INSTRUMENTS IN OPERATIVE DENTISTRY
Dr. SATHYA KUMAR Postgraduate Student
DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS SRI RAMACHANDRA DENTAL COLLEGE AND HOSPITALS CHENNAI
CONTENTS INTRODUCTION HISTORY CLASSIFICATION
INSTRUMENTS FOR TOOTH STRUCTURE REMOVAL o HAND INSTRUMENTS
o SHARPENING OF HAND INSTRUMENTS o POWERED CUTTING EQUIPMENT
o ROTARY INSTRUMENTS
INSTRUMENTS FOR RESTORING PROCEDURES
INTRODUCTION Operative dentistry is an art and science, which requires a high degree of precision for a successful outcome. The armamentarium of operative dentistry has grown tremendously over the years resulting in a highly successful and predictable outcome.
The need for a distinctive instrument in every single step of each treatment procedure is responsible for the huge armamentarium we have today.
The judicious usage of hand cutting instruments along with
mechanical one’s is the key for a successful conservative therapy.
The aim of this compilation is to provide complete information regarding design principles, concepts and operating procedures of various instruments both hand cutting and mechanized used in operative dentistry.
HISTORY OF DENTAL INSTRUMENTS Prehistoric man used sharp pieces of flint for trephineing holes in bones. Hippocrates in 350 B.C. described a drill driven by a cord wound around d a shaft. Celsus (25 B.C. –50 A.D) described two kinds of drillers or “Terebra”. One with a guard to prevent it from sinking deep into the tissues and the other one was similar to a carpenter’s drill.
In 2A.D. Cladius Galenius a celebrated physician reports of Archigenes an eminent surgeon of Asia minor and practicing in Rome successfully treated tooth ache by opening the tooth with a trephine.
Galen (130 –200 A.D) modified Celsus’s “Terbra” and called it “Terebraabatista” or “Modiolus”. Lubrication was done with olive oil or milk or by dipping in cold water.
Abulcasis (936 – 1013 A.D) described a boring instrument “Incisura”.
Perre Fauchard “Father of Dentistry” in his book “The
Chirurgien Dentiste “ in 1728 described the first dental rotary instrument of modern times. It was known as the “Bow Drill” could be rotated at 300rpm and was later on modified into the “Scranton’s drill” which could cut by rotating in either direction.
In 1831 dental chair was introduced. In 1838 John Levis made a hand held drill. Dr. West Cott in 1846 used “Fingerings” with drills. Taft called them “Bur Drills”. ‘Chevalier drill stock” was hand powered like an egg-beater.
Tomes in 1859 described three types of burs. 1. Rose head: a short shank bur inserted in a crutch rotated between thumb and index finger supported at the base of the thumb. 2. Long hand bur: teeth are cut for same distance along the shaft and it is mounted in a handle. 3. Long steel shaft with too cutting blades.
Charles Merry in 1862 used a “Drill Stock” which had a flexible cable drive. George Fellows Harrington in 1865 used “Clock work drill” or “Harrington’s Erado” which is the first motor driven drill. At first burs
were hand cut and ground and were expensive. America in 1860s began mass production of burs from carbon steel. The earliest burs had limited lateral and end cutting action. The diameter varied form 1/32” to 1/5”. These were particularly used for small and medium sized varieties. These carbon steel burs were called “Small milling cutters”.
In 1871 Morison’s foot engine was introduced. Rotation of 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 would be attached to the shaft of the straight hand piece. A speed of 700 rpm was obtained.
In 1873 Coxeter used an electric engine with a speed of 1000 rpm. This is the predecessor of the modern micromotor. This was held in hand and connected to a coil. The motor was open and the spindle of the motor was connected with the hand piece.
In 1874 the electric motor hand piece was invented by S.S white and later he also pioneered the invention of various carbon steel burs and hand pieces.
In 1883 rotary power from an electric engine was transferred to the straight hand piece by a belt that ran over a series of pulleys and a threepiece extension cord arm. A variable rheostat was used as a foot control. Rotary cutting instruments were inserted into the chucking mechanism at the front of the handpiece. The desired angle hand piece is attached to the front of the straight hand piece and a shaft and gears inside the angle section produce rotation of the working instrument.
In 1891 Edward G. Acheson an American invented and produced carborundum and carborundum tools were introduced. In 1901 hand piece with forward (clockwise) and reverse (anticlockwise) direction of rotation and burs for each type movement were brought into use.
In 1910 Emile Huet a Belgian perfected an electric engine to give a speed of 10,000 rpm. In 1935 diamond abrasives were introduced and W.H Drendel introduced the process of galvanized bonding of diamond powder to copper blanks and used at a speed of 5,000 rpm. In 1947 Tungsten carbide was introduced and S.S White in 1948 made tungsten carbide burs which were used at a speed of 12,000 rpm. In 1949 Walsh and Symons used diamond points at a speed of 70,000 rpm.
In 1950 ball bearings were used in contra angel handpieces. In 1951 air abrasive technique was introduced. In 1953 Nelson produced a Hydraulic driven turbine angle handpiece of speed, 60,000 rpm. In 1955 Page-chayes introduced first belt-driven angle handpiece to operate successfully at speeds over 100,000 rpm.
In 1955 Turbo-jet was designed as a compact mobile unit that required no outside plumbing or air connections.
Only a source of
electricity was need. A sound proof cabinet contained a motor, water pump, water reservoirs and necessary plumbing for water circulation. Water was conveyed to and from the hand piece by co-axial type plastic tubing. The small inner tube carried water under high pressure to rotate a turbine in the handpiece head and the larger outer tube returned the water to the reservoir for re circulation.
In 1960 ultrasonics were used for hard tooth structure removal. In 1961 air turbine straight handpiece was introduced. In 1962 air turbine angle handpiece with air bearings were introduced. Most modern angled handpieces also include fireoptic lighting of the cutting site.
Rapid improvements in technology have spawned several computerized devices for use in conservative dentistry such as
1. CAD/CAM system: They are (Computer aided design/computer aided manufacturing0 laboratory based or chairside based 9CERECI & CEREC II) which design and fabricate porcelain restorations. 2. Air Abrasive: Newer equipments have been introduced in the market utilizing this technology. 3. LASER: Various studies are still being done to utilize LASER in a very useful way without any inherent disadvantages.
