Dental Instruments PDF

Dental Instruments Instruments and Equipments for Tooth Preparation In the field of dentistry, many procedures are performed on the teeth or their surrounding tissues. The dental instrument refers to a tool or a device used for specific type of work or procedure. In the field of operat...

Dental Instruments Instruments and Equipments for Tooth Preparation In the field of dentistry, many procedures are performed on the teeth or their surrounding tissues. The dental instrument refers to a tool or a device used for specific type of work or procedure. In the field of operative dentistry, cutting instruments are used to cut, file, grind, plane, cleave or smoothen dental structures. Cutting instruments are classified according to their use into: 1. Hand cutting instrument. 2. Powered (rotary) cutting instruments. 3. Laser equipments. 4. Other equipments. Hand Cutting Instruments This group includes a large number of instruments that are hand-powered. They are usually of lightweight. Hand cutting instruments are manufactured from two main materials: carbon steel and stainless steel. In addition, some instruments are made with carbide inserts to provide more durable cutting edges. Carbon steel is harder than stainless steel, but when unprotected, it will corrode. Stainless steel remains bright under most conditions but loses a keen edge during use much more quickly than those does carbon steel. Carbide, although hard and wear resistant, is brittle and cannot be used in all designs. Other alloys of nickel, cobalt, or chromium are used in the manufactured of hand cutting instruments, but they usually are restricted to instruments other than those used for cutting of tooth structures. 13  Dental Instruments The hand instruments used in the dental operatory may be categorized as: 1. Cutting instruments. a. Excavators (e.g. hatchets, hoes, angle formers and spoons). b. Chisels (e.g. straight chisel, curved chisel, enamel hatchet and gingival marginal trimmers). c. Other cutting instruments may be subdivided as knives, files scalers and carvers. 2. Noncutting instruments. (E.g. amalgam condensers, mirrors, probes and explorers). Instrument Design Most hand instruments, regardless of use, are composed of three parts: handle, shank and blade. For many non-cutting instruments, the part corresponding to the blade is term the nib. The end of the nib, or working surface, is known as face. The blade or nib is the working end of the instrument and is connected to the handle by the shank. Some instruments have a blade in both ends of the handle and are known as double-ended instruments Fig. (1). Fig. (1): double ended instrument illustrating the tree parts of hand instrument. (a) Blade (b) Shank (c) Handle 14  Dental Instruments Powered Cutting Instrument The availability of some method of cutting and shaping of tooth structure is essential for the restoration of teeth. Powered cutting equipment can be seen as a search for improved sources of energy and means for holding and controlling the cutting instruments held in a rotary hand piece, usually powered by compressed air. A handpiece is a device for holding rotary instruments, transmitting power to them, and for positioning them intraorally. Handpieces and associated cutting and polishing instruments developed as two basic types Fig. (2): 1. Straight handpiece. 2. Contra-angle handpiece. -In the straight handpiece, long straight steel bur is used, while the regular contra- angle handpiece has two angles to place the bur nearly vertical to the long axis of the straight part of the handpiece. -Both handpieces are powered by air turbine or indirectly by electric motor. Recent advances in handpieces: 1. Allow for repeated sterilization. 2. Smaller head size. 3. Lower noise levels. 4. Fiber-optic lightening of the cutting side. -All angles handpieces have an air-water spray to provide cooling, cleansing and improved visibility. 15  Dental Instruments Rotary Speed Ranges The rotational speed of an instrument is measured in revolution per minute (rpm). Three speed ranges are recognized: 1. Low or slow speeds (below 12.000 rpm). 2. Medium or intermediate speeds (12.000 to 200.000 rpm). 3. High or ultrahigh speeds (above 200.000 rpm). -Low speed cutting is ineffective, time consuming and require a heavy force of application. This result in heat production in the operating site and produce vibrations. Heat and vibration are the main sources of patient discomfort. In addition, carbide burs do not last long because their brittle blades are easily broken at low speed. Many of these disadvantages of low-speed operation do not apply when the objective is some procedure other than cutting tooth structure. The low- speed is used for cleansing teeth, occasionally caries removal, and finishing and polishing procedures. At low-speeds, tactile sensation is better and there is generally less chance for overheating cut surfaces. -At high speed, the surface speed needed for efficient cutting can be attained with smaller and more versatile cutting instruments. This speed is used for tooth preparation and removing old restorations. Other advantages are: 1. Diamond and carbide cutting instruments remove tooth structures faster with less pressure, vibration, and heat generation. 2. The operator has better control and greater ease of operation. 3. Instruments last longer. 4. Patients are less apprehensive because annoying vibrations and operating time are decreased. 