Instruments 2 l Preclinical Operative MCQs

hand instrument (cutting and non-cutting instruments) and rotary instruments as hand piece l Preclinical Operative MCQs (multiple choice question) for dental students

 

Dental Rotary and Hand Instruments

• The instrument used for operative dentistry field may be hand instrument (cutting and non-cutting instruments) with rotary instruments as hand piece .   

 

Hand Instruments

• These are hand powered dental instruments
• G.V. Black is credited with the first acceptable nomenclature and classifications of hand instruments. His classification enabled both dentists and manufacturers to communicate more clearly and effectively in regards to instrument design and function.
• For Decades Carbon steel was the primary material used in hand instruments because they were harder and maintained sharpness better then Stainless Steel (SS)
• Stainless Steel (SS) currently is the material of choices it remains bright and efficient
• after steam and dry heat sterilization, and because the properties of SS have been improved by incorporating a significant amount of Chromium.
• Hand instruments in Operative dentistry may be categorized as

1. Cutting Instruments
2. Non Cutting instruments

Cutting Instruments :

• These instruments are used to cut hard or soft tissues of the mouth.
• Hand cutting instruments are composed of 3 parts: Handle, Shank and Blade.
• For non cutting instruments the blade is referred to as the “nib” or the “ working end”

The Handle ( shaft) :

• Is the part grasp by the operator hand while using the instrument

The Shank :

• Serves to connect the handle with the blade.
• The shank may be straight, mono-angle, Biangle, tri-angle, or quad-angle. (The term Contra-angle is used when 2 or more angles are present.
• The angles in the shank are important to keep the blade edge within 1-2 mm to the long axis of the instrument, this helps in balancing the force onto the blade and prevents rotation of the instrument during use.

The Blade ( or Nib):

1. Is the working end of the instruments and is connected to the shank.
2. Some instruments have a blade on each end and are referred to as “double ended instruments”.
3. Blades have many shapes, designs and sizes depending on the function they are to perform.

Instrument formula according to G.V. Black:

3 number formula system:

• Cutting edge of the instrument is at a right angle to the blade.

1. first number: Width of the blade in tenth of a millimetre
2. second number : length of the blade in millimetres
3. third number : angle the blade forms with the axis of the handle in centigrade

4 Number instrument formula:

• Cutting edge of the instrument is at an angle other than a right angle to the blade.

1. First number: Width of the blade in tenth of a mm
2. Second Number : Angle the cutting edge forms with the axis of the handle in centigrade
3. Third number :length of the blade in mm
4. Fourth Number : Angle the blade forms with the axis of the handle in centigrade.

Examples of cutting instruments:

Chisel:

• Either has a straight shank or with a slight blade curvature or Bin-angle chisel, and the blade has a bevel only on one side of the edge, Its cutting edge is perpendicular to the axis of the handle.
• Chisels are used for cutting Enamel and Dentin with using motion

Hoe:

• similar to a chisel with the cutting edge perpendicular to the axis of the handle, However, its blade has a greater angle from the long axis of the handle then does that of a chisel.
• It has the same use of chisel.

Hatchet :

• Also referred to as an Enamel Hatchet. The cutting edge is parallel to the long axis of the handle and beveled only from one side.
• It is used for cutting Enamel and dentin. It comes in Right and left types for use in opposite sides of the preparation.

Gingival Marginal Trimmer :

• This instrument is used for beveling of the gingival enamel margin in a proximal box.
• Also used in beveling of the axiopulpal line angle of class II cavities. It is similar in design to a hatchet except the blade is curved, and the cutting edge is at an angle ( other then parallel) to the long axis of the blade.
• It is made as Right and left types. Also it is made so as right and left pair is either a mesial pair or a distal pair.
• When the second number in the formula is 90-100 the pair is used distally, if the number is 75-85 its used to bevel the mesial.

Spoon Excavator:

• The blade is curved and the cutting edge at the end of the blade is in the form of a semicircle, this gives the instrument an outer convexity and an inner concavity that resembles a spoon.
• Like the hatchet the cutting edge at the end is parallel to the handle, therefore, there are right and left cutting spoons.
• The shank of some spoons holds a small disc blade at its end and is knows as a “ discoid”, some hold what resembles a claw and are referred to as a “cleiod”

Hand Instrument Grasp technique

Pen Grasp:

• It is similar to that used in holding a pen, while the tip of the ring finger
• and little finger are placed on a tooth nearby in the same arch to rest and create a fulcrum.

