 Hello everyone, welcome back to another session in the industry and more We have hand instruments from Operative Industry So this will be dealt in two or three sessions So the session is about the hand instruments in Operative Industry So basically the instruments are made up of either stainless steel, carbon steel or stellite Stainless steel as we all know it is a combination of chromium, carbon and iron The advantages are the chromium gives the property of corrosion resistance And the disadvantage is mainly the problem of maintaining the sharpness Whereas a carbon steel it consists of manganese, silicon, iron and apart from carbon It is harder than the stainless steel but there are chances of corrosion Stellite is cobalt chromium also it has tungsten, molybdenum and iron High resistance to acid, hardness is an advantage And we have heat treatment with respect to these alloys That is control heating and cooling of metals to alter their physical and mechanical properties Without changing the product shape The first thing is the hardening and next one the tempering treatment The hardening is nothing but steel It should be heated to 1500 to 1600 Fahrenheit that is around 850 degree Celsius And then quenched in oil to harden the working edge So no more than 1 to 2 m of the tip is heated for hardening purpose Otherwise the instrument will lose its balance after sharpening So hardens the alloy but it also makes it brittle Especially when the carbon content is high Whereas a tempering treatment here the cutting edges are usually tempered to produce additional hardness and to remove some of the brittle properties So what we do is the tip is reheated at a lower temperature So it will be constant solution of oil, acid or mercury at 200 to 450 degree Celsius for 10 Now we have classification which is given by UV Black As cutting or non cutting instruments, hand instruments Cutting includes excavators, g-cells and other cutting instruments Escavators can be hatchet holes, ankle former or spoons G-cells are straight curved by the ankle or enamel hatchet and GMT In general marginal trimmer And other cutting instruments or knives, covers, files and scalars Whereas a non cutting one, amalgam, condensers, mirrors, explorers and props Another classification based on Picard's manner of operative identity That is hand held, rod tree and auxiliary Hand held we know examining like mouth and teeth, mouth mirrors and props Scalars and the cutting teeth includes g-cells hatchets Condensation, plastic instruments and condensers and carving Instrument and rod tree instruments Auxiliary includes ultrasonic scalars, lights used for polymerization and fiber optic lights for illumination According to Charbeno, the principles and practice of operative industry have six categories The cutting instruments, condensing instruments, plastic filling instruments, finishing and polishing instruments The isolation instruments and miscellaneous Whereas according to Mazook, the exploring instruments that further divided into drying for illumination For retraction of soft tissues for probing the lesion or separators Second one is removing the tool structure That is again hand cutting instruments, rod tree instruments and ultrasonics Then ultrasonic and restorative instruments Now this session is basically about the nomenclature, formula and design of a hand instrument So the parts of the hand cutting instruments So it has got a blade This is a blade and a shank on both sides and a handle This is handle, shank on both sides Again blade on either ends So shaft used as handle, straight and is usually without variations in sign It may be serrated So you can see the serrations here to not get more grip So length will be around 5.5 inches, diameter is 5.5 millimeter And it is available in various size and shapes like small, medium, large And it will be like hexagonal or octagonal shape Smooth serrated or knurled will be there In order to facilitate the control and increase the friction for hand gripping Instrument, formula, incorporated on it Manufacturing kit number is also present The handle is either continuous with shank or it is separate Shank reconnects the shaft with the blade or working point or nip Okay, so this is a shank Which connects these two parts So it usually extends from its connection with the shaft To where the blade begins from it starts from here Till the point where the blade begins So it is here where any angulation of the instrument can be It will be like smooth, round, tapered or contriangle And a classified instrument depending on the number of angles in the shank That is mono-angle, y-angle, triple-angle or quarter-angle It is depending on the number of angles one, two, three or four Blade is a part of the instrument bearing a cutting edge Begins at the angle if one angle is present at the shank Or at the last angle if more than one angle is present in the shank Or at the point which terminates in the shank And this blade ends in the cutting edge So cutting edge, it is a working part of the instrument Okay So this is a cutting edge, primary cutting edge and secondary cutting edge It is a working part of the instrument It is usually in the form of a bevel in different shape Like bevel single, by, triple or circumferential bevel Can be a regular bevel, distilled shaft, reverse bevel, measled shaft Now we have the blade angle Which is defined as an angle between the long axis of the blade and long axis of the shaft Okay, long axis of the blade And this is the, this is the long axis of blade and this is the long axis of the shaft And this angle is known as blade angle So non-cutting instruments part corresponding to the blade is known as nip So end of the nip or working surface is called face So cutting edge angle is defined as an angle between the margins of the cutting edge And long axis of the shaft And some instruments have blade on both ends of the handle And are known as double ended instruments So enamel and dentine are difficult substances to cut And require the generation of substantial forces of the tip of the instrument So it must be balanced and should be sharp This balance allow for more concentration of force onto the plate without causing rotation And sharpness concentrate the force onto a small area of the edge producing a high stress So balance is accomplished by designing the angle of the shank So that the cutting edge of the blade lies within the projected diameter of the handle This is the projected diameter And nearby and nearly it coincides with the projected axis of the handle For optimal anti-rotational design the blade edge must not be Off axis by more than one or two mm All dental instruments and equipments need to satisfy this principle of balance Now we have the instrument nomenclature given by G.V. Black It is based on order, suborder, class and angle or subclass Order denotes the purpose of the instrument that is excavator scalar So we have one example here That is the excavator, push, hatchet, bin angle it is moving backward Suborder denotes the position of the manual use of the instrument that is push or pull Then the class that is the form of the blade hatchet or chisel The last one is angular subclass It denotes the number of angles in the shank or shape of the shank It's mona-angular by angle So we go from 4 to 1 So we can