Instruments & Instrumentation Year 2 PDF

Instruments & Instrumentation The British University in Egypt Faculty of Dentistry Operative Department INSTRUMENTS & INSTRUMENTATION Year 2 1  Instruments & Instrumentation Instruments & instrumentati...

Instruments & Instrumentation The British University in Egypt Faculty of Dentistry Operative Department INSTRUMENTS & INSTRUMENTATION Year 2 1  Instruments & Instrumentation Instruments & instrumentation General classification of operative instruments: They are classified according to their use into: 1) Instruments used for Isolation of the operative field 2) Instruments used for Exploring the operative field 3) Instruments used for Removal of tooth substance 4) Instruments used for Manipulation & Packing of restorations 5) Instruments used for Shaping of restorations (Plastic instruments) 6) Instruments used for Finishing and Polishing purposes 7) Miscellaneous instruments 1. Instruments used for Isolation of operative field: It is used to keep the operative field dry, for example: û Using rubber dam à for complete isolation of the field. û Saliva ejector & high suction evacuation. û Cotton roll holder. 2. Instruments used for Exploring the operative field: û Using mouth mirrors & explorers. û Single ended explorer is preferred than double ended to prevent injury by the other end. û Magnifying loups, microscopes and intraoral cameras. 2  Instruments & Instrumentation Exploring instruments Exploring probe Composed of the following parts: 1) Handle or shaft → Serrated or angulated for proper grasping without slippage. 2) Shank → Curved or straight according to accessibility. 3) Exploring tip → Very pointed and sharp rod. Used for: 1) Exploring the presence or absence of caries (probe catch). 2) Determine the consistency of carious dentin either soft or hard by tactile sensation. 3) Carving of restoration especially in areas of supplemental grooves. Types: 1) Straight explorer. 2) Right angle explorer. 3) Inter-proximal explorer. 4) Arch explorer. The periodontal probe Cannot be used for exploring. It is used to detect the depth of periodontal pockets and the dimensions of instruments & preparations. 3  Instruments & Instrumentation 3. Instruments used for removal of tooth substance: a. Hand cutting instruments b. Powered cutting instruments Powered cutting instruments i. Rotary cutting instruments: Burs & abrasive à used for cavity preparation ii. Air abrasion: Air stream + abrasive particles (Aluminum oxide) à remove tooth structure by abrasion. Advantages: 1. Remove tooth structure with minimal heat generation. 2. Painless procedure. Disadvantages: 1. The dentist loses its tactile sensation 2. No definite cavity can be obtained. iii. Laser (waterlase) It is absorbed by the tooth & converted into heat à destruction à necrosis à evaporation (ablasion of the tooth structure) Advantages: Laser mainly used in soft tissues as it has harmful effect on the hard tissues. 4  Instruments & Instrumentation Disadvantages: 1. Heat generation affect the pulp. 2. No definite walls & margins. 3. No tactile sensation. 4. Very expensive. iv. Sonic instruments: They are cutting ends provided with abrasive particles (diamond) on one side & no abrasive particles on the other side à cutting by one side only à to prevent injury of adjacent tooth. Advantages: prevent injury of adjacent tooth (safe-sided tool) Disadvantages: ò cutting efficiency. v. Chemo-mechanical methods (Carisolv) Carisolv gel has been introduced to be used with specially designed non-cutting hand instruments to abrade the carious dentin surface. The gel applied, using the hand instrument, onto the exposed carious dentin and left for 60 seconds prior to abrading away the softened dentin to leave a hard, caries-free cavity. vi. Enzymes Pronase, a non-specific proteolytic enzyme helps to remove carious dentin. 5  Instruments & Instrumentation Cutting instruments a) Hand cutting instruments Definition Hand hold instruments used to cut or cleave enamel or/and dentin, and to plan the walls of the prepared cavity. Parts of hand cutting instrument Any hand cutting instrument composed of: a) Shaft or handle. b) Shank. c) Blade. a) Shaft or handle. Shape: Serrated or angulated to avoid instrument slippage during cutting. Function: Grasping. It carries: 1. Manufacturer’s name. 2. Name of designer. 