The Journal of Adhesive Dentistry, 04/2011

Purpose: The purpose of this study was to assess the influence of adhesive area delimitation on the microshear bond strength of different adhesives to dentin. Materials and Methods: Eighteen bovine incisors were sectioned and the exposed dentin surfaces were prepared with 600-grit SiC paper. These teeth were randomly divided into three groups, according to the adhesive to be applied: two-step etch-and-rinse Adper Single Bond 2 (3M ESPE), two-step self-etching Clearfil SE Bond (Kuraray), and one-step Clearfil S3 Bond (Kuraray). On each dentin surface, 4 samples were built up with the composite resin Z100 (3M ESPE); on 2 of these, a suggested area delimitation technique was employed. After 24 h of storage in water at 37°C, samples were subjected to the microshear bond strength test, and the failure modes were evaluated under optical and scanning electron microscopes. The obtained results were statistical analyzed using two-way ANOVA and Tukey's test. Results: Groups without area delimitation presented significantly higher bond strength results (p 0.05) and a higher incidence of cohesive failures. In these groups, fractures tended to occur beyond the limits of the actual adhesive area, while the area restriction technique succeeded in avoiding this phenomenon. The three adhesives performed similarly when area delimitation was employed (p > 0.05), but Clearfil S3 Bond showed significantly higher bond strength results when no area delimitation was taken into account (p 0.05). Conclusion: The extension of the adhesive area beyond the limits of the composite cylinder may play an important role in the results of microshear bond strength tests, while the suggested area delimitation technique may lead to less questionable outcomes. Keywords: bond strength, microshear, adhesion, adhesive area, dentin

Purpose: To measure the demineralization capacity of 37% phosphoric acid on surface and subsurface bovine enamel after bleaching with hydrogen peroxide (H2O2). Materials and Methods: Three equally-sized sections with 16 mm2 of exposed enamel surface were obtained from the enamel of 10 bovine incisors. One specimen sample from each crown was assigned to one of three groups (n = 10): group I, no bleaching agent; group II, bleached with 38% H202 for 20 min; or group III, 30% H202 for 60 min. After 24 h, the thickness of specimens was measured and they were immersed in 37% phosphoric acid solution, of which 5-ml aliquots were collected at 30 s and 60 s. Specimens were then ground to a depth of 25 µm and again immersed in 37% phosphoric acid solution. This procedure was repeated for enamel depths of 50 and 100 µm. Ca2+ concentrations in the phosphoric acid aliquots were measured by atomic absorption spectroscopy. Results: No significant differences were found in the total amounts of extracted Ca2+ between bleached and unbleached specimens (F = 0.142; p = 0.869). The amount of Ca2+ extracted was similar among the four depth levels in the unbleached and in the 30% H202 bleached specimens. A significantly larger amount of Ca2+ was obtained at 25 µm depth (subsurface) from specimens treated with 38% H202. Conclusions: Pre-bleaching with 38% H202 significantly increased the decalcifying effect of phosphoric acid on subsurface enamel at a depth of 25 µm compared to 100 µm, whereas pre-bleaching with 30% H202 did not modify this effect at any level. Keywords: hydrogen peroxide, decalcifying, subsurface enamel, phosphoric acid, enamel acid etching, atomic absorption spectroscopy

Purpose: To determine the influence of mechanical properties of resin-based composites on the microtensile bond strength to dentin of all-in-one adhesives. Materials and Methods: Microtensile bond strengths were measured with the non-trimming technique for the experimental groups: 1) Bond Force/Estelite Σ (Tokuyama); 2) G-Bond Plus (GC)/Estelite Σ; 3) Bond Force/Gradia Direct Anterior (GC);4) G-Bond Plus/Gradia Direct Anterior; 5) Bond Force/Gradia Direct LoFlo (GC); 6) G-Bond Plus/Gradia Direct LoFlo. The following mechanical properties of the resin-based composites were assessed: tensile strength, flexural strength, tensile elastic modulus, shear elastic modulus, Poisson's ratio, Vicker's hardness, contraction stress. Three-dimensional models of microtensile beams were created for finite element analysis of the first principal stress values and distribution in the adhesive layer during microtensile testing. Statistical tests were applied to microtensile bond strength values (two-way ANOVA) and to data from mechanical tests (one-way ANOVA). In all the analyses, the level of significance was set at p 0.05. Results: While the adhesive did not significantly influence microtensile bond strength, the composite was a significant factor. Regardless of the adhesive, Estelite Σ yielded significantly higher bond strengths than Gradia Direct Anterior and Gradia Direct LoFlo, that were comparable. Adhesive-composite interactions were not statistically significant. Estelite Σ had the highest Vicker's hardness, the highest tensile and shear elastic moduli, the lowest and closest to dentin Poisson's ratio. A more favorable stress distribution in the adhesive layer occurred in the Estelite Σ model. Conclusions: When comparing the bonding potential of several adhesives with the microtensile technique, the same resin composite should be used in all the experimental groups for building up the coronal portion. Keywords: microtensile bond strength, adhesive, resin composite, dentin

