3. OPERATIVE INSTRUMENTS.pptx11111111111

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1. INSTRUMENTS IN OPERATIVE DENTISTRY Presented by, Dr. Monisha Tiwari MDS I Year Guided by, Dr. Rana .K. Varghese, Prof. and Head Dr. Gururaj . M, Reader Dr. Rishidev Yadav , Reader Dr. Minal Daga,Sr . Lecturer

2. CONTENTS : Introduction Classification of Instruments Parts of Instruments Instruments nomenclature Instrument formula Instrument design

3. Mechanism of cutting Instruments Hazards with cutting Instruments References

4. Introduction : > In order to properly prepare a cavity ,the tooth tissues ,enamel and dentin must be excised with specific instruments in an efficiently ordered sequence . > Most cavity preparations required the use of both rotary and hand instruments . > Rotary burs and diamonds are used for gross reduction ,creating angulation and final refinement of the cavity preparation . .

5. >The hand cutting instruments are used to produce intricate details of the cavity preparation and finish the restorative material . > In the use of hand cutting instruments ,there is no vibration ,pressure or pain element as compared to high speed instruments.

6. HAND INSTRUMENTS

7. Classification of Instruments >According to GV Blacks : 1.Cutting instruments a. Hand-cutting instruments -Hatchets -Chisels -Hoes -Excavators b. Rotary instruments -Burs -Stone -Discs

8. 2. Condensing instruments a. Condenser/Pluggers 3. Plastic instruments - Plastic filling instruments - Cement cariers - Carvers - Burnishers - Spatulas

9. 4. Finishing and polishing instruments: A .HAND B. ROTARY - Orangewood sticks -Finishing burs -Polishing points -Mounted brushes -Finishing strips -Mounted stones -Rubber cups

10. 5.Isolation Instruments: - Rubber dam - Saliva ejector - Cotton roll holder - Evacuating tips and equipment

11. 6.Miscellaneous Instruments: -Mouth mirrors -Explorers -Probes -Scissors

12. > According to Marzouck : 1.Exploring instruments : - Tweezers - Retractors - Probes - Separators

13. 2. Instruments for tooth structure removal: a. Hand cutting -Excavators -Chisels -Special form of chisels b. Handpiece -Burs -Ultrasonic

14. Classification (Acc. to Sturdevant) Cutting (excavators ,chisels and others) 2. Non-cutting (amalgam condenser , mouth mirrors , explorer and probes)

15. Nomenclature of instruments : In establishing a nomenclature for hand instruments , Dr. Black prescribed four classes ,similar to a biological classification : Order - Purpose of instrument .

16. Suborder - Position or manner of use . Class - Form of working end. Subclass - Shape of the shank.

17. Designs characteristics of Hand Cutting Instruments

18. Designs of some early hand instruments

19. Blade or Nib: Also may be appropriately termed the point or head. This is the functional end of the instrument.

20. B . Shank: Connecting the shaft and blade or nib. The shank may be straight or single or double or triple-angle.

21. C .Handle: Small ,medium or large diameter smooth, knurled or serrated.

22. Material used to make hand instruments : Stainless steel Carbon steel Blades of tungsten carbide

23. Principles of cutting instrument : 1.Direct cutting and lateral cutting instruments: A direct cutting instrument is one in which the force is applied in the same plane as that of the blade and the handle.

24. It is called a “single planed” instrument . USES: Single planed instruments can be used in direct and lateral cutting.

25. LATERAL CUTTING : Lateral cutting instruments are those in which the force is applied at a right angle to the plane of the blade and the handle . These usually have a curved blade and are called “double plane” instruments.

26. Double planed instruments have an angle or curve in a plane at an angle right angle to that of the handle . USES : It can be used only in lateral cutting .  

27. 2.CONTRANGLING: In order to gain access, many instruments have the shank bent at one or more points to angle the blade relative to the handle . The extent of this arrangement depends on the length of the blade and the degree of angulation in the shank.

