Bioactive glasses, particularly Bioglass® 45S5, have been used to clinically regenerate human bone since the mid-1980׳s, owing to their ability to degrade in physiological solutions, release ions and ...form an apatite surface layer, which cells adhere to and proliferate on. Although low pH conditions do occur in the human body, e.g. during bacterial infections, in vitro dissolution experiments are usually performed at a physiological pH of 7.3 exclusively. Here, we investigated the dissolution behaviour of 45S5 at low pH (5) and high pH (9) in addition to pH 7.3. The results show that ion release occurs significantly faster at low pH, resulting in significantly faster apatite formation (3h vs. 6h at pH 7.3). By contrast, at pH 9 low ion exchange rates were observed, resulting in no significant apatite formation during the time period studied. Results suggest that low pH caused by bacterial infection is unlikely to inhibit apatite formation and, thus, bioactive glass clinical performance.
•Enhanced ion release of Bioglass® 45S5 at low pH.•Enhanced apatite formation of Bioglass® 45S5 at low pH.•Negligible apatite formation of Bioglass® 45S5 at pH 9.
Dental restoration aesthetics, particularly the translucency of modern dental restorative filling materials depends on the refractive index (RI) match between the different components in the ...material. In the case of dental composites (DC), the RI of the polymer must match the RI of the filler otherwise the material is optically opaque and has limited depth of cure. In the case of glass ionomer cements (GICs), the RI of the ion-leachable glass must match the RI of the polysalts to engineer a smart material with a tooth-like appearance. The RI of oxide glasses can be calculated by means of Appen factors. However, no Appen factors are available for the fluoride components in dental glasses. Therefore, the objective of this study is to empirically derive composition-specific Appen factors for the metal fluorides in complex multicomponent glasses for use in dentistry.
Two series of bioactive glasses and two series of ionomer-type glasses were produced for this study. Refractive indices of all glasses were then measured by the Becke Line technique. Thereafter, composition-specific factors for the metal fluorides were derived.
It was found that increasing metal fluoride content reduces the RI of multicomponent dental glasses linearly. A series-specific Appen factors for the metal fluorides were successfully derived and allow RI calculation to within 0.005.
This paper proposes a modified Appen Model with composition-specific Appen factors for the metal fluorides for the development of dental restoratives with enhanced aesthetics and improved depth of cure of dental composites.
Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in ...particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO(2)-P(2)O(5)-CaO-Na(2)O with increasing amounts of CaF(2) were prepared by keeping network connectivity and the ratio of all other components constant. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37 degrees C over up to 2 weeks were investigated. Crystal phases formed in SBF were characterized using infrared spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy ((19)F and (31)P MAS-NMR). Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF(2)) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and possibly favour formation of apatite.
Bioactive glasses convert to a biomimetic apatite when in contact with physiological solutions; however, the number and type of phases precipitating depends on glass composition and reactivity. This ...process is typically followed by X-ray diffraction and infrared spectroscopy. Here, we visualise surface mineralisation in a series of sodium-free bioactive glasses, using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) and X-ray nano-computed tomography (nano-CT). In the glasses, the phosphate content was increased while adding stoichiometric amounts of calcium to maintain phosphate in an orthophosphate environment in the glass. Calcium fluoride was added to keep the melting temperature low. TEM brought to light the presence of phosphate clustering and nearly crystalline calcium fluoride environments in the glasses. A combination of analytical methods, including solid-state NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation. Nano-CT gives insight into bioactive glass particle morphology after immersion, while TEM illustrates how compositional changes in the glass affect microstructure at a sub-micron to nanometre-level.
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.
The influence of substituting strontium for calcium in the following glass series 49.46 SiO
2–1.07 P
2O
5–(23.08-X) CaO–X SrO–26.38 Na
2O was studied on the physical properties. Solid state nuclear ...magnetic resonance and vibrational spectroscopy showed that the glasses were predominantly composed of Q
2 silicate chains. Addition of strontium did not result in any structural alteration of the glass network due to the similar role of SrO compared with that of CaO. The density increased with strontium content whilst the oxygen density decreased indicating a more expanded glass network. The glass transition temperature reduced with strontium substitution in a linear fashion and there was no evidence of a mixed alkaline earth effect with a lower than expected glass transition temperature. Dilatometric softening points also reduced with increasing strontium content, whilst the thermal expansion coefficients increased. The results are consistent with a weaker network as a result of the lower charge to size ratio of Sr
2+ compared to Ca
2+.
Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering ...from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.
•The concentration of fluoride does not reflect the rate of fluoride release.•Calcium phosphate formula and/or additives would influence fluoride ion release.•CPP-ACP or Bioglass® could be source of ...bioavailable calcium and phosphate.
To compare ion release characteristics of three different dental varnishes either containing CPP-ACP and fluoride (CPP-ACPF, MI Varnish GC, Japan), bioactive glass and fluoride (BGAF, Dentsply Sirona USA) or fluoride alone (NUPRO White, Dentsply Sirona USA) using fluoride-Ion Selective Electrode (F-ISE), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), 19F and 31P Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR).
