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.     

Can a soda-lime glass be used to demonstrate how patterns of strength dependence are influenced by pre-cementation and resin-cementation variables?

ObjectivesTo determine how the variability in biaxial flexure strength of a soda-lime glass analogue for a PLV and DBC material was influenced by precementation operative variables and following resin-cement coating.MethodsThe flexural modulus of a transparent soda-lime glass was determined by longitudinally sectioning into rectangular bar-shaped specimens and the flexural moduli of three resin-based materials (Venus Flow, Rely-X Veneer and Clearfil Majesty Posterior) was also determined. Disc shaped soda-lime glass specimens (n = 240) were divided into ten groups and were alumina particle air abraded, hydrofluoric (HF) acid-etched and resin-cement coated prior to biaxial flexure strength testing. Sample sets were profilometrically evaluated to determine the surface texture. One-way analyses of variance (ANOVA) and post hoc all paired Tukey tests were performed at a significance level of P < 0.05. The mean biaxial flexure strengths were plotted against resin-coating thickness and a regression analysis enabled estimation of the ‘actual’ magnitude of strengthening.ResultsThe mean three-point flexural modulus of the soda-lime glass was 40.0 (1.0) GPa and the Venus Flow, Rely-X Veneer and Clearfil Majesty Posterior were 3.0 (0.2) GPa, 6.0 (0.2) GPa and 14.8 (1.6) GPa, respectively. At a theoretical ‘zero’ resin-coating thickness an increase in biaxial flexure strength of 20.1% (63.2 MPa), 30.8% (68.8 MPa) and 36.3% (71.7 MPa), respectively was evident compared with the control (52.6 (5.5) MPa).ConclusionsDisc-shaped specimens cut from round stock facilitated rapid fabrication of discs with uniform surface condition and demonstrated strength dependence was influenced by precementation parameters and resin-cementation variables.     

Experimental composites of polyacrilonitrile-electrospun nanofibers containing nanocrystal cellulose

ObjectiveTo test the effects of addition of polyacrilonitrile (PAN) nanofibers and nanocrystal cellulose (NCC)-containing PAN nanofibers on flexural properties of experimental dental composites.Methods11 wt% PAN in dimethylformamide (DMF) solution was electrospun at 17.2 kVA and 20 cm from the collector drum. NCC was added to the solution at 3 wt%. Fiber mats were produced in triplicates and tested as-spun. Strips (5 cm × 0.5 cm) were cut from the mat in an orientation parallel and perpendicular to the rotational direction of the collector drum. Tensile tests were performed and ultimate tensile strength (UTS), elastic modulus (E) and elongation at maximum stress (%) were calculated from stress/strain plots. Fiber mats were then infiltrated by resin monomers (50/50 BisGMA/TEGDMA wt%), stacked in a mold (2 × 15 × 25) and light-cured. Beams (2 × 2 × 25 mm) were cut from the slabs and tested in a universal testing machine. Data were analyzed by multiple t-test and one-way ANOVA (α = 0.05).ResultsAddition of 3% NCC resulted in higher tensile properties of the fibers. Fibers presented anisotropic behavior with higher UTS and E when tested in perpendicular orientation. The incorporation of 3% NCC–PAN nanofibers resulted in significant increase in work of fracture and flexural strength of experimental dental composite beams.SignificanceNCC was found to be a suitable nanoparticle to reinforce experimental dental composites by incorporation via nanofiber. This fundamental study warrants future investigation in the use of electrospun nanofibres as a way to reinforce dental composites.     

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.     

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

ObjectiveTo fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers.MethodsPRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30 wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60 wt%) by PRG-Ca fillers (wt%): E0 (0) – control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (W_sp), water solubility (W_sl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey’s HSD test (α = 0.05).ResultsAll composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2 = E3 = E4 = E5 = E6. Ra and KHN were not influenced by PRG-Ca fillers (p < 0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p < 0.05). W_sp increased linearly with the content of PRG-Ca fillers (p < 0.05). E6 presented the highest W_sl (p < 0.05), while the W_sl of the other composites were not different from each other (p > 0.05).SignificanceIncorporation of 10–40 wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.     

Effect of silanized nanosilica addition on remineralizing and mechanical properties of experimental composite materials with amorphous calcium phosphate

Objectives

Experimental composite resins with amorphous calcium phosphate (ACP) have the potential to regenerate demineralized tooth structures. The aim of the study was to investigate the effect of the addition of silanized silica nanofillers to the ACP-based composites on their mechanical properties and the kinetics of calcium and phosphate release.

