Influence of sandblasting granulometry and resin cement composition on microtensile bond strength to zirconia ceramic for dental prosthetic frameworks

ObjectivesTo evaluate the effect of the particle size of sandblasting and the composition of the resin cement on the microtensile bond strength (MTBS) to zirconia.MethodsForty zirconia blocks (Cercon, Dentsply) were polished and randomly treated as follows: Group 1 (NT): no treatment; Group 2 (APA-I): airborne particle abrasion (Cobra, Renfert) using 25-μm aluminium-oxide (Al₂O₃)-particles; Group 3 (APA-II): APA with 50-μm Al₂O₃-particles; and Group 4 (APA-III): APA using 110-μm Al₂O₃-particles. Ceramic blocks were duplicated in composite resin. Samples of each pretreatment group were randomly divided into two subgroups depending on the resin cement used for bonding the composite disks to the treated zirconia surfaces. Subgroup 1 (PAN), which was a 10-MDP-containing luting system, used Clearfil Ceramic Primer plus Panavia F 2.0 (Kuraray) and Subgroup 2 (BIF) used Bifix SE (VOCO) self-adhesive cement. After 24 h, bonded specimens were cut into 1 ± 0.1 mm² sticks. MTBS values were obtained using a universal testing machine (cross-head speed = 0.5 mm/min). Failure modes were recorded and the interfacial morphology of the debonded microbars was SEM-assessed. Two-way ANOVA, Student–Newman–Keuls tests, and the step-wise linear regression analysis were performed with the MTBS being the dependent variable (p < 0.05).ResultsDespite the sandblasting granulometry, PAN bonded to air-abraded surfaces attained the highest MTBS and frequently showed mixed fractures. BIF recorded no significant differences in MTBS depending on the conditioning method, and registered the highest rates of premature and adhesive failures.ConclusionsThe 10-MDP-containing luting system seems to be the most suitable to bond zirconium-oxide ceramic, mainly after sandblasting.     

Effect of water aging on microtensile bond strength of dual-cured resin cements to pre-treated sintered zirconium-oxide ceramics

ObjectivesTo evaluate the hydrolytic stability of different dual-cure resin cements when luted to zirconia ceramic.MethodsEighteen cylinder-shaped zirconia blocks (Cercon Zirconia, Dentsply) were conditioned with: Group 1, no treatment; Group 2, sandblasting (125 μm alumina–Al₂O₃-particles); Group 3, tribochemical silica coating (50 μm silica-modified Al₂O₃ particles). Ceramic blocks were duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent). Composite disks were luted to pre-treated ceramic surfaces using: (1) Clearfil Esthetic Cement (CEC; Kuraray); (2) Rely X Unicem (RXU; 3M ESPE); (3) Calibra (CAL; Dentsply Caulk). After 24 h, bonded samples were cut into microtensile sticks (1 mm²). Half of the sticks were loaded in tension until failure (cross-head speed of 0.5 mm/min). The remaining half was tested after 6 months of water storage at 37 °C. Data was analyzed with three-way ANOVA and Tukey’s test (P <0.05). Fractographic analysis was performed by SEM.ResultsAfter 24 h, bond strength of CEC to zirconia was significantly higher than that of RXU and CAL, independently from the ceramic pre-treatment (P <0.001). Using CAL, all samples failed prematurely except when luting to sandblasted surfaces. After 6 months of water aging, bond strength of CEC significantly decreased. RXU did not significantly alter bond strengths. Adhesion of sandblasted specimens luted with CAL fell over time. Micromorphological alterations were evident after water storage.SignificanceResin–ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. CEC and RXU were both suitable for luting zirconia. Water aging played an important role in the durability of zirconia-to-composite chemical bonds.     