A thin layer (0.0674±0.0005g) of each varnish (20×25mm in area) was spread on a roughened glass slide (n=7). They were separately immersed in 10ml Tris buffer (0.06M, pH=7.30), and changed after 1, 2, 4, 6, 24 and 48h. Fluoride-ion concentration at each time using the F-ISE, whilst calcium and phosphate release were investigated using ICP-OES. XRD, FTIR. MAS-NMR analyses were also performed before and after immersion.
The cumulative F-ion release was significantly higher in CPP-ACPF (1.113mmol/g)>BGAF(0.638)>F(0.112) (p<0.001). The cumulative calcium and phosphorus were higher in the CPP-ACPF (0.137mmol/g, 0.119) than BGAF (0.067, 0.015) (p<0.001) respectively. The XRD and 19F MAS-NMR confirmed the presence of NaF peaks in all cases before immersion. There were less prominent signal and appearance of fluorapatite crystals after immersion. 19F MAS-NMR revealed CaF2 formation after immersion in both CPP-ACPF and BGAF. 31P MAS-NMR showed phosphate signals in both CPP-ACPF and BGAF before immersion. FTIR failed to show any signs of apatite formation.
Both CPP-ACP and bioactive glass enhanced ion release without compromising the bioavailability of fluoride. The CPP-ACPF varnish had the most promising ion release.
The aim of this study was to investigate the effects of TiO2/CaO addition on the crystallization and flexural strength of leucite glass-ceramics (GC). Synthesis of translucent and high strength GCs ...is important for the development of aesthetic and durable dental restorations. To achieve this, experimental aluminosilicate glasses (1–3 mol% TiO2 and CaO (B1, B2, B3)) were melted in a furnace to produce glasses. Glasses were ball milled, screened and heat treated via crystallization heat treatments, and characterized using XRD, differential scanning calorimetry, dilatometry, SEM and biaxial flexural strength (BFS). Increasing nucleation hold time (1–3 h) led to a reduction in crystallite number for B2 and B3 GC, and significant differences in leucite crystal size at differing nucleation holds within and across test groups (p < 0.05). A high area fraction of leucite crystals (55.1–60.8%) was found in the GC, with no matrix microcracking. Changes in the crystal morphology were found with higher TiO2/CaO addition. Mean BFS of the GC were 211.2–234.8 MPa, with significantly higher Weibull modulus (m = 18.9) for B3 GC. Novel glass compositions enriched with TiO2/CaO led to crystallization of leucite GC of high aspect ratio, with high BFS and reliability. The study’s findings suggest a potential high performance translucent leucite GC for use in the construction of dental restorations.
•New patented formulation of leucite glass-ceramics (OLG-C), with high BFS and SBS.•Novel leucite G-C with reduced flaw size and similar sandblasted BFS to IPS e.max®.•Resin bonding increased BFS for ...all G-Cs, with 24.6% increase for IPS e.max®.•OLG-C useful for minimally invasive, aesthetic and fracture resistant restorations.
To process novel leucite glass-ceramics and test the effects of surface treatment and resin bonding on the biaxial flexural strength (BFS) and shear bond strength (SBS).
Alumino–silicate glasses were ball-milled, and heat treated to form leucite glass-ceramics (LG-C, OLG-C), then sintered into ingots. Ingots were heat extruded into a refractory mould to form disc specimens (1.3×14mm diameter). IPS e.max® was used as a commercial comparison. Glass-ceramic test groups were sandblasted (Groups. 1, 4, 6), sandblasted, etched and adhesively bonded (Groups. 2, 5, 7) or lapped, etched and adhesively bonded (Groups. 3, 8). Specimens were adhesively bonded with Monobond S, followed by the application of Variolink II® cement and light curing. BFS testing was at 1mm/min and SBS testing at 0.5mm/min. Samples were characterised using XRD, SEM and profilometry.
XRD confirmed tetragonal leucite in LG-C/OLG-C and lithium disilicate/lithium orthophosphate in IPS e.max®. Mean BFS (MPa (SD)) were: Gp1 LG-C; 193.1 (13.9), Gp2 LG-C; 217.7 (23.0), Gp3 LG-C; 273.6 (26.7), Gp4 OLG-C; 255.9 (31); Gp5 OLG-C; 288.6 (37.4), Gp6 IPS e.max®; 258.6 (20.7), Gp7 IPS e.max®; 322.3 (23.4) and Gp8 IPS e.max®; 416.4 (52.6). The Median SBS (MPa) were Gp1 LG-C; 14.2, Gp2 LG-C (10s etch); 10.6 and Gp3 IPS e.max®; 10.8. Mean surface roughness was 5–5.1μm (IPS e.max®) and 2.6μm (LG-C).
Novel leucite glass-ceramics with reduced flaw size and fine microstructures produced enhanced BFS and SBS by resin bonding. These properties may be useful for the fabrication of minimally invasive aesthetic and fracture resistant restorations.
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