Hand instruments (final)


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Hand instruments (final)

  1. 1. Introduction : “Man has become the tool of their tools”. Modern hand instruments, when properly used, produce beneficial results that are advantageous to both the operator and the patients. It should be noted that certain results can be satisfactorily achieved only with hand instruments. The standadization of the design of hand cutting instruments by the manufactures has been helpful to the practioner. All the instruments are identified by a nomenclature and number that describes the size, design and common clinical usage. The proficiency and quality of the clinical treatment depend on the proper selection end use of the cutting instruments; therefore the nomenclature and design of the operative instruments must be mastered and adequate number of sharp and sterile instruments should be available for each clinical procedure.
  2. 2. Metals used in the manufacture of hand instruments : Carbon steel : It is an alloy made by the addition of small percentage of carbon to iron. It is capable of being hardened, softened and tempered. Two varieties (i) Soft (ii) Hard. It is harder than stainless steel, but when unprotected, it will rust and corrode. It maintains the been edge under use, so is used for making blade and actual cutting edge of the instruments. Sterilization by boiling water and steam under pressure (autoclave) will cause discoloration. Dry heat can be used. Stainless metals : a) Stainless steel : It is composed of carbon 6 – 10%; chromium 18% and iron 81 – 81.4%. It is extremely hard but requires very careful and precise heat treatment during manufacture. The resistance to staining of these alloy is attributed to the formation of a thin coating of transparent oxide on their surface, therefore it must be kept highly polished at all times to prevent corrosion. It looses a sharp edge on repeated usage easily as compared to carbon steel so is used for handle, shank and part of blade. b) Monel metal : A natural alloy of nickel, copper and iron, Monel metal contains approximately nickel 67%, copper 28% and iron 5%. It is markedly resistant to acids and super heated system. c) Nichrome : Nichrome contains chiefly of nickel 60 – 80%, chromium 12 – 20% and iron 0.26%. It can be subjected to high degree of temperature, doesnot oxidize easily, and does not maintain a sharp edge. d) Satellite : This product is available in severed grades and consists chiefly of cobalt 65 – 90%, chromium 10.35% with small quantities of tungsten,
  3. 3. molybdenum, iron or nickel. Its chief characteristics are hardness, strength, density, high melting point, maintainance of cutting edge and resistance to action of acids. e) Tarno : Is made of popular chromium alloy and is used for manipulation of the cements. DESIGN CHARACTERISTICS OF HAND CUTTING INSTRUMENTS : Parts : A hand instrument consist of the following essential parts. Handle or shaft : It is mostly straight and octagonal in cross-section and may be serrated to increase friction for hand gripping. They are available in various sizes and shapes. Large, heavy handles are not conducive to delicate manipulation; therefore most instrument handles small in diameter and light. Most hand instrument handles are a continuation of the shank. If the hand and blade are separate from the handle and intended to be screamed into it, the instrument is known as a cone-socket instrument. The advantage with this cone-socket instrument is that, if the working end is broken, it may be easily replaced incurring less expense. The disadvantage is it tendency to loosen at the joint. Shank : It connects the shaft with the blade or working point. It is usually tapers from its connection with the point shaft to where the blade begins. Any angulation in the instruments can be placed at the junction of shaft and shank. Blade / Nib : The working end of cutting instrument is called the blade whereas the working end of the non-cutting instruments such as condenser is called a nib. The working surface or end of the nib is called a face. It begins at the angle where the shaft is terminated. Cutting edge : It is the working part of the instrument. It is usually in the form of a bevel with different shapes.
