The Journal of Adhesive Dentistry, 05/2014

Purpose: To assess the influence of non-ionizing radio frequency signals of magnetic resonance imaging (MRI) on physical properties of dental alloys and metal-ceramic adhesion. Materials and Methods: A total of 120 disk-shaped wax patterns (10 mm x 10 mm x 1 mm) were cast in a base metal alloy (Ni-Cr alloy) and commercially pure titanium (Ti) following the manufacturing recommendation. After casting, air abrasion and ultrasonic cleaning, feldspathic ceramic was applied and fired according to manufacturer's instructions using a standard mold. The specimens were subjected to 3000 thermocycles in distilled water between 5°C and 55°C, then veneered alloy specimens were randomly assigned to three groups according to MRI exposure time: a) 15 min of MRI exposure, b) 30 min of MRI exposure and c) no MRI exposure (control group). The specimens were subjected to shear loading until failure. A separate set of Ni-Cr and Ti specimens were prepared, and after exposure to MRI for 15 and 30 min, x-ray diffraction (XRD) analysis, surface roughness, and Vicker's hardness were measured. Results: Both the alloy type (p 0.005) and exposure duration (p 0.005) had a significant effect on the bond results. While the control group presented the highest bond strength for Ni-Cr and Ti (36.9 ± 1.4 and 21.5 ± 1.6 MPa, respectively), 30 min MRI exposure significantly decreased the bond strength for both alloys (29.4 ± 1.5 and 12.8 ± 1.5 MPa, respectively) (p 0.05). XRD analysis indicated formation of the crystalline phase as well as change in crystal size and position for Ni-Cr and Ti after MRI. Compared to the control group where alloys were not exposed to MRI (Ni-Cr: 0.40 μm; Ti: 0.17 μm), surface roughness increased (Ni-Cr: 0.54 μm; Ti: 1.1 μm). Vicker's hardness of both alloys decreased after 30 min MRI (Ni-Cr: 329.5; Ti: 216.1) compared to the control group c (Ni-Cr: 356.1; Ti: 662.1), being more significant for Ti (p 0.005). Conclusion: Ni-Cr alloy is recommended over Ti for the fabrication of metal-ceramic restorations for patients with a history of frequent exposure to MRI. Keywords: adhesion, base alloy, chipping, magnetic resonance imaging, metal-ceramic, roughness, titanium

Purpose: To analyze the effects of different processes during bonding on endogenous cysteine cathepsin activity in dentin. Materials and Methods: Dentin powder, prepared from extracted human third molars, was divided into 10 groups. Two lots of dentin powder were used to detect the effects of the procedure of protein extraction on endogenous cathepsin activity. The others were used to study effects of different acid-etching or adhesive treatments on enzyme activity. Concentrations of 37% phosphoric acid or 10% phosphoric acid, two etch-and-rinse adhesive systems, and two self-etching adhesive systems were used as dentin powder treatments. The untreated mineralized dentin powder was set as the control. After treatment, the proteins of each group were extracted. The total cathepsin activity in the extracts of each group was monitored with a fluorescence reader. Results: In the control group, there were no significant differences in cathepsin activity between the protein extract before EDTA treatment and the protein extract after EDTA treatment (p > 0.05). The cathepsin activities of the three different extracts in the 37% phosphoric acid-treated group were different from each other (p 0.05). The two acid-etching groups and two etch-and-rinse groups showed significant enzyme activity reduction vs the control group (p 0.05). There were no significant differences between those four groups (p > 0.05). Treating the dentin powder with any of the two self-etching adhesives resulted in an increase in cathepsin activity (p 0.05). Conclusions: The activity of cysteine cathepsins can be detected in dentin powder. Treatment with EDTA during protein extraction exerted an influence on cathepsin activity. Acid etching or etch-and-rinse adhesive systems may reduce the activity of endogenous cathepsins in dentin. Self-etching adhesive systems may increase the enzyme activity. Keywords: dentin, acid etching, bonding, cysteine cathepsin, enzyme activity

