operative instruments in conservative dentistry & endodontics

Instruments in Operative Dentistry

Dr. Ashok Ayer

Assistant Professor

Department of Conservative Dentistry and Endodontics

College of Dental Surgery

B. P. Koirala Institute of Health Sciences, Dharan, Nepal

Outline:

Hand Instruments

Introduction

Classification

Materials

Application

Techniques

Sharpening

Powered cutting equipments

Rotary cutting instruments

Cutting Mechanism

Hazards

Introduction: G.V. Black

Nomenclature & numbering of hand instruments

1. Cutting instruments/ excavators

2. Noncutting

Designs of some early hand instruments

1728 – Pierre Fauchard invented the bow drill 1891 – Edward C Acheson –produced carborundum tools 1935 – W H Drendes - Diamond cutting instruments

MATERIALS

CARBON STEEL:

HARDER THAN STAINLESS STEEL

MAINTAINED BETTER SHARPNESS

CORRODE IN MOIST CONDITIONSCarbon steel

Stainless Steel

Preferred materials

Remains bright under most conditions

Loses keen edge during use much more

quickly

Chromium: corrosion resistance

Carbon: hardness

Stainless Steel

TUNGSTEN CARBIDE

INSERTS OR BLADES TO PROVIDE MORE

DURABLE CUTTING EDGES (BRITTLE).

THEY MAY BE SOLDERED TO STEEL

HANDLES

SOME INSTRUMENTS ARE MADE WITH

CARBIDE TO PROVIDE MORE DURABLE

CUTTING EDGES.

OTHER ALLOYS OF NICKEL, COBALT, OR

CHROMIUM ARE USED IN THE

MANUFACTURE OF HAND INSTRUMENTS.

THEY ARE RESTRICTED TO INSTRUMENTS OTHER THAN

THOSE FOR CUTTING TOOTH STRUCTURE

Hardening and Tempering Heat

Treatments

Heat treatment Furnace

The hardening heat treatment hardens the

alloy, but it also makes it brittle, especially

when the carbon content is high.

Tempering heat treatment relieves strains and

increases toughness.

Classification of Instruments:- by

SturdevantHAND

INSTRUMENT

cutting

excavators

ordinary

hatchets

hoes

Angle

formers

spoons

chisels

straight

curved

bin-angle

Enamel

hatchet

Gingival

margin trimmers

others

files

scalers

carvers

Non cutting

Amalgam

condensermirrors

explorers,

probes others

ORDER

PURPOSE OF THE INSTRUMENT

E.G. EXCAVATOR, SCALER

SUB-ORDER

MANNER OF USE

E.G. PUSH, PULL

CLASS

FORM OF BLADE

E.G. HATCHET, CHISEL

ANGLE

NUMBER OF ANGLES IN THE SHANK: MONOANGLE, BIANGLE,

TRIPLE-ANGLE, QUADRANGLE

E.G. BIANGLED HATCHET EXCAVATOR,

According to G. V. Black

Classification of Instruments:- by Charbeneau

Cutting instruments

Hand- hoes, chiesel etc

Rotary- burs, discs etc

Condensing instruments

Pluggers

Plastic instruments

Carvers, Burnishers

Finishing and polishing instruments

Discs, Strips

Isolation instruments

Cotton roll, Rubber dam

Miscellaneous-

Mirrors, Explorers

CLASSIFICATION BY MARZOUK

EXPLORING

INSTRUMENTS

REMOVAL OF

TOOTH STRUCTURE

RESTORATION

OF TEETH

To dry

To illuminate

Retraction

Probes

Separators

Mixing

Plastic

Condensing

Burnishing

Carvers

Files

Knives

Finishing

& polishing

Hand cutting

Rotary cutting

Design

Blade

Working part of the instrument

Usually in the form of a bevel (acute angle) that

cuts into the tooth structure.

On non cutting instruments e.g. condensers the

part corresponding to the blade is called the nib or

face.

Shank

Connect the handle to the working end of the instrument.

Normally smooth, round and tapered.

Mon-angle, bin-angle, triple angle

Balance is accomplished by designing the angle of the shank so

that the cutting edge of the blade must not be off axis by more

than 1-2 mm (Sturdevant’s)/2-3 mm (Summitt)

Balance allows for the concentration of force onto

the blade without causing rotation of the

instrument.

