Influence of the application of a pre-sintered surface augmentation on zirconia and lithium disilicate bonding using an adhesive composite resin cement

ObjectiveThe purpose of this laboratory study is to evaluate the application of a pre-sintered surface augmentation to zirconia (Zir) and lithium disilicate (LDS) ceramics on the delamination strength of adhesive resin cement. The applied surface augmentation was the ruling of lines to the pre-sintered surface of the ceramics.MethodsNinety milled Zir and sixty pressed LDS specimens (3 mm × 0.5 mm × 25 mm) were created and divided into five groups (n = 30). Group 1: Zir no surface treatment (control Zir-NT); Group 2: Zir airborne particle abraded (Zir-APA) with 30 μm CoJet; Group 3: Zir pre-sintered surface augmentation (Zir-SA); Group 4: LDS etched (control LDS-etched) and; Group 5: LDS with pre-sintered surface augmentation and etching (LDS-SA). A resin adhesive cement (3 mm × 1 mm × 8 mm) was then applied and cured to the ceramic specimens. The delamination strength values of the resin cement from the ceramic were recorded. The delamination strength data were analysed statistically using one-way ANOVA and Turkey post hoc analysis.ResultsThe mean delamination strength and standard deviation, when comparing only the Zir-SA to the resin cement were statistically different (p < 0.001); Zir-SA 63.42 ± 11.85, Zir-NT 26.82 ± 12.07, and Zir-APA 48.11 ± 17.85 MPa. Comparison between LDS groups were not significantly different (p = 0.193); LDS-etched 33.49 ± 16.07 and LDS-SA 28.83 ± 10.15 MPa. The delaminated Weibull modulus was highest for surface augmentation Zir specimens (m = 13.56) but decreasing to less than half for Zir-APA (m = 6.27) and Zir-NT (m = 5.68). The Weibull values for the LDS-SA and LDS-etched specimens was 5.63 and 3.38 respectively.SignificanceIncorporating the pre-sintered surface augmentation to zirconia improved the delamination strength and reliability of Zir to the resin cement but not for LDS.     

Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations

ObjectivesDental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations.MethodsOne hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max^® ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (n_x = 60) were divided in three groups (control, aged for 5 h, aged for 10 h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P < 0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ₀). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy.ResultsA slight increase of the flexural strength after 5 h, and a decrease after 10 h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P < 0.05). Both ceramics presented a t → m phase transformation, with the m-phase increasing from 4 to 5% at 5 h to around 15% after 10 h.SignificanceThe significant reduction of the flexural strength after 10 h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested.     

Curing potential and color stability of different resin-based luting materials

PurposeTo determine the curing potential and color stability of resin-based luting materials for aesthetic restorations.Material and MethodsFour resin-based luting agents were tested: traditional dual-activated resin cement (RelyX ARC, ARC), amine-free dual-activated resin cement (RelyX Ultimate, ULT), light-activated resin cement (RelyX Veneer, VEN), and pre-heated restorative resin composite (Filtek Supreme, PHC). Degree of C = C conversion was determined by infrared spectroscopy (n = 3) with direct light exposure or with interposition of 1.5-mm-thick ceramic (e.max Press HT) between the luting material and light. The curing potential considered the ratio between these two scenarios. Color difference (n = 6) was determined by CIELAB (ΔE_ab) and CIEDE2000 (ΔE₀₀) methods, by spectrophotometer measurements made 24 h after photoactivation and 90 days after storage in water. Data was submitted to ANOVA and Tukey’s test (α = 0.05).ResultsThe luting agents affected both conversion and color stability. With ceramic, ARC produced the highest conversion among the tested groups (75 ± 1%) and the pre-heated composite (PHC) the lowest one (51 ± 3%), but the curing potential was similar for all materials. ULT produced lower ΔE_ab than ARC. PHC presented the lowest color difference when considered both CIELAB and CIE2000 methods (ΔE_ab 2.1 ± 0.4; ΔE₀₀ 1.6 ± 0.2).SignificanceAll luting strategies presented high curing potential. Amine-free dual-activated material was able to reduce color difference than that formulated with the amine component. Pre-heated composite produced the least color variation after storage.     

