Fundamental of cavity preparation

COLLEGE OF DENTAL SCIENCES
DEPARTMENT OF CONSERVATIVE DENTISTRY
AND ENDODONTICS
SEMINAR ON
“FUNDAMENTALS OF
CAVITY PREPARATIONS”
Presented By : -
Dr. Sharno Mathai Varghese

CONTENTS
 INTRODUCTION
 DEFINITION
 NEED FOR RESTORATIONS
 OBJECTIVES OF CAVITY PREPARATION
 FACTORS AFFECTING CAVITY PREPARATION
 CARIES TERMINOLOGY
 TOOTH PREPARATION TERMINOLOGY
 CLASSIFICATION OF TOOTH PREPARATION
 INITIAL TOOTH PREPARATION STAGE
o OUTLINE FORM AND INITIAL DEPTH
o PRIMARY RESISTANCE FORM
o PRIMARY RETENTION FORM
o CONVENIENCE FORM
 FINAL TOOTH PREPARATION STAGE
o REMOVAL OF ANY REMAINING INFECTED DENTIN
/OLD RESTORATIVE MATERIAL
o PULP PROTECTION
o SECONDARY RESISTANCE AND RETENTION FORMS
o PROCEDURES FOR FINISHING EXTERNAL WALLS
o CLEANING, INSPECTING AND SEALING
 ADDITIONAL CONCEPTS IN TOOTH PREPARATION
o AMALGAM RESTORATIONS
o COMPLETE RESTORATIONS
 CONCLUSION

INTRODUCTION :
The basic principles governing the design of cavities and steps in their
preparation was first suggested by American Dentist and teacher Dr.G.V.Black
in the first decade of the last century. He based these principles on what was
known at time about the natural history of caries and the restorative material
available. The wisdom of his work was such that it remained unchallenged for
more than half a century but now with new materials, a better understanding of
caries and research findings into the success of various restorative procedure,
his principles have been largely revised. Modification and rearrangement of
these original principles have been largely revised.
DEFINITION OF CAVITY PREPARATIONS :
“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”.
NEED FOR RESTORATIONS :
Teeth needs restorative intervention for a variety of reasons which are as
follows ;
1. Repair of tooth after destruction from carious lesions.
2. Replacement / repair of restorations with serious defects such as
improper proximal contacts, gingival excess, poor esthetics etc.
3. Restoration of proper form and function of fractured teeth.
4. Restoration of form and function as a result of congenital malformations
5. To fulfill the esthetic demands
6. Restoration for preventive measures
OBJECTIVES OF CAVITY PREPARATIONS :
1. Removal of all the defects and give the necessary protection to the pulp.
2. Location of margins of the restorations as conservative as possible.
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3. Form the cavity so that under forces of mastication the tooth or the
restoration or both will not fracture and the restoration will not be
displaced.
4. Esthetic and functional placement of a restorative material.
FACTORS AFFECTING CAVITY PREPARATIONS
GENERAL FACTORS PATIENTS FACTORS
1. Diagnosis :
1. Prior to any restorative procedure a complete and through diagnosis
must be made assessment of both pulpal and periodontal status will
influence the potential treatment of tooth especially in terms of the
choice of restorative materials as well as the design of cavity
preparation.
2. Assessment of occlusal relationships must be made.
3. Patient concern for esthetics should be considered
4. Other planned treatment should be considered for e.g. such as when
tooth is used as an abutment for FPD or RPD, design of restoration is
altered to accommodate maximum effectiveness of that prosthesis.
5. Risk assessment find out with dietary habits. DMFT index and
microbiological examination.
2. Knowledge of Dental Anatomy :
Direction of enamel rods, thickness of enamel and dentin, position of
pulp relationship of tooth to the investing tissue.
PATIENTS FACTORS :
1) Patients knowledge and appreciation of good Dental Health Influences the
choice of restorative material.
2) Patients economic status
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3) Age of the patient
Elderly patient who are physically or medically compromised require
special positioning for restorative procedure plus less stressful and shorter
appointments.
CARIES TERMINOLOGY :
Caries can be located according to location, extend and rate.
According to Location :
1) Primary caries : Original carious lesion of the tooth. They originate
basically at three sites – pit and fissure, smooth surface, root surface.
2) Forward caries : Is seen when the caries cone in enamel is larger as
atleast the same size as that in dentin.
3) Backward caries- when spread of caries along DEJ exceeds the caries in
contiguous enamel, caries extends into this enamel from the function.
4) Residual caries - Caries that remains in a completed tooth preparation
whether by operator intention or by accident.
5) Secondary caries : Occurs at junction of a restoration and tooth and may
progress sunder the restoration.