Instruments with long blades may required two or

three angles in the shank to bring the cutting edge

near to the long axis of the handle

Such shanks are termed contra angled.

Handle/ Shaft

Serrated for better gripping and control of the

instrument.

a. Standard Stainless steel handle: Diameter 6.4 mm

approx.

b. Padded handles: Diameter 8mm approx.

c. Larger diameter handles: 9.5 mm

More ergonomic

Less likely to develop carpal tunnel syndrome

Occupy more space in instrument tray

Handles are in conjunction with the shank

or it may be separable.

Separate type is known as cone-socket

handle and allows for replacement of several

working ends e.g. mirrors and condensers.

cone-socket handle (mirror)

mirror

Numeric formulas

Describing the dimensions and angle of the working end.

Three number formula

Four number formula:

Cutting edge is not perpendicular to the long axis of the

blade.

Gingival marginal trimmer

Angle former

Instrument shank and

blade design

85

Bevels

Most hand cutting instruments have on the end of the

blade a single bevel that forms the primary cutting edge.

Additional two secondary cutting edges that extend from

the primary cutting edge for the length of the blade.

Allows cutting in 3 directions; facial and lingual walls of

the proximal cavity

Bibeveled instrument have two bevels that form the cutting edge;

e.g. hatched excavator

Single beveled instrument such as spoonexcavator and gingival margin trimmer areused with lateral cutting movement.

Enamel hatchet also as a single beveled instrument

used with direct cutting motion, a planning or

lateral cutting designated for right (R) and left (L) to

the instrument formula.

The cutting edge is perpendicular to

the axis of the handle

e.g. binangle chisel.

Instrument with slight blade curvature

e.g.Wedelstaedt chisel.

Hand cutting instrument

Excavators Chisels

Removal of caries and refinement of the

internal parts of the preparation.

Used primarily for cutting enamel.

Excavators

1. Ordinary Hatchets

2. Hoes

3. Angle formers

4. Spoons

Ordinary Hatchets

It has the cutting edge of the blade directed

In the same plane as that of the long axis of the handle

and

Is bibeveled.

Used primarily on anterior teeth for

Preparing retentive areas and

Sharpening internal line angles, particularly in

preparations for direct gold restorations .

Hoe excavators

Primary cutting edge of the blade perpendicular

to the axis of the handle

Planing tooth preparation walls and forming line

angles.

It is commonly used in Classes III and V

preparations for direct gold restorations.

Hoes with longer and heavier blades, with the

shanks contra-angled.

For use on enamel or posterior teeth.

The blade angle of the hoe: > 12.5 centigrades

The blade angle of chisel: ≤ 12.5 centigrades

Angle former

It is mon-angled and has the primary cutting edge

at an angle (other than 90 degrees) to the blade.

It is available in pairs (right and left )

Used primarily for sharpening line and point angles

and creating retentive features in dentin in

preparation for gold restorations

Also may be used in placing a bevel on enamel

margins

Spoon excavators

Its blades are slightly curved, the shanks may be bin-angled

or triple-angled to facilitate accessibility.

Spoon excavators

discoid cleoid

The cutting edges are

circular

The cutting edges are

claw like.

Left cutting and right cutting

Used mainly for removal of caries and refinement ofinternal opening in a cavity preparation

bin-angled spoon

triple-angled spoon

Cleoid spoon

Discoid spoon

Discoid is disc shaped, with cutting edge around the blade

Chisels:

Straight, Monoangle, Biangle, Wedelstaedt chisels

Enamel Hatchets

Gingival Marginal Trimmers

Straight Chisel

The straight chisel has a straight shank and blade,

with the bevel on only one side.

Its primary edge is perpendicular to the axis of

the handle.

(12-7-0)

The shank and blade of the chisel also may be

slightly curved (Wedelstaedt design)

11½-15-3

Biangled chisel

Force used with chisels : straight thrust

The bin-angle and Wedelstaedt chisels:

Primary cutting edges in a plane perpendicular to theaxis of the handle.

Distal bevel or a mesial (reverse) bevel.

Used for cleaving undermined enamel and for shapingwalls.

Instrument with three cutting motion: vertical, right andleft.

The blade with a distal bevel is designed to plane a

wall that faces the blade's inside surface

The blade with a mesial bevel is designed to

plane a wall that faces the blade's outside surface

Enamel Hatchet

It is a chisel similar in design to the ordinary hatchet

excavator except that the blade is larger, heavier, and is

beveled on only one side

Cutting enamel

Right or Left cutting ends of the double- ended hatchet.

