FUNDAMENTALS IN TOOTH
PREPARATION
Dr. Ramesh Bharti
Assistant Professor
Conservative Dentistry &Endodontics
King George’s Medical University
Lucknow
Definition of Operative Dentistry
Operative dentistry is
the ART and
SCIENCE of the diagnosis, treatment,
prognosis of defects of teeth which do not
require full coverage restorations for
correction, such treatments should results
in the restoration of proper tooth form,
function, and esthetics while maintaining
the physiologic integrity of the teeth in
harmonious relationship with adjacent
hard and soft tissue, all of which enhance
the general health and welfare of the
patient.
Objectives of Cavity Preparation
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Remove all defects and give the necessary
protection to pulp.
Locate the margins as conservatively as possible.
Form the cavity so that both the restoration and
tooth can withstand the load of mastication.
Allow for the esthetic and functional placement of
a restorative material.
Need of Restoration
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Caries
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Malformed, discolored or fractured teeth
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Restoration replacement
Factors affecting tooth preparation
1. General Factors
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Pulpal & periodontal status
Occlusal relationship
2.Dental anatomy
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Direction of enamel rods
Thichness of enamel /dentin
Size and positionof pulp
Relationship of tooth to its supporting tissues
3.Patient factors
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Age
Esthetic consideration
Economic status
Patients with high risk caries
4.Affected & infected Dentine
5. Restorative material factors
Approach of Operative. cont…..
 Cavity preparation
 Matrix application
 Preparation of materials
 Insertion and carving of materials
 Finishing and Polishing
Cavity Preparation
The mechanical alteration of a defective,
injured, or diseased tooth in order to best
receive a restorative material which will reestablish a healthy state for the tooth
including esthetic corrections where indicated,
along with normal form and function.
Cavity Structure
walls
 angles
 Floor
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Classification of cavity
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Class I
Class II
Class III
Class IV
Class V
Class VI
—G.V.Black in 1908
Cavity
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Simple cavity: only one tooth surface
is involved.
Compound cavity: two surfaces are
involved.
Complex cavity: three or more
surfaces are involved.
Class 1
Class 6
Class 1
Class 4
Class 2
Class 2
Class 5
Class 3
Stages and Steps in Cavity
preparation
•Initial cavity preparation stage
•Final cavity preparation stage
Initial cavity preparation stage
Step 1 Outline form and initial depth
Step 2 Primary resistance form
Step 3 Primary retention form
Step 4 Convenience form
FINAL CAVITY PREPARATION STAGE
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures
Outline Form and Initial Depth
Definition:
placing the cavity margins in the positions
they will occupy in the final preparation.
preparing an initial depth of 0.2~0.8 mm
pulpally of the dentinoenamel junction
position or normal root surface position.
Maxillary Class Ⅰ outline form
Mandibular Class Ⅰ outline form
Maxillary Class Ⅱ outline form
Mandibular Class Ⅱ outline form
Common Error
Outline Form and Initial Depth
Principles:
all friable and/or weakened enamel should be
removed
all faults should be included
all margins should be placed in a position to
afford good finishing of
the margins of the restoration.
Margins of the preparation will be located on
finishable, self –cleansing area.
Outline Form and Initial Depth
Features:
preserving cuspal strength
preserving marginal ridge strength
minimizing facio-lingual extension
using enameloplasty
connecting two close faults or cavities
restricting the depth of the preparation into
dentin.
Auxillary Factors
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Conservation
Adjacent enamel cracks or decalcification could
be involved in the preparation.
Type of restorative material.
Extension for access.
anatomy and alignment.
If possible, no margins will be in occlusion with
opposing teeth.
Esthetics
Outline Form and Initial Depth for pit and fissure
cavities
Controlled by three factors
1- Extension to which enamel has been involved
by caries.
2- Extension to achieve sound and smooth
margins.
3- Limited bur depth while extending the
preparaton
Rules
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Capping of cusp should be done when cavity
extension is two-third from central fissure to cuspal
eminence.
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Include all fissures that cannot be eliminated by
enameloplasty.
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Restrict the depth.
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Join two lesions if they are less than 0.5 mm apart.
Outline Form and Initial Depth for smooth
surface cavities
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Extension of cavity.
Sufficient access.
Depth.
Sufficient clearance with adjacent tooth.
Initial cavity preparation stage
Step 1
Step 2
Step 3
Step 4
Outline form and initial depth
Primary resistance form
Primary retention form
Convenience form
Primary Resistance Form
Definition:
The shape and placement of the cavity walls
that best enable both the restoration and the
tooth to withstand, without fracture,
masticatory forces delivered principally in the
long axis of the the tooth.
Primary Resistance Form
Principles:
To utilize the box shape with a relatively flat floor to
resist occlusal loading by virtue of being at right angles
to mastication force.
To restrict the extension of the external walls (keep as
small as possible) to allow strong cusp and ridge areas
to remain with sufficient dentin support.
Primary Resistance Form
Principles:
To have a slight rounding of internal line angles to
reduce stress concentration in tooth structure;
The presence of sharp internal line angles in
GOLD FOIL resist the movement of the
restoration
Sharp internal line and point angles in dentin
serve as convenient “starting” points for
compacting of direct gold.
