STEPS OF CAVITY PREPARATION
DEFINITION OF CAVITY PREPARATION
Cavity preparation is the mechanical alternation of a
tooth to receive a restorative material , which will
return the tooth to proper anatomical form ,
function , and esthetics . The procedure of the
preparing the tooth is the removal of the defective
or friable tooth structure. Any remaining infected
or friable tooth structure may result of further
carious progression, sensitivity or pain or fracture of
the tooth and/restoration.
OBJECTIVES OF CAVITY PREPARATION
To remove diseased tissue as necessary and
at the same time provides the protection to
To locate the margins of the restoration as
conservative as possible.
To ensure the cavity form , it should not be
under the force of mastication of the tooth.
To allow the functional placement of the
PRINCIPLES OF CAVITY PREPARATION
Gain access to caries.
Removal of all carious lesions.
Cut away all significantly unsupported enamel.
Extended margins so that they are accessible
for instrumentation and Cleaning.
(G.V. BLACK CLASSIFICATION)
Black suggested that it was necessary to
Remove additional tooth structure to gain access and
Remove all trace of demineralized enamel and dentin
from the floor , walls and margins of the cavity.
Make room for the insertion of the restorative material
sufficient bulk to provide strength.
Provide mechanical interlocking retentive designs.
Extend the cavity to self-cleansing areas to avoid
The lesions involving the occlusal surfaces of
molars and premolars , the occlusal 2/3 of buccal
and lingual surfaces of molars, and the palatal
pits in anterior teeth.
The lesions involving the proximal surfaces of the
posterior teeth with access established from the
The lesions involving the proximal surfaces of
anterior teeth which may or may not involve a
labial or a lingual extension & not involving
The lesions involving all proximal surfaces of
anterior teeth which involves the incisal edge.
The lesions involving the cervical third of all teeth,
including the proximal surface of posterior teeth
where the marginal ridge is not included in the
Preparations on incisal edges of anterior and cusp
tips of posterior teeth without involving any
other surfacecome under class VI.
STEPS IN THE CAVITY PREPARATION
(GIVEN BY G V BLACK)
A) Stage I
Initial Tooth Preparation Steps:
Obtaining Outline Form
Obtaining Primary Resistance Form
Obtaining Primary Retention Form
Obtaining Convenience Form
B) Stage II
Final Tooth Preparation Steps:
Removal of Remaining Carious Dentin
Providing Pulp Protection, If Indicated
Obtaining Secondary Resistance & Retention Form
Finishing of Enamel Walls & Margins
Final Procedures; Cleaning, Inspecting and Sealing
OUTLINE FORM AND INITIAL DEPTH
Placing the preparation margins to the place
they will occupy in the final tooth preparation
except for finishing enamel walls and
Maintaining the initial depth of 0.2 to 0.8 mm
into the dentin.
Outline form defines the external boundaries
of the preparations.
Outline form should
defective pits and fissures
Initial depth of preparation
should be 0.2 to 0.8 mm into
Outline form should consist of
straight lines and rounded line
and pointed angles
FOLLOWING FACTORS EFFECT THE OUTLINE FORM AND
Extension of carious lesion.
Proximity of the lesion to other deep structural surface defects.
Relationship with adjacent and opposing teeth.
Caries index of the patient.
Need for esthetics.
Restorative material to be used.
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.
During tooth preparation, the margins of preparation not
only extend into sound tooth tissue but also involve adjacent
deep pits and fissures in preparation.
This was referred to it as “extension for prevention” by GV
EXTENSION FOR PREVENTION
Extension for prevention means the placing the
margins of preparations at areas that would be
cleaned by the excursions of food during
chewing. It is done with the objective of
preventing the recurrence of caries at the
margins of fillings where the recurrence of
decay is most commonly seen.
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 long axis of
Factors affecting resistance form:
Amount of occlusal stresses.
Type of restoration used.
Amount of remaining tooth structure.
Enameloplasty is the careful removal of sharp
and irregular enamel margins of the enamel
surface by “rounding” or “saucering” it and
converting it into a smooth groove making it
self-cleansable, finishable and allowing
conservative placement of margins
FEATURES OF RESISTANCE FORM:
A box-shaped preparation.
A flat pulpal and gingival floor, which helps the
tooth to resist occlusal masticatory forces
without any displacement.
Adequate thickness of restorative material
depending on its respective compressive and
tensile strengths to prevent the fracture of both
the remaining tooth structure and restoration.
Restrict the extension of external walls to
allow strong marginal ridge areas with
sufficient dentin support.
Inclusion of weakened tooth structure to
avoid fracture under masticatory forces.
Rounding of internal line angle to reduce the
stress concentration points in tooth
Resistance form also depends upon type of
restorative material being used. For example, high
copper amalgam requires minimal thickness of 1.5
mm, cast metal requires thickness of 1.0 mm and the
porcelain requires a minimum thickness of 2.0 mm to
resist fracture. The composite restorations and glass
ionomer restorations are more dependent on occlusal
wear potential of restorative area and usually require
thickness of more than 2.5 mm.
(A) Resistance form of
tooth provided by flat
pulpal and gingival floor,
(B) In case of rounded
pulpal floor, the rocking
motion of restoration
results in wedging force
which may result in
failure of restoration
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 forces.
Usually, resistance and retention forms are
obtained by providing same features, hence
they are sometimes described
The common factors affecting retention form are
Amount of the masticatory stresses falling on
Thickness of the restoration.
