C.ò.s. Rodionov I.V., c.ò.s. Butovsky
K.G.
materials
bone implants
At
treatment of bone pathologies in modern medicine application implants –
products from not biological material, contacting with bone structures of an
organism for restoration the broken functions during long time extends.
Functions of bone system have as the biological character connected to
participation in processes blood creation and an exchange, and mechanical
character for realization of a support, movement, protection of internal
bodies. Thus implants traumatologic and orthopedic purpose
function in an organism the limited term making 7-8 weeks, and implantation systems
– articulate artificial limbs and stomatologic
implants, playing a role of artificial roots a teeth, are intended for constant
functioning in a bone fabric [1].
The biostructures surrounding implants,
contain a fabric liquid, blood, a lymph which approximately on 90 % will
consist of water at the similar maintenance of other components. The given bioliquids are electrolits and
possess alkalescent character of physical and
chemical properties with size ðÍ = 7 … 8. It causes various
kinds of interaction between implants and the biostructures,
dependent on biological compatibility of a material implant.
Biocompatibility represents ability of a material to function, not
causing immune reactions with the advent of harmful changes in fabrics and
bodies. She is caused by a complex of physical and chemical characteristics of
a material and his biological properties from which the greatest value has
stability of a material influence bioelectrolits.
Metal implants in the specified conditions can be
exposed to electrochemical corrosion with anodi
transition ions of metal in the liquid bioenvironment
and formation secondary superficial films gydroxyds
or îxyds metal. Diffusion ions of
metal in adjoining biofabrics result in their
saturation by ions that causes infringement of normal cellular processes. A
film products of corrosion change the set properties of a surface implant,
worsen stability of his initial installation and parameters functioning.
Polymeric
organic and inorganic materials under influence of bioenvironment
can receive the destruction of molecular structures resulting in the phenomena
of ageing with reduction of durability, increase fragility, transition products
of disintegration in surrounding biofabrics. Because
of it there can be immune reactions and the inflammatory phenomena down to
tearing away implant.
At the specified
interactions of a material and biostructures on a
surface implant there can be own active particles and the connections
interfering adhesion of plasma adsorbed proteins of blood. Depending on ability
to formation of superficial active particles, to bioelectrochemical
destructions implantations materials have a various level of biological
compatibility and can be biotolerant, bioinert and bioactive.
Biotolerant materials
are characterized by formation of superficial active particles and the weakened
adhesion of proteins because what fibrinous fibres of the curtailed blood settle down along a surface
implant. Thus bone cells does not reach a surface implant, on a bone surface
the coarse-fibred structure is formed, and between implant and a bone there is
a layer collagenic fibres.
It represents a capsule around implant from low strong to a fibrous fabric
thickness up to 0,2 mm that can cause infringement of stability of position
implant at action of functional loadings, lead to his shaking and danger of an
inflammation biofabrics. Biotolerant
qualities stainless steels, cobaltchromic alloys,
polythene, polythenetereftalate possess, they are
used at manufacturing implants with small terms of functioning and small loadings.
Bioinert materials do
not create on a surface of active particles that allows to be generated on it
to a film of strongly adsorbed proteins of blood and a mesh layer of fibrinous fibres. On these fibres there is a growth bone cells to a surface implant
and formation of amorphous structures bone matrics on
a surface implant. Due to it there is a biophysical communication between a
bone fabric and a surface implant at presence in this zone of a thin layer of a
fibrous fabric thickness about 0,02 mm. It limits density of formed bone
structures on a surface implants and durability of his position in contact to a
bone. Zirconium, tantalum concern to bioinert
materials, metaloxidics, bioglass,
bioglasscrystal substances, carbon materials, polymethylmetacrilate, polytetrafluorinethene
the titan, they are successfully applied for implants long and constant
functioning, maintaining the raised loadings.
Bioactive materials possess similarity of a chemical compound to a
mineral component bone matrics and ability to
decomposition at interaction with a biofabric. On a
surface of such materials the layer amorphous albuminous
structures providing physical and chemical communication of a bone fabric with
implant is formed. In these conditions there is an ionization of atoms and
diffusion ions through an albuminous layer in bone matrics to course of bioelectrochemical
reactions. Due to it develops decomposition a material, and in formed
structural emptiness germination of bone cells with formation reparative osteogenese and biointegration
implant begins. In result the strong biotechnical
system « a bone-implant » with high stability of functioning is created.
Bioactivity differ calcium-phosphatic connections – hydroxiapatite and threecalciumphosphate,
on a chemical compound corresponding to a mineral component bone matrics [2]. Besides qualities of bioactivity can get such bioinert materials, as metaloxyds,
bioglass, bioglasscrystal
substances, carbon materials, at creation of morphological heterogeneity and
porosity of their surface. Application of bioactive materials for manufacturing
implants provides their most effective functioning due to course of processes osteointegration.
The further improvement of qualities biocompatibility implants is
reached by creation nanîstructured materials, and also by
giving to materials charged conditions with formation negatively-monopolar an electric field implant.
Participation implant in performance of
mechanical functions a bone shows to it requirements of mechanical compatibility
at which his mechanical interaction with a bone does not create in a material
implant and in a bone fabric of the pressure causing inadmissible deformations,
destructions or an inflammation of a biofabric.
The
level of mechanical compatibility implant depends on a necessary combination of
mechanical properties of his material, rigidity and rationality of a design,
the circuit of an arrangement implants in system. The given factors get out according
to mechanical characteristics of a bone and functional loadings on implant.
Thus it is taken into account, that the major biomechanical characteristic bone
implant is his rigidity at a stretching or a bend. Rigidity, for example, bone
segments of the basic-impellent device, for example, the bottom finiteness, considerably
exceeds rigidity metal implants-clamps so at functional loadings the bone
practically is not deformed, and implant can receive deformation of a bend,
twisting, a stretching.
Implant a bone segment of the basic-impellent
device can test average loadings of a bend 500 N, stretching efforts – 50 N,
the braiding moment – 5 Nm, bending moment – 20 Nm. Stomatologic
implants receive action of chewing vertical forces 150 N, lateral forces – 20
N, frequency of their appendix makes 1,0 … 1,3 Hz. The greatest internal
pressure in implant and thus should not exceed a bone 500 ÌÐà,
keeping elastic character for a material implant or coming nearer to pressure
of a limit of fluidity and creating small deformations.
On the resulted bases for bone implants and systems biocompatible
materials with the raised module of elasticity are used at high values bending
rigidity implant and factor of rigidity of his design. Besides the material
should possess the increased limit of fluidity, the minimal allowable
plasticity and the optimum durability, necessary endurance, hardness and wear
resistance. To the greatest degree specified requirements satisfy metal bioinert alloys Ti, Zr, Co-Cr,
corrosion-proof chromnickel steel. Polymeric organic
and inorganic materials do not possess a necessary complex of mechanical
properties that at action on implant functional loadings to provide occurrence
only small elastic deformations. Therefore they are not used for manufacturing
a bearing basis implants, except for the carbon composite used for some kinds
of clamps at an osteosynthesis.
Expansion of the list mechanically compatible implantations materials is
reached due to creation biocomposites on the basis
inorganic, and also organic polymers, drawing of bioceramic
coverings on metal implants, giving to materials nanostructural
conditions.
The
literature:
1. Linkow Leonard I. Implants as I See Them
Today / L.I. Linkow //
Journal of Implant Dentistry. 1976.¹3.
2. Lyasnikova A.V., Protasova N.V. The application of
plasma sprayed coatings in the manufacture of dental implants // 22-nd European Conference on Surface Science «ECOSS 22», September 7-12, 2003.