According to Extend :
1) Incipient caries (Reversible) : It is the first evidence of caries activity in
the enamel.
2) Cavitated caries (Irreversible) : The enamel surface is broken, and
usually the lesion has advanced into dentin.
According to Rate :
1) Acute caries (Rampant caries) : In this, the disease is rapid in damaging
the tooth.
2) Chronic caries (Arrested caries) : The slow rate results form periods
when demineralized tooth structure is almost remineralized.
Enameloplasty :
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It is the removal of a shallow, enamel developmental fissure or patient
to create a smooth, saucer shaped surface that is self cleansing or easily
cleaned.
Prophylactic Odontotomy :
It is characterized by minimally preparing and filling with amalgam any
pits and fissures to prevent caries originating in these sites. It is no longer
advocated as a preventive measure.
Affected Dentin And Infected Dentin :
Affected dentin has no bacteria, is reversibly denatured, remineralizable
and should be preserved.
Infected dentin has bacteria present and the collagen is irreversibly
denatured. It is not remineralizable and must be removed.
TOOTH PREPARATION TERMINOLOGY :
1) Simple, tooth preparation – Only one tooth surface is involved.
2) Compound tooth preparation – Only two tooth surface is involved.
3) Complex tooth preparation – Involves three or more surfaces.
CLASSIFICATION OF TOOTH PREPARATION (According to
G.V.Black)
1) Class I Restorations : Restoration on occlusal surface of premolars and
molars.
Restorations on occlusal two thirds of facial and lingual surface of
molars. (8 line angles, 4 point angles)
Restorations on lingual surface of maxillary incisors (6 point angles, 11
line angles).
2) Class II restorations : Restorations on proximal surface of posterior
teeth.
3) Class III restorations : Restorations on proximal surface of anterior teeth
that do not involve the incisal angle (6 line angles, 3 point angles).
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4) Class IV restorations : Restorations on proximal surface of anterior teeth
that involve the incisal angle (11 line angles, 6 point angles).
5) Class V restorations : Restorations on the gingival third of facial or
lingual surfaces of all teeth (except pit and fissure lesions) (8 line
angles, 4 point angles).
Class VI Restorations : Restorations on the incisal edge of anterior teeth or the
occlusal cusp heights of posterior teeth.
COMPONENTS OF A CAVITY PREPARATION :
Cavity Wall Cavity Preparation Angle Miscellaneous Component
1. Retention groove
External Internal 2. Dovetail
1. Enamel wall 1. Axial 3. Bevel-short
2. Dentin wall 2. Pulpal Long and Full
Line Angles Point Angle Cavosurface Angle
1. Internal
2. External
A) WALLS :
1. Cavity wall
External Internal
Enamel wall Axial
Dentin wall Pulpal
Floor / Seat
One of the enclosing sides of a prepared cavity (it takes the name of the
surface of the tooth adjoining the surface involved towards which it is placed).
EXTERNAL WALL :
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An external wall is a prepared cavity surface that extends to the external
tooth surface and such a wall takes the name of the tooth surface that the wall is
towards.
Enamel Wall : Wall of the prepared cavity that is made up of enamel.
Dentin Wall : The portion of the will of a prepared cavity that is made tip of
dentin.
INTERNAL WALL :
An internal wall is a prepared cavity surface that does not extend to the
external tooth surface.
a) Axial wall : it is an internal wall parallel with the long axis of the tooth.
b) Pulpal wall : It is an internal wall that is perpendicular to the long axis
of the tooth and occlusal to the pulp.
CAVITY PREPARATION ANGLES :
The junction of two or more prepared cavity surfaces is referred to as an
angle which includes line angles and point angles.
a) Line angle : It is the junction of two planar surfaces of different
orientation along a line, which is again classified as internal line angle
and an external line angle.
i) Internal line angle : Is a line angle whose apex points into the
tooth e.g. FP.
ii) External line angle : Is a line angle whose apex points away
from the tooth e.g. ap.
b) Point angle : It is a junction of 3 planal surfaces of different orientation
e.g. mFP (designated by combining the names of the walls forming
angels).
c) Cavo surface angle / Cavo surface margins : The cavo surface angle is
the angle of the tooth structure formed by the junction of a prepared
cavity wall and the external surface of the tooth.
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RETENTION AND RESISTANCE FORM :
1) Undercut : Portion of prepared cavity confined by walls which coverage
towards the surface.
2) Retention groove : Linear channel within a cavity preparation.
3) Dovetail : Widened or fanned out portion of a prepared cavity
established to increase the resistance and retention form.
