DENTAL BURS OTHER MODALITIES OF TOOTH PREPARATION Dr

DENTAL BURS & OTHER MODALITIES OF TOOTH PREPARATION Dr. Ashok kumar, Dept of Conservative Dentistry & Endodontics 6 - 9 - 2014

DENTAL BURS Burs are rotary cutting instruments that have bladed cutting heads. This includes instruments intended for such purpose as finishing metal restorations & surgical removal of bone, as well as those primarily intended for tooth preparation.

HISTORICAL DEVELOPMENT q Earliest burs were hand made and intented to be use with hand powered finger rings. These were made of stainless steel. q Carbide burs introduced in 1947, have now replaced steel burs & steel burs are nowadays used only for some finishing procedures.

STEEL BURS Steel burs are cut from a 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 no. is 800 Steel burs perform well at low speed but dull rapidly at high speed. Steel burs cut dentin more efficiently than enamel.

CARBIDE BURS Tungsten carbide burs are product of metallurgy. The tungsten carbide powder is mixed with powdered cobalt under pressure & heated in vaccum. A blank is then formed & the bur is cut from it with a diamond tool. VHN – 1650 -1700 Carbide burs perform better than steel burs at all speeds & their superiority is greatest at high speeds.

DESIGN CHARACTERISTICS Each bur consist of three parts: 1. shank 2. neck 3. head

SHANK Part that fits in handpiece, accepts the rotary motion & provides a bearing surface to control the alignment & concentricity of the instrument. Design & dimensions vary with the hand piece. Acc. To ADA sp. No. 23 there are 5 classes of shanks of which 3 are most commonly used: A. the straight hand piece shank B. the latch type contraangle handpiece shank C. the friction grip contraangle hand piece shank

NECK It is intermediate portion that connects head with the shank. It transmits rotational & translational forces to the head. It tapers from a large cross-section(shank) to a smaller diameter immediately adjacent to the head. This improves access & visibility.

HEAD Head is the working part of the instrument, the cutting edges or points that perform the desired shaping of the tooth structure. Its shape & material are closely related to its applications & technique of use.

BUR BLADE DESIGN The actual cutting action of a bur occurs in very small region at the edge of the blade. Each blade has 2 sides- the rake face - the clearance face/trailing edge 3 Angles - the rake angle - the clearance angle - the edge angle Flute / chip space : is the space b/w successive bur teeth/blades.

BUR BLADE DESIGN

The optimal value of these angles depends upon the: -mechanical properties of blade material -mechanical properties of the material being cut -the rotational speed & diameter of the bur -the lateral force applied by the operator to the handpiece & to the bur. q If land is present-primary & secondary clearance angle are present q If back surface is curved – radial clearance angle

FACTORS AFFECTING THE CUTTING EFFICIENCY OF BURS 1. RAKE ANGLE: more +ve the rake angle=greater cutting efficiency Radial rake angle = more efficient than –ve rake angle +ve rake angle – chips are larger & clog the chip space -ve rake angle – cut chips move away from the blade For brittle materials- -ve rake angle desirable Materials of low hardness eg. stainless steel should be used with –ve rake angle & hard materials eg. carbide burs can be used with +ve rake angle.

2. CLEARANCE ANGLE Greater clearance angle – greater chip spaceless edge angle-increased chance of fracture. To overcome this problem Clearance face is curved / landed. 3. EDGE ANGLE More the edge angle – less chances of blade fracture Cardide burs are brittle- require greater edge angle

4. NO. OF TEETH/BLADES & THEIR DISTRIBUTION No. of teeth – 6 -8 Increase in no. of flutes-increased heat production & reduced cutting efficiency-good for finishing & polishing A fissure bur with straight flutes produces less temp. rise than one with spiral flutes 5. FINISH OF THE FLUTES Highly finished flutes show greater efficiency

6. HEAT TREATMENT Used to harden a bur made of soft steel. 7. DESIGN OF FLUTE DESIGN 2 types of flute end The relevation cut: flutes come together at the junctions near the diametrical cutting edge. The star cut: the end flutes come together in a common junction at the axis of the bur. The relevation type superior in direct cutting but in lateral cutting both equally efficient