Effect of sintering time on biaxial strength of zirconium dioxide

ObjectivesAim of this study was to evaluate effect of sintering time on mechanical properties of yttrium partially stabilized zirconia (Y-TZP) (ICE Zirkon, ZirkonZahn, Italy).MethodsFifty-six zirconia discs were divided into two groups. Discs of the first group were sintered in sintering oven (ZirkonZahn) at 20–1500 °C temperature using rise time of 3 h and kept at 1500 °C for 2 h. Discs of the second group were sintered at 20–1500 °C using rise time of 1 h 40 min and kept at 1500 °C for 1 h. Half of the discs (n = 15) from both groups were thermocycled in distilled water for 20 000 cycles (5–55 °C). Biaxial flexural strength of the discs (diameter 19.0 mm, thickness 1.6 mm) were measured dry at room temperature. Surface microhardness (VHN) was also measured. X-Ray diffraction analysis was performed to evaluate the ratio of tetragonal to monoclinic phase in thermocycled discs. The data was calculated using Weibull and ANOVA analysis.ResultsNo statistically significant difference (p > 0.05) was found between the groups in terms of sintering time or thermocycling. The biaxial flexural strength of the groups varied from 995 MPa to 1127 MPa. Surface microhardness varied from 1478 to 1532. The relative amount of the monoclinic phase was higher when zirconia was thermocycled and stored in water compared to control discs, which had no monoclinic phase at all.SignificanceVariation in the sintering time from 1.6 h to 3.0 h did not influence mechanical properties of Y-TZP zirconia.     

Tensile bond strength between tooth-colored porcelain and sandblasted zirconia framework

PurposeThe purpose of this study was to examine the bond strength between tooth-colored porcelain and sandblasted zirconia framework.MethodsThe surfaces of zirconia specimens that had been cut into a size suitable for a bending test were sandblasted at three different pressures (0.2, 0.4 and 0.6 MPa). The surface roughness of each specimen was measured and then a 3-point bending test was performed. After that, other zirconia specimens simulating a crown framework were fabricated and their surfaces were sandblasted. Three types of tooth-colored porcelain were fired onto the surface of those zirconia specimens, and the tensile bond strength between the two substances was examined.ResultsWhen the sandblasting pressure was increased, the surface roughness of zirconia specimens tended to become, but the flexural strength remained unchanged. The specimens simulating a zirconia framework had a higher strength of bond when sandblasted at 0.4 or 0.6 MPa than when blasted at 0.2 MPa. The zirconia specimens sandblasted at a pressure of 0.4 MPa had a bond strength to tooth-colored porcelain of 37.7–49.5 MPa.ConclusionWhen sandblasted at a pressure of 0.4 MPa, the zirconia specimens developed a strong bond with the tooth-colored porcelain, regardless of the type of porcelain.     

Mechanical properties of new self-adhesive resin-based cement

PurposeThe aim of this study was to compare the bonding strength, flexural strength, elastic modulus, water absorption and the expansion after water storage of new self-adhesive resin cements to commercially available dental cements.MethodsTwo types (hand-mix and auto-mix) of new self-adhesive resin cements (SAC-H and SAC-A, Kuraray Medical), one conventional resin cement (Panavia F2.0), three self-adhesive resin cements (Relyx Unicem, Maxcem and G-Cem), and two resin-modified glass-ionomer cements (Fuji Luting S and Vitremer) were used. Shear bond strengths, flexural strengths and elastic moduli (ISO 4049), water absorption (ISO 4049), and the expansion rate after water storage were investigated.ResultsBoth SAC-H and SAC-A provided adhesion to enamel and dentin, and had the same bond strength to gold alloy and zirconia as conventional resin cements. SAC-H and SAC-A had greater flexural strengths (86.4–93.5 MPa) than commercial self-adhesive resin cements or glass-ionomer cements. The elastic moduli of self-adhesive and glass-ionomer cements were 5.2–7.4 GPa and 2.3–3.4 GPa, respectively. The water absorption of SAC-H and SAC-A (26.3–27.7 μg/mm³) were significantly lower than commercial self-adhesive resin cements. SAC-H and SAC-A showed significantly lower expansion rates (0.17–0.26%) than commercial self-adhesive cements and glass-ionomer cements after 4 weeks water storage.ConclusionsIt is suggested that the new self-adhesive resin cements exhibited a favorable bonding capability and mechanical properties.     