INSTRUMENTS FOR TOOTH STRUCTURE REMOVAL HAND INSTRUMENTS The term instrument refers to a tool device or on implement used or a specific purpose or type of work.
HAND INSTRUMENTS NON-CUTTING INSTRUMENTS Examining instruments Restoring instruments CUTTING INSTRUMENTS For tooth structure removal For trimming restoration
PARTS OF HAND INSTRUMENTS HANDLE SHANK BLADE o Cutting edge • Blade angle • Cutting edge angle HANDLE or shaft is straight, usually without variations in size, serrated to increase friction for hand gripping and should be light and preferably small in diameter.
SHANK is that which connect the shaft with the blade, is normally smooth, round and tapered.
It is here where any angulation in the
instrument can be placed and can have one or moiré bends to avoid the instrument having a tendency to twist in use when force is applied.
BLADE or working point is the part, which bears the cutting edge. It begins at the termination of the shank or at the last angle in the shank. Double-ended instruments have a blade on both ends of the handle.
CUTTING EDGE is the working point of the instrument and the blade ends in the cutting edge where it is in the long axis of the shaft.
INSTRUMENT NOMENCLATURE AND FORMULA In 1908 G.V. Black in his “Book of Operative Dentistry “Volume II, wrote about the classification, establishment of formula, nomenclature of various instruments used in operative dentistry.
This is widely
accepted even today and used.
NOMENCLATURE G.V. Black in his “Book classified all instruments b y name NOMENCLATURE ORDER Purpose of function of instrument SUBORDER Position or manner of use CLASS Form of working end
Angle Number of angles in the shank Mono angle Bin angle Triple angle
The set-order description is variable and non-specific and for practical purposes usually omitted. Hence identified the working end and the purpose of instrument is sufficient e.g. binangle hatchet excavator.
FORMULA Cutting instruments have formulas describing the dimensions and angles of working end. In order to describe the parts accurately, it is necessary to give three measurements all expressed in the metric system and are placed on the handle using a code of numbers separated by dashes or spaces. INSTRUMENT FORMULA (BASIC 3-UNIT FORMULA) 1st Number o Width of blade in tenths of millimeters 4-unit formula o Primary cutting edge angle expressed in centigrade for instrument with cutting edges at an angle other than a right angle to the long axis of the blade. o Placed in second position of the formula 2nd Number o Blade length in mm 3rd Number o Blade angle relative to long axis of handle in clockwise centigrade. NB: In a four unit formula the instrument is positioned so that this number always exceeds 50 and if the edge is locally perpendicular to the blade, this number is normally omitted resulting in a three number code
In some instances there is an additional number in the handle
which may be the manufacturer identification number. SPECIFIC DESIGNS FOR HAND CUTTING INSTRUMENTS
1. The main principle of cutting with hand instruments is to concentrate forces on a very thin cross section of the instrument, at the cutting edge. Thus the thinner this cross section, the more the pressure is concentrated and more efficient is the instrument. 2. Direct cutting and lateral cutting instrument A direct cutting instrument is one in which the force is applied in the same plane as that of the blade and handle and is called a “single planed” instrument. A lateral cutting instrument is one is which the force is applied at aright angle to the plane of the blade and handle and is called a “double-planed” instrument with a curved blade. The cutting is done such that For direct cutting acts the non-beveled side of the blade should be in contact with the wall being shaved. For lateral cutting acts, move the instrument in a scarping motion from the beveled side to the –beveled side of the blade. 3. Right and left side instruments
Direct cutting instruments are made either right or left by placing a bevel on one side of the blade. The instrument must be made in pairs, having the bevels on opposite sides of the blades. For determining whether the instrument has a right or left bevel, the primary cutting edge is held down and pointing away-if the bevel appears on the right side f the blade, it is the right side instrument of the pair and vice versa for left side instrument. A ring on the shank identifies the right of the pair, or the letter ‘L’ or ‘R’ is added to the instrument formula. 4. Single bevelled instruments These are single planed with cutting edge at a right angle to the long axis of the shaft. If are bevelled on the side away from the shaft, they are called “distally bevelled” and if bevelled on the side of the blade towards the shaft, they are called “mesially bevelled” (i.e. reverse bevels). A ringe in the shank identifies reverse bevel. If the shank angle is 12° or less they are used in push and scraping motion and if exceeds 12°, used in pull (distally bevelled) and push (mesially bevelled) motions. 5. Bi bevelled instruments The blade is equally bevelled on both sides; they cut by pushing them in the direction of the long axis of the blade. 6. Tribe bevelled instruments
Beveling the blade laterally, together with the end, forms three distinct cutting edges, which afford an additional cutting potential.
7. Circumferentially bevelled instruments It is done in double planed instruments where the blade is bevelled at all peripheries. 8. Contra angling Instruments with longer blades or more complex orientations may require two or three angles in the shank to bring the cutting edge near to the long axis of the handle-such shanks are termed centra angle instruments.
The advantages will be of providing better
access and clearer view of the field. 9. Double ended instruments They have blades and shanks on both ends of the handle. The right instrument of the pair is on one end of the handle and the left is on the other end. Similar blades of different widths are placed on either end. Single ended instruments (long-handled instruments) may be safer to use, but double-ended instruments are more efficient because they reduce instrument exchange.
PRINCIPLE OF BALANCE
Hand instruments must be balanced to allow for the concentration of force onto the blade without causing rotation of the instrument in the grasp. This balance is accomplished by designing the angles of the shank so that the cutting edge of the blade lies within the projected diameter of the handle and nearly coincides with the projected axis of the handle. For optimal anti-rotational design the blade edge must not be off the axis by more than 1-2 mm. All dental instruments and equipment need to satisfy this principle.
NON-CUTTING HAND INSTRUMENTS They are used for examining the patient and can also be termed exploring instruments.
EXPLORING INSTRUMENTS Explorers Mouth mirror Tissue reactors Field isolating instruments Source of light
o They are used to probe the lesions, where the tip is pointed which should be cheeked and sharpened frequently.
Explorer Straight Right angled Arch Interproximal Straight explorer has a shank, which is straight except for a slight curvature near the exploring tip. Right-angled explorer has a shank wit a right angle placing the exploring tip at a right angle to the handle Arch explorer wit the shank curved in a semi-circle like an arch, also has the exploring tip at a right angle to the handle. Briault’s probe or interproximal explorer with its shank consisting of two or more angles has the exploring tip pointing toward are handle and is specific for detecting proximal lesions.
