Crown prep / dental implant courses

Principle of tooth
preparation
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Flow chartFlow chart
IntroductionIntroduction
Principles – biologic considerationPrinciples – biologic consideration
- Mechanical considerations- Mechanical considerations
-Esthetic considerationsEsthetic considerations
Biological – prevention of damage during tooth preparationBiological – prevention of damage during tooth preparation
- causes of injury- chemical- causes of injury- chemical
- bacteria- bacteria
- temperaturetemperature
- conservation of tooth structureconservation of tooth structure
methods for controlled tooth reductionmethods for controlled tooth reduction
- considerations affecting future dental health- considerations affecting future dental health
- axial reductionaxial reduction
- margin placementmargin placement
- margin adaptationmargin adaptation
- margin geometry- margin geometry
finish lines and armamentariumfinish lines and armamentarium
- occlusal consideration- occlusal consideration

- MechanicalMechanical
- Retention formRetention form
- Magnitude of the dislodging forcesMagnitude of the dislodging forces
- Geometry of tooth preparationGeometry of tooth preparation
- TaperTaper
- Surface areaSurface area
- Stress concentrationStress concentration
- Type of preparationType of preparation
- Roughness of the surface being cementedRoughness of the surface being cemented
- Materials being cementedMaterials being cemented
- Type of luting agentType of luting agent
- Film thickness of the luting agentFilm thickness of the luting agent
-- Resistance form
- Magnitude of direction of the dislodging forceMagnitude of direction of the dislodging force
- Geometry of the tooth preparationGeometry of the tooth preparation
- Physical properties of the luting agentPhysical properties of the luting agent
- Adequate tooth structureAdequate tooth structure
- Margin designMargin design

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- Esthetic considerationEsthetic consideration
- partial coverage restorationpartial coverage restoration
- metal - ceramic restoration- metal - ceramic restoration
- Conclusion- Conclusion

Introduction
 Teeth do not posses the regeneration ability found in mostTeeth do not posses the regeneration ability found in most
other tissue. Therefore, once enamel or dentin is lost as aother tissue. Therefore, once enamel or dentin is lost as a
result of caries, trauma or wear, restorative materials must beresult of caries, trauma or wear, restorative materials must be
used to reestablish form and function.used to reestablish form and function.
 Teeth require preparation to receive restorations and theseTeeth require preparation to receive restorations and these
preparations must be based on fundamental principles frompreparations must be based on fundamental principles from
which basic criteria can be developed that help predict thewhich basic criteria can be developed that help predict the
success of treatment. A good preparation will ensure thatsuccess of treatment. A good preparation will ensure that
subsequent techniques can be easy accomplished.subsequent techniques can be easy accomplished.www.indiandentalacademy.comwww.indiandentalacademy.com

Objectives of tooth preparations
 Reduction of the tooth in miniature to provideReduction of the tooth in miniature to provide
retainer supportretainer support
 Preservation of healthy tooth structure to securePreservation of healthy tooth structure to secure
resistance formresistance form
 Provision for acceptable finish lineProvision for acceptable finish line
 Performing axial tooth reduction to encouragePerforming axial tooth reduction to encourage
favorable tissue response from artificial crownfavorable tissue response from artificial crown
contourscontours

Principles of tooth preparation
Can be divided into 3 broad categoriesCan be divided into 3 broad categories
 Biologic considerations- which effect the healthBiologic considerations- which effect the health
of oral tissueof oral tissue
 Mechanical considerations- affects the integrityMechanical considerations- affects the integrity
and durability of the restorationand durability of the restoration
 Esthetic considerations-which affects theEsthetic considerations-which affects the
appearance of the patientappearance of the patient

Biologic consideration
•Conservation of tooth
structure
•Avoidance of over
contouring
•Supragingival margin
•Harmonious occlusion
•Protection against tooth
fracture
Mechanical considerations
•Retention form
•Resistance form
Esthetic considerations
•Minimum display of metal
•Maximum thickness of
porcelain
•Porcelain occlusal surface
•Subgingival margin

Biologic considerationBiologic consideration
 Structures which are easily damagedStructures which are easily damaged
during crown preparation areduring crown preparation are
Adjacent teethAdjacent teeth
Soft tissueSoft tissue
PulpPulp

Prevention of damage during toothPrevention of damage during tooth
preparationpreparation
 Adjacent toothAdjacent tooth
- Use of metal matrix band around the- Use of metal matrix band around the
adjacent tooth as protection.adjacent tooth as protection.
Disadvantage is thin band can still beDisadvantage is thin band can still be
perforated and enamel damagedperforated and enamel damaged
- use tooth separators- use tooth separators

 Preferred method- “cut wedge technique”Preferred method- “cut wedge technique”
Use of proximal enamel of the tooth beingUse of proximal enamel of the tooth being
prepared. Teeth are 1.5-2mm wider at the contactprepared. Teeth are 1.5-2mm wider at the contact
area than at the CEJ and a thin tapered diamondarea than at the CEJ and a thin tapered diamond
can be passed through the interproximal contactcan be passed through the interproximal contact
area to leave a slight lip or fin of enamel withoutarea to leave a slight lip or fin of enamel without
causing excessive tooth reduction or undesirablecausing excessive tooth reduction or undesirable
angulations of the rotary instrumentangulations of the rotary instrument

Soft tissueSoft tissue
 Damage to lip, tongue, cheek can be perforateDamage to lip, tongue, cheek can be perforate
by careful retraction with aspirator tip, mouthby careful retraction with aspirator tip, mouth
mirror or flanged saliva ejector.mirror or flanged saliva ejector.
 Greater care should be taken while preparingGreater care should be taken while preparing
the lingual surface of the mandibular teeth.the lingual surface of the mandibular teeth.

 Mouth mirrorMouth mirror
 Front surface photographic mirrorFront surface photographic mirror
 High volume vacuum suction tipHigh volume vacuum suction tip
 Saliva ejectorSaliva ejector
 Rubber damRubber dam
 SvedopterSvedopter
 Anti sialogougesAnti sialogouges
 Tongue depressorTongue depressor
 Mouth propMouth prop
 Cheek retractorCheek retractor
 Bite blockBite block

SvedopterSvedopter
Metal saliva ejector attached to tongue deflectorMetal saliva ejector attached to tongue deflector
Advantages-Advantages-
 No cotton rolls requiredNo cotton rolls required
 Lip retraction with mouth mirror not requiredLip retraction with mouth mirror not required
Disadvantages-Disadvantages-
 Assess to lingual surface of mandibular teeth limitedAssess to lingual surface of mandibular teeth limited
 The metal can cause burnishing of the tissue in the floor byThe metal can cause burnishing of the tissue in the floor by
clinching the clamp below the chinclinching the clamp below the chin
 Over sized reflector produces gagging sensationOver sized reflector produces gagging sensation
 Should be used when patient is sitting in upright position, ifShould be used when patient is sitting in upright position, if
used in supine position then the throat and back of the mouthused in supine position then the throat and back of the mouth
should fill with fluid before it reaches the level of evacuationshould fill with fluid before it reaches the level of evacuation
devicedevice

Anti sialogougesAnti sialogouges
 Methantheline bromide- 50mg-1 tab- 1hrMethantheline bromide- 50mg-1 tab- 1hr
prior to the operative procedureprior to the operative procedure
 Propantheline bromide- 15mg-1 tab- 1hrPropantheline bromide- 15mg-1 tab- 1hr
prior to the operative procedureprior to the operative procedure
 Anti sialogouges hold not be used inAnti sialogouges hold not be used in
patients with hypertension, glucoma,patients with hypertension, glucoma,
asthmaasthma

