ANNOTATION TO THE LESSON № 2 The result of the dental help is defined by three components: art of the doctor, the used technologies and quality of the dental materials. Dental materials science – the science studying physical and chemical, technological and biological properties of the materials applied at the treatment of dental patients, and also changes of these properties at technological stages of and devices production. Prosthetics – replacement of lost or irreversible damaged parts of the body with artificial substitutes – . (or dental prosthetics) is the dental specialty pertaining to the diagnosis, treatment planning, rehabilitation and maintenance of the oral function, comfort, appearance and health of patients with clinical conditions associated with missing or deficient teeth and/or oral and maxillofacial tissues using biocompatible substitutes. The dentures applied in dentistry can be classified by its functional purpose and a way of fixing. By its functional purpose: a) maxillofacial dentures b) the teeth dentures: ü the dentures eliminating the tooth defects: artificial crown, inlay and pin structure ü the dentures eliminating the teeth alingments defects: bridges, prostheses with metal framework and clasps and plastic prostheses (partial and complete).

A dental prosthesis (denture) is an intraoral (inside the mouth) prosthesis used to restore (reconstruct) intraoral defects such as missing teeth, missing parts of teeth, and missing soft or hard structures of the jaw and palate.

Fixed prosthesis – the denture that is fixed on teeth with the help of special fixing materials.

Removable prosthesis – the denture designed in such way that its removal and installation on a jaw is carried out by the patient (user).

The fixed prostheses eliminating defects of the teeth solid tissues.

Inlay. Inlays are dentures which restore an anatomic shape of the tooth filling with themselves defect in its crown. Inlays are referred to microdentures and are applied for the restoration of the form and function of the tooth crown broken as a result of carious and not carious defeats of solid tissues of the teeth. Inlays are used also as a basis of fixed and removable dentures and frames.

Artificial crown – the orthopedic structure which is completely covering the crown of the tooth. They are used to restore the teeth defects that cannot be treated less invasively (like filling, inlay), to change a form, position and color of the teeth. Artificial crowns are used also as basic elements of the bridges and the frames.

Pin structures of the tooth – orthopedic structures, one of which elements is the pin. Pins are fixed by means of cements in root channels and bear on themselves an artificial crown. The fixed prostheses eliminating defects of tooth alignments.

Bridge-like prosthesis – a version of fixed dental prostheses. They are applied for replacement included (limited by teeth) defects of tooth alignments. The structure of the -like denture consists of basic elements providing fastening of the denture on teeth that limit the defect and the intermediate part eliminating the tooth alignment defect. The removable prostheses eliminating defects of tooth alignments.

Plastic prostheses at partial absence of the teeth is a kind of removable dentures. A basic element of the denture is the plastic basis (plate) on which false teeth and the holding elements (klammers) are fastened. The number of false teeth depends on the number of remained teeth on a jaw.

Plastic prostheses at total absence of teeth is a kind of removable dentures. A basic element of the denture is the plastic basis (plate) on which the false teeth eliminating a total defect of the tooth alignment are fastened (absence of all the teeth on a jaw).

All-cast (leaning, arc) denture at partial absence of the teeth is a kind of removable dentures, one of which main constructional elements is an all-cast framework. The framework includes saddle elements (are intended for fastening the plastic basis with false teeth), basic holding and connecting elements (cast basis or an arch).

Maxillofacial prostheses

Kind of the dentures eliminating consequences of the congenital and acquired defects and deformations of the maxillofacial Department. Maxillofacial prostheses restore an anatomic shape of maxillary bones, replace defects, restore face contours and functions of maxillofacial area organs.

In recent years at treatment of dental diseases implants are widely used (from English implant – a class of the products of medical appointment used for implantation in an organism as dentures or their basis). Dental implants – a type of the implants used for implantation in a bone of the upper and lower jaw as a basis for an attachment fixed or removable dental dentures.

A big arsenal of dental materials is used during dental treatment. All dental materials are divided into three groups:

− constructional (metals, plastic, ceramics - materials of which different prostheses are made); − auxiliary (impession, modeling, investment, abrasive, isolating materials, fusible alloys, fluxes and etc. – materials used in laboratory and in clinic during the process of producing the denture); − clinical (filling materials, materials for fixing fixed dentures ant etc. – materials that are used during a therapeutic treatment). Constructional materials are used for the production of dentures. According to the material or materials combination that is used for the denture production there are metal (a), ceramic (b), plastic(c) and combined (d) dentures (fig. 1).

a b c d

Fig.1. Materials used for the denture production

The success of orthopedic treatment depends on properties of constructional and auxiliary materials. Dentures in the oral cavity are a subject of influence of many factors. At the time dentures can make various impacts on fabrics of an oral cavity and an organism in general. The properties of the set material can be conveniently divided into the following categories: • mechanical properties, • thermal properties, • chemical properties, • biological properties.

Mechanical properties Quantities of force ü When a force acts on a body tending to produce deformation, a resistance is developed to this external force application. The internal reaction is equal in intensity and opposite in direction to the applied external force, and is called stress. Both the applied force and internal resistance are distributed over a given area of the body, so the stress in a structure is designated as the force per unit of area. ü When a material undergoes full elastic recovery immediately after removal of an applied load it is elastic ( упругость) ü Strain (деформация). In the discussion of force, it was pointed out that a body undergoes deformation when a force is applied to it. It is important to recognize that each type of stress is capable of producing a corresponding deformation in a body. ü The deformation resulting from a tensile or pulling force is an elongation of a body in the direction of applied force, whereas a compressive or pushing force causes compression or shortening of the body in the direction of loading, strength (прочность). ü The ultimate tensile strength or stress (предел прочности на разрыв) is defined as the maximum stress that a material can withstand before failure in tension, ü whereas the ultimate compressive strength or stress is (предел прочности на сжатие) the maximum stress a material can withstand in compression. ü The stress at which a material fractures is called the fracture strength or fracture stress ( прочность на излом) ü Toughness (жесткость) is the resistance of a material to fracture, it is an indication of the amount of energy necessary to cause fracture , ü Hardness (твердость) may be broadly defined as the resistance to permanent surface indentation or penetration., ü Friction (истирание) is the resistance to motion of one material body over another. ü Materials that have mechanical properties independent of loading rate are termed elastic (эластичные) ü Materials that have mechanical properties dependent on loading rate are termed viscoelastic (вязкоупругие) ü Viscosity (вязкость) is the resistance of a fluid to flow and is equal to the shear stress divided by the shear strain rate can help identify the properties of a material. In general, the stability of a solid under applied load is determined by the nature and strength of atomic binding forces. ü Flexibility, ductility (пластичность) is the ability of a material to be plastically deformed; it is indicated by the plastic strain.

Thermal properties ü temperature, ü heat of fusion (теплота плавления), ü thermal conductivity (теплопроводность), ü specific heat (удельная теплоёмкость), ü thermal diffusivity (температуропроводность), ü coefficient of thermal expansion (коэффициент термического расширения).

Physical properties include color and optical properties, thermal properties, and electrical and electrochemical properties. The color and optical properties are color and its measurement, pigmentation, metamerism, fluorescence, opacity, index of refraction, and optical constants.

Biological properties

Ideally, a material placed into a patient’s mouth should be non-toxic, non- irritant, have no carcinogenic or allergic potential and, if used as a filling material, should be harmles