3. kit number. 4. Black’s formula. 5. Indicating marks (R or L to indicate right or left). b) Shank: It may be straight or contra-angled. Function: Connecting the shaft to the blade. C) Blade: Called “NIB” especially in condensers and burnishers (non cutting instruments). Functions: Bearing the function of the instrument. 6  Instruments & Instrumentation Black’s formula: Definition: A group of figures describing the measurement of the instrument and written on the center of the shaft. Black’s formula includes the followings: 1. First number: Width of blade in tenth of mm. 2. Second number: Length of blade in mm. 3. Third number: Angle of blade from the long axis of the shaft in centigrade. 4. Fourth number: Angle of the cutting edge from the long axis of the shaft in centigrade. Fourth number is added only when à the cutting edge is not perpendicular to long axis of the blade. When it is added, it should be written in the site of the second number, i.e arrangement will be 1, 4, 2, and 3. 7  Instruments & Instrumentation Material of the instruments: P.O.C Carbon Steel Stainless Steal Advantages a. They keep sharpness ñ corrosion resistance b. ñ cutting efficiency Disadvantages a. ò corrosion resistance a. They do not keep sharpness b. Brittleness b. ò cutting efficiency 8  Instruments & Instrumentation Types and classification of hand cutting instruments: a) According to use: I. Excavators. II. Chisels. b) According to direction of cutting: I. Direct cutting: The plane of force coincides with plane of work (single plane). II. Lateral cutting: The plane of force does not coincide with the plane of work. (Double plane). c) According to beveling: i. Single beveled instruments (right or left, mesial or distal) ii. Bi-beveled instruments (bi-beveled hatchet) iii. Triple beveled instruments (Angle former) iv. Circumferential bevels (excavators) d) According to no. of ends: i. Single-ended ii. Double-ended e) According to contra-angling: Definition: additional angle or angles to bring the working end of the blade or nib within 2 to 3 mm from the central axis of the handle to give balance & better accessibility. 9  Instruments & Instrumentation Types: i. Straight ii. Mono-angle (A) iii. Bin-angle. (B) iv. Triple-angled. (C) I. Excavators Functions: 1. Excavation and removal of soft carious dentin. (In dentin only) 2. Shaping of the internal cavity walls. 3. Could be used for carving of amalgam Types: 1) Spoon excavator: The blade is spoon shaped. Used with lateral scrapping action. Large instrument could be used for carving of amalgam. 10  Instruments & Instrumentation 2) Discoid excavator: The blade is circular in form. Used mainly in anterior teeth. It could be used for carving of amalgam or wax. 3) Cleoid excavator: Sharp pointed blade in the form of a claw, Could be used for carving of amalgam or wax. II. Chisels Functions: Planning of enamel undermined either by caries or by cutting dentin away with a bur. (undermined enamel only) Types of chisels: 1) Straight chisel: Used for planning and cleaving enamel. Has no angles in the shank. The set is only one instrument. Described with “3” figures of Black’s formula. Has only single bevel forming the cutting edge. 11  Instruments & Instrumentation 2) Mono-angle chisel: Used to define line and point angles. Has one angle in the shank. The set is two instruments, mesial and distal. 3) Bin-angle chisel: Used to remove enamel rods with a push action. Have two angles in the shank. The set is two instruments, mesial and distal. 4) Wedel steadt chisel: It is modified straight chisel: - Slight curvature starting from the shank up to the cutting edge (about 5º). - The set is two instruments, mesial and distal. 5) Angel former: Used for accentuation of line and point angle in cavities of gold foil restoration. It is a modified straight chisel. The modifications are: i. Triple beveled blade. ii. The cutting edge is not perpendicular to the long axis of the blade. 12  Instruments & Instrumentation The set is two instruments either right or left. It has “4” figures of Black’s formula. 6) Enamel hatchet: Used to cleave enamel from the cavity walls. The set is two instruments, either right or left. 7) Gingival marginal trimmer (GMT): It is a modified enamel hatchet. The set is “4” instruments: Mesial: → Right & left Distal: → Right & Left Uses: 1) Used for trimming of gingival margin (gingival CSA). 