Materials and methods

The test materials comprised 5 wt% (5-ACP) or 10 wt% (10-ACP) of silanized silica admixed to the 40 wt% ACP and 50 or 55 wt% resin. The ACP control (0-ACP) contained 40 wt% ACP and 60 wt% resin. Additionally, composite material CeramX (Dentsply, Germany) was included as control. Three-point bending test was performed to calculate flexural strength and modulus of elasticity. Inductively coupled plasma atomic emission spectroscopy was used for measurement of ion release. The micromorphology of calcium phosphate depositions on composite samples has been qualitatively evaluated using a scanning electron microscope. The results were analyzed using Mann–Whitney and Wilcoxon rank sum tests (α?<?0.05).

Results

Ion release was enhanced by the silica fillers, when compared to the 0-ACP. Although not statistically significant, flexural strength of 10-ACP was improved by 46 % compared to 0-ACP. Flexural modulus of 5-ACP was significantly higher than 0-ACP.

Conclusions

The admixture of silanized fillers seems to be a promising approach for the improvement of mechanical and remineralizing properties of ACP composite resins.

Clinical relevance

ACP-based composite resins with modified composition could serve as an effective remineralizing aid as base materials in restorative dental medicine.     

Effect of the amount of 3-methacyloxypropyltrimethoxysilane coupling agent on physical properties of dental resin nanocomposites

ObjectivesThe purpose of this study was to evaluate the effect of the amount of 3-methacryloxypropyl-trimethoxysilane (γ-MPS) coupling agent on some physical–mechanical properties of an experimental resin composite for understanding the optimum amount of silanization.MethodsSilica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of γ-MPS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water solution. Thermogravimetric analysis was performed in air and in nitrogen atmosphere from 50 to 800 °C.ResultsAt lower silane amounts used (1.0, 2.5 wt%) the silane molecules must have a parallel orientation relative to the silica surface. At higher silane amounts (>2.5 wt%) silane molecules form a layer around the filler particles which now have to occupy a random, parallel and perpendicularly orientation relative to the silica surface. No significant statistic difference was found to exist between the flexural strength and flexural modulus values of composites with different silane contents. Dynamic elastic modulus E′ showed a maximum value for the composite contained 5 wt% silane. The composites with the higher amounts of silane showed the lower values for the tan δ at the T_g revealing that these composites have better interfacial adhesion between filler and matrix.SignificanceThe amount of silane used for the silanization of silica particles affect the orientation of the silane molecules relative to the silica surface. This seems to affect the dynamic mechanical properties of composites.     

A comparison of stress relaxation in temporary and permanent luting cements

PurposeThe stress relaxation and compressive strength of resin, resin-modified glass ionomer, glass ionomer, polycarboxylate, and zinc oxide eugenol cements were measured to determine the characteristics of these materials after setting.MethodsA total of 19 luting cements including 12 permanent cements and 7 temporary cements were used. Cylindrical cement specimens (10 mm long and 6 mm in diameter) were obtained by chemical setting or light curing. The specimens were stored for 24–36 h in water at 37 °C and were then used for the stress relaxation and compression tests. The stress relaxation test was carried out using three constant cross-head speeds of 5, 50, and 100 mm/min. Upon reaching the preset dislocation of 0.5 mm, the cross-head movement was stopped, and the load was recorded for 60 s. Fractional stress loss at 1 s was calculated from the relaxation curves. The compressive strength and modulus were measured at a cross-head speed of 1 mm/min. Data were analyzed with the Kruskal–Wallis test and Holm's test.ResultsA zinc oxide eugenol cement [TempBOND NX] exhibited the largest fractional stress loss. A resin cement [ResiCem] showed the largest compressive strength, while a glass ionomer cement [HY-BOND GLASIONOMER CX] showed the largest compressive modulus among all tested cements (p < 0.05).ConclusionThe fractional stress loss could not be classified by the cement type. Two implant cements [Multilink Implant and IP Temp Cement] showed similar properties with permanent resin cements and temporary glass ionomer cements, respectively. Careful consideration of the choice of cement is necessary.     