Good visualizationGood visualization
Fibro optic hand piece light Use of dual over head lights

PulpPulp
1. Extensive temperature, chemical irritation, or1. Extensive temperature, chemical irritation, or
microorganisms cause irreversible pulpitis hencemicroorganisms cause irreversible pulpitis hence
extreme care should be takenextreme care should be taken
2. Morphology of the pulp chamber should be considered &2. Morphology of the pulp chamber should be considered &
pulp size evaluated on radiographpulp size evaluated on radiograph
3. Average pulp dimensions related to coronal contour3. Average pulp dimensions related to coronal contour

Causes of injuryCauses of injury
 TemperatureTemperature
CausesCauses - Excessive heat produced by friction- Excessive heat produced by friction
between a rotary instrument and the tooth surfacebetween a rotary instrument and the tooth surface
- Excessive pressure- decreases the speed of the- Excessive pressure- decreases the speed of the
instrument resulting in loss of the cutting efficiency,instrument resulting in loss of the cutting efficiency,
which results in fracture and loss of grain causingwhich results in fracture and loss of grain causing
increase in temperature in the area being prepared.increase in temperature in the area being prepared.
- higher rotational speed without coolant- higher rotational speed without coolant
- type and shape and condition of the cutting- type and shape and condition of the cutting
instrumentinstrument

PreventionPrevention--
By using coolants- Water streamBy using coolants- Water stream
Water sprayWater spray
AirAir
- Water stream is most effective but the disadvantage is- Water stream is most effective but the disadvantage is
that it interferes with vision and is not suited for cooling athat it interferes with vision and is not suited for cooling a
tooth during refinement, smoothening and placement oftooth during refinement, smoothening and placement of
the intricate detailsthe intricate details
- indirect vision can be utilized while cutting wet- the- indirect vision can be utilized while cutting wet- the
mirror should be first coated with detergent, this allowsmirror should be first coated with detergent, this allows
water to form a smooth transparent film on the surface ofwater to form a smooth transparent film on the surface of
the mirror with only a moderate decrease in the visibilitythe mirror with only a moderate decrease in the visibilitywww.indiandentalacademy.comwww.indiandentalacademy.com

 Chemical actionChemical action
- Bases, resins, solvents and luting agents can cause- Bases, resins, solvents and luting agents can cause
pulpal damage when applied on freshly cut dentinpulpal damage when applied on freshly cut dentin
- Prevention- application of varnish, acts as a barrier- Prevention- application of varnish, acts as a barrier
- Chemical agents used for cleaning should not be used- Chemical agents used for cleaning should not be used

Bacterial action
 Bacteria that are left behind or that gainBacteria that are left behind or that gain
access because of microleakage- pulpalaccess because of microleakage- pulpal
damagedamage
 Prevention- remove all carious dentinPrevention- remove all carious dentin
before placing restorationbefore placing restoration

Conservation of the tooth structure
 Tooth structure is conserved by employing the following guidelinesTooth structure is conserved by employing the following guidelines
 Use of partial coverage rather than complete coverage restorationsUse of partial coverage rather than complete coverage restorations
 Preparations of teeth with the minimum practical convergence anglePreparations of teeth with the minimum practical convergence angle
(taper) between axial walls(taper) between axial walls
 Preparation of the occlusal surface so reduction follow the anatomicPreparation of the occlusal surface so reduction follow the anatomic
planes to give uniform thickness in the restorationplanes to give uniform thickness in the restoration
 Preparation of the axial surfaces so tooth structure is removedPreparation of the axial surfaces so tooth structure is removed
evenlyevenly
 Selection of a conservative margin compatible with the otherSelection of a conservative margin compatible with the other
principle of tooth preparationprinciple of tooth preparation
 Avoidance of unnecessary apical extension of the pulpAvoidance of unnecessary apical extension of the pulp

Methods for controlled toothMethods for controlled tooth
reductionreduction
 Index method- use of condensationalIndex method- use of condensational
silicon impression materialsilicon impression material
 Use of custom made pre-contouredUse of custom made pre-contoured
transparent templatestransparent templates

Index methodIndex method
 ProcedureProcedure
 Condensational silicon putty material is adapted to the facial andCondensational silicon putty material is adapted to the facial and
lingual surfaces of the tooth being prepared and the adjacent teethlingual surfaces of the tooth being prepared and the adjacent teeth
 The putty index is cut into 2 halves along the incisal edges of theThe putty index is cut into 2 halves along the incisal edges of the
teethteeth
 The lingual is cut evenly into half i.e incisal and gingival halfThe lingual is cut evenly into half i.e incisal and gingival half
 Reduction doneReduction done
 Reduction depth checked by placing the portion of the siliconReduction depth checked by placing the portion of the silicon
impression materialimpression material

 The impression can be cut through the sagittalThe impression can be cut through the sagittal
plane or middle of the preparation incisogingivallyplane or middle of the preparation incisogingivally

Horizontal indexHorizontal index
 Condensation silicon placed on the facial, lingual, andCondensation silicon placed on the facial, lingual, and
occlusal surfacesocclusal surfaces
 The material removed from the teethThe material removed from the teeth
 A segment is removed by first making cuts along theA segment is removed by first making cuts along the
midlines of the cusps mesial and distal to the tooth beingmidlines of the cusps mesial and distal to the tooth being
preparedprepared
 These cuts are joined by a horizontal slice made on eachThese cuts are joined by a horizontal slice made on each
of the facial and lingual surfacesof the facial and lingual surfaces
 This index provides accurate reference for both facial andThis index provides accurate reference for both facial and
lingual reductionlingual reduction

Use of pre-contoured transparent templatesUse of pre-contoured transparent templates
 ProcedureProcedure
- Impression is made and diagnostic cast madeImpression is made and diagnostic cast made
- Cast mounted on the semi-adjustable articulatorCast mounted on the semi-adjustable articulator
- Fabricate a diagnostic waxing in casts, identify the plannedFabricate a diagnostic waxing in casts, identify the planned
location of the occlusal and axial surfaces of the restorationlocation of the occlusal and axial surfaces of the restoration
- Duplicate the diagnostic waxing using alginate impressionDuplicate the diagnostic waxing using alginate impression
materialmaterial
- Fabrication of the transparent templateFabrication of the transparent template
- The tooth is reduced by using the template as the guideThe tooth is reduced by using the template as the guide

Consideration affecting future dental
health
An improperly prepared teeth- adverse effect on long term dental healthAn improperly prepared teeth- adverse effect on long term dental health
1. Axial reduction1. Axial reduction
2. Margin placement2. Margin placement
3. Margin adaptation3. Margin adaptation
4. Margin geometry4. Margin geometry
5. Occlusal consideration5. Occlusal consideration
6. Preventing tooth fracture6. Preventing tooth fracture

Axial reduction
 Excessive axial reduction- gingival inflammation because patient isExcessive axial reduction- gingival inflammation because patient is
unable to maintain plaque controlunable to maintain plaque control
 Tooth preparation provide sufficient space for the development ofTooth preparation provide sufficient space for the development of
good axial contour which enables the junction between teeth andgood axial contour which enables the junction between teeth and
restoration to be smooth and free of any ledgesrestoration to be smooth and free of any ledges
 Crown should duplicate the contours and profile of original tooth, ifCrown should duplicate the contours and profile of original tooth, if
excess made then crown should be slightly under contoured and flat,excess made then crown should be slightly under contoured and flat,
to avoid plaque accumulationto avoid plaque accumulation