Purpose: To evaluate the effect of cariogenic challenge on the bond strength of adhesive systems to sound and artificially demineralized enamel of primary and permanent teeth. Materials and Methods: Eighty molars (40 primary, 40 permanent) were randomly assigned to 16 groups (n = 5) according to the type of tooth (primary [PRIM] or permanent [PERM]), enamel condition (sound [S] or demineralized [DEM]), treatment after the restorative procedure (control [C] or cariogenic challenge [pH]), and adhesive system (Adper Single Bond [SB] or Clearfil SE Bond [SE]). Teeth from the DEM group were subjected to cariogenic challenge by pH cycling prior to restorative procedures and pH group specimens were subjected to cariogenic challenge before the microshear test. One of two adhesive systems was applied to the flat enamel surfaces and composite cylinders (0.45 mm2) were built. The microshear bond test was performed. The data (MPa) were subjected to ANOVA and Tukey's test (α = 0.05). Results: No statistically significant differences were detected between the adhesive systems. The S groups exhibited higher bond strength values than the DEM groups, as did C groups compared to pH groups. PERM groups also had higher bond strength values than PRIM groups, excluding PRIM S and PERM S, which had similar values. Conclusion: The bond strength to demineralized enamel of primary teeth was lower than to the demineralized enamel of permanent teeth. Cariogenic challenge negatively influenced enamel bond strength, regardless of the type of tooth and adhesive system. Keywords: μSBS, adhesion, enamel caries

Purpose: To determine whether high-pressure air blowing during adhesive application affects the infiltration of resin comonomers and nanoleakage manifestation in the resin/dentin interface under simulated pulpal pressure. Materials and Methods: Thirty mid-coronal dentin surfaces were bonded with an etch-and-rinse adhesive (Adper Single Bond 2) under simulated pulpal pressure. In the control group, the adhesive was thinned by ordinary air blowing with a pressure of 0.2 MPa, while in the experimental group, a high-pressure air blowing technique (pressure: 0.4 MPa) was used. All other procedures followed the manufacturer's instructions. Resin tag formation and nanoleakage in the bonding interface were evaluated with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: When adhesive was thinned with high pressure air blowing, longer and more homogeneous resin tags were formed. The bonding interface demonstrated good overall morphology and integrity. Almost perfect infiltration of resin and no obvious nanoleakage were observed. Conclusion: Thinning of adhesive with high-pressure air blowing provides a clinically feasible adjunctive procedure for better resin infiltration. Keywords: bonding, nanoleakage, hybrid layer, adhesive, high-pressure blowing, infiltration

Purpose: To compare manual and sonic adhesive application modes in terms of the permeability and microtensile bond strength of a self-etching adhesive applied in the one-step or two-step protocol. Materials and Methods: Self-etching All Bond SE (Bisco) was applied as a one- or a two-step adhesive under manual or sonic vibration modes on flat occlusal dentin surfaces of 64 human molars. Half of the teeth were used to measure the hydraulic conductance of dentin at 200 cm H2O hydrostatic pressure for 5 min immediately after the adhesive application. In the other half, composite buildups (Opallis) were constructed incrementally to create resin-dentin sticks with a cross-sectional area of 0.8 mm2 to be tested in tension (0.5 mm/min) immediately after restoration placement. Data were analyzed using a two-way ANOVA and Tukey's test (α = 0.05). Results: The fluid conductance of dentin was significantly reduced by the sonic vibration mode for both adhesives, but no effect on the bond strength values was observed for either adhesive. Conclusion: The sonic application mode at an oscillating frequency of 170 Hz can reduce the fluid conductance of the one- and two-step All Bond SE adhesive when applied on dentin. Keywords: tensile strength, dentin bonding agents, dentin, dentin permeability

Purpose: To directly test the effectiveness of ethanol-wet bonding (EW) in improving monomer infiltration into demineralized dentin through quantitative measurement of bis-GMA and TEG-DMA molar concentrations within hybrid layers, and to comprehensively evaluate the effect of EW and chlorhexidine on durability of resin-dentin bonds compared to conventional water-wet bonding (WW). Materials and Methods: A three-step etch-and-rinse adhesive (70% bis-GMA/28.75%TEG-DMA) was applied to coronal dentin using a clinically relevant ethanol-wet bonding protocol (EW) or the conventional water-wet bonding (WW) technique. Bis-GMA and TEG-DMA molar concentrations at various positions across the resin/dentin interfaces formed by EW and WW were measured using micro-Raman spectroscopy. The experiment was repeated at the same positions after 7-month storage in phosphate buffer solution containing 0.1% sodium azide. The μTBS and hybrid layer morphology (TEM) of bonding groups with and without chlorhexidine application were compared immediately and after 1-year storage in terms of nanoleakage, collagen fibril diameter, collagen interfibrillar width, and hybrid layer thickness. Results: Specimens bonded with EW showed significantly higher monomer molar concentrations and μTBS throughout the hybrid layer immediately and after storage, providing direct evidence of superior infiltration of hydrophobic monomers in EW compared to WW. Microscopically, EW maintained interfibrillar width and hybrid layer thickness for resin infiltration and retention. The application of chlorhexidine further preserved collagen integrity and limited the degree of nanoleakage in EW after 1-year storage. Conclusion: EW enhances infiltration of hydrophobic monomers into demineralized dentin. The results suggest that a more durable resin-dentin bond may be achieved with combined usage of a clinically relevant EW and chlorhexidine. Keywords: bonding, collagen(s), matrix metalloproteinases (MMPs), ultrastructure, dentin, adhesives

