Cytotoxicity of modified glass ionomer cement on odontoblast cells

Recently a modified glass ionomer cement (GIC) with enhanced bioactivity due to the incorporation of wollastonite or mineral trioxide aggregate (MTA) has been reported. The aim of this study was to evaluate the cytotoxic effect of the modified GIC on odontoblast-like cells. The cytotoxicity of a conventional GIC, wollastonite modified GIC (W-mGIC), MTA modified GIC (M-mGIC) and MTA cement has been evaluated using cement extracts, a culture media modified by the cement. Ion concentration and pH of each material in the culture media were measured and correlated to the results of the cytotoxicity study. Among the four groups, conventional GIC showed the most cytotoxicity effect, followed by W-mGIC and M-mGIC. MTA showed the least toxic effect. GIC showed the lowest pH (6.36) while MTA showed the highest (8.62). In terms of ion concentration, MTA showed the largest Ca²⁺ concentration (467.3 mg/L) while GIC showed the highest concentration of Si⁴⁺ (19.9 mg/L), Al³⁺ (7.2 mg/L) and Sr²⁺ (100.3 mg/L). Concentration of F^? was under the detection limit (0.02 mg/L) for all samples. However the concentrations of these ions are considered too low to be toxic. Our study showed that the cytotoxicity of conventional GIC can be moderated by incorporating calcium silicate based ceramics. The modified GIC might be promising as novel dental restorative cements.     

Physical properties of resin-reinforced glass ionomer cement modified with micro and nano-hydroxyapatite

Hydroxyapatite is a biologically compatible material and a major component of dental enamel and bone tissue. Because of its biocompatibility and structural similarity to human teeth and the skeletal system, a number of dental studies have evaluated its application as a bone substitute or dental restorative material. This study was to evaluate the differences in bonding strength and resistance to demineralization between micro-hydroxyapatite and nano-hydroxyapatite added to self-cured resin-reinforced/modified glass ionomer cement. RelyX was used as the base glass ionomer cement material and for the control group. 10% micro-hydroxyapatite added glass ionomer cement was named experimental group 1, and 10% nano-hydroxyapatite added glass ionomer cement was named experimental group 2. Physical tests for ISO9917-1:2007 in each group was acceptable, except the setting time of nano-hydroxyapatite added glass ionomer cement, which exceeded maximum setting time. Bonding strength was greatest in nano-hydroxyapatite glass ionomer cement, and cohesive failure was common in all specimens. When fractured surface was observed under SEM, spherical particles were observed in experimental groups containing hydroxyapatite particles, and they were more prevalent in nano-HA added glass ionomer cement group than in micro-hydroxyapatite added group. Both experimental groups exhibited greater resistance to demineralization compared to the control group, and there was no significant difference between the experimental groups. Under SEM, nano-hydroxyapatite added glass ionomer cement exhibited increased resistance to demineralization compared to micro-hydroxyapatite added glass ionomer cement.     

Influence of acid washing on the surface morphology of ionomer glasses and handling properties of glass ionomer cements

Acid washing is known to influence the handling properties of ionomer glasses used in glass ionomer cements due to the production of an ion depleted-zone on the surface of the glass particles. The influence of acid washing on the particle size distribution and surface area of four glasses was examined by scanning electron microscopy (SEM), particle size analysis (PSA) and accelerated surface area porosimetry (ASAP) and the working and setting times of cements, produced from the glasses, correlated to changes in surface morphology. A linear relationship was found between the specific surface area of acid-washed SiO₂–Al₂O₃–XF₂–P₂O₅ glasses (X being either calcium or strontium) and their cement working and setting times. These changes directly correlated with increases in the mesopore volume. However, the influence of acid washing on the surface morphology was also found to be glass composition-dependant with the addition of sodium into the glass network resulting in no significant change in the surface area or mesopore volume despite changes in the working and setting time. Through examination of the influence of acid washing and glass composition on the specific surface area improvements in the control of the working and setting times of glass ionomer cements may be achieved.     

Preparation and evaluation of an experimental luting glass ionomer cement to be used in dentistry

The aim of this paper is to compare the fluoride-releasing and mechanical properties of an experimental luting glass ionomer cement, which has a modified composition and a commercial luting cement. The experimental powder was obtained by sol–gel process and then, it was used to prepare the experimental cements. The properties of cement pastes, such as setting time and working time, microhardness and diametral tensile strength were determined. Fluoride release from GICs was evaluated at time intervals of 1, 7, 14, 21 and 28 days in deionized water. Atomic force microscopy (AFM) analyses showed that the surface of the experimental cements is more homogeneous than commercial GICs. The mechanical properties and the measure of liberation of fluoride of the two cements were influenced by ratio powder:liquid and chemical composition of the precursor powders. Experimental cements released less fluoride than commercial cements. However, this liberation was more constant during the analyzed period. Thus, the results obtained in this study indicated that the composition of the experimental powder modified by the niobium can lead the formation of the polysalt matrix with good mechanical properties. In other words, we can say that experimental powder offered considerable promise for exploitation in dental field.     

