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Today
ScheduleLecture - Principles of Tooth PreparationReadings / Journals / PaperEvaluation RubricLab Session
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PRINCIPLES OF TOOTH
PREPARATION
Ranier M. Adarve, DMD,MS, MHPE
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INTRODUCTION
Tooth Preparationa clinical procedure consisting of removalof tooth structures and / or shaping of
the tooth to accommodate a fixed restoration
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INTRODUCTION
Marginal Leakage
Crown Perforation
Dislodgement / Non-retentionEsthetic Problem
Occlusal ProblemPeriodontal Problem
Problems in Fixed Restorations
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INTRODUCTION
Can be avoided by
Problems in Fixed Restoration
Correct Tooth Preparation
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INTRODUCTION
What is a Correct Tooth Preparation?
What are the principles that govern
Tooth Preparation?
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TOOTH PREPARATION
What is a Correct Tooth Preparation?
Removal of tooth structuredoes not weaken the tooth
Amount of reduction followsthe requirements of restorationResist displacement in all directionsPresence of optimum tooth heightFinish line that can accommodate
robust margin with close adaptation
Provide optimal space for crownwhich is sufficiently thick to prevent
fracture, distortion or perforation
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TOOTH PREPARATION
Incorrect
Tooth Preparation
Unnecessary reductionEndangers the pulpLack of retention and resistance features
Finish line that cause micro leakageInadequate space for crown which is thin
and may cause fracture, distortion or
perforation
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PRINCIPLES
What are the principles that govern
Tooth Preparation?
1.Conservation/ Preservation of Tooth Structure2.Retention and Resistance Form3.Marginal Integrity and
Preservation of Periodontium
4.Structural Durability andEsthetic Considerations
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PRINCIPLES
1.Conservation/ Preservation of Tooth StructureAvoid over reduction of all surfaces
of the tooth
Avoid excessive occlusal reductionAchieve correct occlusal planarreduction
Avoid flat occlusal surface
Reduction based on the
requirement of restoration
Occlusal planar
reduction
Excessive Reduction:Thermal hypersensitivityPulpal inflammation and necrosisLoss of retention and resistance
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PRINCIPLES
2. Retention and Resistance Form
Retention prevents removal of therestoration along the path of insertion or
long axis of the preparation
Resistance prevents dislodgement ofthe restoration by forces directed in an
apical or oblique direction
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PRINCIPLES
2. Retention and Resistance Form
Have an ideal taperPreserve tooth heightRequire Parallelism when neededAppropriate use of retentive featuresAvoid undercutEstablish Path of Insertion
6 degrees TOC
Minimum of 4mm
axial wall Height
Avoid Undercut
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PRINCIPLES
2. Retention and Resistance Form
Preparation primary source of retention and resistanceCementation secondary source of retention and resistance
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PRINCIPLES
2. Retention and Resistance Form
Cementation secondarysource of retention and
resistance
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PRINCIPLES
2. Retention and Resistance Form
Types of Stress
Tension Shear Combination Compression
Cement film
Crown
Tooth
Force
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PRINCIPLES
2. Retention and Resistance Form
Factors under the Operators control:
TAPERLENGTH / HEIGHTSURFACE AREASURFACE ROUGHNESS
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PRINCIPLES
2. Retention and Resistance Form
TAPER
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PRINCIPLES
2. Retention and Resistance Form
TAPER
As the degree of taper of the preparation increases,Its ability to retain a restoration decreases
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PRINCIPLES
2. Retention and Resistance Form
TAPER and R&R
Directly proportional
Inversely proportional
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PRINCIPLES
2. Retention and Resistance Form
LENGTH / HEIGHT
Resisting area
Resisting area
force
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PRINCIPLES
2. Retention and Resistance Form
HEIGHT and R&R
Directly proportional
Inversely proportional
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PRINCIPLES
2. Retention and Resistance Form
SURFACE AREA
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PRINCIPLES
2. Retention and Resistance Form
SURFACE AREA and R&R
Directly proportional
Inversely proportional
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PRINCIPLES
2. Retention and Resistance Form
SURFACE ROUGHNESS
Adhesion of dental cements depends primarily onprojections of the cement into microscopic irregularities
axial surface-roughmargins-smooth
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PRINCIPLES
2. Retention and Resistance Form
SURFACE ROUGHNESS and R&R
Directly proportional
Inversely proportional
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Path of Insertion
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One path of insertion
Path of Insertion
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multiple paths of insertions
Path of Insertion
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no path of insertion
Path of Insertion
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Common path of insertion
Path of Insertion
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Uncommon paths of insertion
Path of Insertion
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Path of Insertion
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Path of Insertion
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Path of Insertion
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PRINCIPLES
3. Marginal Integrity and Preservation of Periodontium
Well-defined marginsContinuous marginsEven and smooth marginsLocated at appropriate level
Follow contour of the ginigival marginBreak contact with adjacent tooth
Margin ConfigurationsShoulderChamferShoulder with bevelFeather / Knife edge
Well-defined, Even andSmooth Margins
Break Contact with
adjacent tooth
Continuous andfollow contour of
gingiva
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Margin Configurations
Shoulder Deep Chamfer
Chamfer
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Biologic Width
The combined width of connective tissue and epithelial attachment superior tocrestal bone.
