Effect of long-term in vitro testing on the properties of bioactive glass-polysulfone composites.

The combination of bioactive ceramics and polymers can allow the preparation of composites with tailorable mechanical properties and bioactive behavior. In these composites, bioactive ceramics can act as a source of both reinforcement and bioactivity, while the polymer matrix can add toughness and processability to the material. On the other hand, the effect of using a highly dimensional unstable phase as a reinforcing agent on the long-term properties of the composite is a major concern regarding the lifetime of possible applications. In this work, a bioactive glass-polysulfone particulate composite was prepared by hot-pressing at 215 degrees C a mixture of polysulfone and different concentrations of bioactive glass particles (Bioglass 45S5, particle size range: 125-106 microm) to yield composites having 20 and 40 vol % of bioactive glass particles. The obtained composites were exposed to a simulated body fluid at 37 degrees C for different periods of time ranging from 1 h to 60 days. After the test, the mechanical properties of the composites were investigated by a four-point bending test, while DMS (dynamic mechanical spectroscopy) was used to identify the effect of water on the structure and behavior of the composite. The interface between glass particles and the polymer was also investigated by SEM/EDX and diffuse reflection infrared spectroscopy. The results showed that a decay in the mechanical properties of the composites within the first 20 h of test can occur. Otherwise, after this initial decay, no more pronounced reduction in properties could be noted. The analyses of the fracture surface of composites tested in vitro indicated the hydration of the surface of the particles. Therefore, it was concluded that water migration through the interface of the composite causes surface dissolution of glass particles and formation of voids, which were responsible for the observed decay in mechanical properties. Composites with modified interfaces revealed less damaged fracture surfaces than composites with untreated interfaces.

The role of ionic release from NovaMin (calcium sodium phosphosilicate) in tubule occlusion: an exploratory in vitro study using radio-labeled isotopes.

OBJECTIVE: The primary objective of this work was to develop a method of quantifying the levels and source of calcium and phosphate deposited on dental hard tissue from a novel calcium phosphosilicate (NovaMin) material using neutron activation analysis (NAA). A second objective was to explore the utility of radiotracing to determine dentin porosity following exposure to calcium phosphosilicate. METHODS: Neutron activation was used to create isotopes of Ca and P in the calcium phosphosilicate particles. Gamma radiation emitted from these isotopes was used to identify and measure their uptake (concentration) onto dental hard tissue. Three experiments were conducted to explore calcium and phosphate uptake to dental hard tissue: 1) a dose response to quantify the relative levels of calcium and phosphate deposited on dental hard tissue as a function of calcium phosphosilicate dose; 2) the effect of calcium phosphosilicate particle size on the relative levels of calcium and phosphate uptake; and 3) the permeability of calcium phosphosilicate-treated dentin by employing the radiotracer technetium. For all experiments, extracted bovine incisors were employed as the test substrate. RESULTS: The results indicate there is a strong dose relationship between the wt% and particle size of calcium phosphosilicate in the dentifrice formulation and new Ca and P deposition. At above 5.0 wt% calcium phosphosilicate, there appears to be an exponential increase in the number of counts from the tooth surface. Finer particle size calcium phosphosilicate appears to deposit much higher levels of Ca and P than the larger range of particle sizes. The results from the technetium study show that when treated with the dentifrice slurry containing calcium phosphosilicate, dentin shows only a slight amount of technetium infiltration, indicating a lowering of dentin permeability. CONCLUSION: This exploratory study has demonstrated that NAA and the use of radio isotopes have utility in monitoring the uptake of Ca and P into both dentin and enamel tooth structure. The data generated from these studies have shown that there is a dose dependence and particle size effect for calcium phosphosilicate on the deposition of calcium and phosphate to dental hard tissue.

A randomized controlled clinical study evaluating the efficacy of two desensitizing dentifrices.

OBJECTIVE: The primary aim of this study was to compare the in vivo efficacy and safety of dentifrices containing either 5% NovaMin or 5% potassium nitrate, and a non-desensitizing dentifrice, on dentin hypersensitivity in a four-week, double-blind clinical study among a population in south India. In addition, a companion scanning electron microscopy evaluation was performed to demonstrate whether or not the test products occlude open dentin tubules in vitro. METHODS: Thirty volunteers with tooth sensitivity were recruited, and a double-blind, randomized, parallel, controlled clinical trial was conducted in a hospital setting. Clinical evaluation for dentin hypersensitivity was done using tactile, air blast, and cold water methods. Following baseline measures, subjects were randomly divided into three groups and treated as follows: Group A--dentifrice containing 5% potassium nitrate; Group B--dentifrice containing 5% NovaMin; and Group C--dentifrice containing no desensitizing ingredients. Clinical evaluations were repeated after two and four weeks of product use. RESULTS: Compared to baseline, there was a significant decrease in dentin hypersensitivity in Groups A and B following four weeks' use of the dentifrice containing 5% potassium nitrate and the dentifrice containing 5% calcium sodium phosphosilicate (NovaMin), respectively. There was a statistically greater reduction in hypersensitivity at both two and four weeks following use of the dentifrice containing NovaMin compared with the use of a non-desensitizing dentifrice, as well as the dentifrice containing potassium nitrate. Air and cold water scores were significantly lower following four weeks' use of the potassium nitrate dentifrice compared to the non-desensitizing dentifrice. Tubule occlusion was observed in the companion in vitro study following treatment with 5% NovaMin, but not after treatment with the 5% potassium nitrate or non-desensitizing dentifrices. CONCLUSION: The results suggest that the dentifrice containing 5% NovaMin occludes dentin tubules, and provides rapid and significantly more relief from dentin hypersensitivity in four weeks compared to a dentifrice containing 5% potassium nitrate or a non-desensitizing dentifrice. All three dentifrices tested in this study were well-tolerated.

Bioactivity of tape cast and sintered bioactive glass-ceramic in simulated body fluid.

A common ceramic processing technique, tape casting, was used to produce thin, flexible sheets of bioactive glass (Bioglass 45S5) particulate in an organic matrix. Tape casting offers the possibility of producing three-dimensional shapes, as the final material is built up layer by layer. Bioactive glass tapes were sintered together to form small discs for in vitro bioactivity testing in simulated body fluid (SBF). Four different sintering schedules were investigated: 800, 900, and 1000 degrees C for 3 h; and 1000 degrees C for 6 h. Each schedule produced a crystalline material of major phase Na2Ca2Si3O9. Tape cast and sintered bioactive glass-ceramic processed at 1000 degrees C formed crystalline hydroxyapatite layers after 20-24 h in SBF as indicated by Fourier transform infrared spectroscopy, Scanning electron microscopy, and EDS data. FTIR revealed that the greatest amount of hydroxyapatite formation after 2 h was observed for samples sintered at 900 degrees C. The differences in bioactive response were likely caused by the variation in the extent of sintering and, consequently, the amount of surface area available for reaction with SBF.