Search Results (7)

Surface treatments play a crucial role in modifying the surface properties and biological performance of dental ceramics. This study investigated the effects of surface conditions on the wettability, cytocompatibility, and bacterial resistance of 4 mol% Y₂O₃-stabilized tetragonal zirconia polycrystal (4Y–TZP) and two lithium disilicate (Li₂Si₂O₅) glass ceramics (Amber^® Mill (AM) and Amber^® Mill Abut-Crown (AC)). Human gingival fibroblast (HGF-1) responses and biofilm formation on the machined, polished, and glazed samples were evaluated. The polished 4Y–TZP sample exhibited the highest water contact angle (WCA; 71.3°), while that of the AC samples decreased as the sample was machined (58.4°), polished (46.8°), and glazed (14.0°). The wettability, cytocompatibility, and bacterial resistance of the dental ceramics were significantly influenced by material type and surface condition. Among the surface-treated samples, the glazed specimens exhibited the lowest WCA and bulk density; thus, wettability is an important factor for cell proliferation and bacterial resistance. Among all samples, HGF-1 cells adhered well to the glazed ceramics and significantly proliferated over time. Particularly, the 4Y–TZP and AC glazed samples exhibited the lowest biomass and strong resistance to biofilm formation and bacterial adhesion. Thus, the glaze dramatically affected HGF-1 cell growth and antibiofilm formation. Full article

Using melt-derived LD glass powders and 5–20 M NaOH solutions, porous lithium disilicate (Li₂Si₂O₅, LD) glass–ceramics were prepared by the cold sintering process (CSP) associated with the post-annealing technique. In this novel technique, H₂O vapor originating from condensation reactions between residual Si–OH groups in cold-sintered LD glasses played the role of a foaming agent. With the increasing concentration of NaOH solutions, many more residual Si–OH groups appeared, and then rising trends in number as well as size were found for spherical pores formed in the resultant porous LD glass–ceramics. Correspondingly, the total porosities and average pore sizes varied from 25.6 ± 1.3% to 48.6 ± 1.9% and from 1.89 ± 0.68 μm to 13.40 ± 10.27 μm, respectively. Meanwhile, both the volume fractions and average aspect ratios of precipitated LD crystals within their pore walls presented progressively increasing tendencies, ranging from 55.75% to 76.85% and from 4.18 to 6.53, respectively. Young’s modulus and the hardness of pore walls for resultant porous LD glass–ceramics presented remarkable enhancement from 56.9 ± 2.5 GPa to 79.1 ± 2.1 GPa and from 4.6 ± 0.9 GPa to 8.1 ± 0.8 GPa, whereas their biaxial flexural strengths dropped from 152.0 ± 6.8 MPa to 77.4 ± 5.4 MPa. Using H₂O vapor as a foaming agent, this work reveals that CSP associated with the post-annealing technique is a feasible and eco-friendly methodology by which to prepare porous glass–ceramics. Full article

Owing to its excellent mechanical properties and aesthetic tooth-like appearance, lithium disilicate glass–ceramic is more attractive as a crown for dental restorations. In this study, lithium disilicate glass–ceramics were prepared from SiO₂–Li₂O–K₂O–P₂O₅–CeO₂ glass systems with various Al₂O₃ contents. The mixed glass was then heat-treated at 600 °C and 800 °C for 2 h to form glass–ceramic samples. Phase formation, microstructure, mechanical properties and bioactivity were investigated. The phase formation analysis confirmed the presence of Li₂Si₂O₅ in all the samples. The glass–ceramic sample with an Al₂O₃ content of 1 wt% showed rod-like Li₂Si₂O₅ crystals that could contribute to the delay in crack propagation and demonstrated the highest mechanical properties. Surface treatment with hydrofluoric acid followed by a silane-coupling agent provided the highest micro-shear bond strength for all ceramic conditions, with no significant difference between ceramic samples. The biocompatibility tests of the material showed that Al₂O₃-added lithium disilicate glass–ceramic sample was bioactive, thus activating protein production and stimulating the alkaline phosphatase (ALP) activity of osteoblast-like cells. Full article

In this paper, we used differential scanning calorimetry (DSC), high-temperature X-ray diffraction (HT-XRD), and confocal scanning laser microscopy (CSLM) to investigate the Li₂O–Al₂O_3–SiO₂ glass crystallization process. At 943 K, lithium disilicate (Li₂Si₂O₅) phase crystals began to precipitate in the Li₂O–Al₂O₃–SiO₂ glass with a crystal size of 50–70 nm. At the temperature of 1009 K, petalite (LiAlSi₄O₁₀) crystals began to precipitate in the vitreous phase, forming composite spherical crystals of LiAlSi₄O₁₀ and Li₂Si₂O₅ with size in the range of 90–130 nm. Furthermore, the Kissinger method and KAS method of the JMAK model were used to calculate the crystallization activation energy and the Avrami index “n”. It was found that the precipitation mechanism of the two kinds of crystals is whole crystallization; accordingly, the selection of crystallization heat treatment system was guided to determine the nucleation and crystallization temperature. Full article

