Purpose of Review
Within this review, the current needs of the dental industry will be discussed with special focus on additive manufacturing (3D printing) of dental restorations. Up to now, ...subtractive manufacturing methods are state of the art for production of monolithic restorations. Here, the challenges and opportunities currently existing for 3D printing of crowns and bridges will be evaluated.
Recent Findings
Over the last 10 years, the LCM technology has evolved to the state of the art 3D printing technique for dense and precise ceramics. A case study will present here the full digital workflow from acquiring the data of the patient to manufacturing the final restoration.
Summary
It can be shown that with the LCM technology, it is possible to manufacture highly accurate parts with exceptional good surface quality. Furthermore, it can be shown that established techniques for staining and glazing conventionally manufactured restorations are also perfectly suitable for parts manufactured by means of the LCM technology. Particularly attractive restorations and outstanding reproduction of the sharp-edged crown margins are possible, together with the exact reproduction of the occlusal surfaces with sharp and natural replication of the fissures.
The use of additive manufacturing (AM) processes has grown rapidly over the last ten years like fused deposition modelling and stereolithography techniques. 3D printing offers advantages in ceramic ...component production due to its flexibility. To enhance quality and reduce resource consumption in ceramics industry, fast, integrated, sub-surface and non-destructive inspection (NDI) with high resolution is needed. This study demonstrates sub-surface monitoring of 3D printed alumina parts to a depth of ∼0.7 mm in images of 400 × 2048 pixels with a lateral resolution of 30 μm and axial resolution of 7 μm, using mid-infrared optical coherence tomography (MIR OCT) based on a 4 μm center wavelength MIR supercontinuum laser. We detected individual printed ceramic layers and tracked predefined defects through all four processing steps and demonstrated how a defect in the green phase could affect the final product. This research sets the stage for NDI integration in AM.
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•Non-destructive inspection of alumina samples using Optical Coherence Tomography (OCT).•Characterisation of intentional defects through 30 layers with a resolution of 7 μm.•Investigation of the impact of intentional defects on the final phase in combination with different printing processes, considering defect position and the type of slurry used.
Ceramics long history in biomedical field is related to their high biocompatibility and mechanical properties. Precisely, for joint replacements, wear resistance is fundamental, so advanced ceramics ...as alumina and zirconia are preferred. Developments in ceramic additive manufacturing allow for dense ceramic parts with improved mechanical properties and shape accuracy.
This paper focuses on the tribological analysis of stereolithography-manufactured components for orthopaedics. Alumina, yttria-stabilised zirconia, 10 and 20 wt% zirconia toughened alumina (ZTA) samples were analysed. The effect of surface finishing, microstructure and microhardness on wear was considered.
Printing orientation does not significantly impact microhardness, wettability, and microporosity. However, some printing artefacts as the staircase effect were observed on spherical surfaces. Zirconia system presented high wear rates and friction coefficient, while alumina system showed more acceptable and stable values, with the formation of a self-mated tribofilm. ZTA composites presented the lowest wear volume and better mechanical and surface properties in general.
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This paper investigates fast and inexpensive measurement methods for defect detection in parts produced by Additive Manufacturing (AM) with special focus on lattice parts made of ceramics. By ...Lithography-based Ceramic Manufacturing, parts were built both without defects and with typical defects intentionally introduced. These defects were investigated and confirmed by industrial X-ray Computed Tomography. Alternative inexpensive methods were applied afterwards on the parts such as weighing, volume determination by Archimedes method and gas permeability measurement. The results showed, that defects resulting in around 20% of change in volume and mass could be separated from parts free of defects by determination of mass or volume. Minor defects were not detectable as they were in the range of process-related fluctuations. Permeability measurement did not allow to safely identify parts with defects. The measurement methods investigated can be easily integrated in AM process chains to support quality control.
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Strength of additive manufactured alumina Schlacher, J.; Lube, T.; Harrer, W. ...
