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Year : 2005  |  Volume : 8  |  Issue : 1  |  Page : 37-44
An SEM evaluation of resin-dentin interface of three adhesive systems used for bonding fibre posts into the root canal dentin - An Invitro Study


Department of Conservative Dentistry & Endodontics, Meenakshi Ammal Dental College & Hospitals, Maduravoyal, Chennai, India

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   Abstract 

The aim of this study was to evaluate the resin­dentin interface of three adhesive systems: (i) 'etch and rinse-single bottle' adhesive (Single bond- 3M), (ii)'self etch' adhesive - (AdheSE - Ivoclar) and (iii) 'glass ionomer' adhesive (Fujibond LC - GC) used for bonding fiber posts (Luscent anchors, dentatus) into the root canal using scanning electron microscope. The thickness of the hybrid layer and the presence of resin tags with lateral branches were detected, and subjected to statistical analysis.

How to cite this article:
Karthik K, Velmurugan N, Kandaswamy D, Bhargavi N. An SEM evaluation of resin-dentin interface of three adhesive systems used for bonding fibre posts into the root canal dentin - An Invitro Study. J Conserv Dent 2005;8:37-44

How to cite this URL:
Karthik K, Velmurugan N, Kandaswamy D, Bhargavi N. An SEM evaluation of resin-dentin interface of three adhesive systems used for bonding fibre posts into the root canal dentin - An Invitro Study. J Conserv Dent [serial online] 2005 [cited 2020 Oct 30];8:37-44. Available from: https://www.jcd.org.in/text.asp?2005/8/1/37/42724

   Introduction Top


The trend towards the use of prefabricated fiber posts along with the adhesive resin cements reduces the risk of root fracture as compared to the custom-­made post and core [1] . Current adhesive techniques and materials can create a 'Monobloc' of multilayered structures, where dentin, adhesive, resin cement, post, core, and the final restoration are directly or indirectly bonded to each other, resulting in higher bond strength at each interface [2] .

It has been demonstrated that bonding of resin based adhesives with the dentin is achieved by a combination of micromechanical retention provided by hybrid layer formation into intertubular dentin, resin tag formation into the dentinal tubules and surface adhesion [3] . The various bonding systems available are the etch & rinse, self- etch & the glass-ionomer based adhesives. The efficacy of these dentin-­bonding systems can be evaluated by observing the hybrid layer, resin tag and adhesive lateral branch formation.

The aim of this in vitro study was to compare the bonding ability of one `Etch & Rinse', one 'Self'- etch' and one `Glass ionomer' based adhesives within the post space of the root canal.


   Materials and Methods Top


Caries free, thirty maxillary central incisors were selected and the crown was sectioned below CEJ to obtain a root length of 14 mm. Step back preparation was done upto 60 and the canals were obturated with cold lateral compaction of Gutta-percha and resin sealer (AH plus, Dentsply). Canals were enlarged with low speed drills (Luminex, Dentatus), sizes of 3 (or) 4 depending on size and shape of the root, upto a depth of 9 mm. The samples were randomly allocated to 3 groups of 10 samples each.

Group I : 'Etch & Rinse'-'One bottle' adhesive (Single Bond -3M ESPE) : Etching with 35% phosphoric acid (Scotch bond - 3M) for 15 seconds, washed & dried. The primer/ adhesive was applied and light cured for 60 seconds using Light Transmitting Post (Luminex LTP, Dentatus) of size corresponding to the size of reamer used for post space preparation.

Group 2 :
'Self-etch' adhesive (AdheSE -lvoclar Vivadent): The primer (AdheSE primer) was applied for 15 seconds and brushed for another 15 seconds, so that the total reaction time was not less than 30 seconds. The self-etching adhesive (AdheSE Bond) was applied & cured for 60 seconds using the corresponding LTP.

Group3 : `Glass ionorner' adhesive (Fuji Bond LC-GC): 20% Poly Acrylic Acid conditioner was applied for 10 seconds rinsed and dried. One scoop of powder with 2 drops of liquid were mixed, for 10 seconds & applied. Light cured for 60 seconds using LTP.

