|Year : 2015 | Volume
| Issue : 2 | Page : 116-121
Comparison of shear bond strength and micro-leakage of three commercially available seventh generation bonding agents in primary anterior teeth: An in vitro study
Mahesh K Duddu1, Radhika Muppa2, Priyanka Panthula2, N Ch Srinivas2
1 Department of Pedodontics and Preventive Dentistry, G. Pulla Reddy Dental College and Hospital, Kurnool, Andhra Pradesh, India
2 Department of Pedodontics and Preventive Dentistry, Panineeya Mahavidyalaya Institute of Dental Sciences and Research Center, Hyderabad, Telangana, India
|Date of Web Publication||15-Apr-2015|
Dr. Mahesh K Duddu
Department of Pedodontics and Preventive Dentistry, G. Pulla Reddy Dental College and Hospital, G.P.R Nagar, Nandyal Road, Kurnool - 518002, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Purpose: The study was conducted with the aim of comparing the shear bond strength (SBS) and microleakage of Tetric N-Bond, G-bond, and Xeno V (seventh generation dentin adhesives) in primary anterior teeth. Materials and Methods: For the shear bond strength, 45 teeth were randomly divided in to three groups namely group A, B, C (n = 15). Samples were mounted horizontally on acrylic block exposing the facial surface and bonded with different adhesives according to manufacturer instructions. A split Teflon mold was used to build the composite resin cylinder and light cured. Shear bond strength was tested using a universal testing machine. The values were statistically analysed. For microleakage, another 45 teeth were similarly grouped. Two class V cavities were prepared on the labial surface and treated with different dentine bonding agents and restored with resin composite (Ivoclar vivadent) A2 shade. The restorations were subsequently thermally stressed for 200 cycles and were subjected to dye penetration test, followed by sectioning through the center of the restoration labiolingually. Each section was examined using stereomicroscope at × 40 magnification to asses dye penetration at the margins of the restoration. Results: The SBS varied between 22.12-23.77 N/mm 2 (P-value = 0.231). The microleakage scores varied between 0.6-1.2 (P-value = 0.03; Post-hoc test A vs B (0.007)).There was a statistically higher degree of microleakage observed in group A when compared to group B. Conclusion: Among the three commercially available bonding agents, there were no statistically significant differences in SBS. G bond had higher microleakage when compared to the others.
Keywords: Bonding agents, microleakage, primary teeth, shear bond strength
|How to cite this article:|
Duddu MK, Muppa R, Panthula P, Srinivas N C. Comparison of shear bond strength and micro-leakage of three commercially available seventh generation bonding agents in primary anterior teeth: An in vitro study. J Indian Soc Pedod Prev Dent 2015;33:116-21
|How to cite this URL:|
Duddu MK, Muppa R, Panthula P, Srinivas N C. Comparison of shear bond strength and micro-leakage of three commercially available seventh generation bonding agents in primary anterior teeth: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2015 [cited 2019 Nov 14];33:116-21. Available from: http://www.jisppd.com/text.asp?2015/33/2/116/155123
| Introduction|| |
As we enter the new millennium, we find a meteoric rise in the use of bonded composite restorations with immense success. In the beginning of the era of restorative dentistry, retention and stabilization of restoration often required the removal of sound tooth structure to provide large undercuts to gain auxiliary retention aids. This problem is greatly solved with the introduction of newer bonding systems in adhesive dentistry.
With advancement in the field of adhesive dentistry, seventh generation bonding agents were introduced which are also known as single-solution or all-in-one products. The important thing to note about these products is that they accomplish all three traditional steps in the bonding process (etching, priming, and bonding/sealing) with a single solution. This simplifies the bonding procedure.
This is of great importance in paediatric dentistry, where a lot of chair side time is saved. Elimination of the etching step also removes the possibility of saliva contamination in slightly uncooperative children. As many seventh generation bonding agents are available in the market, it was felt that a randomized, in-vitro study was necessary to check which bonding agent performed better.
| Materials and Methods|| |
A sample of 90 human primary anterior teeth was selected. They were scraped of any residual tags and cleaned with pumice slurry with rubber cup and they were examined under stereomicroscope to ensure that there were no cracks or fractures and were randomly divided in to two groups of 45 each for checking SBS and microleakage.
