Leucite crystallization from K2O-Al2O3-SiO2 glass-forming melts

It is shown that the K₂O-Al₂O₃-SiO₂ system is promising for obtaining glass ceramic, containing leucite, for fabricating dental prostheses. Glass formation in this system and the crystallizability of glasses, including glasses modified with Li₂O and Na₂O, is studied. The effect of temperature and the time parameters on liquation and crystallization processes is studied.     

Flexural strength and Weibull analysis of Y-TZP fabricated by stereolithographic additive manufacturing and subtractive manufacturing

Digital light processing (DLP) is a relatively mature technology of ceramic additive manufacturing and is promising for fabricating zirconia-based dental restorations. It allows for manufacturing ceramic components with nearly unlimited geometries compared to traditional subtractive manufacturing technology. In order to explore its potential for fabricating dental prosthesis and determine its clinical indications, it is essential to investigate its microstructural characteristics and mechanical behavior. In this study, yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) fabricated by stereolithographic additive manufacturing, namely DLP acquired favorable flexural strength close to that of conventional subtractive-manufactured Y-TZP as indicated by uniaxial (three-point bending) and biaxial (ring on ring) tests, though the Weibull modulus of DLP-manufactured zirconia was lower than that of subtractive-manufactured zirconia. The strength predicting approach that uses effective area calculations was found to be applicable for both DLP-manufactured zirconia and subtractive-manufactured zirconia. Though both materials showed similar microstructures considering grain size and phase composition, significant differences in critical defects were observed.     

Additive manufacturing of fiber reinforced ceramic matrix composites: Advances,challenges, and prospects

Fiber reinforced ceramic matrix composites (FRCMCs) have been used in various engineering fields. Additive manufacturing (AM) technologies provide new methods for fabricating FRCMCs and their structures. This review systematically reviews the additive manufacturing technologies of FRCMCs. In this review, the progress for additive manufacturing of FRCMCs were summarized firstly. The key scientific and technological challenges, and prospects were also discussed. This review aims to motivate the future research of the additive manufacturing of FRCMCs.     

High-performance ceramic parts with complex shape prepared by selective laser sintering: a review

ABSTRACT

Selective laser sintering (SLS) is an additive manufacturing technology which has shown great advantages in direct formation of the polymer, metal and their composites. However, ceramic parts prepared by the SLS still exhibit some fatal defects, including low density and poor mechanical properties. In this respect, recent advances for preparing ceramics have improved the final density and performance by adopting post-processing methods. In this review, three commonly used powder preparation approaches (i.e. mechanical mixing, solvent evaporation and dissolution-precipitation process) and two powder sintering mechanisms for the SLS are introduced. Porous ceramic parts are prepared directly through the SLS by virtue of their high porosity. And dense, high-performance Al₂O₃, ZrO₂, kaolin and SiC ceramic parts with complex shape are prepared by introducing CIP technology into the SLS, indicating that the hybrid technology could be the promising route for preparing high-performance ceramic parts used in various fields.     

Additive manufacturing of silicon nitride ceramics: A review of advances and perspectives

Silicon nitride (Si₃N₄) ceramic has been widely applied in various engineering fields. The emergence of additive manufacturing (AM) technologies provides an innovative approach for the fabrication of complex-shaped Si₃N₄ ceramic components. This article systematically reviews the advances of the AM of Si₃N₄ ceramic in recent years and forecasts the potential perspectives in this field. This review aims to motivate future research and development for the AM of Si₃N₄ ceramic.     

