|Year : 2010 | Volume
| Issue : 3 | Page : 183-188
Technique-sensitivity of dentin-bonding agent application: The effect on shear bond strength using one-step self-etch adhesive in primary molars: An in vitro study
S Bansal1, IK Pandit2, N Srivastava3, N Gugnani3
1 Department of Pedodontics and Preventive Dentistry, Assistant Professor, Guru Nanak Dev Dental College and Research Institute, Sunam, Punjab, India
2 Principal, Professor and Head, DAV (C) Dental College and Hospital, Yamunanagar, Haryana, India
3 Professor, DAV (C) Dental College and Hospital, Yamunanagar, Haryana, India
|Date of Web Publication||11-Dec-2010|
c/o Dr. Amit Jindal, Street No.-7, Prem Basti, Sangrur, Punjab - 148 001
| Abstract|| |
Aim: The present study was undertaken to compare and evaluate the effect of technique-sensitivity on shear bond strength (SBS) of one-step self-etch adhesive, using multiple coats and different applicator designs, to dentin in deciduous molars. Materials and Methods: Flat buccal dentinal surfaces were obtained on 60 extracted human primary molars. The specimens were divided into 3 equal groups (n = 20). Self-etch adhesive was applied on the dentinal surface of group I with cotton pellet, group II with microapplicator tip, and group III using 3M brush. The groups were further divided into 2 subgroups-single coat of dentin-bonding agent (DBA) in subgroups A and triple coat (with no curing in between coats) in subgroups B. The composite was placed on the dentinal surface using split nylon cylinder and cured. SBS was tested for all specimens with Instron Universal testing machine. Data were statistically analyzed using one-way analysis of variance and Student's t test. Results: There was no statistically significant difference in the main study groups, that is, no significant difference in the SBS with the use of different applicator tips. However, the use of triple coat of self-etch DBA exhibited highly significant difference in the SBS as compared with single coat. Conclusion: This study revealed that one-step self-etch adhesive could prove attractive in pediatric dentistry because of its lesser technique-sensitivity; however, increasing the number of coats of DBA (with no curing in between the layers) enhanced the bond strength to dentin owing to the improved resin infiltration.
Keywords: Dentin-bonding agent, primary molars, self-etch adhesive, shear bond strength, technique-sensitivity
|How to cite this article:|
Bansal S, Pandit I K, Srivastava N, Gugnani N. Technique-sensitivity of dentin-bonding agent application: The effect on shear bond strength using one-step self-etch adhesive in primary molars: An in vitro study. J Indian Soc Pedod Prev Dent 2010;28:183-8
|How to cite this URL:|
Bansal S, Pandit I K, Srivastava N, Gugnani N. Technique-sensitivity of dentin-bonding agent application: The effect on shear bond strength using one-step self-etch adhesive in primary molars: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2013 May 21];28:183-8. Available from: http://www.jisppd.com/text.asp?2010/28/3/183/73781
| Introduction|| |
Today every focus is diverted to conserve tooth structure using restorative materials, which adhere to tooth structure by minimal intervention and are tooth colored to provide esthetics. Strong adhesion between the tooth and restorative material would not only eliminate the need for salvaging sound tooth structure for retention form, but also prevent the formation of marginal gaps occurring due to polymerization stress.
The advent of resin composite by Dr. Ray L. Bowen (1962) brought about a revolution in the field of esthetic restorative dentistry.  However, resin composite material, with all its advantages, also poses a challenge to the restorative clinician to find a perfect bonding system and technique.
"True adhesion" has been the "Holy grail" of dental restorative materials for many decades. The first meaningful proof of intraoral adhesion was reported in 1955 by Michael Buonocore.  He introduced the concept of acid etching, that is, chemically treating the enamel to alter its surface characteristics to allow for adhesion of acrylic resins to the enamel surface of the tooth. 
Adhesion of restorative material to enamel has become a routine and reliable aspect of modern restorative dentistry, but adhesion to the dentin has proved to be more difficult and less predictable.  Dentin being a living tissue, poses greater obstacles to adhesive bonding than does enamel. Much of the difficulty in bonding to dentin is due to its tubular and heterogenous nature, high fluid content, presence of smear layer, and the need to achieve the pulpal biocompatibility. ,,
In the beginning, separate chemical components and several application steps were needed for priming and bonding.  Current advances have focused on the development of delivery systems that simplify the steps involved. 