Above theAbove the
gingival crestgingival crest
At the level ofAt the level of
Within theWithin the
Margin placementMargin placement

 Supragingival marginSupragingival margin
AdvantagesAdvantages
-- Can be easily finishedCan be easily finished
- Easily kept clean- Easily kept clean
- Impression easily made and less potential for soft tissue- Impression easily made and less potential for soft tissue
damagedamage
- Restoration can be easily evaluated at recall appointment- Restoration can be easily evaluated at recall appointment

Subgingival margin justified if the followingSubgingival margin justified if the following
conditionsconditions
 Dental caries, cervical erosion, restorations extendingDental caries, cervical erosion, restorations extending
subgingivally and a crown lengthening procedure is indicatedsubgingivally and a crown lengthening procedure is indicated
 The proximal contact area extend to the gingival crestThe proximal contact area extend to the gingival crest
 Additional retention is neededAdditional retention is needed
 The margin of a metal-ceramic crown is to be hidden behindThe margin of a metal-ceramic crown is to be hidden behind
the labioginginval crestthe labioginginval crest
 Root sensitivity cannot be controlled by more conservativeRoot sensitivity cannot be controlled by more conservative
procedureprocedure
 Modification of the axial contour is indicatedModification of the axial contour is indicated

Margin adaptationMargin adaptation
 Junction between restoration and tooth- more prone forJunction between restoration and tooth- more prone for
recurrent caries because cement gets dissolvedrecurrent caries because cement gets dissolved
 Precise figure for marginal fit adaptationPrecise figure for marginal fit adaptation
casting fit- 10µmcasting fit- 10µm
porcelain margin- 50µmporcelain margin- 50µm
 Margin should be smooth and even. If irregular andMargin should be smooth and even. If irregular and
uneven then length of margin increases and substantiallyuneven then length of margin increases and substantially
reduce the adaptation of the restorationreduce the adaptation of the restoration
 Advantages of smooth margin- tissue displacement,Advantages of smooth margin- tissue displacement,
impression making, die formation, waxing, finishing muchimpression making, die formation, waxing, finishing much
easiereasier www.indiandentalacademy.comwww.indiandentalacademy.com

SpeedSpeed
• Speed is defined as revolutions per unit time
or the surface feet per unit time of contact
that the tooth has with the work to cut.

According to speed :
High speed range : 200,000 - 300,000 rpm
Intermediate speed range : 12000 - 200,000 rpm
Low speed range : Below 12000 rpm
By Gilmore-3 Edition:
Regular speed Ultra speed
500-6000 rpm 200,000 rpm
Speed classification

 By G.T.Charbenau
 Conventional or low speed : below 10,000 rpm
Increased or high speed : 10,000-150,000 rpm
Ultra speed : Above 150,000 rpm
 By M.A.Marzouk :
Ultra low speed : 300-3000 rpm
Low speed : 3000-6000 rpm
Medium high speed : 20,000-45,000 rpm
High speed : 45,000-100,000 rpm
Ultra high speed : 1000,000 and above

Low speed:
Low sped range is below 12000 rpm. Although intact tooth
structure can be removed by an instrument rotating at low speed
is a traumatic experience for both patient and dentist.
Uses – 1. Cleaning teeth
2.caries excavation
3. Finishing and polishing
Advantages:
1. Better tactile sensation
2. There is less chance of overheating the tooth.

Disadvantages:
1. Time consuming
2. Requires high force application
3. Generation of heat when used for long time
4.Production of vibration of low frequency and high amplitude
5. Patient discomfort
6. Burs have tendency to roll out of cavity
7. When used with carbide burs higher chance of breakage
because of brittleness.

 Intermediate speed or medium speed:
Speed ranges from12000 to 200000 rpm.
 Uses
- Used for cavity preparation although not efficient and effective.
- For placement of retentive grooves and bevels
• Advantages:
- Used in areas where the vision is limited or a more positive sense of
touch is a need as a guide.
 Disadvantages:
- Time consuming
- Requires high force application
- Generation of heat when used for long time

 High speed :
Speed range is above 200000 rpm
 Advantages :
 Efficient cutting attained
 Used for proper tooth preparation and also removes
old restoration
 Less pressure required
 Less vibration
 No heat generation
 Instruments last longer
 Less patient apprehension
 Operator has better control and greater care of
operation

• BursBurs
• DrillsDrills
• StonesStones
Burs- The term bur is applied to all rotary cutting instruments
that have bladed cutting head.
Drills- are used for boring small diameter holes in tooth
structure.
Stones – remove tooth structure by abrading or wearing awayStones – remove tooth structure by abrading or wearing away
the surface. Most efficient is the diamond chip.the surface. Most efficient is the diamond chip.
ArmamentariumArmamentarium

Torpedo bur
Depth marker
Flame shaped
Inter proximal flame
Round end tapered
Bevelled flame
Flat end tapered

Wheel bur 169L 170 171
713-012
375-012 375-014www.indiandentalacademy.comwww.indiandentalacademy.com

Dimensions of the bursDimensions of the burs
shapeshape TipTip
diameterdiameter
BaseBase
diameterdiameter
CuttingCutting
lengthlength
InclinationInclination
per sideper side°°
ConvergenceConvergence
angle of tipangle of tip
Round end taperedRound end tapered 1.01.0 1.61.6 8.08.0 2.02.0 --
Flat end taperedFlat end tapered
diamonddiamond
1.01.0 1.61.6 8.08.0 2.02.0 --
Long needle diamondLong needle diamond 0.50.5 1.21.2 9.09.0 3.03.0 --
Short needle diamondShort needle diamond -- 1.21.2 6.06.0 3.53.5 --
Small wheel diamondSmall wheel diamond -- 4.04.0 1.41.4 00 --
Torpedo burTorpedo bur -- 1.01.0 6.06.0 00 6060
Flame diamondFlame diamond -- 1.01.0 8.08.0 00 1212
Flamed burFlamed bur -- 1.01.0 8.08.0 00 1212

BurBur Tip diameterTip diameter Base diameterBase diameter Cutting lengthCutting length Inclination perInclination per
sideside
169169 0.540.54 0.90.9 4.24.2 2.52.5
169L169L 0.500.50 0.90.9 5.35.3 2.02.0
170170 0.560.56 1.01.0 4.24.2 3.03.0
170L170L 0.580.58 1.01.0 6.06.0 2.02.0
171171 0.760.76 1.21.2 4.24.2 3.03.0
171L171L 0.780.78 1.21.2 6.06.0 2.02.0
172172 1.141.14 1.61.6 4.44.4 3.03.0
172L172L 1.181.18 1.61.6 6.06.0 2.02.0
Dimensions of the bur

Range of particle sizeRange of particle size
Grit inGrit in µmµm BrasselerBrasseler DenscoDensco StarStar UnionUnion
broachbroach
Extra fineExtra fine 15-3015-30 38-4538-45 38-4538-45 --
FineFine 24-3024-30 53-6353-63 63-7563-75 5353
RegularRegular 75-12575-125 90-15090-150 90-10090-100 106106
CoarseCoarse 100-150100-150 125-150125-150 125-150125-150 115-125115-125
Extra coarseExtra coarse 125-180125-180 180-250180-250 -- --

