Transmission electron microscopy of the interface between bone and pseudowollastonite implant.

This paper reports on the structural morphology of the interface in vivo between implants composed of bioactive synthetic pseudowollastonite ceramic and bone in rat tibias. Thin sections of the interfaces were examined after 6 and 8 weeks of implantation period in a high resolution transmission electron microscope up to the lattice plane resolution level. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. The regions showing direct bone tissue bonding to the implant contained nanocrystals of hydroxyapatite-like phase growing epitaxially across the interface in the [002] direction. The nanocrystals were also identified in the bone tissue formed in the interfacial area. The reactivity of the implant caused in the first instance formation of an amorphous woven type of bone, which transformed into a crystalline lamellar type containing collagen fibres. The Ca/P ratio of the interfacial region was found to be between 1.67 in the mature bone tissue formed about 5 microm from the interface, and 2.06 in the regions right at the interface.

Reactivity of a wollastonite-tricalcium phosphate Bioeutectic ceramic in human parotid saliva.

In a previous study, a new ceramic material (Bioeutectic), prepared by slow solidification through the eutectic temperature region of the wollastonite-tricalcium phosphate system, was found to be reactive in a simulated body fluid. In the present study, the reactivity of the Bioeutectic was assessed in human parotid saliva. Samples of the material were soaked for one month in human parotid saliva at 37 degrees C. The experiments showed the formation of two separate zones of carbonate-hydroxyapatite-like phase on the periphery of the samples. The first zone was formed by reaction of the bioeutectic with the saliva and progressed inside the material. The other zone developed on the surface of the bioeutectic by precipitation from the media. The mechanism of carbonate-hydroxyapatite-like phase formation in human parotid saliva appeared to be similar to that of apatite-like phase found in a simulated body fluid.

Morphological and structural study of pseudowollastonite implants in bone.

In vitro experiments show that pseudowollastonite (alpha-CaSiO3) is a highly bioactive material that forms a hydroxyapatite surface layer on exposure to simulated body fluid and also to human parotid saliva. This finding is very significant, as it indicates that the pseudowollastonite can be physically and chemically integrated into the structure of living bone tissue, and therefore could be suitable for repair or replacement of living bone. The physical and chemical nature of the remodelled interface between the pseudowollastonite implants and the surrounding bone has been studied after in vivo implantation of 20 pseudowollastonite cylinders into rat tibias. The interfaces formed after 3, 6, 8 and 12 weeks of implantation were examined histologically using an optical microscope and also by analytical scanning electron microscopy. SEM and X-ray elemental analysis showed that the new bone was growing in direct contact with the implants. Other examinations found that the bone was fully mineralized. The ionic exchange taking place at the implant interface with the body fluids was essential in the process of the implant integration through a dissolution-precipitation-transformation mechanism. The study found the interface biologically and chemically active over the 12-week implantation period. The rate of new bone formation decreased after the first 3 weeks and reached constant value over the following 9 weeks. The osteoblastic cells migrated towards the interface and colonized the surface at the contact areas with the cortical regions and also bone marrow.

Bioactivity of pseudowollastonite in human saliva.

OBJECTIVES: Pseudowollastonite (CaO.SiO2) was found to be bioactive in a simulated body fluid environment. In the present study, 'in vitro' bioactivity of pseudowollastonite was further assessed in human parotid saliva. The main objective was to compare behaviour of the material in a natural medium of high protein content (human parotid saliva) with its behaviour in an acellular protein-free solution (simulated body fluid). METHODS: Samples of polycrystalline pseudowollastonite were immersed for one month in human parotid saliva at 37 degrees C. Changes in ionic concentrations in the human parotid saliva and the pH right at the interface of pseudowollastonite/human parotid saliva were determined. The products of the interfacial reactions were studied by thin-film X-ray diffraction, scanning and transmission electron microscopy. RESULTS: The results confirmed formation of a hydroxyapatite-like layer on the surface of the material, and also suggested that the mechanism of hydroxyapatite-like layer formation in saliva was similar to that showed in simulated body fluid. CONCLUSIONS: The hydroxyapatite-like layer formed at the interface was found to be compact, continuous and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study also concluded that the high pH conditions (10.32) existing right at the pseudowollastonite/human parotid saliva interface promoted hydroxyapatite-like precipitation. At this stage of the study, similarities of the material behaviour in saliva and acellular simulated body fluid suggest that the pseudowollastonite could be of interest in specific periodontal applications for bone restorative purposes.

Iodinated methacrylate copolymers as X-ray opaque denture base acrylics.

OBJECTIVES: The purpose of this study was to evaluate novel iodinated methacrylate copolymers as X-ray opaque denture base resins. METHODS: The synthesis of specific monomers and suspension copolymerization with methyl methacrylate to produce copolymer beads. The resulting beads were processed in an identical manner to standard PMMA to produce test-pieces for mechanical testing. RESULTS: Samples prepared from beads containing 25 wt% of the iodinated copolymer exhibited an X-ray opacity equivalent to that exhibited by a similar thickness of aluminium. Furthermore, the appearance and mechanical properties were comparable to standard PMMA, while thermal stability proved superior. CONCLUSION: These novel iodinated methacrylate monomers show promise not only as polymerizable additives to methyl methacrylate to produce an X-ray opaque denture base but also as thermally stable copolymerizable additives to other applications where X-ray opacity would be advantageous.