To give a comprehensive review of advancement in dental ceramics, fabrication methods, and the challenges associated with clinical application.
Researches on chemical composition, biomechanical ...behaviors, optical properties, bonding strategies and fabrication methods were included. The search of articles was independently conducted by two authors in the PubMed, Scopus, Medline and Web of Science.
Dental ceramics have shown significant advancements in terms of esthetics and function. However, improving fracture toughness without compromising optical properties remains a challenge. Repairing fractured zirconia or glass-matrix ceramic prostheses with the same material is difficult due to the sintering process. Developing innovative bonding techniques that provide strong and long-lasting bonding strength between ceramics and tooth structures poses a recurring obstacle.
Despite the emergence of dental ceramics and fabrication techniques, certain limitations such as susceptibility to brittleness and fracture still exist. Therefore, the current review provided valuable information around the advanced dental ceramics in tooth repair. The laboratory test data and the clinical outcome are also presented in details, aiming to guide clinicians in making informed decisions regarding ceramic restorations.
Structural rearrangements taking place during relaxation and crystal nucleation in lithium-disilicate (LS2) glass have been investigated by a comprehensive set of solid-state nuclear magnetic ...resonance (NMR) experiments, supported by molecular dynamics (MD) simulations. Samples were subjected to heat treatments at 435 °C, i.e., 20 K below the laboratory glass transition temperature (Tg). Raman and NMR data indicate that under these conditions both relaxation and nucleation occur without detectable changes in the network former unit distribution of the glassy silicon-oxide network. Instead, relaxation of the frozen supercooled melt and nucleation of LS2 crystals occur principally in terms of a changing lithium local environment: 7Li spin-echo decay NMR indicates average Li-Li distances, characterized by homonuclear dipolar second-moment measurements, are reduced after very short heat treatments and approach those found in the isochemical crystal. This finding is supported by molecular dynamics (MD) simulations predicting a dependence of the Li+ ion distribution on the melt-cooling rate. In addition, the structural reorganization also impacts the distribution of electric field gradients as detected by 7Li satellite transition NMR spectroscopy. Finally, crystal nucleation becomes most evident by the appearance of minor amounts of sharp 29Si MAS resonances and a significant change in the 7Li NMR satellite transitions, as visualized by difference spectroscopy. This study defines a new NMR strategy, generally applicable for investigating the structural relaxation process accompanying the internal crystallization of ion-conducting frozen supercooled melts containing suitable NMR active nuclear probes (7Li, 23Na, 133Cs, etc.).
Display omitted
Lithium silicate (LS) glass ceramic with excellent mechanical performance has been used in dental restoration but is seldom used in orthopedics due to its limited bioactivity. Given the ...osteoconductive features of calcium phosphate-based ceramics, optimizing the P2O5 content to adjust the ratio of CaO to P2O5 may improve the bioactivity of glass ceramics. The effect of P2O5 content on the phase formation, mechanical performance, cell proliferation, cell differentiation and mineralization of glass ceramics were investigated in this study. The results indicated that increasing the content of P2O5 increased the formation temperature of LiAlSi2O6 and provided nucleation sites for Li2SiO3 by forming Li3PO4 which, in turn, promoted the transformation from Li2SiO3 to Li2Si2O5. The phase morphology transformed from a lamellar shape to a columnar shape, and then formed an interlocking structure in the specific heat treatment. The phase transformation and formation of Li3PO4 improved cell proliferation, cell differentiation, and mineralization of the glass ceramics. In particular, the glass ceramic with 2.58 mol% P2O5 (LS3) and 4.12 mol% P2O5 (LS4) promoted the expression of alkaline phosphatase (ALP) and achieved the strength requirement of bone. In conclusion, the bioactivity of the glass ceramics was enhanced by increasing the P2O5 content, and the bone-like structure on the surface of the glass ceramic with 4.12 mol% P2O5 may make this material suitable for orthopaedic applications.
