Influence of 0.05% sodium fluoride solutions on microhardness of resin-modified glass ionomer cements

This study aimed to evaluate the influence of fluoride-containing mouthrinse solutions (Fluorgard and Oral B) on the superficial microhardness of two resin-modified glass ionomer cements (Vitremer and Fuji II LC). Fifteen discs-shaped specimens of each glass ionomer cement (Ø10 mm; 2 mm thick) were prepared, thereby forming two groups. After 24-hour storage in artificial saliva, the microhardness was measure and the data were recorded. Next, each group was divided into three subgroups (n = 5), according to the solution to be immersed in. Control specimens were kept in artificial saliva along the whole experiment. The test specimens were kept in mouthrinse solution for 30 days. Vickers surface microhardness was analyzed at predetermined evaluation periods: 24 h, 48 h, 7, 14, 21 and 30 days after specimens’ preparation. Data were subjected to three-way ANOVA and to Tukey test (p<0.05). A better behavior of Fuji II LC was observed and Fluorgard affected most the characteristics of the tested materials. It may be concluded that fluoride-containing solutions influenced the tested characteristics of materials, mainly of Vitremer.     

Adhesion of streptococci to saliva-coated and uncoated composite-based resins

This study was designed to evaluate the bacterial adhesion to five types of experimental composite-based resins and a commercial composite resin used as a control. Physicochemical surface characteristics of composite resins with and without an artificial saliva coating were measured. The relationship between the numbers of adhering cells (Streptococcus sanguis, S. mutans and S. sobrinus) and surface characteristics was analysed. The values of contact angles and the number of adhering cells were small with saliva coating. S. sanguis ATCC 10557 showed a positive correlation (r=0.835, p<0.05) with the contact angles of uncoated resins, whereas no relationship was observed for saliva-coated resins. With S. mutans Ingbritt the cell numbers adhering to resins correlated strongly (p<0.01) with the values of zeta potential of resins for either saliva coated or uncoated. Electrical repulsion forces had a strong contribution to adherence of cells such as S. mutans and S. sobrinus which show a high absolute zeta potential.     

Combined effect of staining substances on the discoloration of esthetic Class V dental restorative materials

The purpose of this study was to determine the combined effect of an organic substance (mucin as a substitute for salivary organic substances), chlorhexidine, and an iron compound/tea solution on the changes in the color of esthetic Class V dental restorative materials. Color of a glass ionomer, resin-modified glass ionomer, compomer and flowable resin composite of A2 shade, respectively, was determined according to the CIELAB color scale relative to the standard illuminant D65. Color was measured at baseline, and after sequential immersion in the following substances: Step-1, mucin in PBS (MCP) for 48 h; Step-2, chlorhexidine (CHX) for 24 h; Step-3, iron compound (IRN) or tea solution (TEA) up to 7 days; and Step-4, ultrasonic cleaning for 1 h. Color change (ΔE _ab *) was calculated by the equation: Δ E _ab* = [(Δ L*)² + (Δ a*)² + (Δ b*)²]^1/2, of which ΔL ^∗ indicates changes in value, Δa ^∗ indicates changes in red-green parameter and Δb ^∗ indicates changes in yellow-blue parameter. Δ E _ab* values after immersion in MCP and CHX were compared, and Δ E _ab* values after immersion in IRN or TEA, and subsequent ultrasonic cleaning were compared with respect to the restorative material and immersion substance. Δ E _ab* and changes in the color parameters (ΔL ^∗, ΔC _ab* and ΔH _ab*) were analyzed by repeated measures, analysis of variance and a post-hoc test at the 0.05 level of significance. Color changes after immersion in MCP were acceptable (Δ E _ab* < 3.3), and those after immersion in CHX were generally acceptable. The range of Δ E _ab* values after immersion in IRN was 3.1–19.6, and that after ultrasonic cleaning was 2.4–9.6. The range of Δ E _ab* values after immersion in TEA was 10.7–21.1, and that after ultrasonic cleaning was 11.9–14.5. Color changes of four Class V restorative materials after combined treatment with mucin, chlorhexidine and an iron compound/tea solution were not acceptable. Colors did not recover to their original values after ultrasonic cleaning. Modifications on the surface of a restoration should be considered to reduce stain accumulation.     

