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Year : 2006  |  Volume : 9  |  Issue : 4  |  Page : 123-130
Comparative evaluation of micro-shear bond strength of adhesive resins to coronal dentin versus dentin at floor of pulp chamber - An Invitro Study


Department of Conservative and Endodontics, College of Dental Sciences, Davanagere, India

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   Abstract 

Background and Objectives: To compare the micro shear bond strengths of coronal dentin and pulp chamber dentin using two bonding systems namely Clearfil SE bond and Single bond.
Methods: Thirty molar teeth were collected for the study out of which sixty samples were prepared. Thirty, 2 mm thick slabs of coronal dentin were prepared from each tooth by removing occlusal enamel perpendicular to the long axis of tooth with low speed diamond disc to expose a flat mid coronal dentin and then thirty pulpal floor dentin samples were prepared by sectioning at mid point between floor of pulp chamber and root furcation. These sixty samples were divided into two major groups depending upon dentin location. GROUP I: 30 samples of coronal dentin. GROUP II: 30 samples of dentin at floor of the pulp chamber. Each group was subdivided into two subgroups depending upon the bonding agent used. Subgroup Ia. IIa: Clearfil SE bond. Sub group Ib, IIb: Single bond).
Results: Micro shear bond strength showed higher values to coronal dentin compared to dentin at floor of the pulp chamber and Clearfil SE bond showed higher values compared to Single bond in coronal and dentin at floor of the pulp chamber, but statistically insignificant.
Interpretation and conclusion: Clearfil SE bond showed higher values compared to Single bond in both coronal dentin and dentin at floor of pulp chamber.

How to cite this article:
Dhanyakumar, Shekhar. Comparative evaluation of micro-shear bond strength of adhesive resins to coronal dentin versus dentin at floor of pulp chamber - An Invitro Study. J Conserv Dent 2006;9:123-30

How to cite this URL:
Dhanyakumar, Shekhar. Comparative evaluation of micro-shear bond strength of adhesive resins to coronal dentin versus dentin at floor of pulp chamber - An Invitro Study. J Conserv Dent [serial online] 2006 [cited 2020 May 27];9:123-30. Available from: http://www.jcd.org.in/text.asp?2006/9/4/123/42313

   Introduction Top


Recent advances in adhesive dentistry have resulted in resin-based restorations becoming routine treatments in clinical dentistry. The concepts of large preparation and extension for prevention proposed by G.V. Black have been gradually replaced by more conservative techniques. Resin bonding to enamel is considered to be a durable and predictable procedure. But adhesion of resin to dentin is more complicated and less predictable. Dentin is a complex biological structure [6] whose structure and properties change with location, age and disease. [9] The conventional belief that all endodontically treated teeth are weaker or more brittle has lead to the philosophy encouraging aggressive reinforcement of remaining tooth structure. Until recently non-vital teeth were usually treated with a crown, core, or post. This often leads to sacrificing of good remaining tooth structure. However, the opportunity for the restoration of non-vital teeth with resin based composite has increased due to development of better, more reliable bonding systems. [1] When composite resin is used to restore the access cavity of a molar or as a core material, it is very important to achieve a good bond to pulpal floor dentin, both to enhance retention and to maximize coronal seal. pulpal floor dentin is a complex biological structure, which includes primary dentin, regular and irregular secondary dentin and this dentin is not usually contacted by cutting instruments. [5] So the thickness of smear layer produced here is less compared to coronal dentin and the tubule diameter is much smaller and tubule density is high making it a more challenging bonding substrate and today growing efforts are made to simplify and shorten bonding procedures. [4] Most recent development have focused on simplification of multi step bonding processes using one of the two different approaches i.e. "Total etch approach" and "Self etch approach".

The objective of this study was to compare and evaluate the micro shear bond strengths of coronal dentin and dentin at floor of pulp chamber using two dentin bonding systems namely two step self etch (Clearfil SE bond) and Single bottle system (Single bond)


   Materials and Methods Top


Materials used for the study:

1) Composite resins:

Clearfil AP-X composite resin system (Kuraray)

Z-250 hybrid composite resin system (3M)

2) Bonding agents:

Clearfil SE bond (Kuraray) Single bond (3M)

3) Acid etchant: 35% Phosphoric acid (3M).

