PURPOSE OF TOOTH PREPARATION
• Restoration is usually required to repair a
diseased, injured or defective tooth structure.
• The restoration helps in maintaining proper
form, function and esthetics.
TYPES OF RESTORATION
• Tooth restoration may be classified as intracoronal,
when it is placed within a preparation made in the
crown of a tooth
• extracoronal, when it is placed outside the tooth as in
the case of a crown.
• Intracoronal restoration is placed directly into the
tooth preparation while extracoronal restoration uses
an indirect technique.
Factors to be considered before
restoration of a tooth
• Tooth factors
Primary or permanent
Quality of tooth (hypoplasia)
Location of tooth
Type of tooth
Type of tooth preparation.
• General patient factors
Patient’s exposure to floride
Presence of any parafunctional habit.
Factors related to clinician and the
restoration to be used
Type of restoration
Physical properties of the restoration
Whether moisture control can be achieved or not
TERMINOLOGY OF TOOTH
• Simple Tooth Preparation
A tooth preparation involving only one tooth
surface is termed simple preparation for
example occlusal preparation.
• Compound Tooth Preparation
A tooth preparation involving two surfaces is
termed compound tooth preparation for
example mesioocclusal or disto-occlusal
• Complex Tooth Preparation
A tooth preparation involving more than two
surfaces is called as complex tooth
preparation for example MOD preparation.
Tooth Preparation Walls
• Internal Wall
It is a wall in the preparation, which is not
extended to the external tooth surface
• External Wall
An external wall is a wall in the prepared tooth
that extends to the external tooth surface.
External wall takes the name of the tooth
surface towards which it is situated.
• Pulpal Wall
A pulpal wall is an internal wall that is towards
the pulp and covering the pulp.
• It may be both vertical and perpendicular to
the long axis of tooth.
• Axial Wall
It is an internal wall which is parallel to the
long axis of the tooth
Floor is a prepared wall which is usually flat and
perpendicular to the occlusal forces directed
occlusogingivally,for example, pulpal and gingival
Cavosurface Angle Margin/Tooth
• Cavosurface angle is formed by the junction of a prepared tooth surface
wall and external surface of the tooth.
• The acute junction is referred to as preparation margin or cavosurface
• The cavosurface angle may differ with the location of tooth and enamel
rod direction of the prepared walls and also differ according to the type of
restorative material to be used.
• Line Angle
It is a junction of two surfaces of different orientations
along the line and its name is derived from the involved
• Point Angle
It is a junction of three plane surfaces or three line angles
of different orientation and its name is derived from its
involved surfaces or line angles.
Steps in tooth preparation
Stage I: Initial tooth preparation steps
• Outline form and initial depth
• Primary resistance form
• Primary retention form
• Convenience form.
Stage II: Final tooth preparation steps
• Removal of any remaining enamel pit or fisure, infected dentin and/or old
restorative material, if indicated
• Pulp protectin, if indicated
• Secondary resistance and retention form
• Procedures for finishing the external walls of the tooth preparation
• Final procedures: Cleaning, inspectig and sealing
• Under special conditions these sequences are changed.
• Outline form defines the external boundaries
of the preparations.
Following principles are kept in mind while preparing an
• • Removal of all weakened and friable tooth structure
• • Removal of all undermined enamel
• • Incorporate all faults in preparation
• • Place all margins of preparation in a position to afford
good finishing of the restoration.
Features for establishing a proper
outline form are
• Preserving cuspal strength
• Preserving strength of marginal ridge
• Minimizing the buccolingual extensions
• If distance between two faults is less than 0.5 mm, connect them
• Limiting the depth of preparation 0.2 to 0.8 mm into dentin
• Using enameloplasty wherever indicated
Primary Resistance Form
Primary resistance form is that shape and
placement of preparation walls to best
enables both the tooth and restoration to
withstand, without fracture the stresses of
masticatory forces delivered principally along
the long axis of the tooth.
Factors affecting resistance form
• Amount of occlusal stresses
• Type of restoration used
• Amount of remaining tooth structure.
