The Journal of Adhesive Dentistry, 04/2019

Purpose: To evaluate the effect of the chelating agents phytic acid and EDTA on the degree of conversion (DC), microhardness, and tensile bond strength (TBS) of two chemical-curing self-adhesive cements. Materials and Methods: A total of 110 samples were prepared, with n = 6 in the control group to measure microhardness, n = 6 for DC measurement, and n = 10 for TBS measurement. The bovine dentin specimens were divided into five groups according to treatment: group A (control group): no treatment; group B, 1% phytic acid with ultrasonic rinsing (UR); group C: 1% phytic acid without UR; group D: 18% EDTA with UR; group E: 18% EDTA without UR. A 1-mm-thick coat of self-adhesive cement, G-CEM LinkAce (GC) or RelyX Unicem 2 (3M) was placed on control and treated dentin surfaces and stored in a dark box at 37°C, 93% ± 1% ambient humidity. DC and microhardness of cement surfaces were measured after 1 hour, 1 day, 3 days, and 1 week using Fourier transform infrared spectroscopy and a Vickers microhardness tester, respectively. TBS on treated and control dentin was evaluated after 1 week of storage in the dark box. Data were analyzed using two-way ANOVA, followed by Tukey's post-hoc test, at the 0.05 level of significance. Results: DC and microhardness of both types of cement without UR were significantly lower than that of groups in which UR was performed. Neither chelating agent had a significant effect on the TBS of G-CEM. For Rely X, the phytic acid treatment with UR showed a significantly higher TBS than the control and the EDTA groups. Conclusion: The chelating agents had a negative effect on DC and microhardness of the resin cements when UR was not used. Phytic acid increased the TBS of RelyX, while EDTA groups did not with either cement. Keywords: self-adhesive cements, chelating agents, degree of conversion, microhardness, tensile bond strength

Purpose: To evaluate the effect of different surface treatments on the surface morphology of CAD/CAM ceramics and on their bond strength to cement. Materials and Methods: Sixty cubic sections were cut from each of three materials (lithium disilicate glass-ceramic [DL], leucite-based glass-ceramic [LC], resin-matrix ceramic composite [RMCC]) and were treated as follows (n = 10): 1. no treatment (C); 2. 5% hydrofluoric acid applied for 20 s plus silane (HF5% 20 s); 3. 5% hydrofluoric acid applied for 60 s plus silane (HF5% 60 s); 4. 10% hydrofluoric acid applied for 20 s plus silane (HF10% 20 s); 5. 10% hydrofluoric acid applied for 60 s plus silane (HF10% 60 s); 6. Self-etching ceramic primer (MBEP). Ceramic cubes were bonded to pre-polymerized composite resin cubes with a composite cement. Each set was cut into stick-shaped specimens (1 ± 0.3 mm2). After 24-h water storage, microtensile bond strength (µTBS) was measured. Data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Failure pattern and surface morphology were assessed using scanning electron microscopy (SEM). Results: Both factors significantly influenced µTBS, while no interaction between factors was found. RMCC presented statistically higher µTBS values than LC and DL, while the surface treatments HF5% 20 s, HF5% 60 s, HF10% 20 s, HF10% 60 s and MBEP, did not show statistical differences between them, although they resulted in statistically significantly higher bond strengths than did C groups. A high number of pre-test failures were detected in the control groups for all materials. MBEP produced less extensive surface alterations than did all HF treatments. Conclusion: All of the hydrofluoric acid treatments tested showed similar cement-ceramic bonding efficacy. The self-etching ceramic primer produced less surface alterations and comparable bonding efficacy compared to separate hydrofluoric acid/silane primer application. Keywords: bond strength, CAD/CAM, hydrofluoric acid etching, self-etching ceramic primer, ceramics, silane