Surface characterisation and bonding of Y-TZP following non-thermal plasma treatment

Objectives(1) To chemically characterise Y-TZP surface via X-ray photoelectron spectroscopy (XPS) and evaluate the surface energy levels (SE) after non-thermal plasma (NTP). (2) To test the microtensile bond strength (MTBS) of Y-TZP bonded to cured composite disks, after a combination of different surface conditioning methods.MethodsTwenty-four Y-TZP discs (13.5 mm × 4 mm) were obtained from the manufacturer and composite resin (Z-100) discs with similar dimensions were prepared. All discs were polished to 600 grit and divided into 8 groups (n = 3 disks each), four control (non-NTP treated) and four experimental (NTP treated for 10 s) groups. All groups received one of the four following treatments prior to cementation with Rely × Unicem cement: sand-blasting (SB), a Clearfil ceramic primer (MDP), sand-blasting + MDP (SBMDP), or baseline (B), no treatment. SE readings and surface roughness parameters were statistically analysed (ANOVA, Tukey's, p < 0.05). Mixed model and paired samples t-tests were used to compare groups on MTBS.ResultsXPS showed increase in O and decrease in C elements after NTP. The polar component increased for BP (42.20 mN/m) and SBP (43.77 mN/m). MTBS values for groups BP (21.3 MPa), SBP (31 MPa), MDPP (30.1 MPa) and SBMDPP (32.3 MPa) were significantly higher in specimens treated with NTP than their untreated counterparts B (9.1 MPa), SB (14.4 MPa), MDP (17.8 MPa) and SBMDP (24.1 MPa).Conclusions(1) Increase of O and decrease of C led to higher surface energy levels dictated by the polar component after NTP; (2) NTP application increased MTBS values of Y-TZP surfaces.     

Effect of silane and MDP-based primers on physico-chemical properties of zirconia and its bond strength to resin cement

ObjectiveTo evaluate the effect of surface treatments on yttria-tetragonal zirconia polycrystal (Y-TZP) characteristics and on resin-mediated zirconia bond.MethodsY-TZP slabs were grit blasted with 45 μm alumina or with 30 μm silica-coated alumina particles. The chemical treatments were: no-chemical treatment (NC), silane-containing primer (SP), MDP (10-Methacryloyloxydecyl dihydrogen phosphate) and silane-containing primer (MPS), MDP-containing primer (MP) and MDP and silane-containing adhesive (MPA). Contact angle as a function of surface roughness (θ_m) and surface roughness parameter (Sdr) were measured using Fringe Projection Phase Shifting (FPPS). Surface free energy (γ_s^TOT) was calculated with a goniometer. Chemical interaction between primers/adhesive and zirconia was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Resin cement microshear bond strength (μSBS) was analyzed at either 24-h or 8-months water storage (37 °C). θ_m values, Sdr values, γ_s^TOT and μSBS values were analyzed using Analysis of variance (ANOVA) and post hoc Tukey test (α = 0.05).ResultsChemical treatment had an effect (p < 0.001) on all surface parameters analyzed: θ_m, γ_s^TOT and Sdr. MP-treated group showed higher incidence of P–O–Zr bonds than the other groups, indicating more chemical linkages. Grit blasting (p < 0.001) and the interaction chemical treatment*storage (p < 0.001) did not affect μSBS; all silane-containing primers showed significant drop in μSBS after aging.SignificanceMDP and/or silane-based solutions affect the physicochemical properties of blasted-zirconia. An MDP-based primer is fundamental to achieve a stable resin-zirconia bonding, but the chemical reactivity of MDP is impaired when this molecule is present in a multicomponent system.     

