Oper.i 10

College of DentistryCollege of Dentistry
Operative Dentistry IOperative Dentistry I
Instruments & Instrumentation -3-Instruments & Instrumentation -3-
Dr. Hazem El AjramiDr. Hazem El Ajrami

Bur head shapes:Bur head shapes:
Round burs:Round burs:
They are numbered from 1/4, 1/2, 1, 2 to 11.They are numbered from 1/4, 1/2, 1, 2 to 11.
They are round in shape and are used for:They are round in shape and are used for:
Gaining access into carious areas.Gaining access into carious areas.
In making retention grooves and starting points.In making retention grooves and starting points.
Excavation of carious dentin in someExcavation of carious dentin in some
inaccessible areas.inaccessible areas.
For removal of the roof of the pulp chamber inFor removal of the roof of the pulp chamber in
the process of obtaining out-line form inthe process of obtaining out-line form in
endodontic treatment.endodontic treatment.

Fissure burs:Fissure burs:
These burs may be straight or spiral fluted,These burs may be straight or spiral fluted,
and their flutes may further be cross-cut. Thereand their flutes may further be cross-cut. There
are many shapes of fissure burs designed forare many shapes of fissure burs designed for
particular purposes:particular purposes:
 Plain cylinder fissure bur,Plain cylinder fissure bur, it is numbered fromit is numbered from
55551/21/2 to 60 and used in shaping the cavity wallsto 60 and used in shaping the cavity walls
to obtain the required resistance form and forto obtain the required resistance form and for
finishing and smoothening enamel walls.finishing and smoothening enamel walls.

 Tapered fissure,Tapered fissure, it is numbered 168-171 and isit is numbered 168-171 and is
used for retention grooves and for slightused for retention grooves and for slight
diverging of cavity walls for indirectdiverging of cavity walls for indirect
restorations.restorations.
 Tinker fissure,Tinker fissure, is used for making gingivalis used for making gingival
chamfers in crown preparations and for makingchamfers in crown preparations and for making
the reverse bevel retentive feature in the gingivalthe reverse bevel retentive feature in the gingival
seat for cast gold restorations.seat for cast gold restorations.
 End-cutting fissure,End-cutting fissure, is used for extending andis used for extending and
flattening the gingival seat.flattening the gingival seat.

Various shapes of burs;Various shapes of burs;
left column going down:left column going down:
round, inverted cone,round, inverted cone,
plain fissure, fissureplain fissure, fissure
with rounded end, cross-with rounded end, cross-
cut fissure, cross cutcut fissure, cross cut
fissure with roundedfissure with rounded
end, while right columnend, while right column
going down: taperedgoing down: tapered
fissure, tapered fissurefissure, tapered fissure
with round end, cross-with round end, cross-
cut tapered fissure, pear-cut tapered fissure, pear-
shaped, long pear-shaped, long pear-
shaped and end-cuttingshaped and end-cutting
bur.bur.

Inverted cone burs:Inverted cone burs:
They are numbered from 33They are numbered from 331/21/2, 34, 35 to, 34, 35 to
40. They are cone-shaped are used mainly for40. They are cone-shaped are used mainly for
lateral extension of the cavity outline and forlateral extension of the cavity outline and for
establishing wall angulations and retentionestablishing wall angulations and retention
features.features.

Pear-shaped burs:Pear-shaped burs:
Pear-shaped burs are present in either normalPear-shaped burs are present in either normal
length (numbered from 229-332) or long-lengthlength (numbered from 229-332) or long-length
bur (long inverted cone with rounded comers,bur (long inverted cone with rounded comers,
numbered 245-246). Normal-length pear bur (No.numbered 245-246). Normal-length pear bur (No.
330) has its length that is slightly greater than the330) has its length that is slightly greater than the
width, and it is advocated for use for conservativewidth, and it is advocated for use for conservative
Class I tooth preparation. A long-length pear burClass I tooth preparation. A long-length pear bur
(No. 245) has the length (3 mm.) that is almost(No. 245) has the length (3 mm.) that is almost
three times the width (0.8 mm.), is used for tooththree times the width (0.8 mm.), is used for tooth
preparation for amalgam.preparation for amalgam.

• The silhouette of the No. 245 long inverted coneThe silhouette of the No. 245 long inverted cone
bur reveals sides that slightly converge towardbur reveals sides that slightly converge toward
the shank, with rounded end corners resulting inthe shank, with rounded end corners resulting in
convergent facial and lingual preparation wallsconvergent facial and lingual preparation walls
and rounded internal line angles. Rounding ofand rounded internal line angles. Rounding of
line angles results in lower stresses in restoredline angles results in lower stresses in restored
teeth, enhance the strength of the tooth byteeth, enhance the strength of the tooth by
preserving vital dentin and facilitate adaptationpreserving vital dentin and facilitate adaptation
of restorative materials.of restorative materials.