Journal of the European Ceramic Society,
November 2020, 2020-11-00, Volume:
40, Issue:
14
Journal Article
Peer reviewed
Open access
The strength of 3D-printed alumina parts fabricated using the Lithography-based Ceramic Manufacturing (LCM) technology is investigated. The influence of the sintering parameters, printing direction, ...surface condition (i.e. machined or as-printed), and/or geometry on the strength distribution is studied under uniaxial and biaxial bending tests. Weibull parameters, i.e. characteristic strength and Weibull modulus, are determined and compared between the different samples. Experimental findings show that samples sintered at higher temperatures yield higher Weibull modulus, associated with a more homogeneous microstructure. Fractographic analyses reveal the influence of surface finish (as-printed or machined) on strength and show the importance of reporting testing configuration along with printing direction to assess the mechanical response of 3D-printed parts. Based on these results, manufacturing recommendations are given which shall advance the progress in optimization of alumina ceramics fabricated using the LCM technology.
Objectives: State of the art biocompatible and biodegradable poly(lactic acid) (PLA) has several disadvantages including bulk erosion mechanism, fast loss of mechanical properties, spontaneous ...release of acidic compounds and the inability to be structured by high resolution Additive Manufacturing Techniques (AMT). It was the aim of the current project to provide low toxic photopolymerizable formulations that can be printed by AMT to form 3D cellular scaffolds for bone tissue engineering with good biocompatibllity and biodegradability. Methods: Currently, most of the used photopolymers for AMT are based on (meth)acrylates. Beside the considerable irritancy and sometimes cytotoxicity of acrylate-based monomers, the formation of high molecular polyacrylic acid through hydrolytic degradation of the polymer is another undesirable aspect of these materials when applied to the biomedical field. Therefore, photopolymers based on vinylesters and vinylcarbonates as polymerizable group, which are FDA approved, low molecular and water-soluble poly(vinyl alcohol) upon hydrolytic degradation, were evaluated. Several monomers based on different substrates were synthesized to examine their cytotoxicity, photoreactivity, mechanical properties and degradation behavior. In vivo experiments of 3D-parts were carried out in New Zealand White Rabbits. Results: In vitro studies with osteoblast-like cells, showed by far lower cytotoxicity than for their (meth)acrylate-based counterparts. By application of hydroxyapatite as filler mechanical properties already approached values from that of natural bone. The degradation behavior of the new polymers can be easily tuned between several months and years. In vivo studies showed excellent biocompatibility and osteoconductivity of the new materials. Conclusions: It has been proven that the new generation of polymers have outstanding properties for the application in the biomedical field. Beside low cytotoxicity of monomers, polymers and degradation products, the polymers have tuneable mechanical properties. Furthermore, the degradation behavior can be tuned over a broad range and advantageous surface erosion mechanism (absence of acidic degradation products) can be seen.
Objectives: The fabrication of 3D-scaffolds with defined pore geometries, which enable good adhesion of cells, is a challenging topic in the field of regenerative medicine. Photopolymers, which can ...be structured by means of Additive Manufacturing Technologies, are promising materials for this application. The possibility of structuring these compounds via processes such as miciostereolithography ( mu SLA), Digital Light Processing (DLP) or Two Photon Polymerization (2PP) enables the fabrication of constructs with complex geometries and high resolution mimicking cellular structures of natural materials such as bone. Methods: Beside the considerable irritancy and sometimes toxicity of acrylate-based monomers, the formation of polyacrylic acid through hydrolytic degradation of the polymer is another undesirable aspect of these materials when applied in the biomedical field. Therefore, photopolymers with different polymerizable groups such as vinylesters, vinylcarbonates and vinylcarbamates, which give water-soluble polyfvinyl alcohol) upon hydrolytic degradation, were evaluated. Several monomers were synthesized to examine the properties of these substance classes with focus on cytotoxicity, photoreaetivity, mechanical properties and degradation behavior. 3D-parts made of the new materials were implanted into New Zealand White Rabbits to examine the behavior under physiological conditions. Results: The biocompatibllity of these new substances, measured by their cytotoxicity towards osteoblast-like cells, showed better results than for their (meth)acrylate-based counterparts. The photoreactivity was found to be between that of acrytates and methacrylates, mechanical properties were on the same level and degradation characteristics could be tailored over a broad range. The in vivo studies showed excellent biocompatibllity of the materials as well as osteoconductivlty due to the layered structure inherent to parts structured with conventional AMTs. Conclusions: The prepared photopolymers based on poly(vinyl alcohol) show interesting properties for the application in the biomedical field. Under the maintenance of mechanical properties and photoreactivity of conventional photopolymerizable monomers based on (meth)acrylates, cytotoxicity and the degradation behavior could be significantly improved.
