3. The organization of the maintenance of a teaching material.

Dentitechnical materials technology.

Materials technology – a science about a structure and properties of materials. The dentitechnical materials technology is the applied division of science referred on creation new and perfection of numerous known materials, studying of their technological and clinical properties concerning stomatologic practice.

The dentitechnical materials technology unites to chemistry, physics and biology under control of orthopedic stomatology.

Mechanical properties.

As mechanical properties of materials understand their ability to resistance rendering to different factors of external influence. Mechanical properties of a material study different methods by means of special cars and devices. Test methods can be static and dynamical. At static tests the material is exposed slow, but to constant influence of force, at dynamical — on the contrary, power influences have fast short-term character of type of blow.

Results of tests express in the standard units of measure. It allows to spend a comparative estimation of materials, to establish their standards, to develop indications to application and technological manufacturing from them different products.

To mechanical properties carry hardness, durability, elasticity, plasticity and weariness.

Hardness - ability of a material to resist at introduction in its surface of other body to influence of certain force. For definition of hardness of materials the greatest diffusion was received by methods of Brinell, Shor, Moos and etc.

Durability - ability of a material to resist to the force, aspiring it to break off. The minimum force at which appendix there comes disturbance of integrity of a material, and is an indicator of durability of this material.

The relation of an indicator of durability to the area of cross-section section of a tested detail is called as border of durability of this material.

The durability indicator is important at a choice of the material used for those or other purposes.

Elasticity - ability of a material to get into condition after force cancellation. Elastic properties of materials depend as by nature substances, and on its structure, therefore in each material they are shown variously. For example, rubber has high elasticity. Under the influence of certain force it is stretched, but after cancellation accepts the initial form. Good elasticity the steel wire owns. Elastic properties in an aluminium and copper wire are weakly expressed.

Plasticity - property of a material without being blasted to take the form, which to it give by means of any force, and to keep this form after force cancellation.

In stomatological practice are widely applied such high-aesthetic materials, as a gypsum, thermoplastic impression compounds, etc.

Weariness - property of a material to be blasted under the influence of often repeated sign-variable forces. If on a material any force that in one in the opposite direction (for example, at a flexion and a wire extension), it is blasted operates. At first in a material, which strikes to such loads, there is a shift of grains, then there are fine cracks. Fine cracks are gradually enlarged, formed the big cracks, and then there comes final fracture — ruptures or a break.

Technological properties

To the technological carry such properties which allow to define, the material, and also possibilities of its most effective use can give in to what technical processing. It first of all smelty, fluidity, viscosity, shrink, deleting, etc.

Smelty - property of a material to accept the necessary form under the influence of pressure forces and to keep this form after force cancellation. This property is inherent almost in all metals.

Fluidity - property of the material which is in plastification or the fused condition to fill funnels or pressing forms. Of these materials a casting or pressing method make details of the most difficult design.

Viscosity - property of a material to change the form under the influence of external force, without being blasted thus. For example, at stretching metal sleeves through apparatus for the purpose of manufacturing from them crowns, sleeves are extended, thinning, change the sizes and the form, but are not blasted. Stretching sleeves from the materials which do not have viscosity, comes to an end with their destruction - rupture.

Shrink - reduction of the sizes of a body at transition from the fused condition in firm or with more heated in less heated condition.

Distinguish volume and linear shrink. Volume shrink - reduction of volume of a body. Linear shrink - reduction of the sizes of a body in a rectilinear direction (on length or width).

Deleting. Depending on a way of the appendix of a load and a material test method as a separate indicator of durability, allocate deleting. Deleting has great value in practice of orthopedic stomatology, especially at a grinding, polishing and other kinds of processing of prostheses. Material deleting should be considered and when in an oral cavity (position of antagonistic surfaces) there are the products made of different alloys, for example, of a steel and an alloy, containing gold. Prostheses and the designs made of materials, having higher deleting much faster wear out.

Physical properties.

At a choice of materials for the stomatological purposes the great value is got by such physical properties of substance, as density, fusion temperature, thermal expansion, a thermal conduction, colour, etc.

Density - substance mass in unit of volume (g/sm3).

Knowing density of materials, it is possible to calculate quantity of the substance necessary for replacement of the given material.

Fusion. Distinguish three modular conditions of substance - firm, liquid and gaseous. Transition of a material from one modular condition in another occurs at warming. Transition of a material from a firm condition in liquid is called as fusion. The temperature at which the firm body passes in a liquid state, is called as temperature of fusion of this body.

Thermal conduction. At warming of a small site of a material warmth of this site extends on the next. Rate of diffusion of warmth at different materials is unequal. Metals quickly transfer warmth, therefore they are good conductors of warmth, glass and plastic badly transfer warmth. Transfer of warmth from more heated material sites to less heated is called as a thermal conduction.

