01 principles of tooth preparation

7/30/2019 01 Principles of Tooth Preparation

1/52

Today

ScheduleLecture - Principles of Tooth PreparationReadings / Journals / PaperEvaluation RubricLab Session


2/52

PRINCIPLES OF TOOTH

PREPARATION

Ranier M. Adarve, DMD,MS, MHPE


3/52

INTRODUCTION

Tooth Preparationa clinical procedure consisting of removalof tooth structures and / or shaping of

the tooth to accommodate a fixed restoration


4/52

INTRODUCTION

Marginal Leakage

Crown Perforation

Dislodgement / Non-retentionEsthetic Problem

Occlusal ProblemPeriodontal Problem

Problems in Fixed Restorations


5/52

INTRODUCTION

Can be avoided by

Problems in Fixed Restoration

Correct Tooth Preparation


6/52

INTRODUCTION

What is a Correct Tooth Preparation?

What are the principles that govern

Tooth Preparation?


7/52

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


8/52

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


9/52

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


10/52

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


11/52

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


12/52

PRINCIPLES


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


13/52

PRINCIPLES


Preparation primary source of retention and resistanceCementation secondary source of retention and resistance


14/52

PRINCIPLES


Cementation secondarysource of retention and

resistance


15/52

PRINCIPLES


Types of Stress

Tension Shear Combination Compression

Cement film

Crown

Tooth

Force


16/52

PRINCIPLES


Factors under the Operators control:

TAPERLENGTH / HEIGHTSURFACE AREASURFACE ROUGHNESS


17/52

PRINCIPLES


TAPER


18/52

PRINCIPLES


TAPER

As the degree of taper of the preparation increases,Its ability to retain a restoration decreases


19/52

PRINCIPLES


TAPER and R&R

Directly proportional

Inversely proportional


20/52

PRINCIPLES


LENGTH / HEIGHT

Resisting area

Resisting area

force


21/52

PRINCIPLES


HEIGHT and R&R




22/52

PRINCIPLES


SURFACE AREA


23/52

PRINCIPLES


SURFACE AREA and R&R




24/52

PRINCIPLES


SURFACE ROUGHNESS

Adhesion of dental cements depends primarily onprojections of the cement into microscopic irregularities

axial surface-roughmargins-smooth


25/52

PRINCIPLES


SURFACE ROUGHNESS and R&R




26/52

Path of Insertion


27/52

One path of insertion

Path of Insertion


28/52

multiple paths of insertions

Path of Insertion


29/52

no path of insertion

Path of Insertion


30/52

Common path of insertion

Path of Insertion


31/52

Uncommon paths of insertion

Path of Insertion


32/52

Path of Insertion


33/52

Path of Insertion


34/52

Path of Insertion


35/52

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


36/52

Margin Configurations

Shoulder Deep Chamfer

Chamfer


37/52

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


38/52

Shoulder Deep Chamfer

Chamfer

Margin Location

SupragingivalEquigingivalSubgingival

Presence of subgingival cariesIncrease retention of preparationEsthetics

Margins of restoration should be placed supragingivallywhenever possible


39/52

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


40/52

PRINCIPLES


Adequate

reduction basedon the

requirement ofthe restoration

Functional cusp bevel


41/52

PRINCIPLES


Inadequate occlusalclearanceDoes not provide neededspace for restoration ofadequate thickness

Compromises the structuraldurability of the restoration


42/52

PRINCIPLES


Avoid flat occlusal surfaceFollow occlusal planarreductionUnnecessary toothreduction


43/52

PRINCIPLES


Lack of functional cuspbevel can cause thin area orperforate the restoration


44/52

PRINCIPLES


Lack of functional cuspbevel can causeovercontouring and poor

occlusion


45/52

PRINCIPLES


Over inclination can causeunnecessary tooth reductionDecrease retention


46/52

Restoration Requirements

1.Biological2.Mechanical3.Esthetics


47/52

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


48/52

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


49/52


50/52

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


51/52

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


52/52

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

01 principles of tooth preparation

Documents