4) Cyanoacrylate adhesive.

5) Storage media - 0.5% distilled water

Specimen Preparation:

Thirty recently extracted mandibular human molars due to periodontal reasons, which are free of caries, restoration, cracks or other structural defects were collected for the study and the teeth were cleaned with ultrasonic scalers and stored in 0.5% distilled water. The occlusal enamel was removed perpendicular to the long axis of tooth with slow speed diamond disc to expose a flat mid coronal dentin. Thirty, 2 mm thick slabs of coronal dentin were prepared from each tooth and then thirty, 2 mm thick pulpal floor dentin samples were prepared by sectioning at mid point between floor of the pulp chamber and root furcation and prepared dentinal slabs were finished with wet silicone carbide sand paper under a stream of water to create smear layer.

These sixty samples were divided into two major groups depending upon dentin location. GROUP I: 30 samples of coronal dentin. GROUP II: 30 samples of dentin at floor of pulp chamber. They were further subdivided into two subgroups of 15 samples each depending upon the bonding agent used. Sub group I a, IIa was bonded with the Two-­step self etch technique Clearfil SE bond according to manufacturer instructions. Sub group Ib, IIb was bonded with Two-step total etch technique single bond according to manufacturer instructions. After adhesive application Teflon mould (1mm high, 1mm diameter) was placed and the resin composite build up corresponding to the bonding system (Clearfil AP-X in subgroup la, IIa and Z250 in Ib, IIb) was light cured for 40 sec. Specimens were stored at 37°C in water. The specimens were attached to the universal testing machine with the help of jig by cyanoacrylate glue. A thin wire (0.6 mm diameter) was looped around resin composite cylinder, around half its circumference and gently held flush against the dentin at resin dentin interface. A shear force was applied at a crosshead speed of 1 mm / min until the failure occurred. The resin dentin interface for the test, the wire loop and the center of load cell were aligned as straight as possible to ensure correct application of the shear force.

Micro shear bond strengths were calculated in MPa and statistical differences between the groups were analyzed. The results were recorded and the data was analyzed with one way ANOVA for multiple group comparison and Student's t- test (unpaired) for Groupwise comparisons at a significance level of P= 0.05.

Chemical formulation of adhesives used in dentistry:

1. Clearfil SE Bond

Primer:
MDP

ITEMA

Hydrophilic DMA

C.Q

N,N,Diethnol P-toludine

Water

Adhesive

MDP

HEMA

BISGMA

Hydrophobic Dimethacrylate

C.Q

N,N,Diethnol P-toludine

Silinanized Collidial silica

2. Single Bond

Etchant

35% phosphoric Acid

Adhesive

HEMA

BISGMA

Dimethacrylate

A methacrylate functional copolymer of poly acrylic and Polyitaconic acid. Photoinititator

Ethanol

Water


   Results Top


Micro shear bond strength values of two groups in terms of Mean, Standard deviation are presented in table number 1 and graph 1 . In group la (coronal dentin group): subgroup Ia (Clearfil SE bond) mean micro shear bond strength value is 45.OMpa which was high compared to subgroup lb which was 41.8Mpa. In-group 1t (pulpal floor dentin group): subgroup lb (Clearfil SE bond) Mean micro shear bond strength value is 32.8Mpa, which was high, compared to subgroup lb that was 29.6Mpa. The One-Way ANOVA test in [Table 2] showed significant difference (P < .001) between the groups. (F= 32.2). The Students t-test (unpaired) was applied for comparison of micro shear bond strength among different subgroups presented in [Table 3],[Table 4],[Table 5],[Table 6] respectively.


