HAND CUTTING INSTRUMENTS

INTRODUCTIONTerm “instrument” refers ‘to a tool, device or

implement used for a specific purpose or type of work.’

They can be used to examine,clean,cut,& restore teeth. The two main types are-

a.Hand instruments-which include a large group of instruments that are hand held when used.

b.Rotary instruments- are operated in a handpiece which in turn is hand held.

• Cutting instrument generally implies, unless otherwise specified ,a hand held instrument used to cut, plane, or cleave tooth structure during the prepration of a cavity to receive a restoration or other treatment.

HISTORY OF HAND CUTTING INSTRUMENTS

When Dr.Jonathen Taft wrote his book of operative dentistry in 1868,cutting procedures on tooth enamel and dentin were carried out using thick bulky chisels and excavators. They were heavy-handled made up of wood, ivory & inferior metals and were as wide as 1\4 inch at the cutting edge .

Chisel was used to gain entrance to the carious dentin which was then removed by the hand excavators .

classificationOperative dental instruments as classified by CHARBENEAU-

1.Cutting instruments- a) Hand -Hatchets -Chisels -Hoes -Excavators -others b) Rotary -Burs -Stones -Disks Others2. Condensing instruments a) Pluggers -Hand -Mechanical

3. Plastic instruments a) Spatulas b) Carvers c) Burnishers d) Packing instruments

4. Finishing and polishing instruments a Hand -Orangewood sticks -Polishing points -Finishing sticks

b.Rotary -Finishing burs -Mounted brushes -Mounted stones -Rubber cups -Impregnated disks

5.Isolation instruments a. Rubber dam b. Saliva ejector c. Cotton roll holder d Evacuating tips 6. Miscellaneous instruments a. Mouth mirrors

b Explorers c Probes d Scissors e Pliers f others

ADVANTAGES OF HAND CUTTING INSTRUMENTS

Self-limited in cutting enamel, cut only enamel undermined by the loss of enamel.

No vibration or heat accompanies the cutting, making it painless and with no adverse effects to tooth tissues.

Most efficient means of precise intricate cutting.

Create the smoothest surface of all cutting instrument.

The longest life span of all cutting instruments.

PARTS OF HAND CUTTING INSTRUMENTS

Parts of instrument

DESIGN CHARECTERISTICS OF HAND CUTTING INSTRUMENTS

Hand instruments regardless of use are composed of 3 parts-

1) Handle/ Shaft-for grasping the instrument. factors to be considered while handle selection- a.weight- hollow-increase tactile transfer. -solid-increase hand fatigue. b.diameter- small-decrease control, increase fatigue. - large-restrict movement in inaccessible areas

c.serrations- knurled-maximize control. smooth-increase muscle fatigue.

SHANK The shank serves to connect the handle to the working end of the instrument They are normally smooth, round and tapered. Any angulation in the instrument is placed at the shaft.

Two Types of instruments

A) If the handle, shank and blade are all made of one piece of steel, the instruments are known as long handled instruments.

B) If the shank and blade or nib are separate from the handle and are intended to be screwed into it the instrument is known as a cone socket instrument.

BLADE / NIB The working end of the cutting instrument is called the blade whereas the working end of the non-cutting instrument is called nib. Face is the end of the nib or working surface. It maybe plain or serrated. Cutting edge is the working part of the instrument. It is in the form of a bevel with different shapes.

- Blade angle is defined as the angle between the long axis of the blade and the long axis of the shaft.

- Cutting edge angle is defined as an angle between the margins of the cutting edge and the long axis of the shaft.

"BLACK'S INSTRUMENT FORMULA"

• G.V. Black established an Instrument Formula that describes:

A)- the dimensions of an instrument (dimension) and

B)- the angulation of the instrument (angulation)

In establishing a nomenclature for hand instruments, Dr. Black prescribed four classes:

• Order:Purpose of the instrument (excavator)• Suborder: Manner of the use (Push)• Class: Form of the working end (Hatchet)• Sub Class: Shape of the shank (Bin angle)

Therefore, an instrument might be described as "Bin angle Hatchet Push Excavator"

INSTRUMENT FORMULA1st no. -Indicates the width of the blade or

primary cutting edge in tenths of a mm.

- 2nd no. - Blade length in mm.

-3rd no. -Indicates the blade angle, relative to the long axis of the handle in clockwise centigrade.

Example -Binangle hatchet-15-8-12( 3 unit formula)

FOURTH UNIT:• When the cutting edge of an instrument is at an angle

other than a right angle to the length of the blade, a fourth unit is added to the basic three-unit formula.

• This additional number, expressed in centigrade.• It represents the angle formed between cutting edge

and central axis of the shaft. It is placed in the Second Position of the formula.

• For example, the distal gingival margin trimmer has a formula 12-95-10-12.

BEVELS OF INSTRUMENT

- Cutting edge at right angle to the long axis of the shaft. - They can be: a.Distally bevelled -if the angle at the junction

of the blade and the shank are observed and if primary bevel is not seen it is distally bevelled .

b.Mesial bevelled /Reverse bevel -

1 ) SINGLE BEVELLED INSTRUMENTS-

2) BIBEVELLED INSTRUMENT Blade is equally bevelled on both sides. Ex - ordinary hatchet.

3) TRIPLE BEVELLED INSTRUMENT They have two laterally placed bevels along

with the bevel on the working end.

Has additional cutting potential. Ex - angle former.

4 ) CIRCUMFERENTIALLY BEVELLED INSTRUMENTS

Usually occurs in double-planed instruments where the blade is bevelled all along the periphery.

Ex spoon excavator ,discoid, cleoid

STERILIZATION OF HAND INSTRUMENT

Accepted methods of sterilization are:-

Steam pressure sterilization (autoclave) Chemical vapour sterilization (chemiclave) Dry heat sterilization (dry clave) Ethylene oxide sterilization

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