The use of explorers can be extended to Determine the mobility of the tooth and periodontal pockets. Evaluate the depth and smoothness of cavity preparation
Diagnose secondary caries between restoration and tooth interface Remove excess cement after luting procedure.
For hygienic purposes pre sterilized packaged disposable explorers with stainless tip and plastic handles are available.
2. MOUTH MIRROR It has handle with detachable mirror part. Used for retraction, illumination and visualization Are available ranging from sizes of ¾” to 11/2”in diameter MOUTH MIRROR Plain glass Magnifying glass Anti fog Light attached Parallelometer mirror Magnifying glass magnify the image Anti-fog mirrors prevents setting of fog on the viewing surface which is very helpful while working in indirect vision Light attached mirror provide better illumination of the required area of examination.
Parallelometer mirror is available which is useful for checking parallelism of various tooth preparation in crown and bridgework. Normally the blunt end of the mouth mirror is used for percussion of the tooth or teeth during examination.
Pre-sterilized packed disposable mouth mirrors made of plastic are also available. 1. Air syringe is used to remove moisture or saliva by blowing air on the surface required. 2. There was syringe is an instrument with a single nozzle and two control buttons, in which a airline and a water line enter the syringe. Three-way action is by: When the air-button is pushed, compressed air comes out of the nozzle and it is used a chip blower. When the water-button is pushed, water jet comes out of the nozzle.
When both buttons are simultaneously pressed air-water spray comes.
TWEEZERS Help in placing cotton for isolation Special type of locking tweezers are used to place wedges and carry gutta percha points into the canal space
TONGUE AND CHEEK RETRACTORS Tongue depressors/retractors are made of wood, plastic or stainless steel to prevent tongue hindrance during examination or while performing operative procedure. Cheek retractors are made of pliable plastic or metal which are placed on the angle of the lips where the retractor stretches the cheeks away such that it produces better visualization by perfect retraction of the soft tissue. Mouth mirrors are also used or this purpose.
HAND CUTTING INSTRUMENTS They are used to cut hard or soft tissues of the mouth.
HAND CUTTING INSTRUMENTS Excavator o Ordinary hatchet o Hoe o Spoon excavator o Discoid o Cleoid Chisel o Straight o Mono angle o Bin angle o Triple angle Special forms of chisels o Enamel hatchet o GMT o Angle former o Wedlstaedt chisel o Off-set hatchet o Triangular chisel o Hoe chisel
ď ś EXCAVATOR ď‚§ Is used for removal of caries and refinement of internal parts of the cavity.
Ordinary Hatchet o Blade is bi-bevelled directed in the same plane as that of long axis of the handle. o Cut by push or pull motion, in the direction of the blade. o Used in anterior teeth for preparing retentive areas and sharpening internal line angles, particularly in preparations of direct gold restorations. Hoe o Primary cutting edge of the blade is perpendicular to the long axis of the handle. o Single planed instrument with four possible cutting moments vertical, pull (push), right and left. o Are distally or mesially bevelled and used for cutting mesial and distal walls of premolars and molars.
o Both hatchet and hoe are used to remove harder varieties of caries as well as to give form to the internal parts of the cavity preparation. Spoon excavators o Are made in pairs with the blade of one curved to the rights and the other to the left. o Cutting edge is ground to as semi-circular circumferential bevel and sharpened to a thin edge. o Double planed instrument with lateral cuttings action o Bin-angled or triple angled for better accessibility. o Used for removal of decayed dentin, carving amalgam or direct was pattern. o Formula 12-8-12 R & L Discoid excavator o Has a circular blade, with cutting edge extending around the periphery except where it is joined to the shank and with the blade placed at an angle with the shaft. o Double planed instrument with right or left cutting movement. Cleoid excavator o Similar to the spoon excavator except for the blade is pointed resembling a claw, hence the name â€œcleoidâ€?
o Double planed instrument with lateral cutting movement. o Discoid and cleoid excavator function similar to the spoon excavator and may be used to trim or burnish inlay â€“ only margins.
ď ś CHISEL o Used primarily for cutting enamel with the basic design of the ordinary carpenterâ€™s tool. Straight chisel o A straight blade in line with the handle and shank o Cutting edge is on one side only, with the bevel of the blade running at a right angle to the shaft. Mono angle chisel o Similar to straight chisel, except the blade is placed at an angle to the shaft with mesial or distal bevel. Binangle chisel o Chisel blade is placed at a slight angle wit the shaft similar to hoe o The straight, mono angle and binangle chisels are used to cleave or split undermined enamel. Triple angle chisel o Has three angles in its shank, used to flatten pulpal floors.
o All the chisels are single planed instruments and posses vertical, right and left cutting movements, with mesial bevel chisel cutting in push motions and distal bevel cutting in pull motions.
ď ś SPECIAL FORMS OF CHISELS These chisel are designed to perform specific functions. Enamel hatchet o A chisel similar in design to the ordinary hatchet except for a large heavier blade, which is bevelled on one side. o The cutting edge is in a plane parallel to the axis of the handle with vertical, push, pull and lateral cutting movements. o They are designed as right or left type for use on opposite sides of the cavity and used for cutting enamel. o Formula: 10-6-12 or 15-8-12.
Gingival marginal trimmer o Similar in design to the enamel hatchet except for the curved blade. o The primary cutting edger is at an angle to the axis of thee handle and is primarily lateral cutting instruments. o They are designed as right and left types and paired such that they form a mesial pair or distal pair.
o Usually the instrument is used in lateral scrapping motion, the right instrument is used form right to left and the left instrument is used for operation left to right. o In distal gingival marginal trimmer the cutting edge makes an acute angle with that edge of the blade furthest from the handle and the second number in the formula is 90 to 100. o In mesial gingival marginal trimmer the cutting edge makes an acute angle with that edge of the blade nearer to the handle and the second number in the formula is 85 to 75. o They are designed to a proper bevel in gingival enamel of proximocclusal preparations; 100/75 pairs are for inlay/only preparations with steep gingival bevels; 90/85 pairs are for amalgam preparations with gingival enamel bevels that decline gingivally only slightly. o Other use is rounding or beveling of the axiopulpal line of two surface preparations and placement of gingival lock in dentine. o Distal GMT 10-92-6-12 mesial GMT 10-80-6-12.
