Jesper Lööf

Integration Mechanisms towards Hard Tissue of Ca-Aluminate Based Biomaterials

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.

In Vitro Mechanical Properties of a Calcium Silicate Based Bone Void Filler

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.

In Vivo Hydrating Calcium Aluminate Coatings for Anchoring of Metal Implants in Bone

Optimal early fixation of metal implants to bone tissue is instrumental both in allowing for early loading of the implant, and to reduce the risk of long-term loosening resulting from micromotions. This paper investigates the prospects of achieving early anchoring of metal implants by exploring coatings based on chemically bonded ceramics, particularly coatings of calcium aluminate which are hydrated in-vivo. There are several chemically bonding ceramic systems, mainly calcium based; e.g. Casilicates, Ca-aluminates, Ca-sulphates and Ca-phosphates. The chemistry of these materials is similar to that of hard tissue in living organisms, the latter being based on apatites and carbonates. Chemically bonded ceramics can be bioactive and generally display great potential as biomaterials. Calcium aluminates have advantages in terms of mechanical strength resulting in a high turn-over of water during hydration. This paper presents results from an investigation of early anchoring for dental implants coated with calcium aluminate films of different characteristics in a rabbit model. Evidence is presented of the anchoring mechanisms of the coating resulting from in-vivo precipitation of hydrates. Introduction For successful implantation of metal implants to bone tissue early stabilisation is of great importance [1, 2]. This includes both orthopaedic and dental implants. Even small gaps may lead to relative micro-motions between implant and the tissue, which increases the risk of implant loosening over time due to formation of zones of fibrous tissues at the implant-tissue interface. Early loading of implants is of particular interest for dental implants [3]. The use of surface coatings technology is today an established method to reduce the problem with poor interfacial stability of implants. With coatings technology, structural characteristics of the implant bulk material (e.g. strength, ductility, low weight or machinability) may be combined with surface properties promoting tissue integration [3-5]. There are several established coating deposition techniques, e.g. physical vapour deposition (sputtering) and thermal spraying techniques [6-7]. Coatings based on calcium phosphates are much used, most commonly they are deposited with thermal spraying techniques. This paper deals with coatings deposited with established methods with the aim of improving particularly the early stage anchoring of metal implants to bone tissue by exploring in vivo hydration of coatings or pastes based on chemically curing ceramics. This work focuses on calcium aluminate in the form of coatings and paste. Results are presented from an implantation study with coated titanium implants and uncoated implants augmented with a calcium aluminate paste in the hind legs of rabbits. Key Engineering Materials Online: 2005-04-15 ISSN: 1662-9795, Vols. 284-286, pp 831-834 doi:10.4028/www.scientific.net/KEM.284-286.831

Antibacterial Properties of Dental Luting Agents: Potential to Hinder the Development of Secondary Caries

A modified direct contact test was used to evaluate the antibacterial properties of four commercially available dental luting agents (RelyX Unicem, Ketac Cem, Ceramir Crown & Bridge and Harvard Cement) and two reference materials (glass-ionomer cement and calcium aluminate cement) compared to a negative-control material (PMMA). Streptococcus mutans bacteria were placed in direct contact with specimens that had been aged for 10 min, 1 day, and 7 days, in order to test the antibacterial properties of the materials. A metabolic assay containing resazurin was used to quantify the amount of viable bacteria remaining after the direct contact tests. The effects of pH and fluoride on bacteria proliferation were also evaluated. Strongest antibacterial properties were found for calcium aluminate cement, followed by Ceramir Crown & Bridge and RelyX Unicem. Ketac Cem, Harvard Cement, and the reference glass-ionomer cement showed bacteria content either higher than or not significantly different from the PMMA control in all instances. pH levels below 6.3 and above 9.0 were found to have negative effects on bacterial proliferation. No correlation between either acidic materials or fluoride release and antibacterial properties could be seen; rather, basic materials showed stronger antibacterial properties.

In Vitro Bioactivity of Injectable Ceramic Orthopaedic Cements

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.

Mechanical Property Aspects of a Biomineral Based Dental Restorative System

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.

In Vitro Biomechanical Testing of Two Injectable Materials for Vertebroplasty in Different Synthetic Bones

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.

Mechanical testing of chemically bonded bioactive ceramic materials

In this thesis different aspects of calcium-aluminate (CA) as biomaterial are presented. Calcium aluminate is a chemically bonded ceramic with inherent properties making it suitable for use as biomaterial in some applications. In this thesis the emphasis is put on the basic chemical, physical and mechanical properties that may be achieved using the CA system as well as synthesis of the CA raw material. The basis for using CA in any application is the synthesis of the raw material. Different synthesis routes for producing CA are presented with focus on high temperature routes and the micro-structural and phase development during synthesis. As a base for further understanding of the CA properties a thorough outline of the reaction chemistry for CA is presented also including a description of how the reactions may be controlled and how formulations can be designed. The surface reactions of CA when subjected to simulated body fluid showed that CA is in vitro bioactive. An in vivo study in teeth also indicates that CA produces apatite at the tooth material interface. Dental materials are subjected to a harsh environment in the mouth with high mechanical forces, erosion and thermal changes. Also the demands on precise handling characteristics are high. For these reasons the in vitro evaluation of physical and mechanical properties are important. In this work several mechanical and physical properties of Ca-based formulations for dental applications has been tested using different methods. Some attention is also put on the specific characteristics of CA and the difficulties that arise when new material classes needs to be tested according to consensus standard methods. Finally studies on a CA-based formulation intended for Vertebroplasty is presented. The studies include basic mechanical properties as well as testing the material in an in vitro model utilising synthetic cancellous bone.

Nano-Size Biomaterials Based on Ca-Aluminate

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.

The Influence of Condensing Technique and Accelerator Concentration on Some Mechanical Properties of an Experimental Bioceramic Dental Restorative Material

In this paper the influence of condensing technique and accelerator conc entration on hardness and dimensional stability of an experimental version of the bioc ramic filling material Doxa T is tested. In addition a simple test of the setting time dependi ng on accelerator concentration has also been done together with a t est showing the temperature increase experienced in the bottom of a cavity when condensing with ul trasonic tips and varying the amplitude. In order to achieve early age hardness (afte r 4 hours) an addition of lithium to the hydration liquid is necessary if condensing is made manually. The ultrasonic vibrations bring the filler grains closer together yielding a dense r end product where the maximum pore size is decreased as compared with a manually conden sed sample. When using ultrasonic condensing no lithium is needed. The ultrasonic tip als o transfers extra energy, mainly in the form of heat, to the material, which may spe ed up the hydration giving improved early age properties. Condensing with the ultrasonic device also gives higher longterm (64 days) hardness than the manual condensing. The samples condens ed with the ultrasonic device and with 0 and 18mM LiCl both showed a hardness of about 150 HV(100g) after 64 days. Both for manual and ultrasonic condensing the highest h ardness is achieved by using no or low additions of lithium. Regarding the dimensional stabili ty no differences could be seen either for the different accelerator concentrations or for the different condensing techniques. The setting time is roughly the same for the three diff rent accelerator concentrations and undetectable with this method when not using any lit hium. The temperature rise in the filling when condensing with the ultrasonic device is dependent on the amplitude of the vibrations and the contact time between tip and filling.