Passive dissolution kinetics of titanium in vitro

The dissolution of titanium in simulated interstitial electrolyte (SIE), human serum in SIE (serum/SIE) and 8.0 mM ethylenediaminetetraacetic acid (EDTA) in SIE (EDTA/SIE) was measured in vitro. Titanium fibre samples were immersed in these solutions and maintained at 37°C, 10% O₂, 5% CO₂ and 97±3% relative humidity for 0–5000 h. The concentration of titanium released was quantified using electrothermal atomic absorption spectroscopy. Changes in oxide stoichiometry were determined by Auger electron spectroscopy after processing and immersion in the test solutions. The oxide became nearly stoichiometric TiO₂ after immersion, suggesting equilibration of the surface with the solutions. Solution ligands enhanced the magnitude of dissolution, with EDTA>serum/SIE>SIE. The dissolution kinetics were empirically fitted by a two-phase logarithmic relationship. The first phase of dissolution (t<300 h) was dominated by equilibration of the oxide with the solution and the second phase (t>300 h) by mass diffusion. The dissolution kinetics were similar for the EDTA/SIE and serum/SIE solutions, indicating that the mechanisms of dissolution for each solution may be the same.     

Antibacterial activity of a triclosan-containing resin composite matrix against three common oral bacteria

This study investigated the antibacterial effect of a resin composite matrix with or without incorporated triclosan (0.3 wt%) on Streptococcus mutans, Actinomyces viscosus and Lactobacillus casei. In the quantitative assay, bacterial suspensions were filled into 20-μl cavities within temporary restorative resins. After 0, 4, 8, 12, 24 and 48 h of incubation, the suspensions were removed from the restoratives and the numbers of viable bacteria were determined. Bacterial suspensions incubated without restoratives served as the controls. Ten replicates were carried out for each experiment. The resin composite containing triclosan demonstrated variable degrees of antibacterial activity against the microorganisms, revealing a significant inhibitory effect on S. mutans within 12 h compared to the control. The viable counts of A. viscosus significantly decreased after 24 h. A significant reduction of L. casei was observed after 48 h. The unloaded resin composite did not reveal a marked antibacterial effect. The resin composite loaded with triclosan might be beneficial in preventing cavity contamination and minimizing the risk of pulpal irritation in the short-term.     

Evaluation of polymerization in fluoride-containing composite resins

Fluoride-containing restorative materials are frequently utilized to delay or inhibit caries. The quality of the fluoride-containing composite resins was evaluated by testing their microhardness, polymerization shrinkage, thermal expansion coefficient, and surface morphology. Some of them were evaluated in conjunction with the thermocycling process. The microhardness values of the thermocycled specimens were similar to those of the specimens immersed only in distilled water. Among the specimens, Surefil showed the highest (68.6 ± 1.2 Hv) value. A linear correlation was found between microhardness and the filler content (vol%) of the specimens regardless of their states. Polymerization shrinkage rapidly increased during the light curing, and then it reached a plateau. The shrinkage values increased as the specimens became thicker. In a temperature range of 30 ∼ 80 °C, the coefficients of thermal expansion of the control specimens ranged between 43 × 10⁻⁶/°C and 77 × 10⁻⁶/°C. An inverse correlations were observed between the filler content (vol%) and the coefficient of thermal expansion and between microhardness and the coefficient of thermal expansion of the control specimens. Tetric Ceram showed a perforated or “Swiss-cheese” morphology after thermocycling. It was unique and occurred only in this product.     

Acid Deactivation of Soils with Ammonium Fluoride To Remove 137Cs

Leaching of ¹³⁷Cs from various contaminated clay soils with fluoride-containing mineral acid solutions was studied. It was demonstrated that the use of fluorides offers advantage over chlorides and nitrates. The decontamination mechanism was studied by infrared spectroscopy. Conditions for simultaneous removal of ¹³⁷Cs and ^238,239Pu with fluoride-containing nitric acid solutions were optimized.     

