| Abstract|| |
Background: Several surface treatments could be used to improve the bond strength (BS) between indirect composites and cement.
Aim: To evaluate the BS of an indirect composite submitted to different surface treatments, cemented to bovine dentin.
Settings and Design: One hundred and fifty conical cavities were prepared in slices of bovine dentin and bulk filled with the composite.
Materials and Methods: After curing and removal from the cavity, the restorations were treated according to the groups (n = 10): C-untreated, S-Sandblasting; SS-Sandblasting + silane; F-hydrofluoric acid; FS-hydrofluoric acid + silane; SF-Sandblasting + hydrofluoric acid; SFS-Sandblasting + hydrofluoric acid + silane; E-ethanol; ES-ethanol + silane; SE-Sandblasting + ethanol; SES-Sandblasting + ethanol + silane; P-H2O2; PS-H2O2 + silane; SP-Sandblasting + H2O2; SPS-Sandblasting + H2O2 + silane. After cementation, push-out test was performed in a universal testing machine.
Statistical Analysis: Data were submitted to nonparametric tests (Kruskal–Wallis and Mann–Whitney U-tests, α = 0.05). The failure mode was observed under a stereomicroscope and the topography by scanning electronic microscopy (SEM).
Results: Sandblasted groups led to the highest BS values, (P < 0.001), except for the SFS group. SE, SES, and SPS led to higher BS values than S and SS groups (P < 0.05). F, E andPgroups showed the lowest BS values. The number of cohesive or mixed failures was related to higher BS values. SEM evaluation showed major irregularities only for sandblasted groups.
Conclusions: Sandblasting was a safe surface treatment for the indirect composite, increasing the BS values. Hydrofluoric acid applied after sandblasting damaged the BS values and should not be recommended while ethanol and H2O2, when applied after sandblasting, were effective in increasing BS values.
Keywords: Bond strength, ethanol, hydrogen peroxide, indirect composites, push-out, surface treatment
|How to cite this article:|
Poskus LT, Meirelles RS, Schuina VB, Ferreira LM, da Silva EM, Guimar„es JG. Effects of different surface treatments on bond strength of an indirect composite to bovine dentin. Indian J Dent Res 2015;26:289-94
The high degree of conversion and crosslinking of indirect composites can be obtained with postcuring by means of heat, light, vacuum and/or pressure., Consequently, the low quantity of free carbon bonds available to link with monomers from the organic matrix of the resin cement encouraged the use of surface treatments to improve bond strength (BS). Sandblasting with aluminum oxide or silica coating, have been used to enhance mechanical interlocking between composite or ceramic materials and resin cement, improving the BS values.,,, As regards chemical treatments, there is controversy in the literature about the action of hydrofluoric acid etching on polymer surfaces; that is, it showed to improve and to reduce,,,,, the BS values.
|How to cite this URL:|
Poskus LT, Meirelles RS, Schuina VB, Ferreira LM, da Silva EM, Guimar„es JG. Effects of different surface treatments on bond strength of an indirect composite to bovine dentin. Indian J Dent Res [serial online] 2015 [cited 2019 May 22];26:289-94. Available from: http://www.ijdr.in/text.asp?2015/26/3/289/162884
As regards silane coupling agents, the better wettability of the roughened surface, created by its application on the substrate, has been related to the higher values of BS to dental structure of indirect composites. However, in other studies, silanation after sandblasting,,, or acid etching, did not influence the BS values.
Hydrogen peroxide and ethanol have been also investigated for surface treatment of posts or composites., On epoxy resins, it is believed that hydrogen peroxide could cause oxidation, breaking covalent bonds. On methacrylate-based fiber posts, higher BS values were also found with this treatment. It was verified that hydrogen peroxide at 10 and 24% was capable to etch posts, exposing the glass fillers., Indeed, when peroxide-based bleaching agents were used on methacrylate-based composites, an increase of surface roughness has been observed. However, hydrogen peroxide at 38% did not increase the BS values in a composite repair study.
With regard to the ethanol, it was verified that it is capable of modifying composite surfaces, as softening of the material was observed when it was stored in absolute ethanol. When used only as a superficial cleaner and not for immersion, ethanol did not influence the BS of indirect composites to a dental structure. For posts, no increase in BS values was observed when composite specimens were immersed in 57.1% ethanol for 3 min.
