s at a concentration of 37% is used.
The SEM examines the resin tag penetration depth thereby helps in the assessment of bonding efficacy of the adhesives. According to Ferrari et al.  in SEM low magnifications (×1000) shows the uniformity of the etch pattern of enamel and the density and real depth of the resin tags, whereas high magnifications (×3500) demonstrate the morphological characteristics of the resin tags penetrating enamel although the evaluations have been essentially subjective regarding the depth of etching.
Clearfil S 3 bond on intact enamel showed significantly less efficient etching in Group A with mean resin tag length of 3.8 μm and low bond strength in Group B with the mean of 14.3 MPa than with PA pre-etched groups. This result is in agreement with other studies that demonstrated that most of the SE adhesives do not form a proper and defined acid etching pattern in intact surfaces ,,, and the shallow etching pattern could compromise the bonding to enamel. Pashley and Tay  reported that the efficacy of SE primers in intact enamel does not depend solely upon their etching aggressiveness, but also on monomeric composition of each material. It is also possible that the low enamel bond strengths might be caused by the high amount of un-polymerized acidic monomers remaining after curing.  Thus, no correlation among degree of primer aggressiveness, enamel etching pattern and bond strength to unground enamel has been reported for SE adhesives. ,
Clearfil S 3 bond is a mild SEA with a pH of approximately 2.4 [Table 4]. Due to its weak acidity; the acidic portion of the primer is neutralized by the calcium and phosphate ions released during decalcification of enamel and thereby the decalcification process of enamel is ceased, which resulted in a shallow, insufficient demineralization of enamel, deficient penetration of resin, resulting in shorter resin tag,  as observed in the present study.
|Table 4: Chemical formulations of the self-etch adhesive Clearfil S3 bond |
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In general, the demineralization effects of SEA systems were proportional to the acidity of the acidic primers or SE adhesive solutions. The SE primers are less aggressive than PA etchants and do not form a proper and defined acid etching pattern and the conditioning effects are also reduced in intact enamel surfaces, except for the strong SEA with a very low pH (0.5), like Tyrian SPE self etching primer. 
The SE primer mechanism of bonding to enamel is based on nanoretentive interlocking between crystallites and adhesive resin. , These morphological features of the resin-enamel bonds are different from that formed with the etch-and-rinse adhesive systems. ,,, This thin hybridized complex of resin in enamel produced by SE without the usual micrometer-size resin tags can be responsible for lower bond strength and questionable effectiveness on enamel surfaces. , Based on scientific evidence, some of the authors have recommended the instrumentation of enamel before bonding, in an attempt to increase the bond strength. ,
By exploration of these findings to those achieved in the present study, it may be assumed that the lower penetration of such adhesive systems to unground enamel surfaces when compared with that of conventional adhesive systems may to some extent lead to low tensile strength. So far there are no specific reports available relating the length of the resin tags to their bonding ability to dental enamel for the material examined in the study. However, Shinchi and Nakabayashi  observed that the tensile bond strength (10 MPa) of a conventional light cured resin to enamel pretreated with various acid concentrations did not vary significantly. However, resin tag length was found to decrease significantly from 22 μm for 35% H 3 PO 4 -12 μm for 20% H 3 PO 4 , 9 μm for 5% and 10% H 3 PO 4 and 5 μm for 3% H 3 PO 4 . Enamel pre-treatment by PA etchants of concentrations lower than 10% may be satisfactorily employed. The use of less aggressive acid concentrations might minimize any potential adverse effects to enamel substrates.
Similar to the results from previous studies, which have demonstrated the beneficial effects of enamel etching with PA, ,,, present study results also found significantly improved enamel bond strengths for surfaces pre-etched with PA. For Group D means bond strength of 18.36 MPa; and for Group C mean resin tag length of 16.17 μm was found. It could be due to greater depth of demineralization with increased penetration of resin, resulting in longer tags.  PA pre-etching removes the outermost enamel, creates micro irregularities, with adherent surface, resulting in higher bond strength values. , In this current study, as enamel surfaces were obtained from central incisors, it was possible that the treated outer enamel layer would be prismless. 
These findings suggest that penetration capacity (resin tags) of adhesive might be improved by previous acid etching of the dental enamel. This is clinically relevant, as retention is fundamental for those restorative procedures that mainly dependent on dental enamel.  Therefore, utilization of previous acid etching or removal of a prismatic enamel layers either by grinding or by preparation of a bevel on the cavity margins, may result in superior retention. Certain procedures such as bonding of orthodontic brackets, preparation for application of the pit and fissure sealants, non-prep veneers, splinting for anterior teeth, restoration of class IV, diastema closure always require bonding to unground enamel.  In such cases utilization of a more aggressive SE system might offer the more favorable alternative. 
Thus, resin bond strength achieved with SE systems are sometimes comparable with those achieved with PA, despite the differences between enamel etching patterns ,,,, However, other studies have found no difference in bond strength between that achieved with mild SE and that with total-etch adhesives when bonding to an intact enamel. ,,,,,
Regarding SE systems, the overall bond strength of these to enamel is also controversially discussed in the literature. Recent studies have reported similar results in comparison with etch-and-rinse systems; , while other studies consider these systems to be less reliable to enamel bonding. ,, These differences may be due to the use of different bonding procedures or different methods for enamel preparation, as these may affect SBS results. SE systems seems to be more dependent on the type of enamel preparation than ER systems.  The evaluation of bond strength through SBS tests is recognized as a simple and reliable mean to assess the adhesive resistance to failure. The failure mode of SEA in the present study was primarily adhesive, when PA was applied prior to application of SEA, an increase in adhesive-cohesive fracture occurred.
Further understanding of the factors that contribute to the durability of the bonded restorations, integrity of the bonded interface and long-term clinical behavior of the newest simplified adhesives are needed.
| Conclusion|| |
The etching pattern, the length of resin tags and enamel SBS of evaluated SEA system Clearfil S 3 bond on intact enamel significantly increased by additional acid etching with 37% PA.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]