Instruments in Fixed Prosthodontics PDF

DR. Shaimaa Ahmed Professor of Fixed Prosthodontics Faculty of Dentistry, Mansoura University 1  Instruments in fixed prosthodontics Introduction The removal and shaping of tooth structure is an essential part of restorative and prosthetic dentistry. Initia...

DR. Shaimaa Ahmed Professor of Fixed Prosthodontics Faculty of Dentistry, Mansoura University 1  Instruments in fixed prosthodontics Introduction The removal and shaping of tooth structure is an essential part of restorative and prosthetic dentistry. Initially, this was a difficult process accomplished entirely by the use of hand instruments. The introduction of rotary equipment is one of the major advances in dentistry. Dental instruments are classified according to their uses into: 1. Diagnostic instruments 2. Cutting instruments 3. Restoring instruments 1. Diagnostic instruments 2. Cutting instruments Depending on whether hand or mechanical force, are utilized to work out these instruments: Hand cutting. Powered rotary cutting. Laser equipment. Others: ultrasonic equipment. Air abrasion equipment. 2  Hand cutting instruments Manufactured from Carbon steel Stainless steel Carbide steel Other alloys of nickel, cobalt, chromium Instrument design Blade (Working End) – A portion of the instrument designed for a specific function Shank – Part of the instrument that attaches the working end of the handle Handle – Portion of the instrument where the operator grasps. Examples of Hand cutting instruments: Chisels Hatchets, Hoes, Marginal Trimmers, Angle Formers. 3 Powered (rotary) cutting Instrument Power sources for dental units *Electric motor driven *Compressed air (Air driven or pneumatic) Air driven hand pieces are most popular because: i) Simplicity of design ii) Ease of control iii)Versatility and patient acceptance Handpiece Definition: A handpiece is a device for holding rotating instruments, transmitting power to them, and positioning them intraorally. According to shape Straight handpiece, Contra angle handpiece. 4 Rotary speed ranges Low speed (below 12000 rpm) Medium speed (12000-200 000 rpm) High or ultrahigh speed (above 200 000 rpm). Disadvantages of low speed 1. Ineffective 2. Time consuming 3. Require ↑ force of application therefore this will result in → heat generation → produce vibrations of low frequency and high amplitude. Indications of low speed. 1. Initial preparation of grooves and pinholes 2. Cleaning of teeth 3. Caries excavation 4. Finishing and polishing procedures Disposable prophy cup and brush (Hygienic) 5 Advantages of high-speed Faster removal of tooth structure with less vibration and heat production Better control and greater ease of operation Patient is less apprehensive because annoying vibration and operating time decreased Instrument last longer Cutting tools: Can be divided into: 1) Dental rotary burs 2) Dental rotary abrasives a) stones b) disc. Design: Rotary cutting instruments consist of three parts: 1) Shank 2) Neck (shaft) 3) Head. 6 The rotary tools used in removing tooth structures may be classified into burs and abrasives depending on whether they work by an actual cutting or an abrading process, Shank design Definition It is the part that fits into the handpiece and accepts the rotary motion from it. 1-Long shank Used with a straight handpiece 2-Short latch shanks Used with latch-type contra-angle handpiece 3-Friction grip shanks Used with an ultra-high-speed handpiece. 7 Neck design It is the intermediate portion of an instrument that connects the head to the shank Function: transmit rotational force to the head. Head design It is the working part of the instrument, the cutting edge or portion of which performs the desired shaping of the tooth structure. Characteristics of the head 1. Type of cutting: Bladed (bur). Diamond abrasive. 2. Head size. 3. Head shape. 4. Material of Construction: Carbon steel. Tungsten carbide. Diamond ships. Sand. ( Dental burs) 8 ( Dental abrasives) A- Stones B- Discs Supplied in the mounted or demounted form mounted demounted 9 Diamond abrasive instruments Diamond burs These are made from diamond chips bonded to blanks (heads). Diamond burs are used for grinding enamel and dentin surfaces. Advantages Long life More effective in cutting enamel and dentin Classification of Diamond stone I) According to the size of diamond particles II) According to head shape and size I) According to the size of diamond particles Diamond particle size is commonly categorized as: a) Super Coarse (180 to 250 µm) b) Coarse (125 to 150 µm) c) Medium (88 to 125 µm) d) Fine (60 to 74 µm) e) Very fine (38 to 44 µm). II) According to head shape and size The wheel stones Round and oval shaped stone Cylindrical stone Tapered stone Inverted cone stone Cup shaped stone 10  Barrel shaped stone Pear shaped Bud shaped Root facer stone 1-Tapered round-ended diamond stone Use For axial reduction (buccal –lingual – mesial-distal) with 6 grades taper and for chamfer finish line 0.5mm Indication Full metal crown palatal surface of metal-ceramic crown (Partial veneer) 2-Tapered flat-ended diamond stone Use Axial reduction with their surfaces and form shoulder finish line 0.8mm: 1mm Indications All ceramic crown, the facial surface of metal-ceramic crown (Partial veneer). Chamfer finish line Shoulder finish line 11 3-Long needle diamond stone Use For interproximal initial access without causing injury to (adjacent tooth and to form knife–edge (chisel) finish line. 4-Wheel-shaped diamond stone Used for the reduction of the occlusal surface, for incisal edge reduction. 5-Football-or flame shaped diamond stone Used for occlusal reduction and for reduction of palatal fossa of anterior teeth 6-Depth marking diamond stone 12 Factors influencing the abrasive efficiency and effectiveness 1-Size of the abrasive particle The larger the particle, deeper the penetration hence rapid removal occurs 2-Shape of the particle. Should be irregular for greater efficiency Irregular particle- sharp edge 3-Density of abrasive particles Refers to the number of particles per unit area, high density-closely spaced low density-widely spaced. 4. Hardness of abrasive particles The greater the hardness more the efficiency 5-Clogging of the abrasive surface Clogging of debris between the spaces of the abrasive particles affects grinding Clogging is enhanced when particles are close together The use of coolant washes away the debris and prevents clogging 6-Speed and pressure The usual cause of failure of abrasive instruments is when excessive pressure is applied to them to increase cutting efficiency at inadequate speeds. B- Discs: Classification: a) According to material: Carborundum, Diamond, and Metal Used for proximal slicing Sand paper Used for smoothening and finishing preparation. 13 14  Classification: b) According to size: i) Small disc 3/8 inch in diameter ii) Medium disc 5/8 inch in diameter. iii) Large disc 7/8 inch in diameter. c) According to shape: i) Flat shaped disc ii) Cup shaped disc d) According to the side of abrasive material: i) Safe sided ii) Double sided 15 ►finishing instruments: 1) Finishing burs 2) Mounted stones 3) Abrasive disc 4) Rubber cups. 5) Impregnated abrasive rubber discs 16 Impregnated abrasive rubber discs Mounted stones 17 laser equipment: ◼ Lasers are devices which produce beams of increased intensity light. 18 Other Equipements 1- Diagnodent Laser: for early caries detection 2- Pulp tester Ultrasonic cleaner Air born particle abrasion with sandblaster 19