Dental Rotary cutting instruments /certified fixed orthodontic courses by Indian dental academy


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Dental Rotary cutting instruments /certified fixed orthodontic courses by Indian dental academy

  1. 1. Seminar on ROTARY CUTTING INSTRUMENTS INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. INDEX 1. Definitions 2. Introduction 3. Dental Hand pieces 4. Improved Cutting Instruments 5. An era of increased speeds and various associated techniques 6. Care and maintenance of Rotary equipment 7. Water air cooling 8. Dental cutting burs (a) Composition and manufacture (b) General design of dental burs © Parts of a bur (d) Classification 9. Diamond Abrasive Instruments (a) Color coding (b) Manufacturing © Classification (d) Diamond/bur dual instrumentation 10. Effects of high speed cutting 11. Advantages of high speed cutting 12. Disadvantages of high speed cutting 13. Abrasion and Polishing Agents 14. Review of literature 15. Summary 16. References
  3. 3. The term “Rotary” is applied to tooth cutting instruments That turn on axis to perform work, these are the units actually responsible for the removal of tooth structure, and may be one of two types: Burs; which are cutting tools, and, Stones, which are abrading tools. SPEED: Speed is the rate of change of position with time (MOSBY’s Dictionary) Speed is the magnitude of velocity without regard to direction. (Stedman’s Dictionary)
  4. 4. Classification of Speed According to Sturdevant Low Speed-Below 12,000 rpm. Medium or Intermediate speed- 12,000 to 2lakh rpm. High or ultra high speed- Above 2lakh rpm. According to Charbenau Conventional or low speed below 10,000 rpm. 1. Increased or high speed- 10,000 to 1, 50,000 rpm. 2. Ultra speed- Above 1, 50,000 rpm. According to MARZOUK Ultra low speed- 300 to 3000 rpm. Low speed- 3,000 to 6,000 rpm. Medium high speed- 20,000 to 45,000 rpm. High speed- 45,000 to 1, 00,000 rpm. Ultra high speed- Above 1, 00,000 rpm. According to Clearence L. Sock well (DCNA-1971) Low or conventional speed- Below 6,000 rpm. High or intermediate speed- 6,000 to 1, 00,000 rpm.
  5. 5. Dental Bur- The term bur is applied to all rotary cutting instruments that have bladed cutting heads. This includes instruments intended for such purposes or finishing metal restorations and surgical removal of bone as well as those primarily intended for tooth preparation. Introduction Before considering the tooth preparation, Prosthodontist must be aware of the instruments at his disposal so that the most suitable one can be used. Teeth are vital organs; therefore they must be treated with consideration. The objectives of the treatment given to the patient are to provide oral function, esthetics, health by restoring teeth and the adjacent structures. Frequently, the efforts of restorations may themselves transform a comfortable tooth into one that is sensitive or pathologic
  6. 6. Dental Hand pieces By the middle of 17th century hand instruments were supplemented with steel burs of various shapes and sizes. These were rotated with thumb and finger because many areas of the teeth could not be reached with this design; the angle hand piece and short shanked bur were developed. From this beginning, two basic designs of hand pieces and cutting instruments, straight and angle have become standard equipment in the dental office.
  7. 7. FOOT ENGINE The old spinning wheel and sewing machine probably inspired the development of a dental foot engine as a source of power around 1871. Rotation of a cutting instrument was made possible by a long belt running over a series of pulleys to the back of a straight hand piece. When the angle hand piece was needed, it could be attached to the shaft of the straight hand piece. ELECTRIC ENGINE One of the most significant advances in the early history of hand piece adoption was the adoption of the electric motor as a power source in 1874.It was incorporated into a dental unit in 1914. Hand piece equipment and operating speeds and maximum of 5000 revolutions per minute remained virtually unchanged until 1946. Based on use, there are 3 hand piece designs Straight  Angle  Prophylaxis These standardized shapes have continued over the years.
  8. 8. Rotary power from an electric engine is transferred to the straight hand piece by a belt that runs over a series of pulleys and a three piece extension cord arm. A variable rheostat sits on the floor and is operated by the foot to control the speed of the hand piece. Rotary cutting instruments are inserted into a chucking mechanism at the front of the hand piece. The electric engine is seldom used as a source of power in a modern dental operatory but is often used in dental laboratories where low speed and high torque are desirable.
  9. 9. IMPROVED CUTTING INSTRUMENTS Progress in dental cutting procedures was delayed by a lack of instruments that could effectively remove hard tooth structures. The steel burs that were used at that time could not cut enamel effectively even with the application of great force. Silicon carbide points, sometimes called carborundum stones, were not hard enough and lost their shape rapidly. Diamond cutting instruments were developed in Germany around 1935, but with the outbreak of World War II and the accompanying scarcity of labor and materials, very few of these instruments were produced for the duration of the war. It was during this period, when large numbers of men had to be treated in a limited amount of time that the need of better and more effective cutting instruments and procedures was dramatized. In a 10 year period, which started in the latter part of 1946, cutting techniques were revolutionized. Diamond instruments were produced commercially and were joined a year later by tungsten carbide burs. For the first time in dental history, instruments became available that could effectively remove hard tooth structure.
  10. 10. INCREASED SPEEDS It was immediately evident that diamond and carbide instruments performed best at the highest speeds available and that increased speeds were available for more effective cutting. Obtaining speeds of 10,000 to 15,000 rpm was a relatively simple matter. The small pulley on the motor drive shaft was replaced with a larger one, while the pulley at the hand piece was reduced in size. Motor resistors were disconnected so that armature could receive the full line current and revolve at maximum speeds. In 1949, it was reported that speeds of 60,000 rpm and above were more effective for cutting tooth structure and were also above the human threshold of vibration perception. Equipment manufactures continued to make improvements in conventional rotary hand pieces, but heat, vibration and wear were major problems, especially in the gear mechanism of angle hand pieces. In the mean time two non-rotary industrial cutting methods, air abrasive technique and ultrasonics were applied in dentistry.