Miscellaneous Components :
1) Margins : Junction of the wall of the cavity with the surface of the tooth
2) Bevel : Inclination that one surface makes with another when not at right
angle or in cavity preparation a cut that procedure an angle other than
90o
with a cavity wall.
a) Short bevel : Bevel involving not more than external one third of
a cavity wall.
b) Long bevel : Bevel involving more than external 1/3 but not more
than external 2/3 of a cavity wall.
c) Full bevel : Bevel which involves the entire wall
STAGES AND STEPS IN CAVITY PREPARATION :
The stages and steps in cavity preparation are as follows ;
INITIAL CAVITY PREPARATION
STAGE
FINAL CAVITY PREPARATION
STAGE
Step-1 Outline form and initial
depth
Step-5 Removal of any remaining
enamel pit fissure and or
infected dentin and /or old
restorative material if
indicated.
Step-2 Primary Resistance form Step-6 Pulp protection
Step-3 Primary Retention form Step-7 Secondary resistance and
retention form
Step-4 Convenience form Step-8 Procedure for finishing
external walls
Step-9 Final procedure; cleaning
inspecting; varnishing
conditioning
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INITIAL CAVITY PREPARATION STAGE :
Definition :
Initial cavity preparation is the extension and initial design of the
external walls of the preparation at a specified, limited depth so as to provide
access to the cavity or defect, reach sound tooth structure, resist fracture of the
tooth or restorative material form masticatory forces principally directed with
long axis of the tooth and retain the restorative material in the tooth.
STEP 1 : OUTLINE FORM / INITIAL DEPTH :
a) Definition :
The outline forms means placing the cavity margins in the position they
will occupy in the final preparation except for finishing enamel walls and
margins.
Initial depth 0.2 – 0.5 mm below D.E. junction (0.5 when restoring with direct
gold).
0.2 – 0.8 mm into dentin for smooth surface caries.
If there is need for additional deepening of the preparation in the assess
of excavation of any remaining faulty tooth structure faulty old restorative or
infected dentin it is carried out during the final stage of cavity preparations.
b) Principles :
There are 3 general principles on which outline from is established
regardless of the type of cavity being prepared.
1) All friable / or weakened enamel should be removed.
2) All faults should be included
3) All margins should be placed in a position to afford good finishing of the
margins of the restoration i.e. extension of the margins of the preparation
far enough on the tooth surface so that the margins of the preparations will
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be located on finishable, self cleansable area because all the restorations
will be surrounded by a microleakage space between itself and adjacent
tooth structure ranging between 20-120 microns in width which can
accommodate micro organisms and food substance thus predisposing to
recurrent decay. Thus this space should be placed in the areas that are
easily cleansable by natural / artificial means. This principle is called as
“extension for prevention”.
c) Factors :
* These factors will affect the outline form of the proposed cavity preparation
and will dictate the extensions, these are as follows
1. Extent of the carious lesions, defect or faulty old restorations.
• Will affect the outline form because the objective is to
extend preparation to sound tooth structure except in a
pulpal direction.
2. Esthetic considerations
• Will not only affect the choice of restorative material but
also the design of cavity preparation in an effort to
maximize the esthetic result of the restoration.
3. Occlusal relationship
• Determines the outline form by avoiding the placement
of cavity margins (outline) in an area of heavy occlusal
contacts such as centric holding area.
4. Proximal tooth contour
5. Cavosurface margin configurations
• Restorative materials which are more effective when
having beveled margins will require cavity preparation
outline form that must anticipate the final Cavo surface
position and form.
d) Features :
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There are six specific, typical features of establishing outline forms
initial depth. There are :
1) Preserving cuspal strength
2) Preserving marginal ridge strength
3) Minimizing the facio-lingual extension
4) Using enameloplasty
5) Connecting two close (less than 0.5 mm apart) faults or cavity
preparations
6) Restricting the depth of the preparations into dentin to a maximum of
0.2 mm for pit and fissure caries and 0.2 to 0.8 mm for the axial wall of
smooth surface caries.
e) Rules :
=> Rules to follow in establishing the outline form for pit and fissure cavities.
1) Extension of the cavity margin until sound tooth structure is obtained.
There should not be any weakened or unsupported enamel.
2) Avoid terminating the margins on extreme eminence such as cusp
heights or ridge crest.
3) Consider the cusp capping : Rule for cusp capping, if the extension form
a primary groove towards the cusp tip is no more than half the distance
then no cusp capping, if this extension is from 1/2 to 2/3 the distance,
then consider cusp capping, If the extension is more than 2/3 the
distance then cusp capping is mandatory.
4) Use of enameloplasty when pit or groove does not penetrate more than
1/3 the thickness of the enamel. Enameloplasty is a procedure of
reshaping / rounding/saucerization of the enamel surface with suitable
rotary cutting instrument (it does not extend the outline form and
restorative material is not placed in recontoured area thus the thickness
of restorative material at enameloplasty margin is decreased.