Tungsten carbide bursTungsten carbide burs
 UsesUses
 For making precise preparation featuresFor making precise preparation features
 Smooth finish lineSmooth finish line
 To cut through metalTo cut through metal
 Burs for cutting- have 6-8 bladesBurs for cutting- have 6-8 blades
 Burs for finishing- have 12 blades or mayBurs for finishing- have 12 blades or may
have 20-40 bladeshave 20-40 blades

 Dentate or cross cut bursDentate or cross cut burs
 Blades are interrupted by cuts across the edgeBlades are interrupted by cuts across the edge
 Not preferred because it leaves deep, severe striations at angleNot preferred because it leaves deep, severe striations at angle
to the path of insertion of the preparationto the path of insertion of the preparation
Advantage- can be used at low speedAdvantage- can be used at low speed

Twist drillsTwist drills
 Cuts only at its tip as it is pushed into the tooth inCuts only at its tip as it is pushed into the tooth in
the direction of the long axis of the instrumentthe direction of the long axis of the instrument
 Has deep twin helical flutes that winds around theHas deep twin helical flutes that winds around the
shaft in a tight spirals, helping to remove chipsshaft in a tight spirals, helping to remove chips
from the holefrom the hole
 Uses- to make holes in dentin to receive retentiveUses- to make holes in dentin to receive retentive
pins for restorationpins for restoration
 Working portion- 3-5mmWorking portion- 3-5mm
 Self limiting collar- depth penetration only tillSelf limiting collar- depth penetration only till
2mm2mm

Diamond/ bur dual instrumentationDiamond/ bur dual instrumentation
 Lusting described the utilization of diamond and carbideLusting described the utilization of diamond and carbide
burs of matching size and configuration matchingburs of matching size and configuration matching
 Diamond for bulk reduction and tungsten carbide forDiamond for bulk reduction and tungsten carbide for
producing smooth finish lines and precise internal featuresproducing smooth finish lines and precise internal features
(boxes, grooves)(boxes, grooves)
 Available because diamond leaves undesirable roughAvailable because diamond leaves undesirable rough
surfaces and irregular cavosurface finish linesurfaces and irregular cavosurface finish line

Turbo double action systemTurbo double action system
 ObjectivesObjectives
 To have the necessary thickness for theTo have the necessary thickness for the
reconstructionreconstruction
 To obtain the most efficacious shape for theTo obtain the most efficacious shape for the
preparation to achieve good stability and correctpreparation to achieve good stability and correct
incorporation of the restoration itselfincorporation of the restoration itself

 SystemSystem ––
 Has cross hatched by a series of deep grooves.Has cross hatched by a series of deep grooves.
 Half the grooves are overted in the direction of rotation and theHalf the grooves are overted in the direction of rotation and the
other half in opposite directionother half in opposite direction
 Grooves meet at 45Grooves meet at 45°which produces a rhomboid isles, these°which produces a rhomboid isles, these
act as blade and produce a surface with no grooves on theact as blade and produce a surface with no grooves on the
tooth surfacetooth surface

 AdvantageAdvantage
 Because of the presence of the groove and the particular directionBecause of the presence of the groove and the particular direction
of the rotary movements, water remains in contact with the toothof the rotary movements, water remains in contact with the tooth
surface instead of being displaced and it recirculates within thesurface instead of being displaced and it recirculates within the
grooves, lubricating and cooling the surface while preventinggrooves, lubricating and cooling the surface while preventing
blockageblockage
 Each isles acts as a cutting blades, the cut surface is smooth henceEach isles acts as a cutting blades, the cut surface is smooth hence
finishing not requiredfinishing not required

Finish linesFinish lines
 Definition- defined as the point at which aDefinition- defined as the point at which a
preparation terminates at the tooth ispreparation terminates at the tooth is
called a finish line.called a finish line.

Functions of a finish lineFunctions of a finish line
 During visual examination it measures the amount of tooth structureDuring visual examination it measures the amount of tooth structure
already removed and delineates the extent of the cut in an apicalalready removed and delineates the extent of the cut in an apical
directiondirection
 Helps to evaluate the accuracy of the impression made for indirectHelps to evaluate the accuracy of the impression made for indirect
procedureprocedure
 On the die, a distinct finish line helps in evaluation of the quality of theOn the die, a distinct finish line helps in evaluation of the quality of the
die and aids in trimming it accuratelydie and aids in trimming it accurately
 The correct marginal adaptation of the wax pattern depends on finishThe correct marginal adaptation of the wax pattern depends on finish
lineline
 The evaluation of the restoration is also aided by a proper finish lineThe evaluation of the restoration is also aided by a proper finish line
 At cementation a sharp finish line aids in determining whether theAt cementation a sharp finish line aids in determining whether the
restoration is fully seated or notrestoration is fully seated or not

Guidelines for Finish linesGuidelines for Finish lines
 Ease of preparation without overextensionEase of preparation without overextension
 Readily identifiable in the impression and on the dieReadily identifiable in the impression and on the die
 A distinct boundary to which the wax pattern can beA distinct boundary to which the wax pattern can be
finishedfinished
 Sufficient bulk of materialSufficient bulk of material
 Conservation of tooth structureConservation of tooth structure

 Kutawa classified margins on the basis of their margin angle-Kutawa classified margins on the basis of their margin angle-
- margin angle between 0- margin angle between 0ºº and 30and 30º- bevelledº- bevelled
-- margin angle between 31margin angle between 31ºº and 60and 60º- chamfersº- chamfers
-- margin angle between 61margin angle between 61ºº and 90and 90º- shouldersº- shoulders
 Pardo classified margins into the two main classes of inclinedPardo classified margins into the two main classes of inclined
planes- vertical or horizontalplanes- vertical or horizontal
- a 90º shoulder was considered a horizontal margin- a 90º shoulder was considered a horizontal margin
- 135º shoulder was considered an inclined vertical design- 135º shoulder was considered an inclined vertical design
Classification of Finish lines

Finish linesFinish lines
 Various finish lines placed are theVarious finish lines placed are the
followingfollowing
• Feather edge
• Chisel edge
• Bevel
• Chamfer
• Shoulder
• Sloped shoulder
• Shoulder with bevel www.indiandentalacademy.comwww.indiandentalacademy.com

Feather edge
Usually not recommended
Indications
• Extremely bell shaped teeth
• Severely tilted teeth where the axial surface of the
tooth meets the path of insertion at an angle greater than 15°
Advantages
• Conservation of tooth structure
Disadvantages
• Does not provide sufficient bulk
• Difficult to visualize
• Irregularities more likely to be present- making it more difficult to fabricate a
restoration that fits accurately
Bur - thin pointed tapered diamond point

Chamfer finish lineChamfer finish line
 Jacobsen & Robinson defined chamfer on the basis ofJacobsen & Robinson defined chamfer on the basis of
their marginal width and/ or geometry.their marginal width and/ or geometry.
they stated that a width greater than 0.3mm at itsthey stated that a width greater than 0.3mm at its
cervical termination precluded any margin being called acervical termination precluded any margin being called a
chamfer.chamfer.
 Bell et al described a chamfer preparation with aBell et al described a chamfer preparation with a
reduction of 1.5mm, round internal line angles, and areduction of 1.5mm, round internal line angles, and a
cavosurface angle of 135cavosurface angle of 135º.º.