  11. 11. AIRBRASIVE TECHNIQUE The air abrasive technique was made available to the dental profession in 1951. The principal involves the use of powered abrasive particles (aluminum oxide) and kinetic energy (mass in motion). Hard tooth structures can be reduced without perceptible vibration, pressure or heat by a stream of abrasive particles traveling at a high velocity. This technique received widespread interest. Advantages  Patient acceptance was excellent.  No significant pulp reaction was reported.
  12. 12. The air abrasive technique never became popular with the dental profession.      Disadvantages Use was limited to areas of good vision because there was no sense of touch b/n the hand-piece and the tooth to act as a guide while cutting. Precise angles and margins were difficult to obtain and the operator had to return to hand or rotary instruments for finishing procedures. Surface of an ordinary mirror was rendered useless in a short period by rebounding abrasive particles. Spent dust was not effectively removed by a large noisy suction apparatus. Possibility of lung damage by inhalation of the abrasive particles was investigated but not found to be a major health hazard.
  13. 13. Ultrasonics Another non-rotary (instrument) industrial cutting method known as ultrasonics was adapted for dental use around 1952. Hard tooth structure can be removed by vibrating a slurry of abrasive particles (aluminum oxide) against the surface to be reduced with various sizes and shapes of preformed instrument tips. Principle involves the conversion of alternating current into high frequency mechanical vibrations in a phenomenon of magnetostriction. The movements of the working tip, back and forth approximately 29, 000 times per second with a thrust of 0.0016” can not be detected by the operator or the patient. Advantages 1. Precise smooth cuts of predetermined shapes and sizes can be made without the annoyance factor of heat, vibration, noise or pressure. 2. Patient acceptance was excellent. 3. Tactile control of the instrument is somewhat improved over the
  14. 14. Disadvantages  Use of preshaped working point is limiting because anatomy and carious areas of  individual teeth vary greatly.  Interchanging the points was a relatively time consuming process.  Cutting rate was slow especially in a lateral direction.  Visibility was obscured because of the accumulation of slurry.  Caries and resilient filing materials such as gold could not be removed effectively.  Maintenance problems resulted from complicated mechanism of operation.
  15. 15. BELT DRIVEN HANDPIECES A belt driven angle hand piece called the page chayres became available in 1955. It was the first angle hand piece to operate successfully at speeds of 1, 00, 000 rpm and was attached to a conventional dental unit with an electric motor as a source of power. It was a very popular angle hand piece and several versions of this design were marketed commercially. Advantages  Free of maintenance problems. Disadvantages  Many moving parts.  Objectionable high pitched noise during operation.
  16. 16. WATER TURBINE HANDPIECES A major break through in the development of rotary equipment for increased speeds came with the elimination of the gear and the belt driven sections of the angle hand piece. In 1933 a hydraulic driven turbine angle hand piece was reported to operate satisfactorily at 60, 000 rpm and was marketed 2 years later. The Turbo-Jet was designed as a compact mobile unit that required no outside plumbing or air connections. Only a source of electricity was needed to operate the unit. Improved models had both straight and angle hand pieces that could operate at speeds up to 1, 00,000 rpm. ADVANTAGE 1. Rotary instruments had a threshold shank to ensure concentricity when attached to shaft of the turbine. DISADVANTAGE 1. Changing the instruments was time consuming and carbide burs did not perform well with water turbine hand piece.
  17. 17. AIR TURBINE HAND PIECES In the later part of 1956 the first clinically successful air driven turbine hand pieces became available with free running speeds of approximately 3,00,000 rpm. Early models were attached to a conventional dental unit and consisted of a hand piece, control box, foot control, various connector hoses and a source of compressed air. When the foot control was activated, compressed air flowed to the control box and was carried by a flexible hose to the back of the hand piece. From there the air was directed to the head of the hand piece through a metal tube and was blown against the blades of a small turbine to produce rotation. Some of the spent air was expelled at the head of the hand piece, while the greater part was exhausted at the back of the hand piece or returned to the control box. Cutting instruments were inserted into the shaft of the turbine and held by friction grip. Although most air turbine angle hand pieces have free running speeds of approximately 3, 00, 000 rpm, it should be noted that this speed drops to approximately 1, 60, 000 rpm with a lateral work load of two ounces.
  18. 18. The reason for this is that air turbines have low torque and will stall at lateral work loads of approximately 4 to 6 ounces. This is an excellent safety feature, since excessive pressure can not be applied easily to the cutting instrument. The application of the turbine principle to the straight hand piece eliminated the necessity of having an electric engine as part of a standard dental unit. This greatly simplified the design and construction of present day dental units. The design of the straight hand piece turbine provided the desirable high torque for low speed operation. Air bearings have been used instead of ball bearings to support the turbine shaft in some air turbine angle hand pieces. By having the turbine suspended in air and rotated by air, practically all friction is eliminated and speeds may be increased to over 8, 00, 000rpm. It is not worthy that hand pieces using this design operated only at full speed and at this speed the dentist was handicapped by virtually no sense of touch. Thus desirable control was reduced, and over cutting often resulted. The hand piece was very quiet in operation. High costs, maintenance problems and the lack of variable speed kept this design from becoming widely used. Air driven hand pieces have been and continue to be the most popular type of hand piece equipment because of the over all simplicity of design, ease of control, versatility and patient acceptance.
  19. 19. CARE AND MAINTENANCE OF ROTARY EQUIPMENT Rotary cutting or polishing instruments should never be left in the hand piece between patients or over night. Some of these instruments have steel shanks that may corrode in the metal chucking system of the hand piece. When cutting instruments become worn, dull, bent or broken, they should be discarded. Such instruments do not operate efficiently and cause added trauma to the tissue. Dental hand pieces are expensive and must receive the utmost care to ensure peak performance, to prolong their life and to reduce overhead costs.
  20. 20. WATER AIR COOLING: With high speed instrumentation, the problem of over heating the tooth during preparation is critical. Cutting dry at high speeds will produce nearly three times as much dentinal burning as cutting with a water spray, and thermal changes can result in pulpal inflammation or necrosis.Brown et al calculated the temperature of dentin at a distance of 0.5mm from a high speed bur cutting dry to be 245 degrees F. In light of this, Zach’s contention that a temperature rise of only 20 degrees F will lead to pulpal death in 60% of teeth is most serious indeed. Even in non vital teeth, dry cutting at high speeds should be avoided, since the thermal stresses will cause micro fractures in enamel. This could contribute to marginal factor of the restoration at some future time. The use of air alone as a coolant is harmful to the pulp and is therefore not an acceptable substitute for a water air spray. Prolonged dehydration of freshly cut dentin will increase pulpal damage producing odontoblastic displacement. To minimize pulpal trauma, a water spray should always be used when cutting a tooth preparation at high speeds.