Angle formers o It may be described as a combination of a chisel and GMT. o It is monoangled with the primary cutting edge at an angle (other than 90Â°) to the blade and available in pairs i.e. left and right. o Used primarily for sharpening line angles and creating retentive features in dentin in preparation for gold restorations and for placing bevel on enamel margins. o Formula 7-80-21/2-9 Wedelstaedt chisel o Has the primary cutting edge in a plane perpendicular to the axis of the handle and may have either a distal bevel or a mesial bevel. o The blade with a distal bevel is designed to plane a wall that faces the blades inside surface and the mesial bevel is designed to plane a wall that faces the bladeâ€™s outside surface. o Used mainly to plane Class II and V cavities with curved walls. Off â€“set hatchet o Similar to regular hatchet, except the whole bade is rotated a quarter of a turn forward or backward around its long axis.
o They may be right or left o Useful in creating shape specific angulation for cavity walls, especially in areas of difficult access. Triangular chisel o The blade is triangular in shape with base of the triangle away from the shaft. o Has a terminal cutting edge like the straight chisel Hoe chisel o Similar to a hoe excavator but has a sturdier blade. o Blade angle is more than 12.5째, distally bevelled and mesially bevelled are available. Jefferey Hatchets o Similar to off-angle hatchets but have their blades more nearly at right angles to the shaft. o Used in preparation of maxillary anterior cavities form the lingual side of the teeth.
INSTRUMENTS Hand cutting instruments are manufactured from two main materials
a. Carbon steel
b. Stainless steel
C 0.6% -1.0%
Fe 81% - 81.4%
Fe 98.4% - 98.6%
Carbon steel is harder than stainless steel but when unprotected it will corrode. Stainless steel remains bright under most condition but loses a keen edge during use much more quickly than carbon steel., Some instrument are made with carbide inserts to provide more durable cutting edge, being hard and wear resistant, is brittle and cannot be used in all designs.
HARDENING AND TEMPERING HEAT TREATMENTS To gain maximal benefits from carbon steel or stainless steel, the manufacturer submits them to two heat treatments. Hardening: this hardens the alloy, but it also makes it brittle especially when the carbon content is high.= Tempering: it relieves strains and increases toughness
These properties are optimized by the manufacturer (heating for 1 hr. at 350°F and quenching in oil)
DISCOLORATION, RUST AND CORROSION PREVENTION Certain methods are advocated to prevent the above mentioned The manufacturer electroplates the instrument, which affords protection except on the blade, where use and sharpening remove the plating. Use of rust inhibitors (soluble alkaline compounds), usually incorporated into sporicidal disinfectant
solutions or certain
preparations are available for use in boiling water and autoclave. Minimizing the effect of moisture by removing instruments properly at the end of the recommended sterilizing period, drying them thoroughly and then placing in the tray set up.
MECHANICS OF HAND INSTRUMENTATION This is important so as to utilize the instrument to gain the maximum advantage out of it. It has been found that movement directed by shoulders and wrists are better oriented and can be give for a longer time than movements given by fingers which fatigue easily, thus leading to operator’s failure quickly. So fingers are used merely to grip the instrument and to prevent it from slipping and rotating.
When force is applied along the long axis the force acts on tooth surface with fingers preventing slipping of the instrument. But if the force is applied at right angles to the tooth, but in the plane of the cutting edge, the resisting tooth structure tries to rotate th4e instrument. This is prevented by the thumb and the finger, which prevents rotation, thereby shearing of the tooth structure and allowing the instrument to move in the direction of the force.
This is of lever action type-I, where the
mechanical advantages always less than I.
Hence the mechanical
advantage and contra angling must be considered for a better orientation of force. GRASPS A proper instrument grasp is essential for performing operative dental procedure. It provides for control of the instrument while allowing flexibility of motion and prĂŠcised adaptation. It aids in prevention of muscle fatigue to the fingers, hand and arm while also allowing application of controlled pressure to the instruments. The grasps are variable, non-specific and variable among operators. There are 4 types of grasps. 1. Modified pen grasp 2. Inverted pen grasp 3. Palm and thumb grasp
4. Modified palm and thumb grasp
The modified pen grasp offers the greatest control during the performance of procedures in the oral cavity. The instrument is held near the junction of the handle and the shank between the first finger and the thumb. The first finger rests on top of the instrument opposite the thumb in the underside. The pad of the second finger is placed on the top of the shank closer to the working end than the thumb and the finger. The handle is rested at the junction of the t finger and the thumb. The grasp should be firm and not rigid to allow for maximal maneuverability of the instrument. In the inverted pen grasp the palm faces upwards while the instruments is held between the first finger and the thumb and this is used for the maxillary arch.
In the palm and thumb grasp the instrument is held in the palm of the hand with the first, the second, third and fourth fingers wrapped round it. The thumb remains free and serves as a rest. It is used only in anterior region owing to lack of tactile sense and flexibility of the movement.
In the modified palm and thumb grasp, the instrument is held by the pulps of the first, second and third finger on one side and the mesial
phalange of the fourth finger and with the tip of the resting on the adjacent tooth surface and very close to the cutting edge. Here the hand is only half closed and permits easy and free movement with greater precision of control. The modified pen and inverted pen grasps are practically universal.
FINGER REST A finger rest or fulcrum is essential for the controlled movement of an instrument. It is the point of support from which the hand moves to activate the instrument and also provides control and prevents injury to the soft tissues from an instrument which inadvertently slips. The third finger is the digit of choice for the finger rest. Additional support is achieved by the second finger, which rests against the third, and the fourth fingers and the entire hand moves as a unit.
additional support is applied when increased pressure is required. Pressure placed on the fulcrum finger is usually directed to the working end of the instrument. Depending on the pressure needed on the working end of the instrument light or heavy pressure is applied on the finger rest. This creates a balance between the working end and the finger rest.
Wherever possible the finger rest is placed close to the area of operation. As it moves away from the working area precise manipulation
and control becomes difficult. The finger rest is usually placed on the occlusal, facial or on the lingual surface. Tooth surface provides the most stable and firm support. Soft tissue is flexible and mobile and therefore not suitable as rests.