28. Accordingly, the working point is moved out of line with the axis of the handle. If this occur more than 3mm from the handle axis , the instrument will be out of balance in lateral cutting motions, and force will be required to keep the instrument from rotating in the hand .

29. To solve this problem , modern instruments are designed to have one or more angles in the shank placing the working point within 3mm from the axis of the handle. This principle of design is called contrangling.

30. The length of the blade required is determined by the depth of the cavity and the blade angle is determined by the accessibility requirements.

31. It follows, then ,that greater angles are necessary for more posterior teeth and incisal portions of proximal cavities in anterior teeth. So , in addition to balance ,contrangling will provide better access and a clearer view for the field of operation.

32. 3 . RIGHT AND LEFT INSTRUMENTS : Direct cutting instruments are made either right or left by placing a bevel on one side of the blade .

33. If the instrument is held with the cutting edge down and pointing away from the operator and bevel is on the right side , it will be a “right” instrument. If the bevel is on the left ,it will be a left instrument .

34. As mentioned before , these are single-planed instruments , and for direct cutting acts the non- bevelled side of the blade should be in contact with the wall being shaved . For lateral cutting acts ,always move the instrument in a scrapping action from the beveled side to the non beveled side of the blade.

35. 4.SINGLE BEVELLED INSTRUMENTS :   These are all single planed instruments with the cutting edge at a right angle to the long axis of the shaft . They all are designed like carpenter’s chisel.

36. If they are regularly beveled on the side away from the shaft ,they are called “distally beveled”. If they are beveled on side of the blade away from the shaft ,they are called “mesially beveled”.

37. When these types of instruments have no angle in the shank ,or an angle of 12 degree or less, they are used in push (direct cutting) and scrapping motions. If this angle in the shank exceeds 12 degree ,the instrument could be used in pull(distally beveled) and push (mesially beveled) motions

38. 5. BIBEVELED INSTRUMENTS : Only hatchets and straight chisel can be bibeveled. The blade is equally beveled on both sides , and they cut by pushing them in the direction of the long axis of the blade.

39. 6. TRIPLE BEVELLED INSTRUMENTS : Bevelling the blade laterally , together with the end, forms three distinct cutting edges. Most modern single planed instruments especially the small ones , are triple beveled , affording the instrument an additional cutting potential which is very useful.

40. 7.CIRCUMFERENTIAL BEVELLED INSTRUMENTS : It usually occurs in double planed instruments where the blade is beveled at all peripheries .

41. 8.SINGLE ENDED AND DOUBLE ENDED INSTRUMENTS: Most modern instruments are double ended, Incorporating the right and left or the mesial and distal form of the instrument in the same handle .

42. Single ended instruments are confined now to those type of instruments have only one specific function . Single planed instruments with no angle in the shank have the potential for five cutting movements-

43. Vertical (parallel to the long axis of the blade) Right Left Push and Pull.

44. Cutting Instruments Bevels : Most hand cutting instruments have on the end of the blade a single bevel that forms the primary cutting edge. Two additional edges ,called secondary cutting edges.

45. Bi-beveled instruments, such as ordinary hatchets , have two bevels that form the cutting edge. Certain single-beveled instruments , such as spoon excavators and gingival marginal trimmers , are used with a scrapping or lateral cutting motion .

46. Black’s Instrument Formula It established an instrument formula that describes the dimension and angulation of the hand instrument.

47. The basic instrument formula consists of three units those measurements are based upon the metric system : The first unit of the formula describes the width of the blade in tenths of millimeter. The second unit describes the length of the blade in millimeter.

48. The basic instrument formula consists of three units those measurements are based upon the metric system : The first unit of the formula describes the width of the blade in tenths of millimeter. The second unit describes the length of the blade in millimeter.

49. The third unit describes the angle of the blade forms with the axis of the handle. This angle is expressed in “hundredths” of a circle or centigrades. By this simple three unit formula , an instrument such as the “binangle hatchet” has a formula 15-8-12.

