A review of engineered zirconia surfaces in biomedical applications

Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications

Tungsten Carbide

Tungsten Carbide - Processing and Applications, provides fundamental and practical information of tungsten carbide from powder processing to machining technologies for industry to explore more potential applications. Tungsten carbide has attracted great interest to both engineers and academics for the sake of its excellent properties such as hard and wear-resistance, high melting point and chemically inert. It has been applied in numerous important industries including aerospace, oil and gas, automotive, semiconductor and marine as mining and cutting tools, mould and die, wear parts, etc., which also has a promising future particularly due to enabling to resist high temperature and are extremely hard

ND:YVO4ナノ秒レーザーを使用したジルコニアコーピングの新しい加工法

The purpose of this work was to fabricate zirconia copings from fully sintered Y-TZP blocks using a Nd:YVO4 nanosecond laser in order to avoid complicated procedures using conventional CAD/CAM systems. To determine the most appropriate power level of a Nd:YVO4 laser, cuboid fully sintered Y-TZP specimens were irradiated at six different average power levels. One-way ANOVAs for the average surface roughness and laser machining depth revealed that an average power level of 7.5 W generated a smooth machined surface with high machining efficiency. Y-TZP copings were then machined using the proposed method with the most appropriate power level. As the number of machining iterations increased, the convergence angles decreased significantly (p<0.01). The accuracy of the machined copings was judged to be good based on 3D measurements and traditional metal die methods. The proposed method using the nanosecond laser was demonstrated to be useful for fabricating copings from fully sintered Y-TZP.日本歯科大学201

FABRICATION OF CERAMIC MICROPATTERNS AND THEIR IMPACT ON BONE CELLS

The main objective of this study is to elucidate possible methods of producing ceramic calcium phosphate micropatterns ranging from 5 to 100 µm. Today, micropatterned ceramic surfaces are of great interest for fundamental materials research as well as for high-end industrial processes, whereas the fabrication of these patterns in the sub-100 µm range is still a challenge. Therefore, six different patterning techniques have been applied in order to generate ceramic patterns: Microtransfer molding (µTM), modified micromolding (m-µM), Aerosol-Jet® printing, CNC-micromachining, laser ablation and direct laser interference patterning (DLIP). The patterning techniques have been evaluated concerning their capability of fabricating ceramic patterns smaller than 100 µm. Another objective of this study has been the investigation of the influence of ceramic patterns on human osteoblasts (HOB). This investigation has revealed that ceramic hydroxyapatite-based patterns ranging from 16 to 77 µm in widths have a strong influence on the contact guidance of the HOB, whereas the cells showed distinct orientations between 0°-15° in reference to the pattern direction

Conventional, Speed Sintering and High-Speed Sintering of Zirconia: A Systematic Review of the Current Status of Applications in Dentistry with a Focus on Precision, Mechanical and Optical Parameters.

The aim of this systematic review was to provide an overview of the technical and clinical outcomes of conventional, speed sintering and high-speed sintering protocols of zirconia in the dental field. Data on precision, mechanical and optical parameters were evaluated and related to the clinical performance of zirconia ceramic. The PICOS search strategy was applied using MEDLINE to search for in vitro and in vivo studies using MeSH Terms by two reviewers. Of 66 potentially relevant studies, 5 full text articles were selected and 10 were further retrieved through a manual search. All 15 studies included in the systematic review were in vitro studies. Mechanical, precision and optical properties (marginal and internal fit, fracture strength and modulus, wear, translucency and opalescence, aging resistance/hydrothermal aging) were evaluated regarding 3-, 4- and 5-YTZP zirconia material and conventional, high- and high-speed sintering protocols. Mechanical and precision results were similar or better when speed or high-speed sintering methods were used for 3-, 4- and 5-YTZP zirconia. Translucency is usually reduced when 3 Y-TZP is used with speed sintering methods. All types of zirconia using the sintering procedures performed mechanically better compared to lithium disilicate glass ceramics but glass ceramics showed better results regarding translucency

The analysis of tool wear mechanisms in the machining of pre-sintered zirconia dental crowns