Flexural resistance of heat-pressed and CAD-CAM lithium disilicate with different translucencies

Objective

To compare flexural strength of CAD-CAM and heat-pressed lithium disilicate.

Response of composite resins to preheating and the resulting strengthening of luted feldspar ceramic

ObjectiveThis study evaluated the influence of preheating different composite resins on their viscosity and strengthening yielded to ceramic.MethodsModulus of elasticity, Poisson’s ratio, and degree of CC conversion were measured for three restorative composite resins (Z100–microhybrid; Empress Direct–nanohybrid; Estelite Omega–supranano) and one photoactivated resin cement (RelyX Veneer). Viscosity was measured during a heating-cooling curve (25 °C–69 °C–25 °C) and also using isothermal analyses at 25 °C and 69 °C. Feldspar ceramic disks simulating veneers were bonded with the luting materials. Biaxial flexural strength, characteristic strength, and Weibull modulus were calculated at axial positions (z = 0 and z = −t₂) of the bilayers. Film thickness was measured and morphology at the bonded interfaces was observed. Data were statistically analyzed (α = 0.05).ResultsA gradual decrease in viscosity was noticed as the rheometer temperature gradually increased. Viscosity differences between the composite resins were large at the beginning of the analysis, but minor at 69 °C. At 25 °C, the composites were up to 38 times more viscous than the resin cement; at 69 °C the difference was 5-fold. CC conversion was similar between all resin-based agents. The resin cement yielded lower film thickness than the composites. All resin-based agents were able to infiltrate the ceramic porosities at the interface and strengthen the ceramic. However, the magnitude of the strengthening effect was higher for the preheated composite resins, particularly at z = −t₂.SignificanceSelection of composite resin impacts its response to preheating and the resulting viscosity, film thickness, and magnitude of ceramic strengthening.     

Effect of sandblasting,etching and resin bonding on the flexural strength/bonding of novel glass-ceramics

Objectives

To process novel leucite glass-ceramics and test the effects of surface treatment and resin bonding on the biaxial flexural strength (BFS) and shear bond strength (SBS).

Effect of thermal cycling on flexural properties of carbon–graphite fiber-reinforced polymers

ObjectivesTo determine flexural strength and modulus after water storage and thermal cycling of carbon–graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM).MethodsSolvent cleaned carbon–graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58 wt% (20, 29, 38 and 47 vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 °C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM.ResultsHydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36 wt% fiber loadings; flexural strength values after thermocycling were 244.8 (±32.33) MPa for 24 wt% and 441.3 (±68.96) MPa for 36 wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (±45.32) MPa) and 58 wt% (310.4 (±52.79) MPa).SEM revealed good adhesion between fibers and matrix for all fiber loadings examined.ConclusionsThe combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36 wt% appear promising for prosthodontic applications such as implant-retained prostheses.     

An in vitro comparison of four intra-oral ceramic repair systems

ObjectivesThis study evaluated the effect of different surface conditioning methods on the tensile bond strength (TBS) and integrity of the leucite-reinforced glass ceramic (Cerana^® inserts)–resin composite interface, using four commercially available ceramic repair systems.MethodsTwo hundred extra-large Cerana^® inserts were mechanically treated and stored in artificial saliva for 3 weeks and subsequently randomly assigned to one of the following ceramic repair systems (n = 40/group): Group 1, Ceramic Repair^® (Ivoclar Vivadent, Liechtenstein); Group 2, Cimara^® (Voco, Germany); Group 3, Clearfil Repair^® (Kuraray, Japan); Group 4, CoJet system^® (3M ESPE, Germany); and Group 5, no surface conditioning and no adhesive system applied: the control group. Subsequently, resin composite material was added to the substrate surfaces and the ceramic–resin composite specimens were subjected to TBS testing. Representative samples from the test groups were subjected to scanning electron microscopy (SEM) to determine the mode of failure. The data were analysed statistically using a one-way multivariate analysis of variance and Kruskal–Wallis test at a 95% confidence interval level.ResultsSurface conditioning with the CoJet^® system resulted in significantly higher bond strength values (5.2 ± 1.1 MPa) than surface conditioning with the other repair systems (p = 0.03). The SEM examination of the failed interfaces revealed that all the specimens examined failed adhesively.SignificanceWhilst highest bond strength values were observed with the CoJet^® system all tested repair systems resulted in relatively weak TBS values and, as a consequence, these repair systems may be indicated only as interim measures.     