Preparation of Zn doped mesoporous silica nanoparticles (Zn-MSNs) for the improvement of mechanical and antibacterial properties of dental resin composites

ObjectiveThe purpose of this work was to explore the enhancement effect of zinc doped mesoporous silica nanoparticles (Zn-MSNs), which could form micromechanical interlocking with resin matrix and sustainably release Zn²⁺, on the mechanical and antibacterial properties of the dental resin composites.MethodsZn-MSNs were prepared by a sol–gel method, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂ adsorption/desorption. The mechanical properties of the dental composites reinforced by Zn-MSNs were measured by a universal mechanical testing machine. Antibacterial activities of dental composites were evaluated by both qualitative and quantitative analysis using Streptococcus mutans (S. mutans). The cytotoxicity of the Zn-MSNs filled dental composites was investigated by osteoblasts (OBs).ResultsThe synthesized Zn-MSNs possessed good monodispersity with an average particle size of about 138 nm. The mechanical properties of the composites gradually increased with the increase of the content of Zn-MSNs. The flexural strength, flexural modulus, compressive strength and micro-hardness of the composites containing 15 wt% Zn-MSNs were 31.21%, 50.47%, 53.83% and 26.79% higher than the samples with no Zn-MSNs, respectively. The antibacterial performance was significantly improved by the addition of Zn-MSNs and the antibacterial rate of the composite with 15 wt% of Zn-MSNs reached 100%. Cytotoxicity tests revealed that all the composites were biocompatible during OBs incubation.SignificanceThe prepared Zn-MSNs can effectively improve the mechanical and antibacterial properties of the dental resin composites.     

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.     

Effects of aging procedures on the topographic surface,structural stability,and mechanical strength of a ZrO2-based dental ceramic

ObjectiveTo determine the effects of different aging methods on the degradation and flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP)MethodsSixty disc-shaped specimens (∅, 12 mm; thickness, 1.6 mm) of zirconia (Vita InCeram 2000 YZ Cubes, VITA Zahnfabrik) were prepared (ISO 6872) and randomly divided into five groups, according to the aging procedures (n = 10): (C) control; (M) mechanical cycling (15,000,000 cycles/3.8 Hz/200 N); (T) thermal cycling (6,000 cycles/5–55 °C/30 s); (TM) thermomechanical cycling (1,200,000 cycles/3.8 Hz/200 N with temperature range from 5 °C to 55 °C for 60 s each); (AUT) 12 h in autoclave at 134 °C/2 bars; and (STO) storage in distilled water (37 °C/400 days). After the aging procedures, the monoclinic phase percentages were evaluated by X-ray diffraction (XRD), and topographic surface analysis was performed by 3D profilometry. The specimens were then subjected to biaxial flexure testing (1 mm/min, load 100 kgf, in water). The biaxial flexural strength data (MPa) were analyzed by 1-way ANOVA and Tukey's test (α = 0.05). The data for monoclinic phase percentage and profilometry (Ra) were analyzed by Kruskal–Wallis and Dunn's tests.ResultsANOVA revealed that flexural strength was affected by the aging procedures (p = 0.002). The M (781.6 MPa) and TM (771.3 MPa) groups presented lower values of flexural strength than did C (955 MPa), AUT (955.8 MPa), T (960.8 MPa) and STO (910.4 MPa). The monoclinic phase percentage was significantly higher only for STO (12.22%) and AUT (29.97%) when compared with that of the control group (Kruskal–Wallis test, p = 0.004). In addition, the surface roughnesses were similar among the groups (p = 0.165).SignificanceWater storage for 400 days and autoclave aging procedures induced higher phase transformation from tetragonal to monoclinic; however, they did not affect the flexural strength of Y-TZP ceramic, which decreased only after mechanical and thermomechanical cycling.     

Mechanical properties of dental resin/composite containing urchin-like hydroxyapatite

ObjectivesTo investigate the reinforcing effect of urchin-like hydroxyapatite (UHA) in bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) dental resin (without silica nanoparticles) and dental composites (with silica nanoparticles), and explore the effect of HA filler morphologies and loadings on the mechanical properties.MethodsUHA was synthesized by a facile method of microwave irradiation and studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). Mechanical properties of the dental resin composites containing silanized UHA were tested by a universal mechanical testing machine. Analysis of variance was used for the statistical analysis of the acquired data. The fracture morphologies of tested composites were observed by SEM. Composites with silanized irregular particulate hydroxyapatite (IPHA) and hydroxyapatite whisker (HW) were prepared for comparative studies.ResultsImpregnation of lower loadings (5 wt% and 10 wt%) of silanized UHA into dental resin (without silica nanoparticles) substantially improved the mechanical properties; higher UHA loadings (20 wt% and 30 wt%) of impregnation continuously improved the flexural modulus and microhardness, while the strength would no longer be increased. Compared with silanized IPHA and HW, silanized UHA consisting of rods extending radially from center were embedded into the matrix closely and well dispersed in the composite, increasing filler-matrix interfacial contact area and combination. At higher filler loadings, UHA interlaced together tightly without affecting the mobility of monomer inside, which might bear higher loads during fracture of the composite, leading to higher strengths than those of dental resins with IPHA and HW. Besides, impregnation of silanized UHA into dental composites (with silica nanoparticles) significantly improved the strength and modulus.SignificanceUHA could serve as novel reinforcing HA filler to improve the mechanical properties of dental resin and dental composite.     