Bacteriological Evaluation of Gingival Crevicular Fluid in Teeth Restored Using Fixed Dental Prostheses: An In Vivo Study

The present in vivo study determined the microbiological counts of the gingival crevicular fluid (GCF) among patients with fixed dental prostheses fabricated using three different techniques. A total of 129 subjects were divided into three study groups: first, cobalt-chrome-based, metal-ceramic prostheses fabricated by the conventional method (MC, n = 35); the second group consisted of cobalt-chrome-based, metal-ceramic prostheses fabricated by the computer-aided design and computer-aided manufacturing (CAD/CAM) technique (CC-MC, n = 35); the third group comprised zirconia-based ceramic prostheses fabricated using the CAD/CAM technique (CC-Zr, n = 35). The control consisted of 24 patients using prostheses fabricated with either MC, CC-MC, or CC-Zr. The GCF was obtained from the subjects before treatment, and 6 and 12 months after the prosthetic treatment. Bacteriological and bacterioscopic analysis of the GCF was performed to analyze the patients’ GCF. The data were analyzed using SPSS V20 (IBM Company, Chicago, IL, USA). The number of microorganisms of the gingival crevicular fluid in all groups at 12 months of prosthetic treatment reduced dramatically compared with the data obtained before prosthetic treatment. Inflammatory processes in the periodontium occurred slowly in the case of zirconium oxide-based ceramic constructions due to their biocompatibility with the mucous membranes and tissues of the oral cavity as well as a reduced risk of dental biofilm formation. This should be considered by dentists and prosthodontists when choosing restoration materials for subjects with periodontal pathology.     

Additive manufacturing of ceramics: Advances,challenges, and outlook

Additive manufacturing (AM) of ceramics is relatively more challenging with respect to polymers and metals, owing to their high melting temperatures and inherent brittleness. Thus, this review aims to provide a comprehensive survey of recent AM technologies successfully employed to produce net shape ceramic components. In recent years, several techniques have been developed and the latest progress in this field are highlighted, as well as the current challenges in the complex shaped ceramic parts production via AM technologies. The state of the art concerning the various 3D printing processes applied to the fabrication of ceramic components is discussed with, for each method, the presentation of its advantages, disadvantages, and possible applications. The potential of AM for producing complex shape ceramic components and the challenges to overcome are discussed as well.     

The workflows of a novel self-glazed zirconia for dental prostheses fabrication: case reports

ABSTRACT

In the clinical application of ceramic prostheses, micro-leakage, porcelain chipping, low-treatment efficiency and quality uncertainty have appeared as the major problems that dentists encountered. However, the full-contour zirconia monolithic prostheses have the potentials for solving the problems. It appears that the full-contour zirconia monolithic prostheses produced through the fully digital workflow can ensure that the restorations can be closely aligned with the abutment and be easy to adjust and to wear, thus to assure the stability and accuracy of occlusal, which are crucial to the ultimate integration of the full-contour zirconia monolithic prostheses by avoiding unfavourable grinding. The newly developed full digital approach can greatly simplify the previous workflow that involved many manual operations. It improves not only the treatment efficiency but also the reliability of the prostheses by avoiding manual operational mistakes.     

Thermomechanical Stability of Polymer—Ceramic Composite Membranes

Abstract

The mechanical stability of thin-film polymer—ceramic composite membranes has been evaluated in a variety of processing steps with temperatures ranging from 25 to 350°C. Although not measured in this work, references for similar materials indicate that the coefficients of thermal expansion for the two layers of the membrane are considerably different. Upon heating, this difference led to the development of thermally-induced stresses. These stress could be relieved if the membrane were heated in an unrestrained manner; however, they were sufficient to cause membrane failure if not relaxed. Heating to temperatures above the glass transition of the polymer resulted in defect formation in that layer due to flow into the ceramic support. These results indicate that, if properly handled, the membranes are sufficiently stable to be used over a wide range of temperatures. However, serious consideration must be given to these issues in the design of larger-scale devices.     