Surface degradation behaviour of sodium borophosphate glass in aqueous media: Some studies

The degradation behaviour of phosphate glass with nominal composition, 40Na₂O-10BaO-xB₂O₃-(50-x)P₂O₅, where 0 ≤ x ≤ 20 mol%, was studied in water, HCl and NaOH solutions at room temperature to 60°C for different periods extending up to 300 h. These glasses were synthesized by conventional melt-quench technique. Dissolution rates were found to increase with B₂O₃ content in the glass. The dissolution rates for the glass having 10 mol% B₂O₃ were found to be 0·002 g/cm² and 0·015 g/cm² in distilled water and 5% NaOH solution, respectively, at room temperature after 225 h of total immersion period, whereas it increased considerably to 0·32 g/cm² in 5% NaOH at 60°C after 225 h. However, glass samples with x = 15 and 20 mol% B₂O₃ were dissolved in 5% HCl solution after 5 h immersion. The degradation behaviour has been correlated with the structural features present in the glass. The optical microscopy of the corroded surface revealed that the corrosion mechanism were different in acid and alkali media.     

Combined effects of staining substances on resin composites before and after surface sealant application

The objective was to measure the combined effect of mucin, chlorhexidine and tea solution on the staining of four dental resin composites, and to determine the effect of surface sealant on staining. One side of cured resin composite specimens of 10 mm in diameter and 2 mm in thickness were polished with 600-grit silicon carbide paper. One group of specimens (n = 5) was treated with a surface sealant [BisCover, Bisco, USA; SS (surface sealant) group], and the other group was not (NO group; control). Specimens were sequentially immersed in the following substances: Mucin in phosphate buffered saline (PBS); chlorhexidine; tea solution; and ultrasonic cleaning and then immersion in PBS. Color was measured on a reflection spectrophotometer. Changes in color (ΔE ^* _ab ) and color parameters, such as hue, chroma and value, after immersion in tea solution and subsequent cleaning were analyzed by repeated measures, analysis of variance at the 0.05 level of significance. The range of ΔE ^* _ab values after immersion in tea solution was 11.4–21.1 for NO group and 10.5–19.6 for SS group, and that after cleaning was 2.4–10.0 for NO group and 2.7–8.3 for SS group. After staining, CIE L ^* value (lightness) decreased, and CIE a ^* and b ^* values increased. Color changes of resin composites were not acceptable after sequential immersion treatment (ΔE ^* _ab > 3.3). The changes in color and color parameters of sealant applied group were not significantly different from those of control group except for a few combinations of color parameters and resin composites.     

Depth of Field Measurements Relevant to Single Photon Detection Using Image-intensified Microscopy

The problems of defining a depth of field d _p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source. The problems of defining a depth of field p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source.     

Pharmacokinetics of a novel nifedipine and pH-sensitive N-succinyl chitosan/alginate hydrogel bead in rabbits

Context: A novel N-succinyl chitosan/alginate hydrogel bead was prepared by the ionic gelation method for controlled delivery of nifedipine (NF). Objective: The delivery behavior of NF from the hydrogel bead was studied in rabbit body. Materials and methods: Nitrendipine was used as the internal standard and the concentration of NF in serum was determined by reversed-phase high-performance liquid chromatography. Results: The assay was linear from 5 to 755 ng/mL. The limit of quantitation for NF was 5 ng/mL in serum, and the recovery was greater than 90%. The method was used to determine the concentration–time profiles of NF in the serum. The pharmacokinetic parameters were calculated by Drug and Statistics (ver 1.0) program. The mean Cmax was 320.2 ± 71.3 μg/L, the mean Tmax was 3.2 ± 0.5 hours, the mean t1/2 was 6.60 ± 2.17 hours, the mean AUC0-24 was 2.03 ± 0.25 mg h/L, the mean AUC0-∞ was 2.50 ± 0.36 mg h/L, the mean MRT0-24 was 8.57 ± 0.19 hours, and the mean MRT0-∞ was 15.2 ± 1.8 hours. Discussion and conclusion: The pharmacokinetic characteristics were found by a two-compartment model following the oral administration of NF-loaded N-succinyl chitosan/alginate hydrogel beads in rabbits.     