5) When pit and fissure involve more than 12 of enamel thickness, extend
the cavity margins to include all of them.
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6) To be as conservative as possible the preparation of an occlusal surface
pit and fissure cavity is first prepared to a depth of 1.5 mm as measured
at the central fissure.
(Restrict the depth of the preparation to a maximum of 0.2 m into dentin
and if gold it should be 0.5 mm).
However if the amount of pit/fissure remaining is greater than 50% of
the pulpal floor the entire floor is deepened to maximum initial depth of
0.2 mm into dentin. Thus the actual depth of the preparation varies form
1.5 mm depending on thickness of enamel and steepness of cusp
inclines.
7) When two pits fissure cavities have less than 0.5 mm of sound tooth
structure between them they should be joined to eliminate a weak
enamel wall between them.
8) Extension of outline form to provide sufficient access for proper cavity
preparation, restoration placement and finishing procedure.
Rules Governing Outline form and initial depth for smooth surface cavities :
Smooth surface cavities are in two different locations.
Proximal surfaces Gingival portion of the facial and Ig surface
For proximal surface cavities (Class II, III, IV) :
1) Extension of cavity margins until sound tooth structure is obtained, all
unsupported to weakened enamel should be removed.
2) Avoid terminating the margins on extreme eminence such as cusp
heights or ridge crest.
3) Extent the margins to allow sufficient access for proper manipulative
procedures.
4) Restriction of axial wall pulpal depth of proximal preparation when it is
in crown 0.5 – 0.6 mm and on root 0.75 – 0.8 mm = (0.2 – 0.8 mm).
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5) Extend the gingival margins of the cavities apically of the contact to
provide a minimum clearance of 0.5 mm between gingival margins and
adjacent tooth and the gingival margins or finish line on the proximal
tooth surface should be 0.5 – 1 mm apical to the crest of healthy free
gingiva with in the gingival crevices, it should not extend to the bottom
of crevice because ;
a) The alkalinity of the crevicular fluid can neutralize acids
produced from plaque activity an d
b) The knife edge relationship of healthy free gingiva to the adjacent
tooth surface will discourage food accumulation on adjacent
restored surface occlusal to the sulcus for considerable period
during after food ingestion.
6) Extension of facial and lingual margins in proximal cavity preparation
into the respective embrasures to provide specified clearance between
the prepared margins adjacent within order to place the margins in self
cleansable area.
When extending the proximal surface incisally in Class III preparation it
is acceptable to position the incisal margins in the area of contact
especially when an esthetic restorative material is used.
Gingival Portion of Facial and Lingual Surface :
1) Outline form is governed by the extend of the lesion, except Pulpally so
extension mesially, lingually, distally and occlusally is limited to that
when sound tooth structure is reached.
2) Depth is no deeper than 0.8 – 1.25 mm Pulpally.
• Lesser axial wall depth (0.8 mm) at Gg wall with out an
enamel portion (i.e. the margin on root.
• The axial wall depth at occlusal wall is 0.5 mm in dentin
and remaining in enamel.
STEP 2 : PRIMARY RESISTANCE FORM :
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DEFINITION :
Primary resistance form may be defined as that shape and placement of
the cavity walls that best enables both the restoration and the tooth to
withstand, without fracture, masticatory forces delivered principally in the long
axis of the tooth.
Principles :
The fundamental principles involved in obtaining primary resistance
form follow :
1) Box shape with relatively flat floors. Flat floor prevents restoration
movement where as rounded pulpal floor is conductive to rocking action
of restoration – producing a wedging force, resulting in shearing of
tooth structure.
2) Restrict the extension of external walls to allow sufficient dentin
support for strong cusp and ridges (resistance against oblique forces and
forces in long axis).
3) Straight rounding / coving of internal line angles reduces stress
concentration in tooth structure (rounding of internal line angles reduces
stress on tooth thus resistance to # of tooth, increased rounding of
external faced angle reduces stress on porcelain and amalgam thus
resistance to fracture of restoration increases).
4) Consider cusp capping for weak cusp according to rule.
5) Placement of enough thickness of restorative material to prevent its
fracture under load. The minimal occlusal thickness for amalgam for
appropriate resistance to fracture is 1.5 mm, cast metal = 1-2 mm and
porcelain = 2 mm.