Variations in finger rest placement may be necessary because of the position of the matrix and wedge, the absence of adjacent teeth, lack of access, or difficulty in attaining the desired angle f the instrument blade. In such situations the fulcrum may be placed on the opposite quadrant. The instrument is then extended to the area of operation, being grasped farther along the handle. SHARPENING OF HAND INSTRUMENTS Repeated use and sterilization renders instrument dull and an effective management of dull instrument is important as this is common occurrence in practice and instruments are used everyday and cannot be discarded. Moreover dull instrument. Reduces quality of work done and effects precision Prolongs operating time. Necessitates use of excessive pressure. Increases risk of trauma to the surrounding soft tissues Contributes operator’s fatigue at an early stage.
Usually cutting edge is formed by two surfaces joining at an acute and angle and objective of sharpening is to convert the dull, blunt edge to sharp cutting edge without significantly diminishing the length of the blade. Four types of materials are in common use for sharpening: Stones: Arkansas stone, silicon carbide, aluminium oxide and diamond.
TECHNIQUE OF SHARPENING MANUAL METHOD It is a good technique, provides good control over the instrument less risk of removing excess metal but its time consuming. Usually Arkansas stone 1” x 2” is used. This is well lubricated by sterile machine oil and stabilized on firm surface. The instrument is held and modified pen grasp is used with third and fourth finger providing rest. The correct bevel angulation is established and entire hand and arm is moved with the fingers holding the instrument firmly. After few times the blade is wiped well and checked and redone if necessary. Sometimes the instruments are held steadily while the stone is moved up and down. MOUNTED STONE METHOD Cylindrical or conical mounted stones are used in a straight handpiece and instrument sharpened. The disadvantage is that it is
difficult to control the angulation of the instrument against rotation of the stone. ď ś MECHANICAL SHARPENERS Here lathe type mounted stones are used. It requires greater control and precision, has chance of removing more metal and change of angulation may occur. ď ś SHARPENING MACHINE. Are available with moving sharpening stones in a reciprocating movement.
The instrument to be sharpened is held fixed an d
supported by an angle guide that maintain the angle of the bevel.
The evaluation of sharpness is done by o Examination of instruments under direct light where the dull instrument will reflect light and will produce a flash while sharp instrument will not reflect light. o Tactile examination is the instrument is dragged along the nail bud where a sharp instrument will dig into nail bud and resist sliding motion while dull rounded cutting edge of dull instrument will slide along nail surface.
POWERED CUTTING EQUIPMENT
The powered cutting equipment is a real asset in operative dentistry, which helps, in cutting ad shaping of tooth structure, which is essential in restoration of teeth.
SOURCES OF POWDER In today’s operative dentistry practice the main powder source for operating use is the air turbine, which has almost made the other previous sources obsolete. Another powder source is the electric engine.
HANDPIECE The handpiece is the device for holding rotating instruments transmitting power to them and for positioning them intraorally. Certain features of handpiece: i.
They are either high speed or slow speed
They are either straight, contra-angled or right angled at the working end and its use depend on the type of work.
The cutting tool is retained in the handpiece by 3 major type of attachment Screw in type (e.g. air motor handpiece straight) Latch type (e.g. Micromotor contraangle handpiece) Friction grip (e.g. Airotor handpiece)
They have a fiber optic light attachment
Available in normal head (adult) size and miniature head (paediatric) sizes.
The following criteria should be used in evaluating handpieces: Friction – will occur in moving parts of the handpiece especially turbine, hence heat generated should be prevented or counteracted. Hence handpiece are equipped with bearings, (bal bearings, glass or resin bearings). Torque – is the ability of handpiece to withstand lateral pressure on the revolving tool without decreasing speed and cutting efficiency. It depends on the bearing and energy supplied. Vibration – unnecessary vibrations are deleterious, hence excessive wear of the turbine bearings is avoided by maintaining the handpiece according to the manufacturer’s instructions.
SPEED RANGES OR GROUPINGS The rotational speed of an instrument is measured in revolutions per minute. Considering the essential requirements of operative dentistry it is necessary to assess the appropriate speed for each activity. manufacturers’ colour code handpiece. The speed ranges are:
SPEED Low speed i. 500 – 1000rpm 1000-25000rpm Intermediate high speed i. 20,000 – 80,000 rpm ii. 20,000 – 1,20,000 rpm
HANDPIECE COLOUR Green band Blue band Red band Orange band
Ultra high speed 2,50.000 – 4,00,000rpm Air turbine only is used
USE ADVANTAGES Caries excavation Better tactile sensation Cleaning teeth Less chance for Finishing and polishing overheating procedures For tooth preparation Efficient cutting with Remove old restorations smaller and versatile instrument Faster, less load, vibration and heat generation Better control and ease of operation Several teeth can be treated in the same appointment Instruments last longer Patient comfortable.
HIGH SPED HANDPIECE < AIROTOR HANDPIECE Working mechanism Is driven by compressed air The head contains a cartridge which contain the air turbine with a central chuck The turbine is held in position by two sets of ball bearings on the upper and lower ends. When air pressure turns the turbine, the central chuck also rotates along with it.
Bearing ensures that while the
turbine rotates, the cartridge doesn’t.
Bur chuck and Central chuck Bur chuck is a device used to loosen or tighten the central collect chuck to insert or remove a bur. The bur is attached to the central chuck, the is hollow. One end of the chuck is split into three or four leaves that can be released or tightened by turning the bur chuck anticlockwise or by pressing the spring activated top in some handpieces. While inserting or removing the bur, the central chuck should be open 9the end leaves released) and the bur chuck is turned in a clockwise direction to tighten the central chuck or the pressure on the spring activated top on the head of handpiece is released.
SLOW SPEED HANDPIECE (AIR MOTOR OR MICROMOTOR) Working mechanism Either an air driven motor (air motor) or a electrically driven miniature motor (micromotor) can be used for driving the handpiece. The motor turns the central shaft, which will be coupled to the drive spindle of the handpiece. In a straight handpiece, the drive spindle ends in a collect chuck for receiving the bur. In a contraangle handpiece, a crown wheel gearbox is provided between two drive shafts, which placed in the head, is attached to drive pinion, which has the bur tube for placing the bur. The two bearings (upper and lower) hold the bur tube and pinion in place Latch type (ratchet) attachment holds the bur.
Types of slow speed contraangle handpieces Commonly used 1:1 handpiece i.e. output is equal to input; blue colour band on the shank and blue dot on the head; speed 5,00040,000 rpm; cavity refinement and groove placement. Speed reducing handpiece 7:1; green band with gear dot; speed 5005,500 rpm; pin channel preparation Speed increasing handpiece 1:4; red coded; speed 16,000-1,60,000 rpm; tow red ring indicate 1:10 increase in speed.