Bur sizes:Bur sizes:
The size of the bur refers specifically to the burThe size of the bur refers specifically to the bur
head diameter. The American Dental Associationhead diameter. The American Dental Association
(ADA) produced a standard classification, which(ADA) produced a standard classification, which
demonstrated the relationship between bur headdemonstrated the relationship between bur head
dimensions, head shapes, and size numbers, i.e.dimensions, head shapes, and size numbers, i.e.
the bur number indicates not only the size of thethe bur number indicates not only the size of the
bur, but also the shape of the head. As the numberbur, but also the shape of the head. As the number
increases, so does the bur size. Round bur areincreases, so does the bur size. Round bur are
available in numbers fromavailable in numbers from 1/41/4 to 11, the invertedto 11, the inverted
cone bur sizes from 33cone bur sizes from 331/21/2 to 40 and the straightto 40 and the straight
fissure bur from 55fissure bur from 551/21/2 to 60.to 60.

• Moreover, numbers proceeded by 1,3,5,7 or 9Moreover, numbers proceeded by 1,3,5,7 or 9
indicate various shapes of bur heads. Forindicate various shapes of bur heads. For
instance, the 500 and 700 series indicate crosscutinstance, the 500 and 700 series indicate crosscut
flutes. Similarly, a 900 prefix is used to indicateflutes. Similarly, a 900 prefix is used to indicate
a head design intended for end-cutting. Fora head design intended for end-cutting. For
example, No. 57 is a plain fissure bur; No. 557 isexample, No. 57 is a plain fissure bur; No. 557 is
a fissure bur with crosscut and No. 957 is an end-a fissure bur with crosscut and No. 957 is an end-
cutting fissure bur. As the effectiveness of smallcutting fissure bur. As the effectiveness of small
burs has increased, they have replaced largerburs has increased, they have replaced larger
burs in many procedures.burs in many procedures.

Bur blades design:Bur blades design:
The head of a cutting bur may be divided intoThe head of a cutting bur may be divided into
6 or 8 blades (also called teeth, flutes). Each flute6 or 8 blades (also called teeth, flutes). Each flute
or blade has a leading side "Face" and trailing sideor blade has a leading side "Face" and trailing side
"Back" with an angle in between, called the "Flute"Back" with an angle in between, called the "Flute
Angle" or "blade angle". The face of the bladeAngle" or "blade angle". The face of the blade
makes an angle with the radius of the bur knownmakes an angle with the radius of the bur known
as the "Rake Angle". Also the back of the bladeas the "Rake Angle". Also the back of the blade
makes an angle with the "work" or the line at rightmakes an angle with the "work" or the line at right
angle to the radius, known as the "Clearanceangle to the radius, known as the "Clearance
Angle". The space between each two successiveAngle". The space between each two successive
blades is called the "Clearance space or Chipblades is called the "Clearance space or Chip
space".space".

FaceFace
BackBack
Flute AngleFlute Angle
Positive Rake AnglePositive Rake AngleZero (radial) Rake AngleZero (radial) Rake AngleNegative Rake AngleNegative Rake Angle
Clearance AngleClearance AngleClearance or Chip SpaceClearance or Chip Space ToothTooth
RotationRotation

• The Rake angle may be positive, zero (radial), orThe Rake angle may be positive, zero (radial), or
negative, depending on whether the radial line isnegative, depending on whether the radial line is
ahead, overlying, or trailing the face of the blade,ahead, overlying, or trailing the face of the blade,
respectively, when the bur is rotating in therespectively, when the bur is rotating in the
correct manner. A positive rake angle enables thecorrect manner. A positive rake angle enables the
blade to cut more effectively than a radial or ablade to cut more effectively than a radial or a
negative one. However, the rake angle can benegative one. However, the rake angle can be
made more positive only at the expense of themade more positive only at the expense of the
bulk of the blade, i.e. by thinning out the bladebulk of the blade, i.e. by thinning out the blade
and decreasing the blade angle. This will causeand decreasing the blade angle. This will cause
the blade to become weak and to bend and lose itsthe blade to become weak and to bend and lose its
effectiveness quite more rapidly. Carbide burseffectiveness quite more rapidly. Carbide burs
normally have blades with slightly negative rakenormally have blades with slightly negative rake
angle.angle.

The Clearance angle acts to decrease theThe Clearance angle acts to decrease the
friction between the back of the bur blade andfriction between the back of the bur blade and
the work or tooth tissues during cutting and,the work or tooth tissues during cutting and,
therefore, decreases heat generation.therefore, decreases heat generation.
The Clearance space is the space where theThe Clearance space is the space where the
chips formed during the cutting procedureschips formed during the cutting procedures
collect and gets eliminated. If this space is toocollect and gets eliminated. If this space is too
small, the formed chips will remain in betweensmall, the formed chips will remain in between
the bur blades, causing its clogging, withthe bur blades, causing its clogging, with
generation of more heat and loss ofgeneration of more heat and loss of
effectiveness.effectiveness.