   Discussion Top


Saunders and Saunders in 1994 have stated that obturation alone is unable to provide a thorough seal, if tooth is not appropriately restored within a short time. [5] Belli S et a1 [2] investigated whether pulp floor dentin should be a good site for bonding and said use of thick layer of bonding resin along the floor of pulp chamber and over canal orifices acts as secondary protective seal. Kijsamanmith K et al [5] have demonstrated that despite an irregular surface morphology and absence of smear layer, bonding to pulpal floor dentin was weaker than previously reported for coronal dentin and said bonding systems may behave differently to pulpal floor dentin when compared to coronal dentin. The tubule density of dentin at floor of pulp chamber was less than in coronal dentin. The central portion of superficial coronal dentin surfaces was used in order to have all tubules oriented perpendicular to the surface. In this way any regional effects on the micro shear bond strength was minimized and Pulpal floor dentin is the most common site used for bonding in cases of non-vital teeth and often used to reinforce remaining tooth structure. Akagawa H et al [1] evaluated the shear bond strength to superficial dentin, deep dentin and dentin at the floor of the pulp chamber using Clearfil liner bond 2V and single bond using a single plane shear test assembly with a 4mm diameter bonded area. However the dentin available at floor of the pulp chamber is limited hence micro shear bond strength test will work better compared to conventional shear bond strength. The specimen size can be greatly reduced and is good for examining adhesion at small areas [9] . Therefore in this study micro shear bond strength test was performed to measure bond strength between two resins and dentin at two different regions.

Group I (coronal dentin group): Showed significant higher values of micro shear bond strength when compared to group II (pulpal floor dentin group). The results were in accordance with previous studies [1],[9]

Differences in bonding to dentin is due to morphological and structural variations in dentin, presence of more inorganic material in coronal dentin may be the cause for increased bond strength, The density and diameter of dentinal tubules was very high which is around 45,000/mm [2] and 2.5µm much larger when compared to pulpal floor dentin.

GROUP II (pulpal floor dentin): showed lower values of micro shear bond strength compared to group I. The results were in accordance with previous studies [1],[9]

The probable reasons may be due to the Ultra structure of dentin at floor of pulp chamber seems similar to secondary or reparative dentin and contains irregular, fewer and narrower tubules. These changes could impart influence penetration of monomers into dentinal tubules resulting in poorer bonding to this region. Pulpal floor dentin seems to be rich in organic components and low in mineral thus resulted in reduced penetration of monomer. Predentin on floor of pulp chamber is thought to affect the bond strength. The reduced surface area of intertubular dentin available for bonding may also contributed to lower bond strength.

Group Ia (coronal dentin with Clearfil SE bond): Showed higher bond strengths when compared to group I b (coronal dentin with single bond) but statistically insignificant. The results were same in accordance with previous studies conducted

There are presence of highly hydrophilic 10- MDP monomer in its composition, is believed to improve wetting of the moist tooth surface more over it has two hydroxyl groups that may chelate to calcium of dentin. Camphoroquinone contained in the primer is likely to enhance adhesion to dentin because it generates free radicals that increase surface energy and wet ability there by increasing bond strength. Fillers present in Clearfil SE bond were necessary to increase bond strength and improve mechanical properties of bonding agents.

Group Ib (coronal dentin with single bond) showed lower bond strengths when compared to group la, which was statistically insignificant. The results were in accordance with previous studies [1],[9]

Use of 35% phosphoric acid quickly removes all inorganic matter in peritubular dentin causing deeper penetration of acid into dentin resulting in over etching and subsequent collapse of collagen network thus leading to porous zone with in hybrid layer. As a result of polyalkenoic co-polymer accumulation on the top of demineralized collagen layer, a barrier could have formed on the surface preventing the penetration of adhesive into demineralized dentin, which led to porous zone within the hybrid layer.