Effect of cleaning protocol on silica deposition and silica-mediated bonding to Y-TZP

ObjectivesTo evaluate the effect of cleaning methods on the deposition of silica on yttria-stabilized zirconium dioxide (Y-TZP) surface and on the silane-silica mediated bond strength between Y-TZP and resin cement.MethodsY-TZP slabs were air-abraded with 30 μm silica-coated alumina particles and distributed in three groups: no cleaning, cleaning with a stream of oil-free air/water spray for 5 s and cleaning with an ultrasonic bath in water for 10 min. The distribution of Si on the Y-TZP surfaces was recorded using energy dispersive spectroscopy (EDS). After the treatment was applied, Y-TZP slabs (n = 20) received a primer application and resin cement cylinders were built on the surface. After storage (24 h) in water storage or 3 months plus thermocycling; n = 10), microshear bond strength test (μSBS) was performed. X- ray Photoelectron Spectroscopy (XPS) characterized the chemical bonds between the silica layer and the silane-containing primer. Data were analyzed using ANOVA and Tukey test, as well as Weibull analysis (α = 0.05).ResultsCleaning method had a significant effect on the amount of Si deposited on zirconia surface (p < 0.001) and, consequently, on bond strength (p < 0.001). Storage/aging also had a significant effect on bond strength (p < 0.001). Low values of Weibull moduli for bond strength were observed for all groups after aging. XPS showed silane-silica chemical interaction for all groups.SignificanceThe silica deposited by tribochemical coating to Y-TZP was removed by the cleaning methods evaluated, compromising bond strength. Stability of the bonding is also a concern when no cleaning method is applied.     

Innovations in bonding to zirconia-based materials: Part I

OBJECTIVES: Establishing a reliable bond to zirconia-based materials has proven to be difficult which is the major limitation against fabricating adhesive zirconia restorations. This bond could be improved using novel selective infiltration etching conditioning in combination with engineered zirconia primers. Aim of the work was to evaluate resin-to-zirconia bond strength using selective infiltration etching and novel silane-based zirconia primers. METHODS: Zirconia discs (Procera Zirconia) received selective infiltration etching surface treatment followed by coating with either of five especially engineered experimental zirconia primers. Pre-aged resin-composite discs (Tetric Ivo Ceram) were bonded to the treated surface using an MDP-containing resin-composite (Panavia F 2.0). The bilayered specimens were cut into microbars and the microtensile bond strength (MTBS) was evaluated. 'As-sintered' zirconia discs served as a control (alpha=0.05). The broken microbars were examined using a scanning electron microscope (SEM). RESULTS: The combination of selective infiltration etching with experimental zirconia primers significantly improved (F=3805, P<0.0001) the MTBS values (41+/-5.8 MPa) compared to the 'as-sintered' surface using the same primers which demonstrated spontaneous failure and very low bond strength values (2.6+/-3.1 MPa). SEM analysis revealed that selective infiltration etching surface treatment resulted in a nano-retentive surface where the zirconia primers were able to penetrate and interlock which explained the higher MTBS values observed for the treated specimens.     

Concurrent evaluation of composite internal adaptation and bond strength in a class-I cavity

ObjectivesThis study investigated class-I cavity floor adaptation by swept-source optical coherence tomography (OCT) in combination with microtensile bond strength (MTBS) using different filling methods.MethodsTwo adhesive systems; Tokuyama Bond Force and Tri-S Bond Plus were used in conjunction with a universal composite (Estelite Sigma Quick) placed either incrementally (oblique) or in bulk with or without a flowable composite lining (Palfique Estelite LV). Ten serial B-scan images were obtained throughout each cavity by OCT (center wavelength: 1319 nm). In order to evaluate adaptation defined as the cavity floor percentage showing no gap, a significant increase in the signal intensity was considered as gap at the bonded interface of the cavity floor. The same specimens were then cut into beams to measure MTBS at the cavity floor.ResultsTwo-way ANOVA demonstrated that the interaction of adhesive systems and filling techniques was significantly affecting both adaptation and MTBS (p < 0.05). There was a significant correlation between MTBS and adaptation at cavity floor (p < 0.05). Cavity floor adaptation and MTBS were improved when incremental filling technique was applied, while the outcome of lining technique was variable.ConclusionsQuantitative assessment by OCT can non-destructively provide information on the performance and effectiveness of dental composites and restoration techniques. There was a moderate correlation between floor adaptation and bond strength in class-I cavities. Incremental application of composite restoration showed the best performance in terms of bond strength and internal adaptation.Clinical significanceIncremental application of composite restoration was the most advantageous placement technique in terms of bond strength and internal adaptation. The lack of placement pressure with flowable composites may affect their adaptation to all-in-one adhesives; therefore, the outcome of cavity lining by flowable composite was variable.     

Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic

ObjectivesTo evaluate the effect of surface conditioning on the microtensile bond strength of zirconium-oxide ceramic to dual-cured resin cements.MethodsEighteen cylinder-shaped zirconium-oxide ceramic blocks (Cercon^® Zirconia, Dentsply) were treated as follows: (1) Sandblasting with 125 μm aluminum-oxide (Al₂O₃) particles; (2) tribochemical silica coating using 50 μm Al₂O₃ particles modified by silica; (3) no treatment. Each ceramic cylinder was duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent) using a silicon mold. Composite cylinders were bonded to conditioned ceramics using: (1) Calibra (Densply Caulk); (2) Clearfil Esthetic Cement (Kuraray); (3) Rely × Unicem (3 M ESPE). After 24 h bonded specimens were cut into microtensile sticks that were loaded in tension until failure. Data were analyzed using two-way ANOVA and Student–Newman–Keuls test for multiple comparisons (p < 0.05). Failure mode was recorded and the interfacial morphology of debonded specimens was observed using a scanning electron microscope (SEM). Surface topography and ceramic average surface roughness were analyzed under an atomic force microscope (AFM).ResultsSignificant changes in zirconia surface roughness occurred after sandblasting (p < 0.001). Bond strength of Clearfil cement to zirconia was significantly higher than that of Rely × Unicem and Calibra, regardless of the surface treatment (p < 0.001). When using Calibra, premature failures occurred in non-treated and silica coated zirconia surfaces.SignificanceThe phosphate monomer-containing luting system (Clearfil Esthetic Cement) is recommended to bond zirconia ceramics and surface treatments are not necessary.     

Microtensile bond strength of resin-based composites to Ti–6Al–4V

ObjectiveThe purpose of this study was to determine the microtensile bond strength of various resin composite/adhesive systems to alumina particle abraded Ti–6Al–4V substrate after aging for 24 h, 10 days, and 30 days in distilled water at 37 °C.MethodsFour laboratory resin composite veneering systems (Gradia, GR; Solidex, SOL; Ceramage, CER; and Sinfony, SF) were bonded to 25 mm diameter machined disks of Ti–6Al–4V with their respective adhesive and methodology, according to the manufacturer's instructions. Microtensile bars of approximate dimensions 1 mm × 1 mm × 6 mm were prepared for each resin composite/adhesive system. After cutting, groups (n = 12) from each adhesive system were separated and either stored in water at 37 °C for 24 h (baseline) or aged for 10 or 30 days prior to loading to failure under tension at a cross head speed of 1.0 mm/min. Failure modes were determined by means of scanning electron microscopy (SEM). Statistical analysis was performed through one-way ANOVA and Tukey's test at 95% level of significance.ResultsSignificant variation in microtensile bond strength was observed for the different systems and aging times. SOL and GR showed the highest mean bond strength values followed by SF and CER at baseline. Aging specimens in water had an adverse effect on bond strength for SOL and CER but not for the SF and GR groups.SignificanceIn vitro bond strength of laboratory resin composites to Ti–6Al–4V suggests that strong bonds can be achieved and are stable for certain systems, making them useful as an alternative for esthetic fixed prosthetic restorations.     

Thermo and mechanical cycling and veneering method do not influence Y-TZP core/veneer interface bond strength