50. This formula accurately describes the type, dimension ,and angulation of this specific instrument:   15-blade width 1.5 mm 8 –blade length 8 mm 12 –blade angled 12 centigrades from axis of handle or shaft.  

51. When the cutting edge and face of an instrument is at an angle other than a right angle to the length of the blade , a fourth unit is added to the basic three unit formula. This additional number , expressed in centigrades , represents the angle formed between cutting edge and central axis of the shaft.

52. It is placed in the second position of the formula. The gingival marginal trimmer has a formula 12-92-10-8. The second unit “92” indicates that , in addition to a blade width of 1.2mm,a blade length of 10mm,and a blade angle of 8 centigrades with shaft axis , the cutting edge of the blade is at an angle of 92 centigrades with the axis of the shaft.

53. TYPES OF HAND INSTRUMENTS :

54. CHISEL: It is characterised by a blade that terminates in a cutting edge formed by a one-sided bevel. The cutting edge of the chisel is an right angle to the plane of the instrument.

55. STRAIGHT CHISELS : They have straight blade in line with the handle and shank . The cutting edge is on one side only , with the bevel of the blade running at a right angle to the shaft.

56. They are single-planed instruments with five possible cutting movements .

57. MONOANGLE CHISELS : They are similar to straight chisels ,except the blade is placed at an angle to the shaft. It may be mesially or distally bevelled .  

58. BINANGLE CHISELS : The chisel blade is placed at a slight angle with the shaft as in the hoe . Like all chisels , it may be mesially or distally bevelled. As the name indicates , there are the two angle between the shaft and the blade .

59. The three aforementioned chisels are all used to cleave or split undermined enamel .

60. TRIPLE-ANGLE CHISEL : They have three angles in its shank and it is usually used to flatten pulpal floors . It may be mesially or distally bevelled .  The monoangle , binangle , or , triple angle chisels are single-planed instruments.

61. All possess three possible cutting movements :vertical , right and left .

62. The mesially bevelled chisels can cut in push movements ,while the distally bevelled ones can cut in pull motions .   USES : A chisel is an excavater primarily used for planning or cleaving enamel and dentin.   Direction of motion : Push motion  

63. 2.HOE: -

64. It is form of chisel in which the angle of the blade is greater than 12.5 centigrades. Uses: It is used to smooth and shape the floor and form line angles in class III and class V restorations.

65. Also used for cutting mesial and distal walls of molars and premolars. Direction of motion : Pull motion.  

66. Types: Monoangle Binangle     Instrument formula : 6-2-12(Right) 12-6-10(left)  

67. 3.HATCHETS:

68. The hatchet shank has one or more angles or curves. The blade is in same plane as this angle or angles , parallel with the shaft.

69. A chisel bladed instrument with the cutting edge in the plane of the instrument is termed as hatchet . These instruments are either paired ,one with a left and other with a right bevel or they may be right bevelled .

70. Viewing the instrument from its working end when the cutting edge is to the right, the instrument is referred to as the “right” of the pair. Conversely , with the cutting edge to the left that instrument becomes the “left” of the pair.

71. Uses : Paired binangle enamel hatchets , right and left , are used for planning and cleaving enamel and dentin walls during cavity preparation. Frequently , these are proximal and gingival walls where access or position would dictate their use.

72. Instrument formula : 15-8-12 Direction of movements: Vertical, push ,pull ,and either right or left lateral cutting.

73. 4. WEDELSTAEDT CHISEL :

74. It is like a straight chisel ,but with a slight curvature in its shank. It is bevelled on one side of the blade only.

75. If this bevel is on the side toward the curvature on the shank, it is mesially bevelled ,if it is on the side of the blade away from the curvature ,it is distally bevelled. They are single planed instruments ,with three cutting motions ; vertical ,right ,and left .

76. USES: It is used for cleaving undermined enamel and for shaping walls . The mesially bevelled can be used in push movements , and the distally bevelled can be used in pull motions.