The most recent innovation in dental adhesive technology involves the introduction of "all-in-one" or "self-etch" adhesive systems. The self-etch adhesives no longer need an "etch and rinse phase," but are capable of conditioning the tooth surface and simultaneously preparing it for adhesion. This not only lessens clinical application time, but also significantly reduces the technique-sensitivity or the risk of making errors during application or manipulation. ,, Even though these systems use fewer separate components, their application still requires that the steps be performed with great attention. A wide range of dentin shear bond strength (SBS) has been reported for these materials that may indicate technical concerns, which are not well identified. Use of these materials remains extremely technique-sensitive. ,
It has been shown that subtle differences in application techniques can affect bond strength. , There are various variables affecting bond strength, which have been investigated, such as bonding to moist vs dry dentin, temperature, and humidity, the use of disinfectants and other possible contaminants, the intensity of curing lights, and the depth of dentin.
Despite the amount of research reported on the bond strength efficacy of resin adhesives to permanent teeth, there is little in the literature on the bond strength on adhesive system to primary teeth.  Primary teeth have been assumed to have similar composition as permanent teeth; however, some differences regarding morphology and mineral content have been well documented in the literature.
The "self-etch" system is attractive in pediatric dentistry because of its "fewer steps" and "lesser time."  Hence, the aim of this in vitro study was to evaluate and compare the SBS of "one-step self-etch" adhesive system using variable number of coats of adhesive and different applicator tips for adhesive application (as variables) in deciduous teeth at the dentin-restoration interface.
| Materials and Methods|| |
Sixty extracted human primary molars (1st and 2nd maxillary and mandibular), which were nearing exfoliation, that is, with physiologic advanced root resorption or those extracted for orthodontic reasons were selected. The teeth chosen had intact buccal surfaces with no evidence of resorption of the coronal part of dentin, caries, or restoration affecting the buccal surfaces, or any structural defects.
Routine prophylactic procedure was done for all the teeth with rubber cup and pumice slurry. The roots were removed with a diamond disk running in a contra-angled micromotor handpiece (NSK, Japan). The teeth were then stored in normal saline at room temperature till the study was conducted.
The buccal surfaces of the teeth were ground to expose a flat dentinal surface. As the depth of dentin is a crucial factor affecting the dentin bond strength values, depth holes measuring 1.0 mm were drilled in the middle of the buccal surface of each tooth using a round diamond bur before grinding flat the dentinal surfaces. The samples were mounted in rectangular aluminum molds using the autopolymerizing acrylic resin with their prepared buccal surfaces exposed to the environment.
The samples were randomly divided into 3 groups (n = 20) according to the technique used: group I-DBA applied with cotton pellet; group II-using microapplicator tip (Shofu, Inc., USA); and group III-with 3M brush (3M ESPE, USA). Each group was further divided into 2 subgroups (n = 10): subgroup A-one coat of DBA and subgroup B-triple coat with no curing in between the coats of DBA.
Each mounted sample was then thoroughly washed with water and dried with air from an oil-free air source. An adhesive tape with a punch hole of 3 mm diameter was applied on the flat dentinal surface, following which the self-etch adhesive (Adper Prompt, 3M ESPE, USA) was applied according to the group assigned (as above). In subgroups A, the adhesive was rubbed-in for 15 s, dried with gentle air stream to obtain smooth and glossy surface, and then light cured for 10 s.
In subgroups B, 3 consecutive coats were rubbed-in for 15 s each followed by air drying after every coat. This was followed by light curing for 10 s.
After the bonding procedure, the composite resin (Z-100, 3M ESPE, USA) was packed into a split nylon cylinder, with dimensions 2.0 mm internal diameter and 2.0 mm height, placed perpendicular to the dentinal surface. Curing was done with a light curing unit for 40 s vertically and for 60 s circumferentially to ensure complete polymerization.