Factors :
The need to develop resistance form in a cavity preparation is a result of
several factors, which are as follows :
a) Occlusal contact : the greater the occlusal force and contacts, the
greater is the potential for future fracture. (The further posterior
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the tooth, the greater is the effective masticatory forces since the
tooth is closer to the condyle head).
b) Amount of remaining tooth structure also impacts the need and
type of resistance form.
e.g. Very large teeth even though extensively involved with
caries or defects may require less resistance from consideration
because remaining tooth structure is still bulky and strong enough
to resist fracture.
c) Type of restorative material used
Amalgam : 1.5 mm for adequate strength and longevity.
Cast metal : 2 mm
Composites : Dimensional needs of composites are more
dependent on the occlusal wear potential of the restored area. In
posterior teeth thickness requirement is more than the anterior
teeth.
Features :
The design features of cavity preparation that enhances primary
resistance form are as following :
1) Relatively flat floors : If large excavation site of infected dentin is
present incorporate at least 3 seats on sound dentin so that restorative
material will have stable contact with tooth so the occlusal forces
directed parallel to the tooth long axis will not cause rocking of
restoration.
2) Box shape
3) Inclusion of weakened tooth structure
4) Preservation of cusp and marginal ridges
5) Rounded internal line angles
6) Adequate thickness of restorative materials
7) Seats on sound dentin periphery to excavation site
8) Reduction of cusp for capping when indicated.
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STEP 3 : PRIMARY RETENTION FORM :
Definition :
Primary retention form is that shape or form of the prepared cavity that
resists displacement or removal of the restoration from tipping or lifting forces.
Principles :
Sincere tension needs are related to the restorative material used, the
principles of primary retention form may vary depending on the material used.
For Amalgam :
a) Convergence of external cavity walls occlusally(Class I and Class II) :
So once the amalgam is placed in the cavity and hardens, it cannot come
out without some type of fracture occurring.
b) Occlusal dovetail which aids in preventing the tipping of the restoration
by occlusal forces.
c) Adhesive systems for bonding amalgam to tooth structure.
d) In other preparation for amalgam such as Class III and V, the external
wall diverge outward to provide strong enamel margins therefore
retention grooves and covers are prepared in dentin.
For Composite :
Retention by mechanical bond that develops between the material and
the conditioned / prepared tooth structure (enamel is etched by an acid and the
dentin is conditioned for a dentin bonding agents) so bevel enamel margins are
kept to increase the surface area to be etched.
For Cast Metals :
1) Parallel, vertical and longitudinal walls to provide retention of the
casting in the tooth.
2) Small angle of divergence 2-5o
per wall is placed which will enhance
the retention form. (Retention is developed by frictional resistance and
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mechanical locking of the cement into the minute irregularities of both
the casting and the cavity wall to counter act the pull of sticky food).
For Gold Foil :
Retention is from elastic compression developed in the dentin as a result
of condensation of the foil.
MEANS OF RETENTION :
- Frictional retention
- Elastic deformation
- Inverted truncated cone
- Dove tail
Frictional Retention : Depends on 4 factors
a) Surface area of contact between tooth and restoration
More surface area more retention.
b) Opposing walls
More opposing walls more retention
c) Parallelism and non parallelism
Higher degree of parallelism increases retention
d) Proximity
Elastic Deformation of dentin : Changing the position of dentinal walls and
floors microscopically by using condensation energy with in dentin limit can
add more gripping action by the tooth on the restorative material. This occurs
when dentin regains its original position while the restorative material remains
rigid, thereby completely obliterating any remaining space in the cavity
preparation.
STEP 4 : CONVENIENCE FORM :
DEFINITION :
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Is that shape or form of the cavity that provides for adequate
observation, accessibility and ease of operation in preparing and restoring the
cavity.
Modifications in tooth preparation for convenience form :
Modification includes flaring some walls more than otherwise necessary
for resistance and retention form such as divergences of vertical walls of cavity
preparation for Class II cast restoration.
Placement of convenience points for starting the foil condensation.
Extending proximal preparations beyond proximal contacts.
Separation : Done by wedging of teeth makes interproximal
instrumentation convenient.
STEP 5 : FINAL CAVITY PREPARATION STAGE :
Removal of any remaining enamel pit or fissure and or infected dentin
or old restorative materials if indicated.
DEFINITION :
It is the elimination of any infected carious tooth structure or faulty
restorative material left in the tooth after initial cavity preparation.
Any old restorative material should be removed if any of the following
conditions are present.
1. The old material may affect negatively the esthetic result of the new
restoration.
2. The old material may compromise the amount of anticipated needed
retention.
3. There is radiographic evidence of caries under the old restorative
material.
4. The tooth was symptomatic preoperatively
5. The periphery of the remaining old restorative material is not intake.
If none of these conditions are present the operator may elect to leave
the remaining old restorative material to serve as a liner or base rather than risk
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unnecessary excavation nearer to the pulp which may result in exposure or
pulpal irritation.
