Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1988-07-05
1989-09-05
Cannon, Alan W.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
4332011, 623 66, A61F 228, A61C 800
Patent
active
048634727
DESCRIPTION:
BRIEF SUMMARY
It has been found that many ceramic materials have properties, which allow their use as bone graft materials. Ceramic materials (bioceramics), which are tissue compatible and/or which form chemical bonds with bone tissue and/or which promote the growth of bone tissue, are e.g. calciumphosphate: apatites like hydroxyapatite, HA, Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2 (R. E. Luedemann et al., Second World Congress on Biomaterials (SWCB), Washington, D.C., 1984, p. 224), trade names like Durapatite, Calcitite, Alveograf and Permagraft; fluoroapatites; tricalciumphosphates (TCP) (e.g. trade name Synthograft) and dicalciumphosphates (DCP); aluminiumoxide ceramics; bioglasses like SiO.sub.2 --CaO--Na.sub.2 O--P.sub.2 O.sub.5, e.g. Bioglass 45S (structure: SiO.sub.2 45 wt-%, CaO 24,5% Na.sub.2 O 24,5% and P.sub.2 O.sub.5 6%) (C. S. Kucheria et al., SWCB, Washington, D.C., 1984, p. 214) and glass ceramics with apatites, e.g. MgO 4,6 wt-%, CaO 44,9%, SiO.sub.2 34,2%, P.sub.2 O.sub.5 16,3% and CaF 0,5% (T. Kokubo et al., SWCB, Washington D.C., 1984, p. 351 ).
The application of the above ceramic materials as synthetic bone grafts has been studied by different means by using them for example both as porous and dense powder materials and as porous and dense macroscopical samples as bone grafts. Also ceramic powder-polymer composites have been studied in this means (e.g. W. Bonfield et al. SWCB, Washington D.C., 1984, p. 77). Hydroxyapatite is applied generally as bone graft material in powder form for alveolar ridge reconstruction by injecting the hydroxyapatite powder/water mixture (particle size typically 10-50 mesh) on the bony surface of alveolar ridge into a cavity which has been formed below the gingival tissue. The bone tissue grows into contact directly with hydroxyapatite particles, which are biostable and remain as part of the forming new bone.
The powder-like bone graft materials have, however, a disadvantage that they remain at their place only after the connective tissue and/or growing bone tissue binds them to their place. For example, in the case of hydroxyapatite powders applied for alveolar ridge augmentation this will take about one month. Before the powder particles have been bound to their place by means of tissue growth, the powder can move easily from the place, where it should be, when mechanical forces (e.g. biting) affect upon the soft tissues which surround the powder particles. This can lead to a deterioration of operation result and in the worst situation the desired bone graft effect is not achieved at all or it is achieved only partially.
The movements of the bone graft powder particles can be prevented by binding powder particles to each other by means of a polymeric material. Such materials have been described e.g. in G.B. Pat. No. 1 562 758, G.B. Pat. No. 1 593 288 and PCT-patent application 86/01113. The ceramic powder-polymer composites have a disadvantage that the presence of binding polymeric material prevents the direct contact of bioceramic powder particles and bone tissue to each other and therefore delays and prevents the growth of the bone tissue on the surface of composite material and inside of it, because the bone tissue does not have such an affinity to grow on the surface of biostable or resorbable organic polymers as it has to grow on the surface of bioceramics or into their internal open porosity. As a consequence the growth of new bone and the healing of tissue proceeds more slowly with bioceramics-polymer composites than with pure bioceramics (e.g. according to S. Ishida et al., ECB, Bologna, Italy, 1986, Abstracts, p. 86 the growth of new bone on the surface of 70% hydroxyapatite filler-triethyleneglycoledimethacrylate composite occured in studies done with rabbits 2-3 times more slowly than the growth of new bone on the surface of pure sintered hydroxyapatite.
The movements of the bone graft powder can be prevented also by closing the particles into a porous, flexible casing, whose pores are smaller than the particle size of the powder, but which pores are big enough
REFERENCES:
patent: 4657548 (1987-04-01), Nichols
patent: 4755184 (1988-07-01), Silveeberg
Helevirta Pertti
Oikarinen Valle J.
Rokkanen Pentti
Tormala Pertti
Vainionpaa Seppo
Biocon Oy
Cannon Alan W.
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