Fibre posts (Luscent Anchors, Dentatus) were then cemented with dual cure resin cement (Rely X ARC, 3M ESPE). After complete setting of the cement, samples were stored in water at room temperature. After one weak, the root samples were sectioned through the center of the long axis of the post using a diamond saw wheel at slow speed under water. Three locating notches for standardized examination of the interfaces were made by a scalpel, 2mm (coronal third), 5mm (middle third) and 8 mm (apical third) apically to the cemento enamel junction.


   SEM Preparation Top


Decalcification : One section of each root was gently decalcified (32% phosphoric acid was applied for 30 seconds) to demineralize any mineral within the hybrid layer that was not protected by the resin infiltration.

Deproteinization : The samples were then deproteinized with 2% sodium hypochlorite solution (for 120 seconds) to solubilize all non protected demineralized dentinal matrix beneath the hybrid layer, if it exists and the dentinal matrix demineralized by the phosphoric acid in the previous step. This procedure exposes the resin tags to their full length and demarcates the bottom, of the hybrid layer.

After rinsing with water, the specimens were air dried, and submitted to increasing concentrations of alcohol for dehydration. Finally, samples were mounted on the aluminum stubs and sputter coated with gold (JEOL, JFC - 1600, Auto fine coater) and observed under the Scanning Electron Microscope (JEOL, JSM, 5610 LV) at different magnifications (x1500, x5000). The thickness of the hybrid layer at 2, 5 and 8mm levels of the post space preparation were measured at the standardized magnification of x 1500, and the presence of resin tags with lateral branches were observed at the magnification of x5000. The results were statically analyzed. One-way ANOVA was used to calculate the P - value. Multiple Range test by Tukey-HSD procedure was employed to identify the significant groups at 5% level.


   Results Top


The hybrid layer thickness values obtained (in mm) for the three test groups evaluated are given in [Table 1],[Table 2] and[Table 3].

Hybrid layer thickness

In the coronal third:
Mean hybrid layer thickness obtained with Single bond (5.19±0.68) was significantly higher than AdheSE (3.06±0.58) and Fujibond LC (0.79 ± 0.30) (P< 0.0001). Also, mean hybrid layer thickness of AdheSE (3.06±0.58) was significantly higher than Fujibond LC (0.79±0.30) (P< 0.0001).

In the middle third: Mean hybrid layer thickness obtained with Single bond (5.17±0.60) was significantly higher than AdheSE (2.79±0.68) and Fujibond LC (0.64 ± 0.21) (P< 0.0001). Also, mean hybrid layer thickness of AdheSE (2.79±0.68) was significantly higher than Fujibond LC (0.64±0.21) (P< 0.0001).

In the apical third: There was no statistically significant difference of mean hybrid layer thickness among Single bond (0.74±1.20), AdheSE (1.29±1.13) and Fujibond LC (0.23±0.38).

Among the 3 groups tested

Single bond: Mean hybrid layer thickness in the coronal (5.19±0.68) and middle (5.17±0.60) third was significantly higher than the apical third (0.74±1.20) (P<0.0001). No statistically significant difference between coronal and middle third.

AdheSE: Mean hybrid layer thickness in the coronal (3.06±0.58) and middle third (2.79±0.63) was significantly higher than the apical third (1.29±1.13) (P<0.0001). No statistically significant difference between coronal and middle third.

Fujibond LC: Mean hybrid thickness in the coronal (0.79±0.30) and middle third (0.64±0.21) was significantly higher than the apical third (0.23±0.38) (P<0.000 1). No statistically significant difference between coronal and middle third.

Presence of resin tags and adhesive lateral branches

In the coronal and middle third, resin tags with numerous lateral branches were observed for both Single bond and AdheSE. In the apical third, the Single bond and AdheSE showed no resin tag formation; only resin plugs were visible.

In the coronal, middle and apical third, Fujibond LC showed no resin tag formation; only resin plugs were visible.


   Discussion Top


The bonding of adhesive systems with the dentin is achieved through a combination of micromechanical retention provided by hybrid layer and resin tag formation. In this study, the bonding ability of the three adhesive systems, "etch & rinse"(Single bond-3M), "self etch" (AdheSE) and "glass ionomer"(Fuji bond LC) adhesive systems has been evaluated using posts. With the introduction of fiber posts, a "monobloc" restoration [2] is created with no inherent weak interlayer interfaces.