  21. 21. The use of water spray does not in itself guarantee that the pulp will be protected from damage. A low quantity of water, poorly directed, will result in a weak spray that can permit localized dentinal scorching. A small orifice that produces a higher water velocity is more likely to allow penetration of the air vortex around the instrument tip. A water spray also increases the efficiency of high speed rotary instruments by cutting the cutting edges washed clean of debris. Eames et al. found that a greater flow of water coolant is required to prevent clogging when diamonds are used under increased pressure. Diamond stones used under high pressure (150 gm) became more effective as the water flow rate increased from 3 to 21 ml/min. If light pressure was used (50 gm), there was still an increase in effectiveness, but it leveled off after the flow rate reached 7 ml/min. The spray enhances visibility in many instances by flushing away blood and debris. Even indirect vision can be utilized while cutting wet, if the mirror is first coated with a film of detergent. This allows the water to form a smooth transparent film on the surface of the mirror with only a moderate decrease in visibility.
  22. 22. DENTAL CUTTING BURS 1. Composition and manufacture: Dental Burs can be classified by their composition into two types: (a). Steel burs: Steel burs are cut from blank steel stock by means of a rotary cutter that cuts parallel to the long axis of the bur. The bur is then hardened and tempered until its Vicker’s hardness number is approximately 800. (b).Tungsten carbide burs: Tungsten carbide burs are best for making precise preparation features and smooth surfaces in enamel or dentin. A logical application of their planning capability is the production of smooth finish lines. Carbide burs can also be used to cut through metal, while both carbide burs and diamonds can be used to cut sound dentin.
  23. 23. The metal in the head of the carbide bur is formed by sintering, or pressure molding, tungsten carbide powder and cobalt powder under heat and vacuum. The tungsten carbide is cut into small cylinders and then attached to steel rods by soldering or welding to form blanks. The tungsten carbide head is machined with large diamond disks to create the specific head for the type of bur being formed. The attachment of the carbide bur is quite secure, and loss of the carbide portion of the bur is rare. Only when the process has been completed is the shank of the instrument shortened, notched, or diminished in diameter to make a straight hand piece, latch, or friction grip bur. Most burs intended primarily for cutting are made with six and occasionally eight blades. Those burs made for finishing usually have 12 blades, but they can have 20, or even as many as 40. Several carbide burs of specific shapes are included in the standard armamentarium. These include at least 2 tapered fissured burs, long and standard length, an end cutting bur and a friction grip no. 4 round bur. For removal of deep caries a low speed hand piece no. 6 round bur is used so that sound dentin can be distinguished from softer carious dentin by its greater resistance to cutting. Tapered fissure burs have a number of uses in preparing teeth for cast metal and porcelain restorations. In addition to the placement of grooves, box forms, and isthmuses, they are especially useful for planning vertical axial surfaces. There are a number of tapered finishing burs whose greater length and diameter make them suited better for this task, the commonly used sizes are shown in the figure below:
  24. 24.
  25. 25. 2. General design of Dental Burs: The dental bur is a small milling (cutting) instrument. A common design is displayed in the figure underneath:
  26. 26. Bur tooth: This terminates in the cutting edge, or blade. It has two surfaces, the tooth face, which is the side of the tooth on the leading edge; and the back or flank of the tooth, which is the side of the tooth on the trailing edge.
  27. 27. Rake angle: The rake angle is the angle that the face of the bur tooth makes with the radial line from the centre of the bur to the blade. This angle can be negative if the face is beyond or leading the radial line (referring to the direction of rotation). It can be 0 if the radial line and the tooth face coincide with each other (radial rake angle). The angle can also be positive if the radial line leads the face, so that the rake angle is on the inside of the radial line. The more positive the rake angle the more acute the edge of the blade, and more effective the cutting action. A positive rake angle, unfortunately, also has a weaker edge. Therefore, the blades are usually made with either negative or neutral (radial) rake angles, and wider bases. These are slightly less efficient for cutting, but because of their greater bulk they are less likely to chip.
  28. 28.
  29. 29. Land: The plane surface following the cutting edge. immediately
  30. 30.  Clearance angle: The angle between the back of the tooth and the work. If a land is present on the bur, the clearance angle is divided into: primary clearance which is the angle the land will make with work, and secondary clearance, which is the angle between the back of the bur tooth and work. When the back surface of the tooth is curved, the clearance is called radial clearance. There is an optimum clearance angle for each diameter of bur, and the larger the diameter, the smaller the clearance angle that is required. The smaller the clearance angle, the stronger the cutting blade. However, if the angle becomes too small, the back of the blade may rub against the cut surface, generating heat and decreasing efficiency.
  31. 31.
  32. 32.    Tooth angle: This is measured between the face and back. If a land is present, it is measured between the face and land. Flute or chip space: The space between successive teeth, which are the grooves between the blades the amount of spiral, or helical angle, of the blades affects the cutting characteristics of the bur. A greater helical angle produces a smoother surface on the preparation, and reduces the “chatter,” or vibration of the bur on the tooth surface. This also reduces chipping of the tungsten carbide during use on a tooth, and it prevents debris from clogging the flutes between the blades. The number of teeth in dental cutting burs is usually 6-8.
  33. 33.    Every bur will have three parts: The head –The portion carrying the cutting blades. The shank-The portion connecting the head to the attachment part, and the Shaft or the attachment part- The portion which will be engaged within the hand piece.