Purpose: Rigid rod polymers (RRPs) can be used as reinforcing fillers, comparable to inorganic particulate fillers, with the exception that RRP fillers can be dissolved from the surface, thus potentially improving their adhesion to polymer matrix. This study evaluated the effect of water storage on the microtensile bond strength (µTBs) of composite resin to dentin using experimental RRP modified primers. Materials and Methods: Experimental primers were fabricated by dissolving RRP (Parmax, 1240, Mississippi PolymerTechnologies, USA) into dichloromethane (DCM) and mixing it with the monomers bis[2-(methacryloyloxy)- ethyl]phosphate (BMEP) and 3(methacryloyloxy)-propyltrimethoxysilane (MPS). Three experimental primers were prepared with different proportions for each dentin substrate. The same commercial etch-and-rinse adhesive was used with each group. Surfaces of human molars were wet ground occlusally. The experimental primers were applied onto dentin prior to light polymerization of the incremental composite resin buildup. Teeth were sectioned after 48 h, 6 months, or 12 months of water storage and then tested with the microtensile tester (Dillon Quantrol, Bisco). Results: ANOVA revealed that the solvent:monomer ratio and RRP had a significant effect (p 0.05) on bond strength in 48-h groups (3-way ANOVA). Increasing the solvent:monomer ratio and addition of RRP into primers increased the µTBS values. However, long-term water storage decreased the µTBS values in the high solvent:monomer ratio group. In the other groups, water storage did not decrease the µTBS values. Conclusion: One-year water storage lowered the dentin bond strength obtained using the primer with a high solvent:monomer ratio, whereas no decrease of bond strength was observed for the other study groups or for the control group. Keywords: adhesion, dentin, primer, rigid rod polymer

Purpose: To evaluate in vitro the microshear bond strength of adhesive systems applied to dentin according to manufacturers' instructions, associated or not with a hydrophobic layer of unfilled resin. Materials and Methods: Six self-etching adhesives (Clearfil SE Bond, Kuraray Medical; AdheSE, Ivoclar Vivadent; Xeno III, Dentsply; I Bond, Heraeus-Kulzer; Bond Force, Tokuyama; Futurabond DC, Voco) were tested. The labial dentin of sixty bovine incisors was exposed, and the teeth were divided into two groups according to the application or not of an extra hydrophobic resin layer (Scotchbond Multi Purpose Plus, bottle 3). Six composite cylinders (Filtek Z250, 3M ESPE) were built up on each treated surface. Specimens were stored in distilled water at 37°C for 24 h and then subjected to the microshear bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. Microshear bond strength values were analyzed by 2-way ANOVA and Tukey's post-hoc test. Failure mode was determined using a stereomicroscope under 20X magnification. Results: The application of the hydrophobic resin layer did not affect bond strength, except for AdheSE. However, the bond strengths with the hydrophobic layer were similar among the six tested systems (Clearfil: 17.1 ± 7.9; AdheSE: 14.5 ± 7.1; Xeno lll: 12.8 ± 7.7; I Bond: 9.5 ± 5.8; Bond Force: 17.5 ± 4.1; Futurabond: 7.7 ± 2.3). When used as recommended by the manufacturers, Bond Force presented statistically higher bond strength than AdheSE and I Bond (p 0.05) (Clearfil 10.4 ± 4.9; AdheSE 1.6 ± 1.6; Xeno lll: 9.0 ± 3.8; I Bond: 3.0 ± 1.5; Bond Force: 14 ± 3.9; Futurabond: 8.8 ± 3.8). Failure mode was predominantly adhesive. Conclusion: The bond strength of the self-etching systems tested was not significantly affected by the application of a hydrophobic layer, but a significant improvement was observed in AdheSE. Keywords: microshear bond strength, adhesive system, hydrophobic adhesive, dentin