A 3D printed melt-compounded antibiotic loaded thermoplastic polyurethane heart valve ring design: an integrated framework of experimental material tests and numerical simulations

Abstract

Heart diseases are one of the commonest causes of death worldwide. These include valve pathologies such as valve stenosis, regurgitation, failure and similar, for which usually a valve substitution procedure is required. Different prosthesis alternatives (both biological and artificial) are nowadays available in the heart surgery panorama, but there are still issues and aspects to improve. The principal requirements for heart valve prostheses are an efficient fluid dynamic function and long-term durability without the need for anticoagulation therapy, coupled with the possibility of patient-specific customization. Given this scenario, the presented tasks might be fulfilled by the recent advances of additive manufacturing technology (AM), which offers versatility of shapes and materials to be printed.

In this work, the full flexibility of AM technique has been exploited to demonstrate the feasibility of a custom drug-loaded polymeric heart valve ring for crimpable prostheses. Two different medical-grade polymeric filaments for AM have been extruded: an aromatic Polyester-Based Thermoplastic Polyurethane (TPU-E) and a Thermoplastic Silicone-Polycarbonate-urethane compound filament (TSPCU). Both materials find different applications in medical fields, thanks to their mechanical and biocompatibility features.

A drug-loading procedure has been set to obtain an antibiotic-filled polymer material and the relative biocompatibility has been consequently investigated. Specimens have been printed with a Fused Deposition Method and uniaxial traction tests have been performed at different printing temperatures and infill orientation angles. To evaluate the damaging risk given by the HVR crimping process, a Finite Element (FE) simulation of the crimping load has been set.

The TSPCU has appeared to be the best material to realize the prosthesis in terms of tensile stress values. The ultimate mechanical characteristics of TSPCU have resulted to be higher if compared with TPU-E, regardless of raster orientation angle and temperature. The qualitative characterization of the drug loading process of TSPCU has been successful: standard disc diffusion method has revealed a well-defined inhibition zone on the bacterial culture. The effectiveness of the antibiotic has been maintained even after the extrusion and the printing process. The simulated crimping procedure on the HVR has revealed that the maximum Von Mises stress value is below the ultimate stress taken from experimental tests. The reported results demonstrate the feasibility of a crimpable antibiotic loaded HVR realized through TSPCU 3D printing.     

Study on Gelcasting of Fused Silica Glass Using Glutinous Rice Flour as Binder

Gelcasting is a colloidal processing method for fabricating high-strength and complex shape ceramic green bodies. However, industry has been reluctant to use the gelcasting technique because the most commonly used gel, acrylamide (AM), is a neurotoxin. Here, we report an attempt at the gelcasting of fused silica glass using a natural and nontoxic gel, glutinous rice flour (GRF) as binder. The GRF-based aqueous system was found to behave excellently in the gelcasting process. Flexural strength of fused silica green bodies solidified with only 3 wt% GRF is up to 11.87 MPa. Bulk density and flexural strength of fused silica glass sintered at 1275 °C are 1.75 g/cm³ and 47.02 MPa, respectively.     

Digital dentistry calls the change of ceramics and ceramic processes

ABSTRACT

Since the start of the new digital impression-taking era which started around 2008 with the introduction of the 3M Lava COS, a slow transformation is gaining momentum and it looks as if this and next year will have a broad impact on the clinicians. From being merely a way of replacing impressions now the total digital workflow enters the industry. This means a whole new way of thinking and a new way to produce prosthetic work where a reproducible constant quality can be achieved. An obvious development of improved ceramic materials that simultaneously can satisfy the mechanical, bio- and aesthetic demands of the prostheses and the corresponding technologies for production that would work for the clinic digital workflow is out of the expertise of the dentists. This calls for a cross-disciplinary collaboration with the experts in the communities of ceramics and digital manufacturing.     

