The purpose of this study was to evaluate the influence of acid etching on the bond strength of a universal adhesive system (Single Bond Universal, 3M) to caries-affected dentin. Forty permanent third molars were selected and carious lesions were induced by the microbiological method with S. mutans ATCC25175. Teeth were allocated randomly across four experimental designs (n = 10): PA-I: phosphoric acid etching and application of the adhesive system, followed by immediate microtensile bond strength testing; PA-CC: phosphoric acid etching and application of the adhesive system, followed by microtensile bond strength testing after a 14-day cariogenic challenge; NPA-I: application of the adhesive system without acid etching, followed by immediate bond strength testing and NPA-CC: application of the adhesive system without acid etching followed by bond strength testing after 14-day cariogenic challenge. For microtensile bond strength testing, a restoration with Charisma composite resin was made and each specimen was sectioned with a cross-sectional area of 1 mm 2 . Only adhesive and mixed fractures were considered for bond strength calculation. Results were evaluated by the Kruskal-Wallis and Friedman tests. The highest bond strengths were observed in the phosphoric acid etching groups (p < 0.05). Cariogenic challenge did not affect bond strength (p > 0.05). The predominant fracture type was adhesive. We conclude that phosphoric acid increased the bond strength of the Single Bond Universal system to caries-affected dentin, and that cariogenic challenge did not interfere with this bond strength.
The minimal intervention dentistry approach is currently advocated for the treatment of carious lesions [
Recently, universal adhesive systems, which may be applied with or without phosphoric acid etching, have become commercially available [
Optimal sealing of the cavity enhances the longevity of dental restorations by cutting off the bacterial nutrient supply, thus halting progression of the carious lesion. However, recurrence of caries and postoperative sensitivity may occur due to the presence of viable microorganisms after cavity preparation. A review of the literature carried out for this study did not find any studies comparing the bond strength of the Single Bond Universal adhesive system to caries-affected dentin with or without phosphoric acid preconditioning. The decision to use a universal adhesive system with or without phosphoric acid can influence the adhesion in caries-affected dentin [
The present study was approved by the institutional Research Ethics Committee (protocol no. 722184).
1) Sample selection
Forty permanent third molars were obtained from a university Dental Clinic.
2) Inclusion criteria
Erupted permanent third molars; no visible cracks, carious lesions or fractures on inspection with a magnifying glass (10X magnification) were included. The selected teeth were stored in saline solution (Eurofarma, São Paulo, Brazil) and disinfected with 0.1% thymol (Carcajon, Campinas, Brazil) [
The apical region of the specimens was sealed with epoxy resin (TecBond, Embu das Artes, Brazil), and the root system and all crown enamel surfaces with nail polish (Impala, Guarulhos, São Paulo). Only the crown dentin was exposed to the cariogenic challenge. The specimens were then autoclaved (Sercon, São Paulo, Brazil) for 15 minutes at 121˚C and 1 atm.
3) Cariogenic challenge
To induce carious lesions in the exposed dentin, the teeth were placed in sterile test tubes containing Brain Heart Infusion medium (BHI, Labcenter, São Paulo, Brazil) supplemented with 0.5% yeast extract (Labcenter, São Paulo, Brazil), 0.5% glucose (Labcenter, São Paulo, Brazil), and 1% sucrose (Labcenter, São Paulo, Brazil)and a standard strain of S. mutans ATCC 25175 (Fundação André Tosello, Campinas, Brazil), standardized to 0.5 McFarland turbidity (Labcenter, São Paulo, Brazil).
Infected dentin was removed by hand with 320-grit silicon carbide sanding discs (3M, Sumaré, Brazil) until affected dentin was reached―characterized by tissue resistant to penetration by the probe (SSWhite, Juiz de Fora, Brazil) without applying pressure [
4) Division of experimental groups
All samples with carious dentin lesions were randomly allocated (http://www.random.org) across four experimental groups (n = 10/each). The number of specimens in each group (n = 10) was obtained by sample size calculation after a pilot experiment. Sample size calculation was performed by ANOVA, with a minimum difference between treatment means = 0.38, standard error = 0.23, number of treatments = 4, statistical power = 0.80, and alpha = 0.05. The sample size was calculated as 10.
Group PA-I: etching of affected dentin with 35% phosphoric acid (Ultradent, South Jordan, UT, USA) for 15 seconds. The specimens were then rinsed and dried with cotton balls, without allowing dehydration. The Single Bond Universal adhesive system (3M ESPE, St Paul, MN, USA) was actively applied with a microbrush (Angelus, Londrina, Brazil) onto the entire dentin surface for 20 seconds. An air jet was then applied over the adhesive for 5 seconds, until the solvent had evaporated. Finally, the adhesive system was light-cured for 10 seconds (VALO-Ultradent, South Jordan, UT, USA). Microtensile bond strength testing was performed immediately.
Group PA-CC: the test specimens were prepared as for the PA-I group, but microtensile bond strength testing was performed after a 14-day cariogenic challenge.
Group NPA-I: the Single Bond Universal adhesive system (3M ESPE, St Paul, MN, USA) was actively applied with a microbrush (Angelus, Londrina, Brazil) onto the entire dentin surface for 20 seconds. An air jet was then applied over the adhesive for 5 seconds, until the solvent had evaporated. Finally, the adhesive system was light-cured for 10 seconds (VALO-Ultradent, South Jordan, UT USA). Microtensile bond strength testing was performed immediately.
Group NPA-CC: the test specimens were prepared as for the NPA-I group, but microtensile bond strength testing was performed after a 14-day cariogenic challenge.