ObjectivesThe purpose of this study was to evaluate the influence of thermal and mechanical cycling and veneering technique on the shear bond strength of Y-TZP (yttrium oxide partially stabilized tetragonal zirconia polycrystal) core–veneer interfaces.Materials and methodsCylindrical Y-TZP specimens were veneered either by layering (n = 20) or by pressing technique (n = 20). A metal ceramic group (CoCr) was used as control (n = 20). Ten specimens for each group were thermal and mechanical cycled and then all samples were subjected to shear bond strength in a universal testing machine with a 0.5 mm/min crosshead speed. Mean shear bond strength (MPa) was analysed with a 2-way analysis of variance and Tukey's test (p < 0.05). Failure mode was determined using stereomicroscopy and scanning electron microscopy (SEM).ResultsThermal and mechanical cycling had no influence on the shear bond strength for all groups. The CoCr group presented the highest bond strength value (p < 0.05) (34.72 ± 7.05 MPa). There was no significant difference between Y-TZP veneered by layering (22.46 ± 2.08 MPa) or pressing (23.58 ± 2.1 MPa) technique. Failure modes were predominantly adhesive for CoCr group, and cohesive within veneer for Y-TZP groups.ConclusionsThermal and mechanical cycling, as well as the veneering technique does not affect Y-TZP core–veneer bond strength.Clinical significanceDifferent methods of veneering Y-TZP restorations would not influence the clinical performance of the core/veneer interfaces.     

Effects of extreme cooling methods on mechanical properties and shear bond strength of bilayered porcelain/3Y-TZP specimens

ObjectivesThis study investigated the effect of extreme cooling methods on the flexural strength, reliability and shear bond strength of veneer porcelain for zirconia.MethodsVita VM9 porcelain was sintered on zirconia bar specimens and cooled by one of the following methods: inside a switched-off furnace (slow), at room temperature (normal) or immediately by compressed air (fast). Three-point flexural strength tests (FS) were performed on specimens with porcelain under tension (PT, n = 30) and zirconia under tension (ZT, n = 30). Shear bond strength tests (SBS, n = 15) were performed on cylindrical blocks of porcelain, which were applied on zirconia plates. Data were submitted to one-way ANOVA and Tukey's post hoc tests (p < 0.05). Weibull analysis was performed on the PT and ZT configurations.ResultsOne-way ANOVA for the PT configuration was significant, and Tukey's test revealed that fast cooling leads to significantly higher values (p < 0.01) than the other cooling methods. One-way ANOVA for the ZT configuration was not significant (p = 0.06). Weibull analysis showed that normal cooling had slightly higher reliability for both the PT and ZT configurations. Statistical tests showed that slow cooling decreased the SBS value (p < 0.01) and showed less adhesive fracture modes than the other cooling methods.Clinical SignificanceSlow cooling seems to affect the veneer resistance and adhesion to the zirconia core; however, the reliability of fast cooling was slightly lower than that of the other methods.     

Chlorhexidine-modified nanotubes and their effects on the polymerization and bonding performance of a dental adhesive

ObjectivesThe purpose of this study was to synthesize chlorhexidine (CHX)-encapsulated aluminosilicate clay nanotubes (Halloysite®, HNTs) and to incorporate them into the primer/adhesive components of an etch-and-rinse adhesive system (SBMP; Scotchbond Multipurpose, 3M ESPE) and to test their effects on degree of conversion, viscosity, immediate and long-term bonding to dentin.MethodsCHX-modified HNTs were synthesized using 10% or 20% CHX solutions. The primer and the adhesive components of SBMP were incorporated with 15 wt.% of the CHX-encapsulated HNTs. Degree of conversion (DC) and viscosity analyses were performed to characterize the modified primers/adhesives. For bond strength testing, acid-etched dentin was treated with one of the following: SBMP (control); 0.2%CHX solution before SBMP; CHX-modified primers + SBMP adhesive; SBMP primer + CHX-modified adhesives; and SBMP primer + CHX-free HNT-modified adhesive. The microtensile bond strength test was performed after immediate (24 h) and long-term (6 months) of water storage. Data were analyzed using ANOVA and Tukey (α = 5%) and the Weibull analysis.ResultsDC was greater for the CHX-free HNT-modified adhesive, whereas the other experimental adhesives showed similar DC as compared with the control. Primers were less viscous than the adhesives, without significant differences within the respective materials. At 24 h, all groups showed similar bonding performance and structural reliability; whereas at the 6-month period, groups treated with the 0.2%CHX solution prior bonding or with the CHX-modified primers resulted in greater bond strength than the control and superior reliability.SignificanceThe modification of a primer or adhesive with CHX-encapsulated HNTs was an advantageous approach that did not impair the polymerization, viscosity and bonding performance of the materials, showing a promising long-term effect on resin-dentin bonds.     