  34. 34. CLASSIFICATION 1. According to their mode of attachment to the hand piece: -Latch type -Friction grip type 2. According to the hand piece they are designed for: -Contrangle bur -Straight hand piece bur 3. They can also be classified as right and left. The most common ones are the right, which cut when they revolve clockwise. 4. According to the length of the head: -Long -Short -Regular 5. According to the function: -Cutting burs -Finishing and polishing burs
  35. 35. DIAMOND ABRASIVE INSTRUMENTS    The second major category of rotary dental cutting instruments involve abrasives rather then blade cutting. Abrasive instruments are generally grouped as diamond or other instruments. Diamond instruments for dental use were introduced in the United States in 1942. These diamond instruments are nothing but small angular particles of diamond held in a matrix of softer material. The diamond employed is industrial diamonds either natural or synthetic that have been crushed to powder and then carefully graded for size and quality. Diamond particle size is commonly categorized as coarse (125 to 150um) medium (88 to 125 um) fine (60 to 74um) and very fine (38 to 44 um).
  36. 36. Color coding is done depending on the particle size i.e., Coarse- Green (125 – 150 um )  Medium-Blue (125 – 88 um )  Fine- Red (60 – 74 um )  Very fine- Yellow ( 38 – 44 um ) The particle size used by four major U.S. dental firms is compared by both U.S. MeshStandard and equivalent metric size. 
  37. 37.
  38. 38. Manufacturing of Diamond Abrasive   Abrasive particles are held together by means of a “binder” (base) of variable nature. A ceramic binder is used in many cases particularly for binding diamond chips. Also, an electroplating process providing a metallic binder may be used. For soft grade stone, rubber or shellac may be used. Sintered types are strongest because abrasive particles are fused together. The type of binder is intimately related to the life of the tool in use with most abrasives, the binder is impregnated through out with abrasive particles of certain grade so that as a particle is wrenched from the binder during use; another will take its place as binder wears. Eames et al. found that they cut tooth structure two to three as burs. times as quickly
  39. 39.   They are deposited in one to three layers on the surface of the instrument. The best diamond stones have abrasive particles evenly spaced over the surface of the instrument. There also should be intimate contact between the chips and the binding material. While there are many shapes and sizes of diamonds to be used for special applications and to suit the taste of every operator, there are a few diamond stones which should be included in a basic set of instruments: the round-end tapered, flat-end tapered, long-needle, short-needle, and small round-edge wheel diamonds. Two other diamonds also commonly used, the torpedo and flame, are frequently paired with carbide burs of matching shapes. Figures and dimensions for these instruments are shown below:
  40. 40.
  41. 41. According to their shapes and sizes they can be classified as: (a)Flat ended tapered diamond cylinder: It is used for bulk axial and occlusal reduction and shoulder preparation on PJC and PFM tooth preparations. End cutting burs are also used to develop and lower shoulder preparation. They are kept perpendicular to the plane being reduced.
  42. 42. (b) Straight cylinder diamond with a tapered point: A suitable instrument for chamfer placement is a Tinker diamond; a straight cylinder with a tapered point. This tapered point creates a chamfer with greater control then the round-end tapered diamond. It is usually indicated for molars.
  43. 43. c)Twelve fluted carbide bur: It is a smooth cutting instrument and gives a highly finished surface to a preparation. The greater the number of blades on a bur, the smoother the cut.
  44. 44. (d)Round-ended tapered diamond cylinders: They are available in various sizes. They are used for axial and occlusal reduction and developing chamfer margins. Less than half the diameter of the tip is used for chamfer margins. Cutting to a depth greater then one-half the diameter of the tip produces a shoulder.
  45. 45. (e)Round diamonds: They facilitate establishing depth grooves before reduction. They vary in size and are measured to determine the cut depth. They are also used to establish rest seats and reduce lingual surfaces of anterior teeth. They are numbered from ¼, ½, 1, 2 to 10.
  46. 46. (f)Round diamond wheels (donut): They are gross reduction instruments and also used in anterior teeth lingual reductions. They are numbered as 14 and 15.
  47. 47. (g)Oblong diamonds (football): Variously shaped football diamonds are available for lingual reduction of anterior teeth. They are available in sizes that uniformly reduce the foosae.
  48. 48. (h)Thin tapered diamond cones (needle): Thin tapered cones are used for proximal slices to isolate teeth from adjacent teeth. They tend to lose their sharpness sooner than coarse diamonds and are replaced frequently.
  49. 49. (i)Tapered oblong diamond (flame): Small flame-shaped diamonds are used in bevel placement. There are many multi fluted flame-shaped carbides that have identical functions.
  50. 50. (j)Cross cut fissure burs: They come in varying sizes and are numbered from 555,556 to 560, both tapered and cylindrical. The tapered burs are used for groove placement in three quarter crowns, flutes, and for seating grooves in complete gold crowns.
  51. 51. (k)Plain fissure burs: They cut smoothly and come in a variety of sizes, both tapered and cylindrical. They may also be used for groove placement and finishing of preparations.
  52. 52. (l)Large carborundum disc (laboratory): Mounted stones, discs, and wheels are all used in finishing cast gold, porcelains, acrylics, and tooth structure. Large, thin carborundum discs quickly section a sprue from a casting. Similar diamond discs can be used to shape bulk porcelain.
  53. 53. (m)Heatless stone (laboratory): Large heatless stones will remove the remnant of the sprue attached to the casting.
  54. 54. (n) Mounted green and white stones (low speed): Various mounted green and white stones exist for straight and contraangle hand pieces. They are not for high speeds. They can be altered by grinding against a coarse/heatless stone. White stones have a finer texture than green stones and are preferable.
  55. 55. (o) Sand paper discs: Sand paper discs of various grits are excellent in finishing marginal areas of castings while maintaining contours. They may also be used in finishing tooth preparations.
  56. 56. (p) Small pin discs: Small-pin sand paper discs are fine for accessible margins in the mouth and finishing axial walls in inlay preparations.
  57. 57. (q) Chamois wheels (laboratory): Chamois wheel are used only with dental rouge and give a luster to the casting.
  58. 58. (r) Rubber burlew discs (laboratory): Rubber burlew discs used after the fine sandpaper stage of finishing provide a smooth surface to the casting. Smaller sulci discs exist for smaller ridge and groove areas but are rarely used intraorally.
  59. 59. (s) Robinson brushes (laboratory): Robinson brushes (stiff, medium, soft) are used with pumice or tripoli. Slow speed with pressure produces greater cutting potential; high speed with light pressure produces a high-lustre finish.