FOR DENTIN :
- The exception to the removal of infected carious dentin is when it has
been decided to perform an indirect pulp capping.
- Its accepted and appropriate practice to allow affected dentin to remain
in a prepared tooth.
- It is not acceptable to leave carious dentin at D.E. junction.
Technique :
When a pulpal or axial wall has been established at the proper initial
cavity preparation position and a small amount of infected carious material
remains, only this material should be removed, leaving a rounded, concave area
in the wall and floor, thus placing the pulpal floor at more than one level. The
first level will be ideal depth of 1.5 mm and other will be at caries cone level.
This shallow (initial depth i.e. 1 mm) level will create flat pulpal floor at
definite angle to surrounding wall thus resist the occlusal forces and laterally
locking the restoration without impinging on pulp this placement of second seat
at caries cone level is called as ledge it can be (1) Circumferential, (2)
Interrupted or (3) Opposing.
CARIES CONTROL TECHNIQUE :
When patient is having numerous teeth with extensive caries in one
sitting or appointment, infected dentin is removed from several teeth and
temporary restorations are placed and then individual teeth are restored as
definitively planned. This procedure stops the progress of caries and is often
referred to as the caries control technique.
If the decay’s soft removal should be done with spoon excavators by
flaking up the caries around the periphery of the infected mass and peeling it
off in layers.
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If the decayed dentin is hard, the excavator may not be sufficient to
remove the diseased tissue, so a large round carbide bur revolving slowly
should be moved in burnishing strokes from the peripheries of cavity
preparation to the center. These strokes should be done with minimal pulpal or
axial pressure and with a water coolant in order to minimize thermal irritation
to the near by pulp tissue.
Removal of remaining old restorative material; when indicated is
accomplished with use of a round carbide bur, at slow speed with air or air
water coolant. The water spray along with high volume evacuation is used
when removing old amalgam material to reduce the amount of mercury vapor.
STEP 6 :
FROM MECHANICAL
PULP PROTECTION THERMAL INSULTS such as
CHEMICAL
1) Some ingredients of various materials.
2) Thermal changes conducted through restorative material
3) Forces transmitted through materials to the dentin
4) Galvanic shock
5) Ingress of noxious products and bacteria through microleakage.
For pulp protection traditional liners or bases are used either to protect
the pulp or to aid pulpal recovery or both.
 When the thickness of remaining dentin is less than 2 mm, heat
generated by injudicious cutting can result in a pulpal burn lesion 
abscess formation  death of pulp.
Thus a water or air water spray coolant must be used with the high speed
rotary instrument.
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 If the remaining dentin thickness is 1.5 mm or more and the cutting was
done atraumatically using high speed with water or air water spray, the
pulp is not irritated enough to form replacement odontoblasts and
therefore no reparative dentin is formed to seal the pulpal side of dead
tracts. Thus it is more important to place a liner or bases to protect the
pulp.
Liners :
Are those volatile or aqueous suspensions or dispersions of zinc oxide or
calcium hydroxide that can be applied to a cavity surface in a relatively thin
film and are used to effect a particular pulpal response.
Liners Provides :
1. A barrier which protects the dentin from noxious agents from either the
restorative material or oral fluids.
2. Electric insulation
3. Thermal protection
Bases :
Bases are considered to be those cements commonly used in thicker
dimensions beneath permanent restoration to provide for mechanical, chemical
and thermal protection of the pulp.
Example are ;
1. Zinc phosphate
2. Zinc oxide eugenol
3. Calcium hydroxide
4. Polycarboxylate
5. Glass ionomer
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If the removal of infected dentin does not extend deeper than 1 mm from
initially prepared pulpal or axial wall. NO LINER IS INDICATED. If
excavation extends into or very close to the pulpal tissue, a calcium hydroxide
liner is selected in order to stimulate reparative dentin, if the excavation depth
is between above two eg. Zn oxide eugenol liner is selected (except for
composite restoration where it may impide the polymerization process) to
provide a palliative sedative pulpal response.
 As a general rule it is desirable to have atleast a 0.5 – 0.75 thickness of
base dimension of bulk between the pulp and a metallic restorative
material. This bulk may include remaining dentin, liner, or bases.
 The ability of calcium hydroxide to stimulate the formation of reparative
dentin when its in contact with pulpal tissue makes it the material of
choice for application to very deep excavation and known pulpal
exposures.
 Liners and bases in exposure areas should be applied with out pressure,
Atleast a 1 mm thickness of calcium hydroxide is placed over near or an
actual exposure which is than over laid with a base.
 In deep excavation where no exposure of suspension of exposure exist,
Zn oxide eugenol is used for its mildly anesthetic effect on the pulp.
