Effect of ferric sulfate contamination on the bonding effectiveness of etch-and-rinse and self-etch adhesives to superficial dentin.

AIM: This study investigated the effect of one hemostatic agent on the shear bond strength of self-etch and etch-and-rinse adhesive systems.
MATERIALS AND METHODS: Sixty extracted third molars were selected. After preparing a flat surface of superficial dentin, they were randomly divided into six groups. Adhesives were Tetric N-Bond, AdheSE, and AdheSE One F. Before applying adhesives, surfaces were contaminated with ViscoStat for 60 s in three groups and rinsed. Then composite were attached to surfaces and light cured. After thermocycling, the bond strength was calculated and failure modes were determined by stereomicroscope. The data were analyzed by t-test and one-way ANOVA with P < 0.05 as the level of significance.
RESULTS: ViscoStat had significantly decreased the shear bond strength of AdheSE (P < 0.0001) to dentin. Modes of failures in all groups were mainly adhesive.
CONCLUSION: Contamination had an adverse effect on the shear bond strength of AdheSE and reduced it.

INTRODUCTION

Demands for esthetic restorations are increased. For achieving a long-term high performance composite restoration, a good isolation especially near or at the gingival margin is needed.[1] In a situation such as sub-gingival caries, class V cavity preparation, taking impression, cementation of all-ceramic restorations with margins near the gingiva, and chronic gingival inflammation preventing or eliminating gingival bleeding or contamination by crevicular fluid is very critical for the longevity of the restoration.[2]

Blood has high-protein content (approximately 6.7%) and fibrinogen macromolecules,[3] on the other hand, because of protein attraction property of dentin, blood proteins can form a layer, which prevents resin infiltration into the dentin structure and reduces 30-70% of bond strength.[4] In the other words, in blood contamination situation, some reactions have occurred between dentin organic layer and the blood proteins that influence resin infiltration.[1]

In recent years, use of hemostatic agents for controlling of gingival bleeding and reducing sulcular fluid are indicated. They have presented in various formulations with different mechanism of action, such as aluminum chloride, ferric sulfate compounds, iron solution, aluminum and potassium sulfate and epinephrine 0.1%.[25] Recent studies showed that most of them have acidic property (pH = 0.7-3) and hydrophilic characteristics that can contaminate each stage of bonding procedure.[26]

By hemostatic agents’ application, smear layer was removed or some change in dentin surface happened that could affect the hybrid layer quality after the self-etch or etch-and-rinse adhesives usage.[6] Contamination prevented penetration of adhesives into dentin surface and ultimately affect bond strength.[4] Therefore, the efficacy of self-etch and etch-and-rinse adhesive systems should be considered first and then recommended for clinical uses. This study evaluated the shear bond strength of one etch-and-rinse and two self-etch adhesives to human dentin contaminated with a ferric sulfate hemostatic agent. The null hypothesis of this study was that contamination with ferric sulfate 20% may not have any effect on shear bond strength of etch-and-rinse and self-etch adhesive systems to dentin.

MATERIALS AND METHODS

In this in vitro experimental study, 60 intact caries-free human third molars were selected and cleaned up of soft tissues. Then, they were stored in a 0.5% Chloramine-T (Fisher Chemical, Fair Lawn, NJ, USA) solution for 24 h. After they were rinsed, about 1.5-2 mm of buccal or lingual tooth structure (enamel and dentin) were removed by using a diamond bur (SS White, Great White Series, Lakewood, NJ, USA) to create flat surfaces of superficial dentin for testing (each bur was discarded after each five preparation). Dentin surfaces were ground with 400 and 600 grit sand paper under running water to produce a standardized smear layer. Teeth were mounted in self-cure acrylic resin. The samples were randomly assigned to six groups. Materials were used according to the manufacturers’ instructions.

AdheSE One FAdheSE One FA plastic mold (2 mm in internal diameter and 4 mm in height) were used to prepare the composite (Tetric N-Ceram, Ivoclar/Vivadent, Schaan, Liechtenstein) cylinders on dentin surfaces. Composite were placed in two increments and each increment was light cured for 40 s. All samples were stored in distilled water for 24 h at room temperature, then were thermocycled for 500 cycles between 5°C and 55°C (with a 60 s dwell time and a 15 s transfer time).