8. BUR DIAMETER Volume of material removed vary with bur diameter os well as torque & energy supplied by power source 9. DEPTH OF ENGAGEMENT Decrease in depth of engagement – increase in force intensity on bur & volume of material removed

10. INFLUENCE OF LOAD It is force exerted by dentist on the tool head Load = 1/rotational speed of the bur For low speed – 1000 -1500 gm For high speed – 60 -120 gm

11. INFLUENCE OF SPEED Rate of increase in cutting is greater b/w 30000 – 1, 50, 000 rpm With constant load, rate of cutting increases with rotational speed 12. RUN-OUT Refers to the eccentricity or max. displacement of the bur head from axis of rotationwhile the bur turns Average value -. 023 mm

BUR CLASSIFICATION SYSTEM: Can be classified in no. of ways: a. )Acc. To the mode of attachment of handpiece -latch type -friction grip b. )Acc. To their composition -stainless steel -tungsten carbide combination c. )Acc. To their motion -right bur -left bur -

d. )Acc. To the length of bur head -long -short -regular e. )Acc. To their use -cutting bur -finishing & polishing bur f. )Acc. To their shape -round -inverted cone -pear shaped -wheel shaped -tapered fissure -straight fissure etc.

BUR SHAPES ROUND BUR: -used for initial tooth penetration & for placement of retentive grooves -Are numbered as ¼, ½, 1, 2 to 10

INVERTED CONE BUR: -head length is approx. the same as the diameter. -portion of rapidly tapering cone with the apex directed towards the bur shank -Used for providing undercuts in tooth prep -numbered as 331/4, 331/2, 34, 35 to 39.

PEAR SHAPED BUR -slightly tapered cone with the small end of the cone directed toward the bur shank -normal length – for class. I gold foil tooth prep. -long length(L=3 W) – for tooth prep. for amalgam -numbered as- 229 -333

STRAIGHT FISSURE BUR -used for amalgam cavity prep. -modified burs of this design are available -numbered as- 55 -59 TAPERED FISSURE BUR -slightly tapered cone with the small end of the cone directed away from the bur shank. -numbered as – 168, 169 -172

BUR SIZES Original numbering system by SS White dental manufacturing company grouped burs into 9 shapes & 11 sizes ½ , ¼ were later added for smaller instruments Crosscut was indicated by adding 5 OO to the no. of the equivalent non-crosscut size eg. no. 57 as 557 End cutting bur was indicated by adding 900 to the equivalent size eg. no. 57 as 957. Round nose fissure bur was indicated by adding 1 to the equivalent size of the fissure bur eg. no. 57 as 157

MODIFICATIONS IN THE BUR DESIGN Modifications in bur design were seen with the introduction of high speed handpieces: 1. Size of the bur 2. Reduced use of cross-cuts 3. Rounding of sharp tip angles

ABRASIVE INSTRUMENTS: Second major category of rotary cutting instruments. Small angular particles of hard substance held in matrix of softer material (binder). Binder can be ceramic, metal, rubber, shellac etc. Rubber & shellac are used for finishing & polishing. Cutting occurs at a large no. of points where hard particles protude from the binder.

ABRASIVE INSTRUMENTS CAN BE GROUPED AS: 1. Diamond Abrasives 2. Non-Diamond abrasives -Molded abrasive instruments silicon carbide(carborandum) Aluminium oxide -Coated abrasive instrument garnet quartz pumice

DIAMOND ABRASIVE INSTRUMENT: For dental use were introduced in 1942 Their preference over tungsten carbide burs is based on their greater resistance to abrasion, lower heat generation & longer life Consist of three parts: - a metal blank - powdered diamond abrasive - bonding material

ON THE BASIS OF PARTICLE SIZE DIAMOND ABRASIVE CAN BE CLASSIFIED AS: coarse : 125 -150 microm particle size medium : 88 -125 micron fine : 60 -74 micron very fine : 38 -44 micron -coarse & medium are used for gross cutting -fine & very fine are used for refining & finishing of tooth preparation.

