Titanium implant. Cylindrical, conical and plate implants
Alexander Modestov dental technician - master, demonstrator of Dentaurum and Esprident, Germany
At present, titanium has taken its rightful place among modern materials.
This material has an interesting history, which brought many discoveries, which it owes to its current success, achieved in a very short time. Today, titanium is successfully used in the automotive and aircraft industries, in spacecraft and shipbuilding, wherever effective corrosion protection is needed and, of course, in medicine.
With the growth of allergic reactions to various metals and metal alloys used in medicine and dentistry, titanium is seen as a decisive alternative.
Due to the remarkable biocompatibility and incredible stability of titanium, this metal has attracted the attention of orthopedics. Today, hip and knee prostheses, various needles and screws are made from titanium. Also cases for cardiac stimulators and hearing aids also titanium.
High biocompatibility is due to the ability of titanium to form a protective oxide layer on its surface in a fraction of a second. Due to which it does not corrode and does not give off free metal ions, which are capable of causing pathological processes around the implant or prosthesis. Today, titanium gives us the opportunity to use only one metal in the oral cavity. We can make almost any design. There are no electrochemical reactions between the various parts of the prostheses, and the tissues surrounding the prosthesis remain free of metal ions.
Inlays and onlays, cast and veneered crowns and bridges, clasp dentures and cast bases for complete removable dentures, combined dentures and prosthetics on implants (including the implants themselves) - this is the range of titanium applications that even the biggest optimists did not dream of.
The influence of titanium on modern dentistry is so comprehensive that even skeptical colleagues rightly pay tribute to its features, closely following its development, especially in modern implantology. Therefore, today we dedicate this article to the issues of titanium casting and its processing in a dental laboratory.
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In medicine, the first experiments on the use of titanium began in the 40s with the implantation of titanium cylinders into the soft tissues of animals, which proceeded without a reaction from the body.
In dentistry, the use of titanium began with the use of this metal in his research work by Professor Brenemark in 1956.
While titanium was asserting itself in dental implantology, the desire to use this metal also in individual prosthetics grew in parallel.
The first experiments with titanium casting in the dental field were made by Dr. Waterstraat in 1977.
Thermal transformation of the form of titanium for dental purposes has been possible since 1981 with the use of a casting machine for casting titanium from the Japanese company Ohara.
Methods of cold working of titanium - such as milling - the manufacture of implants or milling of crown or bridge frameworks using the so-called CAD / CAM technologies, do not entail any particular difficulties. Problems are present in the so-called hot reshaping of the metal, i.e. in casting. We are interested in this process, first of all, because of its not very high cost, in relation to the still developing CAD / CAM technologies, and secondly, as the only method of manufacturing clasp prosthesis frames today.
Titanium casting
As we have noted the high reactivity of titanium, a high melting point is required, a low density requires a special casting machine and investment material. There are currently three systems on the market that are considered the best for titanium casting. These are the Rematitan system from Dentaurum (Germany), the Biotan system from Schutzdental (Germany), and the system from the Japanese company Morita. Today we will get acquainted with the Rematitan casting system in detail. Firstly, because in our opinion this is the best system that allows you to achieve casting of very high and stable quality, and secondly, we already have 4.5 years of experience.
What is meant by titanium casting system?
First of all, this is the Rematitan-Autocast or Autocast-Universal foundry.
Autocast casting machines are based on the principle of melting titanium in a protective atmosphere of argon on a copper crucible by means of a voltaic arc, just like titanium sponge is alloyed in industry to obtain pure titanium. Pouring of metal into the cuvette occurs with the help of vacuum in the casting chamber and increased pressure of argon in the melting chamber - during the overturning of the crucible.
The appearance and principle of how the installation works is shown in fig. 1 and 2.
At the beginning of the process, both melting chambers (at the top) and casting chambers (at the bottom) are washed with argon, then a mixture of air and argon is evacuated from both chambers, after which the melting chamber is filled with argon and a vacuum is formed in the foundry. The voltaic arc is switched on and the titanium melting process begins. After a certain time has elapsed, the melting crucible overturns sharply and the metal is sucked into the form in vacuum, its own weight and the increasing argon pressure at this point also contribute to its driving. This principle makes it possible to obtain good, dense castings from pure titanium.
The next component of the casting system is the investment material.
Since the reactivity of titanium in the molten state is very high, it requires special investment materials, which are made on the basis of aluminum and magnesia oxides, which, in turn, make it possible to reduce the reaction layer of titanium to a minimum. Dentaurum offers several such masses, for example Rematitan Plus - an investment mass for casting clasp prostheses, Rematitan Ultra and Trinell investment masses for casting crowns and bridges (Fig. 3, 4). Trinell for example is a new generation of investment materials for titanium. The world's first high-speed investment for titanium, which saves a lot of time and gives a very clean metal surface, practically without a reaction layer.
Titanium - foundry metal
Tritan 1 and Rematitan M. Min. 99.5% chemical purity. Tritan 1 is grade 1 titanium, suitable for all types of work, very low oxygen content in the metal. Rematitan M - in terms of strength it belongs to titanium grade 4, a significantly increased tensile strength and elasticity, make possible application in clasp clasp prostheses and for bridge work of great length.
What you need to know when working with titanium?
Simulation Features
The frame made for ceramic veneer should have a reduced anatomical shape of the tooth. The internal support of the ceramics by the frame is very important, in addition, for a favorable heat exchange between the ceramics and the metal during firing, the presence of either cooling ribs (Fig. 5) or a garland is required. On bridges of great length, the presence of a garland is also necessary in order to strengthen the framework. The thickness of the caps should be at least 0.4–0.5 mm. The frames of clasp prostheses are also modeled somewhat thicker, in relation to frames made of chromium-cobalt alloys.
pinning
Proper pinning (installation of sprues and creation of a gating system), as well as the correct location in the ditch, plays a huge role and is carried out strictly according to the rules proposed by the manufacturer of foundry installations. Dentaurum offers the following requirements for the Rematitan casting system. For crowns and bridges, the use of only a special casting cone, which allows you to optimally guide the metal to the cast object. The height of the inlet sprue channel from the cone to the feed beam is 10 mm with a diameter of 4–5 mm. The diameter of the feeding beam is 4 mm.
Underwater sprue channels to the cast object with a diameter of 3 mm and a height of no more than 3 mm. Very important: the underwater channels should not be located opposite the inlet gate channel (Fig. 6 and 7), otherwise the possibility of gas pores is very high. All joints must be very smooth, without sharp corners, etc. to minimize the turbulence that occurs during the pouring of the metal, which leads to the formation of gas pores. The sprue system for clasp prostheses, and especially for cast bases for complete dentures, is also different from the sprue systems that we use for casting clasp dentures from chromium-cobalt alloys.
In all three foundry installations mentioned above, the two-chamber principle, titanium is melted in a melting chamber in an argon environment, on a copper crucible using a voltaic arc, and is driven into a mold by means of vacuum or argon pressure. Distinctive are the method of driving the metal and the pinning system, which affect the number of errors during casting.
alpha layer
Through the reaction and diffusion of gaseous and solid elements (oxygen, carbon, silicon, etc.) from the atmosphere of the melting chamber and the investment mass, a reaction zone and a harder titanium surface are formed. This change in hardness depends on the substances from which the investment material is made and the resulting reactions with liquid titanium.
The surface layer or alpha layer is so brittle and contaminated that during the pre-treatment of titanium, especially for ceramic veneering, it must be completely removed.
Change in the crystal structure
For dental applications, the transition of titanium at a temperature of 882.5 ° C from one crystal state to another is of great importance. Titanium passes at this temperature from alpha titanium with a hexagonal crystal lattice to Wetta titanium with a cubic one. What entails is not only a change in its physical parameters, but also an increase of 17% in its volume.
For this reason, it is also necessary to use special ceramics, the firing temperature of which must be below 880 °C.
passive layer
Titanium has a very strong desire at room temperature with atmospheric oxygen to instantly form a thin protective oxide layer, which protects it in the future from corrosion and causes good tolerance of titanium by the body.
The passive layer has the ability to regenerate itself.
This layer, at various stages of working with titanium, must be guaranteed.
After sandblasting, before steam cleaning the framework, it is necessary to leave the framework for at least 5 minutes. be passivated. A newly polished prosthesis must be passivated for at least 10-15 minutes, otherwise there is no guarantee of a good gloss of the finished work.
Processing requirements according to the material
Physical properties, oxidation phases and crystal lattice changes must be taken into account when processing titanium.
Proper machining can only be successfully carried out with special cutters for titanium, with a special cross cut (Fig. 10). The reduced angle of the working surface of which makes it possible to optimally remove rather soft metal, while at the same time good cooling of the tool. Titanium processing must be carried out without strong pressure to the instrument.
With the wrong tool, or strong pressure, local overheating of the metal is possible, accompanied by a strong formation of oxide and a change in the crystal lattice. Visually, on the processed object, there is a change in color and the surface slightly roughens. In these places, there will not be the necessary adhesion to ceramics (the possibility of cracks and chips), if these are not veneered areas, then further processing and polishing will also not meet the requirements.
Titanium cutters should be stored separately from other tools. They should be regularly cleaned with a steam jet and fiberglass brushes to remove any titanium residue.
The use of various carborundum disks and stones, or diamond heads, when processing titanium, greatly contaminates the surface of titanium, which subsequently also leads to cracks and chips in ceramics. Therefore, the use of the above tools is only suitable for processing, for example, clasp prosthesis frames, and the use of diamond heads should be completely excluded. Grinding and further polishing of exposed areas of titanium is only possible using abrasive rubbers and polishing pastes adapted for titanium. Many companies involved in the production of rotary tools currently produce a sufficient range of milling cutters and grinding rubbers for titanium.
For example, in my daily work I use Dentaurum processing tools (Fig. 11).
Suitable machining parameters for titanium:
– Low handpiece rotation speed – max. 15,000 rpm
– Low tool pressure
– Periodic processing.
– Machining the frame in only one direction.
– Avoid sharp corners and metal overlaps.
– When sanding and polishing, use only suitable abrasive rubbers and polishing pastes.
– Periodic cleaning of cutters with a steam jet and a fiberglass brush.
Sandblasting Titanium
Sandblasting before applying the bonding layer for ceramic coating as well as for cladding with composite materials must comply with the following requirements:
– Pure, only disposable aluminum oxide.
– Maximum sand grain size 150 µm, optimal 110–125 µm.
– Maximum pressure from the pencil 2 bar.
– Direction of sand flow at right angles to the surface.
After processing, it is necessary to leave the processed object for 5-10 minutes. passivated, and then steam clean the surface.
Oxide firing or similar procedures when working with titanium are completely excluded. The use of acids or etching is also completely excluded.
In the second part of our article, which will be published in one of the next issues, we will consider aspects of titanium - ceramic veneers, veneers with composite materials, the possibility of manufacturing clasp and combined clasp prostheses from titanium.
Important information:
Titanium is not an alloy - it is a pure chemical element, a metal;
· Ordinal number in periodic system 22;
Titanium has the ability to stay inert for a long time while in the body;
· Pure titanium is used in dentures in four grades (from T1 to T4);
Hardness, depending on the gradation, from 140 to 250 units,
KTR 9.6 x 10 (-6) K (-1);
Ceramic claddings require special ceramics;
· Melting point 1 668 °С, high reactivity;
Use of special casting machines and investment materials;
Density 4.51 g / cm 3;
Approximately four times lower density, and therefore weight, in relation to gold, gives patients increased comfort during the use of dentures;
Cobalt-chromium alloys
Co-Cr alloys were first used in dental practice in the 1930s, and since that time they have successfully replaced gold-containing type IV alloys in the manufacture of partial denture frameworks, primarily due to their relatively low cost, which is a significant factor in the manufacture of such large castings.