10-7-14

Gingival margin trimmer

Blade is curved

Bevel for cutting edge: outside of the curve

Face of instrument: inside of the curve

12½-100-7-1412½-75-7-14

Mesial Distal

Cutting edge angle: 100 and 75 :

Inlay & Onlay preparations.

Cutting edge angle: 90 and 85 :

Amalgam preparations.

Uses:

Beveling of the gingival margins of proximo-

occlusal preparations.

Beveling of the axio-pulpal line angle

Performing a gingival lock (reverse bevel), placed

on the gingival seat

Usage of hand cutting instruments

Horizontal strokes:

Long axis of blade directed between 45 & 90

degree to the surface being planed or scraped

Vertical or chopping strokes:

Pulling stroke

Hoe: beveled end or distal bevel

Pushing stroke

Hoe: contrabeveled end or mesial bevel.

The cutting edge of the hand instrument should

always be kept sharp as

Dull instruments may cause:

1. Loss of control.

2. More pain.

3. Prolonged time for the operative procedure.

4. Reduce the quality and precision of tooth

preparation.

Stationary sharpening stone e.g. Arkansas

stone, silicon carbide.

Mechanical sharpener; moves at low speed while

the instrument is held at the opposite angle and

supported by a rest i.e. easier and less time

consuming.

E.g. Rx Honing Machine

Mechanical sharpener

Principles of Sharpening

Sharpen instruments only after they have been cleaned

& sterilized

Establish the proper bevel angle (usually 45 degree)

and the desired angle of the cutting edge to the blade.

Use light stroke pressure

Use a rest or guide whenever possible.

Remove as little metal as possible

Non cutting Instruments

Diagnostic instruments

Mirror

Probe or explorer

Twizzer

Plastic instruments

Amalgam instruments

Condensers

Burnisher

Carver

Amalgam carrier

MOUTH MIRROR

Most common sizes used are the No. 4 (⅞ inch diameter)

and No. 5. (15/16 inch diameter)

No. 2 (5/8 inch diameter): when working on posterior teeth

with a rubber dam.

For clarity, reflective surface on the external surface of the

glass: Front surface mirror.

Uses for the mouth mirror. A, Indirect vision. B, Light reflection. C, Retraction. D, Tissue protection.

A

D

C

B

Explorers

To feel tooth surface for irregularities

To determine the hardness of exposed dentin

1. Shepherd’s hook: No. 23

2. Cowhorn explorer: No. 2

3. No. 17: back action

Tweezer/ cotton forceps:

Cotton forceps are used for picking up small items, cotton pellets

Plastic filling Instruments

To carry and shape tooth colored restorative material: Composite resin and glass ionomer

For placing of base and lining material

Hard plastic or metal.

Composite placement instrument

Designed specifically for the placement of composite restorative materials.

Anodized aluminum

Teflon

Titanium nitride layer on instruments

A: ash49 B:ash6 C:dycal applicator D:cement spatula.

Amalgam Carriers

An instrument with a hollow cylinder that is filled with amalgam.

Sizes:

Mini: 1.5 mm diameter

Regular: 2.0 mm

Large: 2.5 mm

Jumbo: 3.0-3.5 mm

Amalgam Condensers

Various Amalgam condensers

Carvers

Hand instruments with a blade or nib used to contour the

surface of filling material in their plastic state, waxes,

models and patterns.

Hollenback carver (knifed edged- elongated- bibevelled)

Diamond (Frahm’s) carver : Bibevelled cutedge.

Ward’s ‘C’ carver

Discoid Cleoid

Interproximal carver

Burnishers

Burnishing of the amalgam on the margins of the cavity,

Shaping metal matrix band to have more desirable contours for

restoration.

To bend cast gold restoration (inlay or onlay) near the margin of

the prepared cavity to narrow the gap between gold and the

tooth.

Burnishers

Disposable brush

Used with etching and bonding procedures associated with composite resins.

Accessory Instruments

Scissors

Used for cutting dental dam material, retraction cord, and stainless steel crowns.

Crown and bridge scissors

Dappen Dish

Hold certain liquid dental materials during a procedure.

Howe Pliers

Also referred to as 110 pliers. Useful for holding items, for

carrying cotton products to and from the oral cavity,

removing the matrix band, and placing and removing the

wedge.

