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Table of Contents   
ORIGINAL RESEARCH  
Year : 2012  |  Volume : 23  |  Issue : 6  |  Page : 703-708
Effect of two different dentin desensitizers on shear bond strength of two different bonding agents to dentin: An in vitro study


1 Department of Conservative Dentistry and Endodontics, Teerthanker Mahaveer Dental College and Research Center, Bagarpur, Moradabad, UP, India
2 Department of Conservative Dentistry and Endodontics, J. S. S Dental College and Hospital, Mysore-570015, India

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Date of Submission02-Jul-2011
Date of Decision23-Dec-2011
Date of Acceptance27-Feb-2012
Date of Web Publication3-May-2013
 

   Abstract 

Objective: The objective of the study was to compare the effect of two different desensitizers on shear bond strength of two different fifth-generation single-bottle adhesive agents on dentin surface.
Materials and methods: Sixty human premolars were taken and divided into six groups of 10 samples each. The first two groups were the control groups and were not pretreated with any desensitizer; the remaining four groups were the experimental groups and were pretreated with either Denshield™ or Sensodent-K™ desensitizer. The specimens in each group were subjected to acid etching, application of adhesive (Single Bond or Prime and Bond NT), and application of hybrid composite resin (Z-100) according to the standard protocol. The specimens were subjected to shear bond strength testing, using a Lloyds universal testing machine (EZ20), followed by stereomicroscopic evaluation of the fracture mode at the debonded interface.
Results: Statistically significant difference existed between the two bonding agents in the control groups (group 1 and 2), with Prime and Bond NT showing higher bond strength than Single Bond. No statistically significant difference existed between either control or pretreated with any desensitizer when either of the adhesive systems was used. Prime and Bond NT showed statistically higher bond strength value when teeth were pretreated with Sensodent-K™ (groups 5 and 6). No statistically significant difference in bond strength values were observed between the bonding agents when pretreated with Denshield™ desensitizer.

Keywords: Bonding agents, bond strength, desensitizer

How to cite this article:
Bhatia S, Krishnaswamy MM. Effect of two different dentin desensitizers on shear bond strength of two different bonding agents to dentin: An in vitro study. Indian J Dent Res 2012;23:703-8

How to cite this URL:
Bhatia S, Krishnaswamy MM. Effect of two different dentin desensitizers on shear bond strength of two different bonding agents to dentin: An in vitro study. Indian J Dent Res [serial online] 2012 [cited 2020 Dec 4];23:703-8. Available from: https://www.ijdr.in/text.asp?2012/23/6/703/111242
Over the past decade, the use of resin-based dental composite (RBC) fillings has increased significantly and it is now a well-established dental procedure for the direct restoration of anterior and posterior teeth. With the development of improved adhesives and composite resin systems, RBC treatment has become predictably successful. However, polymerization shrinkage and postoperative sensitivity remain a challenge to practitioners. [1]

Clinical studies indicate that up to 30% of the study population report postoperative sensitivity following application of posterior composite resin restorations. [2] Sensitivity can be related to preparation trauma; leakage of the restoration, with the ingress of bacteria from polymerization shrinkage; deformation of the restoration under occlusal stress, which transmits hydraulic pressure to the odontoblastic processes; and the use of adhesives that require a total etch technique. [3],[4]

In literature, many methods have been suggested to reduce the symptoms of dentin hypersensitivity; these include reducing dentin permeability or fluid flow by occluding dentinal tubules with potassium oxalate, sodium fluoride, or adhesives, or by prevention of repolarization of nerves with potassium nitrate. However, there are conflicting reports on the effect of tubule-occluding desensitizing agents on bond strength of adhesive restoration. This may be due to various properties of adhesives, such as high fluoride content or low pH, which may induce chemical interaction with desensitizer applied after acid etching of dentin. [5]

On the other hand, with potassium nitrate, the desensitizing effect is believed to result from sensory nerves being prevented from repolarizing after initial depolarization. The potassium ions directly reduce nerve excitability by raising the extracellular potassium ion concentration to prevent action potential generation. [6] However, there is a lacuna in the literature with regard to the effect of potassium nitrate-type of desensitizer on shear bond strength of bonding agents. Hence, the purpose of this study was to evaluate and compare the effect of two desensitizers applied after acid etching on shear bond strength of two single-bottle total-etch adhesives.


