|Year : 2012 | Volume
| Issue : 4 | Page : 357-362
|Comparative evaluation of the effect of different bonding agents on the ultramorphology of primary tooth dentin and the resin dentin interface
Pallavi Vashisth1, Mousumi Goswami2, Mudit Mittal3, Seema Chaudhary1
1 Department of Pedodontics, Institute of Dental Sciences, Bareilly, Uttar Pradesh, India
2 Department of Pedodontics, Kothiwal Dental College and Research Centre, Moradabad, Uttar Pradesh, India
3 Department of Periodontics and Implantology, Institute of Dental Sciences, Bareilly, Uttar Pradesh, India
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|Date of Submission||25-Dec-2011|
|Date of Decision||25-Jan-2012|
|Date of Acceptance||23-Jul-2012|
|Date of Web Publication||3-Oct-2012|
| Abstract|| |
Aim: To analyze and compare the changes in the ultramorphology of dentin in primary teeth using different bonding agents and to study the resin/dentin interface produced by them.
Materials and Methods: Occlusal surfaces of 50 extracted human deciduous teeth were grounded to expose the dentin. The teeth were divided into two groups (A) For viewing surface morphology- 18 teeth divided into four groups: (a) for viewing dentinal morphology (3 teeth), (b) Scotchbond multi-purpose (5 teeth), (c) Adhe SE (5 teeth), (d) Futurabond (5 teeth). (B) For viewing interfacial morphology- 32 teeth divided into four groups with 8 teeth each: (a) Scotch Bond Multipurpose (3M, ESPE),), (b) Adhe Se (Vivadent), (c) Optibond All-in-One (Kerr), (d) Futurabond NR (VOCO, Cuxhaven, Germany). The adhesives were applied to each group following the manufacturer's instruction. All the samples were then prepared for viewing under SEM.
Results: The photographs were graded using a four-step (0-3) scale method proposed by Ferrari et al. For Scotchbond, 12 (75%) were graded as 2 Grade 3 was observed in only 1 observation in the entire lot of materials. The results obtained for Adhe SE and Optibond AIO were similar, i.e. in 5 (31.25%) observations each the scores were 0 and in 11 (68.75%) observations each the scores were 1. In case of Futurabond, 3 (18.75%) observations were graded as 0 and 13 (81.25%) were graded as 1, thus showing a mean score of 0.81±0.40.
Conclusion: Three- step bonding agent results in the complete removal of smear layer. While the self- etch approach is not efficient in removing the smear layer and opening of the dentinal tubules. The longest resin tags with lateral branches were seen in two groups- Scotch bond multipurpose and Optibond FL.
Keywords: Deciduous teeth; dentin bonding agents; resin tag; scaning electron microscopy; ultramorphology
|How to cite this article:|
Vashisth P, Goswami M, Mittal M, Chaudhary S. Comparative evaluation of the effect of different bonding agents on the ultramorphology of primary tooth dentin and the resin dentin interface. J Conserv Dent 2012;15:357-62
|How to cite this URL:|
Vashisth P, Goswami M, Mittal M, Chaudhary S. Comparative evaluation of the effect of different bonding agents on the ultramorphology of primary tooth dentin and the resin dentin interface. J Conserv Dent [serial online] 2012 [cited 2019 Apr 20];15:357-62. Available from: http://www.jcd.org.in/text.asp?2012/15/4/357/101905
| Introduction|| |
Over the past few decades, dentin bonding systems have become widely accepted for the clinical placement of resin composite restorations. Due to their inherent hydrophobic nature, composites are not able to maintain a good marginal integrity leading to microleakage, or the ingress of oral fluids and bacteria along the cavity walls, which leads to failure of restorations and development of secondary caries. In order to preserve the tooth structure and maintain the restoration in the cavity, there should be adhesion between the restorative material and the tooth structure. 
The word adhesion is derived from the Latin word adhaerere, which means to stick. Adhesion refers to the forces or energies between atoms or molecules at an interface that hold two phases together. 