After application of the adhesive system (Single Bond Universal, 3M ESPE), a restoration with Charisma composite resin (Heraeus Kulzer, Hanau, Germany) was constructed by the incremental technique atop the dentin surface, in four layers, each approximately 1 mm high, light-cured for 40 s each, until a total height of 3 mm was reached. The composite resin increments were measured with a digital caliper (Mitutoyo, Suzano, Brazil). The curing light used in this study (Valo, Ultradent, South Jordan, UT, USA) had an intensity of 1000 mW/cm2, checked with a radiometer (Curing Light, Brasilia, Brazil).
5) Obtaining the specimens for microtensile bond strength testing
For microtensile bond strength testing, the root portion of each tooth was removed with diamond discs (Fava, São Paulo, Brazil). Each tooth/adhesive/resin block was cut with diamond discs on an Isomet 1000 precision sectioning saw (Buehler, Illinois, USA), into parallel slices following the long axis of the tooth, in the lingual-lingual direction. These slices were again attached to an acrylic plate and taken back to the Isomet 1000 precision cutter (Buehler, Illinois, USA), with a pre-set cutting width of 1.3 mm, so that the resulting stick-shaped specimens would have an area of approximately 1.0 mm2 .
Before microtensile bond testing, the width and thickness of each specimen were confirmed with a digital caliper (Mitutoyo, Suzano, Brazil; accuracy 0.01 mm). Forty-four specimens were obtained from each group.
6) Microtensile bond strength test
The ends of the specimens were attached to the microtensile assay device (Geraldeli jig) with cyanoacrylate glue (Loctite, Henkel Ltda., São Paulo, SP, Brazil), so as to keep the adhesive area perpendicular to the long axis of the tensile force [
The jig was then taken to a universal testing machine (EMIC, São José dos Pinhais, Brazil) and run with a crosshead speed of 0.5 mm/min until fracture occurred [
Score 1: premature fracture;
Score 2: adhesive fracture;
Score 3: cohesive dentin fracture;
Score 4: cohesive resin fracture.
All results were obtained in Newtons (N) and converted to megapascals (MPa) by the following formula:
B S = F S ∗ 0.0981
where BS = bond strength; F = force in Newtons; S = bond surface area of the specimen (cm2); 0.09801 = correction factor for conversion of kp/cm2 into MPa.
7) Statistical analysis
The results were analyzed in Biostat 4.0. D’Agostino’s test showed that the sample departed from normality. Thus, the Kruskal-Wallis non-parametric test (with Student-Newman-Keuls post-hoc test) and Friedman test were used. The significance level was set at 5%.
The highest bond strengths were observed in the groups in which phosphoric acid etching preceded application of the self-etching adhesive system (p < 0.05). There was no significant difference in bond strength before (immediate testing) and after cariogenic challenge (p > 0.05) (
Analysis of fracture mode
There was no significant difference in fracture mode across sample groups (p > 0.05) (
Contemporary dentistry advocates a minimally invasive approach to cavity preparations removing infected dentin while preserving caries-affected dentin that is amenable to reorganization [
PA-I | PA-CC | NPA-I | NPA-CC | |
---|---|---|---|---|
Min | 10.25 | 10.20 | 2.22 | 0 |
Max | 44.37 | 58.89 | 48.73 | 82.84 |
Md (IQR) | 24.30 (11.98)A | 27.10 (21.97)A | 15.31 (23.07)B | 14.93 (20.91)B |
Different letters denote significant differences (p < 0.05). PA-I, phosphoric acid etching followed by immediate testing; PA-CC, phosphoric acid etching followed by testing only after cariogenic challenge; NPA-I, immediate testing with no phosphoric acid etching; NPA-CC, testing only after cariogenic challenge, with no phosphoric acid etching.
PA-I | PA-CC | NPA-I | NPA-CC | |
---|---|---|---|---|
Max | 2.0 | 2.0 | 2.0 | 2.0 |
Min | 2.0 | 2.0 | 2.0 | 1.0 |
Md (IQR) | 2.0 (0.0)A | 2.0 (0.0)A | 2.0 (0.0)A | 2.0 (0.0)A |
Same letters: No significant differences (p > 0.05).
this study used affected dentin as a substrate for bond strength testing, a design consistent with previous work by Nakajima et al. [
In the present study, the microbiological method was used to induce dentinal caries [
Bond strength was evaluated with a microtensile test [
To evaluate the longevity of the bond strength of the Single Bond Universal adhesive system, the specimens were subjected to a cariogenic challenge, i.e., a 14-day stress period in supplemented BHI medium. In the literature, samples have usually been stored in distilled water [
The results of the present investigation demonstrated that phosphoric acid etching enhanced the bond strength of the universal adhesive system to affected dentin. The null hypothesis was not accepted. This is in agreement with the findings of Yoshiyama et al. [
Bond strength was lower when acid etching was not employed. This is consistent with the findings of Pinna et al. [
Within the limitations of an in vitro design, the present study demonstrated that, in caries-affected dentin, a substrate characterized by obliteration of dentinal tubules and altered mineral content, the use of phosphoric acid etching prior to application of the Single Bond Universal adhesive system was associated with better results. However, additional studies in this line of research are needed to contribute further scientific evidence on this matter.
We conclude that:
Phosphoric acid etching increased the bond strength of the Single Bond Universal adhesive system to caries-affected dentin; and the pattern of fracture was predominant adhesive.
Cariogenic challenge did not interfere with bond strength.
Pavanello, R. and Pinheiro, S.L. (2018) Influence of Phosphoric Acid Etching on the Bond Strength of a Universal Adhesive System to Caries-Affected Dentin. Advances in Biological Chemistry, 8, 37-46. https://doi.org/10.4236/abc.2018.83004