Papers by Author: Leif Hermansson

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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.
Authors: Niklas Axén, Tobias Persson, Kajsa Björklund, Hakan Engqvist, Leif Hermansson
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.
Authors: Leif Hermansson, Lars Kraft, Hakan Engqvist
Authors: Leif Hermansson, T. Björneståhl, Håkan Spengler, Hakan Engqvist
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.
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.
Authors: Jesper Lööf, Adam Faris, Leif Hermansson, Hakan Engqvist
Abstract: Two different injectable materials, intended for use in vertebroplasty (VP) treatments of fractured vertebras, were tested in an in vitro bone model. The materials tested were an experimental bioceramic material based on calcium aluminate manufactured by Doxa AB, and Vertebroplastic, a PMMA based material manufactured by DePuy Acromed. The model was earlier developed by others and has been found valid for testing of materials intended for PVP. The model offers alternative data to traditional compressive and diametral tensile testing by adding the infiltration of material into synthetic cancellous bone. Five different synthetic bones with different porosity and pore structure were tested. The results show that for the PMMA the infiltration pattern of the different bones tested seems to have no influence. The material deforms plastically and displays about the same strength in all bones tested. For the bioceramic, linear elastic, material however there is a difference. In the more porous bones, where the material infiltrate the pores and creates a test body with a large amount of crack initiation points, the material displays lower strength compared to that of the more solid bones.
Authors: Hakan Engqvist, S. Edlund, Gunilla Gómez-Ortega, Jesper Lööf, Leif Hermansson
Abstract: The objective of the paper is to investigate the mechanical and the handling properties of a novel injectable bone void filler based on calcium silicate. The orthopaedic cement based on calcium silicate was compared to a calcium phosphate cement, Norian SRS from Syntes Stratec, with regard to the working (ejection through 14 G needle) and setting time (Gillmore needles), Young’s modulus and the flexural (ASTM F-394) and compressive (ISO 9917) strength after storage in phosphate buffer saline at body temperature for time points from 1h up to 16 weeks. The calcium silicate cement is composed of a calcium silicate powder (grain size below 20 µm) that is mixed with a liquid (water and CaCl2) into a paste using a spatula and a mixing cup. The water to cement ratio used was about 0.5. The calcium silicate had a working time of 15 minutes and a setting time of 17 minutes compared to 5 and 10 minutes respectively for the calcium phosphate cement. The compressive strength was considerably higher for the calcium silicate cement (>100 MPa) compared to the calcium phosphate cement (>40 MPa). Regarding the flexural strength the calcium silicate cement had high values for up to 1 week (> 40 MPa) but it decreased to 25 MPa after 16 weeks. The phosphate cement had a constant flexural strength of about 25 MPa. The results show that calcium silicate cement has the mechanical and handling potential to be used as high strength bone void filler.
Authors: Niklas Axén, Hakan Engqvist, Jesper Lööf, Peter Thomsen, Leif Hermansson
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