Primary Retention Form
• Primary retention form is that form, shape
and configuration of the tooth preparation that resists
the displacement or removal of restoration from the
preparation under lifting and tipping masticatory
• Usually, resistance and retention forms are obtained
by providing same features, hence they are sometimes
described together. The retention form is aﬀected by
the type of the restorative material used
Factors affecting retention form
• Amount of the masticatory stresses falling on the
• Thickness of the restoration
• Total surface area of the restoration exposed to
the masticatory forces
• The amount of remaining tooth structure
Retention form for diﬀerent
• Retention is increased in amalgam restoration by the following:
• – Providing occlusal convergence (about 2–5%) of the
dentinal walls towards the tooth surface
• – Giving slight undercut in dentin near the pulpal wall
• – Conserving the marginal ridges
• – Providing occlusal dovetail
• Retention is increased in cast restorations by the following:
• – Close parallelism of the opposing walls with slight
occlusal divergence of two to five degrees
• – Making occlusal dovetail to prevent tilting of restoration
in class II preparations
• – Use of secondary retention in the form of coves, skirts
and dentin slot
• – Give reverse bevel in class I compound, class II, and
MOD preparations to prevent tipping movements
• The convenience form is that form which
facilitates and provides adequate visibility,
accessibility and ease of operation during
preparation and restoration of the tooth.
Features of convenience form
• Suffcient extension of distal, mesial, facial or lingual walls to
gain adequate access to the deeper portion of the
• The cavosurface margin of the preparation should be related to
the selected restorative material for the purpose of
convenience to marginal adaptation.
• In class II preparations access is made through occlusal surface
for convenience form.
Features of convenience form
• Proximal clearance is provided from the adjoining tooth
during class II tooth preparation.
• To make Class II tunnel preparation, for convenience,
the proximal caries in posterior teeth is approached
through a tunnel initiating from the occlusal surface
and ending on carious lesion on the proximal surface
without cutting the marginal ridge.
• In tooth preparation for cast gold restorations occlusal
divergence is one of the feature of convenience form.
Final Stages of Tooth Preparation
• After initial stages of the preparation, the prepared tooth should be
• The remaining carious portion should be removed only
after the initial tooth preparation has been completed. It
provides two advantages:
• 1. It allows optimal visibility and convenience form for
removal of remaining carious lesion.
• 2. Completion of the initial preparation permits immediate
placement of a base and the restoration.
• Removal of Any Remaining Enamel Pit or Fissure,
Infected Dentin and/or Old Restorative Material, if
• After the establishment of external and internal outline
form, if any of the remaining carious tooth structure or
defective restorative material is left in tooth, it is to be
removed in this stage.
• Infected dentin must be removed even if it leads to
exposure of pulp which is treated accordingly
• When remaining dentin thickness is less, pulpal
injury can occur because of heat production, high
speed burs with less eﬀective coolants, irritating
restorative materials, galvanic currents due to
restoration of dissimilar metals, excessive
masticatory forces transmitted through
restorative materials to the dentin and ingress of
microorganisms and their noxious products
• cements used on pulpal and axial walls in thickness of
about 0.5 to 2 mm beneath the permanent
• They provide thermal, galvanic, chemical and
mechanical protection to the pulp.
• Commonly used restorative materials as base are
• zinc phosphate cements,
• Glass ionomers,
• polycarboxylate cements,
• zinc oxide eugenol,
• calcium hydroxide cement. 55
Secondary Resistance and Retention
• This step is needed in complex and compound
tooth preparations where added preparation
features are used to improve the resistance
and retention form of the prepared tooth.
• These are as follows:
• Diﬀerent types of pins of various shapes and
sizes are used to provide additional retention.
• They can be used in all types of restorations
like amalgam, composite and cast
• Skirts are prepared for providing additional
retention in cast restorations.
• They increase the total surface area of the
• Skirts can be prepared on one or all four sides of
the preparation depending upon the required
• Amalgam pins are vertical posts of amalgam
anchored in dentin.
• Dentin chamber is prepared by using inverted
cone bur on gingival ﬂoor 0.5 mm in dentin with
1 to 2 mm depth and 0.5 to 1 mm width.
• Amalgam pins increase the retention and
resistance of complete restoration.
Beveled enamel margins:
• Beveling of the preparation, margins increases
the surface area and thus the retention
in composite restorations.
Enamel wall etching:
• Etching results in microscopic roughness,
which increases the surface area and thus
helps in enhancing the micromechanical
• Dentin conditioning (etching and priming):
Etching and priming of the dentin surface
done in some restorative materials increases
• Adhesive luting cements:
Adhesive luting cements increase the
retention of indirect restorations