ANNOTATION TO THE LESSON 9 Proper finishing and polishing is important for shaping, contouring and removing surface irregularities in restorations in order to avoid plaque accumulation, gingival irritation, surface staining thus providing functional occlusion & esthetics. The process of finishing a restoration involves abrasive wear through the use of hard particles. The finishing and polishing of restorative dental materials are important steps in the fabrication of clinically successful restorations. Abrasion is the process of wear on the surface of one material by another material by scratching, gouging, chiseling, tumbling, or other mechanical means. The material that causes the wear is called an abrasive; the material being abraded is called the substrate. The process of abrasion is affected by the physical and mechanical properties of the material being abraded. Properties such as hardness, strength, ductility, and thermal conductivity are important. Hardness - resistance to permanent indentation on the surface. Brinell and Knoop hardness values are functions of a material's resistance to indentation, whereas Mohs values indicate one material's resistance to scratching by another. (Table 1) Table 1. Mohs hardness of dental abrasives. Abrasive materials can be 2 types: natural and synthetic. (Tables 2,3) Table 2. Natural abrasive materials. Types Source Application Moh s
hardness Arkansas stone Siliceous sedimentary rock mined in arkansas Fine grinding of enamel & metal alloys Chalk Calcite, calcium carbonate Polish tooth enamel,gold foil, amalgam and plastic materials 3 Corundum (White stone) Minerals forms of aluminum oxide in white Grinding metal alloy 9 Natural Natural diamond (Super Abrasive) Transparent colorless hardest mineral, composed of carbon Used on Ceramic and Resin based composite structure 10 Emery Grayish black corundum in fine grain Finishing metal alloys or acrylic resin 7-9 Quartz Very hard, colorless and transparent Finish metal alloys and grind dental enamel 7 Table 3. Synthetic abrasive materials Types Source Application Moh s hardness
Silicone carbide First synthetic abrasive Cutting of metal alloys, ceramics and acrylic resin materials 9-10 Aluminium oxyde Aluminia Sandblasting and finishing base metal alloy, resin based and composite material, polishing paste 9 Synthetic diamond Natural diamond Grind tooth structure, ceramic, resin materials. As polishing paste. 10 Synthetic Rouge Iron oxyde Polish high noble metal alloys 5-6 Tin oxyde Tin oxide as fine abrasive Polishing agent for teeth and metallic restorations 6-7 Characteristics of dental abrasive instruments. Abrasive instrument consists from bonded to its surface hard filler particles. Factors affecting rate of abrasion: 1. Type of the abrasive material 2. Size of the abrasive
By convention, particles are classified as fine (0 to 10 µm), medium (10 to 100 µm), and coarse (100 to 500 µm), according to the average particle size of the sample. Larger abrasive particles will abrade a surface more rapidly than will smaller particles. 3. Pressure of the abrasive against substrate 4. Speed at which the abrasive moves against substrate. 5. Irregularity in shape of the abrasivemore irregular particles, greater efficiency Types of abrasive instruments. Abrasives are nonbladed instruments used to finish and polish restorations and appliances. Some abrasives are also used for cutting. Abrasives come in a wide variety and are categorized by their shapes such as discs, points, and wheels. Abrasives are also categorized by the materials they are made of, such as rubber, stone, and sandpaper. Some restorative materials come with select abrasives that are designed to give the restoration a premium finish. Abrasive instruments can be mounted (Fig.1, a) or unmounted. (Fig. 1, b). Figure 1. Types of abrasive instruments. А b For fixation of unmounted abrasive instruments mandrels are used. Mandrels are rods of various lengths that are used in low-speed handpieces with various abrasives. Mandrels are available in three shanks: latch, friction grip, or straight. The head of the mandrel, where the abrasives attach, is available in snap on, screw-on, or pin designs. (Fig. 2)
Figure 2. A- screw-type mandrels, B- snap-on mandrels FINISHING process by which a restoration is contoured to remove excess material and produce a reasonably smoother surface. POLISHING refers to the final removal of material from a restoration resulting in a very smooth highly reflective surface which does not contain scratches. Carborundum Discs. Carborundum discs, also known as Jo-dandy discs and separating discs, are thin, brittle discs that break easily. They are double-sided and are used primarily in the dental laboratory to cut and finish gold restorations, but they can be used intraorally as well. (Fig. 3,b) Figure 3. A- rubber wheel, B- carborundum discs Stones Stones are available in many sizes, shapes, and grits, similar to discs. They are used for cutting, polishing, and finishing amalgam, gold, composite, and porcelain restorations. Stones are used in the laboratory to adjust and polish appliances and custom trays. The type of abrasive material and the grit control the cutting or polishing action of the stone. The abrasive materials include silicon carbide, garnet, and aluminum oxide. Stones may be mounted or unmounted. Some stones are considered heatless, thereby allowing the operator to polish a restoration without creating frictional heat.