Group 1: ViscoStat hemostatic agent (Ultradent Product Inc., Utah, USA) was applied for 60 s and then it was rinsed for 60 s thoroughly. Then dentin surfaces were etched with 37% phosphoric acid (Ivoclar/Vivadent, Schaan, Liechtenstein) for 10 s, were rinsed for 30 s, were blotted dried and were followed by application of one coat of Tetric N-Bond (Ivoclar/Vivadent, Schaan, Liechtenstein) for 10 s, gently air dried and were light cured for 20 s with a quartz-tungsten-halogen unit with 600 mW/cm2 intensity (Demetron LC, Kerr, USA)

Group 2: No ViscoStat application was done prior to etching. Etching and bonding were done as in group 1

Group 3: After ViscoStat application as in group 1 and 60 s rinsing and blot drying, primer bottle of AdheSE (Ivoclar/Vivadent, Schaan, Liechtenstein) was applied for 30 s, air drying was done and adhesive bottle of AdheSE was applied for 20 s, gently air dried and light cured for 20 s

Group 4: No ViscoStat application was done. AdheSE bonding system was used same as in group 3

Group 5: After ViscoStat application as in group 1 and 60 s rinsing and blot drying, AdheSE One F (Ivoclar/Vivadent, Schaan, Liechtenstein) was applied for 20 s, gently air dried and light cured for 20 s

Group 6: No ViscoStat application was done. AdheSE One F bonding system was used same as in group 5.

The shear bond test was done using a Universal Testing Machine (M350-10CT Testometric, Lancashire, United Kingdom) at a cross head speed of 0.5 mm/min. The shear bond strength was calculated in mega Pascal (MPa). Two examiners evaluated the debonded surfaces at × 40 magnifications by using a stereomicroscope (Olympus, DP 12, Germany) to identify the mode of bond failure whether adhesive, cohesive or mixed. Statistical analysis was done using one-way ANOVA and unpaired t-test with P < 0.05 as the level of significance.

RESULTS

Mean and standard deviation values of shear bond strength test are shown in Table 1.

Table 1

Shear bond strength data in mega Pascal (mean±SD) for each tested group

In comparison with case and control groups, only there was statistically significant reduction in the shear bond strength value in AdheSE groups (P < 0.0001). In Tetric N-Bond and AdheSE One F there was no significant reduction in shear bond strength. In comparison with ViscoStat applied groups, there were statistically significant differences among all groups. Tetric N-Bond had the highest (P < 0.0001) and AdheSE One F had the lowest (P < 0.0001) shear bond strength value. The same results were seen in comparison among groups where ViscoStat was not applied. Modes of failures are seen in Table 2.

Table 2

Mean percentage of failure mode after shear bond strength test

DISCUSSION

Ferric sulfate as a hemostatic agent can coagulate collagen or plasma proteins in dentinal fluids; changes dentinal surface structure due to its acidity and may reduce the shear bond strength.[7]

The null hypothesis was confirmed for Tetric N-Bond and AdheSE One F adhesives, which ferric sulfate 20% contamination had no effect on shear bond strength of these adhesives to dentin, significantly. Phosphoric acid 37% because of its strong acidity (pH = 0.5) accompany with demineralization, can eliminate surface ViscoStat contamination.[6] Furthermore, according to Fischer's study, phosphoric acid can decompose and destroy ferric sulfate.[8]

Kimmes et al.[9] study showed that rinsing contaminated dentin surfaces with ViscoStat and ViscoStat Plus after blood contamination did not alter shear bond strength of Optibond Solo Plus (Kerr, Orange, CA, USA) to dentin.

A study of Harnirattisin et al.[6] has shown that there were no differences in dentinal content between aluminum chloride (a hemostatic agent) contaminated dentin and non-contaminated one after acid etching.

In AdheSE groups, results showed that rinsing ViscoStat, alone, cannot eliminate surfaces contamination and thus the remnant ferric sulfate interfered with diffusion of AdheSE in dentinal tubules and reduce shear bond strength significantly.

In a Scanning Electron Microscope-Energy Dispersive X-ray spectroscopy (SEM-EDX) study by Ayo-Yusuf, contaminated dentinal surfaces with different hemostatic agents were studied. It was mentioned that hemostatic agents because of their acidic property (pH = 0.7-3), can dissolve smear layer and also obturated dentinal tubules orifices. They form an amorphous layer or a granular precipitation on the surfaces.[10]

Because of the weak acidity of the primer of self-etch adhesives in comparison with phosphoric acid, it was predictable that they could not dissolve ViscoStat contamination so that their penetration to deeper areas of dentin was impossible.[6] Several studies emphasize that hemostatic agent can cause derangement in bonding procedure because of dentinal tubules obturation and dentinal surface was demineralized in different values.[1112]

O’Keefe et al.[13] study showed that rinsing ferric sulfate and aluminum chloride hemostatic agents with water before using self-etch adhesives causes higher bond strength than non-rinsing ones.