77. 5 . TRIANGULAR CHISEL :

78. This chisel has a blade which is triangular in shape ,with the base of the triangle away from the shaft . It has a terminal cutting edge like the straight chisel .

79. 6. ANGLE FORMER : The cutting edge of the angle former is sharpened at an angle to the axis of the blade. The angle of the cutting edge to the blade axis of the angle former is usually 80 to 85 centigrades.

80. The acute cutting angle being directed to the right or to the left makes the angle former always a paired instrument. The right of the pair is identified by an intended ring on the shaft or shank .

81. Uses : To accentuate line and point angles in the internal outline form in cavities for cohesive gold to establish retention form. The action of the instrument is essentially one of lateral scrapping. To place bevel on enamel margins.

82. Instrument formula : 8-80-3-9

83. 7.GINGIVAL MARGINAL TRIMMER : It is modified hatchet .  

84. GMT are also a paired instruments and are referred to as “left” and “right” . It is also a lateral cutting instrument so further divided into two ; mesial and distal. It is a double–plane instrument having a curved blade.

85. Uses : Used essentially for bevelling gingival cavosurface margins , both mesially and distally. Distal GMT is designed to plane or bevel the cavosurface margins of distal proximal amalgam and certain inlay preparations.

86. Mesial marginal trimmer is used to plane the mesial cervical margin.

87. 7.SPOON EXCAVATER :

88. It is a double-plane instrument that is modified hatchet. Its cutting edge is rounded. As its name , action is spooning or scooping carious material.

89. Like a double-plane instruments , the spoon is designed for lateral scrapping. It is always a paired instrument , with the curved of one blade directed from right to left and that of the other from left to right.

90. Uses : Removal of carious dentin. Instrument formula : 8-6-12

91. 8.CLEOID-DISCOID INSTRUMENT:

92. The “cleoid” or “claw-like” and the “discoid” or disk like ,hand cutting instrument is a modified double-ended chisel. It provide sharp cutting edges similar in design to the spoon ,but with the blade to the shaft .

93. Uses : For carious removal. Also used as a carving instrument for amalgam and wax . Instrument formula : 10-2-12

94. KNIVES : It is known as finishing knives, amalgam knives ,or gold knives. Most universal is the Bard-Parker knives. Some knives are made for the specific purposes.

95. USES : Wilson’s knife ,used inter-proximally for proximal and gingival manipulation of the restorative materials . Stein’s knife ,which has a trapezoidal nib , is used mainly for direct gold restoration and margination .

96. Also , used for trimming excess restorative material on the gingival , facial, or lingual margins of a proximal restoration or trimming and contouring the surface of a class v restoration .

97. FILES : The nib of the file can be foot-shaped , hatchet-shaped or parallelogram-shaped . USES : Used to trim excess restorative material. Used for margination of restorations .

98. CONDENSING INSTRUMENT Condenser :

99. It may be single or double ended instrument . Most of these instruments have angles and curvatures in their shanks. The nibs have different shapes , e.g., rounded, triangular, diamond, rectangular, parallelogram etc.

100. It may be smooth or serrated . It can be hand or mechanical in nature. Uses : It is used to condense the restorative material in to the prepared cavity.

101. 3. PLASTIC INSTRUMENT :

102. Within this class are an enormous number of instruments . They all differ mainly in the shape of their nibs and angulation or curvature in their shanks. They all have a flat sided nib with blunt edges and corners.

103. They may be made of stainless steel, ivorine or plastic. They also can be plated with teflon to minimize material adhesion to facilitate easy cleaning.

104. USES : They all can be used for carrying and handling materials after mixing while the materials are in their plastic stage.

105. CARVERS :

106. These are basically cutting instruments with their blades (nibs) either bevelled or knife-edged (elongated bibevelling). The most universally used carvers are Hollenback carvers, which possess double-sided knife-edged, point-edged nibs, with curved monangled or binangled shanks.