Total surface area of the restoration exposed to
the masticatory forces.
The amount of remaining tooth structure.
The retention form is affected by the type of the
restorative material used:
Amalgam: Retention is increased in amalgam restoration
by the following:
Providing occlusal convergence (about 2 to 5%) the dentinal
walls towards the tooth surface.
Giving slight undercut in dentin near the pulpal wall.
Conserving the marginal ridges.
Providing occlusal dovetail
Dovetail helps in
Undercut in dentin the
helps in retention of
Cast metals: 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.
Composites: In composites, retention is
Micromechanical bonding between the etched
and primed prepared tooth structure and the
Providing enamel bevels.
Direct filling gold:
Elastic compression of dentin and starting
point in dentin provide retention in direct gold
fillings by proper condensation.
The convenience form is that form which
facilitates and provides adequate visibility, accessibility and
ease of operation during preparation and restoration of the
Sufficient extension of distal, mesial, facial or lingual walls
should be given to gain adequate access to the deeper
portion of the preparation.
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
Provide proximal clearance from the
adjoining tooth during class II tooth
FINAL TOOTH PREPARATION STEPS
REMOVAL OF REMAING CARIOUS DENTIN:
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 fillings of dissimilar
metals, excessive masticatory forces transmitted
through restorative materials to the dentin and ingress
of microorganisms and their noxious products through
Pulp protection is achieved using liners, varnishes and
bases depending upon:
The amount of remaining dentin thickness
Type of the restorative material used.
Liners, Varnishes, Bases:
Liners and varnishes are used where preparation depth
is shallow and remaining dentin thickness is more than
2 mm. They provide:
Barrier to protect remaining dentin and pulp
Galvanic and thermal insulation.
Bases are the cements used on pulpal and axial walls in
thickness of about 0.5 to 2 mm beneath the permanent
restorations. 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, and calcium hydroxide cement.
Secondary Resistance & Retention Form:
This step is needed in complex and compound tooth
preparations where added preparation features are used
improve the resistance and retention form of the
tooth. These are as following:
Grooves and coves: Wherever bulk of dentin is present,
grooves are prepared without undermining the adjacent
enamel. Coves are small conical depressions
prepared in healthy dentin to provide additional
retention. axiolingual so as
retention of the
Slots or internal boxes: These are mainly used in
restorations. They are 1.0 to 1.5 mm deep box like
prepared in dentin to increase the surface area. These
prepared in occlusal box, buccoaxial, linguoaxial and
Locks: Locks are usually prepared for amalgam class II
restoration in the proximal or occlusal box of class II
Pins: Different types of pins of various shapes and sizes
are used to provide additional retention. They can be
in all types of restorations like amalgam, composite and
Skirts: Skirts are prepared for providing additional
in cast restorations. They increase the total surface area
the preparation. Skirts can be prepared on one to all four
Skirt in cast
sides of the preparation depending upon the required
Amalgampins: Amalgampins are vertical posts of
anchored in dentin. Amalgampins increase the retention
and resistance of complete restoration.
Beveled enamel margins: Beveling of the preparation
margins increases the surface area and thus, the
in composite restorations.
Enamel wall etching: Etching results in microscopic
roughness, which increases the surface area and thus
Dentin conditioning (etching and priming): Etching
priming of the dentin surface done in some restorative
materials increases the retention.
Adhesive luting cements: Adhesive luting cements
the retention of indirect restorations.
FINISHING OF ENAMEL WALLS & MARGINS
Finishing of the enamel margins should be done
irrespective of restorative material used. During
finishing there occurs the further enhancement of the
cavosurface design and smoothness that produces
the maximum adaptation of restoration to the walls
and the margins and maximum effectiveness of
The finishing of the preparation walls results in:
Better marginal seal between restoration and tooth
Increased strength of both tooth structure and
restoration at and near the margins.
Strong location of the margins.
Increase in degree of smoothness of the margins.
Degree of smoothness of walls: It depends upon type
restoration used. For example, for cast metal
a very smooth surface is required whereas for direct
amalgam and composite restorations, slight roughness
needed in the preparation walls.
Location of the margins: During finishing of the
walls and margins, one should follow the principles of
paralleling the direction of enamel wall. The knowledge of
enamel rods is necessary for proper finishing of the
preparation margins. At the margins, all the enamel walls
should have full length rods supported by dentin.
Features of finished preparation: The design of
cavosurface angle depends on type of restorative
material being used. For example, for amalgam
restoration, cavo-surface angle of 90 degrees
affords maximum strength to tooth restoration.
FINAL PROCEDURES; CLEANING, INSPECTING AND SEALING
The final step in tooth preparation is cleansing of the
preparation. This includes the removal of debris, drying of
the preparation, and final inspection before placing
The debridement of the preparation serves the following
Cleaning of preparation walls, floors and margins from
enamel and dentin chips resulting during tooth
preparation: Remove all the debris from the preparation,
especially on the margins, otherwise deposits left on them
consequently dissolve, resulting in a microleakage which
further can result in secondary caries. Cleaning of
preparation can be done by using warm water. Immovable
particles of debris can be removed with the help of a small
cotton pellet dampened with water or hydrogen peroxide.
Drying the tooth preparation before insertion of
restorative materials: It can be done using air,
pellets and commercial cleaners. It is important
are not dehydrated by overuse of air or hot air.
Sterilization of preparation walls using very
alcohol free disinfectant: Use of mild