Purpose: To evaluate the effect of grinding and airborne-particle abrasion on the biaxial flexural strength (BFS) and phase transformation of a Y-TZP ceramic, and examine whether sintering the veneering porcelain renders the previous heat treatment recommended by the manufacturer unnecessary. Materials and Methods: Lava zirconia specimens (N = 108) were obtained with the following dimensions: 14.0 mm diameter × 1.3 mm thickness (n = 36) and 14.0 mm × 1.6 mm (n = 72). The thicker specimens were ground with diamond burs under irrigation and received (heat-treated groups) or not (non-heat-treated groups) a heat treatment (1000°C for 30 min) prior to the four firing cycles applied to simulate the sintering of the veneering porcelain. All specimens were air abraded as follows (n = 12): 1) 30-μm silica-modified Al2O3 particles (Rocatec Soft); 2) 110-μm silica-modified Al2O3 particles (Rocatec Plus); and 3) 120-μm Al2O3 particles, followed by Rocatec Plus. Three specimens of each group were analyzed by x-ray diffraction (XRD) to assess the monoclinic phase content (%). The BFS test was performed in a mechanical testing machine (Instron 8874). Data (MPa) were analyzed by two-way ANOVA (grinding × airborne-particle abrasion and heat treatment × airborne-particle abrasion) and Tukey's post-hoc test (α = 0.05). The strength reliability was analyzed using the Weibull distribution. Results: Grinding significantly decreased the BFS of the non-heat-treated groups (p 0.01). Within the ground groups, the previous heat treatment did not influence the BFS (p > 0.05). Air abrasion only influenced the BFS of the ground/heat-treated groups (p 0.01). For the non-heat-treated groups, the grinding did not decrease the Weibull modulus (m), but it did decrease the characteristic strength (σ0). For Rocatec Soft and 120-μm Al2O3 particles + Rocatec Plus, the heat-treated groups presented lower m and higher σ0 than the ground/non-heat-treated groups. The independent variables did not seem to influence phase transformation. Air-abraded surfaces presented higher monoclinic zirconia content than the as-sintered and ground surfaces, which exhibited similar content. Conclusion: Even under irrigation, grinding compromised the Y-TZP ceramic strength. The sintering of the veneering porcelain rendered the previous heat treatment recommended by the manufacturer unnecessary. Airborneparticle abrasion influenced the strength of heat-treated zirconia. Keywords: zirconia, airborne-particle abrasion, grinding, heat treatment, biaxial flexural strength

Purpose: To determine the impact of long-term storage on adhesion between titanium and zirconia using resin cements. Materials and Methods: Titanium grade 4 blocks were adhesively fixed onto zirconia disks with four resin cements: Panavia F 2.0 (Kuraray Europe), GC G-Cem (GC Europe), RelyX Unicem (3M ESPE), and SmartCem 2 (Dentsply DeguDent). Shear bond strength was determined after storage in a water bath for 24 h, 16, 90, and 150 days at 37°C, and after 6000 cycles between 5°C and 55°C. Fracture behavior was evaluated using scanning electron microscopy. Results: After storage for at least 90 days and after thermocycling, GC G-Cem (16.9 MPa and 15.1 MPa, respectively) and RelyX Unicem (10.8 MPa and 15.7 MPa, respectively) achieved higher shear bond strength compared to SmartCem 2 (7.1 MPa and 4.0 MPa, respectively) and Panavia F2 (4.1 MPa and 7.4 MPa, respectively). At day 150, GC G-Cem and RelyX Unicem caused exclusively mixed fractures. SmartCem 2 and Panavia F2 showed adhesive fractures in one-third of the cases; all other fractures were of mixed type. After 24 h (GC G-Cem: 26.0, RelyX Unicem: 20.5 MPa, SmartCem 2: 16.1 MPa, Panavia F2: 23.6 MPa) and 16 days (GC G-Cem: 12.8, RelyX Unicem: 14.2 MPa, SmartCem 2: 9.8 MPa, Panavia F2: 14.7 MPa) of storage, shear bond strength was similar among the four cements. Conclusion: Long-term storage and thermocycling differentially affects the bonding of resin cement between titanium and zirconia. Keywords: titanium, zirconia, long-term storage, thermocycling, shear bond strength

