Papers by Author: Hakan Engqvist

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Authors: Hakan Engqvist, Lars Kraft, Håkan Spengler, Leif Hermansson
Abstract: The area of cements in dentistry is steadily growing with the introduction of new systems that need to be cemented to the tooth, e.g. new inlays and crowns. With the better properties of the implants there is a need for new cements with high bond strength, good esthetic and mechanical properties. The bioactive minerals have not been explored as dental cement. This paper investigates the strength, setting time and film thickness of a novel dental cement based on the biomineral Marokite (calcium aluminate) as bonding system. The reactive Marokite powder is mixed with glass filler (ratio of 1.9 by volume) and water (ratio of 0.4 by weight) to a paste, which hardens within 6 minutes and has a working time of 2 minutes. The compressive strength reaches 143 MPa after 24 hours and the flexural strength almost 40 MPa. When the film thickness is measured at the end of the working time it is about 50 µm. Compared to glass ionomer cement (Fuji Cem) and zinc phosphate cement (Harvad) the biomineral system has higher strength and comparable setting time and film thickness. The investigation shows that it is feasible to develop dental cements based on biominerals, in this case a Marokite based material. The cement complies with the given standards.
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Authors: Niklas Axén, Tobias Persson, Kajsa Björklund, Hakan Engqvist, Leif Hermansson
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Authors: Hakan Engqvist, Tobias Jarmar, Fredrik Svahn, Leif Hermansson, Peter Thomsen
Abstract: A key feature in the understanding of the mechanisms of integration of implant materials is a deepened in-sight of the elemental and molecular composition of the interface zone between the implant and tissue. To analyze the interface at the ultrastructural level, transmission electron microscopy (TEM) is needed. However, techniques to fabricate thin foils for TEM are difficult and time consuming. By using focused ion beam microscopy (FIB) for site-specific preparation of TEM-samples, intact interfaces between bioceramics and calcified tissue can be prepared. The site-specific accuracy of the technique is about 1 mm. By using a dual-beam FIB, which is a combined scanning electron and focused ion beam microscope, the sample can be imaged with both electrons and ions (generating both secondary electrons and ions). Results from interface studies between Ca-aluminate based orthopaedic cement, dental materials, HA-coated Ti-implants and bone are presented. The interfaces were imaged in scanning-TEM and bright field mode, the crystal structures were determined using electron diffraction and elemental composition analyzed with energy dispersive spectroscopy. The technique fulfils a demand to correlate the surface properties of bioceramic implants with the structure and composition of preserved interfaces with tissues.
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Authors: Leif Hermansson, Lars Kraft, Hakan Engqvist
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Authors: Leif Hermansson, T. Björneståhl, Håkan Spengler, Hakan Engqvist
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Authors: Johan Forsgren, Ulrika Brohede, Albert Mihranyan, Hakan Engqvist, Maria Strømme
Abstract: The aim of this study was to investigate if it is possible to fast load hydroxyapatite with antibiotics and still obtain a slow but therapeutic release of drugs during several hours. Physical vapour deposition was used to coat commercially pure titanium with a layer of anatase TiO2. On top of this, a layer of hydroxyapatite was deposited using biomimetic precipitation. This hydroxyapatite coating was then soaked in solutions containing antibiotics for various amounts of times. The release rate of the antibiotics was measured in PBS during 22 hours. The released amount was compared with the results from an antimicrobial susceptibility test and proved to be sufficient to kill several ml of bacterial broth during the time of the release measurements. It was shown that the soaking time does not affect the release rate and the results suggest that it is possible to develop implants with the option to add antibiotics to their surface at the site of surgery by a simple soaking method.