Adhesion with resin modified Glass­-ionomer is based on the micromechanical and chemical adhesion (VanMeerbeek [5] ). Although the predominant one is chemical adhesion, the presence of resin renders it possible for the hybridization to occur. Hence, in the present study, glass ionomer adhesive has been included to evaluate its bonding ability by observing the hybrid layer and resin tag formation.

In this study, the hybrid layer thickness in the coronal and middle third, with Single bond was significantly higher than that of the AdheSE. It has been demonstrated that the self-etching primer do not etch as well as a 35% phosphoric acid etchant because of their relatively high pH [3] . In this study, the pH of the phosphoric acid used with Single Bond is 0.6 and that of the AdheSE primer is 1.4.

Tay and Pashley demonstrated that, irrespective of the thickness of smear layer, self-etching adhesives with a pH around 1.5, created a uniform hybrid layer thickness, but not approachable to that of the dentin etched with phosphoric acid [6] . It also rejected the concept of the acidic primer to get neutralized by the mineralized component of the dentin smear layer. The authors suggested that the buffering capacity of the smear layer was low due to the presence of interconnecting channels within the smear layer that enhanced the diffusion and allowed acidic components to reach the basal portion of the smear layer. Hence, the pH of the phosphoric acid etchant and acidic primer and thus, the etching potential is responsible for the variation in the performance of Single bond and AdheSE, in the coronal and middle third of the post space preparation of the root canal.

Decreased curing with Light Transmitting Post in the apical third could be a reason for lack of significant difference in the mean hybrid layer thickness obtained with Single bond and AdheSE. Roberts et al [7] demonstrated that curing through light transmitting post did not result in adequate curing and has a limited utility in curing of adhesive materials inside the root canal. Moreover, the curing time recommended by the manufacturer might not be sufficient for adequate curing. Miyazaki et al [8] has demonstrated that the active application of primer ensures the penetration of dentin primer into demineralized dentin. In the present study, the application pressure in the apical third might be less resulting in poor performance of Single bond and AdheSE in the apical third. Also, the difficulty in washing out the residual etchant as in Single Bond in the apical third may have interfered with hybrid layer formation. Reis et al [9] reported that under overwet conditions, excess water diluted the monomer and compromised the hybrid layer formation. The difficulty in ensuring optimum wetness also added to the poor performance of Single bond in the apical third.

The mean hybrid layer thickness obtained with Fujibond LC was significantly lower than that of Singlebond and AdheSE. Several studies using Field Emission scanning Electron Microscopy (Fe-SEM) has demonstrated the presence of an acid-­base resistant layer (ABR) between the RMGIC and the dentin. Tanumiharja et al [10] reported that ABR layer observed with RMGIC is a combination of an ion exchange layer and a hybrid- like layer.

One of the problems of investigating the ion exchange layer is that conventional SEM requires dehydration of the specimen resulting in shrinkage and cracking [11] . So, it was determined to evaluate how far the hybrid layer and resin tag formation plays a role in adhesion of Fujibond LC with the dentin.

Fujibond LC has been demonstrated to produce a hybrid layer thickness of 0.5­1.0pm and it was attributed to the partial demineralization through the use of 20% polyacrylic acid conditioner, which removes the smear layer, without removing the smear plugs. Our findings were similar to that of VanMeerbeek et al [12] who demonstrated that bonding with glass ionomer based adhesive is similar to mild self etch approach, where demineralization could occur only to a depth of lµm. Similar to that of AdheSE and Single bond, the inadequate curing of the glass-ionomer adhesive could have lead to poor performance of Fujibond LC in the apical third.

Single bond and AdheSE showed resin tags with numerous lateral branches in the coronal and middle third of the post space preparation. The ability of the etchant or acidic primer to completely remove or dissolve the smear plugs resulted in the penetration of resin inside the dentinal tubules. Reduced application pressure in apical third reduced the tags in apical third.

Fujibond LC showed no resin tag formation in the coronal, middle and apical third, where only resin plugs are visible. This is in accordance with Inoue et al", who demonstrated the inability of the polyacrylic acid conditioner to completely remove the smear plugs.