Effects of low-energy electron beam irradiation on flexural properties of self-curing acrylic resin

PurposeThe purpose of this study was to confirm the effectiveness of LEB irradiation onto the polymer powder for improving the mechanical properties of self-curing acrylic resin.MethodsThe polymer powder of self-curing acrylic resin was irradiated with total LEB doses of 25, 50, 75 or 100 kGy. Non-irradiated powder was used as a control. After LEB irradiation, ESR measurement, weight-average molecular weight measurement and three-point bending test were performed.ResultsESR spectrum of control had no peaks. After LEB irradiation, nine peaks were observed in each ESR spectrum, which indicates the presence of free radicals from main polymer chain. The quantity of free radicals increased linearly up to 100 kGy. Calibrated weight-average molecular weights were as follows: control, 960,000; 25 kGy, 500,000; 50 kGy, 440,000; 75 kGy, 410,000; and 100 kGy, 390,000. Molecular weight decreased with increasing LEB irradiation dose. The mean values of flexural strength (MPa) were as follows: control, 61.5 ± 3.0; 25 kGy, 68.1 ± 4.0; 50 kGy, 73.0 ± 1.9; 75 kGy, 70.4 ± 3.6; and 100 kGy, 67.7 ± 2.3. The flexural strength of the specimens cured with the LEB-irradiated powder was significantly higher than that of control (p < 0.01). These results indicate that flexural strength of polymer materials cured with the LEB-irradiated powder increases because of increase in cross-linking structure.ConclusionIt is confirmed that LEB irradiation onto the polymer powder of self-curing acrylic resin improves the flexural strength.     

The development and testing of glaze materials for application to the fit surface of dental ceramic restorations

ObjectivesThe aims of the study were to develop and test overglaze materials for application to the fit surface of dental ceramic restorations, which could be etched and adhesively bonded and increase the flexural strength of the ceramic substrate.MethodsThree glaze materials were developed using commercial glass powders (P25 and P54, Pemco, Canada). P25 (90 wt%) was mixed with P54 (10 wt%) to produce (P25/P54). P54 (90 wt%) was mixed with P25 (10 wt%) to produce (P54/P25). P25 (90 wt%) was mixed with 10 wt% of an experimental glass powder (P25/frit). Eighty-two disc specimens (14 mm × 2 mm) were produced by heat pressing a leucite glass–ceramic and were sandblasted with 50 μm glass beads. Group 1 control specimens (10) were sandblasted. Groups 2–4 (10 per group) were coated using P25/frit (Group 2), P25/P54 (Group 3) and P54/P25 (Group 4) overglazes before sintering. Groups 1–4 were etched for 2 min using 9.5% HF (Gresco, USA). Composite cylinders (Marathon^® v, Den-Mat) were light cured and bonded to the glazed and prepared disc surfaces and groups water stored for 8 days. Groups were tested using shear bond strength (SBS) testing at 0.5 mm/min. Disc specimens (42) were tested using the biaxial flexural strength (BFS) test at a crosshead speed of 0.15 mm/min. Group 1 was tested as sandblasted (21) and Group 2 (21) after coating the tensile surface with P25/frit. Xrd, Eds and Sem analyzes were carried out.ResultsMean SBS (MPa ± S.D.) were: Group 1: 10.7 ± 2.1; Group 2: 9.8 ± 1.9; Group 3: 1.8 ± 1.0 and Group 4: 2.6 ± 1.7. Groups 1 and 2 were statistically different to Groups 3 and 4 (p < 0.001), but there was no difference between Groups 1 and 2 and 3 and 4 (p > 0.05). The mean BFS (MPa ± S.D.) of the overglazed Group 2 (200.2 ± 22.9) was statistically different (p < 0.001) to Group 1 (150.4 ± 14.3).SignificanceThe P25/frit overglaze significantly (p < 0.001) increased the biaxial flexural strength of the leucite glass–ceramic substrate and produced comparable shear bond strengths to an etched and bonded control. The application of etched overglaze materials to dental glass–ceramic and ceramic substrates may be useful in adhesive dentistry.     