There are two different ways that the current adhesive systems obtain acceptable micromechanical retention between resin and dentin. The first method is based on complete removal of the smear layer and demineralization of subsurface intact dentin, using acid etching. , The second method uses slightly acidic monomers, which partially demineralize the smear layer and underlying intact dentin, incorporating the demineralized smear layer remnants and using them as bonding substrate, called as self etch approach. , There has been a trend to move from the original type of multicomponent bonding systems toward simplified, consolidated adhesive systems that are more user-friendly. 
Clinical indications for tooth colored restorations have increased with advent of dentine adhesives and composite resin systems. These are used widely as esthetic restorations of anterior and posterior teeth that have multi-surface carious lesions or traumatic destruction. But, failure of these restorations in primary teeth is common owing to smaller tooth size and conservative cavity preparation, leading to poor performance of these materials when used in primary dentition.  Moreover, the concentrations of calcium and phosphorus in both peritubular and intertubular dentin are lower in primary teeth. The interface formed in primary teeth is thicker and there is incomplete impregnation of bonding system in the collagen network, resulting in reduced adhesive strength.  The aim of the study was to analyze and compare resin/dentin interface produced by different bonding agents.
| Materials and Methods|| |
Fifty eight extracted human deciduous teeth were collected. Occlusal surfaces of each tooth was ground flat with water cooled air turbine using diamond burs (Shofu Inc, Kyoto, Japan) and were abraded with 240, 400, 600 grit abrasive paper for surface flattening and smear layer standardization. 
The teeth were divided into two groups
To study surface morphology
18 teeth were taken, which were further divided into four groups:
Group A: For dentinal morphology (3 teeth)
Group B: with Scotchbond multipurpose (5 teeth)
Group C: with Adhe SE (5 teeth)
Group D: with Futurabond (5 teeth)
To study interfacial morphology
32 teeth were taken, which were then divided into four groups with 8 teeth each
Group I: Scotch Bond Multipurpose (3M, ESPE)
Group II : Adh Se (Vivadent)
Group III : Optibond All-in-One (Kerr)
Group IV: Futurabond NR (VOCO, Cuxhaven, Germany)
The adhesives were applied to each group following the manufacturer's instruction. [Table 1]
After exposing the dentin and applying the bonding agents the teeth were mounted in acrylic resin with flat dentinal surface facing upwards.
The specimens were rinsed with distilled water. All the samples were then sequentially dehydrated in ascending grades of ethanol i.e. 60% ,70%, 80%, 90% alcohol for 20 min each and in 100% alcohol for 1 h. 
Dentin resin interface
Dentin resin interface was viewed for all the five groups. After exposing the dentin and applying the bonding agents, on each sample a block of composite (Esthet X HD, Dentsply) was built by condensing the material into a mould (having 3 mm internal diameter and 2 mm height). The curing of the material was done in increments.
The teeth were sectioned vertically through the resin buildups and dentin with help of diamond disc under running water into two halves (mesial and distal) to expose the resin-dentin interface. The opposite surfaces (other than the resin-dentin interface) of the sectioned teeth were embedded in self-cure resin. The resin-dentin interfaces were polished with 600, 1200 grit polishing paper and Sof-lex finishing and polishing systems.
Preparation of samples
Specimens were emerged in 4% NaOCl for 20 min, followed by 20% hydrochloric acid for 30 seconds. The specimens were rinsed with distilled water. All the samples were then sequentially dehydrated in ascending grades of ethanol i.e. 60%, 70%, 80%, 90% alcohol for 20 min each and in 100% alcohol for 1 h.
Sample preparation for SEM viewing
All samples were dried, mounted on aluminium stubs which were then placed in vacuum chamber and sputter coated with gold layer and were observed under a scanning electron microscope.
Series of photographs were taken field by field at a magnification of 2000x and 10000x for viewing the surface morphology.
And at 1000x for viewing the dentin resin interface.