The effects of heat treatment on selected properties of a conventional and a resin-modified glass ionomer cement

This study investigated the effects of application of heat alone and heat & pressure on the compressive strength and modulus, the stress relaxation characteristics and the fluoride release of a conventional and a resin-modified glass ionomer cement. Cylindrical specimens were made from both materials and divided into 3 groups. One group was heat treated in an oven at 120 °C for 20 min, another group was subjected to heat & pressure at 120 °C for 20 min at 6-bar pressure. The third group acted as a control. The compressive strength and modulus, stress relaxation and fluoride release were tested over 56 days. The results of this investigation indicate that heat treatment had no significant effect on the conventional GIC used but significantly affected the resin modified GIC by increasing both the compressive strength and modulus and reducing the stress relaxation characteristics and the fluoride release. The use of GIC to produce inlay or onlay restorations that adhere to tooth tissue and release fluoride would be highly desirable. The results of this study indicate that it is possible to improve the strength of RMGIC with heat to a limited extent, but fluoride release may decrease.     

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.     

Effect of novel chitosan-fluoroaluminosilicate resin modified glass ionomer cement supplemented with translationally controlled tumor protein on pulp cells

Dental materials that can promote cell proliferation and function is required for regenerative pulp therapy. Resin modified glass ionomer cement (RMGIC), a broadly used liner or restorative material, can cause apoptosis to pulp cells mainly due to HEMA (2-hydroxyethyl methacrylate), the released residual monomer. Recent studies found that chitosan and albumin could promote release of protein in GIC while translationally controlled tumor protein (TCTP) has an anti-apoptotic activity against HEMA. The aim of this study was to examine the effect of chitosan and albumin modified RMGIC (Exp-RMGIC) supplemented with TCTP on pulp cell viability and mineralization. Exp-RMGIC+TCTP was composed of RMGIC powder incorporated with 15 % of chitosan, 5 % albumin and supplemented with TCTP mixed with the same liquid components of RMGIC. The effect of each specimen on pulp cells was examined using the Transwell plate. From the MTT assay, Exp-RMGIC+TCTP had the highest percentages of viable cells (P < 0.05) at both 24 and 74 h. Flow cytometry revealed that, after 24 h, Exp-RMGIC+TCTP gave the lowest percentages of apoptotic cells compared to other groups. There was no difference in alkaline phosphatase (ALP) activity among different formula of the specimens, while cells cultured in media with TCTP had higher ALP activity. Von Kossa staining revealed that RMGIC+TCTP, and Exp-RMGIC+TCTP had higher percentages of calcium deposit area compared to those without TCTP. It was concluded that Exp-RMGIC supplemented with TCTP had less cytotoxicity than RMGIC and can protect cells from apoptosis better than RMGIC supplemented with TCTP.     

Effects of glass ionomer cements on bone tissue

In vivo biocompatibility of glass ionomer cements (GICs) was evaluated for use in orthopaedic surgery using a rat model and compared with conventional bone cement, Polymethyl methacrylate, PMMA. The unset GICs and PMMA were inserted into the marrow cavities of rat femora and retained in situ for various periods of time. The PMMA bone cement showed complete biocompatibility with no interference with reparative bone. The conventional GIC with smaller glass particles and lower powder/liquid ratio showed an initial minor toxic effect on rat bone tissue with later disturbance of adjacent bone formation. The conventional GIC with larger-size glass particles and higher powder/liquid ratio and resin-modified GIC showed more severe toxic effect on rat tissue with the resin-modified GIC affecting the rat bone tissue later. The causes of toxicity associated with the conventional GIC with larger glass particles and higher powder/liquid ration and the resin-modified GIC are thought to be related with the unreacted acid component of both materials and longer ongoing metallic ion release.     

Influence of curing conditions on durability of alkali-resistant glass fibres in cement matrix

Glass fibres in concrete material often increase the flexural strength. However, these fibres when in contact with cement are altered by alkali reactions due to the presence of portlandite. This study presents the results of investigation to show the effect of curing conditions on the durability of alkali-resistant glass fibres in cement matrix. Test results show that even alkali resistant fibres treated with zirconium oxide present the same degradation phenomenon. They also show that the nature of the cement has a large influence on the protection of the fibres: the Portland CEM II is less damaging than the CEM I. The substitutions of a part of cement by silica fume gave no substantial improvements to the mechanical strength of the glass fibre reinforced cement (GFRC). However, the observed microstructures in the samples show that the degradation is weakened with the addition of silica fumes. The analytical techniques used in this study are scanning electron microscope (SEM) and X-ray diffraction.     