   Materials and Methods Top


Materials [Table 1]
Table 1: Materials used in the study

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Equipments and accessories used in the study

  • A Teflon™ (polytetrafluoroethylene) block of 5 cm × 3.5 cm and thickness of 0.6 cm was milled at the center in a computerized milling machine to create a square of 1.4 cm × 1.4 cm and 4 mm deep. A circular hole of 3 mm diameter was punched at the center of the square in the remaining thickness of 2 mm to form a cylindrical mold of 3 mm diameter and 2 mm thickness.
  • A stabilizing device was made of acrylic resin to accommodate the standardized size of the Teflon™ block. It incorporated two bolts of 2 inches length and 6 mm diameter into which the Teflon™ was seated and secured with the help of tightening nuts to stabilize the specimens during its curing stages [Figure 1].
    Figure 1: Teflon mold with stabilizing device

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  • A regular block of 1 cm × 1 cm × 2 cm made of aluminium was used to embed the experimental tooth specimens.
  • A knife-edge chisel of 4 mm width
  • A customized jig to hold the aluminium block
  • A universal testing machine (EZ20; Lloyds) [Figure 2]
    Figure 2: Lloyds universal testing machine (EZ20)

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Methodology

Sixty recently extracted, caries-free human premolars were used for the present study. The teeth were thoroughly hand-scaled and stored in water.

Specimens were used within 1 month of extraction. The teeth were taken out of distilled water and the crowns were ground on the occlusal surface just below the DEJ in an orthodontic model trimmer, using water as a coolant. Thus, we obtained a flat ground occlusal surface, perpendicular to the long axis of the tooth. The horizontal-sectioned teeth were embedded into the rectangular aluminium blocks of 1 cm × 1 cm × 2 cm and stabilized with the help of self-curing resin, with the cut dentine exposed. The rectangular blocks were then immersed in water to dissipate the exothermic heat of polymerization, thus reducing damage to the test specimens. All the prepared specimens were then stored in distilled water until use.

Groups used in the study

The stored embedded teeth were retrieved and cleaned, and the dentin surface was further polished with the help of wet 600-grit silicon carbide paper. This was done to create a smear layer. The groups were formed as shown in Flowchart 1.[Additional file 1]

In control group 1 the flattened dentin surface was etched with 35% phosphoric acid gel for 15 s, then rinsed with water for 20 s, and finally blotted dry with cotton pellets, leaving a glistening appearance. Two coats of Single Bond bonding agent was applied, dried for 5 s, and then light cured for 10 s. The teeth were then stabilized with the help of a stabilizing device and the Teflon™ mold was properly aligned on the exposed dentin surface and fixed securely in place with tightening nuts. Shade A3 of Z-100 composite resin was dispensed with a Teflon-coated instrument and condensed into the mold. Any excess was wiped away with the same instrument. A Mylar strip was adapted over the mold and light cured for 40 s. The cured cylindrical button of 3-mm diameter and 2-mm thickness was pushed out of the mold with a ball burnisher.

In control group 2, flattened dentin surface was etched similar to group 1. After that, with the help of a disposable brush, Prime and Bond NT adhesive was generously applied to thoroughly wet the entire tooth surface. We ensured that the surface remained fully wet for 20 s. Excess solvent was removed by gently drying with dry air from a dental syringe for at least 5 s and the specimen was light cured for 10 s. Then the teeth were stabilized and restored similar to group 1.

In experimental group 3, the flattened dentin surface was etched similar to group 1. Denshield™ desensitizer (NovaMin particulate + few drops of water) was mixed to form a smooth paste, which was applied with the help of an applicator swab. After application, the product was allowed to remain on the tooth surface for 2 min after which the area was lightly irrigated with water to remove all visible evidence of the product. Single Bond was then applied and teeth were restored similar to group 1.

In experimental group 4, the flattened dentin surface was etched and pretreated with Denshield™ desensitizer similar to group 3. Over that, Prime and Bond NT was applied similar to group 2 and the teeth were restored similar to group 1.

In experimental group 5, the flattened dentin surface was etched similar to group 1. After that Sensodent-K™ desensitizer in paste form (mixed with few drops of water) was applied over the tooth surface with the help of a paint brush and allowed to stand for 9 min. This was followed by light irrigation with water. Subsequently, two more coatings were applied, with each allowed to stand for 9 min. On completion of the application of three coats, the area was lightly irrigated to remove all visible evidence of the products. Finally, Single Bond was applied and the teeth were restored similar to group 1.

In experimental group 6, the flattened dentin surface was etched and pretreated with Sensodent-K™ desensitizer similar to group 5. Prime and Bond was then applied and the teeth restored similar to group 1.

All the bonded specimens of the six groups were color coded and numbered for future reference. The test specimens were then stored in distilled water for 7 days before being subjected to shear bond analysis.