  4. 4. Blade angle : It is defined as the angle between the long axis of the blade and long axis of the shaft. Cutting edge angle : It is defined as an angle between the margins of the cutting edge and long axis of the shaft. INSTRUMENT NOMENCLATURE : Dr. G.V. Black established a nomenclature for hand instruments, similar to the biological classification. 1. Order : Purpose of instrument Eg : excavator or sealer. 2. Suborder : Position or manner of use Eg : Push, pull 3. Class : From of working end, Eg : hatchet, chisel. 4. Subclass : Shape of shank Eg : Monoangle or binangle. Naming usually moves rom 4 to 1. INSTRUMENT FORMULA : Dr. G.V. Black gave an instrument formula that describes the dimension and angulation of the hand instruments. The basic formula consists of three units whose measurements are based upon the metric system. The 1st figure represents : the width of the blade in tenths of the millimeter. The 2nd figure represents : Length of the blade in millimeters. The 3rd figure represents : Angle which the blade forms with the long axis of the handle. This angle is expressed in 100th of a circle or centigrades. These three measurements are sufficient for describing a great percentage of instruments. However for instruments with their cutting edge at on angle. Other than a right angle to the long axis of the blade, a fourth
  5. 5. unit, cutting edge angle is added to the basic three unit formula. This additional number represents the angle formed between the cutting edge and the long axis of the handle. It is placed in the second position of the formula, i.e., before the length of the blade for example, a gingival marginal trimmer has a 4 unit formula. INSTRUMENT DESIGN : 1. Direct Cutting Instrument : It is the instrument that force is applied in the same plane as that of blade and handle. It is called ‘single-planed’ instrument. It may have 2 or more curve/angle in shank but all are in same plane to handle. It is used as direct and lateral cutting instrument. 2. Lateral Cutting Instrument : Are those in which force is applied at a right angle to plane of blade and handle. They are called ‘Double-planed’ instrument. They have curve/angle right angled to handle. It is used in only lateral cutting. 3. Contra angling : To gain access shank 1 or more bends to angle of blade relative to handle. Its extent depends on length of the blade. So the working point is moved out of line with the axis of handle. If this occur more than 3 mm from handle, the instrument is out of balance in lateral cutting motions and force required to control rotating of instrument. So 1 or more angels given in shank to keep working point within 3 mm. Principle is called contra angling length of the blade determined by depth of cavity. Blade angle determined by accessibility. So greater angle for posterior teeth and incisal portion of the anterior teeth. 4. Right and left instruments : Instruments are made right/light by placing bevel on one side of blade. If the cutting edge down pointing away from operator and bevel on right side, it is right instruments. If bevel on left side, it is left instrument.
  6. 6. Single planed instrument for direct cutting, the non-beveled side of blade should be in contact with wall being shaved. For lateral cutting acts, move instrument in scraping action from beveled side to non-bebelled side of the blade. in lateral cutting instrument, blade down, cutting edge away, the instrument have curve directed to right, is right instrument and if the instrument having curve directed to left is left instrument. 5. Single bevelled instrument : These are all single planed instrument. Cutting edge right angle to long axis of shaft. They are designed like carpenter chisel. If the bevel on the blade away from shaft – distal. If the bevel on blade towards shaft. Mesial. When these type of instrument have no angle in shank or an angle of 120 or less, they are used in push (direct cutting) or scraping motion (bevelled to non-bevelled side). If this exceed 120 instrument used in pull motion (distal, beveled) and push motion (mesially beveled). 6. Bibevelled instruments : Hatchets and straight chisels – bibevelled. Blade equally beveled both sides and they are cut by pushing them in the direction of long axis of blade. 7. Triple bevelled instrument : Bevelling blade laterally together with ends – 3 edges. Mostly single planed instrument and small one are tripe beveled. This has additional cutting potential. 8. Circumferentially bevelled : Occur in double planed instrument. Blade bevelled at all peripheries. 9. Single ended and double ended instrument : Double ended – Mesial, distal, right, left in same handle. Single ended – only one specific function. Balance : Balance allows for the concentration of force on to the blade without causing rotation of instrument in the grasps. Balance accomplished by
  7. 7. designing angles of shank so that cutting edge lies within the projected axis of the handle and nearly coincide with projected axis of handle. For optimal antirotational design the blade edge must not be off axis by more than 1 – 2 mm. Sharpness : Sharpness concentrates the force into a small area of the edge producing a high stress. 1. Chisels : These are instruments designed after ordinary carpenter’s tools and are intended for planning and cleaning. These are characterized by a blade that terminates in a cutting edge formed by a one sided bevel. Cutting edge of a chisel is at right angle to the shaft. There are following types of chisels available a. Straight chisel : These have a straight blade in line with the handle and shank. The cutting edge is on one side only. b. Mon angle chisels : In these, the blade is placed at on angle to the shaft. It may be mesially (standard) or distally (Reverse) bevelled. c. Binangle chisels : These have two angles between the shaft and the blade. It may be mesially or distally bevelled. d. Triple – angle chisels : These have three angles in the shank and are usually used to flatten pulpal floor. It may also be mesially or distally bevelled. 2. Excavators : They are used for excavation and removal of caries and sharpening or refinement of the internal parts of the cavity preparation. Types : a. Hatchet : A chisel – bladed instrument with a cutting edge in the plane of the instrument is termed a hatchet. If the blade of a hatchet is at perpendicular angles to the shaft, the cutting edge would be parallel to
