principles of cavity preparation

Road map
Definitions

Objectives of cavity preparation

GV Black’s principles in cavity
preparations

Steps of cavity preparation

Definitions
 What is a cavity?

It is a defect in the hard tooth structure
resulting from an insult as caries and trauma.

 What is tooth preparation?

It is mechanical alteration of a defective,
injured or diseased tooth to receive a
restorative material that re-establish the
health state for the tooth including its
esthetics, normal form and function

Definitions
 Tooth preparation that relates to

amalgam, gold or ceramic
restoration might be considered
conventional preparation that
require specific form, depth and
marginal form

Definitions
 Tooth preparation for bonded

direct restorations as composite
or glass ionomer has less need for
specific depth, wall and marginal
form and is considered to be
modified preparations.

Indications for restorative
intervention:
1.
2.
3.
4.
5.
6.

Repair destroyed tooth
Repair fractured tooth either complete or incomplete
[green stick fracture].
Restore teeth with congenital malformations.
Replace defective restoration.
Replacement of missing teeth.
Need for improved form or esthetic.

Why do we prepare
carious cavities?
To remove caries and
to create a compatible
foundation to the
restoration

Cavity preparation determinants

Material
specific

Lesion
specific

Dental tissue

[site specific]

Mechanism of tooth cutting
 Bladed cutting using burs
 Abrasive cutting using diamonds

What are the basic principles on
which cavities are prepared?

Principles of cavity preparation
according to GV Black
Biologic
principles

Mechanical
principles

Esthetic
principles

What are the basic steps in cavity
preparation?

Steps of cavity preparation
1- Outline form
2- Resistance and Retention form
3- Convenience Form

4- Removal of remaining Caries
5- Finishing of cavity walls

6- Toilet of the cavity

1-The outline form
 It is defined as

Shape of the boundaries of the completed
cavity
 External outline form refers to the
marginal boundaries
 Internal outline form refers to the shape
of the internal form of the preparation.
Internal
outline form

External
outline form

Principles of outline form

 All fault or caries should be removed

 All friable or weakened enamel should be removed to

avoid marginal ditching.
 All margins should be placed in a position to afford
good finishing of the margins of the restoration.
- Giving the cavosurface angle [CSA] the correct
angulations according to the restorative material [ 90o

CSA for amalgam and obtuse for cast gold
restorations].

Rules for outline form
1. Extend to sound tooth structure.
2. Avoid terminating the margins on extreme

eminence such as cusp height or ridge crest.
3. If extension include 2/3 of cusp incline, cusp

capping is done for non adhesive restorations.

4- Extend the preparation margin to include all
fissures that cannot be eliminated by enameloplasty.
Enameloplasty; is reshaping of enamel fissures to be
non retentive.
It is made in pits or fissures that does not penetrate
more than 1/3 of enamel especially at end of fissure.

 Restrict initial depth of penetration
 Depth penetration into dentin should be kept to

minimum [0.2-0.5 mm beyond DEJ; Total 1.5-2 mm]
dictated by
- Strength requirement of the restoration
- Establishment of retention
- Removal of caries.

6- In case of two separate carious lesion, as in upper
molars, cavities are joined if the intervening tooth
structure is
- Carious
- Undermined
- Weak i.e.; Less than 0.5 mm.

2- Resistance and Retention Form
They are two faces for the same coin

Resistance form refers to design features in the cavity
preparation which allows tooth and restoration to
resist the masticatory stresses without fracture.

2- Resistance Form
How cavity design reduce fracture
of tooth or restoration?

90o CSA
Walls parallel or
perpendicular to forces
Rounded line
and point angles

Giving bulk to restoration
[1.5 for amalgam,
2 for porcelain,
1-2 for cast restorations]
Flat and smooth walls

2- Resistance and Retention form
What is the name of this shape?
Box [mortise]
Or modified box form

2- Retention Form
Retention form refers to design features in the cavity
preparation which allows it to retain restoration
securely during function


Wall convergence
[undercut]

increase length of wall
increase frictional retention]

2- Retention Form
Retentive features
A- axial retentive design features
-

2- Resistance and Retention
Form
Retentive features
B- lateral retention
- Buccal or lingual extensions

2- Retention Form
Retentive features
B- lateral retention
- Dove tail lock [common in premolar]

3-

Obtaining the convenience form

 Definition

It describes those features in the prepared cavity
which improves visibility and accessibility during
preparation and restoration
N.B.: Advent of recent methods of instrumentation
limited the application of this step

4- Removal of remaining caries
 Definition

It is the removal of any remaining infected caries
left in the tooth after initial preparation.
In dentin as caries progress, area of decalcification
precedes penetration of microorganisms. It is
called affected dentin.
Infected carious dentin is removed alone leaving a
rounded concave area in the wall.

Manual
excavation

Mechanical
excavation by
burs

Air abrasion
debridement

Laser
debridement

Chemico mechanical
[e.g. Carisolv]

 Sometimes during caries removal, you might find hard

discolored dentin that is stained from pigments
produced by chromogenic bacteria and not
demineralized.

 How to differentiate this dentin from caries?
 Is it removed or not?

5- Finishing of cavity walls
 Definition

It is the development of a specific surface design and
degree of smoothness that produce maximum
effectiveness of the restoration.

5-Finishing of cavity walls
 According to Noy’s principles, the

maintenance of a stronger enamel
wall at the cavosurface angles
1. Enamel should rest on sound dentin.
2. Enamel rods forming the cavosurface angle must have their inner
ends resting on sound dentin.
3. The cavosurface angle is beveled and
covered by strong restoration.

6- Toilet of the cavity
 The cavity should be clean and dry before insertion of

the final restoration.
 It is aimed to
- Remove debris, dentin chips, saliva.
- Improve adaptation of final restoration.

- Hinder recurrence of decay
 This is done using air water spray.

References

Chapter 7: Principles
of tooth preparation

Chapter 6: fundamentals
of tooth preparation

principles of cavity preparation

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