Compound
The alloy contains cobalt (55 - 65%) and chromium (up to 30%). Other main alloying elements are molybdenum (4 - 5%) and less commonly titanium (5%) (Table 3.3.6). Cobalt and chromium form a solid solution with a chromium content of up to 30%, which is the limit of chromium solubility in cobalt; an excess of chromium forms a second brittle phase.
In general, the higher the chromium content, the more corrosion resistant the alloy. Therefore, manufacturers try to maximize the amount of chromium, preventing the formation of a second brittle phase. Molybdenum is introduced to form a fine-grained structure of the material by creating more centers of crystallization during the solidification process. This has the additional advantage that molybdenum, together with iron, provides a significant strengthening of the solid solution. However, the grains are quite large, although their boundaries are very difficult to define due to the coarse dendritic structure of the alloy.
Carbon, which is present only in small amounts, is an extremely important component of the alloy, since slight changes in its quantitative content can significantly change the strength, hardness and ductility of the alloy. Carbon can combine with any other alloying element to form carbides. A thin layer of carbides in the structure can greatly increase the strength and hardness of the alloy. However, too much carbide can lead to excessive brittleness of the alloy. This presents a problem for the dental technician who needs to ensure that the alloy does not absorb excessive carbon during melting and casting. The distribution of carbides also depends on the casting temperature and the degree of cooling, since single crystals of carbides along the grain boundaries are better than their continuous layer around the grain.
Properties
For the dental technician, these alloys are more difficult to work with than gold-bearing alloys because they must be heated to very high temperatures before being cast. The casting temperature of these alloys is in the range of 1500-1550°C, and the associated casting shrinkage is approximately 2%.
This problem has been largely solved with the advent of induction casting equipment and phosphate-based refractory molding materials.
Casting accuracy suffers at such high temperatures, which greatly limits the use of these alloys, mainly for the manufacture of partial dentures.
These alloys are difficult to polish by conventional mechanical means due to their high hardness. For the internal surfaces of prostheses that are directly adjacent to the tissues of the oral cavity, the method of electrolytic polishing is used in order not to reduce the quality of the fit of the prosthesis, but the external surfaces have to be polished mechanically. The advantage of this method is that the cleanly polished surface lasts longer, which is a significant advantage for removable dentures.
The lack of ductility, exacerbated by carbon inclusions, is a particular problem, and in particular because these alloys are prone to pore formation during casting. When combined, these shortcomings can lead to breakage of clasps. removable dentures.
However, there are several properties of these alloys that make them nearly ideal for partial denture frameworks. The modulus of elasticity of the Co-Cr alloy is usually 250 GPa, while for the alloys discussed earlier, this figure is in the range of 70-100 GPa. Such a high modulus of elasticity has the advantage that the prosthesis, and especially the clasp arms, can be made with a thinner cross section while maintaining the required rigidity.
The combination of such a high modulus of elasticity with a density that is about half that of gold-bearing alloys greatly lightens the weight of the castings. This is undoubtedly a great advantage for patient comfort. The addition of chromium provides corrosion resistant alloys that are used in many implants, including hip and knee joints. Therefore, it can be confidently stated that these alloys have a high degree of biocompatibility.
Some alloys also contain nickel, which is added by manufacturers when making an alloy to increase toughness and reduce hardness. However, nickel is a known allergen and its use can cause allergic reactions in the oral mucosa.
titanium alloys
Interest in titanium in terms of its use in the manufacture of removable and non-removable dentures appeared simultaneously with the introduction of titanium.
Vyh dental implants. Titanium has a number of unique properties, including high strength at low density and biocompatibility. In addition, it was assumed that if a metal other than titanium was used for the manufacture of crowns and bridges based on titanium implants, this could lead to a galvanic effect.
The discovery of the element titanium is associated with the name of Reverend William Gregor in 1790, but the first sample of pure titanium was obtained only in 1910. Pure titanium is obtained from titanium ore (eg rutile) in the presence of carbon or chlorine. The TiCl4 obtained as a result of heating is reduced by molten sodium to form a titanium sponge, which is then melted under vacuum or in argon to obtain a metal billet (ingot).
Compound
From a clinical perspective, two forms of titanium are of greatest interest. This is a technically pure form of titanium and an alloy of titanium - 6% aluminum - 4% vanadium.
Commercially pure titanium
Titanium- a metal prone to allotropic or polymorphic transformations, with a hexagonal close-packed structure (a) at low temperatures and a bcc structure (P) at temperatures above 882C. Pure titanium is actually an alloy of titanium with oxygen (up to 0.5%). The oxygen is in solution, so the metal is the only crystalline phase. Elements such as oxygen, nitrogen, and carbon are more soluble in the hexagonal close-packed structure of the α-phase than in the cubic structure of the 3-phase. These elements form intermediate solid solutions with titanium and contribute to the stabilization of the α-phase. Elements such as molybdenum, niobium and vanadium act as P-stabilizers.
Alloy titanium - 6% aluminum - 4% vanadium
When aluminum and vanadium are added to titanium in small amounts, the strength of the alloy becomes higher than that of pure titanium Ti. It is believed that aluminum is an a-stabilizer, and vanadium acts as a B-stabilizer. When they are added to titanium, the temperature at which the rx-P transition occurs is lowered so that both forms can exist at room temperature. Thus, Ti - 6% Al - 4% V has a two-phase structure of a- and 3-grains.
Properties
Pure titanium is a white, lustrous metal that has low density, high strength, and corrosion resistance. It is ductile and is an alloying element for many other metals. Titanium alloys are widely used in the aviation industry and in the military field due to high strength rupture (-500 MPa) and the ability to withstand high temperatures. The elastic modulus of pure titanium tech.h.T is equal to PO GPa, i.e. half the modulus of elasticity of stainless steel and cobalt-chromium alloy.
The tensile properties of pure Tex.4.Ti titanium are largely dependent on the oxygen content, and although the tensile strength, permanent deformation index and hardness increase with increasing oxygen concentration, all this comes at the expense of a decrease in the ductility of the metal.
By alloying titanium with aluminum and vanadium, it is possible to obtain a wide range of mechanical properties of the alloy that exceed the properties of commercially pure titanium of technical purity grade. Such titanium alloys are a mixture of a- and P-phases, where the oc-phase is relatively soft and ductile, and the P-phase is harder and harder, although it has some plasticity. Thus, by changing the relative proportions of the phases, a wide variety of mechanical properties can be obtained.
For the Ti - 6% Al -4% V alloy, a higher tensile strength (-1030 MPa) can be achieved than for pure titanium, which expands the scope of the alloy, including when exposed to high loads, for example, in the manufacture of partial dentures .
An important property of titanium alloys is their fatigue strength. Both pure titanium technical grade T1 and Ti - 6% Al - 4% V alloy have a well-defined fatigue limit with an S - N curve (stress - number of cycles), leveling off after 10 - 10 cycles of alternating stress, the value of which is set 40-50% lower than the tensile strength. Thus, those h. Ti should not be used in cases where fatigue strength is required above 175 MPa. On the contrary, for the alloy Ti - 6% Al - 4% V, this figure is approximately 450 MPa.
As you know, metal corrosion is the main cause of the destruction of the prosthesis, as well as the occurrence of allergic reactions in patients under the influence of released toxic components. Titanium has become widely used precisely because it is one of the most corrosion-resistant metals. These qualities can be fully attributed to its alloys. Titanium is highly reactive, which in this case is its strong point, since the oxide formed on the surface (TiO2) is extremely stable, and it has a passivating effect on the rest of the metal. The high resistance of titanium to corrosion in the biological field of application is well studied and confirmed by many studies.
Casting of titanium alloys is a serious technological problem. Titanium has a high melting point (~1670°C), which makes it difficult to compensate for casting shrinkage during cooling. Due to the high reactivity of the metal, casting must be carried out under vacuum or in an inert atmosphere, which requires the use of special equipment. Another problem is that the melt tends to react with the mold of the refractory molding material, forming a scale layer on the surface of the casting, which reduces the fit of the prosthesis. When constructing implant-supported prostheses (suprastructures), a very tight tolerance must be maintained in order to obtain a good fit to the implant. Otherwise, the retention of the implant in the bone may be impaired. In titanium castings, internal porosity can also often be observed. Therefore, other technologies are used for the manufacture of titanium dentures, such as CAD/CAM technologies in combination with rolling and spark erosion.
Some properties of alloys are not noble metals discussed above are presented in Table 3.3.7.
conclusions
There are many different alloys used in dentistry today. In order to make a rational choice from the existing variety of high-gold alloys or other types of alloys, the dentist, more than ever, needs to have knowledge of the nature of alloys, their physical and mechanical properties.
The cost of the alloy is a significant part of the cost of prosthetics. However, low-cost alloys typically require additional costs to manufacture prostheses, and ultimately the lower cost of the alloy is often offset by the increased cost of manufacturing the prosthesis. It is also important to note that the high content of gold in the alloy opens up a great possibility of manufacturing a high-quality denture.
Clinical Significance
The dentist, not the dental technician, is solely responsible for the choice of materials for the manufacture of dentures.
Fundamentals of Dental Materials Science
Richard van Noort
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Musheev Ilya Urievich. The use of titanium alloys in the clinic of orthopedic dentistry and implantology (experimental clinical study): dissertation ... Doctor of Medical Sciences: 14.00.21 / Musheev Ilya Ureevich; [Place of defense: GOU "Institute for Advanced Studies of the Federal Medical and Biological Agency"]. - Moscow, 2008. - 216 p.: ill.
Introduction
Chapter 1 Literature Review
1.1. Metal alloys used in the manufacture of dentures 12
1.2. The use of implants in orthopedic rehabilitation of patients with defects in the dentition 25
1.3. Titanium and its alloys: properties and applications 31
1.4. Clinical toxic-chemical and allergic reactions when using dental alloys 41
1.5. Theory of corrosion processes 53
Chapter 2. Material and research methods
2.1. Methods for studying the composition, structure and physical and mechanical characteristics of dental alloys 75
2.2.1. Study of mechanical properties by nanoindentation 75
2.1.2. Tribological studies of wear resistance of alloys 77
2.1.3. Methods for comparing cast and milled titanium 79
2.1.4. Method for studying the composition, structure and physical and mechanical properties of the alloy after remelting 80
2.2. Methods for studying the electrochemical parameters of dental alloys 83
2.2.1. Measurement of basic electrode potentials of dental alloys 83
2.2.2. Heat treatment of dental alloys in electrochemical studies 85
2.2.3. Measurement of EMF and current density of contact pairs of dental alloys 86
2.2.4. Investigating the Effect of Dental Alloy Surface Resurfacing 87
2.2.5. Study of the influence of the features of the corrosive environment and the load on the electric potentials of the alloy 87
2.2.6. Estimated corrosion rate in stationary conditions according to the results of measuring the currents of contact pairs 91
2.3. Methods for studying the response of human mesenchymal stem cells to dental alloys 92
2.4. Characterization of clinical material and methods clinical research 96
2.5. Statistical processing of research results 97
Chapter 3. Results of own research
3.1. Comparative study of structural, mechanical and tribological properties of dental alloys98
3.1.1. Comparative evaluation of the mechanical properties of dental alloys 98
3.1.2. Comparative study of wear resistance of dental alloys 103
3.1.3. Comparative study of the structure and properties of milled and cast titanium 114
3.1.4. Influence of thermal cycling and remelting on the alloy structure... 120
3.2. Comparative electrochemical characteristics of dental alloys in different conditions of functioning of prostheses 131
3.2.1. Kinetics of establishment of stationary electric potentials of dental alloys 131
3.2.2. Electrochemical characteristics of alloys after heat treatment when applying ceramic coatings 141
3.2.3. The influence of pH, temperature and aeration of a corrosive environment on the electrochemical behavior of dental alloys 146
3.2.4. Effect of cyclic dynamic load on the corrosion behavior of titanium alloy 166
3.3. Electrochemical interaction of dental alloys with dental implants 181
3.3.1. Electrochemical characteristics of contact pairs "titanium implant-prosthesis frame" 181
3.3.1.1. Measurement of EMF and currents of contact pairs 181
3.3.1.2. Measurement of impulses of potentials and contact currents when updating the surface of elements of contact pairs and studying the kinetics of repassivation of the renewed surface when using titanium implants 183
3.3.2. Electrochemical characteristics of contact pairs "nickel-titanium implant-prosthesis frame" 190
3.3.2.1. Measurement of EMF and currents of contact pairs 190
3.3.2.2. Measurement of pulsed currents during the renewal of the surface of elements of contact pairs and study of the kinetics of repassivation of the renewed surface when using nickel-titanium implants 194
3.4. Experimental evaluation of the proliferation of human mesenchymal stem cells on metal alloys 206
3.4.1. Evaluation of cytotoxicity of samples using the MTT test 206
3.4.2. Study of the influence of the studied samples on the efficiency of MSC 207 proliferation
3.5. Clinical evaluation of orthopedic constructions on metal frames 211
Chapter 4. Discussion of the results of the study 222
References 242
Introduction to work
The relevance of research. In modern orthopedic
metal alloys are widely used in dentistry as cast frames of fixed and removable dentures. In Russia, cobalt-chromium and nickel-chromium alloys are common as metallic structural materials; the use of gold-bearing alloys is negligible. Bioinert titanium alloys are used much less frequently because titanium casting requires special equipment; clinical and technological experience with titanium alloys is not enough.
Meanwhile, the excellent biocompatibility properties of titanium, the lightness and strength of titanium structures are well known; it is possible to veneer titanium frameworks with ceramics. The demand for titanium-containing alloys for dental prostheses is increasing in parallel with the increase in the rate of use of dental implants, which are made overwhelmingly from titanium.
Recently, in addition to casting, it has become possible to mill titanium on CAD / CAM equipment after scanning the model and virtual modeling of the prosthesis. There is insufficient information in the literature on the clinical performance of CAD/CAM technology compared to titanium casting.
The operation of dentures made of metal alloys is associated with
possible electrochemical corrosion processes, since
saliva has electrolyte properties.
With respect to titanium, these processes have been little studied. contact
electrochemical interaction of dental titanium implants with
other dental alloys analyzed in
few studies using standard methods. Recently, new opportunities and methodological approaches have appeared in assessing the anticorrosion resistance of metal alloys,
for example, in tribological studies of wear resistance; measuring electrochemical parameters during surface renewal, when changing the characteristics of artificial saliva, during thermal cycling and, especially, the dynamic load of metal structures. It became possible to study the reaction of human cell cultures to various dental alloys.
Of great interest is the titanium alloy with the effect of form restoration - titanium nickelide, from which fixed and removable prostheses and implants can be made. Its properties in relation to the goals of orthopedic dentistry and implantology are not fully understood, especially in a comparative aspect. From the standpoint of electrochemistry, there was no justification for the choice of optimal alloys for dentures based on titanium nickelide implants with the effect of shape restoration.
Purpose of the study: clinical and laboratory substantiation of the use of titanium alloys and technologies for their processing in the clinic of orthopedic dentistry and implantology.
Research objectives:
Compare physical-mechanical and tribological properties (wear resistance) of dental alloys and titanium alloys.
Compare the composition, structure and properties of titanium alloy for CAD/CAM prosthesis milling and cast titanium, as well as the properties of the alloys after remelting.
To reveal the influence of dental alloys on the proliferative characteristics of human mesenchymal stem cell culture.
To study under laboratory conditions the indicators of corrosion resistance of solid and metal-ceramic prostheses using common dental alloys and titanium alloys.
To establish the electrochemical features of the use of implants made of titanium and titanium nickelide, including in case of violation (renewal) of the surface of prostheses and implants during their operation.
Establish differences in the electrochemical behavior of dental alloys with an experimental change in the characteristics of an electro-corrosive medium (pH, degree of aeration).
To study the effect of dynamic loading of titanium prostheses and implants on their electrochemical parameters.
Conduct subjective and objective assessment prosthetic structures from various dental alloys, including those on implants and those made using CAD / CAM technology, in the long term after the end of orthopedic treatment.
Scientific novelty research. For the first time
Nanoindentation studied under similar experimental conditions the main mechanical properties: hardness, modulus of elasticity, percentage of recoverable deformation - common dental alloys, titanium alloys and titanium nickelide. At the same time, tribological studies of dental alloys, including titanium-containing alloys, were carried out for the first time; a comparison of their wear resistance and the nature of the destruction of alloys according to microphotographs was carried out.
For the first time, the composition, structure, physical and mechanical characteristics of standard titanium billets for casting and milling (using CAD/CAM technology) were compared using metallographic, X-ray diffraction analysis and measuring nanoindentation. For the first time, using local energy-dispersive analysis and semi-quantitative determination of the chemical composition, metallography and X-ray structural phase analysis, the effect of repeated remelting of a dental alloy on its properties was revealed.
For the first time, the electric potentials of titanium alloys and titanium nickelide were studied in dynamics in comparison with non-noble and noble dental alloys in artificial saliva, including after their thermal cycling with ceramic lining of prostheses. For the first time, a change in the electric potentials of alloys was established with a change in the parameters (pH, aeration) of artificial saliva and with a dynamic load of metal structures.
For the first time in comparison, the electrochemical parameters of the contact pairs "prosthesis frame - supporting implant" were studied using titanium nickelide and titanium implants and basic structural alloys for dental prostheses. For the first time, calculations of corrosion losses were carried out in case of damage to the surface of nickel-titanium and titanium implants, as well as metal frames of dentures fixed on them.
For the first time in the culture of human mesenchymal stem cells, the toxicity of dental alloys was studied in terms of cell proliferation, adhesion and viability.
For the first time, a clinical comparison of the corrosion manifestations of prostheses made of non-precious alloys, cast and milled titanium using CAD/CAM technology was carried out.
The practical significance of the study.
The identity of the composition, structure and basic physical and mechanical properties of certified titanium blanks for casting and milling prostheses using CAD/CAM technology has been established; certain metallurgical defects of standard titanium blanks were revealed. On the example of a non-precious dental alloy, the negative effect of repeated remelting on its structure and physical and mechanical properties while maintaining the composition is confirmed.
The main physical and mechanical characteristics are given
dental alloys, titanium alloys and titanium nickelide according to
results of identical bench tests. Clinically important differences in the degree and nature of wear of the studied dental alloys are shown. An important property of titanium nickelide for implantology has been confirmed - the high value of elastic recovery during its loading.
From the standpoint of electrochemistry, the advantages and disadvantages of various dental alloys (including titanium-containing alloys) are shown in different operating conditions: in the presence of solid-cast or metal-ceramic prostheses, including those based on titanium or nickel-titanium implants, and in violation of their surface. The expediency of metal-ceramic prostheses with full lining of metal frames is shown to reduce the risk of developing electrochemical reactions in the oral cavity and reduce the operational resources of prostheses.
The indifference of all dental alloys with respect to the cell culture of human mesenchymal tissue was demonstrated, as well as certain differences in the reaction of mesenchymal stem cells.
The statistics of the decrease in the functional and aesthetic properties of dentures based on metal frames from various dental alloys, as well as toxic and chemical complications, are given. Clinically substantiated the effectiveness of the use of prostheses on cast and milled titanium frames when replacing defects in the dentition and when using titanium implants.
Basic provisions for defense.
1. From the standpoint of electrochemistry and the prevention of toxic and chemical effects on the tissues of the oral cavity, the most optimal for prosthetics on titanium and nickel-titanium implants are fixed prostheses with full ceramic lining on frames made of any dental alloy; the production of one-piece uncoated prostheses on titanium implants is advisable when
the use of titanium- and gold-containing alloys, and on nickel-titanium implants - nickel-titanium or chromium-colbalt alloys.
The factors that reduce the corrosion resistance of dental alloys are changes in pH and deaeration of saliva, low wear resistance and violation of the integrity of the surface of the prosthesis during its operation, as well as repeated remelting of the alloy.
Functional loading of metal prostheses and implants causes significant fluctuations in the electrochemical parameters of dental alloys, as a result of discontinuity of surface oxide films.
The composition and properties of titanium alloys for casting and milling are similar; CAD/CAM titanium prostheses have technological and clinical advantages.
Common dental alloys, titanium alloys and titanium nickelide have no toxic effects on human mesenchymal stem cells.
According to the clinic, toxic-chemical objective and subjective manifestations when using non-precious dental alloys are more common in comparison with titanium-containing alloys; the presence of titanium implants as supports for dentures does not lead to clinical manifestations of contact corrosion, provided that careful oral hygiene is observed.
Approbation of the research results. The results of the study were reported at the All-Russian Conference "Superelastic Shape Memory Alloys in Dentistry", I All-Russian Congress "Dental Implantation" (Moscow, 2001); at the 1st congress of the European Conference on
problems of dental implantology (Lvov, 2002); at the VIII All-Russian Scientific Conference and the VII Congress of the StAR of Russia (Moscow, 2002); at the 5th Russian Scientific Forum "Dentistry - 2003" (Moscow, 2003); at the International Conference "Modern Aspects of Rehabilitation in Medicine" (Yerevan, 2003); at the VI Russian Scientific Forum "Dentistry 2004", (Moscow); at the International Conference on Shape memory medical materials and new Technologies in medicine (Tomsk, 2007); at the scientific-practical Conference dedicated to the 35th anniversary of the formation of the Central Medical School No. 119 (Moscow, 2008); at the V All-Russian scientific and practical conference"Education, Science and Practice in Dentistry" on the topic "Implantology in Dentistry" (Moscow, 2008); at a meeting of the staff of the Department of Clinical Dentistry and Implantology of the Institute for Advanced Studies of the Federal Medical and Biological Agency of Russia (Moscow, 2008).
Implementation of the research results. The results of the study have been introduced into the practice of the Clinical Center of Dentistry of the Federal Medical and Biological Agency of Russia, the Central Research Institute of Dentistry and Maxillofacial Surgery, the National Medical and Surgical Center, the KARAT clinic (Novokuznetsk), the CSP-Lux clinic (Moscow); in the educational process of the Department of Clinical Dentistry and Implantology of the Institute for Advanced Studies of the Federal Medical and Biological Agency of Russia, the Department of Dentistry of General Practice with a course of dental technicians of the Moscow State Medical University, the Laboratory of Medical Materials of MISiS.
