Fluorcanasite Glass-ceramics Research Articles

Influence of TiO2 content on phase evolution, microstructure and properties of fluorcanasite glass-ceramics prepared through sintering procedure for dental restoration applications

This study aims to highlight the role of TiO2 (titanium dioxide) on concurrent densification-crystallization behavior, microstructure as well as mechanical and chemical properties of fluorcanasite glass-ceramics. According to the obtained results, the addition of TiO2 to the base composition (stoichiometric fluorcanasite) and an increase of its content, decreased crystallinity of the relevant glass-ceramics; but improved their sinterability. Fully densified glass-ceramics were obtained from TiO2 containing compositions after sintering at 900–950 °C. Calcium fluoride and fluorcanasite crystallized in all fabricated glass-ceramics during sintering; while goetzenite crystallized as the dominant crystalline phase in those glass-ceramics contained more than 6 weight ratios of TiO2. On the basis of microstructural observation, the interlocking status between the precipitated crystals was remarkably diminished by an increase of TiO2 content. Measurement of mechanical properties confirmed the rise of Vickers micro-hardness and simultaneous decrease of flexural strength and fracture toughness by enhancing of TiO2 content in the examined glass-ceramics.

Manufacture, characterisation and properties of novel fluorcanasite glass–ceramics

ObjectiveThe aim of this study was to investigate the manufacture and characterisation of different compositions of fluorcanasite glass–ceramics with reduced fluorine content and to assess their mechanical and physical properties. MethodsThree compositional variations (S80, S81 and S82) of a fluorcanasite glass were investigated. Differential thermal analysis (DTA) and X-ray diffraction (XRD) identified crystallisation temperatures and phases. X-ray fluorescence (XRF) determined the element composition in the glass–ceramics. Different heat treatments [2h nucleation and either 2 or 4h crystallisation] were used for the glasses. Scanning electron microscopy (SEM) examined the microstructure of the cerammed glass. The chemical solubility, biaxial flexural strength, fracture toughness, hardness and brittleness index of S81 and S82 fluorcanasite were investigated with lithium disilicate (e.max CAD, Ivoclar Vivadent) as a commercial comparison. Statistical analysis was performed using one-way ANOVA with Tukey's multiple comparison tests (P<0.05). Weibull analysis was employed to examine the reliability of the strength data. ResultsAll compositions successfully produced glasses. XRD analysis confirmed fluorcanasite formation with the S81 and S82 compositions, with the S82 (2+2h) showing the most prominent crystal structure. The chemical solubility of the glass–ceramics was significantly different, varying from 2565±507μg/cm2 for the S81 (2+2h) to 722±177μg/cm2 for the S82 (2+2h) to 37.4±25.2μg/cm2 for the lithium disilicate. BFS values were highest for the S82 (2+2h) composition (250±26MPa) and lithium disilicate (266±37MPa) glass–ceramics. The fracture toughness was higher for the S82 compositions, with the S82 (2+2h) attaining the highest value of 4.2±0.3MPam1/2(P=0.01). The S82 (2+2h) fluorcanasite glass–ceramic had the lowest brittleness index. ConclusionThe S82 (2+2h) fluorcanasite glass–ceramic has acceptable chemical solubility, high biaxial flexural strength, fracture toughness and hardness. Clinical significanceA novel glass–ceramic has been developed with potential as a restorative material. The S82 (2+2h) has mechanical and physical properties that would allow the glass–ceramic to be used as a machinable core material for veneered resin-bonded ceramic restorations.

Osteoconductivity of modified fluorcanasite glass–ceramics for bone tissue augmentation and repair

Modified fluorcanasite glasses were fabricated by either altering the molar ratios of Na(2)O and CaO or by adding P(2)O(5) to the parent stoichiometric glass compositions. Glasses were converted to glass-ceramics by a controlled two-stage heat treatment process. Rods (2 mm x 4 mm) were produced using the conventional lost-wax casting technique. Osteoconductive 45S5 bioglass was used as a reference material. Biocompatibility and osteoconductivity were investigated by implantation into healing defects (2 mm) in the midshaft of rabbit femora. Tissue response was investigated using conventional histology and scanning electron microscopy. Histological and histomorphometric evaluation of specimens after 12 weeks implantation showed significantly more bone contact with the surface of 45S5 bioglass implants when compared with other test materials. When the bone contact for each material was compared between experimental time points, the Glass-Ceramic 2 (CaO rich) group showed significant difference (p = 0.027) at 4 weeks, but no direct contact at 12 weeks. Histology and backscattered electron photomicrographs showed that modified fluorcanasite glass-ceramic implants had greater osteoconductivity than the parent stoichiometric composition. Of the new materials, fluorcanasite glass-ceramic implants modified by the addition of P(2)O(5) showed the greatest stimulation of new mineralized bone tissue formation adjacent to the implants after 4 and 12 weeks implantation.