2) Roundation of axio-pulpal line angle à avoid stress concentration 3) Reverse Bevel formation in cast gold cavity (lateral means of retention) à gingival lock 13  Instruments & Instrumentation Advantages of Hand over Rotary cutting instruments 1. It will not cut into sound tooth structure à more conservative cutting. 2. It produces no vibration or heat generation 3. High cutting efficiency à saving time and effort. 4. It produces smoother, better finished surfaces. 5. Have longer life span. Instrument grasps, rests and guards a) Grasps: 1. Pen grasp. 2. Palm and thumb grasp. 3. Modified palm and thumb grasp. 1. Pen grasp: The instrument is hold between the thumb and first two fingers to offer the best control This grasp is used for: 1. Delicate work. 2. Finishing of enamel wall. 3. When direct vision is possible. 2. Palm and thumb grasp: This grasp is used for: 1. Upper teeth especially palatal surface of anterior teeth. 2. When more force is needed during cutting. 14  Instruments & Instrumentation 3. Modified palm and thumb grasp: It is only a slight variation of the two just described grasps. b) Rests: Fingers that are not used in holding they are used to support and prevent slippage. c) Guards: Fingers of the opposite hand to prevent injury of the adjacent tissues. b) Rotary cutting instruments The system composed of: 1) Cutting points: è Burs: Having blades and used for cutting. è Abrasives: Having abrasive surfaces and used for abrasion. 2) Hand piece: According to type: è Latch type – used with low speed è Friction grip – used with high speed According to power source: Electric motors Airotors § Driven by electric motors § Driven by a source of compressed air § Operating speed was low (5000- § Speeds may be increased to over 15,000 rpm) 800,000 rpm 15  Instruments & Instrumentation According to shape: Straight handpieces Contra-angle handpieces Mainly used in laboratory procedures Either low-speed or high-speed According to speed ranges: 1) Low or slow speeds (below 12,000 rpm) 2) Medium or intermediate speeds (12,000 to 200,000 rpm) 3) High or ultrahigh speeds (above 200,000 rpm) The advantages of using high speed are: 1. Remove tooth structure faster with less pressure and vibration. 2. The operator has better control due to the lower Level of vibration produced, 3. The patient is less apprehensive. 4. Several teeth in the same arch can be treated at the same appointment. 16  Instruments & Instrumentation I. Dental cutting burs Ÿ Classification of burs: A) According to material: 1. Tungsten carbide: à High hardness number (Vicker hardness no. 1700) à High melting points à Can withstand heat generation without damage (â dulling) à Accurate in design à Cut in E & D at high speed à Very brittle & expensive 2. Steel: à Low hardness number (Vicker harness no. 600) à Low melting point à Cannot withstand heat generation without damage (á dulling) à Not accurate in design à Cut in E & D at low speed B) According to the shape of working head: 1. Rounded: Used for: - Gaining access during cavity preparation. - Excavation of hard carious dentin. - Placing retentive grooves and pinholes. - Shaping of casted metallic restoration. 17  Instruments & Instrumentation 2. Inverted cone: used for: - Lateral extension of cavity walls by undermining the enamel. - Placing the retentive mechanical undercuts. - Sizes: 33 1/2, 34 ……40 3. Fissure: Used for: - Lateral extension of cavity walls. - Finishing of cavity walls. - Roundation of line angles of the prepared cavity. - Tapered forms are used to place retentive grooves. - Sizes: 55 1/4, 55 1/2, 56 - Types: è Straight or cylindrical è Tapered è 245 or 330à all the cavity is prepared by this bur & it is used mainly for conservative cavity preparation (has round end) è End cutting: mainly for finish line in Crown & Bridge c) According to mode of retention to hand piece: 1. Latch Type: Used with regular speed and having latched shank. If used with ultra-speed, it will produce: 1. Vibration and eccentricity. 2. Heat generation. 2. Friction grip type: Used with ultra-speed and having solid shank. 18  Instruments & Instrumentation d) According to number of blades: 1. Cutting bur: 6-8 blades. Used for cutting tooth structure. 