Tetrahydrofuran as alternative solvent in dental adhesive systems

ObjectiveTo evaluate the influence of tetrahydrofuran (THF) on the resin-to-dentin microtensile bond strength (μTBS) after water storage, for 24 h and 6 months, and to compare its behavior with that of traditional solvents.MethodsSeven versions of monomer/solvent mixtures (primers) were prepared using the following solvent and water combinations: (1) THF, (2) acetone, (3) ethanol, (4) water, (5) THF/water, (6) acetone/water and (7) ethanol/water. An experimental adhesive resin was also synthesized to compare adhesive systems with the different primers. Forty-two bovine incisors, randomly separated into seven groups, had their superficial coronal dentin exposed. After acid-etching and rinsing, the excess water was removed from the surface with absorbent paper. Each experimental primer was applied with agitation (30 s) followed by a mild air stream (10 s). The experimental adhesive resin was applied and light-activated (20 s). Resin composite restorations were constructed incrementally. Restored teeth were stored in distilled water at 37 °C (24 h) and sectioned to obtain sticks with an area of 0.5 mm². Half the specimens were subjected to the μTBS test immediately after being cut and the other half were tested after 6 months of water storage. Data (MPa) were analyzed by two-way ANOVA (solvent type and storage time as factors) and Tukey–Kramer's test at α = 0.05.ResultsFactors and interaction showed a statistical effect. After 6 months storage, acetone groups and primers containing THF showed similar μTBS to initial means.SignificanceTHF seems to be a promising solvent for use in dental adhesive systems, maintaining bond strength on dentin substrate after storage.     

Effect of types of luting agent on push-out bond strength of zirconium oxide posts

ObjectiveThe aim of this study was to investigate the effect of different luting agents on the bond strength of zirconium oxide posts in root canals after artificial ageing.Material and methodsThirty single-rooted extracted teeth were collected. Post spaces were prepared. Custom milled zirconium oxide posts (Cercon, Degudent) were fabricated. Specimens were divided into 3 groups (n = 10), according to the luting agents used: group RA, conventional resin luting agent (RelyX ARC); group RU, self-adhesive resin luting agent (RelyX Unicem); and group Z, zinc phosphate luting agent (DeTrey). Specimens were subjected to thermocycling and water storage at 37 °C. Specimens were horizontally sectioned into three sections and subjected to a push-out test with 0.5 mm/min crosshead speed. The failure mode was assessed by scanning electron microscopy. Data were analysed by using 2-way ANOVA.ResultsThe following bond strength values were obtained: group RA – 8.89 MPa, group RU – 10.30 MPa and group Z – 9.31 MPa. There was no significant difference in bond strength among the groups (P = 0.500). Adhesive failure mode at the cement/post bonded interface was seen in 100%, 66.67% and 83.3% of examined sections in groups RA, RU and Z, respectively. There was no significant difference in bond strength among different root regions (P = 0.367).ConclusionThe type of luting agent had no significant effect on the push-out bond strength of zirconium oxide posts after artificial ageing.Clinical significanceConventional luting agents, such as zinc phosphate cement, seem to provide comparable retention to resin luting agents for cementing custom milled zirconium oxide posts.     

Effect of chlorhexidine application on long-term shear bond strength of resin cements to dentin