107. They are very efficient in carving both amalgam and wax. There are considerable number of special forms of carvers, such as those with triangular nibs , or diamond shaped nibs.

108. Uses : To contour the restoration approximately same to original tooth structure. Sharp cutting edges present in carvers are used to shapen and form tooth anatomy from a restorations.

109. Hollenback carvers are used for carving proximal surfaces. Diamond shape carvers are used for carving occlusal surfaces.

110. BURNISHERS :

111. Burnishers are the kind of instruments which make the surface shiny by rubbing. Burnishers have smooth rounded working ends and come in single and double-ended instruments.

112. Types : Ball burnisher Egg shaped burnisher T-shaped burnisher

113. Ball burnisher a. small b .large Tear drop shape burnisher Peer shaped burnisher Bever tailed burnisher

114. Uses: Final condensation of amalgam . Initial shaping of occlusal anatomy of amalgam. Shaping of metal matrix bands. Burnishing margins of cast gold restorations.

115. ISOLATION INSTRUMENTS :

116. 1.Rubber dam :

117. Rubber dam affords protection from instrumentation and chemicals for the gingiva and periodontal tissues when it is properly applied . Uses : To isolate the operating field .  

118. 2.Saliva ejector :

119. Saliva ejector may be of three types : Metallic type Plastic type Svedopter (saliva ejector with tongue retractor )

120. USES : Moisture control systems , which aid in providing suction , retraction ,illumination and jaw opening support are available .

121. MISCELLANEOUS INSTRUMENT

122. Mouth mirrors :

123. Classification : 1.On the basis of sizes of mirror: No.2 - 5/8” dm No.4 - 7/8” dm No.5 - 15/16” dm ( No.4 and No.5 are commonly used sizes) .

124. 2.On the basis of mirror : Plain Convex 3.On the basis of surface : Front Rear

125. 4.On the basis of material : Plastic Metal   5. On the basis of joint : Cone socket One piece

126. 6. On the basis of number of surfaces: One sided Two sided 7. On the basis of shaft design : Bended Non-bended  

127. USES : Mouth mirrors are used to provide a clear and distinct vision of operating area . FUNCTIONS : Help in direct visualization of the field of operation .

128. Reflect the operating light and thus illuminate the operating area . Provide indirect visualization of obscure areas of the mouth . Retract the soft tissues like the tongue , cheeks or lips .

129. Explorers :

130. Explorer is commonly used as a diagnostic aid in evaluating condition of teeth especially pits and fissures. Parts : Handle of explorer is straight which could be plain or serrated .

131. Shank of explorer is curved with one /more angle. Working tip of explorer is pointed.

132. Types of explorer : Straight explorer: It is bent perpendicular to the handle. This is used for examing occlusal surfaces of teeth .

133. Shepherd’s Crook or curved explorer It has semilunar -shaped working tip perpendicular to the handle. This is used for examing occlusal surfaces.

134. Interproximal explorer : Commonly used for examination of interproximal surfaces of teeth . It is pointed instruments used for tactile examination of tooth surfaces and restorations to identify any irregularities .  

135. 3 . Probes - Straight probe :

136. USES : Used for a general examination. Used to detect occlusal caries . Blunt end is used to detect tenderness.

137. Periodontal probe :

138. USES : i . Used to detect and measure pocket depth . ii . Used to detect the recession .

139. 7. Tweezer : Cotton tweezers or pliers have angled tips .

140. Types: 1.College no.17 2.Meriam no.18   Uses: Used to place cotton roll during cavity preparation for isolation.

141. They can also carry small items like cotton pellets to dry the teeth .

142. RETRACTOR :

143. USES : i . Used for retract lip , tongue , cheek etc.

144. SEPERATORS :

145. USES : For examination of initial proximal caries . Providing proper accessibility to proximal area during preparation of teeth and polishing of restorations . Helps in placement of matrix. Also used to remove foreign bodies .

146. Advantages of Hand Cutting Instruments : They are self limited in cutting enamel ,i.e. they will not cut sound enamel ,but will cut only undermined enamel.