All the specimens were subjected to 500 cycles of thermocycling between 5°C ± 2°C and 55°C ± 2°C with a dwell time of 30 s in each bath. The SBS test was performed using universal testing machine (Instron, Lloyd, UK) running at a crosshead speed of 5 mm/min, using a blunt knife-edged chisel parallel to adhesive interface between composite and dentin. The breaking shear loads obtained in kilogram were then converted into bond strength in megapascal. The data collected were tabulated and subjected to statistical analysis using one-way analysis of variance (ANOVA) and unpaired t test.
| Results|| |
The SBS values (MPa) were calculated from peak load at failure divided by the specimen surface area. The mean (±SD) SBS values for each main group are displayed in [Table 1], and for each subgroup in [Table 2]. For comparison of multiple groups, one-way ANOVA was used, and Student's t test was used for groupwise comparisons [Table 3] and [Table 4].
|Table 3: Intergroup comparison of the mean shear bond strength of the main groups |
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|Table 4: Intragroup comparison of the mean shear bond strength of the subgroups |
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[Table 1] shows that Group II demonstrated the least SBS values, while Group III exhibited the highest values.
[Table 2] depicts that subgroups A showed a lower SBS value as compared with subgroups B of each group.
However, on intergroup comparison [Table 3], there was no significant difference observed among the main study groups (P value > 0.05).
The intergroup comparison [Table 4] of the subgroups exhibited a highly significant difference in the mean SBS values with P value < 0.05.
| Discussion|| |
Adhesive dentistry is a rapidly evolving discipline. For many years, the dental profession has strived to achieve good adhesion for resin composite to tooth substrate.  Therefore, one of the primary objectives of researchers is to achieve a strong, durable, predictable bond, which not only is essential from mechanical stand point but also from biological and esthetic perspectives. For this purpose, SBS was tested at the bonding interface between parent material and the deciduous dentin surface because most masticatory forces are of a shearing nature. 
Generations of dentin-bonding agents (DBAs) have been developed on the basis of complete understanding of the nature of tooth substance, yet a perfect bonding system and application technique is still elusive.  Kanca concluded that subtle differences in application techniques can affect bond strength. ,
This in vitro study measured the SBS of a one-step self-etch adhesive (Adper Prompt, seventh generation) using different applicator designs assumed as a variable affecting the bonding. Also, the effect of varying the number of coats of DBA was studied along with.
The "self-etch" adhesives try to solve difficulties commonly associated with the clinical application of etch and rinse adhesives. Their application procedure is considered less time-consuming and, more importantly, less technique-sensitive, in particular, with regard to keeping the dentin surface in an adequate state of hydration. ,, The resin impregnation proceeds simultaneously with dentin etching, thus limiting the risk of discrepancy between the depth of dentin demineralization and hybridization.
It has been postulated that dentin bond strength in the range of 17-20 MPa are sufficient to resist the contraction of resin composite. ,, In the present study, any of the techniques used produced approximately more than this highly predictable bond strength of resin composite to dentin, even though slight variations within the groups were noted. This range provides ample latitude for error, and clinical success should be routine.
According to the results of this study, when the comparison between the cotton pellet, microapplicator tip (Shofu) and 3M brush applicator techniques was made, the 3M applicator brush design was found to be slightly superior as compared with the other 2 techniques, followed by the cotton pellet applicator technique, and then the microapplicator tip method.
In the present study, the use of different applicator tips for the application of DBA, however, did not produce statistically significant difference in the SBS (P value > 0.05). The probable reason might be that the applicator tip simply acted as a carrier of adhesive, and the bristle design did not interact with the penetration of the monomers into the dentin.
When the intergroup comparisons were made between the subgroups of each group (ie, subgroups A of each group and subgroups B of each group), it was again observed that 3M brush and cotton pellet applicator showed slightly higher mean SBS values than microapplicator tip. It was seen both for the single application of DBA and for a triple coat that the use of different applicator tips showed only a slight variation with the difference in the mean SBS values being statistically insignificant (P > 0.05).
The slight difference in the SBS values with the use of different applicator tips could be attributed only to slight difference in the amount of DBA carried at once by the particular applicator tip to the prepared dentinal surface, thus affecting the SBS. It was demonstrated by Finger and Jorgenson that the minimum thickness of adhesive layer whose polymerization is not inhibited by oxygen varies with materials and that the layers less than 25 ΅m may not polymerize. 