However, the effect of hydrogen peroxide at a lower concentration than 38% and of the absolute ethanol on the indirect composites surfaces and their influence on BS values was not investigated yet. Since there is a controversy in the literature about the effects of surface treatments on composites with regard to improving the BS, and to verify the effect of hydrogen peroxide at a higher concentration and absolute ethanol on the methacrylate composites surfaces, the aim of this study was to evaluate the BS of indirect composites submitted to different surface treatments.
| Materials and Methods|| |
One hundred and fifty bovine teeth were selected and stored in an aqueous solution of 0.5% chloramine (Society Fabbe Ltda., SP, Brazil) for disinfection, at 37°C for a week. After this, they were stored in saline solution at 37°C until the experiment began. After using a diamond disc to remove the root, the buccal surface was cut with a slow-speed diamond saw (ISOMET1000, Buehler, IL, USA), in order to expose a flat dentin surface. The lingual surface was also sectioned in order to obtain a slice thickness of 2 mm and a parallel flat surface to the buccal one. A digital caliper (Mitutoyo, Kanogawa, Japan) was used to standardize the measurements.
A special sample aligning the device and a tapered diamond drill 3131 (KG Sorensen, SP, Brazil) were used to prepare standardized conical cavities (top diameter of 5.0 mm and a bottom diameter of 4.3 mm). The aligning device ensured that the drill was perpendicular to the flat buccal dentin surface. Hence, tapered cavity walls were obtained [Figure 1]. The drills were replaced after each five preparations.
Each tooth slice was placed on a glass surface, and bulk filled with the laboratory composite Sinfony [Table 1]. First, the composite was light-cured with a Visio Alpha Appliance (3M ESPE) for 5 s. The restoration was removed from the cavity and cured under light and vacuum for 15 min (Visio Beta Vario, 3M ESPE), as recommended by the manufacturer.
Prior to the cementation, the restorations were submitted to the different surface treatments as follows:
- Group C (control): No surface treatment was performed
- Group S: The surface was sandblasted with 50 µm Al2O3 for 10 s at 2.0 bar pressure, using an extra oral MicroEtcher (Bio-Art, São Carlos, SP, Brazil), kept 2 cm away from the surface. Running tap water was applied to remove the debris, and the surface was air-dried for 5 s
- Group SS: The surface was sandblasted as described above and the silane RelyX Ceramic Primer [Table 1] was applied with a microbrush and air-dried for 5 s
- Group F: The surface was etched with 10% hydrofluoric acid (Dentsply, Petrópolis, Brazil) for 90 s, rinsed under running tap water for 30 s and air-dried for 30 s
- Group FS: The surface was etched with the hydrofluoric acid as described above. The silane RelyX Ceramic Primer was applied with a microbrush and air-dried for 5s
- Group SF: The surface was sandblasted and etched with the hydrofluoric acid as described above
- Group SFS: The surface was sandblasted and etched with the hydrofluoric acid as described above. After this, the silane RelyX Ceramic Primer was applied with a microbrush and air-dried for 5 s
- Group E: The surface was treated with 96% ethanol (Montenegro, RJ, Brazil) for 5 min and air-dried for 30 s
- Group ES: The surface was treated with ethanol as described above and the silane RelyX Ceramic Primer was applied with a microbrush and air-dried for 5 s
- Group SE: The surface was sandblasted and treated with ethanol as described above
- Group SES: The surface was sandblasted and treated with ethanol as described above. After this, the silane RelyX Ceramic Primer was applied with a microbrush and air-dried for 5 s
- Group P: The surface was treated with 24% H2O2 gel (Crystal Pharm, Niterói, RJ, Brazil) for 10 min, rinsed under running tap water for 30 s and air dried for 30 s
- Group PS: The surface was treated with H2O2 gel as described above and the silane RelyX Ceramic Primer was applied with a microbrush and air-dried for 5 s
- Group SP: The surface was sandblasted and treated with H2O2 gel as described above
- Group SPS: The surface was sandblasted and treated with H2O2 gel as described above. After, the silane RelyX Ceramic Primer was applied with a microbrush and air dried for 5 s.
After treating the composites surfaces, the dentin surfaces were etched with 37% phosphoric acid (Condac 37, FGM, Joinville, SC, Brazil) for 15 s, rinsed with running tap water for 30 s, dried with two absorbent papers and the adhesive system Scotchbond Multipurpose [Table 1] was applied in the following sequence:First, the activator was applied with a microbrush and, after 15 s, it was dried gently for 5 s; the same procedure was then repeated with the primer and catalyst.
A special tip (OptraStick, Ivoclar-Vivadent AG, Schaan, Liechtenstein) was fixed on the buccal side of the restorations, permitting to handle the restorations. The dual-cured resin cement RelyX ARC [Table 1] was dispensed onto a mixing pad, mixed for 10 s and applied around the restorations with a microbrush.
The restorations were put in the cavities, and a digital press was performed until the adaptation of them inside the cavity. Cement excesses of the buccal side were removed with a brush and the tooth restoration interface light was cured for 60 s with an output of1200 mW/cm2 (Radii-Cal, SDI, Australia). Buccal and lingual surfaces were ground with 600-grit silicon carbide paper under running water for 5 s (DP10, Panambra, SP, Brazil) to remove any cement excess.