Purpose: The aim of this study was to detect the influence of (1) storage period of heparinized blood, (2) type of blood and presence of contaminant, (3) application mode of cleansing agents, and (4) efficacy of cleansing agents on contaminated enamel and dentin during the adhesion process of a one-step adhesive system. Materials and Methods: One hundred four human molars were sectioned into halves along the long axis for enamel and dentin tests. Heparinized and fresh blood were obtained from the same donor, applied and dried to maintain a layer of dry blood on the top of samples. The cleansing agents used were hydrogen peroxide, anionic detergent, and antiseptic solution. A one-step adhesive system (Clearfil S3 Bond) was applied on the dental surface, and composite resin cylinders were built up using Tygon tubing molds. After 24 h, the µSBS test (1 mm/min) and fracture analysis were performed. Results: There was no statistically significant difference in bond strength values regarding the storage period of heparinized blood and the types of blood. Groups without contamination presented higher bond strengths than contaminated groups. The application mode of the cleansing agents had no influence on bond strength results. There was no statistically significant difference among cleansing agents and they were as effective as a water stream in counteracting the effect of blood contamination. Conclusion: Heparinized blood can be used as a contaminant for up to one week, and it is a reliable procedure to standardize the contaminant. The cleansing agents can be used without friction. A water stream is sufficient to remove blood contamination from dental tissues, before the application of a one-step adhesive system. Keywords: blood, contamination, self-etching adhesive system, bond strength

Purpose: To evaluate the effect of different surface treatments and bonding procedures on the tensile bond strength (TBS) of resin composites repaired 6 months after polymerization. Materials and Methods: Resin composite sticks were aged in distilled water at 37°C for 6 months. They were divided into 12 groups (n = 10) according to the combination of surface treatment/bonding procedures [none, only bur treatment, XP Bond (XPB/Dentsply/DeTrey) with/without bur, AdheSE (A-SE/Ivoclar/Vivadent) with/without bur, Composite Primer (CP/GC) with/without bur, CP after bur and acid-etching, XPB after acid etching and CP with bur, A-SE after bur and CP]. The ultimate tensile bond strength (UTS) of the resin composites was tested in intact but aged specimens. Tensile bond strengths were tested with a universal testing machine (Shimadzu). Data were analyzed using one-way ANOVA and Duncan Multiple Comparisons tests (p 0.05). Results: All repaired groups showed significantly higher TBS than the group without any sureface treatment (p 0.05). Four groups resulted in TBS similar to those of intact resin composite UTS: A-SE, A-SE with bur, A-SE after CP with bur, and XPB after acid etching+CP with bur. Conclusion: Bur treatment, silane primer or etch-and-rinse adhesive application alone were not successful in the repair process of aged resin composite, whereas self-etching adhesive alone showed similar performance to the intact specimens. Combined procedures generally showed better performance: A-SE with bur, A-SE after CP with bur, and XPB after acid etching +CP with bur showed TBS similar to those of the intact specimens. It was concluded that bur roughening of the surfaces and rebonding procedures were essential for repairing aged resin composites. Keywords: composite repair, silane primer, self-etching adhesive, etch-and-rinse adhesive, surface treatment

Purpose: To assess the influence of preparation design on failure risk of ceramic inlays by means of finite element (FE) analysis. Materials and Methods: Both 2D and 3D models of the maxillary first premolar were constructed. MOD ceramic inlays were designed with an isthmus width of 1.5 to 5.0 mm and a minimum thickness of 1 to 3 mm. Occlusal contact motion and debonding at the tooth/ceramic adhesive interface were simulated in 2D models by downward displacement of a ceramic ball (1.5 mm in diameter) onto the central groove. The stress distributions within the inlays and at the interface were analyzed using 3D models. A maximum occlusal load of 250 N was assumed. Results: The maximum principal stress at the base of the inlays was constant among models of different isthmus widths, although it decreased considerably as inlay thickness increased from 1 mm to 2 mm. The maximum shear stress at the adhesive interface increased as the width of the inlay decreased and the distance between the occlusal contact and the margin decreased to 0.3 mm or less. The maximum principal stress on the occlusal surface was relatively low and insensitive to inlay design; however, it was increased by a simulated adhesive failure. Conclusion: The failure risk at the base of the inlay is minimized by increasing the minimum inlay thickness. As the occlusal contact becomes close to the margin, the adhesive failure risk is increased, potentially leading to an increase in risk of fracture on the occlusal surface. Keywords: ceramic inlay, preparation design, failure risk, finite element analysis