Shear bond strength
The 45 extracted human primary anterior teeth were randomly divided in to three groups namely group A, B, C (n = 15) each. Root portion of all the samples were cut and samples were mounted horizontally on acrylic block exposing the facial surface outward [Figure 1]. Facial surface was reduced to expose flat dentine surface using a diamond disk [Figure 2]. Each group was bonded with different adhesives (Group A-G bond (GC Corp); Group B-Tetric N-bond (Ivoclar Vivadent); Group C-Xeno V (Dentsply)) according to manufacturer instructions. Following the application of adhesive, a split Teflon mold [Figure 3] measuring 2.5 mm in diameter and 3 mm in height was used to build the composite resin cylinder on the dentinal surface of all the samples [Figure 4], in a two layer incremental technique. Each layer was light cured for 40 seconds with curing unit (QHL-75, Dentsply, 450 mW/cm 2 ) vertically for each increment. Additional circumferential curing of the cylinder for 60 seconds was done to ensure complete polymerization of the material after removal of Teflon mold. For all the specimens, the curing tip was placed as closely as possible. After the composite build up, the shear bond strength was performed using a universal testing machine at a cross head speed of 1 mm per minute in a compression mode using a blade parallel to adhesive interface between adhesive and dentin. The values obtained were calculated in Newton peak load at failure divided by the specimen surface area. The data obtained was tabulated and statistically analysed.
|Figure 1: Tooth samples mounted on acrylic block exposing the facial surface|
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|Figure 2: Facial surface was reduced to expose flat dentine surface using a diamond disk|
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In selected 45 extracted human primary anteriors, two class V cavity preparations were prepared on the labial surface of each tooth using a depth oriented bur (Shofu), a high speed handpiece and copious amount of water [Figure 5]. The cavity preparations were done using a depth oriented bur to standardize the preparation to 1.5 mm in depth and 1 mm width approximately. After the preparation 45 teeth were randomly divided into three groups that is group A, B, C (n = 15) similar to the SBS study. Each group was treated with different dentine bonding agents according to manufacturer instructions. For all the three groups the cavities were restored with resin composite (Ivoclar Vivadent) A2 shade using incremental technique and finishing and polishing was done, after which the specimens were stored in 100% humidity for 24 hours. The restorations were subsequently thermally stressed for 200 cycles in PCR chamber (Eppendorf, U.S. A.) with an exposure time of two seconds at 5°C and 55°C and dwell time of 30 seconds.
|Figure 5: Two class V cavity preparations prepared on the labial surface|
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After thermocycling the specimens were subjected to dye penetration test, where the root surface and apices were sealed with sticky wax, followed by application of two coatings of nail varnish all over except for the restored part and 1 mm wide zone adjacent to the margins of the restoration. After drying thoroughly the teeth were immersed in a fresh solution of 2% methylene blue dye solution for 24 hours at room temperature. After staining, the teeth were rinsed to remove residual stain and they were blotted dry. Sectioning of the coronal part through the centre of the restoration labiolingually was done after removing the root portion. Each section was examined using stereomicroscope at 40 × magnification to asses dye penetration at the margins of the restoration [Figure 6].
|Figure 6: Prepared coronal section through the centre of the restoration as seen through a stereomicroscope at 40 × magnification to asses dye penetration at the margins of the restoration|
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Criteria for evaluation
The degree of dye penetration was evaluated and scored as follows:
The mean amount of leakage was recorded for each group and results were tabulated and statistically analysed.
| Results|| |
Following results were obtained after statistical analysis
The mean peak load applied to the samples ranged from 108.41 N to 116.88 N [Table 1]. The SBS was calculated by dividing the mean force by the area and expressed in N/mm 2 . This ranged between 22.12 to 23.85 N/mm 2 .