A four- step (0-3) scale method according to Ferrari et al. ,, was used for evaluation of resin dentin interface
Score 0 - no resin tag formation
Score 1- few and short resin tag
Score 2- when long resin tags were visible
Score 3- dense resin tags with numerous lateral branches.
The evaluation was then subjected to statistical analysis.
| Observations and Results|| |
Analysis of the specimens in cross-sections showed a varied morphology that depended on the various dentin pre-treatments.
Group A (no treatment)
The smear layer covered dentin observed in cross-section showed a surface completely covered by a crust of cutting debris that appeared to have little surface porosity: the orifices of the underlying tubules were completely obstructed by grinding debris. [Figure 1]a
|Figure 1: (a) SEM photograph illustrating the smear layercovered dentin at ×2000, (b) SEM photograph illustrating a cross-section of the dentin surface after treatment with Scotch bond at ×10000, (c) SEM photograph illustrating a cross-section of the dentin surface after treatment with Adhe SE at ×10000, (d) 4 SEM photograph illustrating a cross-section of the dentin surface after treatment with Futurabond NR at ×10000|
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Group B (Scotch bond multipurpose)
Treatment with Phosphoric acid resulted in a demineralized layer that appeared to have collapsed in its outer most part. The smear layer was completely removed and the dentin tubules opened. A higher magnification image focus showed some remnants of smear layer [Figure 1]b.
Group C (Adhe Se)
The self- etch primer was not sufficient to remove the smear layer and open the dentinal tubules. Remnants of smear layer can be seen on the surface of dentin plugging the tubules [Figure 1]c.
Group D (Futurabond)
Showed that treatment with this group was strong enough to dissolve the smear plugs. The demineralization was superficial and did not show that noticeable difference between the intertubular or peritubular dentin collar around the tubules lumen. [Figure 1]d.
Analysis of the specimens in longitudinal sections revealed the difference in resin/ dentin interfaces between the groups which are as follows:
Group I (Scotch bond multipurpose) had a thick hybridized complex, very long tags (10 to 83.30 μm) with small side branches. The tags were numerous in number with good contact with the hybrid layer. The tags were conical in shape at the base. [Figure 2]a.
|Figure 2: (a) SEM photograph illustrating the resin/dentin interface after treatment with Scotch bond multipurpose (×1000), (b) SEM photograph illustrating the resin/dentin interface after treatment with AdheSE (×1000), (c) SEM photograph illustrating the resin/dentin interface after treatment with Optibond-all-in-one (×1000), (d) SEM photograph illustrating the resin/dentin interface after treatment with Futurabond (×1000)|
Click here to view
Group II (Adhe SE) hybridized complex was very thin and irregular, and was not continuous. Length of the tags varied between 0 to 23.30 μm, leaving numerous tubuli empty. [Figure 2]b.
Group II (Optibond all-in-one) showed a thin irregular hybridized complex absent in some areas of the interface. Length of the tags varied between 0 to 23.30 μm, broken in few places with numerous empty tubuli. [Figure 2]c.
Group IV (Futurabond NR) hybridized complex was very thin but was comparatively continuous as compared to the above two groups. Length of the tags varied between 0 to 23.30 μm. [Figure 2]d.
Statistical Analysis of the Resin/ Dentin Interface.
Analysis was done for all the four adhesive materials were i.e. Scotch Bond, Adhe SE, Optibond All in One and Futurabond.
A total of 8 specimen restored with each adhesive material were taken and statistical assessment of their adhesive features was done Visual inspection of two photographs was done. The photographs were graded using a four-step (0-3) scale method proposed by Ferrari et al. Thus, a total of 16 observations for each type of adhesive material.