Dental application of polyfunctional urethane comonomers to composite resin veneering materials

Urethane monomer/diluent monomer mixtures were used in dental composite resin veneering materials filled with various ratios of powder (filler)/liquid (comonomer), P/L. Hardness values of unfilled resins containing benzoyl peroxide only (BP0; 0.5 wt%), and filled resins (included trimethylol propane trimethacrylate (TMPT) composite filler) were tested. Significant increases in hardness were obtained with the use of TMPT composite filler in the resins. Also, their modulus values measured by bend test showed an increasing trend, compared to a commercial composite resin veneering material (a control sample; CONT) with a lower filler content (50 wt%). The DME–DPMDC/HPDM comonomer (dimethacryloxyethyl diphenylmethane-4,4-dicarbamate/hydroxypropyl dimethacrylate), which showed a smaller fraction of surface porosity, gave greater mechanical strength values at P/L ratios of 0.55 (17.8 wt% filler content) to 1.20 (27.3 wt%) than a CONT resin. The coefficient of thermal expansion was smaller in urethane-based filling materials than a CONT resin. Also, greater activation energy of thermal decomposition was observed in the resin samples with P/L ratio 0.75 to 1.20 than in a CONT resin. Thermally-induced decomposition occurred with smaller weight loss in the experimental filled resins than in a CONT resin.     

Damage Resistance of Composites Based on Glass Fibre Reinforced Low Styrene Emission Resins for Marine Applications

Composites based on glass fiber reinforced low styrene emission polyester resins have been widely used over the last 10 years, in order to meet increasingly strict safety regulations, particularly in the pleasure boat industry. Previous studies of their mechanical properties suggested that although these resins are generally more brittle than traditional orthophthalic polyester resins this did not adversely affect the properties commonly used for quality control (short beam shear and tensile failure strength of mat reinforced composites). In the present paper results from a more detailed study of damage behaviour are presented. Tests include fracture toughness (K _Ic ) tests on resins, fibre/matrix interface energy, detection of composite damage initiation in tension by acoustic emission, composite delamnation (G _Ic and G _IIc ), and low energy impact. Overall the results indicate that the low failure strain of low styrene emission resins results in significantly lower composite damage resistance.     

HPLC analysis of components released from dental composites with different resin compositions using different extraction media

Components released from dental composite resins are essential factors in the assessment of biocompatibility of these materials. The effect of different extraction media on monomer release from composite resins based on different monomer types was evaluated. Three types of visible light cured composite resins were formulated based on the following monomers: triethylene glycol dimethacrylate (TEGDMA), bisphenol A glycerolate dimethacrylate (BisGMA), and urethane dimethacrylate (UDMA). Seventy-five composite resin discs were fabricated and light cured for 1 min in the absence of oxygen. Extraction media used were: distilled water, saline solution, artificial saliva, serum-free culture medium, and culture medium with 10% fetal calf serum. The analysis of extracts from the composite resins was carried out by High Performance Liquid Chromatography (HPLC). Quantifiable amounts of TEGDMA were released into the aqueous media. However, BisGMA and UDMA were not detectable in any of the extracts from the composite resins. Statistical analysis by one-way ANOVA followed by Tukey’s test showed that there was a significant difference in TEGDMA release between culture media and other media (p < 0.05). From the results of this experiment it can be concluded that TEGDMA-based composite resins can release a high quantity of monomer into aqueous environments. The type of extraction medium may have a significant effect on monomer release from composite resins.     

Degradation study on ternary zinc magnesium phosphate glasses

Glasses with composition (ZnO)₃₀(MgO) _x (P₂O₅)_70−x (x = 5, 8, 10, 13, 15, 18, and 20 mol.%) have been successfully prepared by the melt-quenching technique. Degradation study has been carried out by means of measuring their chemical durability against buffer solutions with initial pH values of 4.01, 7.00, and 10.01 at an ambient temperature for up to 30 days. The dissolution rate (D _R) was obtained by calculating the measured weight loss of the glasses per unit surface area per unit immersion time. The results show that the glasses have better corrosion resistance in basic solution. It was also found that the weight loss is related to the MgO concentration with lower P₂O₅ concentration exhibiting greater corrosion resistance irrespective of acidic, neutral, or basic solutions as immersion liquid. All the sample surfaces and edges were corroded and the solutions experienced a decrease in pH values during the duration of the corrosion test.     

