Lithium disilicate (Li2Si2O5) glass‐ceramics are currently a more widely used all‐ceramic restorative material due to their good mechanical properties and excellent aesthetic properties. However, ...they have a series of problems such as high brittleness and low fracture toughness, which has become the main bottleneck restricting its development. Therefore, in order to compensate for these shortcomings, we propose to prepare a reinforced glass‐ceramics with better mechanical properties and to test the biosafety and chemical solubility of the material. Li2Si2O5 whiskers were synthesized by a one‐step hydrothermal method, and multi‐scale crystal‐enhanced Li2Si2O5 glass‐ceramics were prepared by reaction sintering. The biosafety of multi‐scale crystal‐reinforced Li2Si2O5 glass‐ceramics was investigated by in vitro cytotoxicity test, rabbit pyrogen test, mice bone marrow micronucleus test, skin sensitization test, sub‐chronic systemic toxicity test, and chronic systemic toxicity test. Additionally, the chemical solubility of multi‐scale crystal‐reinforced Li2Si2O5 glass‐ceramics was investigated. The test results showed that the material was non‐cytotoxic, non‐thermogenic, non‐mutagenic, non‐sensitizing, and non‐systemic. The chemical solubility, determined to be 377 ± 245 μg/cm2, complied with the ISO 6872 standard for the maximum solubility of ceramic materials. Multi‐scale crystal‐reinforced Li2Si2O5 glass‐ceramics' biosafety and chemical solubility met current normative criteria, and they can move on to mechanical property measurements (such as flexural strength test, fatigue life test, friction and wear property study, etc.) and bonding property optimization, which shows promise for future clinical applications.
The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2 ...glass system has been reported here. Increased amount of MgO enhanced the participation of Al2O3 as a glass network former along with SiO4 tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (∼10 GPa) and elastic modulus (∼127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.
Transparent glass-ceramic in the SiO2-Li2O-Na2O-Al2O3-BaO-P2O5-ZrO2 system were prepared by the three-stage heat treatment process. The effects of Al2O3 content on the crystallization behavior, ...microstructure, and physical properties of the glass-ceramics were investigated by differential scanning calorimeter (DSC), X-Ray Diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscope (SEM). As the Al2O3 increases from 4 to 7 mol%, all the Al3+ ions are present in the AlO4 tetrahedra and participate in the glass network, resulting in the more compact structure of glass. The increasing in the glass network connectivity leads to the higher crystallization activation energy, hindering the formation of lithium disilicate and promoting the precipitation of Al-containing crystalline phases. The main crystalline phase of glass-ceramics transform from lithium disilicate and petalite to LixAlxSi1-xO2, and the transmittance of glass-ceramics decrease. Upon the three-steps heat treatments of 540°C/4h + 610°C/2h + 730°C/4h, the glass-ceramic with 4 mol% Al2O3 containing petalite and lithium disilicate crystals shows high transparency of ∼85% in the visible light range, high hardness 8.07 GPa, and fracture toughness of 1.37 MPa·m1/2, which shows great potential in the applications of protective material for mobile devices.
This study introduces an innovative approach to enhance the antibacterial properties of lithium disilicate glass ceramics, widely used in dental restorations. We explored the efficacy of tannic acid ...(TA) and polyethyleneimine (PEI) as coating agents, capitalizing on a robust defense against microbial colonization and biofilm formation. We employed various analytical techniques, including differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), to characterize the physical, chemical, and antibacterial properties of the TA/PEI coated glass-ceramics. Results indicated a notable improvement in the mechanical properties, such as Weibull modulus, elastic modulus, and fracture toughness of the coated samples. Moreover, the TA/PEI coatings displayed superior thermal stability and effective leaching behavior in different pH, pertinent to dental applications. Significantly, the TA/PEI coatings exhibited high antibacterial activity against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria, making them promising candidates for enhancing the bioactivity of dental restorative materials. This study lays the foundation for developing advanced antibacterial coatings for dental applications, aiming to improve patient outcomes in dental care.
•The ZrO2 addition polymerizes the overall glass network by forming the Si-O-Zr bonds.•P2O5 addition further strengthens the glass network by increasing Q4 units.•ZrO2 addition hampers the LS2 phase ...formation.•High Hv (6.7±0.09 GPa) and an optical transmittance 63% have been obtained.