Evaluation of physical properties of fiber-reinforced composite resin

ObjectivesThis study aimed to investigate physical properties of a fiber-reinforced CAD/CAM resin disc, which included woven layers of multi-directional glass fibers.MethodsFiber orientations of CAD/CAM specimens (TRINIA, SHOFU) were specified as longitudinal (L), longitudinal-rotated (LR), and anti-longitudinal (AL). A fiber-reinforced composite (everX posterior, GC (E)) and a conventional composite (Beauti core flow paste, SHOFU (B)) were also tested.A three-point bending test and a tensile test with notchless prism-shaped specimens were conducted using a universal testing machine (AUTOGRAPH AG-IS, Shimadzu). A water absorption test was also carried out after the specimens were stored in water for 24 h or 1 week. Flexural strength and fracture toughness were obtained by conducting a three-point bending test.ResultsTRINIA L and LR groups showed significantly high flexural strength (254.2 ± 22.3 and 248.8 ± 16.7 MPa, respectively). Those were approximately 2.5 times higher than those in AL, E, and B groups (96.8–98.0 MPa) (p < 0.05, ANOVA and Tukey HSD test). No significant difference was shown in flexural modulus among the experimental groups. The fracture toughness in L group (9.1 ± 0.4 MPa/m^1/2) was found to be significantly higher than those in other groups (1.9–3.0 MPa/m^1/2; p < 0.05). TRINIA group demonstrated significantly lower water absorption (4.7 ± 1.9 μg/mm³) than did E (16.1 ± 3.1 μg/mm³) and B (17.3 ± 3.7 μg/mm³) groups (p < 0.05).SignificanceTRINIA demonstrated distinct anisotropy. TRINIA can be used as a superior restorative material when specifying directions of its fiber mesh layers.     

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.     

Effect of denture cleansers on physical properties of heat-polymerized acrylic resin

PurposeThis study aimed to measure the color change, surface roughness and flexural strength of heat-polymerized acrylic resin after its immersion in denture cleansers, simulating a 180-day use.MethodsThirty disk-shaped (15 mm × 4 mm) and 30 rectangular samples (65 mm × 10 mm × 3.3 mm) were prepared from heat-polymerized acrylic resin and immersed in Corega Tabs, Bony Plus, and distilled water. Color measurements (ΔE) were determined by a portable colorimeter. A surface analyzer was used to measure the roughness before and after immersion (ΔRa). The flexural strength (S) was measured using a 3-point bending test. The ΔE values were submitted to statistical analysis by the Kruskal–Wallis test, followed by Dunn's Multiple Comparisons test. The ΔRa and S values were submitted to statistical analysis by ANOVA, followed by a Student–Newman–Keuls test (α = .05).ResultsThe color changes were significantly higher for the Corega Tabs than for the control group. The mean ΔE values quantified by the National Bureau of Standards (NBS) were classified as Trace (0.0–0.5). The Bony Plus group had significantly higher surface roughness than the other groups. Corega Tabs and Bony Plus groups presented lower flexural strength than the control group.ConclusionsAlthough the color changes after the immersion in denture cleansers were clinically insignificant, the Corega Tabs group showed higher color differences. The Bony Plus group showed significantly increased surface roughness. Both effervescent tablets Corega Tabs and Bony Plus significantly diminished the flexural strength of the acrylic resin.     

Effect of finishing/polishing techniques and low temperature degradation on the surface topography,phase transformation and flexural strength of ultra-translucent ZrO2 ceramic