Cutting efficiency:Cutting efficiency:
The cutting efficiency of a bur is usuallyThe cutting efficiency of a bur is usually
defined as its ability to remove adefined as its ability to remove a
maximum amount of tooth tissues with amaximum amount of tooth tissues with a
minimum of effort and time involved. Itminimum of effort and time involved. It
is influenced by several and mostly inter-is influenced by several and mostly inter-
related factors including:related factors including:

1.1. Bur design:Bur design:
As has been mentioned, the more positive theAs has been mentioned, the more positive the
rake angle, the more effective is the bur inrake angle, the more effective is the bur in
cutting, but also the shorter will be its functionalcutting, but also the shorter will be its functional
life. The number of blades on the bur headlife. The number of blades on the bur head
affects its cutting efficiency, i.e., more bladesaffects its cutting efficiency, i.e., more blades
result in a greater cutting efficiency. However,result in a greater cutting efficiency. However,
there is a limit for increasing the number ofthere is a limit for increasing the number of
blades on the bur head. Beyond this limit (moreblades on the bur head. Beyond this limit (more
than 8 blades) gross weakening of the blades, athan 8 blades) gross weakening of the blades, a
decrease in chip space and an increase indecrease in chip space and an increase in
clogging tendency and heat generation willclogging tendency and heat generation will
occur.occur.

• The cross-cutting of "flutes" (cross-cut bur) hasThe cross-cutting of "flutes" (cross-cut bur) has
been a successful attempt to increase the numberbeen a successful attempt to increase the number
of blades on the bur head without undueof blades on the bur head without undue
weakening of blades. At the same time the chipweakening of blades. At the same time the chip
space gets increased and, consequently, thespace gets increased and, consequently, the
clogging tendency and heat generation areclogging tendency and heat generation are
decreased. However, recently its use was reduceddecreased. However, recently its use was reduced
since they were found to produce unduly roughsince they were found to produce unduly rough
surfaces when used at high speeds.surfaces when used at high speeds.

• Increasing the number of blades (more than 8),Increasing the number of blades (more than 8),
decreases its cutting efficiency. Some burs willdecreases its cutting efficiency. Some burs will
have 10-12 up to 40 blades. As expected, theyhave 10-12 up to 40 blades. As expected, they
are not designed for cutting, but rather forare not designed for cutting, but rather for
finishing and polishing of restorations.finishing and polishing of restorations.
Burnishing burs have no blades or flutes inBurnishing burs have no blades or flutes in
their head design.their head design.

2.2. Influence of load:Influence of load:
During tooth structure cutting, the operatorDuring tooth structure cutting, the operator
exerts an amount of force on the bur. This forceexerts an amount of force on the bur. This force
is concentrated at the bur-tooth contact areais concentrated at the bur-tooth contact area
where pressure is induced. The amount of thiswhere pressure is induced. The amount of this
pressure (P), therefore, will depend essentiallypressure (P), therefore, will depend essentially
on both the force (F) exerted by the operator,on both the force (F) exerted by the operator,
and the area of contact (A) between the bur andand the area of contact (A) between the bur and
the tissues of the tooth being cut, according tothe tissues of the tooth being cut, according to
the equation:the equation:
PP ==
FF
AA

• This pressure, while appears to increase theThis pressure, while appears to increase the
cutting rate of the bur, causes:cutting rate of the bur, causes:
Increase in heat generation.Increase in heat generation.
Increase the dulling tendency of the bur.Increase the dulling tendency of the bur.
Causes the edge of the blades of the bur toCauses the edge of the blades of the bur to
bend or chip and hence it decreases the life ofbend or chip and hence it decreases the life of
the bur.the bur.

• It is evident that the technique or manner ofIt is evident that the technique or manner of
use of any type of bur is an important factoruse of any type of bur is an important factor
influencing both its cutting efficiency and life.influencing both its cutting efficiency and life.
Therefore, this operating pressure shouldTherefore, this operating pressure should
always be kept to a minimum, i.e. by exertingalways be kept to a minimum, i.e. by exerting
of minimum load or force on the bur and byof minimum load or force on the bur and by
allowing for a maximum area of contactallowing for a maximum area of contact
between the bur and the cut tissues.between the bur and the cut tissues.

• Based on these facts, it can be deduced that theBased on these facts, it can be deduced that the
round bur is a most efficient end-cutting and is,round bur is a most efficient end-cutting and is,
therefore, used in gaining access through thetherefore, used in gaining access through the
enamel. In doing this, it will be contacting theenamel. In doing this, it will be contacting the
enamel with a wide surface. Consequently, lessenamel with a wide surface. Consequently, less
stresses will be induced in the bur and less heatstresses will be induced in the bur and less heat
will be generated, while the bur will still bewill be generated, while the bur will still be
removing tooth tissues at a faster rate.removing tooth tissues at a faster rate.

• For the same reason, the inverted cone and theFor the same reason, the inverted cone and the
fissure burs are effective as lateral cuttingfissure burs are effective as lateral cutting
tools and must never be used for end-cutting.tools and must never be used for end-cutting.
Otherwise, rapid bending or dulling out of theOtherwise, rapid bending or dulling out of the
edges of their blades and loss of efficiency willedges of their blades and loss of efficiency will
occur due to the considerable pressureoccur due to the considerable pressure
induced. Also they must be applied with theirinduced. Also they must be applied with their
full sides contacting the tooth.full sides contacting the tooth.