The aim of this study is to evaluate the effect of over-the-counter (OTC) at-home whitening products with LED light on partially- and fully-crystalized CAD/CAM lithium disilicate ceramics. Two ...partially-crystalized CAD/CAM lithium disilicate ceramics, Amber Mill and IPS e.max CAD, and one fully-crystalized CAD/CAM lithium disilicate ceramic, n!ce Straumann, were used. The specimens were divided based on treatment with OTC whitening products: no treatment provided, Colgate Optic, Crest 3D and Walgreens Deluxe. The surface roughness of the specimens was evaluated with an optical profilometer and scanning electron microscopy. The three LED whitening products significantly increased the surface roughness and changed surface morphology of Amber Mill and IPS e.max CAD but no differences for n!ce Straumann. OTC at-home whitening products with LED light can significantly increase the surface roughness of restorations fabricated with these partially-crystalized CAD/CAM lithium disilicate ceramic restorations. However, these products do not increase the surface roughness of restorations fabricated with this fully-crystalized lithium disilicate ceramic.
BackgroundInsufficient information exists regarding the fracture resistance and failure pattern of newly developed zirconia-reinforced lithium disilicate (ZL, Vita Ambria) onlays. This in vitro study ...compared the fracture resistance of two types of onlays: monolithic lithium disilicate (LD) and monolithic ZL.MethodsForty-eight ceramic onlay restorations were fabricated on epoxy dies using a maxillary first premolar model. The samples were divided into two main groups: LD and ZL. Half of each group was subjected to thermomechanical fatigue loading (TML) using a chewing simulator. All the samples were cemented with self-adhesive resin cement. Subsequently, they were loaded until failure in a universal testing machine, and the fracture patterns and resistance were recorded.ResultsBefore TML, ZL demonstrated the highest statistically significant mean fracture resistance (499.76±34.14N) compared to LD (470.40±27.38N). After TML, ZL showed the highest non-statistically significant mean fracture resistance (429.27±131.42N), while LD's mean fracture resistance decreased (377.31±62.18N).ConclusionMonolithic zirconia-reinforced onlays demonstrated higher fracture resistance and a more favorable failure mode compared to LD. However, the impact of thermomechanical aging resulted in reduced fracture resistance for both materials, with a notable preference observed for ZL.
Fundamental understanding of the interaction between glass and ceramic phases with a running crack and the mechanisms by which propagation is hindered or altered as compared to the precursor parent ...glasses remains elusive for the lithium disilicate glass‐ceramics. We herein conduct extensive molecular dynamics simulations to reveal some atomic details that are otherwise extremely challenging to be probed by experiments. The results show that the crack propagation pathway in glass‐ceramics is dramatically different as compared to the precursor parent glass. In glassy sample, clean crack branching seems to be triggered by multiple cavitation events ahead of crack tip. In glass‐ceramic samples, however, branching is characterized by microcracks at multiple glass‐nanocrystal interface sites, clean nanocrystal cleavage along certain crystalline plane, and even secondary cracks due to the percolation of multiple microcracks. Additionally, the nanocrystal distribution, total volume fraction, and aspect ratio also have pronounced effects on the propagation of a primary crack and can lead to very diverse crack patterns.
The close‐up of crack front for the glass and glass‐ceramics sample. Multiple cavities are primarily populated in the glass sample, while microcrack originated at the glass‐nanocrystal interface, secondary crack induced by the percolation of microcracks, and cleavage inside the nanocrystal at certain crystalline plane are observed in the glass‐ceramics sample.
This work investigated the variation in fracture strength and toughness of stoichiometric lithium disilicate (LS2) glass-ceramics as a function of crystal size (d) and crystallized volume fraction ...(f), with three average crystal sizes (8, 13 and 34 µm) and a wide range of crystallized fractions (0–100 %). The fracture strength and toughness increased with increasing the crystallized volume fraction. For constant crystallized fraction, KIC increased with crystal size, indicating an R-curve behavior. The mean free path between the crystals limits the maximum size of the critical defect and is the crucial feature controlling fracture strength. Finally, we verified that the contribution to the toughness of R-curve mechanisms in this glass-ceramic is proportional to (f.d)1/2, which agrees with R-curve models for ceramics.