[Table 2] shows the grading scores obtained for different materials under study. Out of 16 observations made for Scotchbond, 3 (18.75%) observed were graded as 1, 12 (75%) were graded as 2 and 1 (6.25%) observation was graded as 3. Grade 3 was observed in only 1 observation in the entire lot of materials. Thus, Scotchbond had a mean score of 1.88 ± 0.50. The results obtained for Adhe SE and Optibond AIO were similar, i.e. in 5 (31.25%) observations each the scores were 0 and in 11 (68.75%) observations each the scores were 1. Both, the materials had a mean value of 0.69 ± 0.48. In case of Futurabond, 3 (18.75%) observations were graded as 0 and 13 (81.25%) were graded as 1, thus showing a mean score of 0.81 ± 0.40.
On comparing the data statistically using Kruskall-Wallis test for multiple independent samples (non-parametric variant of ANOVA), a statistically significant difference was seen.
[Table 3] shows comparison of different groups with each other, which shows significant differences were seen between-, Scotchbond and Optibond AIO, Scotch bond and Futurabond, Scotchbond and AdheSE with P < 0.001 (highly significant). While the difference between AdheSE and Optibond AIO, AdheSE and Futurabond, Optibond AIO and Futurabond were not significant.
Scotchbond had significantly higher grade scores as compared to all the other adhesives. No statistically significant difference was seen for any of the comparisons among Adhe E, Optibond AIO and Futurabond. Thus, on the basis of visual inspection the following order of grade scores were obtained:
Scotchbond > Futurabond ~ Adhe SE ~ Optibond AIO
| Discussion|| |
The current concept for bonding to tooth hard tissues is based upon the infiltration of a low- viscosity resin into enamel and dentin, a process known as hybridization. While bonding to enamel has been considered a reliable procedure due to its uniform composition (hydroxyapatite), bonding to dentin remains a challenge, as it contains higher water content and more organic material, mainly type I collagen. , A prerequisite for bonding is the close approach of bonding agent and substrate. Thus, the inherent wetness of the dentin tends to cause a problem. , Unless the bonding agent can displace or is miscible in the fluid in areas where the dentin is most permeable, it will be difficult to achieve a stable long lasting bond. , Furthermore, when cutting procedures are performed on tooth structure, the dentin surface becomes covered with a 1 μm thick layer of debris composed mostly of submicron particles of mineralized collagen matrix. , The results of our study showed the presences of smear layer in cross-sections as compact crust. Thus, the only two options available include removal of the smear layer or application of such agents that can penetrate the smear layer into the underlying dentin matrix. Sound teeth were used in the study because carious teeth will not give accurate results as the structure of the tooth is influenced by different stages of disease progression and thus are not reliable. , After the dentin becomes carious, its structure alters. In the transparent zone of primary and permanent teeth, dentinal tubules become occluded with mineral content and their hardness decreases compared with intact dentinal tubules. 
The preparations were performed on occlusal surfaces, following the methodology described by Van Meerbeek et al.  and Perdigao et al.  An important characteristic associated with occlusal surfaces used as substrate for bonding is that a flat cut exposes dentin in different depths in relation to the pulp chambers, i.e., the dentin related to the area of pulp horns is proportionally deeper (presenting larger and more concentrated tubules, with less intertubular dentin) compared with the dentin adjacent to the areas between the pulp horns.  And this method also allows standardization for the direction of the dentin tubules. 
Primary dentin has been assumed to be different from permanent dentin due to the variable amounts of mineral components, as well as morphological and structural differences.  The interface formed in primary teeth is thicker and there is incomplete impregnation of bonding system in the collagen network, resulting in reduced adhesive strength. 
The application of total etch and self-etch systems in the present study have shown differences in the surface morphology of the dentin. With total etch system, the dentinal tubules open up completely with only a few remnants of smear layer, while in case of the self-etching primers this result was not seen. When using dentin bonding agents, the smear layer must be removed from the intertubular dentin, opening the dentinal tubules for the formation of hybrid layer, which is ultimately responsible for strong and stable adhesion of composite resin to dentin. ,,
Van Meerbeek et al., reported that when acid is applied to dentin, mineral component is removed exposing the collagen network., , Erickson et al. also supported the above finding and stated that if strong acids are used, apart from removing the smear layer and smear plug completely, excessive demineralization of intertubular and peritubular dentin is seen. ,
Haller reported that self etching primers represents a very simple strategy to prevent exposed collagen mesh from collapsing, avoiding its unprotected exposure. When self-etching primers are applied, there is no need for etching, so the risk of over-etching, over-drying or over-moistening the dentin is eliminated. ,
Application of these bonding agents also showed a great variance between the groups. The resin tags formed by the three-step bonding agents showed a greater depth of penetration and the number or density of the tags formed was also greater in the three-step bonding agents.