The shear bond test

The specimens were placed in a jig that conformed to the dimensions of the prepared aluminium blocks. The jig was held vertically in the lower member of the shear chuck such that the aluminium blocks with bonded surfaces were aligned horizontally. A knife-edge shearing chisel was employed to debond the prepared buttons of composite resin. The chisel was mounted on the upper member of the shear chuck. The cutting edge of the chisel was then engaged at the dentin-composite interface and force was applied perpendicular to the long axis of the specimen.

The equipment was operated at a crosshead speed of 1 mm/min and the maximum load to debond the specimens was recorded in Newtons (N). The shear bond strength was calculated in mega Pascals (MPa) by the ratio of the maximum load (in Newtons) to the cross-sectional area of the debonded interface (in mm 2 ).

After the shear bond testing, the debonded surfaces of all groups were examined under a stereomicroscope at a magnification of 6.5× to define the location of the bond failure. The observations made were categorized into:

Statistical analysis

For statistical analysis we applied the one-way ANOVA and Scheffe's post hoc test. All the statistical manipulations were carried out using SPSS ® for Windows ® (version 16.0).


   Results Top


In the control group, the Prime and Bond NT bonding agent achieved significantly higher bond strength than Single Bond bonding agent (P = 0.009). Within the groups, i.e., either control or groups pretreated with Denshield™ or Sensodent-K™, the Sensodent-K™ pretreated group showed significantly higher bond strength (P=.042). In the experimental group pretreated with Denshield™ desensitizer there was no statistically significant difference in bond strength value, i.e., either treated with Single Bond or Prime and Bond NT bonding agent (P=.059). In the experimental group pretreated with Sensodent-K™ desensitizer, Prime and Bond NT showed significantly higher bond strength than Single Bond (P = 0.044) [Table 2], [Table 3] and [Table 4]; [Graph 1]
Table 2: Mean shear bond strength (with standard deviation) of groups

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Table 3: One-way ANOVA analysis (Single Bond) groups 1, 3, and 5

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Table 4: One-way ANOVA analysis (Prime and Bond NT) groups 2, 4, and 6

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   Discussion Top


Postoperative sensitivity following application of a posterior composite resin restoration is reported to be a common problem. It has been found to be related to many factors and variables. [2]

Total-etch adhesives are more technique sensitive because optimal hybridization and sealing of dentinal tubules with the wet-bonding technique may differ with each bonding system. [7]

Postoperative sensitivity may be reduced by one of four methods. [8] The first of these is the use of HEMA-containing aqueous dentin desensitizers. Their desensitizing action may be the result of precipitation of plasma proteins within dentinal fluid. The second method involves the use of resin-modified glass ionomer cement as a dentin replacement in the sandwich technique. A new technique, the use of oxalate desensitizers after acid etching of dentin, prevents formation of calcium oxalate crystals on the surface; instead, the oxalate crystals are formed deep within the tubules below the surface. But this method is adhesive specific and it showed conflicting reports with low pH, high fluoride containing adhesives like Prime and Bond NT. [5] Finally, self-etching adhesives that do not remove the smear layer may be used, thus reducing hydraulic conductance through the dentinal tubule. But the simpler adhesives themselves have many shortcomings. [8] Therefore, in the present study, two desensitizers with different modes of action were used and the bond strength values were compared.

In previous studies, different types of desensitizers were used, such as monopotassium oxalate, sodium fluoride, strontium chloride + calcium carbonate, Gluma ® desensitizer, etc. [9] These desensitizers, when used with an adhesive system, had given conflicting reports. So, in the present study, we used two different types of desensitizers having different mechanisms of action for reducing sensitivity, e.g., Denshield™ (NovaMin ® ) (calcium sodium phosphosilicate). Total-etch adhesives do not bond well to oxalate-treated dentin since the surface layer of acid-resistant calcium oxalate crystals interferes with resin infiltration through the demineralized collagen matrices (Pashley et al. 1993). It is possible, however, to reduce outward fluid flow from acid-etched dentin during bonding by the adjunctive use of oxalate densensitizers on acid-etched dentin prior to adhesive application (Pashely et al., 2001). Also the bond strength of total-etch adhesives were not compromised with the adjunctive use of oxalate desensitizing gel after acid etching. [10] Hence, based on this finding, in present study the desensitizing agents (Denshield™ and Sensodent-K™) were applied after acid etching and prior to application of adhesive.