Rubber Wheels Wheels are made of rubber material impregnated with an abrasive agent. They come mounted and unmounted and are available in various grits. They are used for finishing and polishing (Fig. 3-a). Rubber Points Rubber points come in a variety of sizes and grits. They are made of rubber material impregnated with abrasive agents. Points are used to polish and are especially adaptable when defining anatomy in the restoration. (Fig.4) Figure 4. Various points, cups, and wheels to define, polish, and finish composite restorations. Coated Disks Are used for contouring of an irregular surface to produce a smooth flat or convex contour on incisal edges, embrasures and to a limited extent on posterior surfaces. Coated disks are available in different diameters. Disks may be attached to a mandrel. Advantage of this type is that the mandrel does not interfere with the working area but its movement is limited to a forward motion only (Fig.5) Figure 5. Coated disks Coated Strips Strips are used to smooth and polish the proximal surfaces of all bonded restorations. Available in metal or plastic backing and with different abrasives. Metal strips are used in very tight contact areas of ceramic, composites and amalgam restorations, but care must be taken to avoid lacerating the gingival tissues.plastic strips are used for composites, compomers, hybrid ionomers,
and resin cements. These strips are used by hand in a back and forth motion. (Fig. 6). Figure 6. Coated strips Polishing pastes. Also called as nonbonded abrasives or polishing pastes. Primarily used for final polishing, need to be applied to the substrate with a nonabrasive device such as synthetic foam, rubber, felt or chamois cloth. Most popular loose abrasives are aluminium oxide and diamonds. Paste Particle size Purpose Condition Aluminium oxide 1µm and 0,3µm Polishing of composite resin material Diamond 3-4µm and 1µm Polishing of composite and ceramic material Wet Dry Number coding system for dental rotary instruments. ISO 6360 provides a general number coding system for all types of dental rotary instruments, including accessories used in connection with these rotary instruments. The benefits of this system for dentistry in its entirety will only be derived if the system is widely adopted; manufacturers of dental instruments, as well as the dental trade, are therefore requested to refer to ISO 6360 in their catalogues. This part of ISO 6360 was prepared in response to a need by the dental trade and industry and the dental profession for a universal system of classification and designation for these instruments. It establishes a comprehensive number coding system suitable for all dental rotary instruments by use of a 15-digit code number identifying general and specific characteristics of instruments or groups of instruments. The first group of three digits identifies the materials used for the working part of instruments. The second group of three digits identifies the shanks and handles used for instruments and the overall lengths of instruments.
The third group of three digits identifies the shapes of instruments. The fourth group of three digits identifies the specific characteristics for groups of instruments. The fifth group of three digits identifies the nominal diameter of the working part of the instruments. The code numbers are generic code numbers. They do not provide exact product information. This information is given in the respective product standards for dental rotary instruments. Samples of number coding. А БВ Г Д The material of head Handpiece that it fits (diameter and length) Form or shape of head Diameter of head
Tungsten carbide For angle handpiece (Ø 2,35 mm,length 22 mm) Round 2,4 мм 500 204 001 001 024 ISO500 204 001 001 024 Grainding, µm Color coding of the shank Notes ISO 8-12 494 White Ultra fine (UF) 15-20 504 Yellow Extra fine (EF) 30-60 514 Red fine (F) 80-100 524 - medium (M) 125-145 534 Green coarse(g) более 150 544 Black Extra coarse (EG) Common features of the burs: