Cuting instrument applications in conservative dentistry

CUTING INSTRUMENT APPLICATIONS

•Used to cut hard & soft tissues of the mouth.Mainly we have:• Excavators.•Chisels.• Other cutting instruments.

EXCAVATORS*Ordinary hatchets*Hoes*Angle formers*Spoons

ORDINARY HATCHET(3-2-28)*It has the cutting

edge directed in the same plane as that of the long axis of the handle &is bibeveled.

* Used primarily on anterior teeth for preparing retentive areas & sharpening internal line angles.

HOE(4 ½ -1 ½ -22)*cutting edge perpendicular

to the axis of the handle.*used for planing tooth

preparation walls& forming line angles.

* Commonly used in classIII & class V preparation for direct gold restoration.

SPOON EXCAVATORS Bin angle spoon(13-7-14) Triple angle spoon (13-7-14)* Spoon (15-7-14)

spoon excavators are used for>removing caries>carving amalgam or direct wax pattern*cutting edge of the spoon excavator are>Discoid(circular)>Cleoid(clawlike)*shank may be bin angled or triple angled

CHISELS1) Depending upon the shank angle& blade, it

may be>straight (12-7-0)>Wedelstaedt(11 ½ -15-3)>Bin angle(10-7-8)2)Enamel hatchet3)Gingival margin trimmer

Straight chisel has a shank & blade with the bevel on one side.

primary edge is perpendicular to the long axis of the handle.

Bin-angle &Wedelstaedt chisel may have either a distal bevel or a mesial(reverse)bevel.

ENAMEL HATCHET(10-7-14) it is a chisel with

larger &heavier blade beveled on only one side.

cutting edge parallel with the axis of handle.

Use for cutting enamel & comes as right or left types.

GINGIVAL MARGIN TRIMMER (12 ½-100-7-14) designed to produce

proper bevel on gingival enamel margins of proximo-occlusal preparations.

cutting edge is angled(other than perpendicular) to the axis of the blade.

comes as right and left types.

OTHER CUTTING INSTRUMENTS Knife File Discoid-cleoid

instruments.

HAND INSTRUMENT TECHNIQUES Modified pen grasp Inverted pen grasp Palm-and-thumb & Modified palm-and-

thumb grasp

MODIFIED PEN GRASPSimilar to that of holding

a penPads of

thumb ,index ,& middle fingers contact the instrument, while the tip of the fingers is placed on a nearby tooth of the same arch as rest.

Palm generally is facing away from the operator.

INVERTED PEN GRASP Finger positions

same as that of the modified pen grasp

Hand is rotated however, so that the palm faces more towards the operator.

Used mostly for lingual approach of the anteriors

PALM-AND-THUMB GRASP Handle is placed in

the palm and grasped by all the fingers, while thumb is free and the rest is provided by supporting the tip of the thumb on a nearby tooth of the same arch or on firm stable structure.

MODIFIED PALM-AND-THUMB GRASP Handle of the

instrument is held by all the fingers whose pads press the handle against the distal area of the palm & the pad & first joint of the thumb.

This grip fosters control against slipage.

RESTS:- the closer the rest areas are to the operating area, the more reliable the are.

GUARDS:- are hand instruments or other items such as interproximal wedges, used to protect soft tissue from contact with sharp or abrassive instruments.

SHARPENING HAND INSTRUMENTS Requires because

instruments with dull cutting edge cause *More pain

*prolong operating time

*more difficult to control

*reduce quality in tooth preparation

STATIONARY SHARPENING STONES(OILSTONES) Available in coarse ,

medium& fine grit. Commonly used stones are:-

arkansas stone, silicon carbide, aluminium oxide& diamond.

Technique; Thin film of light oil should be

placed on working surface. grasp the instruments with

modified pen grasp, Use light stroke Establish proper 45degree

angle of the bevel and the cutting edge of the stone

MECHANICAL SHARPNERS example:- the Rx

Honing Machine. This instrument moves

a hone in a reciprocating motion at a slow speed, while the instrument is held at the appropriate angulation

Interchangable hones of different shapes and coarseness are available

PRINCIPLES OF SHARPENING Sharpen instruments only after they have

been clean & sterilized Establish the proper bevel angle usually of

45degree Use light stroke or pressure to minimze

frictional heat. Use a rest or guide Remove as little metal as possible After sharpening, resterilize the instrument Keep sharpening stones clean.

SHARPNESS TEST Tested by lightly resting the cutting edge on

a hard plastic surface. If it digs in during sliding, the instrument is

sharp. if it slides , the instrument is dull.