16  Dental Instruments 5. Several teeth in the same arch can and should be treated at the same appointment. Fig. (2): a, Straight and b, contra-angle handpieces Laser Equipment Lasers are devices that produce beams of coherent and very high intensity light. Potential uses of lasers in dentistry have been identified that involve the treatment of soft tissues and the modification of hard tooth structures. Several types are available based on wavelengths. The lasers range from long wavelength (infrared), through visible wavelengths, to short wavelengths (ultraviolet). Excimers are special ultraviolet lasers. At the present time, CO2, ND: YAG and Er: YAG lasers have shown the most promise. For any application, it is important to select the correct wavelength for absorption of energy and prevention of side effects from heat generation. 17  Dental Instruments Other equipment Alternative methods of cutting enamel and/or dentine. Abrasive cutting was tested, but several clinical problems precluded general acceptance: 1. No tactile sense was associated with air-abrasive cutting of tooth structure. 2. It is difficult for the operator to determine the cutting progress within the tooth preparation. 3. The abrasive dust interfered with visibility of the cutting site and tended to mechanically etch the surface of dental mirror. 4. Difficulty in preventing the patient or the office personal from inhaling abrasive dust. Contemporary air-abrasive equipments helpful for stain removal, debriding pit and fissures prior to sealing and micro-mechanical roughening of surfaces to be bonded (enamel, cast metal alloys, or dentine). Although promoted for caries excavation, air abrasion cannot produce well-define preparation wall and margin details that are possible with conventional cutting instruments. Rotary Cutting Instruments Instrument intended for use with dental hand pieces are manufactured in hundreds of sizes, shapes, and types. This variation is in part a result of the need for specialized designs for particular clinical application or to fit particular handpieces. 18  Dental Instruments Common Design Each instrument consists of three parts: (a) head, (b) neck, and (c) shank Fig. (3). Shank Design The shank is the part that fits into the handpiece, accept the rotary motion from the handpiece. There are three common classes: the straight handpiece shank, the latch- type angle handpiece shank, and the friction-grip angle hand piece shank. -The shank portion of the straight handpiece is simple cylinder. It is held in the handpiece by metal chunk that accepts a range of shank diameters. Straight hand piece instruments are now rarely used for preparing teeth, except for caries excavation. However, they are commonly, used for finishing and polishing complete restoration. -The latch- type shank has more complicated shape. Their shorter overall length permits improved access to posterior region of the mouth in comparison with straight handpiece instruments. This type of instrument is used predominantly at low and medium speed ranges for finishing procedures. -The friction-grip shank design was developed for use with high-speed handpieces for tooth preparation. This design is smaller in overall length than the latch-type instruments, providing a further improvement in access to the posterior region of the mouth. 19  Dental Instruments Neck Design The neck is the intermediate portion of an instrument that connects the head and the shank. Except in case of larger, more massive instruments, the neck normally tapers from the shank diameter to a smaller size immediately adjacent to the head. The main function of the neck is to transmit rotational forces to the head. Fig. (3): Normal designation of the three parts of rotary cutting instrument. Head Design The head is the working part of the instrument, the cutting edges or points that perform the desired shaping of the tooth structure. The heads of instruments show greater variation in the design and construction than either of the other main portions. For this reason the characteristics of the head form the basis on which rotary instruments are usually classified. They are classified according to the mechanism of cutting into bladed instruments and abrasive instruments. Material of construction, head size, and head shape are additional characteristics that are useful for further subdivision. Bladed and abrasive instruments exhibit substantially different clinical performances, even when operated under nearly identical conditions. This appears to result from differences in the mechanism of cutting that are inherent in their design. 20  Dental Instruments Dental burs The term bur is applied to all rotary instruments that have bladed cutting heads. * Dental burs instruments intended for tooth preparation, finishing of metal restoration, and surgical removal of bone. *Burs are made of steel or carbide. Steel burs perform well, cutting human dentin at low speed, but dull rapidly at higher speeds or when cutting enamel. Once dulled, the reduced cutting effectiveness creates increased heat and vibration. Carbide burs have largely replaced steel burs for tooth preparation. Carbide burs perform better than steel burs at all speeds. Newer classification systems tend to use separate designations for: -Size. Usually a number giving to the head diameter in tenth of a millimeter. -Shape The term bur shape refers to the contour of the head. The basic head shapes are round, inverted cone, pear, straight fissure, and taper fissure Fig. (4). Fig. (4): Basic bur head shape. 