Guards

Interproximal wedges to protect soft tissues from contact

with sharp rotary cutting instruments.

Preset restorative tray

There are four grasps used with the hand

instruments:

Modified pen.

Inverted pen.

Palm and thumb.

Modified palm and thumb.

M o d i f i e d p e n g r a s p

pen grasp Modified pen grasp

Inverted pen grasp

If the hand is rotated so that the palm faces more toward

the operator.

Used in the lingual and labial surfaces of anterior teeth.

inverted pen grasp

Palm and thumb grasp

The handle of the instrument is placed on the palm of the

hand and grasped by all the fingers while the thumb is free of

the instrument and rest on the nearby tooth of the same arch.

Preparing incisal retention in a class III preparation on a

maxillary incisor.

Palm and thumb grasp

The same as in palm and thumb grasp but the

thumb is rested on the tooth being prepared.

Used in the upper arch.

Powered cutting equipments

CHARACTERISTICS:

SPEED

SURFACE FEET PER UNIT TIME OF CONTACT THAT THE TOOL

HAS WITH THE WORK TO BE CUT OR REVOLUTIONS PER

MINUTE

ACCORDING TO MARZOUK:

1. ULTRA LOW SPEED: 300-3000 RPM

2. LOW SPEED: 3000-6000 RPM

3. MEDIUM HIGH SPEED 20,000-45,000 RPM

4. HIGH SPEED 45,000-1,00,000 RPM

5. ULTRA HIGH SPEED > 1,00,000 RPM

According to Charbenau:

1. Conventional or low speed: below 10,000 RPM

2. Increased or high speed: 10,000-1,50,000 RPM

3. Ultraspeed: above 1,50,000 RPM

According to Sturdevant:

1. Low or slow speeds: below 12,000 RPM

2. Medium/Intermediate speeds: 12,000 to 2,00,000 RPM

3. High/ Ultrahigh speeds: above 2,00,000 RPM

Pressure: P=F/A

Low speed: 2-5 pounds of force

High speed: 1 pound of force

Ultra high speed: 1-4 ounces of force

Heat Production

Directly proportional to the Pressure, RPM, and

area of tooth in contact

113˚ F : Pulpitis & pulp necrosis.

130˚ F : Permanent damage of pulps.

Brown et al: Temperature of dentin at a distance of

0.5 mm from a high speed bur cutting dry to be

245˚F (118˚C).

Even in non vital teeth, dry cutting at high speed

should be avoided, since the thermal stresses will

cause microfractures in the enamel. This could

contribute to marginal failure of the restoration.

Higher water velocity.

Clean head system

Greater flow of water coolant is required to prevent clogging when diamonds are used under increased pressure.

42 psi is the optimal air pressure to achieve peak performance

Optic

Drive air

Spray water

Exhaust air

Spray air

Optic

Drive air

Spray water

Exhaust air

Spray air

6-pin

5-hole

VIBRATION:

EQUIPMENT USED & THE SPEED OF ROTATION

EXCESSIVE VIBRATION: ANNOYANCE TO THE PATIENT,

OPERATOR FATIGUE AND RAPID WEAR OF INSTRUMENTS.

TORQUE:

ABILITY OF THE HAND PIECE TO WITHSTAND LATERAL

PRESSURE ON THE REVOLVING TOOL WITHOUT DECREASING

ITS SPEED OR REDUCING ITS CUTTING EFFICIENCY.

Friction:

Occurs in the moving parts of the hand piece especially the

turbine.

Friction is reduced by equipping the hand piece with ball

bearings, needle bearings, glass and resin bearings.

Ceramic Ball Bearings:

40% lighter and 3 times harder than conventional

bearings, they offer an extended turbine life, reduced

operation noise, and less vibration.

Handpieces:

Two basic types of handpieces, the straight handpieceand contra angle handpiece.

The straight is used more frequently for laboratorywork, while contra angle used in the oral cavity.

High speed techniques are generally preferred forcutting enamel and dentin.

Penetration through enamel and extension of the

cavities outline are more efficient at high speed.

Small diameter burs should be used in the high

speed handpiece.

High speed generates considerable heat during

cutting, even with small diameter burs and should

be used with water coolant and high efficiency

evacuation

Design:

This model is the choice for limited access or

when treating children.