 For composite restorations which are thermal insulators and passively
inserted, liner of calcium hydroxide is indicated only when there is a
pulpal exposure of the excavation is judged to be within 0.5 mm of the
pulp.
 Cast restorations : In cavity preparation for casting, deeply excavated
areas in preparation must be covered with suitable retained liners or
bases materials that will withstand the forces. Zn ph. Glass ionomer and
polycarboxylate cements serves this purpose.
Cavity Varnishes :
It is a solution liners which seals most of the dentinal tubules and is
placed on all cavity preparation walls for amalgam and on dentinal walls of
24

cavity preparation for cast gold but not used for composites, (it prevents
penetration of materials into the dentin and helps to prevent microleakage and
reduces post operative sensitivity by reducing the infiltration of fluids and
salivary components at the margins of newly placed restoration.
For Amalgam : Two coats should be applied to the prepared surface in shallow
excavation is the only material of choice.
For cast gold : Two coats on dentin surface reduces pulpal irritation from luting
cements.
For Composite : Should not be used because solvent in varnish may react with
or soften the resin component in the composite and thus affecting
polymerization or free monomer of resin may dissolve varnish film and
rendering it ineffective.
STEP 7 : SECONDARY RESISTANCE AND RETENTION FORMS :
Secondary resistance and retention forms are of 2 types :
a. Mechanical features
b. Cavity wall conditioning features
1. Mechanical features includes :
• Retention / locks, grooves, and coves
• Longitudinally oriented provides retention to proximal
portions of cavity preparations. Locks are for amalgam,
they increases retention of the proximal portion against
movement proximally due to creep and are believed to
increase the resistance form of the restoration against
fracture at the junction of the proximal and occlusal
portions.
• Grooves of cast metal restorations.
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• Horizontally oriented grooves – for Class III and Class V
amalgam.
• Root surface cavity preparation for composites.
• These are placed undercuts for the incisal retention of
Class III amalgams and for Class V and occasionally for
facilitating the start of insertion of certain gold foil
restorations.
• Retention cones – Undercuts placed for incisal retention
of Class III amalgams, occlusal portion of some
amalgam restorations, some Class V amalgams.
Groove Extensions :
Obtained by extending the cavity preparation for molars on to the facial
and lingual surface to include the facial and lingual grooves mainly used for
cast metal restorations (results in parallel wall retention) also enhances
resistance form due to envelopment.
Skirts :
Mainly used in cast gold restorations. In which extension of preparation
is done around all the transitional longitudinal angles of tooth, adds retention
form by opposed longitudinal walls and resistance form by enveloping the
tooth thus resisting fracture of the remaining tooth from occlusal forces.
Beveled Enamel Margins :
Used for cast gold or composites. For cast metal retention form is
improved when there are opposing bevels and provides better junctional
relationship between metal and the tooth.
In case of composite restoration, it increase both the surface area of
etchable enamel and maximize the effectiveness of the bond by etching more
enamel rods.
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Pins, Slots, Steps and Amalgam Pins :
Used to increase resistance and retention form for amalgam.
2. Cavity Wall conditioning features
Enamel Wall Conditioning Dentin Wall Conditioning
Conditioned for bonded restorations
such as porcelain, composites,
amalgam or give (condition consist
of etching the enamel by an
appropriate acids resulting in
microscopic undercuts in which
bonding is mechanical bond.
Conditioned for bonded restoration
such as porcelain, composites,
amalgam or GIC (condition consist
of etching the enamel by an
appropriate acids resulting in
microscopic undercuts in which
bonding material is mechanically
bonds).
STEP 8 : PROCEEDINGS FOR FINISHING THE EXTERNAL WALLS
OF CAVITY PREPARATION :
DEFINITION :
It is the further development when indicated of a specific cavo surface
design and degree of smoothness that produces the maximum effectiveness of
the restorative material being used.
Objectives :
1. To create he best marginal seal possible between the restorative
material and the tooth structure.
2. To afford a smooth marginal junction
3. To provide maximum strength of both the tooth and the
restoration at and near the margin.
Factors :
1. Direction of enamel rods :
Enamel rods radiate from the dentin enamel junction to the external
surface of the enamel and are perpendicular to the tooth surface, all rods
extends full length from the dentin to the enamel surface. The rods converge
towards the center of development grooves i.e. from the dentino enamel
27

junction towards concave enamel surface and diverge towards the height of
cusp and ridges i.e. diverge outwardly toward convex surface. In gingival third
rods incline slightly apically.
Finishing of enamel wall should be such that the cavity should have
strongest enamel margin (i.e. margin which is composed of full length of
enamel rods that are supported on the cavity side by shorter enamel rods all of
which extend to sound dentin) thus increasing the strength of enamel margin.