99(1Li2O:2SiO2)-1K2O glasses have been synthesized by a melt quenching technique with the consecutive addition of ZrO2 and P2O5. The addition of ZrO2 decreases the Q2 units and increases the Q3 units due to the formation of Si-O-Zr bonds. Whereas the P2O5 addition increases the fraction of Q4 units while decreasing the Q2 and Q3 units by forming disordered Li3PO4 and Li4P2O7 regions in the glasses. The changes in the fraction of Q2, Q3 and Q4 units affect the crystallization sequence in glass-ceramics. The ZrO2 addition hampers the Li2Si2O5 phase formation and allows the Li2SiO3 phase formation. Whereas, the P2O5 addition promotes the formation of both the Li2Si2O5 and Li2SiO3 phases. For the glass-ceramic containing 2 mol % P2O5, the highest Hv 6.7±0.09 GPa and an optical transmittance 63 % (at a wavelength of 550 nm for the specimen thickness 2 mm) could be achieved.
To evaluate the marginal and internal fit of lithium disilicate and zirconia crowns using two optical coherence tomography (OCT) systems in order to estimate inter-system variations.
Ten lithium ...disilicate and 10 cubic stabilized zirconia crowns were placed on prepared artificial teeth without cement. Marginal discrepancy and internal cement gap of the crowns were assessed on images obtained using a swept source OCT (SS-OCT) and a spectral domain OCT (SD-OCT). Medians and interquartile ranges were calculated for both materials and OCT systems. Thereafter, Wilcoxon signed rank test was carried out.
No significant difference was found between the two OCT systems for absolute marginal discrepancy of either lithium disilicate (SS-OCT: 182 µm, SD-OCT: 214 µm; p = .922) or zirconia crowns (SS-OCT: 116 µm, SD-OCT: 121 µm; p = .232). Regarding internal cement gap, no significant difference was found between the two OCT systems for lithium disilicate crowns (SS-OCT: 128 µm, SD-OCT: 128 µm; p = .064). However, for zirconia crowns the SD-OCT showed significantly higher (p = .027) internal cement gap (92 µm) than the SS-OCT (68 µm). Moreover, it was not possible to assess the internal fit of zirconia crowns in 47% and 34% of the sites using SD-OCT and SS-OCT, respectively.
No significant difference was noted in the ability of SS-OCT and SD-OCT to assess the marginal and internal fit of lithium disilicate crowns, nor the marginal fit of zirconia crowns. On the contrary, drawbacks regarding the assessment of internal fit of zirconia crowns using both OCT systems were observed.
This study investigates a novel non-stoichiometric lithia-silica glass-ceramic (Bioactive LD) designed for bone tissue engineering applications. Incorporating SiO2–Li2O–CaO–P2O5–K2O–SrO–ZnO, the ...glass-ceramic underwent optimized thermal treatments resulting in a composition predominantly of lithium disilicate (Li2Si2O5 - 87 %) with a minor lithium phosphate phase (Li3PO4 - 13 %). Structural analysis using X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed a refined microstructure with Li2Si2O5 crystals in rod form with a high aspect ratio of around 4:1. Expanding on previous work, this study investigates the in vitro osteoblastic response of Bioactive LD compared to a commercial glass-ceramic (E-Max CAD®). The evaluation, employing live/dead assays, resazurin assays, and alkaline phosphatase activity measurements at different time points, demonstrated comparable cell viability and proliferation on both glass-ceramics. The chemical stability of the samples was tested, and the Bioactive LD showed a higher amount of leached ions in the solution, without significant mass loss, consistent with the standardized values for a class 4 material (ISO 6872), with no significant change in its microstructure. The chemical solubility tests were investigated employing SEM and energy dispersive X-ray analysis (EDS), giving insights into the role of leached ions in the microstructure and bioactivity of the materials. Notably, Bioactive LD exhibits higher alkaline phosphatase activity, indicating enhanced stimulation of osteoblastic cells. Additionally, the Bioactive LD promotes mineralization matrix production, as evidenced by alizarin red S staining. The study also employs SEM-EDS to evaluate the formation of apatite mineralized matrix. Bioactive LD exhibits a homogeneous mineralized matrix with increased Calcium and Sulfur signals, suggesting early hydroxyapatite formation after Alizarin Red S assay. In contrast, Commercial LD shows limited reactivity and bioactivity, with no substantial calcium deposition. An indirect cytotoxicity test indicates minimal cytotoxicity for Bioactive LD, while Commercial LD exhibits slight cytotoxicity, consistent with findings from the literature. The results highlight Bioactive LD's potential for bone regeneration, emphasizing its enhanced bioactivity and the formation of a complex mineralized matrix that could contribute to improved bone integration properties.
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•New insights on the chemical stability and the role of leached ions (Ca, Li, P, Sn, Zn) from residual glass in enhancing cell viability.•Bioactive LD showed better and homogeneous MG63 cells adhesion after 21 days compared with commercial LD, without causing hemolysis.•Bioactive LD promoted good proliferation of cells and the formation of a stable apatite mineralized matrix, as demonstrated by SEM/EDS analyses.•Bioactive LD exhibits higher alkaline phosphatase activity, indicating enhanced stimulation of osteoblastic cells.
