Shear Bond Strength of Two Water-Based Adhesives to Different Dentin Conditions

Shear Bond Strength of Two Water-Based Adhesives to Different Dentin Conditions
Dr. Mohammed Q. Al Qahtani,*

Assistant Professor and Head Division of Operative Dentistry. Department of Restorative Dental Science, College of Dentistry King Saud University, P.O. Box 60169, Riyadh 11545, Saudi Arabia
*Correspondence:Dr. Mohammad Q. Al Qahtani

How to CITE:

J Pak Dent Assoc 2010;19(1): 30 - 33



OBJECTIVE:

To evaluate the shear strength of bonding of two water-based adhesives; namely etch-rinse Syntac Single-Component adhesive and one-step self-etch Adper Prompt L-Pop adhesive to dry or moist dentin.

METHODOLOGY:

A total of 40 extracted teeth and two water-based adhesives were used in this study. Teeth were divided into 4 groups of 10 teeth each according to the adhesive / dentin condition as follows; Syntac Single-Component / dry dentin, Syntac Single-Component / moist Dentin, Adper Prompt L-Pop / dry dentin and Adper Prompt L-Pop / moist dentin. Filtek Z250 resin composite cylinder was built up on each specimen, and then thermocyced. A shear load was applied to the specimens using Instron machine at a crosshead speed of 0.5mm/min until failure occurred. Data were statistically analyzed by one-way ANOVA and Tukey’s multiple comparison test at 95% confidence level.

RESULTS:

The mean shear bond strengths of Syntac Single-Component to dry and moist dentin were significantly higher than Adper Prompot L-Pop bonded to dentin with similar conditions.

CONCLUSION:

The low mean shear strengths of bonding Adper Prompot L-Pop to dry and moist dentin could be attributed to the presence of weak acids and the absence of acetone and ethanol solvents in the adhesive itself

KEY WORDS:

shear bond strength, self-etch adhesives, dry dentin, moist dentin, water based-adhesives.

Introduction

The improvement of adhesive dentistry throughout the life of dentistry makes bonding to tooth structure more simplified. This simplification was done to reduce the steps of clinical application, technique-sensitivity and material-related factors that affect bond strength to tooth structure. An etch-rinse approach involving a two-step application has been developed, followed by a self-etch approach involving either one- or two-step application.1,2 In etch-rinse adhesives, the acidic agents, such as phosphoric, maleic, nitric, or citric acid, were used to remove the smear layer, demineralize the dentin surface, open the dentin tubules, increase the micro- porosities of the inter-tubular dentin, and expose the collagen. 3-5 The bonding mechanism in these types of adhesives is primarily based on micromechanical retention. The collagen network that remains following dentin etching is thought to be the source of high bond strength when infiltrated with resin.6 In self-etch adhesives, the acidic primers or adhesives were used to dissolve the smear layer, incorporate it into the mixture, demineralize the superficial dentin and penetrate into it, then harden after light irradiation to create micromechanical retention of adhesive to the dentin substrate.7, Commercially, adhesives contain a solvent acetone, ethanol, or water, or a combination of two of these solvents. Due to their relatively high volatility, solvents such as acetone and ethanol may displace surface moisture and serve better to carry the monomers in the adhesive into the microporosities of collagen network.9 In the rather new single-step self-etch adhesive systems, the mixture of acidic monomers, solvents and water are used. Water is required to enable dissociation of acidic monomers; the ethanol or acetone solvents are added to accelerate water elimination.7 The purpose of this in-vitro study was to evaluate the shear bond strength of two water-based adhesives; single component etch-rinse adhesive and single step self-etch adhesive, to dry or moist dentin

Methodology

Forty recently extracted, non-caries human molar teeth which had been stored following extraction for less than 4 weeks in jars containing 10% buffered formalin, were selected, cleaned and stored in distilled water at 3-4°C until used.

Specimen Preparation:

The occlusal surfaces of the teeth were ground at slow speed with a 180-grit silicon carbide paper mounted on a water-cooled wheel to create a flat dentin surface. They were examined under a stereomicroscope to make sure that no enamel was left on the bonding area. The teeth were mounted with autopolymerizing acrylic resin in a cylindrical plastic pipe mold. The dentin surface was then finished and polished in order on wet 240, 320, 400, and 600-grit silicon carbide papers. The specimens were placed in distilled water until ready for use.

Restorative Procedures:

The specimens were randomly divided into 4 groups according to adhesive systems and dentin conditions. Two water-based adhesive systems were used in this study and are listed in table I along with their manufacturers, and compositions. Each group contained 10 teeth and were as follows

Group 1. Syntac Single-Component adhesive applied on dry dentin.

Group 2. Syntac Single-Component adhesive applied on moist dentin.

Group3. A d p e r P r o m p t L – P o p a d h e s i v e applied on dry dentin.

Group 4. A d p e r P r o m p t L – P o p a d h e s i v e applied on moist dentin.

The dentin substrate in Groups 1 and 2 was etched using 37% phosphoric acid for 15 seconds, then rinsed under running water for 15 seconds. Prior to application of Syntac Single-Component adhesive agent, the dentin substrate in group 1 was air-dried for 20 seconds using oil-free compressed air, while the dentin substrate in group 2 was kept moist using a blot technique with gauze to absorb the excess water. The dentin substrate in Groups 3 and 4 was rinsed under running water for 15 seconds without etching procedure. Prior to application of Adper Prompt L-Pop adhesive agent, the dentin substrate in group 3 was air-dried for 20 seconds using oil-free compressed air, while the dentin substrate in group 4 was kept moist using a blot technique with gauze to absorb the excess water. The Syntac Single-Component adhesive agent was shaked well before use, then applied on dentin substrate surface for 10 seconds, left undisturbed for 20 seconds, and dried lightly. When the material had visibly thickened, a strong blast of air was directed onto surface to disperse the remaining adhesive, and then light-polymerized for 20 seconds. A second coat of adhesive was applied, dried immediately, and light-polymerized for 20 seconds. For the application of Adper Prompt L-Pop adhesive agent, liquids 1 and 2 were mixed, applied and agitated on dentin substrate surface for 15 seconds, and air-dried. A second coat was then applied and light-polymerized for 10 seconds. Light activated polymerization was accomplished using an Elipar® Highlight at 400 mW/cm2 which was verified with a Model 100 Curing Radiometer.