Mechanical properties of experimental dental composites containing a combination of mesoporous and nonporous spherical silica as fillers

ObjectivesMesoporous fillers have been investigated for use in dental composites because of their potential for creating micromechanical filler/resin matrix interphase bonding. Such a micromechanical bonding could eliminate the need for the silane treatment of fillers for interfacial chemical bonding that is prone to hydrolysis in the oral environment. In the case of micromechanical bonding, dental polymer chains are threaded mechanically (like a “necklace”) through nanosized channels in the fillers.MethodsA combination of mesoporous silica, which was synthesized using the non-surfactant templating method, and nonporous spherical silica (500 nm) was used to prepare experimental dental composites. The porous silica used in this study contained interconnected pores and channels as opposed to porous fillers containing surface pores. The compressive strength, compressive modulus, flexural modulus, and flexural strength of these composites were evaluated.ResultsThe results showed that composites containing a combination of mesoporous and nonporous fillers have better mechanical properties than the composites having either of these fillers alone.SignificanceThe results showed that a combination of mesoporous and nonporous materials can be used to prepare stronger dental materials that may resist hydrolysis and wear.     

Curing potential of experimental resin composites filled with bioactive glass: A comparison between Bis-EMA and UDMA based resin systems

ObjectivesTo evaluate the degree of conversion, light transmittance, and depth of cure of two experimental light-curable bioactive glass (BG)-containing composite series based on different resin systems.MethodsExperimental composite series based on either Bis-EMA or UDMA resin were prepared. Each series contained 0, 5, 10, 20, and 40 wt% of BG 45S5. Reinforcing fillers were added up to a total filler load of 70 wt%. The degree of conversion was evaluated using Raman spectroscopy, while light transmittance was measured using visible light spectroscopy. The depth of cure was estimated from the degree of conversion data and using the ISO 4049 scraping test.ResultsReplacement of reinforcing fillers with BG can diminish the degree of conversion, light transmittance, and depth of cure. The effect of BG on the aforementioned properties was highly variable between the experimental series. While in the Bis-EMA series, the degree of conversion was significantly impaired by BG, all of the composites in the UDMA series attained clinically acceptable degree of conversion values. The reduction of the degree of conversion in the Bis-EMA series occurred independently of the changes in light transmittance. The UDMA series showed better light transmittance and consequently higher depth of cure than the Bis-EMA series. The depth of cure for all composites in the UDMA series was above 2 mm.SignificanceWhile the Bis-EMA series demonstrated clinically acceptable curing potential only for 0–10 wt% of BG loading, an excellent curing potential in the UDMA series was observed for a wide range (0–40 wt%) of BG loadings.     

Effect of etching time and resin bond on the flexural strength of IPS e.max Press glass ceramic

ObjectiveTo evaluate the effect of hydrofluoric acid (HFA) etching time and resin cement bond on the flexural strength of IPS e.max^® Press glass ceramic.MethodsTwo hundred and ten bars, 25 mm × 3 mm × 2 mm, were made from IPS e.max^® Press ingots through lost-wax, hot-pressed ceramic fabrication technology and randomly divided into five groups with forty-two per group after polishing. The ceramic surfaces of different groups were etched by 9.5% hydrofluoric acid gel for 0, 20, 40, 60 and 120 s respectively. Two specimens of each group were selected randomly to examine the surface roughness and 3-dimensional topography with atomic force microscope (AFM), and microstructure was analyzed by the field emission scanning electron microscope (FE-SEM). Then each group were subdivided into two subgroups (n = 20). One subgroup of this material was selected to receive a thin (approximately 0.1 mm) layer of resin luting agent (Variolink N) whereas the other subgroup remained unaltered. Half of subgroup's specimens were thermocycled 10,000 times before a 3-point bending test in order to determine the flexural strength. Interface between resin cement and ceramic was examined with field emission scanning electronic microscope.ResultsRoughness values increased with increasing etching time. The mean flexural strength values of group 0 s, 20 s, 40 s, 60 s and 120 s were 384 ± 33, 347 ± 43, 330 ± 53, 327 ± 67 and 317 ± 41 MPa respectively. Increasing HF etching times reduced the mean flexural strength (p < 0.05). However, the mean flexural strength of each group, except group 0 s, increased significantly to 420 ± 31, 435 ± 50, 400 ± 39 and 412 ± 58 MPa after the application of dual-curing resin cement. In the present investigation, no significant differences after thermocycling on the flexural strengths were evident.SignificanceOvertime HF etching could have a wakening effect on IPS e.max^® Press glass ceramic, but resin cement bonding to appropriately etched surface would strengthen the dental ceramic.     