COOLANT SYSTEM All handpiece have a provision for a coolant system. System should be concealed within the handpiece (high speed) or may be external. At high speed an aerosol spray of water and air-cool the bur better than plain air or water alone. The outlets for water are positioned and angulated in head of handpiece in such a way that the aerosol jet is direct at the cutting portion of the revolving bur heads. Some handpieces have only one coolant outlet while some have three outlets equidistant form one another.
The advantage of multiple
coolant spray is, even if a portion of tooth being cut blocks one spray, the other sprays might reach the revolving bur head.
This variable control to regulate the speed makes the handpiece more versatile. This allows the operator to easily obtain the optimal speed for the size and type of rotating instrument at any state of a specific operation.
ROTARY INSTRUMENTS Rotary instruments can be defined as a single or group of instruments that turn on an axis to perform the work, used on the patient as well as the laboratory.
They are the most universally used instruments for gross removal of tooth structure and are of two types.
ROTARY INSTRUMENTS Rotary cutting (dental burs) o For tooth structure removal Rotary abrasive (diamond abrasive stones) o For tooth structure removal o Shaping, finishing and polishing abrasive
The following are the characteristics of rotary instrumentation: Speed refers to the surface feet per unit time of contact that the tool has the work to be cut and is indicated in rpm. Pressure (P) is a resultant effect of two factors under the control of the operator i.e. P = F/A.
o Force (F) gripping of the handpiece and its positioning and application to the tooth. o Area (A) amount of surface area of the cutting tool in contact with the tooth surface during a cutting procedure.
It has been observed clinically for efficient cutting. o Low speed require 2-5 lbs F o High speed require 1 lb F o Ultra –high speed require 1-4 ounces F Heat production is directly proportional to P, rpm and area of tooth in contact with the tool. It has been shown that when the area of cutting tool is reduced but the speed of rotation is increased, it is an absolute necessary that coolants (copious stream of water or airwater spray) be employed to eliminate pulpal damage. It has bee shown that cutting dentine with no lubricant may result in a temperature rise at the surface of the tooth in contact with the bur of up to 136°C in only 2 seconds. Using an air-water spray with a water flow rate of 35-50ml/min, the temperature rise can be limited to 20-30s°C and water alone is more effective with a flow of 10ml/min, the temperature rise limited to 10°C. combined air water spray is more effective.
Vibration: It is an annoying factor for the patient, causes fatigue for operator, excessive wear of instruments and a destructive reaction in the tools and supporting tissues.
primarily the handpieces, various revolving cutting tools, the speed of rotation all contributes to the quantity an quality of vibration. Hence for better cutting efficiency the ideal requirements are: o Greater rpm o Smaller cutting tool o Less force o Effective lubrication
COMMON DESIGN CHARACTERISTICS. The rotary cutting instruments have certain design features in common. Each instrument consists of three parts: BUR Shank o Straight handpiece o Latch type o Friction grip Neck Head
SHANK DESIGN The shank is the part that fits into the handpiece, accepts th4e rotary motion from the handpiece and provides a bearing surface to control the alignment and concentricity of the instrument.
The ADA specification No.23 for dental excavating bur include five classes of instrument shanks of which three types are common.
Straight handpiece shank (0.520” length / 0,0925”dia) The shank portion of the straight handpiece instrument is a simple cylinder, which is held in the handpiece by a metal chuck that accepts a range of sank diameters. They are commonly used for finishing and polishing completed restorations.
ď ś Latch type angle handpiece shank (0.520â€? length / 0.0925â€? diameter) o Latch type instruments are retained in the handpiece by a retaining latch that slides into the groove found at the shank end of the instrument. o The posterior portion is flattened on one side so that the end of the instrument fits into a D-shaped socket at the bottom of the bur tube and it is thus that the instrument is rotated. o The handpieces have a metal bur tube within which the instruments fit as closely as possible while still permitting easy interchange. o They are used in low and medium speed ranges where the small amount of potential wobbles inherent in the clearance between the instrument and the handpiece bur tube is controlled by the lateral pressure excited during cutting procedures.
o Their shorter overall length permits substantially improved access to posterior regions of the mouth. o They are used for finishing procedures.
Friction grip shank (0.500: length / 0.0628” diameter) o Were originally designed to be held in the handpiece by friction between the shank and a plastic or metal chuck.
handpiece designs have metal chucks that close to make a positive contact with the bur shank. o The shank is a simple cylinder manufactured to very close dimensional tolerances. o Design is smaller in overall length and provides very good access for posterior instrumentation. o They are used for high-speed handpieces.
NECK DESIGN The neck is the intermediate portion of an instrument that connects the head to the shank. It normally tapers form the shank diameter to a smaller size immediately adjacent to the head. It transmits rotational and transitional force to the head.
The neck dimensions represent a compromise between the need for a large cross section to provide strength ad a small cross section to improve access and visibility.
HEAD DESIGN Is the working part of the instrument, the cutting edges or pints of which perform the desired shaping of tooth structures. The shape ad material used to construct it is closely related to its intended application and technique of use. The characteristics of the head form the basis on which rotary instruments are usually classified according to: o Type: bladed or abrasive instrument. o Material of construction: tungsten carbide, steel or diamond abrasives. o Head size: regular or long o Head shape: round, straight, tapering etc.
DENTAL BURS The term bur is applied total rotary cutting instruments that have bladed cutting heads.
COMPOSITION AND MANUFACTURE The dental burs are of two types according to composition:
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 Vickerâ€™s hardness number is approximately 800. They perform well in cutting human dentin at low seeds, but dull rapidly at higher speeds or when cutting enamel. Steel burs now are used mainly for finishing procedures.
Tungsten carbide burs It is a product of powder metallurgy i.e. a process of alloying in which complete fusion of the constituents does not occur. The tungsten carbide powder is mixed with powdered cobalt under pressure and heated in a vacuum. A partial alloying or sintering of the metals take place. A blank is then formed and the bur is cut from it with a diamond tool. The Vickerâ€™s hardness number is in the range of 1650-1700. In most burs the carbide is attached to a steel shank and new by welding or briefing. Carbide is stiffer and stronger than steel, but it is also more brittle.
