K. de Groot

Bioceramics consisting of calcium phosphate salts.

Abstract After a discussion of the chemical considerations involved in the production of calcium phosphate ceramics, animal and clinical studies are reviewed. Specific conclusions are that although these ceramics have high compressive strengths, they are not suitable for joint replacements. Prevention of alveolar ridge resorption is a promising concept, and space-filling and use of aids for jaw-bone enlargement are proposed for routine clinical application.

Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic

The aim of this study was to obtain more information about macropore tissue ingrowth into the pores of sintered hydroxyapatite implanted in the rat middle ear, for the assessment of the usefulness of this material in reconstructive middle-ear surgery. The exudate filing the pores during the early post-operative period was gradually replaced by equal amounts of fibrous tissue and bone. The percentage of the macropore area occupied by bone was directly correlated with the macropore size. Bone was deposited not only from the pore wall towards the pore centre, but also in the opposite direction. Bonding osteogenesis was demonstrated. At sites of mechanical irritation, the presence of multinucleated cells and proliferatively active mononuclear phagocytes persisted for as long as a year. Under appropriate conditions hydroxyapatite seems to be a promising material for bone substitution in reconstructive middle-ear surgery.

Interaction of biodegradable β-whitlockite ceramics with bone tissue: An in vivo study

The biodegradation of different porous beta-whitlockite materials are studied by in vivo experiments, radiographic follow-ups and light microscopy observations. The materials were implanted in rabbit tibiae for 16 month. Micropores play an important role in the biodegradation rate. The resorbing materials evoke an inflammation with plasma cells. The resorption starts in the medulla, and the phagocytosed particles are removed to the lymph nodes. Normal bone function can be restored after all the implant material is resorbed.

Effect of Porosity and Physicochemical Properties on the Stability, Resorption, and Strength of Calcium Phosphate Ceramics

The question of how a given implant will react with surrounding tissue, or the question of how biocompatible a given implant will be, cannot be answered solely in terms of surface properties of the implant. It is well known that both less tangible factors, such as surgical skill and patient condition, and biomechanical parameters are of the utmost importance. Nevertheless, this presentation will only be concerned with surface properties of the implant, and therefore the assumption has been made, from a biomechanical point of view, that an “optimum” situation, whatever this means in quantitative terms, has been achieved. With this limitation in mind, a further simplification will be made: only implants meant to replace or augment bony tissues will be considered. In this case, reactions of bony tissue toward implant surfaces can be classified as follows’:

Induction of Immunological Tolerance by Oral Administration of Nickel and Chromium

Oral administration of nickel-chromium to guinea pigs by way of a fixed occlusal splint, or the incorporation of metallic powder or salts into the pelleted food, did not induce hypersensitivity to these metals. In addition, a subsequent attempt to immunize the pre-treated guinea pigs failed in most animals, whereas non-pre-treated guinea pigs became clearly hypersensitive. These results show that oral administration of nickel and chromium induced a state of (partial) tolerance to both metals.

A comparative study of different β-whiUockite ceramics in rabbit cortical bone with regard to their biodegradation behaviour

Different beta-whitlockite ceramic cylinders of standard size were implanted in the tibiae of rabbits to study the influence of micropores and chemistry on the biodegradation rate. The materials were evaluated by radiography and light microscopy. Surface chemistry was varied by the addition of impurities, while different applied pressures before sintering and different sintering temperatures gave rise to different micropores. Both factors influenced the biodegradation rate.

Preferential protection of Borrelia burgdorferi sensu stricto by a Salp15 homologue in Ixodes ricinus saliva.

BACKGROUNDnIxodes ticks are the main vectors for Borrelia burgdorferi sensu lato. In the United States, B. burgdorferi is the sole causative agent of Lyme borreliosis and is transmitted by Ixodes scapularis. In Europe, 3 Borrelia species-B. burgdorferi, B. garinii, and B. afzelii-are prevalent, which are transmitted by Ixodes ricinus. The I. scapularis salivary protein Salp15 has been shown to bind to B. burgdorferi outer surface protein (Osp) C, protecting the spirochete from antibody-mediated killing.nnnMETHODS AND RESULTSnWe recently identified a Salp15 homologue in I. ricinus, Salp15 Iric-1. Here, we have demonstrated, by solid-phase overlays, enzyme-linked immunosorbent assay, and surface plasmon resonance, that Salp15 Iric-1 binds to B. burgdorferi OspC. Importantly, this binding protected the spirochete from antibody-mediated killing in vitro and in vivo; immune mice rechallenged with B. burgdorferi preincubated with Salp15 Iric-1 displayed significantly higher Borrelia numbers and more severe carditis, compared with control mice. Furthermore, Salp15 Iric-1 was capable of binding to OspC from B. garinii and B. afzelii, but these Borrelia species were not protected from antibody-mediated killing.nnnCONCLUSIONSnSalp15 Iric-1 interacts with all European Borrelia species but differentially protects B. burgdorferi from antibody-mediated killing, putatively giving this Borrelia species a survival advantage in nature.

Bone induction by allogenous rat dentine implanted subcutaneously

Abstract The objective of the present communication is to present data on the stability of bone morphogenetic properties of dentine. Maxillary and mandibular incisor teeth from adult rats were demineralized in 0.6 N HCl at 2 °C for 6 hr, scraped free of pulpal tissues, washed, lyophilized and then incubated at varying pH, temperature and time. Bone induction was evaluated quantitatively by determining Ca content in implants, 28 days following implantation, and by histometric calculations of Ca concentration due to new bone formation and remineralization of old dentine matrix. It was found that bone morphogenetic properties of dentine are labile when incubated at neutral pH, higher temperatures and longer times. Thus, several conflicting observations in the literature can be resolved.

Some considerations about bone-induction

Recently, the problem of bone morphogenesis, i.e. the differentiation of mescnchymal cells into osteoblasts, has received much attention. Depending on the experiments, several theories have been developed about the mechanism of this differentiation. Electric effects, mechanical stimulation, chemical interactions, and other causes have been mentioned as possible explanations. The purpose of this letter is to rearrange representative data from the literature, such that it may be possible to explain the various findings by one common

Improved Cements Containing Phosphate Polymers

The mechanical properties of two commercially available dental cements, a zinc phosphate cement and a carboxylate cement, were substantially improved by adding a polymeric phosphate acid to the cement liquids. The improvements can be explained in terms of the change in physicochemical nature of the modified cements.