Papers by Author: Leif Hermansson

Abstract: Six mechanisms have been identified, which control how Ca-aluminate materials are integrated onto tissue; 1) Main reaction, the hydration step of CA, 2) Apatite formation in presence of phosphate ions in the biomaterial, 3) Apatite formation in the contact zone in presence of body liquid, 4) Transformation of hydrated Ca-aluminate into apatite and gibbsite, 5) Biological induced integration and ingrowth, i.e. bone formation at the contact zone, and 6) Mass increase reaction, especially important when un-hydrated CA is used as coatings or as augmentation pastes. These six mechanisms affect the integration differently depending on a) what type of tissue the biomaterial is in contact with, b) in what state (un-hydrated or hydrated) the CA is introduced, and c) what type of application is aimed at (cementation, dental fillings, endodontic fillings, sealants, coatings and augmentation products). Both a pure nanostructural mechanically controlled integration, and a chemically induced integration seem plausible.

Abstract: Vertebral compression fractures were simulated by making a hole into sheep vertebrae and by injecting a stabilizing material. The injectable bio-ceramic Xeraspine™ was evaluated together with a commercially available PMMA (Vertebroplastic™) as the reference material. The Vertebrae were harvested after 7 days and prepared for microscopy. The samples were deposited with gold on the surface and thereafter subjected to SEM and EDX analysis. It was found that the Xeraspine-bone interface was composed of a mixture of elements. The Vertebroplastic implant was embedded in a carbon containing tissue, likely a soft tissue capsule. The Xeraspine sample was subjected to high resolution analysis in the TEM combined with EDX measurements. The TEM sample was prepared with a novel technique for preparation of the tissue-material interface (FIB). In the TEM analysis it was found that the interface region consists of ZrO2 together with a mixture possibly consisting of katoite and apatite formed during setting and/or originating from the boneapatite.

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.

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.

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.

Abstract: This study deals with the microstructure and property profile of biomaterials within the Ca-aluminate system (CA). Hydrated CA materials are stable in bone tissue, and thus not resorbable as the Ca-phosphate materials are. Identified possible applications for CA-based materials are within vertebroplasty and odontology. CA with ZrO2 particles as well as CA with glass particles were examined with regard to mechanical properties, biocompatibility and bioactivity. The hydrates formed - examined by HRTEM - are in the size range of 20-50 nm. With the studied systems it is possible to obtain a combination of high and early strength, shape stability including low expansion pressure, and in vivo bioactivity.

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.

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.

Abstract: A two component, capsule mixed dental restorative system based on a biomineral has been developed. After mixing the two components the material is to be regarded as a chemically bonded ceramic (CBC). In this work some basic mechanical properties has been evaluated and compared to high strength glass ionomer cement (GIC) and an amalgam. In addition the microstructure and fractured surfaces of the material has been investigated. The strength measurements show that the CBC material have comparable initial strength to an amalgam as measured by DTS. The flexural and the compressive strength of the fully hardened CBC material are comparable with a high strength GIC. The setting time showed to be easily adjustable and a final setting under 6 minutes can be reached. The microstructure of the CBC material shows that all components have been fully dispersed resulting in a homogenous microstructure. When looking at the fracture surface of tested DTS samples of the CBC material a “pull-out” effect was revealed originating from the fibres added to the composition to increase the strength.