Purpose: To evaluate the effect of different application modes of a recently introduced self-etching ceramic primer on the microshear bond strength (μSBS) and ceramic surface-etching pattern of two glass-ceramic surfaces. Materials and Methods: Twenty-two CAD/CAM blocks of lithium disilicate (LD) and feldspathic glass ceramic (VTR) were each cut into 4 rectangular sections (n = 88 for ceramic surface). The LD and VTR specimens were divided into one control group (hydrofluoric acid + silane coupling agent [HF+SII]), and 10 experimental groups using Monobond Etch and Prime (MEP) applied for a combination of scrubbing times (5, 10, 20, 40, and 60 s) and reaction times (20 or 40 s). After each treatment, Tygon matrices (n = 8) were filled with a resin cement and light cured for each ceramic specimen. The specimens were stored in water at 37°C for 24 h and subjected to the μSBS test. The failure pattern and μSBS were statistically evaluated (α = 0.05). In addition, the ceramic surface etching pattern was analyzed using scanning electron microscopy. Results: For the LD groups, the application of MEP 60/40 resulted in a higher mean μSBS compared to HF+SI (p 0.05). Groups 5/40, 10/40, and 20/40 resulted in mean μSBS similar to that obtained by HF+SI (p > 0.05). For VTR, no significant difference was observed among the groups (p = 0.32). Compared with MEP, HF better promoted the dissolution of glass matrix for both ceramics. However, prolonged MEP scrubbing or reaction caused significant dissolution of the glass matrix for both evaluated ceramics. Conclusion: Active and prolonged application of MEP may be a viable alternative to HF+SI for increasing the bond strength to LD. Keywords: hydrofluoric acid, lithium disilicate, scanning electron microscopy, self-etching ceramic primer

Purpose: To evaluate the immediate and aged bond strength and interfacial nanolaekage of different adhesives and protocols on dental elements prepared with diamond burs and Er:YAG laser. Materials and Methods: Forty molar crowns were flattened and a standardized smear layer was created. Teeth were divided into two main groups according to the dentin cutting technique: 1. Er:YAG laser for 30 s at 30 Hz repetition rate, 250 mJ energy per pulse, and water spray irrigation set at level 8; and 2. diamond bur. Each group was then divided into subgroups according to the adhesive protocol: SG1: dentin etching for 15 s followed by universal adhesive application (All Bond Universal, Bisco); SG2: universal adhesive application (All Bond Universal); SG3: two-step self-etch adhesive application (Clearfil SE Bond 2, Kuraray Noritake); SG4: etching followed by 3-step etch-and-rinse adhesive application (Optibond FL, Kerr). After curing the adhesives, resin composite buildups of 4 mm were made and specimens were sectioned to obtain 1-mm-thick sticks in accordance with the μTBS test technique. Sticks were stressed to failure at baseline and after 6 months of storage in artificial saliva. Three teeth per group were prepared for nanoleakage interfacial analyses. Data were statistically analyzed with three-way ANOVA and Tukey's post-hoc test (p 0.05). Results: A significant difference in bond strengths was found for treatment, aging, and adhesive protocol. Nanoleakage analysis showed higher marginal infiltration in Er:YAG-treated groups both at baseline and after aging. Conclusions: Surfaces prepared with diamond burs presented higher bond strengths than did those prepared with Er:YAG laser. Adhesive protocols and aging could influence the adhesive-dentin interface. Further studies are necessary to validate the results obtained. Keywords: adhesion, adhesive interface, bond strength testing, Er:YAG laser

Purpose: To analyze the influence of epigallocatechin-3-gallate (EGCG) and chlorhexidine (CHX) on adhesive-dentin bond strength of a self-etch adhesive to sound dentin (SD) and eroded dentin (ED). Materials and Methods: Thirty-six middle-dentin samples were assigned to six groups (n = 6) according to pretreatment (DW: distilled water, control; 0.1% EGCG; or 2% CHX) and erosive challenge (presence or absence). Specimens were subjected to 2-h acquired pellicle formation, then half of them were exposed to 1% citric acid three times a day for five days. SD and ED were treated with the tested solutions for 60 s, and then Clearfil SE Bond was applied before resin composite buildup. Bonded teeth were longitudinally sectioned into sticks and half were immediately tested, while the remaining specimens were tested after six months. The mode of fracture was examined and the microtensile bond strength (µTBS) measured. Statistical analysis was performed with ANOVA and Bonferroni tests. Results: At both time periods, regardless of the dentin substrate, EGCG groups did not show bond strengths that were significantly different from those obtained with DW (p > 0.05), while CHX generated lower values than did DW (p 0.05). On SD, there was a bond strength reduction only in the CHX groups after six months. However, for ED, the bond strength significantly decreased in all groups. Conclusion: CHX negatively affected both dentin substrates, while the pretreatment with EGCG did not affect µTBS over time on SD. µTBS may be influenced by the substrate over time and EGCG can be used as an alternative to CHX to maintain the bond strength of self-etching adhesives. Keywords: catechin, chlorhexidine, dentin, matrix metaloproteinase, erosion, adhesive