DIAMOND ABRASIVE HEAD SHAPE & SIZES Available in shapes & sizes that corresponds to the burs except the smallest diameter bur. Due to lack of any standard & uniform nomenclature it can be selected visually to obtain the desired shape & size.

FACTORS INFLUENCING THE ABRASIVE EFFICIENCY & EFFECTIVENESS Size of the abrasive particles Shape of the abrasive particles- should be irregular Density of the abrasive particles- refers to the no. of abrasive particles/area Hardness of the abrasive particles-should be greater than the hardness of the work. Clogging of the abrasive particles Speed & pressure

DISPOSABLE DIAMOND ABRASIVES: “ single patient use” bur is a recent introduction to risk of cross contamination Some of the marketed disposable diamond burs are cobra, monosteryl, neo, patriot, SS white & spring.

ADVANTAGES OF BURS & ABRASIVES It is familiar & well known procedure. Precision is obtained i. e. margins are clearly identifiable. It is easy to control the cutting. The practitioner has tactile perception of the extent of cutting. Debris can be removed by water lavage & use of suction. Practitioner’s vision while cutting is relatively good.

DISADVANTAGES OF BURS & ABRASIVES Cutting with these instruments usually causes pain Vibration usually cracks/fractures tooth Noise Constant use & sterilization cause them to break down Dull burs produce lot of heat & pulpal damage Overcutting if operator loses control or pt. moves inadvertently

EVALUATION OF CUTTING Measured in terms of effectiveness & efficiency. Cutting Effectiveness: is the rate of tooth structure removal(mm/min or mg/s). Effectiveness doesn’t consider side effects eg. heat, noise Cutting Efficiency: is the % of energy actually producing cutting

CUTTING MECHANISM: Rotary instrument cutting can be of 2 types: 1. BLADED CUTTING: with burs 2. ABRASIVE CUTTING: with abrasives

245 BUR Multi purpose or all in one bur. It is a non standard carbide bur that do not conform to the current ADA standard numbering system. It is a pear shaped long length bur. used for amalgam class II cavity preparation. No need to change the bur during cavity prep.

SITE SPECIFIC BURS FOR CONSERVATIVE PREPARATION IN PREVENTIVE RESIN RESTORATION Originally , smaller burs e. g no. 1/2, 1 round, 331/2 inverted cone were recommended for preparing PRRs. Recently new burs that are thin enough to allow easy penetration into pits & fissures are introduced – FISSUROTOMY BURS (SS white burs, lakewood, new jersey) These burs allow the clinician to prepare the pit & fissure in many cases owing to the smaller surface area of the tip.

FISSUROTOMY BURS ARE AVAILABLE IN THREE CONFIGURATIONS: 1. Fissurotomy original(1. 1 mm wide by 2. 5 mm long) 2. Fissurotomy micro NTF(0. 7 mm wide by 2. 5 mm long) 3. Fissurotomy micro STF(0. 6 mm wide by 1. 5 mm long) other manufacturers have developed thin diamonds to mimic the fissurotomy shape

POLYMER BUR Recently , a unique polymer instruments, the SMARTBUR has been introduced SMARTBURS are available in round shapes – RA no. 2, RA no. 4, RA no. 6 with an innovative flute design. q It has hardness less than healthy enamel & dentin but harder than carious dentin to remove carious tooth structure without damaging healthy tooth structure.

Polymer burs are used at slow rotary speed of 500 -800 rpm using light touch with a slow speed handpiece & a latch contra angle attachment.

PRECAUTIONS Pulpal precautions: -damage occur by exposure to vibration, heat, dessication. -it is hazardous to use them in prep. Deeper than. 5 -1 mm from the pulp -for removal of dentin 2 mm or more from the pulp carbide burs are efficient. Soft tissue precautions: Rubber dam, cotton rolls, retractors must be practiced to avoid soft tissue injury.

Eye precautions -Protective glasses are always indicated when rotary instrumentation is being used Inhalation precautions -Aerosols & vapors created by cutting tooth structure a health hazard. -Use of evacuators, face mask, rubber dam protects the patient from inhalation.