Purpose: To analyze the cytotoxic effects of 2-hydroxyethylmethacrylate (HEMA) in human gingival fibroblasts using quantitative x-ray microanalysis (EXPMA) and two classical methods (DNA and LDH release in culture medium). Materials and Methods: Different concentrations of HEMA (5, 10, 20, 30, and 40 mM) in DMEM medium were used and the effects on human gingival fibroblasts after 6, 12, and 24 h were determined. As controls, fibroblasts cultured with DMEM culture medium (negative control) and fibroblast incubated in 1% triton X (positive control) were used. Results: The results showed that correlation between the concentrations of HEMA and the amount of LDH and DNA released to the medium were statistically significant for all times analyzed. LDH and DNA released from cells incubated in the lowest concentrations of HEMA (5 and 10 mM) were not significantly different to negative controls. In contrast, cells incubated in the highest HEMA concentrations (20, 30, 40 mM) showed a significant increase of both LDH and DNA released to the culture medium at 6, 12, and 24 h. On the other hand, the ionic concentration of the different elements analyzed in this work revealed that the contents of P, S, Cl, and K were significantly higher in the controls than in samples incubated for 6 h in 5 mM or 10 mM HEMA (p 0.01). K/ Na index (an excellent marker of cell viability) showed a significant decrease, and therefore, viability was significantly reduced. Conclusion: The results suggest that EXPMA is a sensitive method that is able to detect early cell damage even before the cell membrane is altered. Keywords: HEMA, cell death, apoptosis, necrosis, microanalysis, LDH, DNA

Purpose: To evaluate the clinical usefulness of directly fabricated glass and polyethylene resin-bonded fiberreinforced composite (FRC) inlay-retained fixed dental prostheses (FDPs) in posterior single missing teeth over a short period of time. Materials and Methods: Fourteen inlay-retained FRC FDPs with tub-shaped or box-shaped retainers were directly constructed in patients of both genders. A baseline examination was performed and the patients were examined regularly at 6-month intervals. The sulcus bleeding index, Silness-Löe plaque index, and probing depths of the abutments were checked regularly. Modified US Public Health Service (USPHS) parameters were used to compare the restorations at baseline and final examination. The Kaplan-Meier survival estimation method was performed to detect the overall survival rates and mean survival times of the restorations at the end of the follow-up. Results: The length of the clinical observation was between 16 and 40 months for the FDPs still functioning after the end of the follow-up. No partial or total debonding of the prostheses or fracture of the frameworks was detected. Four veneering composite fractures at the veneer layer/fiber framework interface occurred in the pontic elements of 2 glass FRC FDPs and 2 polyethylene FRC FDPs after 6 and 10 months, and 20 and 22 months, respectively. Periodontal evaluation revealed clinically acceptable results, as did the USPHS evaluation. The overall survival curves of Kaplan-Meier at the end of the follow-up illustrated a 71% survival rate for the both glass and polyethylene FRC FDPs with mean survival times of 27 and 35 months, respectively. Conclusion: This study reported a mean period of service of 19 and 31 months for directly fabricated inlayretained glass and polyethylene FRC FDPs, respectively, with a 71% survival rate for the two framework constructions. Within the limitations of the study, these results can only be considered as preliminary. However, because of the lack of clinical data available for directly fabricated inlay-retained FRC FDPs, the results of this clinical observation may contribute to the still-evolving clinical knowledge of the FRC restorations. Keywords: fiber-reinforced composite FDPs, inlay-retained FRC FDPs, directly fabricated FRC FDPs, resin-bonded FRC FDPs, glass FRC, polyethylene FRC