Purpose: To evaluate whether different etching methods with reduced etching times would improve the enamel bonding efficacy of universal adhesives. Materials and Methods: Three enamel etching methods were evaluated - 1. phosphoric acid ester monomer etching (PPM); 2. phosphoric acid etching (PPA); and 3. polyalkenoic acid etching (PLA) - as were three universal adhesives: 1. BeautiBond Universal (BU); 2. Prime&Bond elect (PE); and 3. Scotchbond Universal Adhesive (SU). The shear bond strengths of the universal adhesives to ground enamel and ground enamel etched for 1, 5, 10, and 15 s with different etching methods were determined after 24 h and 10,000 thermal cycles. Surface roughness average (Ra) and surface area ratio (surface area:planar area) were measured using a confocal laser scanning microscope. Field-emission scanning electron microscope (FE-SEM) observations of enamel with different etching protocols were also conducted. Results: The bond strengths of universal adhesives to enamel subjected to PPA etching with maximum times of 1-15 s and PLA etching for 15 s were significantly higher than those to ground enamel. The bond strength to enamel subjected to PPM etching did not increase and was similar to that for ground enamel. PPA and PLA etching were effective at increasing the Ra and surface area ratio of enamel. Although both values were significantly higher than those of ground enamel, those subjected to PPA etching were significantly higher than those which underwent PLA etching. In addition, the Ra and surface area of enamel subjected to PPM etching were similar to those of ground enamel, regardless of the etching time. Conclusions: Phosphoric acid etching for 1-15 s and polyalkenoic-acid etching for 15 s both improve the bonding of universal adhesives, the Ra, and the surface area ratio of enamel. However, phosphoric acid ester monomer etching was not effective, regardless of the etching time. Keywords: acid etching, confocal microscopy, enamel bonding, shear bond strength, scanning electron microscopy, shear bond strength

Purpose: To evaluate the effect of different firing stages (without firing, additional crystallization and glaze firings), hydrofluoric acid (HF) concentrations (5% and 10%), and thermocycling on the bond strength between resin cement and a zirconia-lithium silicate (ZLS) ceramic. Materials and Methods: ZLS ceramic (Celtra Duo, Dentsply Sirona) blocks were cut into smaller blocks and divided into 12 groups (N = 72), according to the HF concentration used, firing stage, and thermocycling (n = 6). All specimens were silanized (Monobond N, Ivoclar) and cemented with resin cement (Multilink N, Ivoclar) onto blocks of composite resin (Filtek Z250 XT, 3M). The specimens were immersed in distilled water for 24 h. The blocks were cut into sticks and tested immediately or thermocycled for 10,000 cycles in water (5°C-55°C). Microtensile bond strength (μTBS) testing was then performed in a universal testing machine (0.5 mm/min, 50 kgf load cell). The failure modes of the sticks were examined using SEM and classified as adhesive, predominantly adhesive, or cohesive. Fracture surfaces were topographically evaluated using SEM. The 5% and 10% HF groups were analyzed separately and the data submitted to two-way ANOVA and Tukey's test (p 0.05). Additional samples were used for SEM topographic analysis of representative ceramic surfaces. Results: The most frequent types of failure were predominantly adhesive between cement and ceramic and adhesive (cement completely covered the composite). Statistically significant differences were found only for the thermocycling factor (p 0.05) for both HF concentrations. However, for the 10% HF groups, a marked decrease in μTBS was observed after firing and thermocycling. SEM showed superficial irregularities on ZLS without etching, partial and total dissolution of the vitreous matrix and exposure of the crystals using 5% and 10% HF, respectively. Conclusion: The crystallization and glaze firings of ZLS ceramics conditioned with 5% HF promoted bond strength maintenance after thermocycling. Thermocycling decreased the bond strength in all groups, but mainly for fired ZLS conditioned with 10% HF. Keywords: aging, bond strength, ceramic, firing, hydrofluoric acid, lithium silicate