147. Can remove large pieces of under-mined enamel quickly thus saves time and effort. No vibration or heat is produced during cutting. Are the most efficient way for precise intricate cutting .

148. Can create the smoothest surface of all cutting instruments . Have the longest life span provided if they are resharpened .

149. INSTRUMENT STERLIZATION AND DISINFECTION : Dental instruments utilized in the treatment of patients must be considered contaminated .

150. Because potentially pathogenic micro- organisms are everpresent , instrument must be treated in such a manner as to eliminate the transmission of potentially disease producing forms of microbial life to another patient. Sterlization implies the complete destruction of all microbial life ,including spores and resistant viruses .

151. Commonly, dental instruments are sterilized by : Autoclaving (saturated steam under pressure) Application of dry heat, Application of gas (ethylene oxide)

152. The autoclave is the most reliable sterlization device available. Instruments , textiles ,and glassware can be sterilized effectively in a reasonable period of time.

153. Steam under pressure of 15 pounds increases the boiling point to a temperature of 121 degree celcius for 10 minutes at which all known organisms are destroyed. In dentistry, disinfection commonly has been accompalished by –

154. Immersion in chemical solution Use of boiling water Use of hot oil (mineral and silicone) Flaming .

155. When acceptable sterlization methods are not possible to use ,disinfection can be carried out by the following methods : Immersion in 100 degree celcius (boiling) water for 30 minutes.

156. Soaking in activated 2 % alkaline glutareldehyde for atleast 10 minutes . Immersion in 1 % sodium hypochlorite (1.5 dilution of commercial liquid chlorine bleach) for 10 minutes. One to 2 % formaldehyde for 20 to 30 minutes.

157. STORAGE : Storage of any hand cutting instruments should be in a sterile , wrapped tray setup or in an individual sterile wrapping .

158. ROTARY CUTTING INSTRUMENTS

159. Rotary instruments are the most universally used instruments for gross removal of tooth structure . The term “rotary” applied to tooth cutting instruments describes a group of instruments that turn on a axis to perform work .

160. Applied to dental procedures ,the character of work performed is primarily: Cutting Abrading Burnishing Finishing and Polishing tooth tissues or various restorative materials.

161. The rotational speed of an instrument is measured in revolutions per minute (rpm). Three speed ranges are generally recognised (According to Charbeneau) : a. Conventional or low speed: Below 10,000 rpm

162. b. Increased or high speeds- 10,000 to 150,000 rpm c. Ultrahigh speeds- Above 150,000 rpm

163. The following are the characteristics of rotary instrumentation :  SPEED : Speed refers not only to the revolutions per minute , but also to the surface feet per unit time of contact that the tool has with the work to be cut.

164. For dental purposes we classify speeds as follows (According to Marzouk ) : A .Ultra-low speed (300-3000 RPM) B .Low-speed (3000-6000 RPM) C .Medium high speed (20,000-45,000 RPM)

165. D .High speed (45,000-100,000 RPM) E .Ultra-high speed (100,000 RPM and more)

166. PRESSURE : It is resultant effect of two factors under the control of the dentist . 1.Force(F) :The gripping of the handpiece and its positioning and application of the tooth .

167. 2.Area (A) :The amount of surface area of the cutting tool in contact with the tooth surface during a cutting operation . Pressure relates as follows : P =F/A

168. 3.Heat production: Heat is directly proportional to : a. Pressure b. RPM c. Area of tooth in contact with the tool

169. VIBRATION : Vibration is not only a major annoying factor for the patient ,but it also causes fatigue for the operator, excessive wear of instruments and most importantly , a destructive reactions and the tooth and supporting tissues .

170. PATIENT REACTION : The factors that cause patient apprehension consist primarily of heat production , vibrational sensation ,length of operating time, and number of visits .