•Here we evaluate the SEPB method using large datasets of two fine dental grade ceramics to assess the sensitivity of the validity criteria in ISO 15732 and ASTM C 1421 and the effect of their ...violations in the obtained fracture toughness value (KIc).•We compile datasets including or excluding validity criteria and combine those of the two standards to establish their effect on the mean and scatter of the data.•We find that most criteria have little impact on the obtained KIc, whereas increases in precrack frontline asymmetry result in a near-linear decrease in the KIc-value.•We argue for tightening the criterion precrack frontline asymmetry and for the dropping of criteria regulating the extent of stable crack extension.
The Single-Edge-Precracked-Beam (SEPB) method for the testing of fracture toughness (KIc) of ceramic materials is a variation of the Single-Edge-Cracked-Beam (SEPB) method for the test of metallic materials that creates a sharp precrack not by fatigue, but by a “bridge indentation” technique that induces a crack to pop-in under compression loading. This precrack is sharp and overcomes the issue of blunt notch-root radii resulting from the Single-Edge-V-Notched-Beam (SEVNB) method, which overestimates the KIc of ceramics with submicrometric microstructures. However, the difficulties in obtaining a valid precrack and measurement make of the SEPB a low-yield, time- and cost-intensive method. Here we evaluate the SEPB method using large datasets of two fine dental grade ceramics to assess the sensitivity of the validity criteria in ISO 15732 and ASTM C 1421 and the effect of their violations in the obtained KIc. We compile datasets including or excluding validity criteria and combine those of the two standards to establish their effect on the mean and scatter of the data. We discuss the appropriateness of the validity ranges and of some criteria as a whole, while arguing for tightening the criterion precrack frontline asymmetry and for the dropping of criteria regulating the extent of stable crack extension.
During the last decades, the nucleation and crystallization of the Li2O−SiO2 system has been widely investigated and its particular theoretical features disclosed. However, multicomponent lithium ...disilicate systems, being of higher technological interest, still require further studies aiming at better tailoring their relevant mechanical and chemical properties. Here we report on the effects of SiO2/Li2O molar ratio and the addition of P2O5 on the structure and crystallization behaviour of multicomponent lithium disilicate based glasses. Two non-stoichiometric P2O5-free lithium disilicate based glasses featuring equimolar contents of K2O and Al2O3 and with SiO2/Li2O molar ratios of 2.62 and 2.92 were synthesized in the Li2O−SiO2 system through the melt-quench technique. The influence of partially replacing (K2O + Al2O3) by P2O5 while keeping the same SiO2/Li2O molar ratios of P2O5-free glasses was investigated. The structural features of glasses were assessed by nuclear magnetic resonance. Differential thermal analysis was used to study crystallization kinetics and the crystalline phase evolution was followed by X-ray diffraction. The results showed that an increase in SiO2/Li2O molar ratio decreased the overall crystallization rate, preventing the formation of lithium disilicate. However, adding P2O5 had an opposite effect, enhancing the formation of fine lithium disilicate crystals. The nucleating role of P2O5 is discussed.
•Devitrification of Li2O−SiO2 glasses depends on SiO2/Li2O ratio and P2O5 addition.•NMR spectroscopy was an essential tool for disclosing the glass structure.•DTA and heat treatments disclosed the crystallization behaviour.•The specific role of P2O5 as nucleating agent is discussed.
In order to obtain lithium disilicate glass-ceramics for dental restoration with both high strength and high translucency, lithium disilicate glass-ceramics with different MgO contents were prepared ...by melt-casting and heat treatment method. The effects of MgO content on the crystallization temperature, microstructure and flexural strength of lithium disilicate glass-ceramics were investigated. The results indicate that Mg2+ exists in the form of MgO4 in the network of lithium disilicate glass-ceramics when the MgO content is 0.56 mol% (M0.56), which is beneficial to increasing the homogeneity and thermal stability of the glass system, and short rod-like lithium disilicate crystals can be formed after heat treatment at 840°C. Thus, the obtained lithium disilicate glass-ceramics exhibit excellent comprehensive performance, with the flexural strength being 312 ± 23 MPa, and the average transmittance of visible light being 37.3% (d = 1.62 mm). Especially, the glass-ceramic sample shows better translucency than the commercially available products. The research results are of great significance for developing high performance lithium disilicate glass ceramics and promoting its broad application in the field of dental restoration.
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•Lithium disilicate glass-ceramics with high flexural strength and good translucency were prepared.•The coordination number of Mg2+ with oxygen in the glass-ceramic is closely related to the content of MgO.•MgO6 is beneficial to crystallization of lithium disilicate and improvement of strength, but is not good for translucency.•MgO4 is conducive to improving the uniformity of lithium disilicate glass-ceramic, which is good for translucency.