Rear-facing exhaust vents direct air flow away

from the surgical site for patient protection

Commonly used couplings

Zero Suck Back Technology

Prevents the intake of aerosol and other

particles when it is stopped.

Drive air flows into an Anti Suck Back

Diffuser (ASBD) within the capsule.

Air in the ASBD is pressurized through

centrifugal force created by the

impeller rotation.

Through the centrifugal force and

rotation of the impeller, air continues

to flow into the ASBD and remains

pressurized even after drive air is

stopped.

The pressurized air in the ASBD is

released to the outside at the

bottom of the head

Low-Speed Handpiece

Design

Straight in appearance.

Standard length and “short.”

Speed ranges from 10,000 to 30,000 rotations per minute (rpm).

Operates the rotary instrument in either a forward or backward movement.

Uses of the low-speed handpiece Intraoral Removal of soft decay and fine finishing of a

cavity preparation. Finishing and polishing of restorations. Coronal polishing and removal of stains.

Extraoral Trimming and contouring temporary crowns. Trimming and relining of removable partials and

dentures. Trimming and contouring of orthodontic

appliances.

Low-Speed Attachments

Straight attachment receives a long-shank laboratory

bur, the contra-angle attachment, and the prophy

angle attachment.

Contra-angle attachment receives latch type rotary

instruments and mandrel.

Prophylaxis Angle

Used during polishing procedures to hold the

prophy cup and bristle brush.

Two types

Plastic disposable “prophy” angle

Metal “prophy” angle

High-Speed Handpiece

Cellular Glass Optics

Uses of the high-speed handpiece

Removes decay.

Removes an old or faulty restoration.

Reduces the crown portion of the tooth for the preparation of a crown or bridge.

Prepares the outline and retention grooves for a new restoration.

Finishes or polishes a restoration.

Sections a tooth during a surgery.

Ultrasonic Handpiece

Design

Attached to the dental unit.

Powered by electricity.

Attachments are similar in appearance to scaling instruments.

Delivers a pulsating spray of water.

Uses of the ultrasonic handpiece

Removes calculus.

Removes stain.

Removes bonding materials from a tooth surfaceafter orthodontic appliances are removed.

Removes cement after orthodontic bands areremoved.

Laser Handpiece

Design

Uses a laser light beam instead of rotaryinstruments.

The laser is conducted through a fiber-optic cable.

Resembles a standard handpiece.

Maintains a water-coolant system.

Maintains an air-coolant system

Uses:Cauterizes soft tissue.Vaporizes decayed tooth structure.

Advantages:Usually painless.Patient usually does not require anesthesia.Proceed with procedure faster.

Disadvantage:Cannot be used on teeth with existing restorations.

AIR-ABRASION HANDPIECE

Design

Small version of a sandblaster.

Compressed air at pressure of 7 to 11 atm (40

to 140 psi)

Produces a high-pressure delivery of aluminum

oxide particles (of 20 to 50 pm) through a small

probe.

Uses:

Prepares teeth for sealants.

Removes external stains.

Class I through class VI preparations.

Endodontic access.

Crown margins.

Prepares a tooth surface for the cementation of a castrestoration, such as a crown or veneer.

Disadvantages:

More effective on hard normal dentine than soft

dentine affected dentine

When using composite, the air abrasion doesn’t

provide the micromechanical roughness needs for

retention thus needs acid-etchant.

Loss of tactile sensation.

Possible iatrogenic damage especially on thecementum and root dentine.

Can induce asthma –> thus needs high volume suction

Can’t remove amalgam restoration.

Can’t perform massive reduction for crown.

Laboratory Handpiece

Design

Operates at speeds up to 20,000 rpm.

Uses laboratory burs.

Provides greater torque than handpieces used intraorally.

Rotary instruments

Cutting Abrasive

Carbide burs

Made from

1- tungsten carbide

2- steel carbide

1- Diamond burs

2- Discs

3- Stones

4- Rubber wheels

According to composition:

1. Steel burs

2. Tungsten Carbide burs

According to mode of attachment to handpiece

1. Latch type

2. Friction grip type

According to handpiece they are designed for;

1. Clockwise

2. Anticlockwise

Rotary instruments consist of three parts :

1- shank

2- neck (shaft)

3- head

head shaft Shank

Shank design

Long shank – used for straight hand piece (low speed)

Short latch shank – used for contra-angle (low speed)

Friction grip shank - used for high speed hand piece

Dental Burs

A group of instruments that can turn on an axis with different

speed of rotation to perform different types of work.

