Remineralising fluorine containing bioactive glass composites.

OBJECTIVES: The objective was to investigate the mechanical properties, fluoride release and apatite formation of resin based dental composites based on a fluoride containing Bioactive Glass (BG) with and without a silylating agent. METHODS: A SiO2-P2O5-CaO-SrO-Na2O-CaF2 BG was synthesized by the melt quench route. This glass and a commercially available inert glass (IG) were incorporated into a light cured BisGMA-TEGMA resin. The composite resins were then evaluated in terms of their ability to form apatite by Fourier Transform Infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM) following immersion in artificial saliva at pH 4 (AS4) and pH 7 (AS7). The experiments were performed with and without silylation of the BG. The compressive strength and flexural strength were determined after 1, 28 and 84 days of immersion in the AS4 and AS7 immersion media. RESULTS: The FTIR spectra of the BG composites exhibited split bands at approximately 560 and 600 cm-1 corresponding to a apatite formation in the surface or on the surface under all immersion conditions. SEM showed the presence of a reacted layer of glass particles in the composite surface and the presence of a surface layer of apatite in AS7. The compressive strength and flexural strength were significantly higher for the silylated BG composites. The strengths of both silylated and non silylated BG composites and IG composites decreased upon immersion. SIGNIFICANCE: BG composites exhibit reduced strengths upon immersion but still exhibit strengths comparable to existing composites after 84 days of immersion.

Characterization of the bioactivity of two commercial composites.

The aim of this study was to characterize the ion release, pH changes and apatite formation ability of two potentially bioactive composites Cention N (CN) and Activa (ACT). Ion release and apatite formation was investigated in three different immersion media: Tris buffer pH 7.3 (TB), Artificial Saliva pH 4 (AS4) and Artificial Saliva pH 7 (AS7) in order to mimic the conditions present in the mouth. Fluoride release was followed using an ion selective electrode, whilst all other ions were determined by inductively coupled plasma optical emission spectroscopy. Apatite formation was followed by FTIR and XRD. SEM was used to follow glass degradation and apatite formation on both polished cross-sections and surfaces of the composites. ACT released very few ions including fluoride upon immersion in TB and AS7, but released more ions including significant quantities of Al in AS4. This would suggest the glasses in ACT are acid degradable fluoro-alumino-silicate glasses similar to the glasses used in glass ionomer cements. There was no evidence of any apatite formation with ACT. CN released more ions in TB and AS7 than ACT and formed an apatite like phase in AS7. The calcium fluoro-silicate glass in CN was observed to degrade significantly in AS4. CN has bioactive properties that may explain the low incidence of secondary caries found clinically with this composite.

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.

Fluoride containing bioactive glass composite for orthodontic adhesives - Apatite formation properties.

OBJECTIVES: Dental materials that can form apatite offer the potential to not only prevent demineralisation but enhance remineralisation of the enamel. The objective of this study was to investigate the ability of a novel BAG-resin adhesive to form apatite in 3 immersion media. METHODS: A novel fluoride containing BAG-resin adhesive described previously, with 80% by weight filler load, was used to fabricate 90 disks. Each disk was immersed in 10ml of either tris buffer (TB), or artificial saliva at pH=7 (AS7) or pH=4 (AS4). At ten time points (from 6h to 6 months), three disks were taken from each of the solutions and investigated by ATR-FTIR, XRD and SEM. RESULTS: The BAG-resin formed apatite on the disk surface, which increased with time, especially in AS4 and AS7. The apatite crystals formed in AS7 were highly oreintated and the oreintation increased with time. SIGNIFICANCE: This novel BAG-resin adhesive differs from the currently used adhesives by promting apatite formation, particularly under acidic conditions. Thus, applied in the clinical situation to bond orthodontic brackets, it may discourage the frequent occurrence of white spot lesion formation around the brackets.

Fluoride containing bioactive glass composite for orthodontic adhesives - ion release properties.

OBJECTIVE: Dental materials that release calcium, phosphate and fluoride ions could prevent demineralisation and/or enhance remineralisation of enamel. The objective was to develop a novel bioactive glass (BAG) resin and investigate pH changes and ion release in 3 immersion media. METHODS: Quench melt derived BAG (35.25% SiO2, 6% Na2O, 43% CaO, 5.75% P2O5, and 10% CaF2) was incorporated into a resin (42.25% BisEMA, 55% TEGDMA, 0.25% DMAEM, 0.5% camphorquinone and 2% 4-Meta), with a filler load of 80% by weight. Ninety composite disks for each BAG loading of 80%, 60%, 50%, 40%, 20%, and 0% were made and each disk was immersed in 10ml of either tris buffer (TB), or artificial saliva at pH=7 (AS7) or pH=4 (AS4), n=30 for each solution. Three disks of each loading were taken from each of the solutions, at ten time points (6h-6months), for measurement of pH, fluoride, calcium and phosphate. RESULTS: The BAG adhesive raised the pH in all the solutions, release Ca, PO4 and F ions especially in AS4. The rise in pH and the release of Ca and F are directly related to the BAG loading and the time of immersion. The pH and the ion releases were maintained and continued over 6months. SIGNIFICANCE: Unlike glass ionomer resins, favourable ions F, Ca and PO4 releases were maintained over a long time period especially in acidic condition for this novel BAG-resin composite. This indicates the resin has the potential to prevent formation and progression of early caries lesions.