AdheSE One F had moderate acidity strength (pH = 1.5) with 0.05 μ penetration depth in dentin.[14] On the other hand, it seems that demineralized property of ViscoStat could be increased AdheSE One F dentinal diffusion depth and may be ViscoStat dissolved smear layer and smear plugs, which helps to better diffusion of AdheSE One F (or not interfered with AdheSE One F diffusion). Furthermore, in one study, it seems that despite control group that had a thick smear layer, in group with Aluminum chloride hemostatic agent contamination, the smear layer was partially removed.[6]

In our study, there were significant differences between contaminated groups. According to manufacturer's claim, ViscoStat is a water soluble gel and rinsing with water before bonding procedure is necessary. In etch-and-rinse adhesives because of lower pH of phosphoric acid and its capability for removing contaminants that lead to better diffusion of adhesive, the shear bond strength was higher than the others, where the demineralization effect on contaminated dentin was inhibited.[6]

Also, there were significant differences among control groups where Tetric N-Bond had the highest and AdheSE One F had the lowest bond strength value. Phosphoric acid could cause much more microporosities in dentin than achieving better contact between adhesives and dentin substrate. Removing more smear layer resulted in more mechanical retention and bond strength,[15] which can explain the higher bond strength in Tetric N-Bond in comparison with AdheSE and AdheSE One F. Hybrid layer in self-etch adhesives were uniform cylindrical resin tags but in etch-and-rinse adhesives were thicker with funnel-shaped resin tags.[6]

Methacrylates in most of the self-etch adhesives (such as AdheSE) in acidic solutions are not stable, because of hydrolysis of ester groups that causes weaker cross-linking, an inadequate polymerization, lower bond strength and lower bonding durability.[16]

The presence of HEMA in AdheSE composition, prevents phase separation and collagen collapse in adhesive bottle and helps better adhesive diffusion[17] unlike it can maintain water in adhesive layer and weakened mechanical strength in long-term[15] Hence to prevent this problem, “HEMA free” adhesives were introduced (such as AdheSE One F). In “HEMA free” adhesives, higher concentration of solvents was necessary but after solvent evaporation, homogeneity of one-step self-etch adhesives was disturbed and phase separation and water blister formation happened. These water blisters promoted to reduce hydrolytic stability of adhesive even after polymerization and bond strength reduction happened. Hybrid layer in one-step and two-step self-etch adhesives were semi permeable that water can transfer through the tooth-composite interface even after polymerization.[17]

The differences in depth of penetration in dentin (AdheSE: 1.2-2.2 μ[18], AdheSE One F: 0.05 μ[14]) could explain the differences of their bond strength, which resulted from this study.

The presence of hydrophobic monomers and hydrophilic acids in one bottle in one-step self-etch adhesives could compromise polymerization steps and also waters in dentinal tubules, caused incomplete polymerization at the interface.[19]

All these problems can explain lower bond strength in AdheSE One F group in comparison with AdheSE and these findings were in agreement with Grégoire et al.[17] and Knobloch et al.[20] studies.

In filled adhesives such as AdheSE and AdheSE One F, polymerization shrinkage reduced but because of lesser diffusion in dentin, bond strength reduced as well.[21]

According to Mousavinasab and Kavian[22] study, one-bottle adhesive (such as AdheSE One F) had a very thin hybrid layer where polymerization may be damaged because of the oxygen inhibiting layer formation.

Some self-etch adhesives could not diffuse through smear layer because of their weak acidity in which they buffered with smear layer, enamel and dentin. Buffered primer or adhesive had lower penetration.[23] Tooth demineralization with self-etch adhesives has contrary with tooth buffering capacity and these adhesives could show different behavior. AdheSE One F was one of the new presented products, which had an unknown behavior in adhesion.

According to Proença et al.[24] study in 2009, lower degree of conversion of self-etch adhesive and water trees builds up (pertain to water diffusion from underlying dentin to hybrid layer) was the main reason of lower bond strength of self-etch adhesive in comparison with etch-and-rinse adhesives.

If bond strength to dentin or enamel was more than 20 MPa, mode of failure dominantly happened cohesively in tooth structure or composite.[25] In this study, cohesive failure was seen in etch-and-rinse groups more than self-etch groups. Indeed, the higher bond strength in control groups showed the lower adhesive failures.

CONCLUSION

Within the limitations of this study, it can be concluded that dentin contamination with ViscoStat hemostatic agent had an adverse effect on the shear bond strength of two-step self-etch adhesive, AdheSE, and reduced it.