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week 4 rotary cutting instrument.ppt
- 1. 1 Elif Ilgi Sancak DDS, PhD Assistant Professor Rotary Cutting Instrument
- 2. ROTARY CUTTING INSTRUMENTS (BURS) 2 Variable size, type, shape….. to: • Accommodate particular handpiece. • Accommodate particular clinical application. Common design characteristics Shank Neck Head
- 3. CLASSIFICATION OF BURS 3 According to Material used Steel burs: Well cutting human dentin but Mainly used now for finishing procedures, Why??? Dull easily. Heat production. Vibration. Carbide burs: Stiffer and stronger than steel but unfortunately: Rust easily, Easily fractured at neck when subjected to sudden blow, so replaced by steel neck. Again steel neck may bend and producing a risky eccentric rotation (run- out) vibration.
- 4. 4 According to shank design Grasped by D-shape socket and retaining latch Grasped by metal chuck Grasped by plastic or metal chuck A = Straight. B = Latch type. C = Friction grip.
- 5. NECK DESIGN NECK PERMIT BETTER VISION FOR THE OPERATION FIELD AND TRANSMIT THE ROTATIONAL FORCE FROM THE SHANK TO HEAD. LARGER DIAMETER IS STRONGER BUT INTERFERE WITH VISION. 5
- 7. ROUND: INITIAL CAVITY PREPARATION. EXTENSION OF PREPARATION. PREPARATION OF RETENTION GROOVES. REMOVAL OF CARIES. STRAIGHT FISSURE: FOR AMALGAM CAVITY PREPARATION. INVERTED CONE: PROVIDING UNDERCUTS AND PLANING CAVITY FLOORS. PEAR: FOR CAVITIES OF GOLD OR AMALGAM. TAPERED FISSURE: FOR INDIRECT WORKS (INLAY/ONLAY, CROWN….) FREE OF UNDERCUTS. 7
- 8. BLADES DESIGN 8 Plain-cut (non cross-cut) Advantages: High quality surface Durable. Disadvantages: Less cutting efficiency. Cross-cut: Advantages: High cutting performance. Disadvantages: Low quality surface (rough). Less durable.
- 9. BUR FEATURES AFFECTING CUTTING EFFICIENCY 1- CROSS-CUT: MORE PRESSURE PER UNIT AREA. 2- NECK DIAMETER: LARGER PERMITS MORE PRESSURE WITHOUT FRACTURE 3- HEAD DIAMETER: LARGER = MORE SURFACE SPEED. 4- SPIRAL ANGLE: EXCESSIVE INCREASE OF THE ANGLE DECREASE CUTTING EFFICIENCY. 9 Axis Blade direction
- 10. 5- NUMBER OF BLADES 10 6-10 Excavator 12-40 Finishing
- 11. 11
- 12. 12 Blank Cutting based on large number of small angular particle that protrude from softer bonding matrix Bonding may be done by electroplating
- 13. 13
- 14. SIZE: COARSE (125-150 μm), MEDIUM (88-125 μm), FINE (60- 74 μm), VERY FINE (38- 44 μM). LARGER FOR EXCAVATION, SMALLER FOR FINISHING. SPACING: INCREASING THE SIZE AND NUMBER OF PARTICLES DECREASING SPACES AND THUS INCREASING CUTTING EFFICIENCY AS MORE PARTICLES CONTACTING THE SURFACE TO BE CUT AT ANY ONE TIME. UNIFORMITY: AFFECT NUMBER OF PARTICLES THAT COME IN CONTACT AT ANY ONE TIME. EXPOSURE: RELATED TO SPACES AND UNIFORMITY, PLUS THE OPERATOR SKILLS AND TECHNIQUES. BONDING: DURABILITY AND CUTTING EFFICIENCY DIRECTLY PROPORTIONAL WITH BONDING STRENGTH. 14 Diamond particles factors
- 15. OTHER ABRASIVE INSTRUMENTS 15 Matrix & Abrasives 1- Molded Blank Mold Molded abrasives are durable as when the surface layer wear, the subjacent layer still possess the same characteristics
- 17. 17 2- Coated Blank Mostly used for polishing discs fabrication Cemented Thin layer of abrasive material
- 18. 18 Coated abrasive disc / Unmounted molded disc Screw mandrel Double sided coating
- 19. MATERIALS MATRIX: PHENOLIC RESIN (NON FLEXIBLE) OR RUBBER (FLEXIBLE). ABRASIVES: SILICON CARBIDE (CARBORUNDUM™): GRAY-GREEN (DISC IS BLACK) IN COLOR, PRODUCE MODERATELY SMOOTH SURFACE. ALUMINUM OXIDE: WHITE IN COLOR AND PRODUCE SMOOTHER SURFACE. GARNET (RED) AND QUARTZ (WHITE): USED FOR INITIAL FINISHING PROCEDURES. PUMICE: POWDER ABRASIVE FORMED BY CRUSHING FOAMED VOLCANIC GLASS INTO THIN GLASS FLAKES. USED WITH RUBBER DISCS FOR INITIAL POLISHING. CUTTLEBONE: DRIVEN FROM CUTTLEFISH, ONLY USED WITH COATED POLISHING DISCS FOR FINAL FISHING PROCEDURES. 19
- 20. THE END 20
Editor's Notes
- Despite the great variation among rotary cutting instruments, they share certain design features. each instrument consists of three parts: (1) shank, (2) neck, and (3) head. Each has its own function, inluencing its design and the materials used for its construction.
- can be classified according to the material used.
- A round bur is spherical. This shape customarily has been used for initial entry into the tooth, extension of the preparation, preparation of retention features, and caries removal. An inverted cone bur has a rapidly tapered cone with the apex of the cone directed toward the bur shank. Head length is approximately the same as the head diameter. This shape is particularly suitable for providing undercuts in tooth preparations. A pear-shaped bur has a slightly tapered cone with the small end of the cone directed toward the bur shank. The end of the head either is continuously curved (see Fig. 14.20) or is flat with rounded corners where the sides and flat end intersect (Fig. 14.21A; 245).
- The second major category of rotary dental cutting instruments involves abrasive cutting rather than blade cutting. Diamond instruments have had great clinical impact because of their long life and great efectiveness in cutting enamel and dentin.
- Diamond instruments consist of three parts: (1) a metal blank, (2) the powdered diamond abrasive, and (3) a metallic bonding material that holds the diamond powder onto the blank.
- Diamond instruments currently are marketed in a myriad of head shapes and sizes.
- Molded abrasive instruments have heads that are manufactured by molding or pressing a uniform mixture of abrasive and matrix around the roughened end of the shank or cementing a premolded head to the shank. Other molded instrument heads use flexible matrix materials, such as rubber, to hold the abrasive particles. These are used predominantly for finishing and polishing procedures. Molded unmounted disks or wheelstones are attached by a screw to a mandrel of suitable size for a given handpiece that has a threaded hole in the end.