The volume and structure of the dissertation. The work is presented on 265 sheets of typewritten text, consists of an introduction, a literature review, three chapters of own research, conclusions, practical recommendations, and an index of literature. The dissertation is illustrated with 78 figures and 28 tables. The literature index includes 251 sources, of which 188 are domestic and 63 are foreign.
Metal alloys used in the manufacture of dentures
There are fundamental differences in chemical and physical properties between these two groups. In the process of dental work, these differences should be taken into account. Pure titanium occupies a dual position. From a chemical point of view and in terms of dental processing, it, belonging to base metal alloys, has mechanical properties that are more characteristic of noble metal alloys.
The composition of gold-bearing alloys includes gold (39-98%), platinum (up to 29%), palladium (up to 33%), silver (up to 32%), copper (up to 13%) and a small amount of alloying elements. The composition of palladium alloys includes (35-86%) palladium, up to 40% silver, up to 14% copper, up to 8% indium, etc. Silver-containing alloys contain 36-60% silver, 20-40% palladium, up to 18% copper and others
The composition of non-precious alloys, in particular, cobalt-chromium, includes 33-75% cobalt, 20-32% chromium, up to 10% molybdenum and other additives. Nickel-chromium alloys contain 58-82% nickel, 12-27% chromium, up to 16% molybdenum. Titanium nickelide contains approximately equal parts of nickel and titanium. Iron-containing alloys (steels) contain up to 72% iron, up to 18% chromium, up to 8% nickel, up to 2% carbon. Titanium alloys contain at least 90% titanium, up to 6% aluminum, up to 4% vanadium and less than 1% iron, oxygen and nitrogen.
Almost all cobalt alloys contain nickel impurities. But the nickel content in them should be at a level that does not pose a danger. Thus, the nickel content in a clasp prosthesis, which is made of a high-quality cobalt-chromium alloy, approximately corresponds to the amount of nickel consumed daily with food.
At present, carbon-free cobalt-chromium alloys are widely used for the manufacture metal-ceramic crowns and bridges, for example, Western companies produce: KRUPP - Bondi-Loy alloy, BEGO - Wirobond, DENTAURUM - CD alloy. In the USA, MINEOLA A.ROSENS ON INC manufactures the Arobond alloy. Similar alloys "KH-DENT" and "Cellite-K" are produced in Russia.
At present, along with cobalt-chromium alloys, nickel-chromium alloys are widely used for metal-ceramic work. The prototype of these alloys was the heat-resistant alloy "NIKHROM" -Kh20N80, used in industry for the manufacture of heating elements. For greater rigidity, it is alloyed with molybdenum or niobium, to improve casting qualities - with silicon.
The most popular of these alloys is the BEGO Wiron 88 alloy; similar alloys are produced in Russia: Dental NSAvac, NH-DENT NSvac, Cellite-N.
Titanium is the most difficult element to obtain in an absolutely pure form. Based on its high reactivity, it binds some elements, primarily oxygen, nitrogen and iron. Therefore, pure titanium (called unalloyed) is divided into different purification groups (from category 1 to category 4). Due to mechanical properties, it is not always advisable to use a metal of the highest category. Titanium containing impurities has better mechanical properties.
Alloy developers recommend the manufacture of certain orthopedic structures from various dental alloys. So for the manufacture of inlays, gold is recommended with the manufacturer's reference - "excellent"; with the reference "possible use" refers to alloys based on palladium, silver, cobalt, nickel and titanium. For the manufacture of crowns and bridges with plastic lining, alloys of gold, palladium, silver, cobalt, nickel and titanium are “excellent”, and with ceramic lining - gold, palladium, cobalt, nickel, titanium (it is possible to use silver-based alloys). For clasp prostheses, cobalt-based alloys are “excellent” and alloys based on gold, palladium, cobalt, nickel and titanium are “possible to use”. According to manufacturers, implants are great for making from titanium, but possibly from a cobalt-chromium alloy. Supraconstructions are recommended to be made with the “excellent fit” marking from gold, palladium, cobalt, nickel, titanium. As for the materials to be used for implants and suprastructures, the author of this dissertation does not agree, since he considers it correct to use the principle of monometal (titanium) in implantology.
In addition to physical and mechanical characteristics, the choice of alloy is important for its biological compatibility. The benchmark for biological safety is the corrosive behavior of a material. In noble metal alloys, the content of the noble metals themselves (gold, platinum, palladium and silver) should be as high as possible. Considering the corrosion behavior of base metal alloys (cobalt-chromium and nickel-chromium alloys), the chromium content should be taken into account. The chromium content must be above 20% to ensure sufficient stability in the oral environment. Contents less than 20 (15%) may cause high ion release. It is well known that there are differences between the biological functions of the metal. These are the so-called essential elements, non-essential elements and toxic metals. Elements of the first group are necessary for the human body for its functioning. Such elements are components of enzymes, vitamins (eg cobalt for vitamin B12) or other important molecules (eg iron in hemoglobin for oxygen transport). Non-essential elements do not harm the body, but the body does not need them. The last group is elements that are dangerous to the body. Such metals should not be used in dental alloys.
Clinical toxic-chemical and allergic reactions when using dental alloys
The urgency of the problem of toxic-chemical and allergic reactions when using dental alloys does not disappear.
So Dartsch RS, Drysch K., Froboess D. studied the toxicity of industrial dust in a dental laboratory, in particular, containing alloys of noble and non-precious dental alloys. For the study, L-929 cell cultures (mouse fibroblasts) were used to determine the number of living cells and calculate the cell growth factor in the presence of metal dust for three days. In this case, three exposure options were modeled: when dust got into the mouth (solution of synthetic saliva according to EN ISO 10271 - pH 2.3), when it got on the skin of the hands (acidic solution of synthetic sweat according to EN ISO 105-E04 - pH 5.5), when exposed to detergent solutions for washing hands (acidic synthetic sweat solution according to EN ISO 105-E04 - pH 5.5) in combination with antibiotic additives (Penicilin/Streptomycin).
While for the control cell culture, the growth factor was 1.3 population doublings (i.e., each cell of the colony divided in two about 1.3 times per day), the level of decrease in the growth factor of cells with sample extracts depended on the degree of their dilution. The maximum toxicity has a sample collected directly at the workplace of the technician, the composition of which includes dust of noble and base metals. This means that the processing of alloys in the production of cermets is associated with obvious health risks. This fully applies to the sample taken from the central ventilation system of the laboratory.
Intolerance to structural dental materials is based on the characteristics of the body's reaction to their composition; Various methods have been proposed to diagnose these conditions. Tsimbalistov A.V., Trifonov B.V., Mikhailova E.S., Lobanovskaya A.A. list: pH analysis of saliva, study of the composition and parameters of saliva, blood tests, use of the method of acupuncture diagnostics according to R. Voll, continuous pinpoint diagnostics, measurement of the bioelectromagnetic reactivity index of tissues, exposure and provocative tests, leukopenic and thrombopenic tests, epicutaneous tests, immunological methods of research . The authors have developed intraoral epimucosal allergological tests, in which the state of the microvasculature is assessed using contact biomicroscopy using an MLK-1 microscope. To process the qualitative and quantitative characteristics of microcirculation, the microscope is supplemented with a color analog video camera and a personal computer.
Marenkova M.L., Zholudev S.E., Novikova V.P. conducted a study of the level of cytokines in the oral fluid in 30 patients with dentures and manifestations of intolerance to them. Enzyme-linked immunosorbent assay was used with the corresponding kits of reagents of ZAO Vector-Best. An increase in the content of pro-inflammatory cytokines in saliva in patients with intolerance to prostheses, activation of the cellular immune response without activation of autoimmunization and allergic processes was established. Thus, in persons with intolerance to dentures, a nonspecific inflammatory process and destructive changes in the oral mucosa are detected.
Oleshko V.P., Zholudev S.E., Bankov V.I. proposed a diagnostic complex "SEDC" to determine the individual tolerance of structural materials. Physiological mechanism diagnostics is based on the analysis of changes in the parameters of weak pulsed, complexly modulated low-frequency electromagnetic fields that are most adequate to a living organism. A feature of the complex is the processing of the response signal from the sensor at carrier frequencies from 104 Hz to 106 Hz. The response signal from the sensor always contains information about the microcirculation and metabolism in the tissue at the cellular level. The studied sample of dental material is placed between the lips of the patient, which causes a chemical microreaction and a change in the chemical composition of the medium at the interface. The appearance of components that are inadequate to the chemical composition of the oral environment irritates the receptors of the lip mucosa, which was reflected in the readings of the device. In addition, the device has 2 light guides; in the initial state, the light guide is on, corresponding to the absence of galvanic processes.
Lebedev K.A., Maksimovsky Yu.M., Sagan N.N., Mitronin A.V. describe the principles of determining galvanic currents in the oral cavity and their clinical rationale. The authors examined 684 patients with various metallic inclusions in the oral cavity and signs of galvanism in comparison with 112 individuals with prostheses and without signs of galvanism; the control group of 27 people had no metallic inclusions. The potential difference in the oral cavity was measured with an APPA-107 digital voltmeter.
Methods for studying the composition, structure and physical and mechanical characteristics of dental alloys
Continuous indentation of the alloys to study the mechanical properties was carried out on an automated Nano-Hardness Tester (CSM Instr.) at loads of 5 and 10 mN in air using a Vickers diamond indenter (Fig. 1) . At such low loads, the method can be considered non-destructive on a macroscale, since the penetration depth of the indenter did not exceed 0.5 μm, which made it possible to test wear resistance on the same samples. The advantage of the nanoindentation method is that the analysis of a series of experimental loading-unloading curves makes it possible to quantify the mechanical properties of both relatively soft and superhard (more than 40 GPa) materials using a sample of simple geometry with a flat area of several mm2. Calculations of hardness and modulus of elasticity were carried out according to the Oliver-Farr method using the calculation and control program "Indentation 3.0". According to the experimental data, the elastic recovery of the material is also calculated as the ratio of elastic deformation to the total R=(hm-hf)/hm-100%, where hm is the maximum immersion depth, hf is the imprint depth after the load is removed. Each value was averaged over 6-12 measurements.
General view of the Nano-Hardness Tester setup. The test sample is placed on the object table, then a sapphire ring is lowered onto the surface of the sample, which remains in contact with the test material during the loading and unloading cycle (Fig. 2). The normal load is applied by means of an electromagnet and transmitted to the indenter via a vertical rod. The movement of the rod relative to the position of the ring is measured by a capacitive sensor, which is connected to the computer via an interface board.
Scheme of testing during nanoindentation The loading-unloading cycle takes place at a certain speed and exposure. The resulting data is presented as a graph of the dependence of the load on the depth of indentation (Fig. 3).
To calibrate the nanohardness tester, tests are first carried out on a standard sample, and only then on the material under study. Fused quartz with known hardness and Young's modulus (E = 72 GPa, H = 9.5 GPa) is taken as a standard sample.
Tribological studies of wear resistance of alloys.