  8. 8. the shaft. These are poised i.e. R & L, with an indented ring on the shank or shaft of the right instrument. Certain hatchets are bibevelled also with the cutting edge in the centre. Application : These are used for delicate cutting within the preparation especially in incisors. b. Hoe excavators : A hoe is a descriptive term gives to a form of chisel in which the angle of the blade more nearly approaches a right angle i.e. 25 centigrade. It is a single planed instrument, which can be distally bevelled or mesially bevelled and used with pull motion. Application : These are used for cutting mesial and distal walls of premolars and molars. Both hatchets and hoes are used to remove harder varieties of caries as well as to give form to the internal parts of the cavity preparation. c. Spoon excavators : In these, the cutting angle is ground to a semi- circular circumferential bevel and sharpened to a thin edge. These are available in pairs with the blade of one curved to the right, and the blade of the other curved to the left. The spoon excavators all double-planed instruments with right or left cutting movement only. Application : Used for removal of decayed dentin. d. Cleoid (claw like) excavator : It is similar to the spoon excavator, except that the blade resembles a claw, hence the name ‘cleoid’. It is used in carving amalgam and excavating decay from areas of difficult access. 3. Special forms of chisels : These are designed to perform specific functions. a. Enamel hatchet : These are used for splitting or clearing undermined enamel in proximal cavities and on buccal and lingual walls where it is not possible to
  9. 9. use a chisel. The smaller sizes are primarily used in anterior teeth and larger sizes are mainly used in posterior teeth. b. Gingival marginal trimmer (G.M.T) : It is a (used for forming sharp angles in internal parts of preparation) modified form of hatchet. Two distinct modifications of the basic hatchet design are noted as : i) Cutting edge of a hatchet is at a perpendicular angle to the axis of blade while cutting edge of a gingival margin trimmer is at an angle other than a perpendicular angle to the axis of the blade (so a 4 unit formula). ii) Hatchet has a straight blade, the blade of a G.M.T is curved. iii) Hatchet is a single plane instrument while G.M.T with curved blade is a double plane instrument, so is primarily a lateral cutting instrument. It is paired with right and left sided bevels. G.M.T. is used for creating a proper bevel at the gingival floor. It is also used for trimming the margins of various walls of cavity, preparation. c. Angle former : It is a modified form of chisel. In this instrument, the primary cutting edge is sharpened at a angle to the axis of the blade. The angle of cutting edge to the blade axis is usually 80-850 (4 unit formula). Blade of the angle former is bevelled on the sides also, to form three cutting edges. The acute cutting angle being directed to the right or left makes the angle former a paired instrument. Right of the pair is identified by an indented ring. It is a single planed instrument. It is used to accentual line and point angles in the internal outline form. It is frequently used in cavity preparation for cohesive gold to establish retention form.
  10. 10. d. Wedelstaedt chisel : It is like a straight chisel, but with a slight vertical curvature in its shank. It is bevelled on one side only which can be placed mesially or distally. It is used for cleaving undermined enamel and for shaping walls. 4. Miscellaneous : a. Dental probes : Various types of probes are available, these can be straight, curved or graduated (used in periodontology). b. Knives : Nibs of these instruments carry knife edges faces on one of their sides only the knives known as finishing knives, amalgam knives are made in various sizes and shapes. They are used for trimming off excess filling material on the gingival, facial or lingual margins of a proximal restoration or trimming and contouring the surface of a class V restorations. c. Knives for specific purposes : Wilson’s knife : In this nib is in a plane at perpendicular angle to that of the shaft, so that it can be introduced interproximally for use. Stein’s knife : It has a trapezoidal nib and is used mainly for direct gold restorations for continuous and margination. Files : Nib in files can be foot-shaped, hatchet shaped or parallelogram shaped with serrations of the serrations are directed away from the handle, it is a push file, and if the serrations are directed towards the handle, it is a pull file. These are used for smoothening of margins; if knives and carvers are not sufficient to produce the requisite caw surface margins at the gingival and, files can be used to achieve above said requisite. INSTRUMENT GRASPS :
  11. 11. It is more than just a manner of holding the instrument and must be taken quite seriously otherwise bad habits may be acquired that result in loss of operating efficiency and accumulation of unnecessary strain on the operator. Fundamentally, there are four grasps used with hand instruments. 1. Pen grasp : It is similar to the method of holding a pen, except that the pulps of the thumbs, 1st and 2nd fingers contact the instrument, while the tip of the 3rd and 4th fingers are placed on the adjoining teeth (as rests). The position of 2nd finger is important for good control and thrust to the instrument. This way, due to greater length of the 2nd finger, the application point for the force will be near the working point of the instrument. 2. Inverted pen grasp : This is similar to the pen grasp, but the hand is rotated so that the palm is facing upwards. It is usually used in upper teeth. Not used two frequently, but on certain occasions, depending on the area of operation, type of instrument used and position of the point and operator, modifications of the inverted pen grasps are used. 3. Palm and thumb grasp : It is similar to the method of holding a knife, when cutting a piece of wood. The handle is placed in the palm of the hand and grasped by the four fingers, while the thumb rests on an area other than that being operated on. A supporting rest provided by thumb is necessary because distal control is somewhat insufficient. This grasp is used when the thumb must rest at some point distant from the operating site. It may be used on maxillary teeth particularly the right side, when working form the right rear chair position. Conclusion :
  12. 12. It has to be remembered that rotary instruments are for gross reduction, but refinement is brought about best by hand cutting instruments. Thus with this vision of hand cutting instruments let's strive towards precision in operative dentistry.