Chamfer finish lineChamfer finish line
 Indications
Full metal restorations,
lingual margin of metal-ceramic crown
Advantages
• Distinct margin
• Adequate bulk
• Easier to control
• Rounded internal line angle- less stress
concentration
Disadvantages
Care needed to avoid unsupported lip of enamel
Burs used- torpedo diamond/ bur
- round end tapered diamond/ bur
A chamfer should not be wider than ½ theA chamfer should not be wider than ½ the
bur used to form it, or else may result inbur used to form it, or else may result in
lip formationlip formation

Shoulder
 Shoulder has been defined using marginal geometry, where theShoulder has been defined using marginal geometry, where the
discriminating features are an external cavosurface angle of 90discriminating features are an external cavosurface angle of 90ºº andand
a corresponding butt joint of restoration/tooth at the margins.a corresponding butt joint of restoration/tooth at the margins.
 Indications
- Facial margin of metal- ceramic crowns
- complete ceramic crown
• Advantages
- Bulk of restorative material
- The wide ledge provides resistance to
occlusal forces and minimizes stresses
that might lead to fracture of porcelain
• Disadvantages
- Less conservation of tooth structure
- Sharp 90° internal line angle concentrates stress in
the tooth leading to coronal fracture

MS 1 instrumentsMS 1 instruments
Flat end taperedFlat end tapered
Burs used
Hand instruments for finishing
Enamel hatchet
Hoe

Radial shoulder
It is modified form of shoulder finish line
Indications
Facial margin of metal- ceramic crowns
Advantages
Bulk of material
Less concentration of the stress
Disadvantages
Less conservation of tooth structure
Bur used- Radial fissure burBur used- Radial fissure burwww.indiandentalacademy.comwww.indiandentalacademy.com

 Procedure-Procedure-
Initial ledge is accomplished with the flat endInitial ledge is accomplished with the flat end
tapered diamondtapered diamond
A small radius rounded internal angle isA small radius rounded internal angle is
instrumented by and end-cutting parallel sidedinstrumented by and end-cutting parallel sided
carbide finishing burcarbide finishing bur
Finishing- special modified bin- angle chiselFinishing- special modified bin- angle chisel

Shoulder with bevel
Indications
• Facial margin of posterior metal- ceramic crowns with supragingival
margin
• Extremely short walls- as it permits that critical portion of the axial walls
just coronal to the finish line to formed nearly parallel with the path of
insertion
• Gingival finish line on the proximal box of inlays and onlays
• Occlusal shoulder of onlays
• Mandibular three- quarter crown
Advantages
Bulk of material
Disadvantages
• Less conservative, extends preparation apically

Bevel placementBevel placement
 Bevel is formed by tip of the instrumentBevel is formed by tip of the instrument
 Instruments used-Instruments used-
 Fine flame shaped diamond followed by finishing done using the tip of theFine flame shaped diamond followed by finishing done using the tip of the
long carbide burlong carbide bur
 Torpedo bur- can be used but technique sensitiveTorpedo bur- can be used but technique sensitive
Disadvantage- tends to produce scalloping in the bevel and the finishDisadvantage- tends to produce scalloping in the bevel and the finish
lineline
- bur cannot be guide by contact with a longer axial wall- bur cannot be guide by contact with a longer axial wall
 Gingival marginal trimmer- not recommended because it produces a roughGingival marginal trimmer- not recommended because it produces a rough
irregular bevelirregular bevel
Torpedo diamond burTorpedo diamond bur
Tungsten carbide bur-282-010Tungsten carbide bur-282-010
Fine flame shaped diamondFine flame shaped diamond
Tungsten carbide bur-H48L-010Tungsten carbide bur-H48L-010
Hand instrument
for finishing

Bevel made with diamond
Bevel made with torpedo
diamond
Bevel made with gingival
marginal trimmer
Bevel finished with
tungsten carbide bur

0cclusal bevel0cclusal bevel
 Indications-Indications-
 InlaysInlays
 OnlaysOnlays
 Partial veneer crownsPartial veneer crowns
 The cavosurface line angles of the preparation in the occulsalThe cavosurface line angles of the preparation in the occulsal
portion of the tooth should be finished with a bevel to avoid rightportion of the tooth should be finished with a bevel to avoid right
angle “butt joint” which would leave a brittle easily fractured edge ofangle “butt joint” which would leave a brittle easily fractured edge of
tooth structuretooth structure
 The acute edge of metal and obtuse angle of the enamel created byThe acute edge of metal and obtuse angle of the enamel created by
a bevel can withstand impacts much better than can a square edgea bevel can withstand impacts much better than can a square edge
of enamelof enamel

Impact striking the enamel nest to the
bevel can be withstood without damage
Area where no bevel- unprotected enamel
rods near the restoration fractures more
easily
A- no bevel- acute edge of unsupported
enamel
B. Occlusal forces deforming the thin
restoration to fracture the brittle
enamel
C. With bevel- margin strengthened
D. Contrabevel in flat occlusal surfacewww.indiandentalacademy.comwww.indiandentalacademy.com

FlaresFlares
 The vertical finish of the inlay, onlay or partial crown
preparation is finished with a flare which forms an acute
edge of metal in the casting and extends it into an
accessible area

Flare
It is a geometric plane inclined
slightly to the path of insertion
and cutting through the
contour of the tooth
Bevel
Follows the contour of the tooth
and placed only on the finish
lines that are more or less
perpendicular to the path of
insertion

 InstrumentInstrument
 Flame diamond bur with parallel sidesFlame diamond bur with parallel sides
 Abrasive paper discsAbrasive paper discs

 Abrasive paper discs-Abrasive paper discs-
 require light touch to avoid overheating and should berequire light touch to avoid overheating and should be
frequently changedfrequently changed
 DisadvantagesDisadvantages
- limited to areas of good accesslimited to areas of good access
- can injure the soft tissues if care not takencan injure the soft tissues if care not taken
- although produces a smooth flare but if coarse disc if used then mayalthough produces a smooth flare but if coarse disc if used then may
produce grooves in the flareproduce grooves in the flare

Finishing of the finish linesFinishing of the finish lines
 Done by using the followingDone by using the following
Fine grit diamond pointsFine grit diamond points
Tungsten carbide finishing bursTungsten carbide finishing burs
Mounted disksMounted disks
StonesStones

Preventing tooth fracturePreventing tooth fracture
 Likelihood of a resorted tooth to fracture can beLikelihood of a resorted tooth to fracture can be
lessened if the tooth preparation is designed tolessened if the tooth preparation is designed to
minimize potentially destructive stressminimize potentially destructive stress
 eg- inlay has a greater potential for fractureeg- inlay has a greater potential for fracture
because when occlusal forces are applied to thebecause when occlusal forces are applied to the
restorations it tends to wedge opposing walls of therestorations it tends to wedge opposing walls of the
tooth apart. This wedging must be resisted by thetooth apart. This wedging must be resisted by the
remaining tooth structure and if it is thin then theremaining tooth structure and if it is thin then the
tooth might fracture. Proving a cuspal coveragetooth might fracture. Proving a cuspal coverage
restoration rather than an inlay lessens the chance ofrestoration rather than an inlay lessens the chance of
such fracturesuch fracture www.indiandentalacademy.comwww.indiandentalacademy.com

Mechanical considerationMechanical consideration
 Providing retention formProviding retention form
 Providing resistance formProviding resistance form
 Preventing deformation of the restorationPreventing deformation of the restoration

