Physicomechanical properties of strontium and fluoride modified biodentineTM

Objectives: To investigate the effect of bioactive glass addition on the physicomechanical properties of BiodentineTM. The study compares the setting time, compressive strength and radiopacity of BiodentineTM modified by three different compositions of bioactive glassesDesign: This was an exploratory lab based quasi-experimental studySetting: The study was conducted in the laboratory at Queen Mary, University of London Dental Physical Sciences Unit.Materials and methods: Dental cements based on BiodentineTM and its modifications were used in the study. Original unmodified BiodentineTM cement was coded BO. Three bioactive glasses based on high fluoride (Q), high strontium (I) and high fluoride + strontium (H)were synthesized and 0.07g of each of the bioactive glasses added to BiodentineTM powder to yield 3 additional types of cements which were coded BQ, BI and BH respectively. A set mass of each cement type was prepared by adding 5 drops of the liquid supplied with BiodentineTM to the powders and triturating for 30 seconds in a 4000rpm electric amalgamator. These cements were subjected to setting time determination, compressive strength testing and radiopacity testing according to ISO 9917-1: 2007.Setting time and compressive strength were statistically analysed using T-test at 95% confidence level at a significance level of 0.05.Results: Bioactive glass addition resulted in initial setting times of11.31+0.18, 12:22+ 0.11, 11:59+ 0.15 and 13:35+0.23 minutes for BO, BQ, BI and BH respectively. The increased setting time of BQ and BH were statistically significant. Student t-test analysis of compressive strength demonstrated statistically higher 14 day compressive strengths for BI (p=0.036) and BH (p=0004). BH cement had the highest grey scale value equivalent to 2.9mm of aluminium, which was consistent with the best radiopacity among the 4 BiodentineTM based cements.Conclusion: Bioactive glass addition to BiodentineTM improved the radiographic detectability and compressive strength of the cement. This is important since current use of BiodentineTM is limited owing to inadequate strength and detection on radiographs. However, further studies are needed to explore alternative modifications that could shorten the setting time of this cement

Diopside Glass-Ceramics for Dental and Biomedical Applications.

A series of glass compositions with varying equimolar amounts of Na2O:Al2O3 were designed using Appen factors. High purity batch reagents were ball milled for 30 min and transferred to Pt/Rh crucible and melted in an electric furnace (EHF1700, Lenton, UK) at high temperatures then held for 90 min. The molten glass was poured into a graphite mould, annealed at 50oC below the glass transition temperature for 1h and the remaining glass was quenched into water. Glass frits were crushed and ball milled into powders with different particle sizes. Glass powders (PS<125μm) were heat-treated via two-step heat treatment cycles and air quenched. Experimental glasses and glass-ceramics were characterised using X-Ray Diffraction (XRD), Dilatometry, Scanning Electron Microscopy (SEM) and solid state Nuclear Magnetic Resonance (NMR)

Quantifying the Effect of Adding Alkaline Phosphatase Enzyme to Silicate/Phosphate Glass Mixtures to Enhance Bone Regeneration

Bioactive silicate glass-based (PerioGlas®) has been previously used to enhance periodontal bone regeneration. However, the degradation of this glass in the body fluid generates a high pH (>8) which may enhance the growth of periodontopathic bacteria, such as Porphyromonas gingivalis (P. gingivalis) thereby inhibiting osteoblastic activity. The aim of this study was to: (i) develop a mixture of a phosphate and silicate glass to produce a more neutral pH environment where the alkaline pH arising from the bioactive silicate glass can be offset by the acidity of phosphate glass, (ii) whether the alkaline phosphatase enzyme (ALP) when added to the silicate/phosphate glass mixture can enzymatically hydrolyse the Q2 metaphosphate chains to release Q0 orthophosphate species that can be used in forming apatite and bone mineralization. For this purpose, nine compositions of bioactive silicate/ phosphate glass-mixtures were prepared. The glass bioactivity was performed by immersing the prepared glass mixtures in ALP containing Tris buffer solution. The pH change in solutions was measured as a function of time. The glass mixtures degradation and apatite formation were investigated by 31P Solid and 31P Solution Nuclear Magnetic Resonance (NMR) spectroscopies. The results showed that the pH behaviour was modulated by immersing the glass-mixtures in buffered solutions. Solid and Solution NMR revealed that the terminal Q1 species belonging to the Q2-metaphosphate chains was hydrolysed by the ALP and converted into a Q0 orthophosphate species. In conclusion, the glass mixtures regulated the pH through its degradation stepwise on immersion. The output of the NMR spectra significantly supported the enzymatic degradation of glass mixtures with ALP enabling apatite precipitation for new bone formation. The concept of using silicate/phosphate glass mixtures with ALP is innovative and pioneering technology, suggesting its potentiality to develop new biomedical materials for different applications

Strontium- and Zinc-Containing Bioactive Glass and Alginates Scaffolds.