171. OPERATOR FATIGUE : The major causes for fatigue are :duration of operation, vibration produced in the handpiece, forces needed to control the rotating instrument, apprehension on the part of the dentist, regarding the possibility of producing a pulp exposure or injuring adjacent oral, intra-and paraoral tissues , and lack of patient co-operation .

172. SOURCES OF POWER : The introduction in the 1950’s of the air turbine as a power source changed the shape of dental practice. The belt driven handpiece was rendered absolute for operatory use . The air turbine remains the main power source .

173. INSTRUMENT DESIGN : Instrument design for rotary instrumentation should be evaluated in two parameters: one ,the handpiece, which will hold and provide power for the cutting tool; and two ,the cutting tool itself (bur , stone , etc).

174. 1 .Handpiece : Handpieces come in a variety of sizes and shapes :straight , contra-angled ,and right-angled. Each is designed for a specific range of functions

175. They will retain the cutting tool by a screw-in ,latch, or friction grip type of attachment . The following criteria should be used in evaluating handpieces :

176. A. Friction : It will occur in the moving parts of a handpieces , especially the turbine. B. Torque : Torque is dependent upon the type of bearing used and the amount of energy supplied to the hand piece.  

177. 2.THE ROTARY TOOLS FOR THE REMOVAL OF TOOTH STRUCTURE : 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.

178. A . Dental cutting burs : The term bur is applied to all rotary cutting instruments that have bladed cutting heads.

179. Every bur will have a three parts : The head - it is the portion carrying the cutting blade. The shank – portion connecting the head to the attachment part. The attachment part –the portion which will be engaged within the handpiece.

180. It includes : i . Instruments intended for finishing metal restorations . ii . Surgical removal of bone . iii . Instruments primarily intended for tooth preparation .

181. Historical development of dental burs : First machine made bur introduced in 1891. Early burs were made of steel . Carbide burs were introduced in 1947.

182. I .Composition and manufacture : Dental burs can be classified by their composition in two types ; a. Steel bur b. Tungsten carbide bur

183. ii. General designs of dental burs: The dental bur is a small milling (cutting) instrument.

184. a. Bur tooth : This terminates in the cutting edge, or blade. b. Rake angle : It is most important design characteristic of bur blade .

185. The rake angle is the angle that the face of the bur tooth makes with the radial line from the center of the bur to the blade. Negative rake angle minimizes fracture of cutting edge and increases tool life. It is said to be negative when rake face is ahead of the radius .

186. 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).

187. 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 . c. Land : The plane surface immediately following the cutting edge.

188. d. Clearence 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 the work.

189. When the back surface of the tooth is curved, the clearance is called radial clearance. f. Flute or chip space : The space between successive teeth .

190. CLASSIFICATION OF BURS : According to Marzouk : 1 .According to their mode of attachment to the handpiece dental burs can be classified as: A . Latch type B . Friction grip type

191. 2 .May be classified according to the handpiece they are designed for , i.e ; A . Contrangle bur B . Straight hand piece bur  

192. 4.According to the length of the blade ,bur can be classified as : A . Long B . Short ( pedominiature) C . Regular

193. 5.According to their shapes and sizes, they may be classified as follows: a .Round burs : They are numbered from ¼ , ½ , 1,2,to 10. They are round in shape. They are used for initial tooth penetration and for the placement of retention grooves .

194. B .Wheel burs: They are numbered as 14 and 15. They are wheel shape. They are used to place grooves and for gross removal of tooth structure .

195. C .Inverted cone burs : They are numbered from 33 ¼,33 ½, 34,35 ,to 39. They are an inverted cone shape. They used mainly for cavity extension and occasionaly for establishing wall angulations and retention forms .

196. D .Plain cylindrical fissure bur : They are numbered from 55 to 59. The bur teeth can be cut parallel to the long axis of the bur, which are designed straight or cut obliquely to the long axis of the teeth, which are called spiral.

197. E .Cross cut cylindrical fissure bur : They are numbered 555,556 ,to 560. Their teeth can also be cut parallel to the long axis of the bur(straight)or obliquely(spiral). They are used for gross cutting ,cavity extension and creation of walls .