Inverted Pen Grasp:

• similar to the pen grasp but the hand is rotated so that the palm is more towards the operator.
• This grasp is mostly used for Maxillary teeth and indirect vision

Palm and Thumb Grasp:

• handle is in the palm of the hand and grasped by all the fingers, while the thumb is free. to rest on other teeth or use when excessive force is needed ( rarely inside the mouth )

Non cutting instruments:

• here the blade is replaced by a nib.

I. Diagnostic Instruments :

• These are the basic set needed during any and all dental appointment ( please do not come to any clinic without a sterile set)

1. Mirror: Used for indirect visualization of any tooth surface, for reflection of the light into the area examined or being treated, also to retract the soft tissue ( tongue, cheek, lip) to aid access and visualization.
2. Probe or explorer: pointed instrument used to “feel” the tooth surface in order to detect irregularities and determine hardness of dentine during caries detection. they can be straight, sickle, or angled.
3. Tweezer or cotton forceps ( pliers) : Used to carry items into and out of the patients mouth.

II. Plastic Instruments:

• Used to carry and shape tooth colored restorative material such as Composite and GI, or for packing temporary filling material inside unfilled cavity preps. Also used to place bases and liners, these instruments are made of metal or hard plastic.

1. Ash 6: Similar to a carver with non sharp margins of the working end
2. Ash 49: double ended instrument with Cylindrical nibs and rounded ends
3. Dycal applicator: A small hand instrument with a small round nib used for mixing and placing liners into a cavity.
4. Cement Spatula: used for mixing a variety of materials on glass or paper

III. Amalgam instruments :

• Used primarily for placing Ag but can also be used while placing resins

1. Amalgam Carrier: used to carry the Ag and place it into the cavity.
2. Condensers: used to compress Ag into all areas of the prepared cavity. the working end ( nib) is usually round with a flat face, but the face can also have a mesh to aid in condensing. These instruments may also be used to place resin into a prep.
3. Burnisher: Instruments which have different nib shapes such as: round, oval, or rounded cone ( egg shaped) and also different sizes. they are used to burnish Ag at the margin of the restoration, and to smooth the carving of an Ag. Also used to shape matrix bands for better adaptation.
4. Carver: Used to shape Ag or resin material after being placed into the preparation, they have many shapes but are usually flat with a sharp margin.

Rotary Instruments

Handpieces: either straight or contra angle.

• The straight is usually used for lab work or surgical bone removal, while contra angle is used for teeth inside the mouth. Contra angles are further divided according ti their speed of rotation into :

1. Low speed HP
2. High speed HP

Low Speed Handpiece:

• they usually have a range of running speed from 500-15000 rpm. Using a low speed contra angle slowly is helpful when

1. Removing carious dentin. also may be used with different bur shapes 
2. To finish a cavity preparation.
3. Used in finishing and polishing a Restoration

High speed handpiece :

• Have a running speed of 160000-500000 rpm.
• Generally preferred for cutting enamel and dentin.
• Penetration of the cavity through the enamel and extension of the outlines are more efficient at a high speed.
• High speed HP usually generate heat during cutting and should be used with water coolant.

Dental burs

• A group of instruments that can turn on an axis with different speed of rotation and different shapes to perform different types of work.
• They can be used for cutting, finishing and polishing amongst other things.
• Burs used for cutting are made from different materials, such as SS, carbide, diamond, and more recently Ceramic.
• Each bur consists of a : shank, neck and head.

Shank of burs :

• is the part that fits into the HP and accepts the rotation motion of the HP, and which locks the bur into the HP head.

Neck of burs :

• Connects the head to the shank

Head of burs:

• Is the working end of a bur which contains the cutting edges or points.
• Burs have hundreds of shape and sizes.
• The basic bur shapes though are : round , inverted cone and fissure Round Bur: the head is spherical. used for preparation of retentive holes and removal of carious dentin

Inverted Cone:

• from its name the head is a cone with the apex towards the shank. it is used for flattening the floor and providing undercuts ( mainly a Ag bur)

Fissure bur:

• is an elongated cylindrical head bur used to obtain outline form and to cut walls, floor or margin of a cavity. it can be further classifies into straight or tapered.