  60. 60. (t) End cutting burs: They are cylindrical in shape with just the end carrying blades. They are very efficient in extending preparations apically without axial reduction. They are numbered from 900 to 904.
  61. 61. Diamond/bur dual instrumentation:   Diamonds remove tooth structure more efficiently than do burs, but they leave undesirably rough surfaces and irregular cavosurface finish lines. Tungsten carbide burs produce smooth finish lines and precise internal features, but they cut more slowly. Therefore, to take advantage of the best features of both types of instrument, diamonds should be used for the bulk reduction and carbide burs for finishing the preparation and placing internal features such as grooves, box forms, isthmuses, etc. The technique of choice in this situation utilizes diamonds and carbide burs of matching size and configuration as described by Lustig. These instruments are manufactured by making both the diamond and bur from a common blank configuration. This assumes that the shape of the instrument and the resultant contour of the tooth will match exactly when the diamond and carbide finishing bur are used for each step of the preparation.
  62. 62.
  63. 63. EFFECTS OF HIGH SPEED CUTTING ENAMEL: Enamel is composed of 92% mineral and 8% of organic material and water. It is recognized as the hardest human tissue. The basic structure of enamel is mushroom shaped enamel rod, which begins at the dentinoenamel junction and ends at enamel surface. Usually enamel originates at right angles to the dentin surface and follows a spiral pattern towards the surface ending at near right angles to the surface. Eccentric burs that do not run true in the high-speed hand piece can produce crazing of the enamel. Crazing can also be brought about by internal stresses, such as might be induced by thermal changes or a retentive pin i.e., angled outward and that has been forced into enamel.
  64. 64. DENTIN Dentin is composed of 65% inorganic material. The remaining 35% is organic matter and water, which allows it to be cut more readily than enamel with a dental bur. Dentin is organized in the form of tubules that are supported by calcified network of collagen fibers. The tubules contain the living extensions of the odontoblasts whose cell bodies are in the periphery of the pulp. Crown preparations involve the exposure of dentinal tubules, cutting of odontoblast processes. Generation of heat, desiccation and pressure. The deeper the dentin is cut, more severly odontoblasts may be damaged. If the water coolant does not reach the interface between the cutting instrument and the tooth surface in the crown preparation a surface “dentin burn” lesion will occur. The odontoblast destruction will be extensive.
  65. 65. PULP The pulp of a tooth is unique among other body tissues or organs. It is very small, but it is able to fulfill sensory and nutritional functions for a tooth. It also forms additional dentin and form provides a defense against infection. The pulp responds very quickly to external stimuli and the response depends on the severity of the stimuli. The degree of pulp reaction is proptionately increased in direct relation to the depth and particularly the extensiveness of crown preparation. If the odontoblasts are injured primarily by desiccation, the disintegration products of these cells will act as an irritant and cause an inflammatory response in the pulp in that area where cut dentinal tubules terminate. When there is dentin burn odontoblast destruction will be extensive. Photo and Schenin (1958) showed if pulp temperature was raised above 46 degree C irreversible changes such as stasis and thrombosis could occur in the pulp. Drying the tooth with a constant air blowing also cause irreversible pulp damage, even if the cavity is prepared under sufficient water coolant. Therefore the preparation should be dried with careful blasts of air at short duration and with sterile cotton after preparation.
  66. 66. Advantages of high speed cutting 1. Increased cutting efficiency. 2. Faster tooth removal, hence less pressure, less vibration and less heat generation. 3. Operator has better control and less fatigue. 4. Great ease of operation. 5. Patients less apprehensive because less vibration, less noise and less operation time. 6. Reduced tension and fatigue for both operator and the patient due to reduced operation time. 7. Greater ease of operation. 8. As a whole, it is possible to manage more patients in less time.
  67. 67. Disadvantages of high speed cutting Desiccation of dentinal tubules.  Impaired visibility due to water spray.  Mechanical injury to soft tissues due to coarse speed. This can be avoided by Using rubber dams. Taking care while removing hand piece.  Over reduction of tooth This can be avoided by properly following the steps during preparation and experience.  Eye damage Due to flying tooth restorative material particles. This can be avoided by protective eyewear for dentist, patient and assistant.  Noise Hi pitched noise from air turbine can cause hearing damage.  Cross contamination Use of face masks for the protection from air borne infections like tuberculosis etc reduces the risk. 
  68. 68. ABRASION AND POLISHING AGENTS   The finishing and polishing of restorative dental materials are important steps in the fabrication of clinically successful restorations. The techniques employed for these procedures are meant not only for removal of excess material but also to smoothen rough surfaces. The finishing of dental restorations prior to their placement in the oral cavity has therefore three benefits:    To promote oral hygiene. Enhance oral function. To improve esthetics.
  69. 69. DESIRABLE CHARACTERISTICS OF AN ABRASIVE     It should be irregular in shape so that it presents a sharp edge. (Jagged particles are more effective. Round sand particles and cubicle particles of sand paper are poor abrasives). It should be harder than the work it abrades. If it cannot indent the surface to be abraded then it cannot cut it and therefore wears out. Abrasive should posses a high impact strength or body strength. Abrasive point should always fracture than dull out so that always, a sharp point or edge is available. The cuts also help in shredding debris accumulated from work for eg, a grinding wheel against a metal. Abrasive should posses attrition resistance so that it does not wear.
  70. 70. DESIGN OF ABRASIVE INSTRUMENTS The abrasives employed could be one of the three types,  Abrasive Grits.  Bonded Abrasives.  Coated Abrasive Disks and Strips.
  71. 71. A. Abrasive Grits Abrasive grits are derived from (abrasive) materials that have been crushed and passed through series of mesh screens to obtain different particle size ranges. The grits are classified as COARSE, MEDIUM COARSE, MEDIUM FINE and SUPER FINE according to the particle size ranges.