ObjectiveTo investigate the effect of different surface finishing and polishing regimes and low temperature degradation on flexural strength, phase transformation and surface topography of ultra-translucent ZrO₂ ceramic.Methods300 (n = 15/group) of conventional zirconia (Z: Ice Zirkon Transluzent) and ultra-translucent zirconia (UT: Prettau Anterior) bar-specimens were made and divided according to the "Finishing/Polishing" - (C — Control, B — diamond rubber polishers, P — adjusting with burs, PB — adjusting with burs + diamond polishers, PG — adjusting with burs + glaze), "Low temperature Degradation (LTD)" (with or without a treatment at 127 °C, 1.7 bar/24 h). Then, a 3-point mini flexural test was performed in a universal testing machine (1 mm/min, 500 kgf load cell). SEM, EDS, XDR, AFM, optical profilometry and Weibull analysis were performed. Data were analyzed by 3-way ANOVA and Tukey’s post-test (5%).ResultsGroups ZPB_D (1670 ± 253 MPa), ZB_D (1664 ± 217 MPa), and ZB (1655 ± 3678 MPa) showed significantly higher flexural strength than the UTPG group (372 ± 56 MPa). The Weibull modulus was significantly higher for the ZP_D group compared to the UB, UC_D, UP_D and UPB_D, while UTB, UTC_D and UTP_D had the lowest value. Monoclinic phases were observed only in the conventional zirconia groups and were more evident after LTD. Diamond rubber polishers presented less roughness for both zirconias.SignificanceThe use of diamond rubber polishers is the most suitable finishing/polishing method for zirconia ceramic restorations and that final glazing reduces the fracture resistance of these materials.     

Manufacture,characterisation and properties of novel fluorcanasite glass–ceramics

ObjectiveThe aim of this study was to investigate the manufacture and characterisation of different compositions of fluorcanasite glass–ceramics with reduced fluorine content and to assess their mechanical and physical properties.MethodsThree compositional variations (S80, S81 and S82) of a fluorcanasite glass were investigated. Differential thermal analysis (DTA) and X-ray diffraction (XRD) identified crystallisation temperatures and phases. X-ray fluorescence (XRF) determined the element composition in the glass–ceramics. Different heat treatments [2 h nucleation and either 2 or 4 h crystallisation] were used for the glasses. Scanning electron microscopy (SEM) examined the microstructure of the cerammed glass. The chemical solubility, biaxial flexural strength, fracture toughness, hardness and brittleness index of S81 and S82 fluorcanasite were investigated with lithium disilicate (e.max CAD, Ivoclar Vivadent) as a commercial comparison. Statistical analysis was performed using one-way ANOVA with Tukey's multiple comparison tests (P < 0.05). Weibull analysis was employed to examine the reliability of the strength data.ResultsAll compositions successfully produced glasses. XRD analysis confirmed fluorcanasite formation with the S81 and S82 compositions, with the S82 (2 + 2 h) showing the most prominent crystal structure. The chemical solubility of the glass–ceramics was significantly different, varying from 2565 ± 507 μg/cm² for the S81 (2 + 2 h) to 722 ± 177 μg/cm² for the S82 (2 + 2 h) to 37.4 ± 25.2 μg/cm² for the lithium disilicate. BFS values were highest for the S82 (2 + 2 h) composition (250 ± 26 MPa) and lithium disilicate (266 ± 37 MPa) glass–ceramics. The fracture toughness was higher for the S82 compositions, with the S82 (2 + 2 h) attaining the highest value of 4.2 ± 0.3 MPa m^1/2(P = 0.01). The S82 (2 + 2 h) fluorcanasite glass–ceramic had the lowest brittleness index.ConclusionThe S82 (2 + 2 h) fluorcanasite glass–ceramic has acceptable chemical solubility, high biaxial flexural strength, fracture toughness and hardness.Clinical significanceA novel glass–ceramic has been developed with potential as a restorative material. The S82 (2 + 2 h) has mechanical and physical properties that would allow the glass–ceramic to be used as a machinable core material for veneered resin-bonded ceramic restorations.     

Effect of repeated firings and staining on the mechanical behavior and composition of lithium disilicate