The characteristics of this work are either cutting , abrasive,

finishing or polishing.

Steel burs cut human dentin at low speeds, but dulls rapidly at

higher speeds or when cutting enamel

Steel necks bends easily causing vibration

Carbide burs

Burs possess blades that shear (cut) toothstructure.

They are used for making preciseintracoronal preparation features such asplacing groove, and boxes.

Used for smoothing surface in enamel anddentin

They are not used for bulk reductionbecause to producing undulations on thetooth surface

Shapes: Round Bur:

Initial entry into the tooth

Extension of the preparation

Retentive features and caries removal

Inverted cone bur Undercuts in the tooth preparation

Pear shaped bur Tooth preparation for amalgam, gold foil.

Straight fissure bur Tooth preparation for amalgam

Tapered fissure bur Tooth preparation for indirect restorations.

Basic bur head shapes

Regular –cut

Fine Cut

Coarse-cut

Its used for highly smoothing of prepared surfaces of tooth

Because of its blades in a diagonal to the instrument shaft

Its have a torpedo shape

Twelve-fluted carbide bur

Plain fissure bur

Its tapered and cylinder shape its used for placinggroove and boxes and they also used for finishing ofpreparation.

Groove seating

Bur numbering systems

In the united states the burs have been traditionallydescribed in term of arbitrary i.e. numerical code

eg, 2 =1 mm diameter round bur,

34 = 0.8mm inverted,

57 = 1mm diameter straight fissure

Number 500 is added to indicate cross cutting

Number 900 is added to indicate end-cutting only

So no. 57 ,557 and 957 are all had the same head size

Iso system(international standard organization)

FDI (Federation dentaire internationale)

Usually tend to use head shape name and size

(in tenth of a millimeter)

Eg. Round 010 = 1mm diameter

Straight fissure plain 010 = 1mm diameter

Inverted cone 008=0.8mm diameter

Shapes & diameters of regular carbide burs used for tooth preparation

RoundBur size: 1/16 1/8 ¼ ½ 1 2 3 4 5 6 7 8 9 11

Diameter: 0.30 0.40 .50 .60 .80 1.0 1.2 1.4 1.6 1.8 2.1 2.3 2.5 3.1

Inverted coneBur size: 33½ 34 35 36 37 39 40

Diameter (mm): .6 .8 1.0 1.2 1.4 1.8 2.1

Straight Fissure:Bur size: 55½ 56 57 58 59 60

Diameter (mm): .60 .80 1.0 1.2 1.4 1.6

Straight fissure, round end:Bur size: 1156 1157 1158

Diameter (mm): .80 1.0 1.2

Tapered fissure:Bur size: 168 169 170 171

Diameter (mm): .80 .90 1.0 1.2

Tapered fissure, rounded end

Bur size: 1169 1170 1171

Diameter (mm): .90 1.0 1.2

Pear:Bur size: 329 330 331 332

Diameter (mm): .60 .80 1.0 1.2

Long inverted cone, rounded corners (amalgam preparation)

Bur size: 245 246

Diameter (mm): .80 1.2

End-cutting:

Bur size: 956 957

Diameter (mm): .80 1.0

Bur head design:

The number of blades on a bur is always even

Number of blades on an excavating bur may vary from 6 to8 t0 10.

Finishing bur: 12 to 40 blades

Concentricity:

Measurement of the symmetry of the bur head.

Runout:

Test measuring the accuracy with which all blade tipspass through a single point when the instrument isrotated.

Average value of clinically acceptable run-out is about0.023 mm

Is the primary cause of vibration

Bur blade design

Rake angle:

Angle that the face of the bur tooth makes with the radial line.

Radial rake angle: radial line & the tooth face coincide.

Negative rake angle: blade face is leading the radial line Increases the life expectancy of the bur & provides for the most effective

performance in low and high speed ranges.

Positive rake angle:

Produce acute edge angle

Edge angle:

In the range of 90˚ to provide strength to the blade &longevity of cutting efficiency of the bur.

Land: plane surface immediately following the cutting edge.

Flute/ Chip space:

Space between successive bur teeth or the blades of the bur.

Provides an exit for removal of the fractured matter andcreates a clearance angle.

