lecture 3, principles of cavity preparation i

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)

lecture 3, principles of cavity preparation i

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