21  Dental Instruments Abrasive Instruments Abrasive instruments are based on small, angular particles of a hard substance held in a matrix of softer material. Abrasive instruments are generally grouped as diamond or other instruments. Diamond Instruments Diamond instruments consists of three parts: a metal blank, the powdered diamond abrasive, and metallic bonding material that holds the diamond powder onto the blank. Classification: they are classified according to: -Head Shapes and Sizes Diamond instruments are available in a wide variety of shapes and in sizes; therefore, it is often necessary to select them from catalogue Fig. (5). -Diamond Particle factors The clinical performance of diamond abrasive instruments depends on the size, spacing, uniformity, exposure, and bonding of the particles. Increased pressure causes the particles to dig into the surface more deeply, leaving deeper scratches and removing more tooth structure. Diamond particles size is categorized as coarse (125 to 150µm), medium (88 to 125 µm), fine (60 to 74 µm), and very fine (38 to 44µm) for diamond preparation instruments. These ranges correspond to standard sizes for separation particle size. When using large particle sizes, the number of the abrasive particles that can be 22  Dental Instruments placed on a giving area of the head is decreased. Thus, for any giving force that operator applies; the pressure on each particle tip is greater. Diamond finishing instruments use even finer diamonds (10 to 38µm) to produce relatively smooth surfaces for final finishing with diamond polishing pastes. Fig. (5): Shapes and designs of diamond cutting instruments. a. Rounded end wheel b. Flame shape c. Fine taper d. Taper stone with flat end e. Taper stone with round end Dental rotary instruments are supplied in two categories: a. Mounted type: Supplied with their mandrel firmly attached to the working points. (E.g. diamond stones, burs and some abrasive stones). b. Demounted type: These are mounted to shank (mandrel), which carries a variety of interchangeable demounted rotary points Fig. (6). the working points are made that attach by a screw to a mandrel of suitable size for given handpiece that has a threaded hole at the end. 23  Dental Instruments Fig. (6): Demounted disc with a mandrel. Other Abrasive Instruments. Many types of abrasive instruments are used in dentistry in addition to diamond instruments. They were used for tooth preparation, but now their use is restricted to shaping, finishing, and polishing restorations. Classification: In these instruments, the cutting surfaces of the head are composed of abrasive particles held in continuous matrix of softer material. They are divided into two groups, molded instruments and coated instruments. Each uses various abrasives and matrix materials. Molded Abrasive Instruments Instruments that heads that are manufactures by molding or pressing a uniform mixture of abrasive and matrix a round the roughened end of the shank, or 24  Dental Instruments cementing a premolded head to the shank. In contrast to the diamond instruments, molded instruments have a much softer matrix and wear during use. Hard and rigid molded instruments heads use rigid polymer or ceramic materials for their matrix and commonly used for grinding and shaping procedures. Other molded instruments heads use flexible matrix materials, such as rubber, to hold the abrasive particles. These are used for finishing and polishing procedures Fig 7. Fig. 7: molded abrasive instruments a, flexible b, rigid. Coated Abrasive Instruments Are mostly discs that have thin layer of abrasive cemented to a flexible backing. This construction allows the instrument to confirm to the surface contour of a tooth or restoration. Coated abrasive instruments may be used in finishing/ polishing procedures of certain enamel walls (and margins) of tooth preparation for indirect restorations, but most often in finishing procedures for restorations. They are used with conventional and standard speed and supplied either in mounted or demounted form. 25  Dental Instruments Classification of discs According to the abrasive material. Carborandum, diamond, metal and sandpaper According to the side of abrasive martial. a. Safe sided: abrasive materials are on one side to prevent injury of adjacent teeth. b. Double sided: abrasive materials in both sides for economic purpose. According to the size. a. Small disc (3/8 inch in diameter). b. Medium disc (5/8 inch in diameter). c. Large disc (7/8 inch in diameter) According to the shape. a. Flat shaped disc. b. Cup shaped disc. Abrasives versus Burs For cutting, it is necessary to apply sufficient pressure to make the cutting edge of a blade or abrasive particle dig into the surface. Burs are miniature- milling cutters with blades that shear tooth structure from tooth surface, cutting primary from the sides of the instrument. Abrasives remove tooth structure by abrading, or wearing away the surface. The most efficient abrasive for removing tooth structure is diamond stone. Diamonds remove tooth structure more efficiently then do burs, but leave undesirably rough surfaces and irregular cavosurface finish lines. Carbide burs produce smooth finish lines and precisely internal features, but they cut more slowly. Therefore, to take the advantages of both types of instrument, diamonds 26  Dental Instruments should be used for the bulk reduction and carbide burs for finishing the preparation and placing internal features such as grooves, box forms and pinholes. The technique of choice in this situation utilizes diamonds and burs of matching size and configuration. These instruments are manufactured by making both the diamond and the bur from common blank configuration. This assures that the shape of the instrument and the resultant contour of the tooth will match exactly when diamond and carbide finishing bur are used for each step of the preparation. 27