After storage in distilled water at 37°C for 24 h, the specimens were positioned in the universal testing machine (EMIC DL 2000, São José dos Pinhais, São Paulo, Brazil) and a cylindrical punch tip (3.7 mm in diameter) was attached to this machine and aligned to come into contact on the lingual side, only with the composite resin restoration. A continuously increasing, controlled load was applied at a crosshead speed of 0.5 mm/min until failure. The load (N) of failure was divided by the bonded cross-sectional surface area (mm2) and expressed in MPa.
The data were submitted to Shapiro-Wilk's and Levene's tests to determine their normality and homogeneity, respectively. As neither normality of data distribution nor homogeneity of variances was verified, the data were analyzed with the nonparametric Kruskal–Wallis test, followed by the Mann–Whitney U for post-hoc comparisons at a significance level of P < 0.05. All analyses were performed with Statgraphics 5.1 software (Manugistics, Rockville, MD, USA).
The fractured surfaces were observed under a stereomicroscope at ×40 magnification (Olympus FZ40, Tokyo, Japan). Failure modes were categorized as: Adhesive (along the adhesive interface); cohesive (in dentin or in the composite); or mixed (adhesive and cohesive).
In addition, to analyze the topography of the treated surfaces a scanning electronic microscopy (SEM, JSM-6510LV, JEOL, Tokyo, Japan) was performed. One sample of each experimental condition was prepared using a metal matrix (2 mm × 2 mm × 2 mm). To remove debris on the surface, specimens were washed in distilled water, followed by washing in deionized water in an ultra-sonic bath (Ultrasonic Cleaner/USC 750 Thornton-Unique, Indaiatuba, SP, Brazil) for 10 min. The samples were coated with 10 nm of gold in a metallizer (Coating System Bal-Tec Med 020, Bal-Tec, Liechtenstein) and kept in a desiccator until the time of analysis.
| Results|| |
Significance differences can be observed at [Table 2]. It can be observed that hydrofluoric acid, ethanol, and H2O2 were unable to enhance the BS. Except for SFS group, sandblasting was an efficient treatment to improve the BS values, in comparison with the control group. The treatment of sandblasted samples with hydrofluoric acid afterward was unable to increase the BS values (SF=S=SS). After sandblasting, the treatments with ethanol or ethanol and silane were efficient, leading to higher BS values than those obtained for the sandblasted or the sandblasted and silanized groups (SE=SES>S=SS). It should be noted that the application of the silane agent on sandblasted samples, which had also been treated with hydrogen peroxide, led to higher BS values (SPS>SP=S=SS). Moreover, the silane agent was able to increase the BS values of the samples treated only with hydrofluoric acid or H2O2 (FS > F and PS > P). It should be emphasized that the SPS, SE, and SES groups showed the highest BS values.
|Table 2: Means, SD, medians, minimum, and maximum values for bond strength (MPa)|
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With respect to the failure modes, the adhesive failures were more prevalent for nonsandblasted groups [Figure 2]. On the other hand, for sandblasted groups, except for the SFS group, the number of cohesive and mixed failures increased.
From the SEM evaluation [Figure 3], it can be noted that all sandblasted groups showed marked roughness. The group treated with hydrofluoric acid showed some porosity. The other nonsandblasted groups showed similar images with no severe irregularity.
|Figure 3: Scanning electronic microscopy image, ×1000. Representative images for nonsandblasted groups treated with hydrofluoric acid (a), the other nonsandblasted groups (b) and sandblasted groups (c)|
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| Discussion|| |
In this study, bovine teeth were used due to their similarity with human tooth regard to their clinical and micro-morphological aspects. Besides, it has not been shown differences in BS tests between human and bovine teeth., Furthermore, for making possible the construction of a composite indirect restoration, its secondary cure under light and vacuum and its posterior cementation in the dentin cavity, the push-out BS test was chosen.
The purpose of this study was to evaluate different treatments which could improve the BS to the dental structure of restorations made of a composite with a high degree of conversion. In the present study, for all sandblasted groups, a deep rough surface can be seen [Figure 3], which would lead to a greater mechanical interlocking between the composite and the resin cement. Indeed, higher BS values were found for these groups (S, SS, SF, SE, SES, SP, SPS), except for SFS, when compared with the nonsandblasted groups (C, F, FS, E, ES, P, PS), which is in accordance with previous studies.,,,,,
The unexpectedly lower BS values for the SFS group could be explained by the disorganization of the silane layer around the inorganic particles, which were exposed by sandblasting and etched by hydrofluoric acid. According to the method used, the specimens had been immersed in distilled water for 24 h before running the push-out test. Hence, a monolayer of water could penetrate into the porous particles, disorganizing the silane layer. This would weaken the bond between the organic matrix and the inorganic particles, facilitating their detachment when the test was performed, reducing the BS values. The combination of these procedures sandblasting-hydrofluoric acid-silane agent has also not been recommended by others authors,,, as lower BS values were also found.
The surface treatment with hydrofluoric acid only, caused some superficial irregularities and pores that could be observed by SEM [Figure 3], but this treatment was unable to increase the BS [Table 2]. Instead, this group showed lower BS values when compared with the control group, which is in agreement with another study. In a previous study, it was speculated that hydrofluoric acid could soften the organic matrix of composites, impairing the BS.
However, another study found higher BS values for composites treated with hydrofluoric acid only when compared with the sandblasted group. In the above-mentioned study, the lower hydrofluoric acid concentration (1%) and application time (30 s), in comparison with the present study, could have minimized the negative effect of the acid on the surface.
It should be observed that the silane agent application after hydrofluoric acid etching caused an increase in the BS values, making them similar to those of the control group. Other studies have found similar,,, or better results, when silane agents or adhesives were applied after hydrofluoric acid etching when compared with the control group. The silane agent may have improved the surface wetting by the cement or the acidification of the etched surface could have contributed to the effectiveness of the silane.
In agreement with other studies,,,,, the silane application on the sandblasted composite (SS group) was unable to improve the BS values. Mechanical interlocking was perhaps the principal factor responsible for the better BS results in this group.
It is known that the storage in absolute ethanol could potentiate the deleterious effects of the process of composite degradation since its solubility parameter is very close to that of polymers., Indeed, a lower hardness was found for absolute ethanol than for a 75% ethanol solution. Thus, this study used 96% ethanol solution, in addition to a longer immersion time, to potentiate its deleterious effects. It could be speculated that a softening of the composite surface occurred, diminishing the BS values of the E Group when compared with the control group. Previous studies have not found better or worse BS values when an ethanol solution was used on composites or posts,, which could be explained by the lower concentration of and shorter immersion time in the ethanol used.
On the contrary, when ethanol was applied after sandblasting, higher BS values were achieved than those obtained for S and SS groups, irrespective of silane application. Papacchini et al. speculated that ethanol molecules could be trapped in the irregularities of the sandblasted surface, facilitating the interaction with the silane ceramic primer, which contains ethanol as a solvent. Thereby, composite surface wetting by the cement would be increased, improving the BS.
The 24% hydrogen peroxide was chosen for this study, as it is considered the most simple and effective agent for etching methacrylate-based polymer materials. However, its application on the composite surface led to lower BS values when compared with the control group. In agreement with another study, in the present study the application of silane reversed the negative effect of the hydrogen peroxide, making the BS values similar to those of the control group. Another study has mentioned the conversion into hydroxyl groups due to a cleavage of C=C and C-C bonds of polymers through an oxidation process involving hydrogen peroxide. As is known, silanes are bifunctional molecules, which establish bonds with OH-covered inorganic particles and with organic substrates. Therefore, these hydroxyl groups (OH-) could react with the silane agent, improving the wettability and chemical bond through van der Waals' forces and covalent bonds. Moreover, the ethanol used as a solvent in the silane agent ceramic primer could minimize or reverse the inhibitory effect of hydrogen peroxide on the polymerization reaction by removing oxygen by-products thanks to its water chasing action., This positive effect of the silane agent on samples treated with hydrogen peroxide could also explain the significantly higher BS values achieved in the SPS group when compared with the SP group.
As regards failure mode, except for the SFS group, cohesive and mixed failures were more frequent in the sandblasted than in nonsandblasted groups [Figure 2], a result in agreement with other studies.,,, This finding is related to the higher BS found for the sandblasted groups in this study. The higher adhesive failure values for the SFS group are in accordance with the lower BS values found for this group. Obviously, the number of adhesive failures was higher for nonsandblasted groups, justified by the lower BS values. Thus, it can be speculated that there is a direct relationship between the number of cohesive and mixed failures and the increase in BS.,,,
| Conclusions|| |
Within the limitations of this study, this investigation showed that the different treatments on composite surfaces significantly influenced the BS between dentin and the indirect composite studied. It could be concluded that sandblasting is a safe and effective procedure for increasing BS, while ethanol and hydrogen peroxide at the concentrations studied, were effective only on sandblasted surfaces, and further studies with these substances are recommended. The treatment with hydrofluoric acid only, ethanol or hydrogen peroxide is questionable, as BS values were reduced, and their use should not be recommended. The silane agent was safely used, as its application improved the BS in some cases, but at no time compromised the results.
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Laiza Tatiana Poskus
Analytical Laboratory of Restorative Biomaterials, School of Dentistry, Federal Fluminense University, Rio de Janeiro
Source of Support: The authors are grateful to 3M ESPE for granting the materials for this study and thank PIBIC/UFF for the financial support., Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]