Bonilla et al., demonstrated an interaction between different application techniques and the bonding agent tested and, that the application of DBAs to dentin to achieve strong bond with resin composite is dependent on many factors. ,
While comparing the subgroups with each other, it was observed in all the groups that the use of triple coat of adhesive exhibited a higher mean SBS value than with the use of single application. Thus, multiple coats of one-step self-etch adhesive proved to be superior as compared with single coat of the adhesive. The results were statistically significant (P < 0.05) as shown by Student's t test.
The reason might be that the increased extent of resin impregnation into collagen caused by the consecutive coating method might remove residual water, thereby, improving resin infiltration and cross-linking of the adhesive comonomers within the hybrid layer. It is well accepted that bond strength is affected by the extent of resin infiltration into the exposed collagen network. ,
Hashimoto et al. demonstrated that the method of multiple consecutive coating during dentin bonding improved the bond strength of the 2 total-etch adhesive systems.  The repeated procedure of adhesive application and subsequent solvent evaporation improved the resin infiltration within the exposed collagen fibrils.
Asakawa et al. reported that the repeated application of DBA had been found to be effective in prevention of contraction gap formation because of the infiltration of adhesive into decalcified dentin, thus forming a hybrid layer. 
Platt et al. found improved SBS with the use of a second application of Prime and Bond NT following the manufacturer's instructions, whereas there was no increase in SBS of 'One Step' by the use of second application. In their study, Platt et al. observed increased bond strength by the technique of applying multiple layers and curing successive layers using Prime and Bond NT. This technique eliminated the oxygen-inhibited zone at the top of the first coating of bonding resin layer. 
However, our method of multiple coating without light curing between each layer increased the resin saturation into the collagen web. That is, by not polymerizing the comonomers, monomers can continue to diffuse inward, while solvents are diffusing outward.
The improvement in bond strength produced by these 2 methods has different underlying mechanisms. When multiple coats are applied but not cured, the resin infiltration of hybrid layer and the removal of residual water may be more complete without increasing the thickness of overlying adhesive layer. When each successive layer is light cured, the adhesive layer becomes thicker without changing the quality of hybrid layer.  This may increase bond strength by improving stress distribution via increased elasticity of thicker adhesive layer and thus, is beneficial as a shock absorber between the teeth and the composite. ,
However, a statistically insignificant trend toward decreased SBS with multiple applications of the single bottle adhesives has been reported by Swift et al. They concluded that the idea that a specific number of coats were required for a specific material was erroneous and the most important point was enough penetration of adhesive into the etched dentin surface to provide adequate mechanical interlocking. 
An investigation by Miyazaki et al. showed that longer resin application times increased resin-dentin bond strength, presumably due to the formation of deeper demineralized dentin layer, with the resin monomer penetrating into the total depth of etched, demineralized dentin.  Similarly, the use of multiple applications of adhesives without curing in between the layers might allow more time for removal of water from the interfibrillar spaces and more time for inward diffusion of adhesive monomers.
Insufficient infiltration and low polymerization rate of adhesive resin are reported to result in the formation of exposed collagen fibrils over time, which possibly degrade both in vitro and in vivo. , Multiple applications of the adhesive are considered to prevent the above-mentioned defects of resin bonding and improve the bond performance to dentin.
However, it is recommended that more elaborate studies along with clinical trials are necessary to evaluate the technique-sensitivity of the wide range of DBAs, especially in relation to the pediatric patients, where patient co-operation is expected to be the least.
| Conclusions|| |
Within the limitations of this study, it can be concluded that
The self-etch adhesive, Adper Prompt, was found to exhibit more than the highly predictable bond strength of resin composite to dentin (ie, more than 17-20 MPa), irrespective of the technique used.
The application of multiple coats of the self-etch adhesive (with no curing done in between the layers) enhanced the bond strength to dentin owing to the improved resin infiltration.
There was no significant effect of using different types of adhesive applicator on the SBS of the self-etch adhesive tested, indicating the self-etch DBA to be less technique-sensitive. Thus, One-step Self-etch adhesives seem to provide a reliable approach in pediatric dentistry as they are easier and faster to be applied and are less technique-sensitive.
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[Table 1], [Table 2], [Table 3], [Table 4]