Wear resistance tests according to the “rod-disk” scheme were carried out on an automated “Tribometer” (CSM Instr.) installation (in a biological solution medium (Fig. 4, 5, Table 2). This scheme allows laboratory studies to be brought closer to the real interaction of a cast product with tooth enamel.A certified ball with a diameter of 3 mm made of aluminum oxide (Young's modulus E = 340 GPa, Poisson's ratio 0.26, hardness 19 GPa) served as a stationary counterbody. Aluminum oxide was chosen as a non-metallic, non-conductive material similar in structure to tooth enamel , the hardness of which exceeds the hardness of the alloys under study.The ball was fixed with a stainless steel holder, which transferred the specified load to the ball and was connected to a friction force sensor.The contact zone was inside a cuvette filled with a biological solution.
A comprehensive tribological study included continuous recording of the coefficient of friction (c.f.) during testing according to the "fixed rod - rotating disk" test on an automated Tribometer (CSM Instr.), as well as a fractographic study of the wear groove (including groove profile measurements) and wear spots on the counterbody, the results of which were used to calculate the wear of the sample and the counterbody. The structure of wear grooves (on disks) and the diameter of wear spots (on balls) were studied under observation in an AXIOVERT CA25 optical microscope (Karl Zeiss) at a magnification of x (100-500) and an MBS-10 stereomicroscope (LZOS) at a magnification of x (10-58 ).
Measurements of the vertical section of the grooves were carried out at 2-4 diametrically and orthogonally opposite points on the Alpha-Step200 profilometer (Tensor Instr.) at a load of 17 mg and the average value of the cross-sectional area and depth of the wear groove was determined. The quantitative assessment of the wear of the sample and the counterbody was carried out as follows. Ball wear was calculated using the following formula: V= 7i h2(r l/3h), where I =r-(-[(W]2)1/2, d is the wear scar diameter, r is the ball radius, h is the segment height. Sample wear was calculated by the formula: V= S% where / is the circumference, 5 is the cross-sectional area of the wear groove Test results and fractographic observations were processed using the computer program InsrtumX for Tribometer, CSM Instr.
Methods for comparing cast and milled titanium.
The structure and properties of standard blanks for milling titanium frameworks of prostheses using CAD/CAM technology and titanium obtained by investment casting were compared.
An analysis of the macro and microstructure of titanium alloy samples in the form of plates 2–3 mm thick was carried out using modern methods digital macro and micro photography MBS-10 (LZOS) and AXIOVERT25CA (Karl Zeiss). Studies were carried out on polished sections, which were treated with an etchant of the composition 2% HF + 2% NZh)3 + distilled water (remaining) to reveal the micro and macrostructure.
The evaluation of the mechanical properties (hardness and Young's modulus) was made by the Oliver-Pharr method according to the measurement nanoindentation (ISO 14577) carried out on a NanoHardnessTester precision hardness tester (CSM Instr.) at loads of 10 and 20 mN using a Berkovich diamond indenter. According to the experimental data, the elastic recovery of the material R was also calculated as the ratio of elastic deformation to the total R-(hm-hf)/hm-100%, where hm is the maximum indenter immersion depth, h/ is the imprint depth after the load is removed. The calculation results were averaged over 6–12 measurements by the ANOVA method.
Electrochemical characteristics of contact pairs "titanium implant-prosthesis frame"
Typical experimental curves reflecting the resistance of alloys to the penetration of a diamond indenter with an increase (upper branch) and decrease (lower branch) of the applied load YumN are shown in Figure 11, and the results of calculating the mechanical properties of the alloys are given in Table 6.
The hardness of dental alloys according to the results of nanoindentation lies in the range of 2.6 - 8.2 GPa (Fig. 12, Table 6). The closest in properties to tooth enamel (according to the literature data H = 3.5-4.5 GPa) are alloys containing titanium, including titanium nickelide (4.2-5.2 GPa), as well as an alloy based on Nickel Cellite N.
The hardness of zirconium and gold-platinum alloys is almost 2 times lower (up to 2.6 GPa), while cobalt-chromium alloys and Remanium 2000 nickel-chromium alloy are almost twice as high (up to 8.2 GPa).
The modulus of elasticity of tooth enamel is about 100 GPa, for dental alloys - from 65.9 to 232.2 GPa. Similar properties for zirconium, slightly higher for alloyed titanium and gold-platinum alloy. All other alloys, except titanium nickelide, have a higher modulus of elasticity.
As is known, for bone it is much less and amounts to E=10 - 40 GPa.
Judging by the very low value of E (65.9 ± 2.5 GPa), the titanium nickelide alloy under test conditions is close to the martensitic transformation range in a special structural state, which is characterized by
The rest of the alloys exhibit elastic recovery values of 10–20% typical for metals. A slight excess of this level for cobalt-chromium alloys, alloyed titanium and Remanium 2000 nickel-chromium alloy and increased values of the elastic modulus can be associated with the formation of intermetallic phases (ordering), texture or residual internal stress fields after casting or rolling.
Thus, the basic physical and mechanical parameters of titanium alloys occupy a middle position among common dental alloys of a different composition. The titanium nickelide alloy is of interest due to the particularly high value of elastic recovery. Alloy nanoindentation data are important for the choice of structural materials for dentures and implants.
Comprehensive tribological study, wear groove fractography formed the basis for the wear resistance of dental alloys. Measurements of the elastic modulus made it possible to estimate the Hertzian stresses in the friction pair.
Figure 14 shows the calculated values of pressure arising from the contact of a flat sample of the alloy under study with a spherical alumina indenter 3 mm in diameter (the designations of the alloys correspond to their composition in accordance with Table 1).
1 According to the values of contact stresses, 2 groups of alloys can be distinguished. The first includes nickel- and cobalt-chromium alloys, which are characterized by values of 1.36–1.57 GPa, which corresponds to a Young's modulus of 167–232 GPa. All of these alloys are characterized by high wear resistance (6.75106 mm3/N/m), and wear seems to follow the same mechanism.
Another group with contact stress values (1.07-1.28) is made up of titanium and zirconium alloys, which have shown significant wear (3.245-10 "4 mm3 / N / m). Outside this classification are nickel-titanium and gold-platinum alloys, which formally can be assigned to the second group.These alloys have their own wear mechanism.Specimens of cobaltchromium, nickelchromium and goldplatinum alloys withstood the test under specified conditions, for the rest of the test
As can be seen from the illustrations in figures 16-17 and in table 7, the least wear (2.45-10" mm / N / m) is observed in the gold-platinum alloy, as well as in the cobalt-chromium alloy Remanium 2000 - 1.75-10-6 mm / N / m The greatest wear was shown by samples of Rematitan and zirconium - 8.244-10-4 and 8.465-10 "4 mm / N / m, respectively.
When comparing figures 16-20, it can be concluded that there is a special wear mechanism for gold-platinum alloy and titanium nickelide. The most wear-resistant gold-platinum alloy has a special wear mechanism associated with its chemically inert surface in a biosolution environment.
Despite the low modulus of elasticity, it exhibits record low wear and minimum initial and final friction coefficients. There is also a special wear mechanism for the titanium nickelide sample, in which one of the lowest initial friction coefficient (k.f.) (0.107) and the maximum final c.f. (0.7), which is associated with the occurrence of a reversible martensitic transformation in titanium nickelide, initiated by an external load. This is evidenced by the large amplitude of the c.t. and its increase by the end of the test by 7 times.
It should be noted that increased wear of titanium-containing alloys is associated with metal sticking to the ball surface, which leads to a change in the contact geometry (contact area decreases) and counterbody properties (formation of an intermetallic compound of the TIA1 type with a high Young's modulus), which ultimately leads to a sharp increase in contact stresses compared to the calculated ones.
Thus, the tests carried out on the wear resistance of dental alloys in a biological solution medium showed that pure metals titanium (DA2) and zirconium (DA7) exhibit the greatest wear (8.24-8.47-10"4 mm3 / N / m), as well as titanium nickelide (DA1) (5.09-10" 4mm3/N/m). Alloying of titanium (DA8 and DA9) increases wear resistance: the wear of alloys VT5 (Ti-Al-Sn system) and VT 14 (Ti-Al-Mo-V) is reduced by approximately 2.5 times compared to pure titanium.
The most wear-resistant alloy is DA10 based on Au-Pt (2.45-10 7 mm3/N/m).
Sufficiently high wear resistance, but an order of magnitude worse than gold-platinum, was shown by the DA5 alloy (Remanium 2000) based on the Co-Cr-Mo-Si system (1.7540-6 mm3/N/m). The remaining alloys DA2, DA4, DA11 (nickelchromium and Cellite K) have satisfactory wear resistance in the range of (4.25-7.35)-10"6 mm3 / N / m.
Titanium and tantalum - "compromise" metals for medicine
The use of various metal products in medicine has been practiced since ancient times. The combination of such useful properties metals and their alloys, as strength, durability, flexibility, plasticity, elasticity, has no alternatives, in particular, in the manufacture of orthopedic structures, medical instruments, devices for the speedy fusion of fractures. And in recent decades, thanks to the discovery of the “shape memory” effect and the introduction of other innovations, metals have also become widely used in vascular and neurosurgery for the manufacture of suture material, mesh stents for expanding veins and arteries, large endoprostheses, in ophthalmic and dental implantology.
However, not all metals are suitable for use in the medical field, and the main destructive causes here are susceptibility to corrosion and reaction with living tissues - factors that have devastating consequences for both the metal and the body itself.
Of course, gold and platinum group metals (platinum, iridium, osmium, palladium, rhodium, etc.) are out of competition. However, the possibility of using precious metals for mass use is practically absent due to their prohibitive high cost, and the combination of useful properties that are in demand in certain specific clinical situations is not always inherent in noble metals.
A significant place in this area to this day is occupied by stainless steels alloyed with certain additives to obtain the required characteristics. But such metal materials, which are hundreds of times cheaper than precious metals, do not effectively resist corrosion and other aggressive influences, which significantly limits the possibility of their use for a number of medical needs. In addition, an obstacle to the engraftment of stainless steel products implanted inside the body is their conflict with living tissues, which causes high risk rejection and other complications.
A kind of compromise between these two poles are metals such as titanium and tantalum: strong, malleable, almost not subject to corrosion, having a high melting point, and most importantly - completely biologically neutral, due to which they are perceived by the body as their own tissue and practically do not cause rejection. As for the cost, for titanium it is not high, although it significantly exceeds that of stainless steels. Tantalum, being a fairly rare metal, is more than ten times more expensive than titanium, but still much cheaper than precious metals. With the similarity of most of the main operational properties, in some of them it is still inferior to titanium, although in some it surpasses it, which, in fact, determines the relevance of the application.
It is for these reasons that titanium and tantalum, often referred to as "medical metals", as well as a number of their alloys, are widely used in many medical industries. Differing in a number of characteristics and, thus, mutually complementing each other, they open up truly immense prospects for modern medicine.
Below, we will talk in more detail about the unique characteristics of titanium and tantalum, the main areas of their use in medicine, the use of various forms of production of these metals for the manufacture of tools, orthopedic and surgical equipment.
Titanium and tantalum - definition, actual properties
Titanium for medicine
Titanium (Ti) - a light metal with a silvery hue that looks like steel - is one of the chemical elements Periodic table placed in the fourth group of the fourth period, atomic number 22 (Fig. 1).
Figure 1. Titanium nugget.
It has an atomic mass of 47.88 with a specific density of 4.52 g/cm 3 . Melting point - 1669 ° C, boiling point -3263 ° C. In industrial grades with high stability, it is tetravalent. It is characterized by good plasticity and malleability.
Being both lightweight and having high mechanical strength, twice that of Fe and six times that of Al, titanium also has a low coefficient of thermal expansion, which allows it to be used in a wide temperature range.