3.3. Composition of the bur:Composition of the bur:
It has already been mentioned that carbideIt has already been mentioned that carbide
burs are much more efficient than steel burs.burs are much more efficient than steel burs.
Carbide burs thus cut both enamel and dentinCarbide burs thus cut both enamel and dentin
quite effectively, and their cutting efficiencyquite effectively, and their cutting efficiency
increases as the rotational speed is increased.increases as the rotational speed is increased.
On the other hand, steel burs are effective onOn the other hand, steel burs are effective on
dentin and only at low speed ranges. If used ondentin and only at low speed ranges. If used on
enamel or at high speeds, the edges of the steelenamel or at high speeds, the edges of the steel
bur will soon bend or dull out, and thus losebur will soon bend or dull out, and thus lose
efficiency due to:efficiency due to:

Their lower hardness which causes the blades toTheir lower hardness which causes the blades to
lose sharpness readily, and thus generate morelose sharpness readily, and thus generate more
heat.heat.
The lower melting point of the steel inThe lower melting point of the steel in
comparison to the tungsten carbide which causescomparison to the tungsten carbide which causes
the steel to soften and bend more readily underthe steel to soften and bend more readily under
the effect of the generated heat.the effect of the generated heat.
Both of these factors act mutually to decreaseBoth of these factors act mutually to decrease
the cutting efficiency and life span of the steelthe cutting efficiency and life span of the steel
burs.burs.

4.4. The Tissues to be cut:The Tissues to be cut:
The enamel has a high hardness numberThe enamel has a high hardness number
which, together with its peculiar structuralwhich, together with its peculiar structural
architecture, makes this tissue highly resistantarchitecture, makes this tissue highly resistant
to cutting with burs. The dentin, on the otherto cutting with burs. The dentin, on the other
hand, is softer and, therefore, easier to cut withhand, is softer and, therefore, easier to cut with
burs. Consequently, the burs will cut moreburs. Consequently, the burs will cut more
effectively on dentin than on enamel, providedeffectively on dentin than on enamel, provided
other factors are constant.other factors are constant.

5.5. Eccentricity or Run-out:Eccentricity or Run-out:
Concentricity is a direct measurement of theConcentricity is a direct measurement of the
symmetry of the bur head during rotation. Run-symmetry of the bur head during rotation. Run-
Out is a dynamic test measuring the accuracyOut is a dynamic test measuring the accuracy
with which all the blades tips pass through awith which all the blades tips pass through a
single point when the instrument is rotated. Asingle point when the instrument is rotated. A
bur or a stone is said to have eccentricity if thebur or a stone is said to have eccentricity if the
maximum displacement of the periphery of themaximum displacement of the periphery of the
working point of the tool from its central axis isworking point of the tool from its central axis is
more than 0.025 of a mm.more than 0.025 of a mm.

• Eccentricity causes vibration, loss of efficiency,Eccentricity causes vibration, loss of efficiency,
and the generation of much heat. The operatorand the generation of much heat. The operator
will also lose tactile sense, and thus becomes lesswill also lose tactile sense, and thus becomes less
able to control the instrument. Eccentricityable to control the instrument. Eccentricity
mainly results from bending of the bur neck.mainly results from bending of the bur neck.
• It could also result from loss of precision of theIt could also result from loss of precision of the
hand piece or engine attachments.hand piece or engine attachments.

6.6. The influence of speed:The influence of speed:
This is the rotational speed at which a rotaryThis is the rotational speed at which a rotary
tool will be cutting at its maximum rate. Ittool will be cutting at its maximum rate. It
corresponds to the cutting rate which depends oncorresponds to the cutting rate which depends on
the time of cutting, the rotational speed (rpm),the time of cutting, the rotational speed (rpm),
and the area of tooth to-tool contact. In otherand the area of tooth to-tool contact. In other
words, the increase of rotational speed willwords, the increase of rotational speed will
enable using small size bur or abrasive to affectenable using small size bur or abrasive to affect
a maximum rate of cutting provided other factorsa maximum rate of cutting provided other factors
are constant. The beak of cutting efficiency ofare constant. The beak of cutting efficiency of
carbide burs is reached at speed rates higher thancarbide burs is reached at speed rates higher than
those for diamond points and stones.those for diamond points and stones.

B.B. Abrasives:Abrasives:
The second major category of rotary cuttingThe second major category of rotary cutting
instruments involves abrasive rather than bladeinstruments involves abrasive rather than blade
cutting. Abrasive instruments are based oncutting. Abrasive instruments are based on
small, angular particles of a hard substancessmall, angular particles of a hard substances
held in a matrix of softer material. Theheld in a matrix of softer material. The
efficiency of an abrasive point, stone or disk isefficiency of an abrasive point, stone or disk is
mainly a function of the size, shape, andmainly a function of the size, shape, and
abrasion resistance of the abrasive particlesabrasion resistance of the abrasive particles
employed.employed.