LASER TOOTH PREPARATION First introduced to dentistry in 1989. Introduction of yttrium-scandium-galliumgarnet(YSGG) allowed for the preparation of enamel, dentin & carious tooth structure. The YSGG laser cuts hard tissues using a pulsed high energy photonic laser beam at 2780 nm. The focussed laser beam allows for precise tooth structure removal in T/t of carious lesions of all sizes.

KINETIC CAVITY PREPARATION The concept of application of Kinetic energy in the field of dentistry was conceived as early as 1945, Dr. R. B. Black ‘AIR ABRASIVE TECHNIQUE’ technique was invented in 1951 which is now modified and improved as Kinetic Cavity Preparation (KCP) system

THE COMPONENTS OF KCP UNIT 1. Precision built device containing a source of suitable gaseous propellant and means of regulating its pressure. 2. Reservoirs for containing abrasive materials. 3. An intricately designed disposable handpiece where tip is made up of sintered tungsten carbide with an inner diameter of 0. 45 mm.

4. Device for recovering spent abrasive powder and debris 5. Master switch for activation of the machine and Foot control. 6. The other components are: Movable cabinet, Gauges and dials for controls, a suction hood with an accessory.

Abrasive particles: The KCP system utilizes particles of alpha alumina. The particle size varies form 10 -50 u with an average size of 27 u. It has a Mohs scale hardness of 9. 04. Magnesium carbonate or dolomite is also used as abrasive but it is chosen for prophylaxis as it has properties of softness and less weight.

Propellant: Though compressed air can be used as a propellant, the gas propellant of choice is carbon dioxide because the former is not free from moisture. Carbon dioxide with average pressure of 700 -1300 PSI which is being reduced to 8045 PSI at the tip of the handpiece is used. The flow of gas is approximately 1/3 cubic foot/minutes.

ADVANTAGES OF KCP SYSTEM: 1. Performs conservative cavity preparation rapidly and precisely usually without anesthesia 2. Old filling materials like composites can be removed quickly. 3. Modifies enamel and doubles the bond strength of dentine thereby allowing a strong bond without acid etching.

4. Facilitates the maintenance of a dry operating field. 5. It eliminates objectionable features of vibration bone conducted noise, pressure and heat. By eliminating vibration, the KCP system also reduces the risk of microfracture and chipping which may lead to premature failures of the restoration. 6. It not only saves steps and time but also make it possible for a dentist to perform multiquadrant restorations in a single visit. A typical KCP takes just 20 -30 seconds. This speed, combined with the elimination of LA in most cases maximize productivity

DISADVANTAGES OF KCP SYSTEM 1. Use limited to areas of good vision. 2. No Tactile sensation between the handpiece and tooth surface to act as a guide while cutting. 3. Precise angles and margins difficult to obtain. 4. Mirror surface was made useless in a short of time by rebounding the abrasive particles. 5. Possible ill effects due to inhalation of abrasive particles

The drawbacks of Airbrasive Technique' can be eliminated as follows: 1. Fibroptic light, halogen light improve the field of vision. 2. Though there is no sense of touch between the handpiece and tooth surface, the improved visibility can guide in cutting. 3. Conservative cavity preparation need not have precise angles and margins. 4. Scratch free mirror be used. 5. Extensive research regarding the ill effects of abrasive particles concluded that the amount of alumina particle inhaled is far below the detectable limits

INDICATIONS 1. Mainly for MID, specially for composites without the use of acid etching. 2. Sealant therapy. 3. For pits & class I preparation 4. Removal of old composites, amalgam filling, # porcelain facing & porcelain jackets. 5. For removal of high points on crown 6. To remove casting irregularities & to modify surface that will receive porcelain. It is done with 50 u alumina particles for 30 sec. 7. For prophylaxis 8. Moderate class II & V 9. Access opening in Endo therapy 10. As an adjunct to rotary instruments for all dental preparations.

IF “ THE ART OF BEING WISE IS THE ART OF KNOWING WHAT TO OVERLOOK WHAT NOT”