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Authors: Leif Hermansson, Lars Kraft, Karin Lindqvist, Nils Otto Ahnfelt, Hakan Engqvist
Abstract: Flexural strength of a dental material reflects its ability to withstand tensile stresses and thus the fracture risk of a filling. The flexural strength of an experimental bioceramic Calcium aluminate-based (CA) dental restorative material was measured using three different methods with a composite (Tetric Ceram), a glass ionomer cement (Fuji II) and a phosphate cement (Harward) as references. The three test methods were: a) ISO 4049 for dental composites, 3-point bend test b) EN 843-1 for ceramic materials, 3-point bend test and c) ASTM F-394, biaxial ball-on-disc for ceramic materials. The strength of the CA-material, tested in the ball-on-disc method, is close to the theoretical strength based on the microstructure of the material (max. grain size of 15 μm). The composite material and the phosphate cement were rather insensitive to the test method, while the glass ionomer cement as the CA-material showed sensitivity towards the test method. A modified biaxial test method for evaluation of strength of dental materials in a close to real-life component is proposed.
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Authors: Sahin Altundal, Kārlis Agris Gross, Caroline Ohman, Hakan Engqvist
Abstract: In the investigation of mechanical properties, calcium phosphate cements exhibit large sample-to-sample deviation due to its porous nature, possibility of unhomogenous distribution and small specimen size. This situation generates difficulties for obtaining accurate results and creates an obstacle for testing different composition where only a small batch size is available. In this respect, specimen shape, whether being injected, porosity ratio, surface quality, bearing support design have significant matter on variability in terms of three-and four-point bending test. Therefore, different methods have been studied to reduce variability with a simpler material preparation than common methods on injected and moulded cement. The entire comparison is made with the consideration of three-and four-point bending testing, the eccentric loading error calculation with engineering calculation software “Mathcad 15”, porosity measurement with Archimedes method, microstructure investigation on Scanning Electron Microscope (SEM), macro-porosity distribution measurement by Micro CT Scanner.
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Authors: Jannica Heinrichs, Tobias Jarmar, Marten Rooth, Hakan Engqvist
Abstract: A non-bioactive implant device can easily be changed to in vitro bioactive with a thin coating of crystalline TiO2. This crystalline coating can be deposited very thin with great step coverage at a low temperature with Atomic Layer Deposition (ALD). An anatase TiO2 coating was built up atomic layer by atomic layer using TiI4 and H2O as precursors in a hot wall furnace. Several hundreds of cycles resulted in a 10-30nm well defined TiO2 of anatase phase on both Si and Ti substrates. These coatings were shown to be bioactive when immersed in simulated body fluid in vitro, as hydroxyapatite (HA) formed on the surface. The surface roughness of the substrates affected the adhesion of the HA. The adhesion was low on the smooth Si but much better on the 100 times rougher Ti. The ALD technique is promising for coating substrates of all shapes with bioactive crystalline TiO2 at a low temperature.
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Authors: Adam Faris, Hakan Engqvist, Jesper Lööf, Mikael Ottosson, Leif Hermansson
Abstract: The objective of this paper is to investigate and compare the in vitro bioactivity of three injectable cements for orthopaedic applications. The cements were all based on chemically bonded ceramics technology; calcium phosphate (Norian SRS), and experimental versions of calcium silicate and calcium aluminate cements. The cements were mixed with their respective liquids and were after setting stored in phosphate buffered saline at 37 °C for time periods of 1h, 24 h, 7 days and 30 days. After storage the samples were analysed with scanning electron microscopy (SEM), thin film X-Ray diffraction (TF-XRD) and energy dispersive spectroscopy (EDS) for the presence of possible apatite on the sample surface. The SEM and EDX analyses showed that surface films containing Ca and P (along with the other atoms present in the materials) were formed on all materials. Thus reactions with the storage medium had occurred. The TF-XRD analysis confirmed the presence of apatite for the calcium phosphate cement and the calcium aluminate cement. On the calcium silicate cement most of the surface zone seemed to be amorphous with only broad peaks corresponding to apatite. Thus all the tested materials showed signs of in vitro bioactivity.
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