say that by angle hatchet push excavator Okay so it starts from angle then class, suborder, finally order This is the nomenclature on instrument But as an instrument formula we have many parts here that is This is a blade width then the cutting edge angle Then we have the blade length and we have the blade angle Okay so this is the blade width Then cutting edge angle Then the blade length and blade angle So to describe the parts of an instrument accurately we use this formula So three measurements all expressed in metric system So carved on one side of the instrument shaft So it is in the following sequence The first one that is the width of the blade It is expressed in 1 by 10th of a millimeter The second thing is cutting edge angle That is primary cutting edge angle It is measured from a line parallel to the long axis of the handle Sorry so this is a line parallel to the long axis of the handle Okay so it is measured from line parallel to the long axis of the handle In clockwise centigrade in percentage of 360 degree So if edge is perpendicular to the blade this number is omitted Okay so we take like this So this is a cutting edge If this is perpendicular we will not take this angle Since it is in an angle so we use this Okay so this is a line parallel to the axis of the angle So this bold line not this dotted line bold line Which is just touching the cutting edge So this is a line parallel to the long axis And also touching the cutting edge And we take a clockwise centigrade in percentage Till the cutting edge line meets That is the second one that is the primary cutting edge angle Whereas the third one is a blade length in millimeter So this is a blade length from the cutting edge to the Point of blade where it originates from this Shank Next one is a blade angle So this is a blade angle This line is again a perpendicular Sorry a line which is parallel to the long axis of the handle And a line which is just parallel to the blade Okay so that is a blade angle In some instances an additional number on the handle that is Manufacturers identification number to assess the Manufacturers in cataloging and ordering So this is a four points formula that is width of blade Then the primary cutting edge angle Then third is a blade length that is millimeter The first and third one are in millimeter That is width of blade and blade length The second and the second one and fourth one is not millimeter So that is all about the instrument formula which is very important Instrument formula is important Instrument nomenclature is important It's very commonly asked short notes And these parts of the hand cutting instruments are important So three short notes will be asked from this one Parts Then the instrument nomenclature and instrument formula Okay and classification also is important Now we have the instrument design So an instrument is made of either stainless steel Carbon steel or blades of tungsten carbide Which is soldered to a steel handle So carbon steel has better cutting edge Compared to stainless steel However this carbide blades are most efficient in cutting Even though they are brittle The main principle of cutting with hand instrument Is to concentrate force on a very thin cross section Of the instrument at the cutting edge So thinner the cross section What happens is more the pressure that is concentrated And more efficient the instrument will be Okay so you can see the force applying here is 100 lbs And the angulation here it is 70 and here it is 20 But the net force is here the 200 But here it is just 20 lbs So lesser the angle we have more force So 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 That is single plane instrument Whereas the lateral cutting instruments are those In which the force is applied at right angle To the plane of the blade and handle Actually you have curved blade That is double plane instrument So the single plane instrument may have two or more curves Or angles in their shank All in the same plane as a handle Whereas the double plane has angle or curve in plane At right angle to that of handle So used in direct and lateral cutting But double plane used only in lateral cutting Whereas a contra-angling in order to gain access Many instruments have shank bent at one or more points to angle The blade relative to the angle Depends on the length of the blade or degree of the angulation So the working point is more out of the line with the angle of angle So if this occurs more than 3 mm from the handle axis The instrument will be out of balance in lateral cutting motion So it should be within 3 mm And force will be required to keep the instrument from rotating in one hand To solve this problem The modern instruments are designed to have one or more angles in the shank Placing a working point within 3 mm Which is known as contra-angling So contra-angling The short blades Short blade and small blade angle requires only Bine angle contra-angling Whereas a longer blade and greater blade angle requires triple contra-angling So length of the blade required is determined by the depth of the cavity And the blade angle is determined by the accessibility requirement The greater angles are required for more posterior teeth And incisional portion of proximal cavities in anterior teeth So in addition to balance contra-angling will provide better access And a clearer view for the field of operation So we have this right and left instruments Many instruments are paired Four direct cutting instruments are made either right or left By placing the bent on one side of the blade So if the instrument is held with the cutting edge down And pointing away from the operator Okay Held with the cutting edge down and pointing away from the operator The bevel is on the right side That is the right instrument If bevel on the left It is the left instruments For lateral cutting Move instrument from bevel side to non-bevel side That is lateral scraping motion Lateral cutting instruments are made left and right by having curve or ankle Which is at right angle to the principal plane Either on right or left So single beveled instrument A single plane instrument with cutting edge at right angle to the long axis of the shaft If beveled on side away from the shaft That is known as distally beveled If beveled on side of the blade towards the shaft Which is measly beveled If these instruments have no ankle in shank Or an ankle 12 degree or less Which is used in push and scraping motion And if it is more than 12 degree So known as pull and push So by beveled instrument hatchets and straight chisels Cut by pushing them in the direction of long axis of the blade Triple beveled instruments beveling in the blade laterally together with the end That is forms three cutting edge Then we have circumferential beveled Usually occurs in double plane instrument where blade beveled at all peripheries It is the spoon excavator is a common example That was all about the course session of operative instruments Basically hand instruments So we covered the basic classification Then instrument design Instrument formula Instrument nomenclature And basic parts and classification All are very very important for university exams So next session will be about instrument uses Various instruments and its uses So I will come up with that topic in my next session Thank you