Evaluation of the effect of tracer pH on the sealing ability of glass ionomer cement and mineral trioxide aggregate

OBJECTIVES: The aim of this study was to evaluate the sealing ability and physical and chemical properties of glass ionomer cement (GIC) and mineral trioxide aggregate (MTA) using Rhodamine B at different pHs as tracer. METHODS: Chemical analysis, pH and micro-hardness of GIC and MTA were performed. In addition dye leakage was assessed by tracer leakage using Tandem Scanning Confocal Microscope (TSM) after immersion of premolar teeth in a stock and a buffered fluorescent Rhodamine B for 24 h. Ultra-structural changes within the materials were evaluated by viewing under the field emission scanning electron microscope (FESEM). RESULTS: GIC and MTA showed elemental peaks for silicon, aluminium and calcium while MTA also had bismuth. GIC was acidic (P = 0.001) and caused an increase in dye pH (P = 0). Immersion of MTA in any of the test solutions resulted in an increase in the pH of the solution (P < 0.05). Use of a dye solution of lower pH than the material under test increased the cement micro-hardness. GIC demonstrated marginal leakage on TSM and both increase in marginal leakage and material porosity on FESEM. MTA was not affected by the use of acidic dye but showed a tendency to take up dye within the material shown on TSM. CONCLUSIONS: Evaluation of marginal adaptation of dental materials was shown to be dependent on the technique used for viewing the material to tooth interface, the properties of the material under study and the pH of the dye used.     

Structural evaluation of ZnO substitution for CaO in glass ionomer cement synthesized by sol-gel method and their properties

Journal of Materials Science - The substitution of ZnO for CaO site and the limitation of ZnO addition in the sol-gel ionomer glass composition at different calcination temperatures were evaluated...     

Effects of sandblasting metal bracket base on the bond strength of a resin-modified glass ionomer cement: an in vitro study

The introduction of air abrasion (sandblasting) technology to orthodontics may allow reaching optimum bond strength between the metal bracket and resin-modified glass ionomer cement. This study examined the effects of sandblasting metal bracket bases on the in vitro tensile bond strength of a resin-modified glass ionomer cement. Two-hundred foil-mesh based brackets were divided into ten groups and combinations of three sizes of aluminum oxide powder (25, 50 and 110 μm) and three sandblasting times (3, 6 and 9 seconds) were tested. One group was not sandblasted and used as control. Analysis of variance showed that bond strength was significantly affected by the sandblasting time (p < 0.001) and size of the aluminum oxide powder (p < 0.001). Only the group (SO₂₅) sandblasted with 25 μm aluminum oxide powder for 3 seconds yielded higher mean bond strength than that of the control group. The bond strength values were also analyzed using a Weibull analysis, which showed the most favorable size (25 μm) and time combination (3 seconds), and the 5% and 90% probabilities of failures. This study suggests that sandblasting time and particle size have and important effect on the bond between the metal bracket and resin-modified glass ionomer cement.     

Influence of the water/cement ratio on the air permeability of concrete

The durability of concrete structures is mainly affected by the transport of gaseous and liquid substances through its pore system which can potentially cause deterioration of the concrete. Thus, an important indicator of long-term durability is the relative ease with which each aggressive substance is transported through the concrete, in other words, its permeability. Studies were conducted to deepen knowledge of concrete permeability and, in particular, to understand how it is affected by the water-cement ratio, preconditioning temperature and testing pressure. The water-cement ratio is one of the main factors affecting concrete permeability; small changes in this ratio promote large permeability variations. An important increase of air permeability with the water-cement ratio and preconditioning temperature has been noticed. On the other hand, insignificant differences have been observed in the air permeability coefficient at the four testing pressures.     

Influence of 2-hydroxyethyl methacrylate content on the optical properties of experimental 2-hydroxyethyl methacrylate-added dental glass ionomer