Microstructure and mechanical properties of fluorcanasite glass-ceramics for biomedical applications

Four fluorcanasite glass-ceramics were fabricated by controlled heat-treatment of as-cast Glasses A–D. These compositions have been reported previously but essentially, Glass A had the stoichiometric composition (Ca5Na4K2Si12O30F4) and Glasses B–D were modified by reducing the Na2O concentration (B), adding excess CaO (C) and P2O5 (D). The latter two compositions have been shown to have promising bioactive response in cell culture and simulated body fluid experiments. Devitrification of the stoichiometric composition resulted in poor mechanical properties with crumbling often observed on machining. As a result, no mechanical data could be obtained. In all modified compositions, heat-treatment between 780 °C and 900 °C resulted in measurable indentation fracture toughness (IFT) and biaxial flexural strength (BFS). IFT was optimised in Glass C at 800 °C (2.53 ± 0.02 MPa m½), but the biaxial flexural strength (BFS) was low, 167 ± 17 MPa, compared to other compositions. For heat- treated Glass D optimum mechanical properties were obtained at 800 °C with BFS and IFT, 249 ± 23 MPa and 1.95 ± 0.01 MPa m½, respectively. The relationship between the mechanical properties and microstructure is discussed.

In vitro osteogenesis on fluorcanasite glass-ceramic with three different chemical compositions

This study aimed at investigating in vitro osteogenesis on three fluorcanasite glass-ceramic compositions with different solubilities (K3, K5, and K8). Osteoblastic cells were obtained from human alveolar bone fragments and cultured under standard osteogenic condition until subconfluence. First passage cells were cultured on K3, K5, and K8 and on Bioglass((R)) 45S5 (45S5-control). Cell adhesion was evaluated at 24 h. For proliferation and viability, cells were cultured for 1, 4, and 10 days. Total protein content and alkaline phosphatase (ALP) activity were measured at 7, 14, and 21 days. Cultures were stained with Alizarin red at 21 days, for detection of mineralized matrix. Data were compared by ANOVA followed by Duncan's test. Cell adhesion, cell proliferation, viability, total protein content, and ALP activity were not affected by fluorcanasite glass-ceramic composition and solubility. Bone-like formation was similar on all fluorcanasite glass-ceramics and was reduced compared to 45S5. The changes in the chemical composition and consequently solubility of the fluorcanasite glass-ceramics tested here did not significantly alter the in vitro osteogenesis. Further modifications of the chemical composition of the fluorcanasite glass-ceramic would be required to improve bone response, making this biomaterial a good candidate to be employed as a bone substitute.

The effect of investment materials on the surface of cast fluorcanasite glasses and glass–ceramics

Modified fluorcanasite glass-ceramics were produced by controlled two stage heat-treatment of as-cast glasses. Castability was determined using a spiral castability test and the lost-wax method. Specimens were cast into moulds formed from gypsum and phosphate bonded investments to observe their effect on the casting process, surface roughness, surface composition and biocompatibility. Both gypsum and phosphate bonded investments could be successfully used for the lost-wax casting of fluorcanasite glasses. Although the stoichiometric glass composition had the highest castability, all modified compositions showed good relative castability. X-ray diffraction showed similar bulk crystallisation for each glass, irrespective of the investment material. However, differences in surface crystallisation were detected when different investment materials were used. Gypsum bonded investment discs showed slightly improved in vitro biocompatibility than equivalent phosphate bonded investment discs under the conditions used.