Diamond points and stones:Diamond points and stones:
Diamond points and stones are the mostDiamond points and stones are the most
popular rotating abrasives. Diamond particles arepopular rotating abrasives. Diamond particles are
used for hardness, and they are fused to steelused for hardness, and they are fused to steel
blanks that are shaped as cylinders, wheels,blanks that are shaped as cylinders, wheels,
tapering points and disks. They remove enameltapering points and disks. They remove enamel
more efficiently than carbide burs if a generousmore efficiently than carbide burs if a generous
coolant of water is utilized. Diamond pointscoolant of water is utilized. Diamond points
could be differentiated according to:could be differentiated according to:

Head shapes and sizes:Head shapes and sizes:
Diamond instruments are available in a wideDiamond instruments are available in a wide
variety of shapes and in sizes that correspond tovariety of shapes and in sizes that correspond to
all applications. More than 200 shapes and sizesall applications. More than 200 shapes and sizes
of diamond are currently marketed. Micro-of diamond are currently marketed. Micro-
preparation diamonds are recently introducedpreparation diamonds are recently introduced
with very small working parts to allowwith very small working parts to allow
minimally invasive shaping of the cavities andminimally invasive shaping of the cavities and
maximum preservation of tooth structure.maximum preservation of tooth structure.

Diamond particles factors:Diamond particles factors:
The efficiency of an abrasive point is aThe efficiency of an abrasive point is a
function of the size, shape, spacing, uniformity,function of the size, shape, spacing, uniformity,
bonding and abrasive resistance of the abrasivebonding and abrasive resistance of the abrasive
particles used. Diamond particle size isparticles used. Diamond particle size is
categorized as coarse, medium, fine and verycategorized as coarse, medium, fine and very
fine used for preparation. Diamond finishingfine used for preparation. Diamond finishing
instruments use even finer diamonds to produceinstruments use even finer diamonds to produce
relatively smooth surface of restorations.relatively smooth surface of restorations.

Influence of diamond particle size on its degree of cutting.Influence of diamond particle size on its degree of cutting.

The pressure of cutting is increased when usingThe pressure of cutting is increased when using
large particle sizes or when the particles arelarge particle sizes or when the particles are
widely spaced. Proper diamond instrumentwidely spaced. Proper diamond instrument
speed and pressure are the major factors inspeed and pressure are the major factors in
determining service life span. Many types ofdetermining service life span. Many types of
abrasive instruments are used in dentistry inabrasive instruments are used in dentistry in
addition to diamond instruments.addition to diamond instruments.
Synthetic or natural abrasives may be used,Synthetic or natural abrasives may be used,
including silicon carbide, aluminum oxide andincluding silicon carbide, aluminum oxide and
quartz.quartz.

Particle size and distribution; smaller particles with close distributionParticle size and distribution; smaller particles with close distribution
(A) and larger particles with wider spacing (B).(A) and larger particles with wider spacing (B).

• Applications of burs and abrasives:Applications of burs and abrasives:
The difference in design between burs andThe difference in design between burs and
abrasives causes differences in the mechanism ofabrasives causes differences in the mechanism of
cutting, and thus in applications for which theycutting, and thus in applications for which they
are suited. Abrasives are most efficient whenare suited. Abrasives are most efficient when
used to cut brittle materials and are thus superiorused to cut brittle materials and are thus superior
to burs in cutting enamel. On the other hand,to burs in cutting enamel. On the other hand,
dentin causes rapid clogging of the abrasive withdentin causes rapid clogging of the abrasive with
increased heat generation. Carbide burs are moreincreased heat generation. Carbide burs are more
effective for end cutting, produce lower heateffective for end cutting, produce lower heat
generation and are more efficient in cuttinggeneration and are more efficient in cutting
dentin.dentin.

Surface cutting of a 6-fluted bur (A), a 12-fluted bur (B),Surface cutting of a 6-fluted bur (A), a 12-fluted bur (B),
a 24-fluted bur (C) and a diamond stone (D)a 24-fluted bur (C) and a diamond stone (D)

• Carbide burs are thus effectively used forCarbide burs are thus effectively used for
intracoronal tooth preparations (cavityintracoronal tooth preparations (cavity
preparations), while diamond abrasives are morepreparations), while diamond abrasives are more
effective in extracoronal tooth preparations, e.g.effective in extracoronal tooth preparations, e.g.
preparations for veneers, beveling enamel marginspreparations for veneers, beveling enamel margins
of cavity preparations and enameloplasty.of cavity preparations and enameloplasty.
However, because diamonds produce a rougherHowever, because diamonds produce a rougher
surface than burs, they may be preferred for use insurface than burs, they may be preferred for use in
cavity preparations for bonded restorations. Thecavity preparations for bonded restorations. The
roughened surface increases the surface area androughened surface increases the surface area and
therefore increases the bonding potential. In suchtherefore increases the bonding potential. In such
case, the use of copious amounts of water coolantcase, the use of copious amounts of water coolant
is mandatory to control the heat generated.is mandatory to control the heat generated.