Titanium is characterized by a low thermal conductivity, four times lower than that of iron and more than an order of magnitude lower than that of aluminum. The coefficient of thermal expansion at 20°C is relatively small, but increases with further heating.
This material is also distinguished by a very high electrical resistivity, which, depending on the presence of foreign elements, can vary in the range of 42·11 -8 ... 80·11 -6 Ohm·cm.
Titanium is a paramagnetic metal with a low electrical conductivity. And although in paramagnetic metals, the magnetic susceptibility, as a rule, decreases as it is heated, titanium in this respect can be classified as an exception, since its magnetic susceptibility, on the contrary, increases with increasing temperature.
Due to the sum of the above properties, titanium is absolutely indispensable as a feedstock for various areas practical medicine and medical instrumentation. And yet the most valuable quality of titanium for use for this purpose is its highest resistance to corrosive effects, and, as a result, hypoallergenicity.
Titanium owes its corrosion resistance to the fact that at temperatures up to 530-560 ° C, the metal surface is covered with the strongest natural protective film of TiO 2 oxide, which is completely neutral with respect to aggressive chemical and biological media. In terms of corrosion resistance, titanium is comparable to, and even superior to, platinum and platinum metals. In particular, it is extremely resistant to acid-base environments, not dissolving even in such an aggressive "cocktail" as aqua regia. Suffice it to say that the intensity of the corrosion destruction of titanium in sea water, which has a chemical composition in many respects similar to human lymph, does not exceed 0.00003 mm/year, or 0.03 mm for a millennium!
Due to the biological inertness of titanium structures to the human body, during implantation they are not rejected and do not provoke allergic reactions, quickly being covered with musculoskeletal tissues, the structure of which remains constant throughout the subsequent life.
A significant advantage of titanium is its affordability, which makes it possible to use it on a mass scale.
Titanium grades and titanium alloys
The grades of titanium most in demand by medicine are technically pure VT1-0, VT1-00, VT1-00sv. They contain almost no impurities, the amount of which is so insignificant that it fluctuates within the limits of zero error. So, the VT1-0 grade contains about 99.35-99.75% pure metal, and the VT1-00 and VT1-00sv grades, respectively, contain 99.62-99.92% and 99.41-99.93 %.
To date, medicine uses a wide range of titanium alloys, different in their chemical composition and mechanotechnological parameters. Ta, Al, V, Mo, Mg, Cr, Si, Sn are most often used as alloying additives in them. The most effective stabilizers include Zr, Au and platinum group metals. With the introduction of up to 12% Zr into titanium, its corrosion resistance increases by orders of magnitude. Reach the same the greatest effect succeeds by adding a small amount of Pt and platinoids Pd, Rh, Ru to titanium. The introduction of only 0.25% of these elements into Ti makes it possible to reduce the activity of its interaction with boiling concentrated H 2 SO 4 and HCl by tens of orders of magnitude.
The Ti-6Al-4V alloy has become widely used in implantology, orthopedics and surgery, significantly surpassing its “competitors” based on cobalt and stainless steels in terms of operational parameters. In particular, the elastic modulus of titanium alloys is two times lower. For medical applications (implants for osteosynthesis, joint endoprostheses, etc.) this is a great advantage, as it provides a higher mechanical compatibility of the implant with dense bone structures of the body, in which the modulus of elasticity is 5–20 GPa. Even more low scores in this respect (up to 40 GPa and below), titanium-niobium alloys are characterized, the development and implementation of which are especially relevant. However, progress does not stand still, and today the traditional Ti-6Al-4V is being replaced by new medical alloys Ti-6Al-7Nb, Ti-13Nb-13Zr and Ti-12Mo-6Zr, which do not contain aluminum and vanadium - elements that, although insignificant, but still toxic effect to living tissues.
Recently, biomechanically compatible implants, the material for the manufacture of which is titanium nickelide TiNi, have become increasingly in demand for medical needs. The reason for the growing popularity of this alloy is its inherent so-called. shape memory effect (SME). Its essence lies in the fact that the control sample, being deformed at low temperatures, is able to constantly retain the newly acquired shape, and upon subsequent heating, restore the original configuration, while demonstrating superelasticity. Nickel-titanium structures are indispensable, in particular, in the treatment of spinal injuries and dystrophy of the musculoskeletal system.
Tantalum for medicine
Definition and useful characteristics
Tantalum (Ta, lat. Tantalum) is a heavy refractory metal of a silvery-bluish "lead" hue, which is due to the film of Ta 2 O 5 pentoxide covering it. It is one of the chemical elements of the Periodic Table, placed in a secondary subgroup of the fifth group of the sixth period, atomic number 73 (Fig. 2).
Figure 2. Tantalum crystals.
Tantalum has an atomic mass of 180.94 with a high specific density of 16.65 g/cm 3 at 20 °C (for comparison: the specific density of Fe is 7.87 g/cm 3 , Pv is 11.34 g/cm 3 ). The melting point is 3017 °C (only W and Re are more refractory). 1669°C, boiling point - 5458°C. Tantalum is characterized by the property of paramagnetism: its specific magnetic susceptibility at room temperature is 0.849·10 -6 .
This structural material, combining high hardness and ductility, in its pure form lends itself well to machining by any means (stamping, rolling, forging, broaching, twisting, cutting, etc.). At low temperatures, it is processed without strong work hardening, being subjected to deformation effects (compression point 98.8%) and without the need for preliminary firing. Tantalum does not lose plasticity even if it is frozen to -198 °C.
The value of the modulus of elasticity of tantalum is 190 Gn/m 2 or 190 102 kgf/mm 2 at 25 °C, due to which it is easily processed into wire. The production of the thinnest tantalum sheet (about 0.039 mm thick) and other structural semi-finished products is also carried out.
A kind of "twin" of Ta is Nb, characterized by many similar properties.
Tantalum is distinguished by exceptional resistance to aggressive environments. This is one of its most valuable properties for use in many industries, including medicine. It is resistant to aggressive inorganic acids such as HNO 3 , H 2 SO 4 , HCl, H 3 PO 4 , as well as organic acids of any concentration. In this parameter, it is surpassed only by noble metals, and even then not in all cases. So, Ta, unlike Au, Pt and many other precious metals, "ignores" even aqua regia HNO 3 + 3HCl. A somewhat lower stability of tantalum is observed with respect to alkalis.
The high corrosion resistance of Ta also manifests itself in relation to atmospheric oxygen. The oxidation process begins only at 285 °C: a surface protective film of tantalum pentoxide Ta 2 O 5 is formed on the metal. It is the presence of a film of this, the only stable of all Ta oxides, that makes the metal immune to aggressive reagents. Hence, such a characteristic of tantalum, which is especially valuable for medicine, is its high biocompatibility with the human body, which perceives tantalum structures implanted into it as its own tissue, without rejection. The medical use of Ta in such areas as reconstructive surgery, orthopedics, and implantology is based on this most valuable quality.
Tantalum is one of the rare metals: its reserves in the earth's crust are approximately 0.0002%. This causes the high cost of this structural material. That is why the use of tantalum in the form of thin films of protective anti-corrosion coatings deposited on the base metal, which, by the way, is three to four times greater than pure annealed tantalum, is so widespread.
Even more often, tantalum is used in the form of alloys as an alloying addition to less expensive metals to give the resulting compounds a complex of the necessary physical, mechanical and chemical properties. Steel, titanium and other metal alloys with the addition of tantalum are in great demand in chemical and medical instrumentation. Of these, in particular, the manufacture of coils, distillers, aerators, X-ray equipment, control devices, etc. is practiced. In medicine, tantalum and its compounds are also used to manufacture equipment for operating rooms.
It is noteworthy that in a number of areas, tantalum, being less expensive, but having many adequate performance characteristics, is able to successfully replace the precious metals of the platinum-iridium group.
Tantalum grades and alloys
The main grades of unalloyed titanium with impurity content within the statistical error are:
- HDTV: Ta - 99.9%, (Nb) - 0.2%. Other impurities such as (Ti), (Al), (Co), (Ni) are contained in thousandths and ten thousandths of a percent.
- HDTV 1: The chemical composition of the indicated grade is 99.9% Ta. Niobium (Nb), which is always present in industrial tantalum, corresponds to only 0.03%.
- PM: Ta - 99.8%. Impurities (not more than%): Nb - 0.1%, Fe - 0.005%, Ti, H - 0.001% each, Si - 0.003%, W + Mo, O - 0.015% each, Co - 0.0001%, Ca - 0.002%, Na, Mg, Mn - 0.0003% each, Ni, Zr, Sn - 0.0005% each, Al - 0.0008%, Cu, Cr - 0.0006% each, C, N - each 0.01%.
- T: Ta - 99.37%, Nb - 0.5%, W - 0.05%, Mo - 0.03%, (Fe) - 0.03%; (Ti) - 0.01%, (Si) - 0.005%.
The high hardness of Ta makes it possible to manufacture structural hard alloys on its basis, for example, Ta with W (TV). Replacing the TiC alloy with a tantalum analogue of TaC significantly optimizes the mechanical characteristics of the structural material and expands the possibilities of its application.
Relevance of Ta application for medical purposes
Approximately 5% of the tantalum produced in the world is spent on medical needs. Despite this, the importance of its use in this industry cannot be overestimated.
As already noted, tantalum is one of the best metallic bioinert materials due to the thinnest, but very strong and chemically resistant Ta 2 O 5 pentoxide film self-forming on its surface. Due to the high adhesion, which facilitates and accelerates the process of fusion of the implant with living tissue, there is a low percentage of rejection of tantalum implants and the absence of inflammatory reactions.
From such semi-finished tantalum products as sheets, rods, wires, and other forms of production, constructions are made that are in demand in plastic, cardio-, neuro-, and osteosurgery for suturing, fusion of bone fragments, stenting, and clipping of vessels (Fig. 3).
Figure 3. Tantalum attachment structure in the shoulder joint.
The use of thin tantalum plate and mesh structures is practiced in maxillofacial surgery and for the treatment of traumatic brain injuries. Fibers of tantalum yarn replace muscle and tendon tissue. Using tantalum Surgeons use tantalum fiber for abdominal operations, in particular, to strengthen the walls of the abdominal cavity. Tantalum meshes are indispensable in the field of ophthalmic prosthetics. The thinnest tantalum threads are even used for the regeneration of nerve trunks.
And, of course, Ta and its compounds, along with Ti, are widely used in orthopedics and implantology for the manufacture of joint endoprostheses and dental prosthetics.
Since the beginning of the new millennium, the innovative field of medicine has become increasingly popular, based on the principle of using static electric fields to activate human body desired bioprocesses. The presence of high electret properties of the Ta 2 O 5 tantalum pentoxide coating has been scientifically proven. Titanium oxide electret films of the snake have become widespread in vascular surgery, endoprosthesis, and the creation of medical instruments and devices.
Practical application of titanium and tantalum in specific branches of medicine
Traumatology: structures for fusion of fractures
Currently, for the speedy fusion of fractures, such an innovative technology as metal osteosynthesis is increasingly being used. In order to ensure a stable position of bone fragments, various fixing structures are used, both external and internal, implanted in the body. However, previously used steel products show low efficiency due to their susceptibility to corrosion under the influence of the aggressive environment of the body and the phenomenon of galvanization. As a result, both the rapid destruction of the fixators themselves and the rejection reaction occur, causing inflammatory processes against the background of severe pain due to active interaction Fe ions with the physiological environment of the musculoskeletal tissues in the electric field of the body.