Bone response to three different chemical compositions of fluorcanasite glass‐ceramic

The aim of this study was to evaluate the bone response to three fluorcanasite glass-ceramic compositions with different solubilities (K3, K5, and K8) after implantation in a femur rabbit model. Fluorcanasite glass-ceramic rods were implanted bilaterally in the mid-shafts rabbit femurs. Implants were harvested at 8 and 12 weeks and prepared for histological and histomorphometric analyses at the light microscope level. Bioglass 45S5 rods were used as a control material. At 8 weeks, all fluorcanasite glass-ceramics were entirely surrounded by a nonmineralized connective tissue. At 12 weeks, reduced areas of bone tissue were observed in the cortical area in direct contact with the K3 and K5 fluorcanasite glass-ceramics compared to Bioglass 45S5, whereas no bone tissue was observed in direct contact with the K8 surface. Bone-to-implant contact in the cortical area was affected by the material chemical composition and ranked as follows: Bioglass 45S5>K3>K5>K8 (p=0.001). In the bone marrow, a layer of fibrous connective tissue formed in direct contact with the fluorcanasite glass-ceramics and Bioglass 45S5, and only rarely exhibited contact osteogenesis. All the fluorcanasite glass-ceramics appeared to degrade in the biological environment. The solubility ratio did not alter significantly the biological reply of the fluorcanasite glass-ceramics in vivo. Further modifications of the chemical composition of the fluorcanasite glass-ceramic are required to increase the stability of the material in vivo.

In vitro biocompatibility of fluorcanasite glass‐ceramics for bone tissue repair

Fluorcanasite glass-ceramics were produced by controlled two stage heat-treatment of as-cast glasses. These glasses were modified from stoichiometric fluorcanasite composition by either adding P(2)O(5) or altering the molar ratios of Na(2)O and CaO. Commercial bioactive 45S5 Bioglass(R) was also prepared in-house to evaluate the relative in vitro biocompatibility of fluorcanasite glass-ceramics. The scanning electron microscopy (SEM) images showed that cells had colonized the surfaces of fluorcanasite glass-ceramics to form a confluent sheet. Quantitative MTT assay results were in good agreement with the qualitative SEM observations. It was concluded that incorporation of excess calcium oxide or P(2)O(5) in stoichiometric glass composition improved in vitro biocompatibility. Controlled heat-treatment further improved the biological response of cultured bone cells to modified fluorcanasite glass-ceramics when compared with their parent glasses. Ion release and pH data suggested a strong correlation between solubility (in particular, Na ion release) and biocompatibility. Reduced solubility, Na ion release, and related pH effects appeared to be the principal mechanisms responsible for improvement in in vitro biocompatibility.

Castability and Biocompatibility of Novel Fluorcanasite Glass-Ceramics

Novel fluorcanasite based glass-ceramics were produced by controlled two stage heattreatment of as-cast glasses. Castability of parent glasses was determined using a graduated spiral cast piece. Fluorcanasite glasses were also cast to form complex shapes using the lost wax casting technique. Gypsum and phosphate bonded investments were used to investigate their effect on the casting process, cast surface crystallinity and biocompatibility. The stoichiometric composition had the greatest castability but the other two modified compositions also had good castability. X-ray diffraction showed similar bulk crystallisation for each glass irrespective of the investment material. However, some differences in surface crystallisation in the presence of different investment materials were detected. Discs cast using gypsum bonded investment showed greater in vitro biocompatibility than equivalent discs cast using phosphate bonded investment under the conditions used. Gypsum and phosphate bonded investments could both be successfully used for the lost wax casting of these novel fluorcanasite glasses.

Evaluation of Modified Fluorcanasite Glass-Ceramics for Bone Tissue Augmentation

Evaluation of Modified Fluorcanasite Glass-Ceramics for Bone Tissue Augmentation

Effect of Alumina on the Strength, Fracture Toughness, and Crystal Structure of Fluorcanasite Glass‐Ceramics

The influence of alumina content (0‐15 wt% Al2O3) on the indentation strength, fracture toughness (KIc), and crystal structure of fluorcanasite (Al2O3‐CaO‐F‐K2O‐Na2O‐SiO2) glass‐ceramics was analyzed. Increasing the Al2O3 content from 0 wt% (CAN0) to 8 wt% (CAN8) caused the mean indentation strength and KIc values to decrease from 213 ± 14 MPa and 2.7 ± 0.1 MPa·m1/2, respectively, for the CAN0 glass‐ceramic to 78 ± 16 MPa and 1.3 ± 0.2 MPa·m1/2, respectively, for the CAN8 glass‐ceramic. Increased Al2O3 concentrations (0‐15 wt%) significantly affected the crystal size, crystal shape, aspect ratio, and crystal aggregation characteristics of the fluorcanasite glass‐ceramics. The addition of greaterthan equal to8 wt% of Al2O3 to fluorcanasite glass caused a transformation from canasite to leucite.