With an increasingly elderly population, there is a proportionate increase in bone injuries requiring hospitalization. Clinicians are increasingly adopting tissue-engineering methods for treatment due to limitations in the use of autogenous and autologous grafts. The aim of this study was to synthesize a novel, bioactive, porous, mechanically stable bone graft substitute/scaffold. Strontium- and zinc-containing bioactive glasses were synthesized and used with varying amounts of alginate to form scaffolds. Differential scanning calorimetric analysis (DSC), FTIR, XRD, and NMR techniques were used for the characterization of scaffolds. SEM confirmed the adequate porous structure of the scaffolds required for osteoconductivity. The incorporation of the bioactive glass with alginate has improved the compressive strength of the scaffolds. The bioactivity of the scaffolds was demonstrated by an increase in the pH of the medium after the immersion of the scaffolds in a Tris/HCl buffer and by the formation of orthophosphate precipitate on scaffolds. The scaffolds were able to release calcium, strontium and zinc ions in the Tris/HCl buffer, which would have a positive impact on osteogenesis if tested in vivo

Magnesium substitution in calcium and strontium fluoro-phospho-aluminosilicate glasses by multinuclear 19F, 31P, 27Al, and 29Si MAS-NMR spectroscopy

Department of Trade and Industry, UK, under the project number of TP/5/REG/6/I/H0669

Bioactive glass composite for orthodontic adhesives - Formation and characterisation of apatites using MAS-NMR and SEM.

OBJECTIVES: To study the dissolution and fluoroapatite (FAP) formation of a new bioactive glass (BAG)-resin adhesive in an acidic solution in reference to neutral solutions, using the magic angle spinning-nuclear magnetic resonance (MAS-NMR) and the scanning electron microscopy (SEM). METHODS: BAG composite disks (n = 90) were prepared from, novel fluoride-containing BAG-resin. Three sample groups (n = 30) of the disks were immersed in Tris buffer pH = 7.3 (TB), neutral artificial saliva pH = 7 (AS7) and acidic artificial saliva pH = 4 (AS4) at ten time points (from 6 h to 6 months). Half of the immersed disks at each time point were crushed into a powder and investigated by the solid state MAS-NMR. SEM studies were undertaken by embedding the other half of the immersed disk in a self-cure acrylic where the fracture surface was imaged. RESULTS: MAS-NMR results show that the BAG composite degraded significantly faster in AS4 compared to TB and AS7. At the end of the immersion period (6 months), around 80% of the glass particles in AS4 had reacted to form an apatite, evidenced by the sharp peak at 2.82 ppm in 31P signals compared to a broader peak in TB and AS7. It also shows evidence of fluorapatite (FAP) formation, indicated by 19F signal at -103 ppm, while signal around -108 ppm indicated the formation of calcium fluoride, from the excess Ca2+ and F- especially on longer immersion. SEM images confirm higher degradation rate of the BAG composite in AS4 and reveal the impact of time on the dissolution of more glass particles. The images also indicate apatite formation around the glass particles in TB and AS4, while it forms predominantly over the disk surface in AS7. SIGNIFICANCE: BAG composite demonstrate smart reactivity in response to pH change which has a potential clinical benefit against demineralization and promoting remineralisation to form more stable fluorapatites

Characterization of chemical reactions of silver diammine fluoride and hydroxyapatite under remineralization conditions.

INTRODUCTION: Silver Diammine Fluoride (SDF) is a clinically used topical agent to arrest dental caries. However, the kinetics of its chemical interactions with hydroxyapatite (HA), the principal inorganic component of dental enamel, are not known. The aim was to characterize the step-wise chemical interactions between SDF and HA powder during the clinically important process of remineralization. METHODS: Two grams of HA powder were immersed in 10 ml acetic acid pH = 4.0 for 2 h to mimic carious demineralization. The powder was then washed and dried for 24 h and mixed with 1.5 ml SDF (Riva Star) for 1 min. The treated powder was then air-dried for 3 min, and 0.2 g was removed and stored in individual tubes each containing 10 ml remineralizing solution. Powder was taken from each tube at various times of exposure to remineralization solution (0 min, 10 min, 2 h, 4 h, 8 h, 24 h, and 10 days), and characterized using Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. RESULTS AND DISCUSSION: 19F MAS-NMR spectra showed that calcium fluoride (CaF2) started to form almost immediately after HA was in contact with SDF. After 24 h, the peak shifted to -104.5 ppm suggesting that fluoride substituted hydroxyapatite (FSHA) was formed with time at the expense of CaF2. The 31P MAS-NMR spectra showed a single peak at 2.7 ppm at all time points showing that the only phosphate species present was crystalline apatite. The 35Cl MAS-NMR spectra showed formation of silver chloride (AgCl) at 24 h. It was observed that after the scan, the whitish HA powder changed to black color. In conclusion, this time sequence study showed that under remineralization conditions, SDF initially reacted with HA to form CaF2 which is then transformed to FSHA over time. In the presence of chloride, AgCl is formed which is subsequently photo-reduced to black metallic silver