• Heat generation:Heat generation:
During removal of tooth structure by rotaryDuring removal of tooth structure by rotary
instruments, heat is generated due to:instruments, heat is generated due to:
The friction between the tool and the tooth.The friction between the tool and the tooth.
Part of the energy delivered for working thePart of the energy delivered for working the
tool being expended in the form of heattool being expended in the form of heat
instead of work at its head.instead of work at its head.

The amount of heat generation will be a functionThe amount of heat generation will be a function
of:of:
The amount of friction, which is increasedThe amount of friction, which is increased
through application of greater pressure, use ofthrough application of greater pressure, use of
higher speeds or if larger size tools are employed.higher speeds or if larger size tools are employed.
The cutting efficiency of the tool used. SimilarlyThe cutting efficiency of the tool used. Similarly
heat generation will increase if a dull orheat generation will increase if a dull or
inefficient tool is used. This is attributed to:inefficient tool is used. This is attributed to:
The greater pressure needed to affect cutting.The greater pressure needed to affect cutting.
The greater area of friction the dull blade willThe greater area of friction the dull blade will
provide in contacting the tooth.provide in contacting the tooth.
The increase in the amount of energyThe increase in the amount of energy
expended in the form of heat at the bur head.expended in the form of heat at the bur head.

The time of cutting; the longer the time theThe time of cutting; the longer the time the
rotary tool remains in contact with the tooth,rotary tool remains in contact with the tooth,
the more is the amount of heat generation.the more is the amount of heat generation.

The frictional heat generated during operativeThe frictional heat generated during operative
procedures will be dissipated through:procedures will be dissipated through:
The tool; the part of heat dissipated throughThe tool; the part of heat dissipated through
the tool depends upon its bulk and thermalthe tool depends upon its bulk and thermal
conductivity in a direct ratio; i.e. increase inconductivity in a direct ratio; i.e. increase in
the size of a more thermally conductivethe size of a more thermally conductive
instrument will increase the heat dissipated.instrument will increase the heat dissipated.

The tooth structure itself; the amount of heatThe tooth structure itself; the amount of heat
dissipated through the tooth is the mostdissipated through the tooth is the most
biologically relevant. The dentin is an excellentbiologically relevant. The dentin is an excellent
thermal insulator with a thermal tolerance of 85°thermal insulator with a thermal tolerance of 85°
to 132°F. That is to say, it can protect the pulpto 132°F. That is to say, it can protect the pulp
against temperatures between these extremes.against temperatures between these extremes.
However, if it is subjected to temperatureHowever, if it is subjected to temperature
changes beyond these extremes, it retains heatchanges beyond these extremes, it retains heat
with consequent pain and pathologic changes inwith consequent pain and pathologic changes in
the pulp.the pulp.

The surrounding atmosphere and the formedThe surrounding atmosphere and the formed
chips; the atmosphere surrounding the workingchips; the atmosphere surrounding the working
tool furnishes the most important medium fortool furnishes the most important medium for
the control of such an amount of heat reachingthe control of such an amount of heat reaching
the vital tooth tissues. For this reason, it isthe vital tooth tissues. For this reason, it is
essential that a type of coolant be used,essential that a type of coolant be used,
especially if higher speeds are employed, toespecially if higher speeds are employed, to
control the rise of temperature.control the rise of temperature.

• Coolants do not prevent production of heat butCoolants do not prevent production of heat but
it does serve to control it. This coolant may beit does serve to control it. This coolant may be
water, air, or water-air spray; the water-airwater, air, or water-air spray; the water-air
spray is considered to be the most effective,spray is considered to be the most effective,
since water alone impairs visibility and airsince water alone impairs visibility and air
alone could cause desiccation of dentin.alone could cause desiccation of dentin.

• The coolant serves to:The coolant serves to:
Control the temperature of the cut surface ofControl the temperature of the cut surface of
the tooth and to keep it within the thermalthe tooth and to keep it within the thermal
tolerance of the dentin. Therefore, thetolerance of the dentin. Therefore, the
temperature of the coolant must be close totemperature of the coolant must be close to
that of the body.that of the body.
Keep the working field clean and thusKeep the working field clean and thus
improve visibility.improve visibility.
Clean the tool and prevent its clogging withClean the tool and prevent its clogging with
debris and loss of efficiency. The life of thedebris and loss of efficiency. The life of the
tool will thus be extended.tool will thus be extended.

Lubricate the tooth surface and hence makeLubricate the tooth surface and hence make
cutting easier and more rapid.cutting easier and more rapid.
Decrease the need for local anesthesia. This isDecrease the need for local anesthesia. This is
advantageous not only to the patient but it allowsadvantageous not only to the patient but it allows
the pulp to respond under a natural conditionthe pulp to respond under a natural condition
without vasoconstriction, i.e., the pulp is notwithout vasoconstriction, i.e., the pulp is not
anesthetized at the time of trauma from cuttinganesthetized at the time of trauma from cutting
procedure, thus it will have more reparativeprocedure, thus it will have more reparative
power.power.