2. Finishing bur: 8-12 blades till 40 Used for finishing of restoration only. d) According to length of shank: 1. Regular shank àfor most of cases 2. Long shank à for surgery work 3. Short shank à for inaccessible cases as limited mouth opening Bur design 1) Parts of the bur: Shank: Latch type or friction grip type. Shaft. Head: Carries the cutting blades. It may be → rounded inverted cone or fissure. 19  Instruments & Instrumentation 2) Number of blades (Flutes or teeth): Finishing bur: 8-12 blades till 40 Cutting bur: 6-8 blades 3) Each blade: Each blade or tooth has → Face. → Back 4) Tooth or blade angle: The angle between the face and back of the same blade. It is always acute angle. 5) Clearance angle: The angle between the back of the blade and the work surface. 6) Clearance space: The space between two successive blades. It allows removal of cut dentin chips. Too small clearances space will lead to: i. Bur clogging. ii. Loss of effectiveness of the bur. iii. Heat generation 7) Rake angle (R.A) The angle between the face and radius of the blade. R.A may be: → Positive, negative or zero. a) Positive R.A.: à The face contacts the work surface after radius. à It provides very sharp blade but it will be too weak. 20  Instruments & Instrumentation b) Negative R.A: à The face contacts the work surface before radius. à It provides strong but dull blade. c) Zero R.A: The face coincides with the radius at the work surface. Cutting efficiency Definition: It is the ability of the bur to cut maximum amount of tooth structure with minimal effort and time. Factors affecting cutting efficiency: 1) Bur material: Either: à Tungsten carbide. à Steel. Cutting efficiency of tungsten carbide is more than steel as it has: 1. High hardness number (V.H.N 1700) 2. High melting point. 3. Could withstand heat generation without damage. 4. Accurate design. 21  Instruments & Instrumentation 2) Bur design: a) Number of blades: - Increasing the number of blades will increase the cutting efficiency of the bur within limits, as it will decrease the clearances space. - Cross cutting of fissure bur blades will increase the number of blades without undue weakening of blades or decreasing the clearance space. - Cross cutting is only with conventional speed, if used with high speed à destruction & roughening of surface. b) Rake angle: - Positive rake angles increase cutting efficiency but will lead to fracture of the blade - Zero rake angles are considered the most suitable. 3) Tissue to be cut: a) Enamel: has ñ hardness number à ò cutting efficiency of the bur. b) Dentin: Softer than enamel & easier to cut with burs 4) Pressure: P=F/A Increasing the pressure will increase the cutting efficiency of the bur. The amount of pressure depends on: 1- Force exerted by the operator. 2- The area of contact between the bur and tooth tissue being cut. 22  Instruments & Instrumentation Increased pressure: 1- Increase cutting efficiency. 2- Increase heat generation. 3- Increase dulling tendency of the bur. 4- Cause the edges of bur blades to turn down decreasing life of bur. 5) Speed: Increasing the speed will increase the cutting efficiency of the bur. N.B. The inverted cone burs more efficient than the fissure bur of the same size by “15” times because of: → the area of cutting is less. → It cuts only in dentin while fissure bur cuts in both enamel and dentin. 23  Instruments & Instrumentation Eccentricity or run out of the bur: Definition: It is the maximum displacement of the periphery of the working point of an instrument or tool from its central axis. Maximum lateral displacement → 0.025 mm Run-Out is a dynamic test measuring the accuracy with which all the blades tips pass through a single point when the instrument is rotated Causes: 1- Defect in the tool 2- Defect in the mode of attachment with the hand piece 3- Defect in the hand piece 4- Defect in the junction between the motor and the hand piece Effects: 1- Vibration, that leads to: Loss of control. 2- Decreased cutting efficiency. 3- Increased heat generation. 4- Decreased bur life. 24  Instruments & Instrumentation Heat generation Causes: 1 - Friction between the bur and the tooth surface. 2- Part of the energy is transformed into heat instead of work at the head of the bur. Factors affecting the amount of friction: 1- Pressure: Increased pressure → increased friction. 2- Speed: increased speed → increased friction. 