Instruments 1 l Preclinical Operative MCQs

 Hand , cutting and non cutting instruments in dentistry (describing design and material of each instrument ) l Preclinical Operative MCQ for dental students

Dental Instruments and equipment for tooth preparation

• Removal and shaping of tooth structure are mandatory for esthetic dentistry.  this process is completely difficult process achieved by the use of hand instruments.
• are categorized as Hand cutting and rotary cutting instrument.

Hand Instrument used in operative dentistry can be classified as:

1. Instrument used for exploration, e.g. explorer.
2. Instrument used for cutting or removing tooth structure, e.g. Excavators, chisels, enamel hatchets, gingival margin trimmer, knives file, scalers and carver.
3. Instrument used for restoration of the tooth structure-Plastic filling instruments, condenser, burnisher

 

Hand instrument can also be classified as cutting and non cutting instruments.

Non cutting instruments :

• Mirror, explorer, condenser, etc.

Cutting instruments:

• Excavators, chisels, enamel hatchet, etc.

Material used for making instrument:

Hand instrument used in operative dentistry are made up of carbon steel, stainless steel, carbide inserts(to make more durable cutting).

Hand Instrument Design

1. Hand instrument consists of three part-Handle, Shank and Blade or Nib.
2. Handle is the grasping end of the instrument.
3. Shank is the part of the instrument which connect handle with the working end of the blade.It may be curved or straight.
4. Blade/Nib : It is the working end of the blade and it may have a cutting edge,bevel,point,beaks or nibs.
5. The part corresponding to Blade of noncutting instrument is known as Nib.The end of nib is known as face or working surface.

Some important definition:

• Cutting edge angle : It is an angle between the margins of the cutting edge and the long axis of the shaft
• Blade angle: It is the angle between the long axis of the blade and the long axis of the shaft.

Instrument formula:

• Hand cutting instrument are given a formula describing the dimensions and angles of the working end.
• The formula is written on the handle of the instrument. The formula consists of three or four codes separated by hypen, for, e.g. 9-70-8-15.

1. The first no of the formula indicates the width of the blade in tenth of a millimeter.
2. The second number indicates primary cutting edge angle expressed as percent of 360 degree. This number always exceeds 50.
3. Third number indicates-the length of the blade in millimeter.
4. Fourth number of the formula indicates blade angle relative to the long axis of handle in clockwise centigrade.

• The instrument is designed in a way that this angle is less than 50.

Instrument used for exploring

• Mirror, explorer and periodontal probes.

1. Mirror are used to visualize the area and retract soft tissue. Mirror are available in sizes no 2,4,5.
2. Explorer are sharp end instrument used to tactile the surface roughness,irregularities,softness or hardness.
3. Example: straight explorer, right angled explorer, Shepherds hook or no 23, Cowhorn or pigtail,No 17,Interproximal explorer.
4. Periodontal probes: Instrument used to detect and measure the width of the periodontal pocket. Example-Michigan probe, williams's probe, periodontal screening probe(PSR).

Forceps used in operative dentistry:

• Cotton forceps No.17 and No.18 and Hemostat(Halstead mosquito striaght and curved)and Articulating forceps.

Other instruments in dental field

• Instrument used for restoration of tooth, e.g. plastic filling instrument, condenser, burnisher, matrices retainer.
• Chisels are primarily used for cutting enamel and are subdivided into straight and curved chisels, Bin angle chisels, enamel hatchets and gingival margin trimmer.

Hand Cutting Instrument

• The instrument can also be designed to have function from both the ends(Double ended instruments).

1. Direct cutting instrument are the instrument in which the force is applied in the same plane as that of the blade and handle. These instruments are called a single planed instrument.
2. Lateral cutting instrument is the instrument in which the force is applied at right angle to the plane of the blade and the handle. These instrument usually have curved blade and are called double planned instruments.
3. Single beveled instruments are instrument having bevel on only one side of the instrument blade. The instrument beveled on the side away from the shaft, are called distally beveled. The instrument beveled on the side of the blade towards the shaft are known as mesially beveled.
4. Bibeveled instrument are the instrument having two bevels on the opposite side of the instrument blade which meet together to form the cutting edge, e.g. Ordinary hatchets.
5. Triple bevelled instruments: If the blade is also beveled laterally,together with ends,It forms three distinct cutting edges. Such instruments are known as Triple beveled instruments, e.g. Angle former.
6. Circumferentially beveled instruments are the double planned instruments with blade beveled at all the peripheries.

Hand Cutting instrument type:

• Chisels, Excavators and other instrument (enamel hatchet, gingival margin trimmer, etc.)

Chisels dental instrument :

•  These instrument are designed for planning and cleaving and are characterized by one sided bevel. Chisels have cutting edge at right angle to the shaft. Chisels are usually used in pushing motion.
• Straight Chisels-Cutting edge is one side (single bevel)and straight blade in line with handle and the shank. The instrument Can be single or double ended. Function-to cleave and plane enamel during cavity preparation.
• Monangle chisels : he blade is placed at angle to shaft and is either mesially beveled (Standard)or distally beveled (Reverse)
• Biangle chisels-These chisels have two angles between the shaft and the blade either beveled mesially and distally. It is used with push motion. Function is to cleave and plane the enamel in cavity preparation.
• Triple angled chisels have three angles in the shank. The instrument is either beveled mesially and distally.

EXCAVATORS dental instruments :

• are the instruments designed for gross removal of the caries and for the internal refinement of the cavity preparation.

Types of excavators

1. Hatchets are bladed instruments with a cutting edge in the same plane of the instruments and are designed as right (a indented ring on the shank or shaft identify the instrument)and left hatchets. Function is To clean and smooth wall in cavity preparation and to remove unsupported enamel. The instrument is used with a push motion.
2. Hoe excavators is single planned instrument in which the angle of the blade with the handle approaches a right angle. Function is The instrument is used for cutting the internal part of the cavity and for removing hard caries.
3. Spoon excavator are double planned instrument in which the cutting edge is ground to a semicircular circumferential bevel. Function is to remove carious dentin and the secondary function are to remove the temporary crowns and temporary restorations
4. Cleoid excavatorThe blade of the instrument has a shape of claw and hence the name cleoid.

 

Other Instrument

• Enamel hatchet is a instrument used for cleaving the undermined enamel.
• Gingival margin trimmer is double planned instrument with curved blade. The cutting edge angle of the Gingival margin trimmer is not perpendicular to the axis of the blade as it is in case of hatchet. Gingival margin trimmer is used for trimming the cavity margin and for placing bevel at the gingival floor.