Clearance angle:

Angle between the back of the blade and the tooth surface.

If a land is present on the bur:

1. Primary clearance angle: the angle the land will make with work.

2. Secondary clearance angle: the angle between the back of the bur

tooth and work.

3. Radial clearance angle: is formed when the back surface of the bur

tooth is curved.

Provides clearance between the work & the cutting edge to prevent

the tooth back from rubbing on the work.

Abrasive instruments

Head consists of small angular particles of hard substance

embedded in a soft binder (ceramic, metal, shellac,

rubber).

Diamond abrasives

Other abrasives –Silicon carbide (carborundum),

aluminium oxide, garnet, quartz, pumice, cuttlebone.

Deposited by Electroplating, sintering or microbrazing.

These are made from diamond chips bonded to blanks(heads). Diamonds used for grinding enamel anddentin surfaces

Diamond burs may divided according to :

1- coarseness ( medium grit - fine grit )

2- shape

Diamond stones

Medium grit

Fine grit

Diamond particle size:

1) Coarse: 125~150 um

2) Medium: 88~125 um

3) Fine: 60~74 um

4) Very fine:38~44 um

Diamond instruments consists of three parts:

A metal blank,

The powdered diamond abrasive

A metallic bonding material that holds the

diamond powder onto the blank

Color coding:

Coarse: 120-150µ

Standard: 106-125µ

Fine: 53-63µ

Extra- fine: 20-30µ

TF: Taper flat end; TR: Taper round end; TC: Taper conicalend; FO: Flame Ogival end; SF: Straight flat end; SO:Straight Ogival end; BR: Ball round; WR: wheel round edge;

Green

Blue

Red

Yellow

Discs, Mandrel, Stones, and Wheels

Moulded abrasive instrument –

Manufactured by pressing a uniform mixture of abrasive

and matrix around roughened end of shank,

Points and stones; finishing & polishing

Coated abrasive instrument –

Disks that have a thin layer of abrasive cemented to a

flexible backing.

surface contouring, finishing

SmartPrep Instruments

SmartPrep Instruments (Smart Bur, Polymer Bur)

Medical polymer that has the ability to remove decayed dentine

while keeping the healthy dentin.

Its hardness is less than healthy dentine while harder than the

carious dentin.

Ability to self-limit(selectively)

It will only cut what is carious and if it’s in contact with

healthy dentin the bur will only wear away (when extensive

force isn’t used).

Advantages:

Conservative Minimal to none disease transfer (because its singleuse only). No need for Local Anesthesia. For Students to start with first clinical cases.

Disadvantages:

Single-patient-use = Expensive.

Technique sensitive ( too much pressure and you will cut the healthy dentine)

The bur breaks down when it touches enamel.

It can sometimes leave large amounts of decayed tissue (use caries dye to locate the left amount.

Access should be done by a different type of bur that can penetrate the enamel.

Cutting Mechanisms

Bladed Cutting:

Brittle fracture: crack production, by tensile loading.

High speed cutting, especially of enamel

Ductile fracture: plastic deformation, by shear.

Low speed cutting.

Abrasive Cutting:

Diamonds are most efficient when used to cut

brittle materials, are superior to burs for removal of

the dental enamel.

Burs are generally preferred for cutting ductile

materials such as dentin.

CUTTING RECOMMENDATIONS

Use of contra-angled handpiece, air-water spray

for cooling, high operating speed (above 200,000

rpm), light pressure.

Carbide burs are better for end- cutting, produce

lower heat, and have more blade edges per diameter

for cutting.

Diamonds are more effective than burs for both

intracoronal & extracoronal tooth preparations,

beveling enamel margins on tooth preparation, &

CHEMO-MECHANICAL CARIES REMOVAL

Carisolv (Chemo‐mechanical caries removal )

Composition:

0.5% sodium hypochlorite and 0.1 M amino acids “Glutamine, leucine and lycine”

This is a technique used to remove caries and decay with minimal invasive techniques. Hypochlorite: dissolves the decayed dentine

Amino acid: buffering solution to prevent damage to the healthy tissue.

[The amino acid and hypochlorite will react with the denaturedCollagen Tissue of dentine (Infected dentine) making soft and easilyremoved with hand instruments.]

Advantages:

Less anesthesia is used

Useful for children, dental‐phobic patients.

Useful for removing root or coronal caries in easily accessible areas.