   Conclusion Top


  1. The lower pH (0.6) of the acid used in the 'etch & rinse-Single bottle' adhesive system caused better demineralization resulting in maximum hybridization and resin tag formation, compared to other, systems used in this study.
  2. The main reason for self-etching adhesive performing less than that of `etch and rinse - single bottle' adhesive is its higher pH.
  3. The adhesion of glass ionomer has been proved to be predominantly, a chemical adhesion and the resin component is added only to protect the chemical reaction. Hence, it is no surprise that the glass ionomer based adhesive produced lesser hybridization and resin tag formation.
  4. In the apical third, all the adhesive systems performed poorly, probably due to inadequate transmission of light through Light Transmitting Post, difficulty in washing out the etchant completely, overwetness due to inadequate drying and the difficulty in active application of primer/ adhesive.[13]


 
   References Top

1.Marcela P.Newman, Peter Yaman, Joseph Dennison, Mary Rafter, Edward Billy. Fracture resistance of endodontically treated teeth restored with composite posts. J Prosthet Dent 2003: 89:360­-367.  Back to cited text no. 1    
2. George A. Freedman. Esthetic post and core treatment. Dental Clinics of North America 2001. New techniques in esthetic and restorative dentistry;45: 103-116.  Back to cited text no. 2    
3. Robert P. Chappell, Chaeles M. Cobb, Paulette Spencer, J. David Eick. Dentinal tubule anastomosis: A potential factor in adhesive bonding? J Prosthet Dent 1994; 72: 183-188.  Back to cited text no. 3    
4. Francesco Mannocci, Sheriff M, Ferrari M, Watson.F. Microtensile bond strength and confocal microscopy of dental adhesives bonded to root canal dentin. Am J Dent 2001;14: 200-204.  Back to cited text no. 4    
5. Vanmeerbeek B, Yoshida Y, Inoue S, Vargas M, Vijay P, Lambrechts P, Vanherle g. Adhesion to Enamel and Dentin: Current Status And future Challenges. Oper Dent 2003; 28-3:215­-235.  Back to cited text no. 5    
6. Franklin R. Tay, David H. Pashley. Aggressiveness of contemporary self-etching systems. I: depth of penetration beyond dentin layers. Dent Mater 2001; 17: 296-308.  Back to cited text no. 6    
7. Howard W.Roberts, David L.Leonard, Kraig S. Vandewalle, Mark E. Cohen, David G. Charlton. The effect of a translucent post on resin composite depth of cure. Dent Mater 2004; 20: 617­-622.  Back to cited text no. 7    
8. Miyazaki M, J A Plat, H Onose, BK Moore. Influence of dentin primer application methods on dentin bond strength. Oper Dent 1996: 21: 167-172.  Back to cited text no. 8    
9. Alessandro Reis, Alessandro Dourado Longercio, Cain Lucidius Naberenzy Azeredo, Ricardo Marins de CArvalho, Julio Da Motta Singer. Moisture spectrum of demineralized dentin for adhesive systems with different solvent bases. J Adhes Dent 2003; 5: 183-192.  Back to cited text no. 9    
10. Tanumiharja M, M F Burrow, A cimmino, M J Tyas. The evaluation of four conditioners for glass ionomer cements using field emission scanning electron microscopy. Journal of Dentistry 2001; 29:131-138.  Back to cited text no. 10    
11. Ngo H, Mount GJ, Peters MCRB. A study of glass ionomer cement and its interface with enamel and dentin using a low temperature, high resolution scanning electron microscopic technique. Quintessence Int 1997; 28:63-69.  Back to cited text no. 11    
12. Vanmeerbeek B, Yoshida Y, Inoue S, Vargas M, Vijay P, Lambrechts P, Vanherle G. Adhesion to Enamel and Dentin: Current StatusAndFuture Challenges. Oper Dent 2003;28­3:215-235.  Back to cited text no. 12    
13. Inoue S, Vanmeerbeek B, Yoshida Y, Abe Y, Lambrechts P, VAnherle G, Sano H. Effect of remaining dentin thickness and the use of conditioner on microtensile bond strength of a glass ionomer adhesive. Dent Mater 2001; 17: 445-455.  Back to cited text no. 13    

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Correspondence Address:
K Karthik
Department of Conservative Dentistry & Endodontics, Meenakshi Ammal Dental College & Hospitals, Maduravoyal, Chennai
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.42724

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    Abstract
    Introduction
    Materials and Me...
    SEM Preparation
    Results
    Discussion
    Conclusion
    References

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