This includes the width of supra-alveolar connective tissue fibers (average 1.07)and the junctional epithelium (average 0.97), which totals an average of 2.04 mm.
During placement of restorative margins, an additional 1-2 mm of sound structurecoronal to the epithelial attachment is needed, hence the minimum distancebetween the alveolar crest and the restorative margin should be 3-4 mm (to allow
a gingival sulcus of approx. 1 mm.
Impinging on this width by a restoration will trigger loss of bone and epithelialattachment. An interproximal encroachment leads to osseous crater that will be
unmanageable from oral hygiene standpoint
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Shoulder Deep Chamfer
Chamfer
Margin Location
SupragingivalEquigingivalSubgingival
Presence of subgingival cariesIncrease retention of preparationEsthetics
Margins of restoration should be placed supragingivallywhenever possible
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Avoid Under ReductionProvide Occlusal ClearanceFunctional Cusp BevelAvoid Sharp Angles and CornersAvoid Damage to adjacent teeth
Functional Cusp BevelBuccal cusps of mandibular teethLingual cusps of maxillary teeth
Avoid Damage to
Adjacent Teeth
Avoid Sharp Angle
and Corners
Functional Cusp
Bevel
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Adequate
reduction basedon the
requirement ofthe restoration
Functional cusp bevel
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Inadequate occlusalclearanceDoes not provide neededspace for restoration ofadequate thickness
Compromises the structuraldurability of the restoration
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Avoid flat occlusal surfaceFollow occlusal planarreductionUnnecessary toothreduction
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Lack of functional cuspbevel can cause thin area orperforate the restoration
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Lack of functional cuspbevel can causeovercontouring and poor
occlusion
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PRINCIPLES
4. Structural Durability and Esthetic Considerations
Over inclination can causeunnecessary tooth reductionDecrease retention
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Restoration Requirements
1.Biological2.Mechanical3.Esthetics
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COMMON ERRORS
1. Over Reduced / Under Reduced2. Over Tapered / Under Tapered3. Sharp Angles / Corners4. Undefined Margin5. Irregular Margin6. Margin Position7. Marred Adjacent Tooth8. Contact Unbroken9. Functional Cusp Bevel location
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RELEVANT
INFORMATION FROM JOURNALS Preservation of tooth structure in some cases may require that limited amounts of sound tooth
structure be removed to prevent subsequent uncontrolled loss of larger quantities of tooth
structure. Retention prevents removal of the restoration along the path of insertion or
long axis of the preparation
Resistance prevents dislodgement of the restoration by forces directed in an apical or obliquedirection
Essential element of retention is two opposing vertical surfaces in the same preparation Taper permits the restoration to seat Inclination vs taper Occlusogingival length is an important factor in both retention and resistance Longer preparation will have more surface area and therefore be more retentive The shorter the wall, the more important its inclination Internal features such as groove, the box form and pin hole can be substituted for an axial wall Path of insertion must be considered in two dimensions: faciolingually and mesiodistally A restoration must contain a bulk of material that is adequate to withstand forces of occlusion. The restoration can survive in the biologic environment of the oral cavity only if the margins
are closely adapted to the cavosurfaces finish line of the preparation Whenever possible, the finish line should be placed in an area where the margins of the restoration
can be finished by the dentist and kept clean by the patient
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CLINICALLY RELEVANT
INFORMATION Violation in principles of tooth preparation has
biologic, mechanical and / or esthetic repercussion
Configuration of the preparation depends on thetype of restoration
Axial walls provide for retention and stability. Increase Taper, decrease in retention Decrease in height, decrease in retention Height of prepared molar tooth should be at least 3-4mm Surface area and roughness increase retention
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Today
ScheduleLecture - Principles of Tooth PreparationReadings / Journals / PaperEvaluation RubricLab Session
Tooth #18Simulate clinical procedure
Wear eye protection, mask and gloveChair position / ergonomics
ALWAYS REFER TO RUBRICDISCUSS WITH YOUR FACULTY
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TOOTH PREPARATION
1.0 mm occlusal reductionAdditional 0.5 mm bevel forfunctional cusp
6 degree taper0.5 mm chamfer margin0.5 mm above the margin ofgingivaRough surface finishSmooth margin finish