• For a coolant to be efficient, it should be used inFor a coolant to be efficient, it should be used in
adequate quantities and be directed in such a wayadequate quantities and be directed in such a way
that it covers the entire surface of the workingthat it covers the entire surface of the working
tool.tool.
• In conclusion, to decrease and control heatIn conclusion, to decrease and control heat
generation during cutting, the following shouldgeneration during cutting, the following should
be considered:be considered:

Correct use of sharp efficient tools of appropriateCorrect use of sharp efficient tools of appropriate
size. Burs must be cleaned with a soft brass-wiresize. Burs must be cleaned with a soft brass-wire
bur brush to remove dentin chips which clog thebur brush to remove dentin chips which clog the
clearance space.clearance space.
Application of only slight force on the rotatingApplication of only slight force on the rotating
tool, excessive pressure should be avoided.tool, excessive pressure should be avoided.
Selection of the proper rotational speed.Selection of the proper rotational speed.
Deliberate use of coolants.Deliberate use of coolants.

IV.IV. Instruments used for finishing and polishingInstruments used for finishing and polishing
purposes:purposes:
After restoration, the restorative materialsAfter restoration, the restorative materials
should be finished and polished to smoothshould be finished and polished to smooth
lustrous surface. This can be done either using:lustrous surface. This can be done either using:
 Hand instruments:Hand instruments: knifes, scalpels andknifes, scalpels and
finishing strips.finishing strips.
 Rotary instruments:Rotary instruments: finishing burs, finefinishing burs, fine
diamond finishing instruments, abrasivediamond finishing instruments, abrasive
discs, and rubber polishing point or cupdiscs, and rubber polishing point or cup
rotating at low speed.rotating at low speed.

Composite finishing instruments: across the top: finishingComposite finishing instruments: across the top: finishing
strip, from left: fine white stone, 2 medium grit (yellow ring)strip, from left: fine white stone, 2 medium grit (yellow ring)
and 2 fine (red ring) finishing diamonds,and 2 fine (red ring) finishing diamonds,
rubber disc, a mandrel for single-sided flexible discsrubber disc, a mandrel for single-sided flexible discs
and color-coded flexible discs with their mandreland color-coded flexible discs with their mandrel

Finishing and polishing instruments for amalgam; from left: 5 finishingFinishing and polishing instruments for amalgam; from left: 5 finishing
steel burs, 2 white stones, 3 abrasive rubber points and a rubber cup.steel burs, 2 white stones, 3 abrasive rubber points and a rubber cup.

V.V. Instruments used for manipulation andInstruments used for manipulation and
packing or condensation of restoratives:packing or condensation of restoratives:
These instruments include matrices,These instruments include matrices,
separators, mixing spatulas, hand andseparators, mixing spatulas, hand and
mechanical condensers, burnishers andmechanical condensers, burnishers and
carvers.carvers.

Matrices:Matrices:
A dental matrix is that piece of metal or non-A dental matrix is that piece of metal or non-
metal which is used to support and give form tometal which is used to support and give form to
the restoration during its packing and hardening.the restoration during its packing and hardening.
Different types of matrices may be usedDifferent types of matrices may be used
according to the cavity preparation design and theaccording to the cavity preparation design and the
type of restorative material being used.type of restorative material being used.

• Importance of Matrices:Importance of Matrices:
1)1) It serves as a temporary wall or resistanceIt serves as a temporary wall or resistance
during condensation of plastic restorativeduring condensation of plastic restorative
material. This will make it possible for thematerial. This will make it possible for the
operator to apply the force necessary foroperator to apply the force necessary for
thorough condensation or packing of thesethorough condensation or packing of these
materials into compound cavities. Otherwise,materials into compound cavities. Otherwise,
adequate density and adaptation of theadequate density and adaptation of the
restorative material to cavity walls andrestorative material to cavity walls and
margins cannot be obtained.margins cannot be obtained.

2)2) To give shape and contour to the restorationTo give shape and contour to the restoration
and prevent marginal overhangs.and prevent marginal overhangs.
3)3) To maintain this form of the restoration untilTo maintain this form of the restoration until
it hardens.it hardens.
4)4) To keep the gingival tissues and rubber damTo keep the gingival tissues and rubber dam
away from the cavity margins during theaway from the cavity margins during the
whole procedures.whole procedures.

Marginal OverhangsMarginal Overhangs

• Requirements:Requirements:
Easy to adapt to teeth and to maintain thisEasy to adapt to teeth and to maintain this
adaptation to the cavity margins during theadaptation to the cavity margins during the
whole procedures.whole procedures.
Rigid enough to resist condensation pressureRigid enough to resist condensation pressure
necessary for adaptation of the restoration tonecessary for adaptation of the restoration to
cavity margins.cavity margins.
Compatible with the restorative material used.Compatible with the restorative material used.