  72. 72. B. Bonded Abrasives       These consist of abrasive particles incorporated through a binder to form grinding tools. The abrasive particles are bonded by 4 general methods:  Sintering.  Vitreous bonding (Glass/Ceramic)  Resin bonding (usually phenolic resin).  Rubber bonding (usually silicon rubber). Sintering- Sintered abrasives are the strongest variety since the abrasive particles are fused together. Vitreous bonded- Are mixed with a glassy or ceramic matrix material, cold pressed to the instrument shape and fired to fuse with the binder. Resin bonded- are cold or hot pressed and then heated to cure the resin. Rubber bonded- made in a manner that is similar to resin bonded.
  73. 73. C. Coated Abrasive Disks and Strips These abrasives are supplied as disks and finishing strips. They are fabricated by securing abrasive particles to a flexible backing material (heavy weight paper or Mylar).  The disks are available in different diameters with thin and very thin backings. Moisture – resistant backings are advantageous, as the abrasive stiffness is not reduced by water degradation. 
  74. 74. ABRASIVE ACTION The mode of action of the abrasives is similar to that of the dental burs, that is, it is meraly a cutting action. Each fine abrasive particle thus presents as a sharp edge, which cuts through the surface similar to a pointed chisel. During this cutting process, the shaving thus formed is powdered and usually clogs the abrasive which thus makes periodic cleaning of the abrasive necessary.
  75. 75. FACTORS AFFECTING RATE OF ABRASION Rate of abrasion of a given material by a given abrasive is determined primarily by three factors:  Size of the abrasive particle – larger the size – greater the abrasion.  Pressure of the work against the abrasive. When work is pressed against the abrasive, scratches are deeper and abrasion is more rapid – so greater chances of the abrasives to fracture.  Speed at which the abrasive particles travels across the work. Greater the speed, greater would be the rate of abrasion.
  76. 76. FACTORS INFLUENCING EFFICIENCY OF THE ABRASIVES These factors are as follows:  The hardness of the abrasive particle (diamond is hardest; pumice and garnet etc. are relatively mild).  The shape of the abrasive particle (particles with sharp edge are more effective).  Particle size of the abrasive (longer particle size will cut deeper grooves).  Mechanical properties of the abrasive (If the material breaks, it should form a new cutting edge. Therefore brittleness can be an advantage).  Rate of movement of the abrasive particles (slower abrasion – deeper scratches).  Pressure applied to the abrasive (too much pressure can fracture the abrasive instrument and increase heat of friction that has evolved).  Properties of material that is being abraded. (a brittle material can be rapidly abraded whereas ductile / malleable metal like pure gold will flow instead of being removed by the abrasive).
  77. 77. TYPES OS ABRASIVES    According to Craig : The abrasives used can be classified and grouped as Finishing Abrasives. Polishing Abrasives. Cleaning abrasives.
  78. 78.    Finishing Abrasives These are hard, coarse abrasives used initially to develop desired contours and remove off gross irregularities. Polishing Abrasives These have a smaller particle size and are less hard than abrasives used for finishing. They are used for smoothening surfaces that are typically roughened by finishing abrasives. Cleaning Abrasives These are soft abrasives with small particle size and are intended to remove softer materials that adhere to enamel or a restoration.
  79. 79. 2. Skinner has grouped the abrasives employed in dentistry as follows: A. Natural Abrasives. B. Manufactured Abrasives.
  80. 80. Under Natural Abrasives we have: 1. Arkansas stone - Semi translucent, light gray, siliceous sedimentary rock, mined in Arkansas. - It contains microcrystalline quartz. - Small pieces of this mineral is attached to metal shanks and trued to various shapes for fine grinding of tooth enamel and metal alloys. 2. Chalk - Mineral form of calcite. - Contains calcium carbonate. - Used as mild abrasive paste to polish teeth enamel, gold foil, amalgam and plastic materials.
  81. 81. 3. Corundum - Is largely replaced by alpha Aluminum oxide due to its superior physical properties. However corundum is primarily used for grinding metal alloys and is available as a bonded abrasive. 4. Diamond is a transparent colorless mineral composed of carbon called super abrasive because of its ability to abrade any other known substance. It is used on ceramic and resin based composite materials. Supplied as: Bonded abrasive rotary instrument. Flexible metal backed abrasive strips. Diamond polishing pastes.
  82. 82. 5. Emery - This abrasive is grayish black corundum that is prepared in a fine grain form. - Supplied predominantly as coated abrasive disks. - Used for finishing metal alloys or plastic materials. 6. Garnet – the term garnet includes several minerals which possess similar physical properties like Silicates of Al, Co, Fe, Mg and Mn. - Garnet is dark red, extremely hard and when fractured during abrasive abrasive activity forms sharp chisel shaped plates – therefore making Garnet an effective abrasive. - Garnet is available on coated disks and Arbor box. - Used in grinding metal alloys and plastic materials.
  83. 83. 7. Pumice - Is produced from volcanic activity. - Flour of pumice is an extremely fine grinded volcanic rock derivative from Italy. - Used in polishing teeth enamel, gold foil, dental amalgam and acrylic resins. 8. Quartz – the particles are pulverized to form sharp angular particles which are useful in making coated disks. - Used to finish metal alloys and may be used to grind dental enamel. 9. Sand - Is a mixture of small mineral particles predominantly silica. - Particles have rounded to angular shape. - Used to remove refractory investment material from base metal castings. - It is coated on paper disks for grinding of metal alloys and plastic materials.
  84. 84. 10. Tripoli - Derived from a light weight, siliceous sedimentary rock. - Could be white, gray, pink, red or yellow. - Gray and red are most frequently used. - Used for finishing metal alloys and some plastic materials. 11. Zirconium silicate - Off white mineral, ground to various sizes used to make coated disks and strips. - Also used as a component of dental prophylaxis pastes.
  85. 85. Under Manufactured Abrasives we have: 1. Silicon Carbide - This is the first of the synthetic abrasive to be developed. - Two types were manufactured 1. Green form and 2. Blue form. Both are having similar physical properties. - However, the green variety is preferred because substrates are more visible against the green color. - The cutting efficiency of silicon carbide abrasives is higher as the particles are sharp and break to form new sharp particles. - Supplied as air abrasive in coated disks and vitreous and rubber bonded instruments. - Used in cutting metal alloys, ceramics and plastic materials.