Corrosion behaviour of sintered 6061 aluminium alloy-graphite particle composites

The corrosion behaviour of sintered 6061 aluminium alloy and its composite dispersed with 7.0 vol% graphite particles is described. Techniques, namely immersion, tafel and impedance, were employed to study the corrosion behaviour. Immersion tests were performed in different media, namely HCl, NaCl and lubricating oil (used and fresh) while tafel and impedance tests were performed in 0.1 N HCl and 3% NaCl solution. Corrosion behaviour was monitored by measuring the weight change in immersion studies and corrosion current, i_corr, in tafel and impedance tests. The values of corrosion potential, E _corr, and i _corr were calculated from the tafel plots obtained at a scanning rate of 1 mV s^–1. In impedance study, i _corr was calculated from the value of polarization resistance, R _p, obtained from the Nyquist plot; the latter was obtained by merging the lock-in and FFT plots. Aluminium alloy and its composite suffered from corrosion in HCl and NaCl. However, the extent of severity was greater in the case of HCl. The i _corr values obtained by the impedance method also revealed a similar trend. The higher corrosion rate of the alloy and composites in HCl was due to the dissolution of the thin oxide (protective) film in the solution. The decreased corrosion rate of the composite and the base alloy in NaCl was attributed to the formation of stable corrosion product, Al (OH)₃, on the surface, which prevented further attack on the surface of the specimen. There was practically no evidence of corrosion attack on the alloy and the composite surface in used and fresh lubricating oil.     

In vitro studies of novel CaO–SiO2–MgO system composite bioceramics

In this study, a series of CaO–SiO₂–MgO composites with different β-CaSiO₃ (CS)/Mg₂SiO₄ (M₂S) composite ratios were prepared to produce new bioactive and biodegradable biomaterials for potential bone repair. The mechanical properties of CS–M₂S composites increased steadily with the increase of M₂S ratios in composites. Dissolution tests in Tris–HCl buffer solution showed obvious differences with different CS initial composite ratio in composites. The dissolution rate increased with the increase of CS composite ratio, which suggested that the solubility of composites could be tailored by adjusting the initial CS/M₂S composite ratio. Formation of bone-like apatite on a range of CS–M₂S composites with CS weight percentage ranging from 0 to 100 has been investigated in simulated body fluid (SBF). The presence of bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM). The results showed that the apatite formation ability of the CS–M₂S composite with 70% CS was detected after 10 days immersion. In vitro cell experiments showed that the 50 and 70% CS composites supported greater osteoblast-like cell proliferation as compared with pure M₂S (p < 0.05). The results of this study suggested that the CS–M₂S composites with 50 and 70% initial CS composite amount might be more suitable for preparation of bone repair materials.     

Composites of amorphous calcium phosphate and poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) for bone substitution: assessment of the biocompatibility

Composites of amorphous carbonated apatite and poly-(R)-3-hydroxybutyrate (PHB) and poly-(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate (PHBHV), respectively, were studied by pH monitoring upon immersion in water and by long-term osteoblast culture. For comparison, α-tricalcium phosphate (α-TCP), one glass ceramic (GB 9N), and one bioglass (Mg 5) were subjected to the same experiments. Excellent cell proliferation was found on the composite of calcium phosphate with PHB and on the reference materials (α-TCP, glass ceramic, bioglass). In contrast, cell death was observed repeatedly on the composite with PHBHV. A composite of amorphous calcium phosphate and PHB appears to be well suited as slowly biodegradable bone substitution material.No benefit of any kind will be received either directly or indirectly by the authors.W. Linhart and W. Lehmann contribute equally and therefore share first authorship     

Microstructure,mechanical property and corrosion behaviors of interpenetrating C/Mg-Zn-Mn composite fabricated by suction casting

A novel interpenetrating C/Mg-Zn-Mn composite was fabricated by infiltrating Mg-Zn-Mn alloy into porous carbon using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composite have been evaluated by means of SEM, XRD, mechanical testing and immersion test. It was shown that the composite had a compact structure and the interfacial bonding between Mg-Zn-Mn alloy and carbon scaffold was very well. The composite had an ultimate compressive strength of (195 ± 15) MPa, which is near with the natural bone (2–180 MPa) and about 150-fold higher than that of the original porous carbon scaffold, and it still retained half of the strength of the bulk Mg-Zn-Mn alloy. The corrosion test indicated that the mass loss percentage of the composite was 52.9% after 30 days′ immersion in simulated body fluid (SBF) at 37 ± 0.5 °C, and the corrosion rates were 0.043 mg/cm²h and 0.028 mg/cm²h after 3 and 7 days′ immersion, respectively. The corrosion products on the composite surface were mainly Mg(OH)₂ and hydroxyapatite (HA).