ObjectiveTo evaluate the composition, flexural strength and fatigue behaviour of lithium disilicate ceramic (LD) after repeated firings and different staining techniques.MethodsLD discs were fabricated and divided according to number of firing cycles and staining technique: CO - control, discs were crystallized (850 °C/10 min); SC – single-step characterization – crystallization and staining (applied with a thin brush) were performed in a single step with one firing cycle (850 °C/10 min); and DC – double-step characterization – crystallization firing cycle was performed first (850 °C/10 min), followed by staining firing cycle (770 °C/90 s). Specimens were fired two, four or six times (one crystallization firing cycle and one, three or five staining firing cycles), resulting into 9 groups (n = 30): COII, COIV, COVI, SCII, SCIV, SCVI, DCII, DCIV and DCVI. The composition of the specimens was investigated (EDS, XRD, Raman spectroscopy), and the biaxial flexural strength (n = 10) and staircase tests (n = 20, 5 × 10⁴ cycles, 5 Hz) were performed. Data were subjected to one-way ANOVA and Tukey’s test (α = 0.05).ResultsEDS and XRD revealed amorphous content for stained groups. Biaxial flexural strength was not affected by repeated firings in any group, but stained groups presented lower flexural strength than control groups (p = 0.001). The fatigue limit results decreased in all groups compared to flexural strength. SC groups showed similar (SCII and SCIV) or even higher fatigue limits (SCVI) than the control groups, and DC showed the lowest fatigue limit values. SEM and Raman suggested that the interfaces between staining and the LD showed only an overlap for the DC groups, whereas for the SC it was suggested an interaction between the stain and the LD.SignificanceRepeated firings did not result in decreased lithium disilicate flexural strength.Staining affected flexural strength and also resulted in increased amorphous content in the characterized specimens. Single-step staining resulted in the highest fatigue limit.     

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.     

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.     

Curing efficiency of four self-etching,self-adhesive resin cements

ObjectivesTo evaluate the degree of cure (%DC) of four self-etching, self-adhesive resin cements, and one conventional resin cement, in their self- and dual-curing mode.MethodsThe self-etching, self-adhesive resin cements studied were RelyX? Unicem (3M? ESPE? AG), Maxcem? (Kerr Corporation), Biscem? (Bisco, Inc.) and Multilink^® Sprint (Ivoclar Vivadent^® AG) and the classic resin cement was Multilink^® Automix (Ivoclar Vivadent^® AG). Twelve specimens of each material (1.8 mm × 4 mm × 4 mm) were prepared in room temperature (23 ± 1) °C following the manufacturers’ instructions. Six of them were treated as dual-cured, thus irradiated for 20 s with a halogen light curing unit and left undisturbed for 5 min. The other six were treated as self-cured and were not irradiated, but left in dark and dry conditions for 10 min. The assessment of the %DC was made using micro-ATR FTIR spectrometry.ResultsThe %DC in their self-curing mode was very low (10.82–24.93%), with Multilink Sprint exhibiting the highest values among the five. In the dual-curing mode the values obtained were also low (26.40–41.52%), with the exception of Multilink Automix (61.36%). Maxcem was found to have the lowest DC.SignificanceThe low %DC found raises questions as to whether these materials can be successfully used in clinical applications, where light attenuation takes place. Increased irradiation times could potentially lead to higher %DC, in applications where light is not completely blocked by the overlying restoration.     

Impact of thermal misfit on shear strength of veneering ceramic/zirconia composites

ObjectivesThermal misfit is discussed as one reason for chipping of veneered zirconia restorations. The aim of the investigation was to assess the effect of thermal misfit on the shear strength of zirconia/veneering ceramic composites.MethodsShear strengths of 12 different veneering ceramic/zirconia composites were measured (n = 10). The veneering ceramics were fired onto polished Y-TZP. In order to create a strong thermal mismatch, one of the veneering ceramics was intended for use on alumina and one for the metal–ceramic technique. The glass transition temperatures of the veneering ceramics and the coefficients of thermal expansion of all ceramics were measured (n = 6). Statistical analysis was performed with one-way ANOVA and a post hoc Bonferroni test (p < 0.05).ResultsShear strength ranged from 21.9 ± 6.2 to 31.0 ± 7.1 MPa. The ceramic for the metal–ceramic technique showed spontaneous debonding. The differences in the coefficients of thermal expansion of core and veneer (Δα) were calculated. In addition the differences between glass transition temperatures of the veneering ceramics and room temperature (ΔT) as the effective temperature range for stress formation were calculated. Highest shear strength was observed when ΔαΔT ≈ 1000 × 10^?6.ConclusionsThermal expansion and glass transition temperature of the veneering ceramic have an impact on the shear strength of veneer/zirconia composites.