  86. 86. 2. Aluminium Oxide - This is the second synthetic abrasive to be manufactured. - This form of alumina is much harder than its natural counterpart (CORUNDUM) because of its purity. - The forms usually prepared are: a. White stones – made of sintered aluminium oxide are used for contouring of enamel and finishing metal and ceramic materials. b. Variations of aluminium oxide include those with chromium compound additions, these obtained in pink and ruby colours are obtained as vitreous bonded noncontaminating mounted stones – used for preparation of metal ceramic alloys to receive porcelain.
  87. 87. 3. Synthetic Diamond – developed in 1955. - Synthetic or manufactured for of diamond is produced at 5 times the level of the natural diamond abrasive. - This synthetic diamond is used for the manufacture of diamond saws, wheels and burs and also diamond locks employed for truing of bonded abrasives. - Synthetic diamond abrasives are used primarily on tooth structure, ceramic materials and resin based components.
  88. 88. 4. Rouge - Principle component is iron oxide blended with various binders. - Used to polish high noble metal alloys. - May be impregnated in paper or fabric known as CROCUS CLOTH. 5. Tin Oxide - Is composed of very fine abrasive particles. - May be employed in an abrasive paste form along with water, alcohol or glycerin. - Used as a polishing agent for teeth and metallic restorations.
  89. 89. REVIEW OF LITERATURE 1. In 1952, Lawrence H. Clayman described the modern techniques for the full crown and plastic faced gold veneer crown preparations using diamond instruments. The introduction of diamond cutting instruments into dentistry has been a great aid for crown and bridge prosthesis. Diamond instruments have enabled us to prepare teeth faster and have also reduced trauma incident to operative dentistry procedures by cutting more efficiently, more quickly, and with less friction and resulting heat. For maximum cutting efficiency, diamond instruments should be used at high speed with light pressure and should be well lubricated by a continuous stream of water.
  90. 90. 2. In 1953, Edwin S. Smyd mentions the importance of diamond tools in dentistry; diamond tools are distinct from burs or cutting tools in that they work by a scoring action, that is, each diamond particle scrapes off the surface of the object it is abrading to the depth of the diamond protruding from the tool. Light pressure minimizes frictional heat. Experimental studies in Germany indicates that diamond tools are best used wet or dry in a moist loose slurry of the abraded material- both too much water and dryness should be avoided. Diamond tools are not selective in their grinding action. They will grind enamel, dentin and cementum at equal rate.
  91. 91. 3. In 1957, Rex Ingraham, did an evaluation of recent progress in the field of increased speeds and modern instrument design. Increased speeds for the rotary instruments is one of the newest fields in dental science and one involving the most rapid and dramatic changes in the history of the profession. The ultra high speeds (above the threshold of vibration perception) produce a favorable response. Operating at about 10,000 rpm and above requires only a light ‘feather like’ touch which reduces digital fatigue for the operator. However, it becomes necessary to operate with much more exactness and a keen visual sense must be employed to safeguard against overcutting and inadvertent damage to adjacent tooth surfaces.
  92. 92. 4. In 1958, Allison G. James, discussed the subject of high speeds and concluded that unless steps are taken to bring adequate instruction to the vast majority of dentists who are influenced to use high speed rotary instruments, it may be anticipated that an era of slovenly tooth preparations will plague dentistry for some time to come. 5. In 1959, Edmund V. Street, did a critical evaluation of ultrasonics in dentistry and concluded that pulps of vital permanent teeth appear to be unaffected, but operations on children’s teeth should not be attempted until future research indicates no ill effects. The ultrasonic method of cutting instruments carious or sound enamel, carious or sound dentin and certain types of restorative materials does not approach the effectiveness that can be demonstrated with the ultra high speed rotational instruments.
  93. 93. 6. In 1960, Alexander Leff, did an evaluation of high speed in full coverage preparations. From a practical point of view, high speed can be defined as rotational speeds starting at 1, 00,000 rpm. This is the beginning range of speed at which tools can be used efficiently with light pressure. 7. In 1965, Schuchard and Watkins, compared the efficiency of rotary cutting instruments. a. Any of the high or low torque rotary cutting equipment will operate efficiently in its useful range, if properly used. b. The various low torque ultrahigh speed contra angle instruments are comparable, and are most efficient at the higher operating air pressures. c. Simplicity of design and size of equipment are significant in evaluation. d. High torque air driven straight hand pieces are not as efficient as comparable electric driven equipment.
  94. 94. 8. In 1970, Charles Watkins, elaborated on the cutting effectiveness of rotary instruments in a turbine hand piece and concluded that in enamel, diamond cutting instruments compare favorably with TC burs. The carbide burs remove dentin more rapidly than do the diamond points. The ‘lubricating’ effect of water to enhance the cutting effectiveness of diamonds in not documented in this study. 9. In 1988, Robert Cooley et al, did a study on the effect of air powder abrasive instrument on porcelain. The effects of an air powder abrasive instrument on porcelain were evaluated. Sample disks made from two commercial porcelains and three porcelain strains were treated for 80 seconds with this instrument. It was recommended that the air powder abrasive instrument be used cautiously or not at all on porcelain restorations, especially those with staining and / or specific characterizations.
  95. 95. 10. In 1988, Price and Sutow, conducted a micrographic and profilometric evaluation of the finish produced by diamond and TC finishing burs on enamel and dentin and concluded thata. Minimal marginal chipping combined with low surface roughness suggests that a superfine diamond is indicated for producing clinically acceptable margins on all surfaces of the teeth. b. Where the rotation of the bur was away from the margin, multifluted tungsten carbide burs frequently produced chipping of the enamel margin.
  96. 96. 11. In 1988, Prattern and Johnson, did an evaluation of finishing instruments for an anterior and a posterior composite. The same finishing instruments and techniques revealed no significant differences in the surface roughness of the anterior and posterior composites. The smoothest surface was achieved with Mylar strips; the smoothest instrumented surface was achieved with a series of abrasive disks, but a fine diamond bur with 25 um particles produced the roughest surface. However an X-fine diamond with 15 um particles produced a surface smoothness superior to that produced with a white stone and similar to the smoothness produced with a carbide bur and rubber point. Diamond finishing with slow speed produced a somewhat smooth finish than with high speed.