Prime and Bond NT group showed significantly higher mean bond strength than Single Bond, probably because of its composition. Prime and Bond NT is an acetone-based adhesive that is known to have high vapor pressure and, hence, better penetration of acidic monomer. From previous studies it has been established that water-tree formation was predominantly observed in ethanol-based adhesives [11] and the presence of any remaining water may also lead to an incomplete polymerization of adhesive due to the ability of ethanol to form hydrogen bonds with water. [12] In the presence of excessive water some of the resin appears to undergo phase separation of the hydrophobic components of the resin composition, resulting in resin globule formation and thereby causing decrease in bond strength.

When Single Bond or Prime and Bond NT adhesive systems were used either in the control groups or the pretreated experimental groups (with Denshield™ desensitizer or with Sensodent-K™) there was no statistically significant difference in bond strength values. This was probably because Denshield™ desensitizer blocked the tubules deep inside the dentin and which thereby did not hinder the resin infiltration similar to the effects of oxalates used as desensitizer after acid etching which did not affect the bond strength values. On the other hand, Sensodent-K™ desensitizer, whose primary action is blocking conductivity of the nerve, had to some extent a tubule-blocking action after sequential application, but this also did not seem to affect the bond strength values in the present study. Since both these desensitizer have not been used in conjugation with any adhesive system in previous studies, further research is necessary to confirm the compatibility of these desensitizers with adhesive systems.

The result of the stereomicroscopic examination revealed that the predominant mode of failure in all groups was adhesive (at interface) (31 samples), while 21 samples showed mixed failure. The difference was statistically nonsignificant (P > 0.05) [Graph 2]. It should be noted that the bond strengths obtained in the present in vitro study indicate only short-term results and do not take into account the effects of thermal or mechanical stresses. With long-term observation in vivo, one could expect deterioration in bond strength in the hostile oral environment due to the effects of pulpal pressure, dentinal fluid, C-factor, and tooth dynamics, all of which are factors of considerable importance. Hence, further investigation on these lines may contribute to better understanding of the variables affecting the bond strength of adhesives.



 
   References Top

1.Auschill TM, Koch CA, Wolkewitz M, Hellwig E, Arweiler NB. Occurrence and causing stimuli of Postoperative sensitivity in Composite Restorations. Oper Dent 2009;34:3-10.  Back to cited text no. 1
    
2.Gordan VV, Mjor IA. Short and long term clinical evaluation of Post operative sensitivity of a New Resin based Restorative material and Self etching primer. Oper Dent 2002;27:543-8.  Back to cited text no. 2
    
3.Unemori M, Matsuya Y, Akashi A, Oto YG, Akamine. Composite resin restoration and Postoperative sensitivity: Clinical follow-up in an undergraduate program. J Dent 2001;29:7-13.  Back to cited text no. 3
    
4.Akpata ES, Behbehani J. Effect of bonding systems on Post operative sensitivity from posterior composites. Am J Dent 2006;19:151-4.  Back to cited text no. 4
    
5.Yiu CKY, King NM, Suh BI, Sharp LJ, Carvalho RM, Pashley DH, et al. Incompatibility of Oxalate desensitizers with acidic fluoride-containing total etch adhesives. J Dent Res 2005;84:730-5.  Back to cited text no. 5
    
6.Turkkahraman H, Adanir N. Effect of Potassium nitrate and Oxalate desensitizer agents on shear bond strength of orthodontic brackets. Angle Orthod 2007;77:1096-100.  Back to cited text no. 6
    
7.Hashimoto M, Ito S, Tay FR. Fluid movement across the resin dentin interface during and after bonding. J Dent Res 2004;11:843-8.  Back to cited text no. 7
    
8.Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic. J Can Dent Assoc 2003;69:726-31.  Back to cited text no. 8
    
9.Franco A, Carlos J, Gabriel R. Occlusion of dentin tubules by desensitizing agent's. Am J Dent 2004;17:368-72.  Back to cited text no. 9
    
10.Tay FR, Pashley DH, Mak YF, Carvalho RM, Lai SC, Suh BI. Integrating Oxalate desensitizers with total etch two step adhesives. J Dent Res 2003;82:703-7.  Back to cited text no. 10
    
11.Tay FR, Pashley DH. Water treeing -A potential mechanism for degradation of dentin adhesives. Am J Dent 2003;16:6-12.  Back to cited text no. 11
    
12.Duarte S Jr, Perdigao J, lopes MN. Effect of dentin conditioning time on nanoleakage. Oper Dent 2006;30:500-11.  Back to cited text no. 12
    

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Correspondence Address:
Shekhar Bhatia
Department of Conservative Dentistry and Endodontics, Teerthanker Mahaveer Dental College and Research Center, Bagarpur, Moradabad, UP
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.111242

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

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

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