Colour - property of a material to reflect the surface light radiations that allows to distinguish one material from another and to define, in what condition there is a material.

Chemical properties.

To chemical properties of materials carry their interaction with medium in which they constantly are, or with special medium in which test of materials is carried out.

For stomatology the greatest interest is represented by electrolytic dissociation, corrosion and some other changes of materials in their interaction with medium of an oral cavity, acids, air, etc.

Biological properties.

As biological properties of materials understand their influence on surrounding living tissues and an organism as a whole.

All materials of the basic (constructional) group should not render an adverse effect on tissues and medium which they face, to change structure of a saliva and an oral cavity microflora, to cause the inflammatory phenomena on a mucosa, etc.

The basic materials for manufacturing of partial demountable prostheses

The doctor should choose correctly the basic (constructional materials), that is materials of which the prosthesis consists. The basic materials – group of the materials which are a part of a ready design.

They should meet such demands: not to influence harmfully tissues and oral cavity organs, to be strong, not to be blasted under the influence of the stomatic liquid, different alimentary substances, air, to maintain chewing pressure and processing at manufacturing at which the prosthesis gives in to extension, curving pleasant taste and a smell; availability and material cost also matters.

The basic materials concern:

• Basic plastic;

• the False teeth;

• Metals and alloys.

PLASTIC

Plastics - the big group of the high polymer organic materials which basis is made by the natural or artificial high-molecular bonds capable under the influence of warming and pressure to be formed and then steadily to keep the form given to it. The main components of this special kind of plastic compositions the such:

1) a monomer - a plastic basis;

2) a binder (phenol phormaldegid or other pitches);

3) excipients (a wood flour, asbestos, fiber glass);

4) plasticizers (dibutyl phthalate, threecresyl phosphates), raising plasticity and elasticity;

5) stains;

6) polymerization or polycondensation accelerators.

BASIC (BASIC) CONSTRUCTIONAL MATERIALS

The materials applied to manufacturing of bases of demountable plate prostheses, are called as basic materials. The basis is the basis of a demountable prosthesis on which a false teeth, clasps and other components of a prosthesis becomes stronger. According to with appointment, application and processing conditions basic materials should have such characteristics:

1) sufficient durability and necessary elasticity which provide integrity of a prosthesis without its deformation under the influence of chewing efforts;

2) high resistance to a flexure;

3) high resistance to blow;

4) a small specific gravity and low thermal conductivity;

5) sufficient hardness, low erasability;

6) indifference to action of a saliva and various alimentary substances;

7) not to change colour under the influence of light, air and other factors of environment;

8) not to harm to tissues of a cavity of companies and an organism as a whole;

9) absence of adsorption of alimentary substances and an oral cavity microflora.

For bases of prostheses use plastic of such types: acrylic, vinyl-acryl, on the basis of the modified polystyrene, copolymers or admixtures of the above-named plastic.

The basic material "Etakril" (“АКР-15”) - static triad copolymer ММА, Aether aethylicus metacryl acids, a methyl Aether of acrylic acid is issued by the domestic industry. Powder structure: a methyl metacrylate–89 %, aethylmetacrylate - 8 %, methylacrylate - 2 %, dibutilftalat-softener - 1 %. Liquid structure: a methyl metacrylate–89 %, aethylmethacrylate - 8 %, methylacrylate - 2 %, a hydroquinone (watch-0,005), a plasticizer-dibutilftalat - 1 %.

In a domestic basic material "Akrel" the liquid component contains in quality of the sewing agent methylolmethacrylamid, admixed with ММА. In the course of material hardening there is copolymerization ММА with methylolmethacrylamid to simultaneous ligation next sopolimer chains.

“Ftoraks” – ftor-containing rubber, an acrylic copolymer. Is issued industrially and consists of a powder and a liquid. For reception of forming mass the powder and a liquid admix in the ratio 2:1 then should take place maturing (swelling) within 10-12 minutes Plastic "Ftoraks" has good physical and chemical properties: the raised durability, chemical firmness. It translucent and on colour corresponds to soft tissues of an oral cavity.

The basic disadvantages of these basic materials are low indicators of durability and high enough contents of the residual monomers which have not entered reaction.

“Bakril” - high-strength acrylic plastic for bases of the demountable prostheses, having in comparison with others the raised fastness to cracking fissuring, erasibility, the big impact strength and high durability on a flexure. The powder "Bakril" is the polymethyl metacrylate modified elastomer (low-molecular copolymers buthylacryl rubber, alcylmethacrylate and ММА). Plastic has good adaptability to manufacture.

“Acronil” - the basic plastic used for manufacturing of maxillofacial and orthodontic apparatus, demountable splints etc. the Powder "Akronil" - inoculated copolymer ММА to polivenylmethylal. A liquid - ММА – binding agent – dimethacrylate of threeaethylenglicol. The inhibitor and the substance which is slowing down ageing of plastic are entered Into a liquid. “Acronil” possesses reliability close to reliability of "Ftoraks", smaller water absorption, good technological indicators.