Type of occlusal forcesType of occlusal forces
 3 types of forces act on the tooth3 types of forces act on the tooth
 Tipping forces- buccolingual or mesiolingual direction depending onTipping forces- buccolingual or mesiolingual direction depending on
the direction of forcethe direction of force
 Twisting or rotational forces- restoration moves circumferentiallyTwisting or rotational forces- restoration moves circumferentially
around the tootharound the tooth
 Path of insertion forces- forces applied occlusally or apically uponPath of insertion forces- forces applied occlusally or apically upon
whether the mandible is closing into a bolus of food or opening withwhether the mandible is closing into a bolus of food or opening with
sticky foodsticky food

Retention and resistance formRetention and resistance form
 No cement possess adequate adhesiveNo cement possess adequate adhesive
properties to hold a restoration in placeproperties to hold a restoration in place
solely through adhesion, hence thesolely through adhesion, hence the
geometric configuration of the toothgeometric configuration of the tooth
preparation must place the cement inpreparation must place the cement in
compression to provide the necessarycompression to provide the necessary
retention and resistanceretention and resistance

Force directed away from
tooth- tensile stress
Force parallel with the
interface- shear stress
Force directed at an angle-
combination of shear and
compression
Force perpendicular- compression
stresswww.indiandentalacademy.comwww.indiandentalacademy.com

 Retention form- prevents removal of theRetention form- prevents removal of the
restoration along the path of insertion orrestoration along the path of insertion or
long axis of the tooth preparationlong axis of the tooth preparation
 Resistance form- prevents dislodgementResistance form- prevents dislodgement
of the restoration of the restoration byof the restoration of the restoration by
forces directed in an apical or obliqueforces directed in an apical or oblique
direction and prevents any movement ofdirection and prevents any movement of
the restoration under occlusal forcesthe restoration under occlusal forces

 Retention and resistance form depends onRetention and resistance form depends on
the following factorsthe following factors
TaperTaper
Freedom of displacementFreedom of displacement
LengthLength
Substitution of internal featureSubstitution of internal feature
Path of insertionPath of insertion

TaperTaper
 2 opposing external walls must gradually converge or 2 opposing2 opposing external walls must gradually converge or 2 opposing
internal surfaces of tooth structure must diverge occlusally (angle ofinternal surfaces of tooth structure must diverge occlusally (angle of
convergence or angle of divergence)convergence or angle of divergence)
 The more parallel the opposing walls of the preparation- greater theThe more parallel the opposing walls of the preparation- greater the
retention. Parallel walls impossible to create in mouth without producingretention. Parallel walls impossible to create in mouth without producing
preparation undercutspreparation undercuts
 Tapered wallsTapered walls
 Help to visualize preparation wallsHelp to visualize preparation walls
 Prevent undercutsPrevent undercuts
 Compensate for inaccuracies in the fabrication processCompensate for inaccuracies in the fabrication process
 Permit more nearly complete seating of restorationPermit more nearly complete seating of restoration

 Taper should be minimal because it adverselyTaper should be minimal because it adversely
affects the retention, but Mack- minimum taperaffects the retention, but Mack- minimum taper
of 12° necessary to ensure the absence ofof 12° necessary to ensure the absence of
undercutsundercuts

 The tendency to over taper must be constantlyThe tendency to over taper must be constantly
guarded to produce preparations with the leastguarded to produce preparations with the least
possible taper and greatest possible retentionpossible taper and greatest possible retention
 Consciously attempting to cut a taper result in overConsciously attempting to cut a taper result in over
taper and non retentive preparationtaper and non retentive preparation

 Greater the surface area of a preparation, greaterGreater the surface area of a preparation, greater
the retention. Surface area are can be increasedthe retention. Surface area are can be increased
by adding boxes and groovesby adding boxes and grooves
A full crown is more retentive on a molar than on a premolar, because
the molar has greater surface area

Surface area are can be increasedSurface area are can be increased
by adding boxes and groovesby adding boxes and grooves
Box Groove

Paralleling device used during placing the taperParalleling device used during placing the taper

Optimum degree of tooth
preparation taper
Arch Mesio-distal Facio-lingual Overall
Maxillary
Anteriors
Premolars
Molars
Isthmus
Box
10
14
17
10
14
21
10
14
19
7
7
Mandibular
Anteriors
Premolars
Molars
Isthmus
Box
10
16
24
10
12
20
10
14
22
12
12www.indiandentalacademy.comwww.indiandentalacademy.com

Freedom of displacementFreedom of displacement
 Retention is improved by geometrically limiting the number of path alongRetention is improved by geometrically limiting the number of path along
which a restoration can be removed from the preparationwhich a restoration can be removed from the preparation
 Single path or one path-maximum retentionSingle path or one path-maximum retention
Eg- Full veneer preparationlong, parallel axial wallsEg- Full veneer preparationlong, parallel axial walls
and groovesand grooves
 Infinite path of insertion- minimum retentionInfinite path of insertion- minimum retention
Eg- short over tapered preparationEg- short over tapered preparation

 Limiting the freedom of displacement fromLimiting the freedom of displacement from
torquing or twisting force in a horizontal planetorquing or twisting force in a horizontal plane
increases resistanceincreases resistance
 A groove whose walls meet the axial wall at anA groove whose walls meet the axial wall at an
oblique angle does not provide the necessaryoblique angle does not provide the necessary
resistance, the walls of a groove must beresistance, the walls of a groove must be
perpendicular to rotating forces to resistperpendicular to rotating forces to resist
displacementdisplacement
 Forces producing rotating movement producesForces producing rotating movement produces
shear and slippage along the surface oblique toshear and slippage along the surface oblique to
the direction of forcethe direction of force

 V- shaped groove- one half resistance toV- shaped groove- one half resistance to
lingual displacement as groove withlingual displacement as groove with
definite lingual walldefinite lingual wall

 For proximal box- the buccal and lingual wallsFor proximal box- the buccal and lingual walls
must meet the pulpal wall at angle near 90must meet the pulpal wall at angle near 90° so° so
that these walls will be perpendicular to anythat these walls will be perpendicular to any
forces which would tend to rotate the restoration.forces which would tend to rotate the restoration.
A flare is added to the box so that there can beA flare is added to the box so that there can be
acute edge of metal at the cavosurface margin ofacute edge of metal at the cavosurface margin of
restorationrestoration

The planes of two facial flares
should intersect slightly facial to
the path of insertion and well
above the occlusal surface
The planes of the lingual
surface should intersect lingual
to the path of insertion

LengthLength
 Occlusogingival length is important for bothOcclusogingival length is important for both
resistance and retention formresistance and retention form
 Longer preparation- more surface area hence moreLonger preparation- more surface area hence more
retentive, this is because the axial wall occlusal toretentive, this is because the axial wall occlusal to
the finish line interferes with the displacement, thethe finish line interferes with the displacement, the
length and inclination of the wall become factors inlength and inclination of the wall become factors in
resistance to tipping forcesresistance to tipping forces

 The preparation on the small diameter tooth willThe preparation on the small diameter tooth will
have a rotational radius for the arc ofhave a rotational radius for the arc of
displacement, and the incisal portion of the axialdisplacement, and the incisal portion of the axial
wall will resist displacement.wall will resist displacement.
 The longer rotational radius on the largerThe longer rotational radius on the larger
preparation allows for a gradual arc ofpreparation allows for a gradual arc of
displacement, and the axial wall does not resistdisplacement, and the axial wall does not resist
removalremoval