The microleakage scores ranged between 0.6 and 1.2 [Table 2]. The least was in group B and the highest was in group A. The P-value was 0.03. The post-hoc test showed A vs B as 0.007 which was significant.
| Discussion|| |
The seventh generation bonding agents are very user friendly. They reduce the etching, priming and bonding agent application steps into one step. This drastically reduces the application time and makes this stage less technique sensitive because the etching and rinsing step is not needed. These bonding agents bond the composite to the enamel and dentine. Because of the morphological, compositional and histologic differences between enamel and dentine, the bond to dentine has not been as good as it is with enamel. Research continues to progress in this area and advancements have been made. The trend had been to combine the etching, priming and bonding into one step.
Traditionally bonding agents contained HEMA (2-hydroxy-ethyl-methacrylate) in significantly high quantities. This was done mainly because HEMA has the characteristic of wetting the tooth surface in a positive way. It also has a very high penetration capacity into the etched dentine. This is important in when using fifth generation bonding agents as the separately used etchant causes a much deeper etching as compared to the seventh generation bonding agents. HEMA also helps mix the hydrophilic and hydrophobic components of the bonding agent into one solution. It also acts as a co-solvent by dissolving the various components into water. Water is needed in the seventh generation bonding agents to enable self-etch.
HEMA has the problem of allergic effects to the patient and the dentist. It even penetrates through the gloves after some time. , HEMA polymerises in a linear fashion without crosslinking and thus the interface is less strong. HEMA also contains water within the adhesive layer and therefore impedes the polymerization process. It also enhances water uptake and therefore the bond is more prone to breakage over time. 
The seventh generation bonding agents used in this study were HEMA free. These bonding agents are acidic primers and these systems try to superficially demineralise dentine and simultaneously penetrate it to the depth of demineralization with monomers that can be polymerised immediately in that area. The depth of demineralization by the seventh generation bonding agents is significantly less than the fifth generation. This is also a reason why HEMA is not essential as deep penetration is not required.
Seventh generation bonding agents can be classified as Strong (pH < 1), Intermediate Strong (pH about 1.5) and Mild Self-Adhesives (pH of about 2). G-bond has a pH of 2. N-bond self etch is 1.5 and Xeno V bond has <2. Therefore G-Bond is a mild self-adhesive and N-Bond and Xeno V are Intermediate Strong adhesives. Mild Self-Adhesives have comparatively weaker bond potential to enamel.  This may be a reason why there was statistically more microleakage in G-Bond Group in this study. In contradiction to this study, according to Nikhil V, Singh V and Chaudhry S,  mild self etch adhesives appear most promising especially with regard to bond stability. This is because mild self etching adhesives do not remove all the hydroxyapatite and therefore more calcium is available for additional interaction with adhesive monomers. This makes the bonds stable even in the aqueous environment and prolongs the clinical lifetime of the restorations. 
Composite resin is the most aesthetic restorative material currently available for restoring anterior teeth. It provides acceptable aesthetics and has relatively good handling properties. Nevertheless, problems still exist in terms of polymerization shrinkage and subsequent inadequate adhesion to cavity walls which leads to microleakage.  Microleakage may be the precursor of secondary caries, marginal deterioration, postoperative sensitivity and pulp pathology. Microleakage poses a particular problem in the paediatric patient in whom the floor of the cavity preparation in primary dentition may be close to the pulp. 
One more important characteristic of the restoration is bond strength. In a clinical situation, debonding might occur soon after the restoration has been placed if it is subjected to stress. Such stress may be due to the restorative procedure, contraction shrinkage of the resin composite, or normal oral function such as mastication. Sufficient bond strength is one of the factors contributing to the clinical success of dental restorations. Shear bond strength evaluation is one of many in-vitro screening tests that could be done to try and predict the ultimate clinical success of bonding agents. , In this study a flat dentin surface was preferred, according to  flat dentin surface would give wider area of dentin to be treated and bonded to resin, in addition, the oblique pattern of tubule orientation in primary teeth would not be a variable in bond strength of adhesive. The shear bond strength was measured using universal testing machine using a wedge technique. The advantage of this method is that specimens and loading arrangements are easy to produce, which makes it by far the most popular systems used. In the present study the shear bond strength values in N/mm 2 were obtained by using the following formula:
(Area was calculated by πr 2 which was equal to 4.9 mm 2 )
The Teflon mould which was used was of 2.5 mm in diameter, smaller diameter was used to restrict the bonding surface area which would result in fewer defects occurring in the smaller area of bonding and higher bond strength. During placement of composite inside the mould, incremental technique was used to decrease the polymerization shrinkage.