2. Support enamel rods both at the Dent-E junction and laterally on cavity side.
3. Type of restorative material used
4. Location of margin
5. Degree of smoothness desired
Features :
There are two primary features to the finishing of the external walls.
1. Design of cavo surface angle.
2. Degree of smoothness of the walls.
1. Design of Cavosurface Angle :
It depends on type of restorative material used.
For amalgam : Because of low edge strength or friability of amalgam
cavosurface of angle of 90o
produces maximal strength for both the amalgams
tooth and prevents fracture.
For cast restorations and composites : Beveling the external walls used for intra
coronal cast gold and composite restoration.
Beveling can serve 4 useful purposes in the cavity preparation for
casting.
1. Produces stronger enamel margins.
2. Permit marginal seal in slightly undersized casting
3. Provides marginal metal that is more easily burnished and adapted.
28

4. Assists in adaptation of gingival margins of cating that fail to seat by a
very slight amount.
For casting, bevel should produce a cavosurface angle that will result in 30-40o
marginal metal.
Gingival Margin :
For amalgam in Class II restoration 15-20o
bevel on the enamel portion
of the wall in order to remove unsupported enamel rods (because of gingival
orientation of enamel rods).
For casting, 30o
will result in sliding, lap fit that improves adaptation of
metal to this margin.
Degree of Smoothness :
It is dictated primarily by the restorative material being used.
Inlay or onlay preparation requires a smooth surface to permit
undistorted impressions and close adaptation of the casting to the enamel
surface.
With gold foil, amalgam and composite very smooth preparation wall is
not as desirable as cast gold.
STEP 9 : FINAL PROCEDURE CLEANING, INSPECTING,
VARNISHING, CONDITIONING :
DEFINITION :
Cleaning or debridement is the act of freeing the preparation walls and
margins from the objects that may interfere with the proper adaptability and
behaviour of the restorative material.
There are 3 main objectives for debriding the preparations.
a) Freeing of all preparation walls, floors and margins from enamel
and dentin chips resulting form excavation and grinding.
29

b) Drying the preparation walls, floor and margins from any
moisture, saliva, blood, exudates.
c) Sterilization of preparation walls and floors.
Methods :
1. Water, air or combination of air water jets, use of air water syringe or
the water and air accompanying any rotary cutting with a high speed
handpiece will be efficient in removing gross debris.
2. Dry cotton pellet (best way no chance of desiccation).
3. Cavity cleansers – Solution of low concentration of
Citric acid + ascorbic and acetic acid (1-10%) followed by long period
of water jet only used in shallow cavities (can irritate P-D organ).
4. Scarping of walls, floors and margins with sharp instruments.
Whichever debridement technique used, microscopic layer of dentinal
smear will be always present on cut dentin and can be eliminated with a
10o
EDTA.
ADDITIONAL CONCEPTS IN CAVITY PREPARATIONS FOR
AMALGAM RESTORATION :
a. Box Only Cavity Preparation :
 Given for those posterior teeth in which proximal surface requires
restoration but occlusal surface does not.
 Proximal box is prepared without occlusal step.
b. Tunnel Cavity Preparations :
 Preparation joins an occlusal lesion with a proximal lesion by means of
prepared tunnel under the involved marginal ridge.
 Marginal ridge remains intact.
c. Bonded amalgam
 Use of various bonding agents which bonds amalgam to tooth structure.
 More weakened, remaining tooth structure is retained.
For Composite Restorations :
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1. Box only type of cavity preparation
2. Tunnel preparations
3. Sandwich technique
 Use of glass ionomer liner material
Advantages are :
1. Glass ionomer bonds both to tooth structure and composite and thus
increases in retention.
2. Fluoride content in the GIC reduces caries (recurrent).
3. Provides a better seal when seal when used at non enamel margins.
CONCLUSION :
A cavity preparation is determined by many factors and each time a
tooth is to be restored each of these factors must be assessed. If the principles
of cavity preparation are adhere to, the success of restoration is great increased.
The factor that should be considered before initiating a cavity
preparation are as follows :
1. Extent of caries
2. Occlusion
3. Pulpal involvement
4. Esthetics
5. Patients age
6. Patients home care
7. Gingival status
8. Anesthesia
9. Bone support
10.Patients desires
11.Operation skill
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12.Pulp protection
The improved ability to bond restoration with tooth structure will likely
to alter significantly the entire cavity preparation procedure and thus the
emphasis will shift away form cavity preparation to knowledge of restorative
materials and dental anatomy.
32

Fundamental of cavity preparation

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Fundamental of cavity preparation