Single particle adhesion variability in additive manufacturing powders

ABSTRACT

The adhesion properties of powder particles could profoundly influence the quality of parts made by Additive Manufacturing (AM) processes. Accurate experimental characterization of adhesion and the spatial surface adhesion distribution of a single microparticle has been a significant challenge, due mainly to difficulties associated with the micro-scale handling/manipulation in a controllable manner and uncertainty in the nature of micro/nano-scale contacts. In current work, an approach for determining the spatial energy/adhesion distribution on the surfaces of single microparticles used in AM is introduced and demonstrated using Molybdenum (Mo) metal particles as model particles. Both ultrasonic base and Surface Acoustic Wave (SAW)-based excitation techniques coupled with laser Doppler vibrometry are utilized to excite and acquire the vibrational rocking motion and to drive the rolling motion of single Mo particles on a Silicon (Si) substrate in a controllable manner and, thereby determining the spatial adhesion distribution on the particle surfaces. Spatial surface energy distribution data of microparticles could be utilized in Discrete Element Method (DEM) simulations as a statistical input for simulating local powder bed dynamics with increased accuracy, which would potentially lead to more predictable AM processes.     

CERAMIC HEAT PIPES FOR HIGH TEMPERATURE HEAT RECOVERY

Difficulties in finding metal or protected metal components that exhibit both strength and corrosion resistance at high temperature have severely restricted the application of effective heat recovery techniques to process heat furnaces. A potential method of overcoming this restriction is to use heat pipes fabricated from ceramic materials to construct counterflow recuperators. A development program has been initiated to demonstrate the technical and eventually the economical feasibility of ceramic heat pipes and ceramic heat pipe recuperators. The prime candidate for heat pipe construction is SiC. Closed-end tubes of this material have been prepared by chemical vapor deposition (CVD). These tubes were lined internally with tungsten by a subsequent CVD operation, partially filled with sodium, and sealed by brazing a tungsten-lined SiC plug into the open end with a palladium-cobalt alloy.

Heat pipes constructed in this manner have been successfully operated in vacuum at temperatures of 1225 K and in air at a temperature of 1125 K. The heat source used initially for the air testing was an induction heated metallic sleeve in thermal contact with the test unit. Subsequent testing has shown that a silicon carbide heat pipe can be successfully operated with natural gas burners providing the input heat. Methods of fabricating and testing these devices are described.     

Using Si/SiC solid waste to design urchin-like mullite whiskers for oil-water separation

Using recyclable industrial waste Si/SiC and Al₂(SO₄)₃ as starting materials, urchin-like mullite whiskers were successfully synthesized via the molten salt method. The characterizations were focused on the phase transformations and morphology evolution of mullite whiskers. The circular oxidation-dissolution-precipitation mechanism was proposed for the growth of urchin-like mullite whiskers. Then, the pressing-sintering process was used for fabricating porous whisker-structured mullite ceramics for oil-water separation applications. Physical properties of porous ceramic, including bulk density, apparent porosity, mechanical and thermal shock resistance were measured. It was found that excessive reaction temperature could decompose the mullite, and a suitable temperature for pure urchin-like mullite whiskers was found to be 900°C. To achieve oil-water separation, bionic surface grafting technology was used for coating a hydrophobic and lipophilic material (octadecylamine, ODA) on mullite ceramic. Oil adsorption capacities of the ceramic/ODA for various oils, that is, .27 and .24 g/g for cooking and motor oil, respectively, were successfully achieved.     

Highly dense 0.3CaCeNbWO8-0.7LaMnO3 composite ceramics fabricated by cold sintering process

The cold sintering process (CSP) has been used for fabricating functional ceramics at a low sintering temperature. In this study, highly dense 0.3CaCeNbWO₈-0.7LaMnO₃ composite ceramics have been successfully fabricated by CSP. The phase structure, microstructure, and electrical properties of composite ceramics have been investigated. The composite ceramic is mainly composed of a tetragonal CaCeNbWO₈ phase with scheelite structure and an orthorhombic LaMnO₃ phase with perovskite structure. The relative density of composite ceramic is 94.5%, and is higher than that of single phase ceramic. The resistivity of composite ceramic exhibits negative temperature coefficient characteristics, with an aging coefficient less than 2%. Such a sintering methodology is of great significance, since it provides a feasible idea for preparing composite ceramics.     