Plastic the colourless basic. Plastic on the basis of the polymethyl methacrylate cleared of the stabilizer containing thynuvyn which interferes with ageing of plastic under the influence of an excited environment. Consists of a powder and a liquid. A powder - suspension polymethyl methacrylate containing thynuvyn. Thynuvyn promotes also to rising of reliability of plastic. The liquid represents stabilized ММА.

Colourless basic plastic is applied to manufacturing of bases for tooth prostheses when is contraindicative painted basis, and also for other purposes of orthopedic stomatology when the transparent basic material is necessary. Unlike similar materials has the raised durability and a transparency. In a preparation time of the test the powder and a liquid carefully admix in the ratio 2: 1 or 0,9 parts of a liquid on mass. Time of "maturing" of mass depends on ambient temperature. Mass are considered ready if it loses stickiness.

At breakage full and partial demountable plate prostheses to repair of their bases apply so-called sopolimer compositions which on structure are similar to basic materials. The main difference of these compositions consists that they are materials of cold hardening. Lower-temperature copolymerization of these structures is reached by use of usual initiators of cold hardening - redox systems: peroxide of benzoyl + the replaced aniline. "Repair" compositions are applied widely because repair process is simple, and change of the sizes and the form of the prostheses repaired by a composition of cold hardening, insignificant.

"Redont" and "Protakril" are issued by the domestic industry. “Protakril” contains powdery fraction which represents a suspension polymethyl methacrylate containing the initiator - a benzoyl peroxide and the activator - disulfanilinum, and also liquid ММА with the polymerization activator - dimetil-paratoluidinom. “Protakril” intended for repairing and correctings of demountable tooth prostheses and manufacturing of orthodontic apparatus.

“Redont” has two components: a powder containing copolymer ММА, aethylmethacrylate, a benzoyl peroxide and a stain, and also a liquid – an Aether methacryl acids with the activator dimetil-paratoluidinom and an inhibitor a hydroquinone. “Redont” use for repairing of demountable plate prostheses at their insufficient adjunction to a prosthetic bed or insufficient bracing and stabilization of prostheses.

Plastic are intended for manufacturing of bases of prostheses “Palavit 55” (“Palavit 55”) firms "Kulzer" (Germany), "Kronzin" (“Cronsin”) firms "Merz" (Germany).

FALSE TEETH

False teeth is issued industrially.

Porcelain (face-to-face – crampone, lateral – diatorical (porous, tubular).

The plastic.

Metal (gold, platinum, from stainless steel).

The combined.

Self-sharpened (Rubies, 1959).

Porcelain face-to-face teeth has crampons two kinds – button-like and cylindrical; crampons are made from platinum, alloys of gold, stainless steel. Structure of porcelain for manufacturing of teeth the such: feldspar (60-75 %), Kaolinum (a white chalk – alumo silicate 3-10 %), quartz (15-35 %), stains. Quartz – a version cremnezem - silicon dioxides. Feldspar – the most widespread mineral in the nature which makes 50 % of earth crust. Consists of alkaline materials, alumina and cremnezem. Feldspar is entered into a porcelain admixture as the most fluid material, at roasting fills product pores as if with a cementing material.

False teeth from plastic is issued by the complete set of two kinds: face-to-face, chewing. They have many positive properties: simple process of manufacturing, remind an enamel of tooth and have different shades and colours, bond with basis, easily give in to processing, can be used at any occlusion (deep, pathological deleting of natural teeth). At the Kharkov factory of stomatologic materials it are developed and introduced in 1965г. An album of sets with the special scheme facilitating selection of teeth.

Sets of face-to-face teeth have 17 sizes. The size of set is defined by two sizes: in height of a crown of tooth from 11 to 13,9мм and width of full face-to-face set it agree arches of an average production line of an alveolar process from 37,2мм to 51,8мм. The basic share of set of the top face-to-face teeth consists of 3 styles: rectangular, wedge-shaped and oval. Sets of the bottom face-to-face teeth are issued two styles: rectangular and wedge-shaped. Sets of chewing teeth are issued 5 styles in process of augmentation of the sizes. On colour teeth is issued 7 colours.

False teeth from metal is let out by the St.-Petersburg factory of teeth-treatment materials. Sets are completed: face-to-face on 2-4 teeth, chewing on 2-3 teeth (accordingly on each jaw and its party).

The artificial combined teeth consists only of standardly made metal basis. The vestibular surface of cast teeth has an excavation – a bed for facing – a facing. The palatal surface of cast teeth (chewing or cutting) has the expressed anatomic form. On a forward concave surface (in an excavation) there are fastenings, stirrups for mechanical fastening of plastic. Facing is produced from plastic "Sinma" after soldering of an intermediate part of a prosthesis with crowns.