In the present study shear bond strength among the three materials was as follows: Mean of G-Bond was 22.12 N/mm 2 , Tetric N-Bond was 23.85 N/mm 2 and Xeno V-23.77 N/mm 2 . The intergroup comparison was not significant. But shear bond strength of G- Bond was comparatively less when compared to Tetric N-Bond and Xeno V. Hegde and Bhandary  compared the self etching adhesives - Clearfil S3, Xeno III, Clearfil protect bond and G bond and among these self etch adhesives G bond showed less bond strength. It has been postulated that minimum bond strength of 17-20 Mpa is needed to resist contraction forces of resin composite.  Our observation revealed that the seventh generation dentin bonding agents which were chosen for the study achieved the optimal bond strength value which is required for clinical success of the restoration. Besides this, as these bonding agents are easy to handle and takes less time to apply, they are preferable in children in whom isolation is a problem and co-operation for treatment is less.
In a study done by Ho AC et al.,  G-Bond and iBOND (Heraeus Kulzer, USA) may well sufficiently with stand the alignment and occlusal forces imparted by light archwires during immediate archwire tie-in and over the initial levelling and alignment phase. iBOND is another seventh generation bonding agent which was not used in this study.
The second objective of the study was to check the microleakage among the three commercially available seventh generation agents. Microleakage occurring along the restoration-tooth interface is possibly the greatest determinant to the development of an 'ideal' restorative material. Leakage can occur after a period of functioning because of chemical, thermal and mechanical stress on the interface. Thermocycling is usually used to expose the restoration to simulated clinical situations that normally stress the marginal seal.  In the current study class V restorations were chosen, as they are the true test of adhesive-mechanic performance as no macromechanical retention is available and restorative margins exist in both enamel and dentin.  Many techniques have been devised to test the cavity sealing properties of restorations. The use of organic dyes as tracers is the most common method in detecting the marginal leakage in vitro. , In the present study, a 2% aqueous solution of methylene blue dye was used. A concentration of 2% was preferred because, greater the concentration, greater the ease of detection and classification of the degree of microleakage.
Microleakage mainly occurs as a result of polymerization shrinkage of the composite resin. Other factors, such as the difference in coefficient of thermal expansion between the composite resin and tooth structure or presence of voids or porosities in the resin may contribute to the microleakage.  In the present study the dye penetration reached the axial wall in 30% of the teeth in group A (G-Bond), 13.3% of the in group B (Tetric N-Bond) and in 33.3% of the teeth in group C (Xeno V). The microleakage was significantly higher in G bond group when compared to Tetric N-Bond. Microleakage was not observed in 48.3% of the samples in G Bond group, 71.7% in Tetric N-Bond and in 65% of Xeno V group. This result matches with the study conducted by Chandra PV et al.,  in which Xeno V was superior to G bond in terms of preventing microleakage.
From the present study it can be observed that when compared to G Bond, Tetric N-Bond and Xeno V performed better in preventing the microleakage. It is also observed that none of these adhesive systems were able to completely prevent microleakage of the class V restorations. More research needs to be focused on the aspect of improving the dentin adhesives, so as to prevent the microleakage at tooth and restorative interface which would, in turn, improve the clinical success and longevity of the restoration.
| Conclusion|| |
The three commercial products from seventh generation, that is G Bond, Tetric N-Bond, Xeno V, had no statistical difference in shear bond strength. There was a statistically higher degree of microleakage observed in G bond when compared to Tetric N-Bond. Tetric N-Bond and Xeno V were better in preventing the degree of microleakage in primary teeth when compared to the G bond.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]