The pressureless sintering process is essential to densify near net shaped parts with good shape fidelity. In this work, the impact of the particle size distribution and crystallization state on the ...processing and properties of final sintered multicomponent lithium disilicate (SiO2-Li2O-K2O-P2O5-Al2O3-ZnO) was evaluated. Higher densification was achieved by pressureless sintering at lower temperatures for samples prepared with fine glass-based powders (825 °C; ≈96%) rather than coarse crystallized powders (975 °C; 92.9%). However, samples based on fine powders presented a microstructure characterized by low aspect ratio crystals, while those based on coarse powders presented needle-like crystals with high aspect ratio. Best mechanical properties were found in samples prepared with coarse glass powders (relative density≈ 95.1%; Vickers Hardness≈ 5.2 GPa; indentation fracture toughness≈ 2 MPam0.5; flexural strength≈ 317 MPa) sintered at 875 °C-1 h. These results can provide valuable orientations for the post-processing of lithium disilicate glass-ceramics prepared by additive manufacturing techniques.
BackgroundAlthough, the influence of cement and background shade on the final color and translucency of zirconia reinforced lithium silicate (ZLS) and lithium disilicate (LDS) ceramics has been ...previously investigated, there is still little data on the translucency of LDS and ZLS ceramics in decreased thickness (0.4 and 0.6 mm). The aim of this study was to investigate ceramic thickness', background and cement shades' effects on the zirconia reinforced lithium silicate (ZLS) and lithium disilicate (LDS) ceramics' translucency.Material and MethodsTotally 160 square-shaped A1 shade LDS and ZLS samples produced in 0.4 and 0.6 mm thicknesses were cemented with light and neutral shade resin cement on A2 and A3 shade composite resin backgrounds. The color notations of specimen were measured and translucency parameter (TP) values were calculated. Factorial ANOVA and Tamhane's T2 multiple comparison statistical analyzes were used.ResultsHighest TP values (11.82±0.97) were obtained in ZLS specimens that were 0.4 mm in thickness, cemented on A2 background with light shade resin cement. While, the lowest TP values (9.60±0.55) were calculated in LDS samples that had 0.6 mm thickness, cemented on A3 background with neutral shade resin cement.ConclusionsMaterial type, thickness, and background shade affected TP values of specimens. The cement and background shade used might change the final translucency of ZLS and LDS ceramics that had 0.4 and 0.6 mm thickness. Key words:Ceramics, lithium disilicate, spectrophotometry, zirconia, dental materials.
The introduction of the new generation of particle-filled and high strength ceramics, hybrid composites and technopolymers in the last decade has offered an extensive palette of dental materials ...broadening the clinical indications in fixed prosthodontics, in the light of minimally invasive dentistry dictates. Moreover, last years have seen a dramatic increase in the patients' demand for non-metallic materials, sometimes induced by metal-phobia or alleged allergies. Therefore, the attention of scientific research has been progressively focusing on such materials, particularly on lithium disilicate and zirconia, in order to shed light on properties, indications and limitations of the new protagonists of the prosthetic scene.
This article is aimed at providing a narrative review regarding the state-of-the-art in the field of these popular ceramic materials, as to their physical-chemical, mechanical and optical properties, as well as to the proper dental applications, by means of scientific literature analysis and with reference to the authors' clinical experience.
A huge amount of data, sometimes conflicting, is available today. Both in vitro and in vivo studies pointed out the outstanding peculiarities of lithium disilicate and zirconia: unparalleled optical and esthetic properties, together with high biocompatibility, high mechanical resistance, reduced thickness and favorable wear behavior have been increasingly orientating the clinicians' choice toward such ceramics.
The noticeable properties and versatility make lithium disilicate and zirconia materials of choice for modern prosthetic dentistry, requiring high esthetic and mechanical performances combined with a minimal invasive approach, so that the utilization of such metal-free ceramics has become more and more widespread over time.
PDF