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8/3/2019 Lecture 3, Principles of Cavity Preparation I
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Principles of Cavity Preparation I
Dr.Ghada Maghaireh
BDS, MS, ABOD
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Lecture Outline
Objectives of tooth preparation
Factors affecting tooth preparation
Stages and steps of tooth preparation
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Definition of Tooth Preparation
The mechanical alteration of defective,injured, or diseased tooth to best receive a
restorative material that will reestablish ahealthy state for the tooth, includingesthetic corrections where indicated, along
with normal form and function.
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Objectives of Tooth Preparation
Remove all defects & provide necessary protection to the
pulp.
Extend the restoration as conservatively as possible.
Form the tooth preparation so that under masticatory
forces the tooth or restoration will not fracture or the
restoration will not be displaced.
Allow for functional & esthetic placement of restorative
material.
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Factors Affecting Tooth Preparation
1. Diagnosis:
The reason for placing the restoration in the tooth
Periodontal & pulpal status
Esthetic factor
Relationship with other treatment plans
The risk potential of the patient for other dental caries
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2. Knowledge of DentalAnatomy:
Gross picture of the tooth both
internally and externally mustbe visualized.
The thickness of enamel,
dentin and position of the
pulp.
Relation to other supporting
tissues.
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3. Patient Factors:
The patient knowledge & appreciation for good dental
health.
Patients economic status.
The patient age.
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4. Conservation of Tooth Structure:
Preservation of the vitality of the tooth by avoiding the
application of poor or careless operative procedures on
the tooth.
Restorations should be made as small as possible.
Small tooth preparations result in restorations that has
little effect on both inter-arch & intra-arch relationships
as well as esthetics.
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5. Restorative Material Factors:
Amalgam Vs resin composite.
The ability to isolate the operating field.
The extension of the problem (i.e. caries).
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Stages and Steps of Tooth Preparation
Stages & Steps of Tooth Preparation
Initial Stage
1. Outline form & initial
depth
2. Primary resistance form3. Primary retention form
4. Convenience form
Final Stage5. Removal of any remaining infected dentin
6. Pulp protection if indicated
7. Secondary resistance & retention forms
8. Procedures for finishing external walls9. Final procedures: cleaning, inspecting &
sealing
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Initial Tooth Preparation Stage
Placing the preparation margins
in the positions they will occupy
in the final preparation.
Preparing an initial depth of 0.2
to 0.8 mm pulpally of the DEJ
position.
1. Outline form & initial depth
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3 principles:
1. All weakened enamel should beremoved.
2. All faults should be included.
3. All margins should be placed in
position to afford good finishing
of the margins of the restoration.
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2. Primary resistance form:
The shape & placement of the preparation walls that
best enable both the restoration and the tooth towithstand, without fracture, masticatory forces delivered
principally in the long access of the tooth
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Principles of resistance form:
1. Box shape with relatively flat floor.
- Masticatory forces are directed along the longaccess of the tooth
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2. Keep the cavity as small aspossible.
- Pulpal & axial walls should bemaintained just in dentin if at allpossible.
- If caries invaded the interjacentdentin, only the carious dentinshould be removed.
DEJ
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3. Rounded well-defined internal line angles.
- Well-defined line angles aid in establishing uniform depth and
prevent rotation of the restoration.
4. Cap cusps or include weakened tooth structurewithin the restoration.
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5. Provide enoughthickness of restorative
material to prevent itsfracture.
- The restorative material
may fracture if the cavitypreparation is tooshallow.
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6.To bond the material to tooth structurewhen possible.
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Factors Affecting Resistance Form
Remaining tooth structure: Affect need
and type of resistance form.
Type of restorative material: amalgam Vs
composite.
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3. Primary Retention Form:
The shape or form of the conventional preparation thatresist displacement or removal of the restoration fromtipping or lifting forces
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Principles: Depends on the
restorative materialAmalgam
In most Class I and Class II,walls should converge
occlusally. In class II, occlusal dovetail
aid in retention.
In Class V, walls diverge
outward to provide strongenamel margin, retentionobtained by grooves in thedentinal walls.
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Composite
Micromechanical bond by acid etching &bonding
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References:
The Art & Science of operative Dentistry
(chapter # 6)