3- Area of cutting: increased area (bur size) → increased friction. 4- Cutting efficiency: decreased cutting efficiency → increased friction. 5- Time of cutting: increased time of cutting → increased friction. Dissipation of heat in: 1- The tool: → Depending on its bulk and thermal conductivity. 2-The tooth: → within the thermal tolerance of detain (85-135° F), above this pulp damage occurs. 3- The surrounding atmosphere. 4- The formed dentin chips. Effect of heat generation on the pulp: Thermal irritation to the pulp above 85-135° F causes: a. Dehydration of dentin. b. Burning lesions in dentin. 25  Instruments & Instrumentation c. Pulp hyperemia. d. Irreversible pulpal inflammation. e. Thermal pulp shock. If the temperature of the pulp á by 5oc à pulpitis Control of heat generation: (How to control heat) 1- Decreasing friction: Selection of small sized instrument. Selection of proper speed. Decreasing the working time. 2- Using sharp tools with high cutting efficiency. 3- Application of only force of rotation. 4- Use of coolants. 5- Using recent cutting tools: Laser, ultrasonic (sonic-sys) or air abrasion à no heat generation Coolant: Requirements: 1. Biologically compatible. 2. Has the same body temperature 3. Sufficient amount. 4. Directed at the area to be cut. Types: 1- Water → increased humidity and decreased vision. 2- Air spray → increased dehydration of dentin. 3- Air- water sprays → the best. 26  Instruments & Instrumentation Functions of coolant: 1- Control of heat generation. 2- Clean the operating 3- Lubricate the tooth surface to be cut. 4- Improve visibility. 5- Clean the tool and prevent its clogging increasing its life. 6- Decease pain during cutting. 7- ò need for local anesthesia. N.B. Multi-directional coolant à more expensive 27  Instruments & Instrumentation II- Dental stones or abrasives: It is the second category of rotary cutting instruments Diamond points & stones are the most popular rotary abrasives It differs from dental burs in that: 1 - The working head has abrasive particles rather than cutting blades. 2- Used for abrasion rather than cutting. 3- Associated with increased heat generation due to increased friction so, it is a must to be sued with copious coolant. è The Difference in design between burs & abrasives causes difference in mechanism of cutting & applications: Abrasives Carbide Burs Most effective in cutting brittle More effective in cutting DENTIN materials. i.e., cutting ENAMEL With dentin it causes clogging of Produces less heat generation abrasives & more heat generation Used for EXTRACORONAL tooth Used for INTRACORONAL tooth preparations e.g. Preparations for preparations e.g. cavity veneers preparations 28  Instruments & Instrumentation 4. Instruments used for manipulation & packing restorations: a) Hand. b) Mechanical. Amalgam carrier: û It is an instrument with hollow end, filled with amalgam increment & pushed into the preparation. Condensers: û It is a hand instrument of different sizes & forms used for packing & condensation of amalgam restoration. Plastic instruments for composite: û They are named so because they are used to handle & shape plastic restorative materials as composite. û we use gold plated instruments or instruments made of Teflon or zirconia à to prevent stickiness of the composite to the instrument. Triturating & Mixing instruments: û As mortar & pestle, amalgamator & amalgamizer are used for mixing amalgam restoration û mixing spatulas Matrices Light curing units: û used to polymerize resinous materials as resin composite. 29  Instruments & Instrumentation 5. Instruments used for shaping of restorations (Plastic instruments): Burnishers: û used to burnish amalgam & cast gold restorations. û Available in different sizes & shapes as, round, anatomical and ovoid. Carvers: û Used to shape amalgam restoration after being packed into restoration. û Has different shapes as, Cleoid, discoid, diamond, hollenback & interproximal carvers. Plastic instruments for composite û used to handle & shape plastic restorative materials as composite. 6. Instruments used for Finishing and polishing purposes: a) Hand: → Orange wood sticks. → Finishing strips for composite. b) Rotary: → Finishing burs → Finishing stones → Abrasive finishing discs → Brushes and rubber wheels, cups or points 7. Miscellaneous instruments: As Mouth mirror, probe, pliers and others. 30