The influence of 2-hydroxyethyl methacrylate (HEMA) on the properties of HEMA-added dental glass ionomer (HAGI) should be determined systematically to develop a smart restorative material. The purposes of this study were to determine the influence of incrementally added HEMA in experimental HAGIs on the color, translucency, opalescence, fluorescence and compressive strength, and to compare with those of commercial resin-modified glass ionomer (RMGI) materials. A varied amount of HEMA (10–50 wt.%) was added into commercial glass ionomer liquid (Fuji II), which was then mixed with three shades of the same glass ionomer powder (shade nos. 21, 22 and 23). RMGIs from the same manufacturer were also investigated. Five specimens, 10 mm in diameter and 2 mm in thickness, were fabricated for each condition. Color of the HAGIs and RMGIs was measured with a reflectance spectrophotometer in the reflectance and the transmittance modes. Translucency, opalescence and fluorescence parameters were calculated. Compressive strength was determined. As the HEMA content increased, CIE L^* value (lightness) decreased while the chroma increased. CIE a^* value showed small and CIE b^* value showed high increase as the HEMA content increased. Increase in translucency was generally dependent on HEMA content except for 30% HEMA condition of shade no. 21. Opalescence decreased as the HEMA content increased while the trend of fluorescence change was shade-dependent. Compressive strength significantly increased after HEMA addition except 50% HEMA condition. The influence of HAMA on the optical properties of HAGIs varied by the shade of powder and the amount of HEMA. For the most relevant simulation of the optical properties of teeth, addition of 30–40% HEMA is recommended when formulating HEMA-added glass ionomers.     

The effect of glass synthesis route on mechanical and physical properties of resultant glass ionomer cements

Glass ionomer cements (GICs) have potential orthopaedic applications. Solgel processing is reported as having advantages over the traditional melt-quench route for synthesizing the glass phase of GICs, including far lower processing temperatures and higher levels of glass purity and homogeneity. This work investigates a novel glass formulation, BT 101 (0.48 SiO₂–0.36 ZnO–0.12 CaO–0.04 SrO) produced by both the melt-quench and the solgel route. The glass phase was characterised by X-ray diffraction (XRD) to determine whether the material was amorphous and differential thermal analysis (DTA) to measure the glass transition temperature (T _g). Particle size analysis (PSA) was used to determine the mean particle size and X-ray photoelectron spectroscopy (XPS) was used to investigate the structure and composition of the glass. Both glasses, the melt-quench BT 101 and the solgel BT 101, were mixed with 50 wt% polyacrylic acid (M _w, 80,800) and water to form a GIC and the working time (T _w) and the setting time (T _s) of the resultant cements were then determined. The cement based on the solgel glass had a longer T _w (78 s) as compared to the cement based on the melt derived glass (19 s). T _s was also much longer for the cement based on the solgel (1,644 s) glass than for the cement based on the melt-derived glass (25 s). The cements based on the melt derived glass produced higher strengths in both compression (σ_c) and biaxial flexure (σ_f), where the highest strength was found to be 63 MPa in compression, at both 1 and 7 days. The differences in setting and mechanical properties can be associated to structural differences within the glass as determined by XPS which revealed the absence of Ca in the solgel system and a much greater concentration of bridging oxygens (BO) as compared to the melt-derived system.     

Bond strength of experimental cyanoacrylate-modified dental glass ionomer cements

Glass ionomer cement (GIC) has been successfully used in dental field for more than 40 years. Despite numerous advantages of GIC, low bond strength and slow setting rate limited conventional GICs for use only at low stress-bearing areas. To improve bond strength to tooth, two kinds of cyanoacrylates such as ethyl 2-cyanoacrylate (EC) and allyl 2-cyanoacrylate (AC) were added in a commercial GIC. Changes in setting time of cyanoacrylate-modified GICs (CMGICs) according to the concentration of cyanoacrylates and/or p-toluene sulfonic acid (TSA) was investigated using a rheometer. Shear bond strength to human dentin was measured. Biocompatibility was determined by the viability of fibroblasts. Optimal concentrations for EC and TSA were 5–10% of the GIC powder and 30% of the GIC liquid, respectively. EC-based CMGIC showed twofold increase of initial bond strength compared with conventional GIC. Also, AC-based CMGIC showed three times higher bond strength and similar biocompatibility compared with the GIC. Therefore, CMGIC materials can be widely applied in dental adhesive restoration field because they showed improved bond strength and proper setting time.     

Properties of glass fibres in cement environment

Fibres produced from a soda-silica-zirconia glass were reacted with Portland cement extracts at 20 and 65° C for various lengths of time and their strength and stiffness determined. The results indicate that these glass fibres resist the attack of cement extracts reasonably well at ambient temperatures. Fibre strengths of the order of 1200 to 1300 N mm^–2 are obtainable after 2 years at 20° C, sufficient to reinforce cement, and there is no change in the Young's modulus of the fibre during this period. At higher temperatures both strength and stiffness are reduced but these temperatures are unlikely to be encountered in practice over extended periods of time. When fibres removed from cement composites containing commercially made alkali-resistant glass fibres are examined, it is found that fibre strengths depend very strongly on the environment in which the composites were kept. For air storage, fibre properties remain relatively unaffected but for composites kept under water continuously, an initial loss in fibre strength is observed. This difference in fibre strength is reflected in the relative strength of the cement composites.