198. F . Plain tapered fissure bur : They are numbered from 168,169,to 172. They have a tapered cylindrical head; their teeth can be straight or spiral. 

199. G . End-cutting burs : They are numbered from 900 to 904. They are cylindrical in shape , with just the end carrying blades . They are very efficient in extending preparations apically without axial reduction .  

200. Factors influencing the cutting efficiency of burs : 1.Rake angle : The more positive the rake angle is, the greater is the bur’s cutting efficiency. Also burs with radial rake angles cut more effectively than designs with negative rake angles.

201. 2.Clearance angle :

202. This angle provides clearance between the work and the cutting edge to prevent the tooth back from rubbing on the work. There is always a component of frictional force on any cutting edge as it rubs against the surface , following the dislodgement of the chip.

203. 4. Run-out : It refers to the maximum displacement of the bur head from its axis of rotation while the bur turns .

204. The average value of clinically acceptable run-out is about 0.023mm. Run-out is depend not only on the eccentricity of the bur itself but also depend on the precision on the dental handpiece.

205. 5.Depth of cutting : As the depth of cutting is decreased, the force intensity on each small portion of the bur tooth still cutting is correspondingly increased and accordingly the average displacement per flute revolution should also be increased.

206. Procedures For Tooth Tissue Removal With Rotary Instruments : The practical application of rotary procedures associated with cavity preparation is best categorized by the following classifications :

207. Penetration Extension Excavation Refinement With some exceptions ,penetration is most effectively carried out at ultra speeds of rotation.

208. DENTAL ABRASIVE STONES : Abrasives Such as carborundum (green) or alumdum (white or pink) Fixed directly into bur shank. Abrasive particles are held together by means of “binder”(base)of variable nature.

209. According to the composition of the abrasive particles ,dental stones can be classified as follows: Diamond stones Carbides Sand Aluminium oxide Garnet  

210. Types of dental stones : Mounted Unmounted

211. FINISHING AND POLISHING INSTRUMENTS : Most of these are rotary type instruments : 1.Finishing burs : It should be atleast 12 fluted . However, some of them are upto 40 fluted.

212. They may be made of stainless steel (for amalgam) or tungsten carbide (for composite resin). They do not grossly cut the restorative materials, but only remove the excesses, creating a smoother surface. Such burs come in different shapes, e.g ,. rounded ,apple-shaped, pear-shaped, flame-shaped , tapered, cylindrical, inverted cone .  

213. 2. Paper-carried abrasives : These are usually sand, cuttle , garnet or boron carbide glued to paper discs or strips . The paper discs should be attached to a mandrel(screw-in or screw headed) for rotary finishing. The paper strip carried abrasives are used by hand in a back and forth motion similar to a shoe polishing action .

214. 3. Brushes : They come in different forms , e.g , wheels, cylinders , cones etc. They can be screwed in the handpiece , attached to a mandrel ,or have their own frictional attachment extension . Brushes can be used be alone or with intermediate abrasive pastes .

215. 4. Rubber : Plain ,rubber ended rotary tools are essential for polishing procedure. They come in variety of shapes , e.g.,cups wheels , cones etc. They can be attached to the handpiece either via mandrel, a screw-in device , or their own frictional or latch extension .  

216. HAZARDS WITH CUTTING INSTRUMENTS For patients there are pulpal dangers from the tooth preparation and restoration procedures. There also are soft tissue dangers . Everyone is potentially susceptible to eye , ear and inhalation dangers .

217. REFERENCES : Art and Science of Operative Dentistry, Sturdevant ,5 th edition. Fundamentals of Operative Dentistry, James.B.Summitt,2 nd edition. Picards manual of Operative Dentistry, 8 th edition.

218. Operative dentistry ,Modern Theory and Practice , M.A.Marzouk , First Edition. Principles and practice of Operative Dentistry , Gerald T. Charbeneau , third edition.

219. THANK YOU