The aim of this in vitro study was to evaluate the effects of substrate and cement shades on the translucency and color of lithium-disilicate and zirconia CAD/CAM materials. Two light-cured resin cements (RelyX Veneer Cement; 3M; Choice 2 Veneer Cement; Bisco Dental) with a standardized thickness (0.1 mm) were tested in combination with two different monolithic CAD/CAM materials (E-Max CAD (LI₂SI₂O₅); Ivoclar Vivadent; Katana (ZrO₂); Kuraray-Noritake Dental) on two different colored composite substrates used as a dentin (Filtek Supreme XTE; 3M); for a total of 12 combinations (n = 10). The specimens’ color was measured with a spectrophotometer (Spectroshade; MHT). Measurements were taken using the CIELAB color coordinate system (L*a*b*) against black and white backgrounds. L*a*b* values were statistically analyzed for the variables Substrate, Ceramic, and Cement by applying a Three-Way ANOVA followed by the Tukey Test for post-hoc comparison (p < 0.05). Translucency Parameter (TP) and Constant Ratio (CR) were assessed to evaluate translucency; acceptability and perceptibility thresholds (ΔE₀₀ 1.8 and 0.8) were used. Statistically significant influence was found for factors ceramic material, cement shade, and substrate color (p < 0.05). Unacceptable color differences were reported for Li₂Si₂O₅. Opacity was significantly higher when white opaque cement shade was employed. Ceramic type and cement shade significantly influenced L*a*b* color coordinates. The final translucency and color of ceramic restorations can, therefore, be influenced by ceramic material, cement shade, and substrate color. Full article

Digital dentistry is increasingly replacing conventional methods of manually producing dental restorations. With regards to computer-aided manufacturing (CAM), milling is state of the art. Additive manufacturing (AM), as a complementary approach, has also found its way into dental practices and laboratories. Vat photo-polymerization is gaining increasing attention, because it enables the production of full ceramic restorations with high precision. One of the two predominantly used ceramic materials for these applications is lithium disilicate, Li₂Si₂O₅. This glass ceramic exhibits a substantial fracture toughness, although possesses much lower bending strength, than the other predominantly used ceramic material, zirconia. Additionally, it shows a much more natural optical appearance, due to its inherent translucency, and therefore is considered for anterior tooth restorations. In this work, an optimized formulation for photo-reactive lithium disilicate suspensions, to be processed by vat photo-polymerization, is presented. Following the fundamental theoretical considerations regarding this processing technique, a variety of solvents was used to adjust the main properties of the suspension. It is shown that this solvent approach is a useful tool to effectively optimize a suspension with regards to refractive index, rheology, and debinding behavior. Additionally, by examining the effect of the absorber, the exposure time could be reduced by a factor of ten. Full article

Crystal nucleation can be described by a set of kinetic equations that appropriately account for both the thermodynamic and kinetic factors governing this process. The mathematical analysis of this set of equations allows one to formulate analytical expressions for the basic characteristics of nucleation, i.e., the steady-state nucleation rate and the steady-state cluster-size distribution. These two quantities depend on the work of formation, $\Delta G\left(n\right)=-n\Delta \mu +\gamma n^{2/3}$ , of crystal clusters of size n and, in particular, on the work of critical cluster formation, $\Delta G\left(n_c\right)$ . The first term in the expression for $\Delta G\left(n\right)$ describes changes in the bulk contributions (expressed by the chemical potential difference, $\Delta \mu$ ) to the Gibbs free energy caused by cluster formation, whereas the second one reflects surface contributions (expressed by the surface tension, $\sigma$ : $\gamma =\Omega d_0^2\sigma$ , $\Omega =4\pi {(3/4\pi )}^{2/3}$ , where $d_0$ is a parameter describing the size of the particles in the liquid undergoing crystallization), n is the number of particles (atoms or molecules) in a crystallite, and $n=n_c$ defines the size of the critical crystallite, corresponding to the maximum (in general, a saddle point) of the Gibbs free energy, G. The work of cluster formation is commonly identified with the difference between the Gibbs free energy of a system containing a cluster with n particles and the homogeneous initial state. For the formation of a “cluster” of size $n=1$ , no work is required. However, the commonly used relation for $\Delta G\left(n\right)$ given above leads to a finite value for $n=1$ . By this reason, for a correct determination of the work of cluster formation, a self-consistency correction should be introduced employing instead of $\Delta G\left(n\right)$ an expression of the form $\Delta \tilde{G}\left(n\right)=\Delta G\left(n\right)-\Delta G\left(1\right)$ . Such self-consistency correction is usually omitted assuming that the inequality $\Delta G\left(n\right)\gg \Delta G\left(1\right)$ holds. In the present paper, we show that: (i) This inequality is frequently not fulfilled in crystal nucleation processes. (ii) The form and the results of the numerical solution of the set of kinetic equations are not affected by self-consistency corrections. However, (iii) the predictions of the analytical relations for the steady-state nucleation rate and the steady-state cluster-size distribution differ considerably in dependence of whether such correction is introduced or not. In particular, neglecting the self-consistency correction overestimates the work of critical cluster formation and leads, consequently, to far too low theoretical values for the steady-state nucleation rates. For the system studied here as a typical example (lithium disilicate, ${\mathrm{Li}}_2\mathrm{O}·2{\mathrm{SiO}}_2$ ), the resulting deviations from the correct values may reach 20 orders of magnitude. Consequently, neglecting self-consistency corrections may result in severe errors in the interpretation of experimental data if, as it is usually done, the analytical relations for the steady-state nucleation rate or the steady-state cluster-size distribution are employed for their determination. Full article