The growth of Digital Dentistry has opened new potentials in the dental restoration sector where personalised restorations could be made in a much shorter time than before. Zirconia has been widely used due to its excellent wear properties and bio-compatibility. Zirconia is machined primarily in its pre-sintered state, using carbide tools. Even in its pre-sintered state, zirconia is abrasive and caused tool wear. Tool wear is affected by tool substrate used, cutting conditions used, machining method employed, etc. Tool substrates are such as tungsten carbide, steel, etc. Cutting conditions refer to speed, feed, depth of cut, etc. Machining methods refer to milling wet or dry. Understanding tool wear helps in better tool design. Tools that lasted longer would mean the end users i.e. dental technicians would have less unproductive downtime changing tools. Also, worn tool would produce broken restorations which is undesirable. With this in mind, the aim of this paper was to study tool wear by identifying the wear mechanism that occurred when carbide tools machined pre-sintered zirconia. Test was constructed using recommendations from ISO 8688:1989. Cutting conditions used were adapted from those used in desktop dental milling machines. Pre-defined stopping criterion was set and flank wear of tool was measured every 15 minutes using an optical microscope. When tools reached the stopping criterion, Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD) were used to analyse worn tool in details. Findings showed transgranular and intergranular fractures were the wear mechanisms on carbide tools when machining pre-sintered zirconia

Significance of Diamond as a Cutting Tool in Ultra-Precision Machining Process

This chapter focuses on the purpose of using diamond as a cutting tool in various ultra-precision machining applications. The complicated structures such as resin and ceramic mold used for making optical lenses are machined by the diamond tool to improve the precision of the finished product. It is difficult to machine hard and brittle materials such as glasses, ceramics, and composites with the assistance of diamond tool due to the complexity in the aspheric surfaces. Moreover, the tool wear is a major problem in machining these hard materials to a fine dimensional accuracy and tolerances. The microscopic defect forms at the cutting edge lead to the damage of the surface finish of the workpiece material. Therefore, the discussions are associated with the achievement of machining hard materials using a diamond tool in ultra-precision applications

Micro-Drilling of ZTA and ATZ Ceramic Composit: Effect of Cutting Parameters on Surface Roughness

Ceramics are a class of materials widely used during last fifteen years for orthopaedic applications. It is well known that they are characterized by low wear rate, and friction coefficient. However, these materials are very difficult to machine into complex shapes because of their brittleness and high hardness. The most effective method to increase the crack resistance is the formation of a composite structure. This class of materials, composed by two or more different ceramics, can present higher characteristic respect to the single component, like fracture toughness and flexural strength. This paper presents a study of the influence of cutting parameters (cutting speed, feed rate and step number) onto the hole surface roughness and deformation due to the drill operation. The ceramic composite materials AZT (alumina toughened zirconia) and ZTA (zirconia toughened alumina) were first characterized in terms of hardness and roughness. After the drilling test, the holes were analyzed using scanning electron microscope (SEM) and an advanced 3-dimensional non-contact optical profilomete

Advanced Microstructural Characterization of Functionally Graded Dental Ceramic Material for Materials-Informed Finishing

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) has gained popularity as the choice of material for dental prosthetics. Ivoclar Vivadent’s IPS e.max ZirCAD Prime dental ceramic incorporates a unique gradient technology that varies the yttria content over the thickness of the material. The top layer is composed of 5Y-TZP which is desired for its optical properties while the bottom layer is composed of a much stronger 3Y-TZP. In between the two layers, 5Y-TZP and 3Y-TZP are mixed to form a transition layer. Varying the amount of yttria allows for more esthetically pleasing translucency in the visible areas of the restoration without compromising mechanical strength in the body. This study aims to address the gap between microstructural characterization of this dental ceramic and machining parameters that are relevant to the dental professionals performing surface finishing. The material was examined, before and after sintering, via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS), from which average grain size, crystallographic orientation, and elemental composition were analyzed. Critical linear feed rates were derived from these measured parameters. The recommendation of using high cutting speeds addresses the variability in linear feed rate of handheld finishing tools as well as the ductile-to-brittle transition of IPS e.max ZirCAD Prime

Zirconia responses to edge chipping damage induced in conventional and ultrasonic vibration-assisted diamond machining

Machining-induced edge chipping damage represents a common challenge in ceramic applications. This paper reports on responses of zirconia materials with porous and dense microstructures to edge chipping damage induced in conventional and ultrasonic vibration-assisted diamond machining. The machining-induced damage was evaluated using optical and scanning electron microscopies. The results show that edge chipping damage produced in these processes was associated with brittle fracture and depends on the material microstructure and the vibration amplitude. Pre-sintered porous zirconia with a high brittleness index yielded significantly larger edge chipping damage than sintered dense zirconia with a low index in these processes. Ultrasonic machining at an optimal vibration amplitude minimized the scale of brittle fracture at the micro level, and thus significantly diminished edge chipping damage in zirconia materials with distinct microstructures. The investigation underpins the transition from conventional to ultrasonic vibration-assisted machining for manufacturing of ceramics to achieve better product quality.Afifah Z. Juri, Yanzhong Zhang, Andrei Kotousov, Ling Yi