The manufacture of titanium and tantalum fixatives-implants, which have the property of biocompatibility with living tissues, makes it possible to avoid undesirable consequences (Fig. 4).
Figure 4. Titanium and tantalum constructions for osteosynthesis.
Similar designs of simple and complex configurations can be used for long-term or even permanent introduction into the human body. This is especially important for older patients, as it eliminates the need for surgery to remove the retainer.
Endoprosthetics
Artificial mechanisms that are surgically implanted into bone tissue are called endoprostheses. Most widespread received arthroplasty of joints - hip, shoulder, elbow, knee, ankle, etc. The process of arthroplasty is always complex operation when a part of a joint that is not subject to natural restoration is removed with its subsequent replacement with an endoprosthesis implant.
A number of serious requirements are imposed on the metal components of endoprostheses. They must simultaneously have the properties of rigidity, strength, elasticity, the ability to create the necessary surface structure, resistance to corrosive effects from the body, eliminating the risk of rejection, and other useful qualities.
For the manufacture of endoprostheses, various bioinert metals can be used. The leading place among them is occupied by titanium, tantalum and their alloys. These durable, strong and easy to process materials provide effective osseointegration (perceived bone tissue as natural tissues of the body and do not cause negative reactions on its part) and rapid bone fusion, guaranteeing the stability of the prosthesis for long periods of decades. On fig. 5 shows the use of titanium in hip arthroplasty.
Figure 5. Titanium hip replacement.
In arthroplasty, as an alternative to the use of all-metal structures, the method of plasma spraying of protective biocompatible coatings based on Ti and Ta oxides onto the surface of non-metallic components of the prosthesis is widely used.
Pure titanium and its alloys. In the field of endoprosthetics, both pure Ti (eg CP-Ti with a Ti content of 98.2-99.7%) and its alloys are widely used. The most common of them Ti-6AI-4V with high strength, is characterized by corrosion resistance and biological inertness. The Ti-6A1-4V alloy is distinguished by particularly high mechanical strength, having torsion-axial characteristics extremely close to those of bone.
To date, a number of modern titanium alloys have been developed. Thus, the chemical composition of the Ti-5AI-2.5Fe and Ti-6AI-17 Niobium alloys does not contain toxic V, in addition, they are distinguished by a low value of the elastic modulus. And the Ti-Ta30 alloy is characterized by the presence of a thermal expansion modulus comparable to that of metal-ceramic, which determines its stability during long-term interaction with the metal-ceramic components of the implant.
Tantalum-zirconium alloys. Ta+Zr alloys combine such important properties for arthroplasty as biocompatibility with body tissues based on corrosion and galvanic resistance, surface rigidity, and trabecular (porous) structure of the metal surface. It is due to the property of trabecularity that a significant acceleration of the process of osseointegration is possible - the growth of living bone tissue on the metal surface of the implant.
Elastic endoprostheses made of titanium wire mesh. Due to the high plasticity and lightness in modern reconstructive surgery and other medical industries, innovative elastic endoprostheses in the form of the thinnest titanium wire mesh are actively used. Resilient, strong, elastic, durable and bioinert, the mesh is an ideal material for soft tissue endoprostheses (Fig. 6).
Figure 6. Titanium alloy mesh endoprosthesis for soft tissue plasty.
"Web" has already been successfully tested in such areas as gynecology, maxillofacial surgery and traumatology. According to experts, mesh titanium endoprostheses are unmatched in terms of stability with an almost zero risk of side effects.
Titanium Nickel Medical Shape Memory Alloys
Today, in various fields of medicine, titanium nickelide alloys, which have the so-called. with shape memory effect (SME). This material is used for endoprosthesis replacement of the ligamentous-cartilaginous tissue of the human musculoskeletal system.
Titanium nickelide (international term nitinol) is an intermetallic TiNi, which is obtained by alloying Ti and Ni in equal proportions. The most important characteristic of nickelide-titanium alloys is the property of superelasticity, on which the EZF is based.
The essence of the effect is that the sample is easily deformed upon cooling in a certain temperature range, and the deformation is self-removing when the temperature rises to the initial value with the appearance of superelastic properties. In other words, if a nitinol alloy plate is bent at a low temperature, then in the same temperature regime it will retain its new shape for an arbitrarily long time. However, it is only necessary to raise the temperature to the initial one, the plate will straighten again like a spring and will take on its original shape.
Samples of nitinol alloy medical products are shown in the figures below. 7, 8, 9, 10.
Figure 7. A set of titanium nickelide implants for traumatology (in the form of staples, staples, fixators, etc.).
Figure 8. A set of titanium nickelide implants for surgery (in the form of clamps, dilators, surgical instruments).
Figure 9. Samples of porous materials and titanium nickelide implants for vertebrology (in the form of endoprostheses, lamellar and cylindrical products).
Figure 10. Titanium nickelide materials and endoprostheses for maxillofacial surgery and dentistry.
In addition, nickel-titanium alloys, like most titanium-based products, are bioinert due to high corrosion and galvanic resistance. Thus, it is an ideal material in relation to the human body for the manufacture of biomechanically compatible implants (BMCI).
The use of Ti and Ta for the manufacture of vascular stents
Stents (from the English stent) - in medicine they are called special, having the form of elastic mesh cylindrical frames, metal structures placed inside large vessels (veins and arteries), as well as other hollow organs (esophagus, intestines, bile ducts, etc.) on pathologically narrowed areas in order to expand them to the required parameters and restore patency.
The use of the stenting method is most in demand in such a field as vascular surgery, and, in particular, coronary angioplasty (Fig. 11).
Figure 11. Samples of titanium and tantalum vascular stents.
To date, more than half a thousand vascular stents have been scientifically developed and put into practice. various types and designs. They differ from each other in the composition of the original alloy, length, hole configuration, type of surface coating, and other operating parameters.
The requirements for vascular stents are designed to ensure their impeccable functionality, and therefore are diverse and very high.
These products must be:
- biocompatible with body tissues;
- flexible;
- elastic;
- durable;
- radiopaque, etc.
The main materials used today in the manufacture of metal stents are compositions of noble metals, as well as Ta, Ti and its alloys (VT6S, VT8, VT 14, VT23, nitinol), which are completely biointegrable with body tissues and combine a complex of all other necessary physical and mechanical properties. properties.
Stitching of bones, vessels and nerve fibers
Peripheral nerve trunks damaged as a result of various mechanical injuries or complications of certain diseases require serious surgical intervention. The situation is exacerbated by the fact that similar pathologies are observed against the background of injury to related organs, such as bones, blood vessels, muscles, tendons, etc. In this case, it is developed comprehensive program treatment with the imposition of specific sutures. As a raw material for the manufacture of suture material - threads, staples, clamps, etc. – titanium, tantalum and their alloys are used as metals that have chemical biocompatibility and the whole complex of necessary physical and mechanical properties.
The figures below show examples of such operations.
Figure 12. Stitching the bone with titanium staples.
Figure 13. Stitching of a bundle of nerve fibers using the finest tantalum filaments.
Figure 14. Sewing of vessels using tantalum staples.
Currently, more and more advanced technologies of neuro-osteo- and vasoplasty are being developed, however, the titanium-tantalum materials used for this continue to hold the palm over all others.
Plastic surgery
Plastic surgery is the surgical removal of organ defects in order to recreate their ideal anatomical proportions. Often, such reconstructions are performed using various metal products implanted in tissues in the form of plates, meshes, springs, etc.
Particularly indicative in this regard is cranioplasty - an operation to correct the deformity of the skull. Depending on the indications in each specific clinical situation, cranioplasty can be performed by applying rigid titanium plates or elastic tantalum meshes to the operated area. In both cases, it can be used pure metals without alloying additives, and their bioinert alloys. Examples of cranioplasty using titanium plate and tantalum mesh are presented in the figures below.
Figure 15. Cranioplasty using a titanium plate.
Figure 16. Cranioplasty with tantalum mesh.
Titanium-tantalum structures can also be used for cosmetic restoration of the face, chest, buttocks and many other organs.
Neurosurgery (imposition of microclips)
Clipping (English clip clip) is a neurosurgical operation on the vessels of the brain, which aims to stop bleeding (in particular, when an aneurysm ruptures) or turn off injured people from blood circulation. small vessels. The essence of the clipping method lies in the fact that miniature metal clips - clips - are superimposed on the damaged areas.
The demand for the clipping method, primarily in the neurosurgical field, is explained by the impossibility of ligating small cerebral vessels traditional ways.
Due to the variety and specificity of emerging clinical situations, a wide range of vascular clips is used in neurosurgical practice, differing in specific purpose, method of fixation, dimensional and other functional parameters (Fig. 17).
Figure 17. Clips for turning off brain aneurysms.
In the photographs, the clips seem large, but in reality they are no larger than a child's fingernail and are installed under a microscope (Fig. 18).
Figure 18. Surgery to clip an aneurysm of a cerebral vessel.
For the manufacture of clips, as a rule, flat wire is used from pure titanium or tantalum, in some cases from silver. Such products are absolutely inert with respect to the medulla, without causing counteraction reactions.
Dental orthopedics
Titanium, tantalum and their alloys have found wide medical use in dentistry, namely in the field of dental prosthetics.
The oral cavity is a particularly aggressive environment that negatively affects metal materials. Even such precious metals traditionally used in dental prosthetics, such as gold and platinum, in oral cavity cannot completely resist corrosion and subsequent rejection, not to mention the high cost and large mass that causes discomfort to patients. On the other hand, lightweight orthopedic structures made of acrylic plastic also do not stand up to serious criticism due to their fragility. A real revolution in dentistry has been the manufacture of individual crowns, as well as bridges and removable dentures based on titanium and tantalum. These metals, due to such valuable qualities inherent in them as biological inertness and high strength at relative cheapness, successfully compete with gold and platinum, and even surpass them in a number of parameters.
In particular, stamped and solid titanium crowns are very popular (Fig. 19). And plasma-sprayed crowns made of titanium nitride TiN are practically indistinguishable from gold in appearance and functional properties (Fig. 19)
Figure 19. Solid titanium crown and titanium nitride coated crown.
As for the prostheses, they can be fixed (bridges) to restore several adjacent teeth or removable, used in case of loss of the entire dentition (complete jaw adentia). The most common prostheses are clasp (from German der Bogen "arc").
The clasp prosthesis is favorably distinguished by the presence of a metal frame on which the base part is attached (Fig. 20).
Figure 20. Clasp prosthesis of the lower jaw.
Today, the clasp part of the prosthesis and clasps are usually made of pure high-purity medical titanium of the HDTV brand.
A true revolution in dentistry has been the ever-increasing demand for implant dentures. Prosthetics on implants is the most reliable way of fixing orthopedic structures, which in this case serve for decades or even for life.
A dental (tooth) implant is a two-piece structure serving as a support for crowns, as well as bridges and removable dentures, the base part of which (the implant itself) is a conical threaded pin screwed directly into the jaw bone. An abutment is installed on the upper platform of the implant, which serves to fix the crown or prosthesis (Fig. 21).
Figure 21 Nobel Biocare dental implant made of grade 4(G4Ti) pure medical grade titanium.