 Resistance can be improved by placingResistance can be improved by placing
grooves in the axial wall of short walledgrooves in the axial wall of short walled
preparation on a large toothpreparation on a large tooth

Use of internal walls for retention Use of external walls for retention
Intracoronal restoration Extracoronal restoration

Substitution of internal featuresSubstitution of internal features
 If the walls are destroyed previously or a surfaceIf the walls are destroyed previously or a surface
is left uncovered for a partial veneer restoration, ifis left uncovered for a partial veneer restoration, if
the walls have a greater inclination than desiredthe walls have a greater inclination than desired
than the internal features such as grooves, boxthan the internal features such as grooves, box
form and the pin hole can be substituted for anform and the pin hole can be substituted for an
axial wall or for each otheraxial wall or for each other
Box Groove Pinholewww.indiandentalacademy.comwww.indiandentalacademy.com

M.Harry Parker DCNA 2004-April
 Retention increases as taper decreases but noRetention increases as taper decreases but no
clue as to minimal acceptability, it shows onlyclue as to minimal acceptability, it shows only
that less taper is better in that it provides morethat less taper is better in that it provides more
retention.retention.
 Resistance form indicates “on-off ” natureResistance form indicates “on-off ” nature

AA BB CC
DD EE FF
GG HH
II JJ
10mm
4mm

•Limiting taper- the dividing point between tapers that do & do notLimiting taper- the dividing point between tapers that do & do not
provide resistance formprovide resistance form
•Limiting average taper- the on-of nature of resistance form can beLimiting average taper- the on-of nature of resistance form can be
applied to the average taper of the entire preparationapplied to the average taper of the entire preparation
It is mathematically determined as 0.5 arcsineIt is mathematically determined as 0.5 arcsine

 Measurement of resistance formMeasurement of resistance form
- Lewis and Owen method- Lewis and Owen method
- Weed and Baez- Weed and Baez
- Zukermans method- Zukermans method
WeedWeed
ww zukermanzukerman
AA
CC DD
BB
LewisLewis

 Type of preparationType of preparation
-- Different types of preparation- different retentive valuesDifferent types of preparation- different retentive values
- eg. Retention of a complete crown is about double that of- eg. Retention of a complete crown is about double that of
partial coverage restorationpartial coverage restoration
- Adding grooves or boxes- limits the path of withdrawal,- Adding grooves or boxes- limits the path of withdrawal,
increases retentionincreases retention
 Roughness of the surfaces being cementedRoughness of the surfaces being cemented
Internal surface of a restoration very smooth-Internal surface of a restoration very smooth-
retentive failure occurs not through the cement but at cementretentive failure occurs not through the cement but at cement
restoration interfacerestoration interface
- Retention increased- restoration is roughened or grooved,- Retention increased- restoration is roughened or grooved,
done by air abrading with 50µm aluminadone by air abrading with 50µm aluminawww.indiandentalacademy.comwww.indiandentalacademy.com

Path of insertionPath of insertion
 It is an imaginary line along which theIt is an imaginary line along which the
restoration will be placed onto or removedrestoration will be placed onto or removed
from the preparationfrom the preparation
 Should be determined before theShould be determined before the
preparation and all the features of thepreparation and all the features of the
preparation should coincide with that linepreparation should coincide with that line

Path of insertion- viewed
from one eye at a distance
of 30cm, all the axial
surfaces of a preparation
with an ideal taper or angle
of convergence of 6° can
be seen
Binocular vision should never be
employed to evaluate a
preparation for correct taper. With
both eyes open, a preparation that
is undercut can appear to have an
acceptable degree of taper

A mirror is used to evaluate a preparation where direct vision is not
possible. The mirror is held at an angle approximately ½ inch above
the preparation, and viewed with one eyewww.indiandentalacademy.comwww.indiandentalacademy.com

 It should be considered in two dimensionsIt should be considered in two dimensions
FaciolingualFaciolingual
mesiodistalmesiodistal
 Faciolingual- important for metal ceramicFaciolingual- important for metal ceramic
and partial veneer crownand partial veneer crown
 Mesiodistal inclination- must parallel theMesiodistal inclination- must parallel the
contact area of adjacent teeth, if inclinedcontact area of adjacent teeth, if inclined
mesially or distally then the restoration willmesially or distally then the restoration will
be locked out.be locked out.

 Path of insertionPath of insertion
 for full crown restoration or ¾ crown on posteriors- parallel tofor full crown restoration or ¾ crown on posteriors- parallel to
the long axis of the tooththe long axis of the tooth
Path of insertion parallel to the long axis of the tooth

 Path of insertionPath of insertion
for full crown restoration when the tooth is tiltedfor full crown restoration when the tooth is tilted
mesially or distally- preparation should be mademesially or distally- preparation should be made
perpendicular to the occlusal plane and not parallelperpendicular to the occlusal plane and not parallel
to the long axis of the tooth because it may preventto the long axis of the tooth because it may prevent
seating of the restoration by the adjacent toothseating of the restoration by the adjacent tooth
which protrude into the path of insertionwhich protrude into the path of insertion

 If the adjacent teeth migrates into the longIf the adjacent teeth migrates into the long
standing carious teethstanding carious teeth

For anterior 3/4For anterior 3/4thth
crown - parallel to the incisal 2/3crown - parallel to the incisal 2/3rdrd
of the labial surfacof the labial surfac
This done because it will avoid unnecessary display of the metalThis done because it will avoid unnecessary display of the metal
Path of insertionPath of insertion
Comparison between preparation made parallel to the long axis of
the tooth and the preparation made parallel to the incisal 2/3rd
of
the labial surface

Structural durabilityStructural durability
 A restoration must contain a bulk of material that isA restoration must contain a bulk of material that is
adequate to withstand the forces of occlusion and theadequate to withstand the forces of occlusion and the
bulk must be confined to the space created by the toothbulk must be confined to the space created by the tooth
preparation.preparation.
 The features that provide structural durability areThe features that provide structural durability are
Occlusal reductionOcclusal reduction
Functional cusp bevelFunctional cusp bevel
Axial reductionAxial reduction

Occlusal reductionOcclusal reduction
 Occlusal clearance – most important feature for providingOcclusal clearance – most important feature for providing
adequate bulk of metal and strength to the restorationadequate bulk of metal and strength to the restoration
 For gold alloys-For gold alloys-
Functional cusp- 1.5mmFunctional cusp- 1.5mm
Non functional -1mmNon functional -1mm
 For metal ceramic crown-For metal ceramic crown-
Functional cusp- 1.5-2mmFunctional cusp- 1.5-2mm
Non functional -1-1.5mmNon functional -1-1.5mm
 All ceramic- 2mmAll ceramic- 2mm

 Basic inclined plane pattern of the occlusal surfaceBasic inclined plane pattern of the occlusal surface
should be duplicated to produce adequate clearanceshould be duplicated to produce adequate clearance
without overshortening the preparationwithout overshortening the preparation
 Inadequate clearance- weaker restorationInadequate clearance- weaker restoration
if anatomic grooves of occlusal surface not clearedif anatomic grooves of occlusal surface not cleared
adequately than the restoration will be easilyadequately than the restoration will be easily
perforated by finishing procedure or by wear in theperforated by finishing procedure or by wear in the
mouthmouth