Removes the smear layer and doesn’t affect the bond strength of the adhesive materials.

No histological effect on the pulp even with direct contact.

Ozone treatment Ozone gas has a high oxidation potential and is

effective against bacteria, viruses, fungi, and protozoa.

Capacity to stimulate blood circulation, platelets, and immune response.

Ozone is used in dentistry in gaseous, ozonated water and as ozonated oils

Ozone has been proven to halt root caries and alsoreverse lesions (pit and fissure carious lesions) byallowing the natural remineralisation process to proceed.

Remineralised lesions are known to be more resistant tofurther dissolution than sound tooth surfaces.

Disruption of the protected ecological niche of the micro-flora allows remineralisation from the saliva.

Intracanal irrigants in endodontic treatment.

Treatment of alveolitis, avascular osteonecrosis of the jaw,and herpes virus infection.

Inhibits plaque formation: periodontal surgical andmaintenance phase.

Used in dental unit water line to disinfect water.

Advantage of ozone therapy is it is an atraumatic,biologically based treatment.

O3 delivered from the HealOzone unit:(2100 ppm O3, 615 ml/min) through a handpiece with a silicone cup that sealed thetooth.

Once sealed, the device automaticallydelivered the O3 for the treatment groupfor 10 seconds followed by 10 secondsvacuum.

Recall:

After one and three months.Prophylaxis of teeth Re-examination using the DIAGNOdent® and ECM readings. Ozone treatment repeat on each of these two recall visits.

HAZARDS WITH CUTTING INSTRUMENTS

PULPAL PRECAUTIONS:

MECHANICAL VIBRATION, HEAT, DESICCATION, LOSS OF

DENTINAL TUBULE FLUID, AND OR TRANSECTION OF

ODONTOBLASTIC PROCESSES.

PULPAL SEQUELAE (RECOVERY OR NECROSIS) TAKE FROM 2 WEEKS

TO 6 MONTHS OR LONGER, DEPENDING UPON EXTENT AND

DEGREE OF TRAUMA.

The remaining tissue is effective in protecting the pulp

in proportion to the square of its thickness.

Steel burs produce more heat than carbide burs because

of inefficient cutting.

Dull instruments will plug debris, do not cut efficiently

and result in heat production.

When used without coolants, diamond instruments

generate more damaging heat than carbide burs.

Air alone as coolant: much lower heat capacity than

water, desiccates dentin, damage odontoblasts.

Soft tissue precautions: Lips, tongue and cheeks of the patient.

Good access and visibility.

Isolation of the operating site: rubber dam, retraction type salivaejector tip.

Wait for the instrument to stop or extremely careful while removing thehandpiece from the mouth.

Large disc

Sudden reflex by the patients.

Hand excavators: soft caries removal in the deep preparation may leadto mechanical pulp exposure: round bur at low speed.

Eye Precautions

Airborne particles, old restorations, tooth structure,

bacteria, debris.

Strong high volume evacuation.

Ear Precautions:

Loud noise: mental and physical distress, increase accident

proneness, reduce overall eficiency.

Noise level in excess of 75 db, 1000 to 8000 cps(frequency)

may cause hearing damage.

Inhalation Precautions

Amalgams or composites produce submicron particles and

vapor.

Alveolar irritation and tissue reactions.

During cutting or polishing: thermal decomposition of

polymeric restorative materials (sealants, acrylic resins,

composites) : Monomers.

Mask : do not filter either mercury or monomer vapors

Conclusion:

The removal and shaping of the tooth structure are

essential aspects of restorative dentistry. Modern high

speed instruments has eliminated the need of many

hand instruments, but hand cutting instruments are

still important for finishing many tooth preparations

and thus they remain as an essential part of the

armamentarium for quality restorative dentistry.

References:

1. Sturdevant’s Art & Science of Operative Dentistry :4th edition

2. Fundamentals of Operative Dentistry; James B. Summitt; 3rd edition.

3. Operative Dentistry of Modern Theory and Practice: M K Marzouk

4. Black GV. A work on Operative Dentistry. Chicago: Medico-Dental Publishing, 1908

5. Dental Hand Instruments, 2003: Elsevier Science (USA). ISBN 0-7216-9770-4

6. Fundamentals of Tooth Preparation: Shillingburg

7. Journal of Interdisciplinary Dentistry / Jul-Dec 2011 / Vol-1 / Issue-2