Purpose: This in vitro study investigated whether aging different restorative materials influences secondary caries development using a short-term in vitro biofilm model, hypothesizing that the antibacterial adhesive employed may lose its effect over time. Materials and Methods: Sixty enamel-dentin blocks were divided into 6 groups with n = 10 per group. The groups were restored with three different restorative materials, of which each sample contained an artificial gap: composite with conventional adhesive (CCA; negative control), composite with an antibacterial adhesive (CAA), and amalgam (A; positive control). Half of the groups were prepared fresh and half of the groups were submitted to an aging protocol consisting of water storage, thermocycling, storage in human saliva, and storage in 0.9% saline solution. All specimens were subjected to an intermittent 1% sucrose biofilm model for 20 days to create artificial caries lesions. Lesion progression in the enamel and dentin next to the different materials was measured as lesion depth (LD) and mineral loss (ML), using transverse wavelength independent microradiography (T-WIM). Regression analysis was used to evaluate the effect of aging on LD and ML per restorative material, corrected for gap size. Results: In the amalgam group, aging led to shallower lesions and less mineral loss. Fresh amalgam samples showed an average lesion depth of 156.65 ± 39.18 µm at wall dentin locations. Aged amalgam samples had an average lesion depth of 73.42 ± 73.50 µm. Fresh CAA samples showed lower average surface mineral loss values (9104 ± 2631 µm•vol%) than did fresh CCA samples (13166 ± 4769 µm•vol%). After aging, this effect was absent, and the average mineral loss in the CAA group was 13382 ± 5586 µm•vol%, while in the CCA group it was 15518 ± 9283 µm•vol%. Conclusion: Aging can influence secondary caries development either positively or negatively depending on the kind of restorative material. Antibacterial adhesives may lose their effectiveness over time. Keywords: adhesives, aging, amalgams, antimicrobial monomers, antibacterial adhesive, bacterial challenge, adhesives, composite restorations, secondary caries

Purpose: To evaluate the influence of different ceramic surface conditioning methods on the fatigue failure load of adhesively cemented simplified lithium-disilicate glass-ceramic restorations. Materials and Methods: Ceramic (IPS e.max CAD, Ivoclar Vivadent) (Ø = 10 mm; thickness = 1.2 mm) and epoxy resin (Ø = 10 mm; thickness = 2.3 mm) disks were produced. The ceramic bonding surfaces were treated as follows: no etching and MPS-silane primer application only (MN); etching with 10% hydrofluoric acid (HF) for 20 s followed by primer application (HF + MN); HF + universal multimode adhesive application (HF + SU); etching with a one-step etching primer (ME&P); HF + primer + conventional adhesive (HF + MN + PAB). The epoxy resin disks were etched with 10% HF for 20 s followed by a coat of bonding agent (Multilink Primer A+B). Pairs of ceramic/epoxy resin disks were cemented with composite cement (Multilink N, Ivoclar Vivadent). The mean fatigue failure load was determined by the staircase method (100,000 cycles at 20 Hz frequency; initial load = 1435 N; step size = 72 N). Results: ME&P had the highest fatigue failure load, followed by HF etched groups, while the non-etched condition (MN group) had the lowest. All samples presented radial cracks originating from defects at the conditioned ceramic surface (interface). Conclusion: The simultaneous physicochemical conditioning with one-step self-etching ceramic primer promoted the best fatigue behavior results of the glass-ceramic restorations. It might indicate that this one-step conditioning reduces the number of flaws at the ceramic surface due to the slighter surface alterations than those produced by hydrofluoric acid etching, improving the fatigue behavior. Keywords: glass ceramics, adhesive strategies, surface conditioning, primers, cementation, fatigue