The harnessing of the waste arising from Y-TZP dental ceramics manufactured by CAD/CAM to be used as alternative dental materials

A large amount of yttria-stabilized zirconia (Y-TZP) waste is produced during the manufacture of dental prostheses by the CAD/CAM milling process. This work investigated the recycling and processing of zirconia waste powder (ZWP), generated from the manufacture of dental prostheses (CAD/CAM milling process). The physical and mechanical characteristics of the bodies produced with ZWP were evaluated. The received ZWP was calcined at 500 °C and de-agglomerated with a roll jar mill under different experimental conditions. The grinding condition with a relation between grinding medium mass (GM) and ZWP mass of 13 and a milling time of 90 min presented the best results. This procedure produced ZWP with the smallest mean particle size (0.4 μm) and the lowest tetragonal-monoclinic transformation (16.9%). The water absorption, apparent porosity, bulk density, and mechanical properties were evaluated from ZWP non-deagglomerated and ZWP de-agglomerated after sintering at 1300 °C, 1400 °C, and 1500 °C. ZWP de-agglomerated samples reached bulk density, microhardness, and flexural strength values of 5.8 ± 0.1 g/cm³, 1523 ± 173 HV, and 342.8 ± 66.7 MPa, respectively. The achieved values of bulk density and microhardness were similar to those of commercial ZrO₂ bodies processed under the same conditions, 6.0 ± 0.1 g/cm³ and 1412 ± 70 HV, respectively. But flexural strength of ZWP bodies was lower than that of commercial ZrO₂, 680.5 ± 96.0 MPa. However, the achieved strength is higher than that observed for porcelain and glass-ceramic dental materials used for single-unit anterior or posterior prostheses (<200 MPa), which depicts the ZWP potential as an alternative low-cost and high-strength material in ceramic prostheses.     

Bioceramics and their application for dental restoration

Abstract

This review article covers the historical development of ceramics, from the beginnings to the present. Feldspar based ceramic biomaterials for veneering metal frameworks, which are based on the jacket porcelain crown, have firmly established themselves in restorative dentistry since the 1970s. Currently, the development of restorative dental materials that can be used to replace metal represents a major challenge. As a result, this review will focus on the latest materials in this field. These materials include glass ceramics as well as high performance sintered ceramics. Glass ceramics exhibit more favourable optical properties, such as translucency and colour, compared with high performance ceramics, while the latter demonstrate high flexural strength and toughness. Both groups of materials have specialised applications in restorative dentistry and are capable of covering all the indications of dental restorations. The two types of materials, that is, glass ceramics and ceramics, have to be processed in accordance with their properties. As a result, the processing techniques, such as moulding, sintering and machining, will be discussed in detail in addition to the properties of the materials. Additional development possibilities for the materials will be presented on the basis of customer/patient needs and the successful long term use of glass ceramics and ceramics. In this context, it is clear that high performance ceramics and layered composites (consisting of high performance ceramics veneered with glass ceramics) offer the best possible solution for indications in the posterior region of the mouth. In contrast, glass ceramics are used to fabricate inlays and onlays for all parts of the jaw. In addition, glass ceramics can be used to fabricate crowns and small bridges to replace anterior dentition.     

CONDUCTIVE DRIlNG CHARACTERISTICS OF GELATINIZED RICE STARCH

ABSTRACT

The drying mechanism of shaped ceramics is reviewed and some methods for eliminating defects produced by drying are discussed in this report. The types of defects depend upon the shaping method, shape, properties of the raw materials, drying process and other items. Most defects of dried ceramics are produced during the initial or middle drying stage when large shrinkage of the ceramic body occurs. These defects may be successfully eliminated by heating the body from the inside. Self-deformation caused by weight is also a serious defect. The near net shaping of fine ceramics to reduce machining requires uniform body shrinkage and hence, highly controlled drying. Examples of electric current drying, dielectric drying, and dewaxing are also shown in this report.