Functional cusp bevelFunctional cusp bevel
 Is an integral part of the occlusal reductionIs an integral part of the occlusal reduction
 Provides space for an adequate bulk of metal in anProvides space for an adequate bulk of metal in an
area of heavy occlusal contactarea of heavy occlusal contact
 Placed onPlaced on
 lingual inclines of the maxillary lingual cusplingual inclines of the maxillary lingual cusp
 Buccal inclines of mandibular buccal cuspsBuccal inclines of mandibular buccal cusps

 If bevel not placed – casting will be extremely thin in theIf bevel not placed – casting will be extremely thin in the
area overlying the junction between the occlusal andarea overlying the junction between the occlusal and
axial reduction, to prevent this over contouring is doneaxial reduction, to prevent this over contouring is done
which results in overcontoured restoration and deflectivewhich results in overcontoured restoration and deflective
occlusal contactocclusal contact

 Functional cusp bevel for teeth with cross biteFunctional cusp bevel for teeth with cross bite
Placed on the buccal
cusps of maxillary teeth
and the lingual cusps of
mandibular teeth

Method to check occlusal clearanceMethod to check occlusal clearance
 After placing the functional cusp bevel the occlusal clearance isAfter placing the functional cusp bevel the occlusal clearance is
checked by using a strip of red utility wax of approximately thechecked by using a strip of red utility wax of approximately the
same width as the mesiodistal dimension of the prepared toothsame width as the mesiodistal dimension of the prepared tooth
 Compare the translucency of the wax over portions of theCompare the translucency of the wax over portions of the
preparation that have known adequate clearance with thepreparation that have known adequate clearance with the
translucency of those cusps and areas of the preparation thattranslucency of those cusps and areas of the preparation that
are too far lingual to be seen in the mouth. If the imprints ofare too far lingual to be seen in the mouth. If the imprints of
unseen segments are more translucent than those known tounseen segments are more translucent than those known to
have adequate clearance, more reduction is neededhave adequate clearance, more reduction is needed

Axial reductionAxial reduction Plays an important role in securing space for anPlays an important role in securing space for an
adequate thickness of restoration materialadequate thickness of restoration material
 If axial reduction inadequate- results in thin castingIf axial reduction inadequate- results in thin casting
leading to distortionleading to distortion
 To compensate for the above overcontouring isTo compensate for the above overcontouring is
done with wax- casting overcontoured leading todone with wax- casting overcontoured leading to
disastrous effect on periodontiumdisastrous effect on periodontium

 Features which improve the rigidity and durability oFeatures which improve the rigidity and durability o
restorationrestoration
 OffsetOffset
 Occlusal shoulderOcclusal shoulder
 IsthmusIsthmus
 Proximal boxProximal box
 GrooveGroove
 Isthmus- connects the boxesIsthmus- connects the boxes
 Offset- ties the grooves together to enhance theOffset- ties the grooves together to enhance the
truss effecttruss effect

Guidelines for tooth preparationGuidelines for tooth preparation
Charles J. GoodacreCharles J. Goodacre
1.Total occlusal convergence- it is the angle formed between two1.Total occlusal convergence- it is the angle formed between two
opposing prepared axial surfaces.opposing prepared axial surfaces.
TOC should be 10TOC should be 10°- 20°°- 20°
2. Occlusocervical/ Incisocervical dimension2. Occlusocervical/ Incisocervical dimension
OC for anteriors- minimum of 3mmOC for anteriors- minimum of 3mm
OC for molars- minimum of 4mmOC for molars- minimum of 4mm
3. Ratio of Occlusocervical/ Incisocervical dimension to faciolingual3. Ratio of Occlusocervical/ Incisocervical dimension to faciolingual
dimension- should be 0.4 or higher for all teethdimension- should be 0.4 or higher for all teeth
4.Circumferential form of the prepared tooth4.Circumferential form of the prepared tooth
 teeth should be prepared so that they possess circumferentialteeth should be prepared so that they possess circumferential
irregularity whenever possibleirregularity whenever possible
 Pyramidal preparations provide increased resistancePyramidal preparations provide increased resistancewww.indiandentalacademy.comwww.indiandentalacademy.com

5. Reduction uniformity5. Reduction uniformity
Teeth should be uniformly reduced, to enhance the potentialTeeth should be uniformly reduced, to enhance the potential
for normal crown form and an improved esthetic resultfor normal crown form and an improved esthetic result
6. Finish line location6. Finish line location
7. Finish line form7. Finish line form
8.Reduction depth8.Reduction depth
9. Line angle form9. Line angle form
10. Surface texture10. Surface texture

Esthetic considerationsEsthetic considerations
 Partial coverage crownPartial coverage crown
-Proximal margin- mesial margin- placed-Proximal margin- mesial margin- placed
just buccal to the proximal contact areajust buccal to the proximal contact area
- Distal Margin- should be placed beyond- Distal Margin- should be placed beyond
the contact point to allow easierthe contact point to allow easier
preparation and finishing of the restorationpreparation and finishing of the restoration

- Extend just beyond occlusofacial line angle
- Short bevel placed to prevent chipping of enamel
- Molars if buccal surface is visible- chamfer is
recommended than bevel because it provides
greater bulk of metal around functional cusp
- Incisors- incisolabial line angle
Facial marginFacial margin

Metal ceramic crown
Facial tooth reduction- minimum of 1.5mm
Incisal reduction- 2mm
Proximal reduction- predetermined by
location of metal- ceramic junction in
completed restoration

References
1.Fundamentals of fixed prosthodontics- H.T.Shillinburg : 3rd
edition
2.Contemprary Fixed Prosthodontics- Rosenstiel: 3rd
edition
3.Tylman’s Theory and Practice of fixed prosthodontics- 8th edition.
4.Charles J.Goodacre, Designing tooth preparations for optimal success.
DCNA 2004- April- Fixed Prosthodontics.
5.M.Harry Parker, Resistance form in tooth preparation. DCNA 2004- April-
Fixed Prosthodontics.

6.Terry E.D, Winston W.L, Cervical margin design with contemporary esthetic
restorations. DCNA 2004- April- Fixed Prosthodontics.
7.J.R. Gavelis et al, The effects of various finish line preparations on the marginal
seal and occlusal seat of full crown preparation- the Journal of prosthetic
dentistry 2004; 92:1-7.
8. A.J. Hunter et al, Gingival crown margin configurations- A review and
discussion. Journal of Prosthetic Dentistry 1990; 64:548-52.
9. Christopher D.L. controlled tooth reduction for fixed restorations using custom
made pre-contoured transparent templates. Journal of prosthetic dentistry 2004;
91: 499-500.

Thank youThank you

Following factors must be considered in decidingFollowing factors must be considered in deciding
whether retention is adequatewhether retention is adequate
 Magnitude of dislodging forceMagnitude of dislodging force
 Geometry of the tooth preparationGeometry of the tooth preparation
 Roughness of the fitting surface of the restorationRoughness of the fitting surface of the restoration
 Material being cementedMaterial being cemented
 Type of luting agentType of luting agent
 Film thickness of the luting agentFilm thickness of the luting agentwww.indiandentalacademy.comwww.indiandentalacademy.com

Magnitude of dislodging forceMagnitude of dislodging force
 Forces that tend to remove a cementedForces that tend to remove a cemented
restorations along its path of withdrawalrestorations along its path of withdrawal
are small compared to those that tend toare small compared to those that tend to
seat it or tilt itseat it or tilt it
 The magnitude of dislodging forcesThe magnitude of dislodging forces
depends on the stickiness of the food anddepends on the stickiness of the food and
the surface area and texture of thethe surface area and texture of the
restoration being pulledrestoration being pulled

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