Chapel RP et al. showed that after polymerization, the penetration of resin into lateral canals produced a three-dimensional structure that resembled a network of interconnected adhesive tags. Such an adhesive network may contribute to a strong dentin/ resin bond. 
Andia-Merlin RY et al, found that the monomers of tags and microtags of the three-step adhesive establish intimate contact with dentinal collagen fibrils. The lateral branches or microtags were numerous and profusely penetrated the canalicular system of dentin, establishing an intimate relationship with the mineralized collagen fibrils of intertubular dentin. 
The increased length and density of tags may be responsible for the increased values of shear bind strength. These findings were supported by Courson F, who found that the bond strength of scotch bond multipurpose was higher than the other two-step or single-step bonding agents in primary and permanent teeth.  Apart from the total removal of smear layer the other factor which is responsible for the better penetration of the resin monomers in case of the three-step bonding agents is that after phosphoric acid application for a brief etching period, a lower diffusion flux of hydrogen ions has been observed due to the buffering action of the mineral phase of dentin, which restricts the extension of demineralization. ,, This fact may contribute to the improved impregnation of the demineralized dentin, producing a more complete phenomenon of dentin infiltration, increasing the bonding efficacy. 
But studies state that if phosphoric acid is used for a longer period of time, then along with removal of smear layer it also demineralized the dentin to a greater extent, which leads to the presence of unsupported collagen fibers. These fibers without the support are weak and fragile, which may lead to easier fracture of the bonding interface. , The degree of demineralization is higher in case of primary teeth, so the etching protocol should be different for primary teeth, which has been shown by Nor et al.  They found that application of dentine conditioners produced increased thickness of the hybrid layer in primary teeth and the subsequent lack of complete penetration of adhesive resin into previously demineralized dentin may contribute to the lower bond strength to primary teeth.  Hence, to produce a conditioned dentine surface in primary teeth with morphological features similar to that of permanent teeth, the time of conditioning for the dentine of primary teeth should be approximately 50% less than the time recommended for permanent teeth. 
The above results were also confirmed by Puppin-Rontani RM in deciduous teeth, who tested two adhesive Scotchbond multi-purpose and prime and bond with same concentration of phosphoric acid for varying time interval and reported higher values of SBS at 7 and 15 seconds of application as compared to 20 seconds application period. 
The results of our study showed that three-step bonding agents produce more dense and long resin tags, which may be factor responsible for improved strength at the bonding interface. The additional step of etching and rinsing helps in the complete removal of smear layer and better penetration of the adhesive. But, precautions have to be taken to prevent collapsing of the collagen fibers. The only obstruction in the use of three-step adhesives, is the greater number of steps for the application of the adhesive system, which may increase the probability of incorporating errors during the restorative procedure.  Two-step self-etching bonding agents can be used as a substitute in primary teeth to reduce the number of applications and operating time, which might become necessary in some cases.
However, more research is required in the field of adhesive dentistry to develop such a bonding agent, which combines the mechanical properties of fourth generation bonding agents, requires fewer number of application steps, thus obtaining the best retention and saving on time.
| Conclusion|| |
Three-step bonding agent resulted in complete removal of smear layer.
More dense and numerous tags with lateral branches were seen with three-step bonding agents i.e. Scotchbond multi-purpose. It showed significantly superior results as compared to the other bonding agents.
The three simpler versions Futurabond NR, Optibond- all-in-one and Adhe SE did not differ significantly.
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Department of Pedodontics, Institute of Dental Sciences, Bareilly, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]
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