GENERAL DESIGN OF DENTAL BURS (BLADE DESIGN) The common design and the standard nomenclature are:
ď ś Dental bur: is a small cutting instrument. ď ś Bur tooth: terminates in the cutting edge or blade. It has two surfaces, the tooth face, which is the side of the tooth, which is the side of the tooth on the trailing edge. ď ś 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. Referring to the direction of rotation, the angle can be. Negative: If the face is beyond or leading the radial line. Zero: If the radial line and the tooth face coincide with each other i.e. radial rake angle. Positive: If the radial line leads the face i.e. the rake angle is inside the radial line.
Land: The plane surface immediately following cutting edge. 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:
The angle the land will make with work. Secondary clearance: The angle between the back of the bur tooth and work. If the back surface of the tooth is curved, the clearance is called radial clearance. Tooth angle: This is measured between the face and back. If a land is present, it is measured between face and land. Flute or chip space: The space between successive teeth.
FACTORS INFLUENCING THE CUTTING EFFICIENCY OF BURS RAKE ANGLE A negative rake angle is ideal and long lasting such that the cut chip moves directly away from the blade edge and fractures into the small bits or dust and hence clogging prevented and efficiency increased.
CLEARANCE ANGLE Any slight wear of cutting edge will increase the dulling perceptibility, hence a large clearance angle will help in less raid dulling of the bur.
NUMBER OF TOOTH OR BLADES AND THEIR DISTRIBUTION The number of blades on a bur is always even because even numbers are easier to produce in the manufacturing process. The number of blades on an excavating bur may vary from 6 to 8 to 10. Fewer blades provide increased space between the teeth reducing clogging tendency. Burs intended mainly for finishing procedures usually have 12-40 blades.
RUN OUT AND CONCENTRICITY Concentricity is a direct measurement of the symmetry of the bur head. It measures how closely a single circle can be passed through the tips of all of the blades. It indicates whether one blade is longer or shorter that the others and is a static measurement. Run out is a dynamic test measuring the accuracy with which all blade tips pass through a single point when the instrument rotates. It measures the concentricity and also the accuracy with which the center of rotation passes through the center of the head. concentric head will exhibit substantial run out if:
Even a perfectly
The head is off center on the axis of the bur The bur neck is bent The bur is not held straight in the handpiece chuck The chuck is eccentric relative to the handpiece bearings
The average value of clinically acceptable run out is about 0.023mm. it is the factor that determines the minimum diameter of the hold that can be drilled by a given bur.
FINISH OF THE FLUTES As mentioned cutting each flute into the bur blank with a rotating cutter forms the dental bur. During the first cut or pass of the cutter the flute is roughly formed. Making subsequent passes or cuts on the bur flute may remove the roughness. Tests for cutting efficiency were done on different types of bur undergoing tow, four and six flute cuts. Those cut six times were the most efficient while those cut two times were the least efficient. HEAT TREATMENT Is used to harden a bur that is made of soft steel. It preserve’s the edge placed on the bur flute by the cutter and hardens the bur to increase cutting life.
DESIGN OF FLUTE ENDS Dental burs are formed with two different styles of end flutes: The revelation cut, where the flutes came together at two junctions near a diametrical cutting edge. The star cut, where the end flutes come together in a common junction at the axis of the bur. The revelation type shows superiority in cutting efficiency during direct cutting but in lateral cutting both are equal.
BUR DIAMETER With the length of cut as a constant the volume of materials removed will vary directly with the bur diameter.
DEPTH OF ENGAGEMENT Volume of materials removed by a shallow cut exceeds that of deeper cuts because as the depth of engagement is decreased, the force intensity on each small portion of the bur tooth cutting is correspondingly increased. INFLUENCE OF LOAD Load signifies the forces exerted by the dentist on the tool head and is related to the rotational speed of the bur of a give design the minimum and maximum loads for: Low speed 1000-1500 gm
High speed 60-120 gm
BUR SHAPE The term bur shape refers to the contour or silhouette of the head. There are various shapes: Round bur: It is spherical in shape and used for –initial entry into the tooth, extension of the preparation, preparation of retention pot holes cries removal. Wheel burs: Wheel shaped and used for – placing grooves and gross removal of tooth structure. Inverted cone bur: It is a portion of a rather rapidly tapered cone with the apex of the cone directed toward the bur shank. Head length is about to the same as the diameter. Its is used for cavity extension, and providing undercuts in cavity preparation. Plain cylindrical fissure bur: The straight fissure bur is an elongated cylinder with teeth parallel to the axis of the bur or if teeth cut obliquely is called a spiral fissure bur, in use for amalgam cavity preparation. Crosscut cylindrical fissure bur: They can be either straight or spiral. Plain tapered fissure bur: It is a portion of a slightly tapered cone with the small end of the cone directed away from the bur shank. It can be straight or spiral and used for inlay and crown preparations.
Cross cut tapered fissure bur. Round nose fissure burs: All eight types of fissure burs can be round ended. Pear shaped bur: It is a portion of a slightly tapered cone with the small end of the cone directed toward the bur shank. The end of the head either is continuously curved, or is flat with round corners, where the sides and flat end intersect. A normal length pear bur (length slightly greater than the width) is used in class I preparations for gold foil, and long-length pear bur is advocated for cavity preparation for amalgam. End cutting burs: They are cylindrical in shape, with just the end carrying blades and efficient in extending preparations apically without axial reduction.
Among these basic shapes, variations are possible. Fissure and inverted cone burs may have half round or domed ends. Taper and cone angles may be varied.
BUR CLASSIFICATIONS SYSTEMS In order to facilitate description, selection and manufacture of burs it is highly designation, which represents all of the variables of a particular head design by some simple code.
The numbering system for burs was originated by the S.S White Dental Manufacturing Company in 1891 bur their first machine â€“ made burs. The original numbering system grouped burs by 9 shapes and 11 sizes.
The Â˝ and Âź designations were added later when smaller
instruments were included in the system. All original bur designs had continuous blade edges. The crosscut modification was indicated by adding 500 to the number of the equivalent non cross cut size. (eg.No.57 with crosscut was designated No.557). Similarly a 900 prefix was used to indicate a head design intended for end cutting only. Except for differences in blade design e.g. a No.957; No.557 and No.57 bur all had the same head dimensions.