Most often, for the manufacture of the screw part of the implant, pure medical titanium with a surface tantalum-niobium coating is used, which contributes to the activation of the process of osseointegration - the fusion of metal with living bone and gum tissues.
However, some manufacturers prefer to manufacture not two-piece, but one-piece implants, in which the screw part and the abutment do not have a separate, but a monolithic structure. At the same time, for example, the German company Zimmer produces one-piece implants from porous tantalum, which, in comparison with titanium, has greater flexibility and is embedded in bone tissue with an almost zero risk of complications (Fig. 22).
Figure 22 Zimmer one-piece porous tantalum dental implants.
Tantalum, unlike titanium, is a heavier metal, so the porous structure significantly lightens the product, without causing, moreover, the need for additional external deposition of an osseointegrating coating.
Examples of implant prosthetics of individual teeth (crowns) and by installing removable dentures on implants are shown in Fig. 23.
Figure 23. Examples of the use of titanium-tantalum implants in dental prosthetics.
Nowadays, in addition to the existing ones, more and more new methods of prosthetics on implants are being developed, showing high efficiency in various clinical situations.
Manufacturing of medical instruments
Today in the world clinical practice hundreds of varieties of various surgical and endoscopic instruments and medical equipment are used, manufactured using titanium and tantalum (GOST 19126-79 "Medical metal instruments. General specifications". They compare favorably with other analogues in terms of strength, ductility and corrosion resistance, which determines biological inertness.
Titanium medical instruments are almost twice as light as steel counterparts, while being more comfortable and durable.
Figure 24. Surgical instruments made on a titanium-tantalum basis.
The main medical industries in which titanium-tantalum instruments are most in demand are ophthalmological, dental, otolaryngological and surgical. The extensive range of tools includes hundreds of types of spatulas, clips, dilators, mirrors, clamps, scissors, forceps, scalpels, sterilizers, tubes, chisels, tweezers, all kinds of plates.
The biochemical and physical-mechanical characteristics of light titanium instruments are of particular value for military field surgery and various expeditions. Here they are absolutely indispensable, because in extreme conditions, literally every 5-10 grams of excess cargo is a significant burden, and corrosion resistance and maximum reliability are mandatory requirements.
Titanium, tantalum and their alloys in the form of monolithic products or thin protective coatings are actively used in medical instrumentation. They are used in the manufacture of distillers, pumps for pumping aggressive media, sterilizers, components of anesthesia and respiratory equipment, the most complex devices for duplicating the work of vital important organs such as "artificial heart", "artificial lung", " artificial kidney" and etc.
Titanium heads of ultrasonic devices have the longest service life, despite the fact that analogues from other materials, even with irregular exposure to ultrasonic vibrations, quickly become unusable.
In addition to the above, it can be noted that titanium, like tantalum, unlike many other metals, has the ability to desorb (“repel”) the radiation of radioactive isotopes, and therefore are actively used in the production of various protective devices and radiological equipment.
Conclusion
The development and production of medical devices is one of the most intensively developing areas of scientific and technological progress. With the beginning of the third millennium, medical science and technology became one of the main driving forces modern world civilization.
The importance of metals in human life is steadily increasing. Revolutionary changes are taking place against the background of the intensive development of scientific materials science and practical metallurgy. And now, in recent decades, such industrial metals as titanium and tantalum have been raised “on the shield of history”, which, with all good reason, can be called structural materials of the new millennium.
The importance of titanium in modern medicine cannot be overestimated. Despite a relatively short history of use in practical purposes, it has become one of the leading materials in many medical industries. Titanium and its alloys have the sum of all the necessary characteristics for this: corrosion resistance (and, as a result, bioinertness), as well as lightness, strength, hardness, rigidity, durability, galvanic neutrality, etc.
Not inferior to titanium in terms of practical significance and tantalum. With the general similarity of most of the useful properties, in some qualities they are inferior, and in some they are superior to each other. That is why it is difficult, and hardly reasonable, to objectively judge the priority of any one of these metals for medicine: they rather organically complement each other than conflict with each other. Suffice it to say that now they are actively developing and finding real application medical structures based on titanium-tantalum alloys, combining all the advantages of Ti and Ta. And it is far from accidental that in recent years more and more successful attempts have been made to create full-fledged implantable directly into the human body. artificial organs from titanium, tantalum and their compounds. The time is approaching when, say, the concepts of "titanium heart" or "tantalum nerves" will confidently move from the category of figures of speech to a purely practical plane.
Cobalt Chrome Alloys
Cobalt-chrome alloys grade KHS
cobalt 66-67%, which gives the alloy hardness, thus improving the mechanical properties of the alloy.
chromium 26-30%, introduced to give the alloy hardness and increase corrosion resistance, forming a passivating film on the surface of the alloy.
nickel 3-5%, which increases the plasticity, toughness, malleability of the alloy, thereby improving the technological properties of the alloy.
molybdenum 4-5.5%, having great value to increase the strength of the alloy by making it fine-grained.
manganese 0.5%, which increases strength, casting quality, lowers the melting point, helps to remove toxic granular compounds from the alloy.
carbon 0.2%, which reduces the melting point and improves the fluidity of the alloy.
silicon 0.5%, improving the quality of castings, increasing the fluidity of the alloy.
iron 0.5%, increasing fluidity, increasing the quality of casting.
nitrogen 0.1%, which reduces the melting point, improves the fluidity of the alloy. At the same time, an increase in nitrogen over 1% worsens the ductility of the alloy.
beryllium 0-1.2%
aluminum 0.2%
PROPERTIES: CCS has high physical and mechanical properties, relatively low density and excellent fluidity, which makes it possible to cast openwork dental products of high strength. The melting point is 1458C, the mechanical viscosity is 2 times higher than that of gold, the minimum tensile strength is 6300 kgf/cm 2 . The high modulus of elasticity and lower density (8 g/cm 3 ) make it possible to produce lighter and stronger prostheses. They are also more resistant to abrasion and retain the mirror shine of the surface, imparted by polishing, for a longer time. Due to its good casting and anti-corrosion properties, the alloy is used in orthopedic dentistry for the manufacture of cast crowns, bridges, various designs of cast clasp prostheses, metal-ceramic denture frameworks, removable dentures with cast bases, splinting devices, cast clasps.
RELEASE FORM: produced in the form of round blanks weighing 10 and 30 g, packed in 5 and 15 pieces.
All produced metal alloys for orthopedic dentistry are divided into 4 main groups:
Bygodents - alloys for cast removable dentures.
KX-Dents - alloys for ceramic-metal prostheses.
HX-Dents - nickel-chromium alloys for metal-ceramic prostheses.
Dentans are iron-nickel-chromium alloys for dentures.
1. Bygodents. They are a multicomponent alloy.
COMPOSITION: cobalt, chromium, molybdenum, nickel, carbon, silicon, manganese.
PROPERTIES: density - 8.35 g/cm 3 , Brinell hardness - 360-400 HB, alloy melting point - 1250-1400C.
APPLICATION: used for the manufacture of cast clasp prostheses, clasps, splinting devices.
Byugodent CCS vac (soft)- contains 63% cobalt, 28% chromium, 5% molybdenum.
Bygodent CCN vac (normal) - contains 65% cobalt, 28% chromium, 5% molybdenum, and also increased content carbon and does not contain nickel.
Bygodent CCH vac (hard)- the basis is cobalt - 63%, chromium - 30% and molybdenum - 5%. The alloy has maximum content carbon - 0.5%, additionally alloyed with niobium - 2% and does not contain nickel. It has exceptionally high elastic and strength parameters.
Byugodent CCC vac (copper)- the basis is cobalt - 63%, chromium - 30%, molybdenum - 5%. The chemical composition of the alloys includes copper and a high carbon content - 0.4%. As a result, the alloy has high elastic and strength properties. The presence of shallows in the alloy facilitates polishing, as well as other mechanical processing of prostheses from it.
Bygodent CCL vac (liquid)- in addition to cobalt - 65%, chromium - 28% and molybdenum - 5%, boron and silicon are introduced into the composition of the alloy. This alloy has excellent fluidity, balanced properties.
2. KH-Dents
APPLICATIONS: used for the manufacture of cast metal frameworks with porcelain facings. oxide film, formed on the surface of the alloys, allows you to apply ceramic or glass-ceramic coatings. There are several types of this alloy: CS, CN, CB, CC, CL, DS, DM.
KH-Dent CN vac (normal) contains 67% cobalt, 27% chromium and 4.5% molybdenum, but is free of carbon and nickel. This significantly improves its plastic characteristics and reduces hardness.
KX-Dent CB vac (Bondy) has the following composition: 66.5% cobalt, 27% chromium, 5% molybdenum. The alloy has good combination casting and mechanical properties.
3. NH-Dents
COMPOSITION: nickel - 60-65%; chromium - 23-26%; molybdenum - 6-11%; silicon - 1.5-2%; do not contain carbon.
NH-Dent alloys based on nickel-chromium
APPLICATION: for high-quality metal-ceramic crowns and small bridges, they have high hardness and strength. Frameworks of prostheses are easily ground and polished.
PROPERTIES: alloys have good casting properties, contain refining additives, which makes it possible not only to obtain a quality product when casting in high-frequency induction melting machines, but also to reuse up to 30% of sprues in new melts. There are several types of this alloy: NL, NS, NH.
HX-Dent NS vac (soft) - in its composition contains nickel - 62%, chromium - 25% and molybdenum - 10%. It has high dimensional stability and minimal shrinkage, which allows casting long bridges in one step.
HX-Dent NL vac (liquid) - contains 61% nickel, 25% chromium and 9.5% molybdenum. This alloy has good casting properties, allowing to obtain castings with thin, openwork walls.
4.Dents
PROPERTIES: Dentan-type alloys are designed to replace cast stainless steels. They have a significantly higher ductility and corrosion resistance due to the fact that they contain almost 3 times nickel and 5% more chromium. Alloys have good casting properties - low shrinkage and good fluidity. Very malleable in machining.
APPLICATION: used for the manufacture of cast single crowns, cast crowns with plastic lining. There are several types of this alloy: DL, D, DS, DM.
Dentan D contains 52% iron, 21% nickel, 23% chromium. It has high ductility and corrosion resistance, low shrinkage and good fluidity.
Dentan DM contains 44% iron, 27% nickel, 23% chromium and 2% molybdenum. Molybdenum was additionally added to the composition of the alloy, which increased its strength in comparison with previous alloys, when comparing the same level of machinability, fluidity and other technological properties.
For some nickel-chromium alloys, the presence of an oxide film can be negative, since at high temperature firing nickel and chromium oxides dissolve in porcelain, coloring it. An increase in the amount of chromium oxide in porcelain leads to a decrease in its coefficient of thermal expansion, which may cause the ceramics to chip off the metal.
Titanium alloys
PROPERTIES: titanium alloys have high technological and physical-mechanical properties, as well as biological inertness. The melting point of titanium alloy is 1640C. Products made of titanium have absolute inertness to the tissues of the oral cavity, the complete absence of toxic, thermally insulating and allergic effects, small thickness and weight with sufficient rigidity of the base due to the high specific strength of titanium, high accuracy of reproduction of the smallest details of the relief of the prosthetic bed.
VT-100 sheet- used for the manufacture of stamped crowns (thickness 0.14-0.28mm), stamped bases (0.35-0.4mm) of removable dentures.
VT-5L - cast - used for the manufacture of cast crowns, bridges, frames of clasp splinting prostheses, cast metal bases.