  97. 97. 12. In 1988, Jeffrey Norlandes and Dennis wies and Warren Stoffer, studied the taper of clinical preparations for fixed prosthodontics and concluded thata. The ideal convergence angle of 4-10 degrees is seldom achieved in clinical practice. b. Mean convergence angles for mandibular preparations were greater than mean maxillary convergence angles. c. No significant differences were found between the mean convergence angles of crowns and FPD retainers. d. Auxiliary retention should be used in the molar region because these preparations were found to have large convergence angles.
  98. 98. 13. In 1990, Robert W. Schutt, did a procedure to sterilize dental burs with dry heat. a. After dental treatment, debride the bur and wipe dry with gauze. Both short and long shank burs can be used. b. Place the burs in screw-cap 13 x 100 mm glass test tubes with a maximum of 10 burs per tube. c. Place the tubes in wire racks and insert in a dry heat even at a monitored temperature of 170 degree C for a minimum period of 60 minutes. d. After the sterilization period, remove the wire racks and allow the tubes to cool. The glass tubes containing the sterile burs may be stored and indefinitely and will maintain the sterility of the burs.
  99. 99. 14. In 1991, Kevin M. Gureckis et al, conducted a study on the cutting effectiveness of diamond instruments subjected to cyclic sterilization methods and concluded thata. The cutting effectiveness of rotary dental diamond instruments was not influenced by the sterilization method. b. There are considerable differences in the cutting efficiency of new individual diamond instruments. 15. In 1999, a study was done which investigated a new diamond rotary instrument made of a continuous diamond film obtained by chemical vapor deposition (CVD). This bur characterized by a pure diamond cutting surface without metallic binder between crystals was compared with a conventional diamond bur and they came down to a conclusion that the new CVD bur not only proves to be more efficient in its cutting ability and longevity, but also excludes the risk of metal contamination.
  100. 100. 16. In 2001, Katoh Y and Sunico M, did a study on the newly developed diamond points and said that the rapid decrease in size of dental restorations has increased the demand for the smallest rotary cutting instrument possible. The width of cavities prepared with two experimental diamond points and the smallest commercial diamond point were compared and significant differences found. SEM observation of the head surfaces of the three diamond points revealed that the experimental points had comparable cutting characteristics with the commercial diamond point.
  101. 101. 17. In 2002, Bruno Neves Cavalcanti, Choyu Otani and Sigmourmello Rode, did a study and evaluated the efficiency of 3 different water flows for 2 different tooth preparation techniques to determine which one is safe for use. Cavity and tooth preparations generate heat because the use of rotary cutting instruments on dental tissues creates friction. Dental pulps cannot survive temperature increases greater than 5.5 degree C. The results of this study confirms that thenecessity of using a low-load technique and water coolants during cavity and tooth preparation procedures.
  102. 102. SUMMARY AND CONCLUSION Tooth preparations for cast restorations have been influenced at least in part, by the technology of instrumentation. This is seen in the development of hand pieces and power sources as well as in the evolution of abrasives and cutting instruments. This seminar considers all the aspects of instrumentation in fixed prosthodontics and is based on the current available literature.
  103. 103. REFRENCES       M A Marzouk- Operative Dentistry, modern theory and practice. Herbert T Shillingburg- Fundamentals of fixed prosthodontics- third edition. Tylman’s- Theory and practice of fixed prosthodonticseight edition. Stephen F Rosenstiel- Contemporary fixed prosthodontics. Gerald T Charbeneau- Principles and practice of operative dentistry. Sturdewant’s- Art and science of operative dentistryfourth edition.
  104. 104.       Bruno Neves Cavalcanti, Choyu otani, Sigmar mello rode- High speed cavity cutting preparation techniques with different water flows.JPD 87(2) 158-161, FEB 2002. Katoh Y, Sunico M- Newly developed diamond points for conservative operative procedures.Oper Dent 2001 Jan 26(1)76-80. Dental diamond burs made with a new technology.JPD 1999 July, 82(1), 73-79. Kevin Guruckes- Cutting effectiveness of diamond instruments subjected cyclic sterilization. JPD 1991, 56 300-306. Robert Schutt- Sterilization of dental burs with dry heat. JPD 1990,42 22-26. Pratten and Johnson- Evaluation of finishing instruments for an anterior and a posterior composite.JPD 1988, 38, 362-365.
  105. 105.       Price and Sutow- Micrographic and profilometric evaluation of the finish produced by diamond and tungsten carbide finishing burs on enamel and dentin. JPD 1988; Vol39,30-35. Robert Colley- Effect of air powder abrasive instrument on porcelain.JPD1988,vol39,88-92. Jeffrey Norchlander & Dennis Wies & Warren ClofferTips of clinical preparation for fixed prosthodontia.JPD 1988;Vol38,42-46. Charles Watkins- Cutting effectiveness of rotary instruments in a turbine hand piece. JPD 1970; Vol 19; 88-105. Schuchard & Watkins- Comparison of cutting efficiency of tungsten carbide burs and diamond points at ultra high rotational speeds. JPD 1967; Vol 20; 362-366. Schuchard & Watkins- Comparison of efficiency of rotary cutting instruments. JP 1965; Vol 18; 25-28.
  106. 106.      Alexander Leff- Evaluation of high speed in full coverage preparations. JPD 1960; Vol 10; 220-224. Allison G. James- High speeds. JPD 1958; Vol 8; 168-172. Rex Ingraham- Evaluation of recent progress in the field of increased speeds and modern instrument design. JPD 1957; Vol 7; 112-118. Edwin Smyd- Importance of diamond tools in dentistry. JPD 1953; Vol 3; 361-364. Lawrence Claywan- Modern techniques for full crown and plastic faced gold veneer crown preparations using diamond instruments. JPD 1952; Vol 2; 272-276.
  107. 107.      Griscome- History of dentistry-Weinburg. Robert Arthur- History of dentistryWeinburg Archigenes- History of dentistryWeinburg; ‘Instrumentation’. Dendel & Zweiling- History of dentistryWeinburg; ‘Instrumentation’. Brown et al- Operative dentistry by Sturdevant; Cutting instruments.
  108. 108. THANK YOU