Group IIa (pulpal floor dentin with Clearfil SE bond): showed higher bond strengths when compared to group IIb, which was statistically insignificant. The results were in accordance with previous studies conducted [1],[9]

The reasons postulated are pulpal floor dentin is usually not contacted by any cutting instruments. S o it is largely devoid of smear layer. Acid conditioning of primer in Clearfil SE bond appeared sufficient to demineralize the dentin and envelop collagen fibers and hydroxyapatite crystals. Clearfil SE bond combines conditioning and priming in one-step and followed by adhesive application. Acidic conditioning primer dissolves smear layer and incorporates into primer, as it deminerlizes the dentin and envelopes the collagen fibers and hydroxyapatite crystals. As demineralization and resin infiltration into collagen occur simultaneously to same depth of dermineralized dentin. It is presumed that no gap or void exist. Camphoroquinone contained in the primer is likely to enhance adhesion to dentin because it generates free radicals that increase surface energy and wetting ability there by increasing bond strength.

Group IIb (pulpal floor dentin with single bond): showed lower bond strengths when compared to group Ila, which was statistically insignificant. The results were in accordance with previous studies conducted [1],[9] .

The reasons postulated are pulpal floor dentin is usually not contacted by any cutting instruments. So it is largely devoid of smear layer. Acid etching with 35% phosphoric acid will lead to over etching of surface leading to decreased bond strengths. Pulpal floor dentin is rich in organic components and less in mineral. Use of 35% phosphoric acid will result in over etching and collapsing of collagen fibers leading to decreased bond strengths


   Conclusion Top


The following conclusions have been drawn from this invitro study:

  1. Coronal dentin shows high micro shear bond strengths over pulpal floor dentin.
  2. Clearfil SE bond shows high micro shear bond strengths over Single bond at both coronal dentin and dentin at floor of the pulp chamber. (Though statistically not significant).


However, further studies are needed to investigate the bond strengths of these adhesive systems under clinically acceptable conditions.[10],[Table 1],[Figure 1],[Figure 2],[Figure 3],[Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8],[Figure 9].

 
   References Top

1.Akagawa H, Nikado T, Takada T, Burrow MF, Tagami J. Shear bond strengths to coronal dentin and pulp chamber floor dentin. American Journal of dentistry 2002; 15(6):383-388.  Back to cited text no. 1    
2.Belli S, Zhang Y 1, Pereira PNR, Ozer F, Pashley DH: Regional bond strength of adhesive resins to pulp chamber dentin. Journal of Endodontics 2001;27(8):527-532.  Back to cited text no. 2    
3.Chirstensen GJ. Self-etching primers are here. Journal of American Dental Association 2001; 132:1041-1043.  Back to cited text no. 3    
4.Haller B: Recent developments in dentin bonding. American Journal of dentistry 2000; 13(l):45-50.  Back to cited text no. 4    
5.Kijsamanmith K, Timpawat S, Harnirattisai C, Messer HH: Micro-tensile bond strength of bonding agents to pulpal floor dentin. International Endodontic Journal 2002; 35(10): 833-839.  Back to cited text no. 5    
6.Phrukkanon S, Burrow MF, Tyas MJ. Effect of cross-sectional surface area on bond strengths between resin and dentin. . Dental materials 1998; 14(3): 120-128.  Back to cited text no. 6    
7.Sattabanasuk V, Shimada Y, Tagomi J. The bond of resin to different dentin surface characteristics. Operative Dentistry 2004; 29(3): 333-341.  Back to cited text no. 7    
8.Sensi LG, Lopes GC, Monoterio S, Baratien LN, Vieira LCC. Dentin bond strength of self ­etching primers and adhesives. Operative Dentistry2005; 30(1):63-68.  Back to cited text no. 8    
9.Toba S, Veerapravati W, Shimada Y, Nikaido T and Tagami J: Micro shear bond strengths of adhesive resins to coronal dentin versus the floor of pulp chamber. American Journal of Dentistry 2003; 16(9): 52A-56A.  Back to cited text no. 9    
10.Yoshiyama M, Matisho T, Ebisu SY, Pashley D: Regional bond strengths of self etching or self priming adhesive systems. Journal of Dentistry 1998;26(7):609-616  Back to cited text no. 10    

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Correspondence Address:
Dhanyakumar
Department of Conservative and Endodontics, College of Dental Sciences, Davanagere
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.42313

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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    Abstract
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    Materials and Me...
    Results
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