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.