To provide enough thickness of restorative
material to prevent its fracture under load.
Primary Resistance Form
Feature:
Box shape
Relatively flat floors
Inclusion of weakened tooth structure
Preservation of cusps and marginal ridges
Rounded internal line angles
Adequate thickness of restorative materials
Reduction of cusps for capping if indicated
Primary Resistance cont….
Designing the outline form so that minimal
of restoration is exposed to occlusal stress.
 Seat on sound dentin.
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Vale Experiments
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1 MR at 1/4th ICD -10% Loss of FR
2 MR at 1/4th ICD - 15% Loss of FR
1 MR at 1/3th ICD -30% Loss of FR
2 MR at 1/3th ICD -35% Loss of FR
1 MR at 1/2 of ICD -40% Loss of FR
2 MR at ½ of ICD -45% Loss of FR
Initial cavity preparation stage
Step 1
Step 2
Step 3
Step 4
Outline form and initial depth
Primary resistance form
Primary retention form
Convenience form
Primary Retention Form
Definition:
The shape or form of the prepared cavity
that resists displacement or removal of the
restoration from tipping or lifting forces.
Primary Retention Form
Principles: depending on the materials
Amalgam restoration:
developing external cavity walls that
converge occlusally and dovetail design
The devotail design provide retention form
to the occlusal portion of the cavity.
The occlusal convergence of the walls offers
retention in the proximal portion of the cavity
against displacement occlusally.
Primary Retention Form
Principles: depending on the materials
Composite restoration:
a mechanical bond between the material
and conditioned, prepared tooth structure.
Dentin etched with 32% phosphoric acid Collagen exposed
by the acid.
FIG
Bonding of resin to dentin, using a "total-etch" technique
16 Bonding to dentin using a self-etching primer.
Scanning electron micrograph of the transition between
composite resin (C) adhesive (A), adhesive-hybrid layer
(H), and hybrid layer-dentin.
Initial cavity preparation stage
Step 1
Step 2
Step 3
Step 4
Outline form and initial depth
Primary resistance form
Primary retention form
Convenience form
Convenience Form
Conception:
The shape or form of the cavity that
provides for adequate observation,
accessibility, and ease of operation in
preparing and restoring the cavity.
Convenience Form
Principles:
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Allow access for caries removal
Allow access for restoration placement
Allow access to margins for finishing,
evaluation and cleaning
Convenience Form
Final cavity preparation stage
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures
Removal of any remaining infected dentin if
indicated
Definition:
The elimination of any infected carious tooth
structure or faulty restorative material left in the
tooth after initial cavity preparation.
Removal of dentinal caries using round burs and spoon excavators
Pulp protection
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Using liners or bases to protect the pulp or
to aid pulpal recovery or both.
If the infected dentin more than 2 mm
deeper from the initial pulpal or axial wall
then a Liner is indicated.
Final cavity preparation stage…..
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures
Secondary resistance and retention forms
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Most compound and complex cavity preparations
require additional resistance and retention form.
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The exception being those preparations that are very
conservative.
Secondary resistance and retention forms
Mechanical forms
Cavity wall conditioning form
Mechnical form:
 Proximal locks
 Proximal slots
Proximal locks
Slot on gingival wall
Final cavity preparation stage….
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Finishing external walls
Step 9 Final procedures
Finishing the external walls
Definition:
Finishing the preparation walls is the further
development of a specific cavosurface design and
degree of smoothness that produces the
maximum effectiveness of the restorative material
being used.
Finishing the external walls
Objectives:
 To create the best marginal seal possible
between the restorative material and tooth
structure;
 To afford a smooth marginal junction;
 To provide maximum strength of both the
tooth and the restorative material at and
near the margin.
The strongest enamel margin is that margin which is
composed of full-length enamel rods that are supported
on the cavity side by shorter enamel rods, all of which
extend to sound dentin.
Finishing the external walls
The design of the cavosurface angle
The degree of smoothness of the wall
The design of the cavosurface angle depending
on the material:
 Amalgam:
90°
 Composite: beveling 30°~ 40°
Final cavity preparation stage……..
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures
Final procedures
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cleaning
inspecting
varnishing
conditioning
Multiple Choice Questions
Q.1. In cavity prepartion cavo-surface margin will be
a junction between :
a) Cavity wall/floor and adjacent tooth surface.
b) Cavity wall and floor.
c) Floor of the occlusal box and aproximal box
d) Axial wall and occlusal floor.
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Q.2 Toilet of the cavity is:
a) Removal of debris by washing with water
b) Removal of debris by cold air
c) Removal of debris by hot air
d) Washing the cavity with water.
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Q.3 Most common fracture seen in amalgam
restoration at:
a) Cavosurface margin.
b) Contact area
c) Isthmus area
d) Proximal box
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Q 4 G. V Black concluded that following area of
tooth surface are relatively non-selfcleansing:
A) Pit and fissures
B) Tips and cusps
C) Fossa
D) Marginal ridge
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Q.5 Class III amalgam restorations areusualy
prepared on:
a) Distal surface of anterior teeth
b) Mesial surface of canine
c) Distal surface of canine
c) Mesial and distal surface of all teeth.