Purpose: To examine the influence of etching duration on the bond strength of PEEK substrate in combination with different resin composite cements. Materials and Methods: In total, 448 PEEK specimens were fabricated, etched with sulfuric acid for 5, 15, 30, 60, 90, 120, and 300 s and then luted with two conventional resin cements (RelyX ARC and Variolink II) and one self-adhesive resin cement (Clearfil SA Cement) (n = 18/subgroup). Non-etched specimens served as the control group. Specimens were stored in distilled water for 28 days at 37°C and shear bond strengths were measured. Data were analyzed nonparametrically using Kruskal-Wallis-H (p 0.05). Results: Non-etched PEEK demonstrated no bond strength to resin composite cements. The optimal etching duration varied with the type of resin composite: 60 s for RelyX ARC (15.3 ± 7.2 MPa), 90 s for Variolink II (15.2 ± 7.2 MPa), and 120 s for Clearfil SA Cement (6.4 ± 5.9 MPa). Regardless of etching duration, however, the self-etching resin composite cement showed significantly lower shear bond strength values when compared to groups luted with the conventional resin composites. Conclusion: Although sulfuric acid seems to be suitable and effective for PEEK surface pre-treatment, further investigations are required to examine the effect of other adhesive systems and cements. Keywords: PEEK, polyetheretherketone, bond strength, sulfuric acid, etching duration

Purpose: To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning methods. Materials and Methods: Two types of MZ (BruxZir Solid Zirconia, n = 60; Prettau-Zirkon, n = 60) with two types of surface finish (glazed, n = 30 per group; polished, n = 30 per group) were tested after two surface conditioning methods: 1. air abrasion with 30-μm silica coated aluminum oxide (Al2O3) particles (CoJet), or 2. air abrasion with 50-μm Al2O3 particles. The non-conditioned group acted as the control. A universal primer (Monobond-Plus) and an orthodontic primer (Transbond-XT Primer) were applied to all specimen surfaces. Orthodontic resin composite (Transbond-XT) was bonded using a mold and photopolymerized. The bonded specimens were subjected to μSBS testing (0.5 mm/min). Data were analyzed statistically using three-way ANOVA and the Sidac adjustment post-hoc test (α = 0.05). Failure modes were analyzed using a stereomicroscope (30X). Results: Mean μSBS values (MPa) did not show a significant difference between the two brands of MZ (p > 0.05). In both glazed (44 ± 6.4) and polished (45.9 ± 4.8) groups, CoJet application showed the highest μSBS values (p 0.001). The control group (34.4 ± 6) presented significantly better results compared to that of Al2O3 (30 ± 3.8) (p 0.05) on glazed surfaces, but it was the opposite in the polished groups (control: 20.3 ± 4.7; Al2O3: 33.8 ± 4.7; p 0.001). Adhesive failure was the dominant type in all groups. Conditioning MZs with Al2O3 and CoJet increased the percentage of mixed failure type. Conclusion: Air abrasion with CoJet followed by the application of universal primer improved the μSBS of orthodontic resin to both the polished and glazed monolithic zirconium oxide materials tested. Keywords: air abrasion, monolithic zirconium oxide, zirconia, microshear bond strength, orthodontic bonding, surface conditioning method

Purpose: To evaluate the clinical performance of porcelain laminate veneers (PLVs) after 2 years. Materials and Methods: Twenty-eight patients were treated with 125 PLVs. The experimental variables were preparation design (incisal overlap [IO] and incisal bevel [IB]) and adhesion surface (enamel [E], enamel with minimal dentin exposure [MDE], and enamel with severe dentin exposure (SDE)]. Marginal adaptation, marginal discoloration, secondary caries, postoperative sensitivity, and patient satisfaction were assessed according to the modified United States Public Health Service criteria. Each restoration was examined for fractures and debonding. In addition, gingival tissue health by gingival plaque, bleeding, and recession was recorded. An experienced clinician evaluated the restorations at baseline and after 6, 12, and 24 months, and survival rates evaluating relative and absolute failures were calculated (p = 0.05). Results: Eleven (8.8%) veneers failed, and the overall cumulative survival rate was 91.2% after 2 years of followup. IB and IO preparation designs exhibited survival rates of 94% and 85.7%, respectively, but this difference was not statistically significant (p > 0.05). PLVs bonded to SDE were more likely to fail than those bonded to E and MDE (p 0.05). There was no significant difference between the failure rate of PLVs bonded to E and those bonded to MDE (p > 0.05). Conclusions: PLVs have high survival rates when bonded to enamel only, as well as to enamel with minimal dentin exposure. However, extensive dentin exposure should be avoided during the preparation. Keywords: porcelain laminate veneers, dentin exposure, preparation design