In the United States dental burs traditionally have been described in terms of an arbitrary numerical code for head size and shape, eg.2 = 1.00 mm diameter round bur, 34=0.8 mm diameter inverted cone bur. Despite the complexity of the system, it is still in common use.
Newer classification systems, such as that developed by the International Dental Federation (FDI) and International Standards Organization (ISO) tend to use separate designations for shape, usually a
shape name, and size, usually a number giving the head diameter in tenths of a mm. E.g. round 010, inverted cone 008.
The International Standards Organization has developed a classification ISO 6360. The essential dimension of burs, including the material, shank shape, overall length, shape and type of finish of the working head and the size of the head have been ordered numerically.
ISO number has 15 digits. Every three numbers provide the details. st
A. 1 3 digits Type of material B.2nd 3 digits Shank form
3rd digits bur head
No. 310 or 330 500 615, 625,635 806 or 807 103,104,105 124 202,204,205,206 313,314,315,316 900 001 &002 010-020 030-039
Interpretation Steel Tungsten carbide Aluminium oxide Diamond Standard straight handpiece Special heavy duty laboratory handpiece Conventional contra angle handpiece Airotor handpiece Unmounted stones Round head Inverted cone head Double cone head
040-099 100-150 160-229 243 260 284 320-329 4th 3 digits Surface finish & grain coarseness of abrasive points
Machine cut steel tungsten carbide bur
494 504 514 524 534 544
or 001 006 007 019 071 072 140 175 215
5th set of 3 digits
Wheel head Cylinder head (St. fissure) Cone head (tapering) Pear shaped head Flame shaped head Bud shaped head Torpedo shaped head Torpedo shaped head Discs Superfine (15µ) Extra fine (30µ) Extra fine (50µ) Medium (100- 120µ) Coarse (135-140µ) Extra coarse (180µ) Straight Right hand twist Cross cut twist Double diagnol Coarse flute Fine flute Fine diamond cut Medium tooth lab-bur Coarse tooth lab-bur Maximum diameter of the bur head in one tenth of a millimeter E.g., 307, 314, 107, 534, 018
INSTRUMENTS FOR RESTORING PROCEDURES There are a variety or a combination of restoring instruments. They may b either a hand, rotary or mechanized instruments. The various types are:
1. MIXING INSTRUMENTS Most common are the spatulers (hand instruments).
They have flat and wide nibs with blunt edges and straight shank or a double-ended instrument with other end sharp. Are of different sizes with different degrees of stiffness in their nibs to suit various sizes. May be made of stainless steel, ivorine or plastic. Stainless steel is used for mixing lining cements and intermediate base restorative materials whereas agate spatulas are used for mixing glass ionomer and composite resin materials in order to prevent incorporation of metal and corrosive particles in the cement. 2. PLASTIC INSTRUMENTS Used for carrying and handling materials after mixing while the materials are in plastic stage in the prepared cavities or tooth. Usually double ended hand instruments, with a flat sided nib with blunt edges and corners, but may differ in their nib shapes and angulation or curvature of shanks. May be made of stainless steel, ivorine or plastic and also plated with teflon or anodized aluminum titanium nitrate coated to minimize
facilitate easy cleaning. 3. AMALGAM CARRIER
Single ended hand instrument with a cylindrical hollow working tip, with a curved tip or straight tip with different tip diameter (1.25mm or 2.3mm). They have a spring action handle and may be made of stainless steel or plastic. Used to carry the mixed silver amalgam into the prepared cavity or calcium hydroxide powder to the exposure site in pulp capping procedures. Modified amalgam carries are available for retrograde filling after apicoectomy (Hill carrier, Messing carrier and Dimaskieh carrier). 4. CONDENSING INSTRUMENTS Used to condense filling materials into the prepared cavity for better adaptation without any voids. They can be hand condensing instruments or mechanical condensers. Depending upon the material (amalgam, direct gold, composite) they will differ in the surface configuration of the nib-face: (smooth or serrated) and have different shapes: round, triangular or diamond and of different sizes for each shape and shank angulation. AMALGAM CONDENSER
Double ended, cylindrical working end with smooth or serrated face of various size and shapes, hand instruments are available. Serrated face is said to increase the surface area and also to provide a mechanical interlock between the already condensed amalgam to the freshly introduced plastic mass and better adaptation to cavity and prevent slimage of amalgam. With condenser of 2mm diameter the ideal condensation pressure would be 1.4 and 1.8 kg and spherical alloys requires less condensation pressure than lathe cut and admix alloy. COHESIVE GOLD CONDENSERS Available as single end or double end instrument, with straight or angular shank with serrated nib. Mechanical condenser are also available wherein the handpiece is adjusted so that it delivers 360-3600 blows / minute. COMPOSITE INSTRUMENTS With the use of posterior composite special hand instruments made of special materials such that the composite does not stick to instruments are available with round, rectangular or rhombic end, which help in insertion and condensation of composite material. 5. CARVERS
Cutting instruments with their blades either beveled on knife-edged [e.g., Hollenback, ward-C, cleoid discoid carver, Frahm’s carver (diamond cravers)]. Hollenback carver possess double-side knife edged point edged nibs with curved monoangled or binangled shanks-efficient in carving amalgam and wax. Cleoid discoid carver used for direct gold restorations. Other carvers with triangular nibs or diamond shaped nibs are also available. 6. BURNISHERS Double and hand instrument with smooth working ends of various shapes such as ball shaped, beaver tail shaped, conical, egg-shaped, apple shaped etc., are available. They can be in the form of burs with perfectly smooth heads to perform a burnishing operation by rotary action.
7. FILES Used for margination of restorations. Nibs can be foot-shaped, hatchet-shaped or parallelogram shaped. Serrations can be directed away from the handle: push file or directed towards the handle: pull file. 8. KNIVES
Nibs carry knife edged faces on one of their sides only. E.g., Bard-Parker knife, Black’s knife, Wilson’s knife and Stein’s knife. Black’s knife has the nibs at various angulations from acute to obtuse, may be push or pull knife used for various purposes. Wilson’s knife has the nib in a plane a right angle to the shaft, introduced interproximally for proximal and gingival manipulation of restorative tips. Stein’s knife trapezoidal nib is used mainly for direct gold contouring and margination. 9. APPLICATOR TIPS Various types of applicator tips made of synthetic bristles are available for pinpoint take-up, transfer and application of Etchant, conditioners or bonding agents to the prepared tooth surface for adhesive restorations.