Comparison of four silane primers and an isocyanate primer for bonding of tri-n-butylborane resin to a leucite-reinforced glass ceramic

PurposeThe purpose of the present study was to compare the effectiveness of an isocyanate monomer and four different silane monomers as primer components for bonding a leucite-reinforced glass ceramic (GN-Ceram Block).MethodsFour different methyl-methacrylate based primers, each with three different concentrations (1, 4, or 16wt%) of 2-methacryloxyethylisocyanate (MOI), 3-methacryloxypropylmethyldimethoxysilane (MDS), 3-methacryloxypropyltrimethoxysilane (MTS), and 3-acryloxypropyltrimethoxysilane (ATS) were prepared. A commercially available silane primer (ESPE?Sil) was also used as a control. The GN-Ceram Block specimen was ground with silicon carbide paper, rinsed, primed, and then bonded to a resin composite disk using a tri-n-butylborane-initiated self-curing luting agent. After 24-h immersion in water, the shear bond strengths were determined.ResultsThe highest level of bond strength was obtained with 4wt% MTS (45.2 MPa) and 4wt% ATS (38.7 MPa), followed by 4wt% MOI (29.8 MPa), ESPE?Sil (28.1 MPa), and 4wt% MDS (27.9 MPa). For each MTS, ATS, MOI, and MDS, the bond strengths for concentrations of 4wt% and 16wt% were not significantly different. No significant differences were found between 4wt% ATS, 4wt% MOI, ESPE?Sil, and 4wt% MDS. The use of any of these primers led to a significant increase in bond strength compared to an unprimed control (13.8 MPa).ConclusionsThe type and concentration of monomers dissolved in the primer influence the bond strength between a tri-n-butylborane resin and a leucite-reinforced glass ceramic GN-Ceram Block. The effectiveness of MOI was found to be comparable to that of MDS, ATS, and ESPE?Sil, but inferior to that of MTS.     

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.     

Nucleation efficacy and flexural strength of novel leucite glass-ceramics

ObjectivesTo optimize the nucleation mechanism in leucite glass-ceramics to allow more efficacious glass-ceramic manufacture and improvements in microstructure and mechanical reliability.Materials and methodsAn alumino-silicate glass was designed and synthesized using melt quench methods. The glass was crushed and milled using various milling times (48–93 h) and spray drying. Nucleation and growth heat treatment schedules were applied to synthesize glass-ceramics. Glass/glass-ceramic powders and frit specimens were characterized using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) and X-ray diffraction analyses (XRD). Glass-ceramic specimens were tested using the biaxial flexural strength test (BFS).ResultsApplication of defined nucleation heat treatments resulted in the synthesis of Na/Ca titanates. NMR indicated changes to the ²³Na glass spectra in the nucleated glass and TEM/EDX the presence of Na/Ca/Ti domains (<200 nm) within the leucite crystals and associated with the nucleation of the leucite phase. XRD confirmed the presence of a bulk leucite phase in the glass-ceramics. SEM/TEM confirmed the crystallization of the leucite phase (65.5–69.3%) in a thermally matched glass, in conjunction with the nano Na/Ca titanate phase. The leucite glass-ceramics resulted in a high BFS (255–268 MPa), with reduction in powder milling time prior to heat treatments having no significant effect on flexural strength and reliability (p > 0.05).SignificanceNa/Ca titanates were synthesized in leucite glass-ceramics for the first time and associated with its nucleation and efficacious growth. This nucleation optimization provides opportunities for more efficient manufacturing and microstructural/mechanical reliability improvements. Improved synthesis of high strength/reliable leucite glass-ceramics is useful for construction of esthetic minimally invasive restorations.     

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.