After Adhesive procedures, a 2-mm long vinyl tube with an internal diameter 4 mm placed onto the dentin substrate. FiltekTM Z250 resin composite (3M ESPE, shade A2) was applied in the vinyl tube and condensed against the bonding agent to form a resin composite cylinder. Light activated polymerization was accomplished for 40 seconds using an Elipar® Highlight at 400 mW/cm2 which was verified with a Model 100 Curing Radiometer.

Testing Procedure:

After storage in distilled water at 37ºC for 24hrs, the specimens were thermocycled between 5ºC and 55ºC water baths for 2,500 cycles with a 30-second dwell time, and a 10-second transfer time. Then, the specimens were returned to storage until the one-week storage time was completed. Specimens were each mounted on a universal testing (Instron Model 8500 Plus Dynamic Testing System -1341 Instron Instron Corporation) machine for shear testing with the long axis of the specimen being perpendicular to the direction of the applied force. The circular knife-edge was located at the interface between the composite cylinder and the dentin surface. Bond strength was measured in the shear mode at a cross-head speed of 0.5 mm/min until failure occurred All statistical analyses were carried out using SPSS statistical software (V. 16, SPSS, Chicago, IL, USA). Data were submitted to a one-way ANOVA and Tukey’s multiple comparison test at 95% confidence level

 

Results

p>The mean shear bond strengths of two water-based adhesives Syntac Single-Component, and Adper Prompt L-Pop to dry and moist dentin conditions are presented in Table II

The mean shear bond strength of Syntac single-component to dry dentin (18.85 ± 3.86 MPa) was higher than moist dentin (15.77 ± 3.43 MPa) but without significant difference at (p value = 0.075). The mean shear bond strength of Adper Prompt L-Pop to dry dentin (12.65± 2.19 MPa) was higher than moist dentin (10.73 ± 2.31 MPa) but without significant difference at (p value = 0.073). The mean shear bond strength of Syntac single-component to dry dentin was significantly higher than Adeper Prompot L-Pop to dry dentin at (p values <0.0001). The mean shear bond strength of Syntac single-component to moist dentin was significantly higher than Adeper Prompot L-Pop to moist dentin at (p value = 0.013).

Discussion

The beneficial effect of moisture in improving the bond strengths of certain systems was proven by multiple studies 10-14; however excessive moisture can result in reduced conversion of the resin or porosities within the adhesive that will compromise the bond strength.15For Syntac Single-Component, there was no significant difference in mean shear bond strengths to dry dentin (18.85 ± 3.86 MPa), and moist dentin (15.77 ± 3.43 MPa). The higher bond strength to dry dentin may be due to the contents of this bonding agent (43.6% HEMA, and 46% deionized water), which could assist in rehydrating or rewetting air-dried dentin and thus collapsed collagen, transforming it into a loosely arranged network that simultaneously allows the hydrophilic monomer to interdiffuse.16 However, the mean shear bond strength to moist dentin was less than that to dry dentin; this may be due to being overwet, which could cause phase separation of the hydrophobic and hydrophilic monomer components and resulting in the blister and globule formation at the resin-dentin interface.15 For Adper Prompt L-Pop self-etch adhesive, there was no significant difference between the mean shear bond strength to dry dentin (12.65 ± 2.19 MPa), and moist dentin (10.73 ± 2.31 MPa). The higher bond strength to dry dentin may also be due to the presence of water and HEMA contents, which could assist in re-moisting the dried dentin. On the other hand, the lower mean shear bond strength to moist dentin may due to overwet phenomena and the absence of co-solvents (ethanol or acetone), which adversely affect the adhesive performance and make it difficult to eliminate excess water.7,17 The mean shear bond strengths of Syntac Single-Component to dry dentin and moist dentin were significantly higher than Adper Prompt L-Pop to dry dentin and moist dentin. This can be explained by the use of strong phosphoric acid to condition the dentin before the application of Syntac Single-component, and the presence of modified polyacrylic acid and maleic acid in the adhesive itself, which may help in removing of smear layer, demineralizing of the dentin surface, and opening of the dentin tubules, as well as increasing the micro-porosities of the inter-tubular dentin, exposing of the collagen network and increasing the micromechanical retention. 3-5. The absence of acid condition step before the application of Adper Prompt L-Pop and the presence of weak methacrylate phosphoric and polyalkenoic acids in the self-etch adhesive itself make it more difficult to dissolve the smear layer, demineralize the dentin and exposed college network. Also, the absence of acetone and ethanol solvents in Adper Prompot L-Pop self-etch adhesive make it less effective on dry and moist dentin

Conclusion

Based on the findings of this study, it can be concluded that:

moist dentin were significantly higher than self- etch Adper Prompot L-Pop adhesive bonded to dentin with similar conditions.

 

  • The low mean shear strengths of bonding self-etch Adper Prompot L-Pop adhesive to dry and moist dentin could be attributed to the presence of weak acids and the absence of acetone and ethanol solvents in the adhesive itself

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