PurposeThe purpose of this study was to investigate the effect of chlorhexidine [CH] on dentin bond strength of three resin cements after 1 year of water storage.MethodsA flat middle dentin surface was prepared on 120 extracted premolars. The teeth were randomly divided into 6 groups of 20 specimens each according to the resin cement used: Panavia F2.0, Variolink II, and RelyX Unicem, with or without CH application. After cementation of an indirect composite rod [Z250], one subgroup [n = 10] was tested after 24 h in water at 37 °C and the other subgroup [n = 10] was tested after 1 year storage in water plus thermocycling. A shear bond strength [SBS] test was performed. The data [in MPa] were analyzed with ANOVA and Tukey tests [P < 0.05].ResultsThree-way ANOVA [resin cement, CH and time] indicated that Variolink II had the highest strength [16.65 ± 3.60] and RelyX Unicem had the lowest strength [9.30 ± 4.07]. Chlorhexidine application increased SBS [13.31 ± 4.61] compared to samples without CH [12.16 ± 5.04] [P = 0.04]. Initial SBS [15.63 ± 4.37] was significantly higher than after 1 year of storage [9.85 ± 3.36] [P < 0.001]. Separate two-way ANOVA for 24-h and 1-year data showed that cement had a significant effect but CH and its interaction had no significant effect at 24 h, whereas at 1 year the two factors and their interaction differed significantly [P ≤ 0.001].ConclusionsChlorhexidine 2% can diminish the loss of bonding effectiveness over time associated to etch-and-rinse and self-etch cements, although it appears not have any effect on self-adhesive cement.     

Surface structuring of zirconia to increase fibroblast viability

ObjectiveThe neck area of zirconia implants or abutments is currently either machined, polished and in some cases additionally heat-treated. The aim of the present study was to determine how the surface topography and crystalline structure of zirconia affects the viability of human gingival fibroblasts (HGF-1).MethodsZirconia discs with a diameter of 13 mm were either polished [Zp], polished and heat-treated [Zpt], machined [Zm], machined and heat-treated [Zmt] or sandblasted, etched and heat-treated [Z14] which is the surface topography of the endosseous part of a zirconia implant. The specimen surfaces were analyzed using scanning electron microscopy (SEM), characterized in terms of monoclinic to tetragonal phase ratio, storage effect on wettability and roughness. The viability and morphology of HGF-1 cells was then tested on all surfaces after 24 h.ResultsThe effect of the heat-treatment was visualized for the polished specimens with SEM. Contact angle of water was significantly decreased after 2 weeks air storage of the zirconia. Cell viability was significantly higher on smooth surfaces (Zpt, Zm, Zmt) when compared to Z14. HGF-1 cells spread very flat and attached tightly to the smoother surfaces Zp, Zpt, Zm and Zmt while on Z14, cells did not fully extend into the etched morphology of zirconia and stretched over longer distances.SignificanceFor the structuring of the neck part of zirconia implants or abutments, a smooth surface with exposed grains might be suggested as the optimal substrate for human gingival fibroblasts. The wettability with water of zirconia decreases with prolonged air storage.     

Effects of a fluoride etchant and a phosphate primer on bonding of veneering composite to Ti–6Al–4V alloy for CAD/CAM restorations

PurposeTitanium abutments and superstructures are commonly veneered or covered with esthetic materials. The present investigation was carried out to evaluate the effects of an experimental surface treatment using etchant and primer on bond strength between a resin composite and Ti–6Al–4V alloy.MethodsDisk-shaped Ti–6Al–4V alloy was machine milled, the surface was air abraded with alumina, and the alloy was chemically etched with 5wt% ammonium hydrogen fluoride (F-etch) for 30 s. A phosphate primer (MDP-primer) was applied to the bonding area, and then a resin composite, with or without milled-fiber resin composite (FRC), was veneered on the specimen. Shear bond strengths were determined after thermocycling for 20,000 cycles. Bond strength data were analyzed by means of ANOVA and a multiple comparison test (α = 0.05). The surface of Ti–6Al–4V alloy was observed using a scanning electron microscope before and after the etching procedure.ResultsNo-FRC/F-etch/MDP-primer exhibited the highest bond strength (28.2 MPa), followed by No-FRC/No-etching/MDP-primer (24.2 MPa), FRC/F-etch/MDP-primer (19.9 MPa), FRC/No-etching/MDP-primer (17.8 MPa), No-FRC/No-etching/No-primer (13.6 MPa), while FRC/No-etching/No-primer (2.5 MPa) resulted in the lowest value. Microphotographs showed that numerous micro and nano pits were created on the Ti–6Al–4V alloy surface modified with F-etch.ConclusionsThe bond strength between Ti–6Al–4V alloy and the veneering resin composite was the highest when the alloy surface was modified with alumina blasting, fluoride etchant, and phosphate primer successively.