Smooth and highly polished to give theSmooth and highly polished to give the
restoration a smooth surface texture especially atrestoration a smooth surface texture especially at
the proximal contact area which is difficult tothe proximal contact area which is difficult to
finish.finish.
Provide proper contouring of the restorationProvide proper contouring of the restoration
without interference.without interference.
Easy to contour.Easy to contour.
Easy to introduce and remove.Easy to introduce and remove.
Thin enough not to occupy much space so that itThin enough not to occupy much space so that it
does not interfere with the tightness of the contactdoes not interfere with the tightness of the contact
when removed.when removed.

• Types of matrices:Types of matrices:
I.I. Patented/ready-made matrices:Patented/ready-made matrices:
Consist of manufactured matrix retainerConsist of manufactured matrix retainer
(holder) and matrix band usually made of(holder) and matrix band usually made of
stainless steel of about 0.0012-0.002 inchstainless steel of about 0.0012-0.002 inch
thickness. Several types are availablethickness. Several types are available
including:including:

• Ivory matrix holder No.1;Ivory matrix holder No.1; this type provides onethis type provides one
proximal wall and is used in compound Class IIproximal wall and is used in compound Class II
cavity preparation, either OM or OD for amalgamcavity preparation, either OM or OD for amalgam
restorations.restorations.
• Ivory matrix holder No.8;Ivory matrix holder No.8; this type is used forthis type is used for
compound and complex cavity preparations sincecompound and complex cavity preparations since
its matrix band totally encircles the toothits matrix band totally encircles the tooth
structure. It is suitable for use for compound OBstructure. It is suitable for use for compound OB
or OP amalgam restorations.or OP amalgam restorations.

Ivory matrix No.1; retainer and band.Ivory matrix No.1; retainer and band.

Ivory matrix holder No.8.Ivory matrix holder No.8.

• Tofflemire/Universal matrix system;Tofflemire/Universal matrix system; this matrixthis matrix
(designed by B.R. Tofflemire) is ideally(designed by B.R. Tofflemire) is ideally
indicated for compound or complex Class IIindicated for compound or complex Class II
restorations. It is considered the best in itsrestorations. It is considered the best in its
stability, anatomic adaptation, suitability forstability, anatomic adaptation, suitability for
most of the cases and ease in introduction andmost of the cases and ease in introduction and
removal. However, its rules of application shouldremoval. However, its rules of application should
be strictly followed. The matrix band is availablebe strictly followed. The matrix band is available
in two thicknesses (0.0015 and 0.002 inch) andin two thicknesses (0.0015 and 0.002 inch) and
various occluso-gingival widths.various occluso-gingival widths.

• The proper width should be selected such thatThe proper width should be selected such that
the band is extended 1 mm. above the heightthe band is extended 1 mm. above the height
ofof
the marginal ridge to be restored. The matrixthe marginal ridge to be restored. The matrix
band should be shaped by burnishing on aband should be shaped by burnishing on a
resilient paper pad to achieve proper contactresilient paper pad to achieve proper contact
and contour at the proximal surface/s to beand contour at the proximal surface/s to be
restored.restored.

Burnishing of the matrix band with a suitable burnisher.Burnishing of the matrix band with a suitable burnisher.

• Rules of application of Tofflemire matrix:Rules of application of Tofflemire matrix:
A.A. When the matrix band is folded, the loopWhen the matrix band is folded, the loop
will have a narrower end and a wider end.will have a narrower end and a wider end.
The narrower end should be placedThe narrower end should be placed
gingivally and the wider end placedgingivally and the wider end placed
occlusally.occlusally.
B.B. The matrix band should be placed in theThe matrix band should be placed in the
retainer so that the slotted side of the retainerretainer so that the slotted side of the retainer
is placed gingivally.is placed gingivally.

Narrow and wide ends of the bandNarrow and wide ends of the band
SlottedSlotted of the retainerof the retainer

• Thus, the occlusal (wider) end of the matrix isThus, the occlusal (wider) end of the matrix is
placed first such that the narrower end isplaced first such that the narrower end is
directed gingivally when the slot is placeddirected gingivally when the slot is placed
gingivally. Placing the slot gingivally allows forgingivally. Placing the slot gingivally allows for
easy separation of the matrix band from theeasy separation of the matrix band from the
retainer during removal.retainer during removal.

C.C. The straight matrix retainer is normally placedThe straight matrix retainer is normally placed
on the buccal side. Contra-angled retainer mayon the buccal side. Contra-angled retainer may
be placed on the buccal or lingual side, since itsbe placed on the buccal or lingual side, since its
contra-angling allows its placement on thecontra-angling allows its placement on the
lingual side without being pushed by the anteriorlingual side without being pushed by the anterior
teeth and tongue movement.teeth and tongue movement.
D.D. The loop of the band could be placed to theThe loop of the band could be placed to the
right, left or parallel to the long axis of retainer,right, left or parallel to the long axis of retainer,
depending on the location of tooth. Suchdepending on the location of tooth. Such
positioning will ensure that the matrix retainer ispositioning will ensure that the matrix retainer is
parallel to buccal surfaces of teeth and notparallel to buccal surfaces of teeth and not
disturbed by cheek movements.disturbed by cheek movements.

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