Rotary Cutting Instruments

Rotary Cutting InstrumentsGUIDED BY: -Dr. Mandeep Grewal -Dr. Prashant Bhasin -Dr Vijaya DharPresented By:Dixit Arora

The term rotary cutting instruments refers to a group of instruments that turn on an axis to perform cutting ,abrading ,burnishing ,finishing or polishing tooth structure or a restoration.It comprises of two devices: 1)Handpiece-these are the power devices. 2)Burs or abrasives-these are the cutting tools.Evolution Of Rotary Cutting Equipment In DentistryYear Instrument Speed(rpm)1728 Hand-rotated instruments 3001871 Foot engine 7001874 Electric engine 1,0001914 Dental unit 5,0001942 Diamond cutting instruments 1947 Tungsten carbide burs1946-50 Modified versions of old equipment 15,000-60,0001953 Ball-bearing handpieces 25,0001955 Water turbine contra-angle handpiece 50,000 1957 Air turbine contra-angle handpiece 250,000 1994 Contemporary air turbine handpiece 300,000Handpiece Is a device for holding rotating instruments transmitting power to them ,and for positioning them intraorally. Speed Range: 1)Low Speed- below 12,000rpm 2)Medium Speed- 12,000-200,000rpm 3)High Speed- Over 200,000rpm Two Types: a)Straight Handpiece b)Contra-angle HandpieceStraight HandpieceThe long axis of the bur is the same as the long axis of the handpiece. Frequently Used in LAB work

Contra-angle HandpieceUsed in mouthHead first angled away then back towards the long axis of the Handpiece Improved access and visibility while in use.Two types:Micromoter HandpieceAirotor Handpiece

Micromotor Handpiece: Attached to electric micromotor . Speed Range 500-50000 rpmLess speed higher torque Also provided with a water spray

Air rotor Handpiece: Connected to air water line Activated with compressed air Speed Range about 200000 rpm Higher speed Low Torque Water spray dissipates the Heat produced Also available With Fiber Optic Light for better illumination

Dental Bur A bur is a rotary cutting instrument which has a bladed cutting head.Parts of a Bur:ShankNeck Head

ShankFits into handpieceAccept rotary motionProvides bearing surface to control the alignment of the instrument.Types:Straight handpiece shankLatch-type angle handpiece shankFriction-grip angle handpiece shank

Straight handpiece shankSimple cylindricalHeld by a metal chuckCommonly used for finishing & polishing

Latch-type shankShorter lengthPosterior portion is flattenedImproved access to posterior region of mouthUsed in contra-angle micromotor handpieceRetained by a latch that slides into the groove found at the shank end.Used at low & medium speed for finishing proceduresPotential wobble controlled by lateral pressure during cutting.

Friction-grip shankSmaller then latch typeImproved accessSimple cylindricalHeld by friction b/w the shank & a plastic or metal chuck.

NeckIntermediate portion ,connects the head to the shank.Tapers from the shank diameter to a smaller size immediately adjacent to the headDesign allows the greatest possible visibilityHeadWorking part of the instrument ,the cutting edges or points that perform the desired shaping of tooth structure.Characteristics of head form classify rotary instrument

Stainless steel burFirst material usedUseful to cut dentin at slow speedDull rapidly at higher speed which decreases cutting efficiency causing increased heat and vibration.Not effective in cutting enamelUsed for removing soft carious dentin &finishing procedures.

Carbide bursBetter then steel bur at all speedHeads of cemented tungsten carbide held in matrix of cobalt & nickleCarbide is stiffer & stronger then steel , but it is also more brittle.

ShapesRefers to contour or silhouette of the headRound burIs sphericalUsed for 1) initial entery into the tooth 2) Extension of the preparation 3) preparation of retention feature 4) caries removal

Inverted cone burRapidly tapered cone with apex toward the shankHead length is same as the diameterUsed for providing undercuts in tooth preparation.

Pear shaped burSlightly tapered cone with apex toward the shankHead end is continuously curved or is flat with rounded cornersLength is greater then the widthAdvocated for class 1 preparation

Straight fissure burElongated cylinderAdvocated for amalgam preparationSlightly curved tip angles are also available

Tapered fissure burSlightly tapered cone with the small end of the cone directed away from the bur shank.Used for indirect restorations to get freedom from undercutsAlso available as flat end with the tip corner slightly rounded.

SizesThe no. designating bur size also traditionally has served as a code for head design.Numbering system was originated by the S.S. White Dental manufacturing Company in 1891 for their first machine made burs.

Modification in Bur DesignReduced use of cross-cut burs as they produce unduly rough surfaces at high speedExtended head length for effective cutting with extremely high pressureRounding of the sharp tip corners of the bur head to create rounded internal line angles in the cavity preparation.Bur Blade DesignBlades has two sides: 1)Rake Face: surface of the bur blade on the leading edge of the bur 2)Clearance Face: surface on the trailing edgeThree angles: 1)Rake Angle: -b/w rake face and the radial line -Negative: rake face is ahead of radial line -Positive: rake face trails the radial line -Zero: rake face & radial line coincide with each other 2)Clearance Angle: b/w the clearance face & tooth surface 3)Edge Angle: b/w rake face & clearance face

Concentricity Measure symmetry of bur head when the bur is staticIndicate whether blades are uniform or notRun outMeasure maximum displacement of the bur head from its axis of rotation when bur is in motionOccurs when neck is bent head is not in line with the axis of the burIncreases the vibrationProduces excessive removal of tooth strGenerates more heat Diamond Abrasive instrumentDiamond abrasives held by metallic bonding on a steel blankGrater resistance to abrasionLesser heat generationMore efficient Available in various particle size: Coarse- 125-150um Medium- 88-125um Fine- 60-74um Very Fine- 38-44um

Cutting MechanismFor effective cutting bur should be used at high speedAdequate pressure must be applied so that blade digs into the tooth strTooth str undergoes brittle & ductile fractureHazards with rotary cutting instrumentPulpal damage: due to mechanical vibrations or heat generationSoft tissue damage: due to lack of access, visibility, sudden reflex movement by the patientDamage to eye: due to airborne particles such as bits of old restoration, tooth debris etcEar dangers: due to loud noise produces from handpieceInhalation dangers: aerosols and vapours created by cutting instruments can be inhaled by the patient or dentist and can cause irritation and tissue reaction in the lungs.Thank you