Objectives: Diseases of the cardiovascular system account for a significant number of morbidities and mortalities in developed counties. Hence, the need of suitable materials for artificial ...replacements for damaged blood vessels arose over the last decades, especially in the field of narrow blood vessel substitutes. This research focuses on the fabrication of blood vessel substitutes based on elastomeric photopolymers. Methods Additive manufacturing technologies (AMTs) such as digital light processing are very capable techniques for the fabrication of constructs with complex geometries and high resolution mimicking the cellular structures of biological materials. For the application as blood vessel substitutes, polymers possessing urethane groups are Interesting candidates since they exhibit elastic properties and also show good blocompatibility. various urethane oligomer acrylates were tested in combination with different monofunctional acrylates as reactive diluents. In order to match the material properties of native blood vessels, a combination of low crosslink density and high urethane group concentration was desirable. To accomplish this, dithiols were added to formulations allowing the resulting thlol-ene reaction to compete with acrylate homopolymer-ization and thus lower crosslink density. Results: The high content of urethane groups caused a high density of reversible crosslinks due to H-bonds. With this polymer architecture the material had elastomeric properties comparable to native vascular tissue and exhibited similar tensile strength and suture tear resistance tests. Due to the hydrolyrJcally cleavable ester bonds along the back bone and the branches, these polymers possess an inherent degradability similar to that of polyjactic acid). The polymers also exhibited good endothellal cell attachment, which is crucial for the long-term performance of the vascular grafts. Conclusions: Structuring photopolymers by means of AMT enables the fabrication of artificial grafts with complex geometries. Implementation of the thlol-ene concept leads to materials with both highly elastomeric mechanical behavior and good blocompatlbllity.
The use of additive manufacturing (AM) processes for industrial fabrication has grown rapidly over the last ten years. The most well-known AM technologies are fused deposition modelling and ...stereolithography techniques. One particular industry where 3D printing is advantageous over traditional fabrication techniques is within ceramic components due to its flexibility. To establish a new and improved level of print quality and reduce resource consumption in the 3D printing ceramics industry, there is a need for fast integrated, sub-surface and non-destructive inspection (NDI) with high resolution. Several techniques have already been developed for high-resolution NDI, such as X-ray computed tomography (XCT), but none of them are both fast, integrable, and non-destructive while allowing deep penetration with high resolution. In this study, we demonstrate sub-surface monitoring of 3D printed alumina parts to a depth of \(\sim\)0.7 mm in images of 400\(\times\)2048 pixels with a lateral resolution of 30\(~\mu\)m and depth (or axial) resolution of 7\(~\mu\)m . The results were achieved using mid-infrared optical coherence tomography (MIR OCT) based on a MIR supercontinuum laser with a 4\(~\mu\)m center wavelength. We find that it is possible to detect individual printed ceramic layers and track predefined defects through all four processing steps: green, preconditioned, debinded, and sintered. Our results also demonstrate how a defect in the green phase could affect the final product. Based on the understanding of how defects develop in maturing printed parts, we pave the way for NDI integration in AM, which can be combined with artificial intelligence and machine learning algorithms for automatic defect classification in volume production of a new standard of high quality ceramic components.
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