Fundamentals of Cavity preparation

FUNDAMENTALS
OF
CAVITY
PREPARATION
Dr Shazeena Qaiser

CONTENTS
 INTRODUCTION
 DEFINITION
 NEED FOR RESTORATIONS
 OBJECTIVES OF CAVITY PREPARATION
 HISTORICAL DEVELOPMENT
 FUNDAMENTALS OF CAVITY PREPARATION
 FACTORS AFFECTING CAVITY PREPARATION
 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
o Infected Dentin /Old Restorative Material
o Pulp Protection
o Secondary Resistance And Retention Forms
o Procedures For Finishing
External Walls
o Cleaning, Inspecting, Sealing
 ADDITIONAL CONCEPTS IN TOOTH PREPARATION
o Amalgam Restorations
o Complete Restorations
 CONCLUSION
 REFERENCES

Success is neither magical nor mysterious…
Success is the natural consequence of
consistently applying the basic fundamentals.
JIM ROHN
“
”

• In the past, most restorative treatment was due to caries
(decay)
• ‘Cavity’ was used to describe a carious lesion in a tooth that
had progressed to the point that part of the tooth structure
had been destroyed.
• Tooth was cavitated ; referred to as a cavity.
• Affected tooth was repaired; cutting or preparation of
remaining tooth was referred to as a cavity preparation.
• Now many indications for treatment for teeth are not due to
caries.
• Preparation of the tooth is no longer referred to as cavity
preparation but as tooth preparation.
• Term cavity used as a historical reference.
Roberson T. Sturdevant's Art And Science Of Operative Dentistry ( Fifth Edition). St. Louis : Mosby Elsevier; 2006.

“
Tooth preparation is the mechanical
alteration of a defective, injured, or
diseased tooth to receive a restorative
material that re-establishes a
healthy state for the tooth including
esthetic corrections, where indicated.
DEFINITION
~Sturdevant
“

Need For The Restoration
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 tooth preparation
1. Removes all defects and provides necessary protection to the pulp.
2. Extension of the margins of restoration as conservatively as possible
3. Cavity is formed such that under forces of mastication, the tooth or
restoration, or both will not fracture and restoration will not be displaced
4. Allows for aesthetic and functional placement of a restorative material

EVOLUTION OF
CONTEMPORARY CAVITY
PREPARATION

WEBB
1883
• First published work
• Mentioned in his textbook:
• “Every cavity must be so prepared that no
decalcified tissue remains, except where
there be a little discoloured dentine near
pulp, and that should be left for its
protection”.
• “Prevention of extension of decay” :
supported the extension of preparation into
the contact-free “self-cleansing” areas to avoid
food accumulation especially on proximal
surface
Webb MH (1883) Notes on Operative Dentistry. S.S. White Manufacturing Co., Philadelphia. 72-88.

GV Black
1891
“EXTENSION
FOR
PREVENTION”
“In no case should any decayed and softened
material be left. It is better to expose the pulp of
the tooth than leave it covered only with softened
dentine”
 Removal of all infected, affected dentine.
 Healthy tooth structure can be removed for
better access and visibility
 Extension of preparation in adjacent pits and
fissures for prevention
 Should have definite mechanical retention in the
restoration
+ Self-cleansing area –prevents recurrence of decay
in tooth surface adjoining restoration
Black GV (1891) The managment of enamel margins. Dental Cosmos 33 :85-100.

Fundamentals of Cavity preparation

Slagle
1904
“EXTENSION FOR
RETENTION”
• Focused more on “anchorage” or retention of
restorative material inside prepared cavities after
careful evaluation of occlusal forces.
• Introduced some secondary features to cavity
preparation for increasing the retention of
restorative materials (e.g. grooves, locks, coves).
Slagle CE (1904) The Fundamental Principles of Extension in Approximal Cavities in Bicuspids and Molars. Dental Cosmos 46: 443-445.

1928
PRIME
CONCEPT
 Adapt the filling material to the tooth.
 Achieve a proximal triangular form.
 Achieve 'independent surface retention
 Extension for prevention - not necessary
Prime, J.M. A plea for conservatism in operative procedures. JADA 15(1}:1234-1246,1928

Bronner
1931
• Proximal outline forms should converge
• Gingival wall should be inclined axially to
• prevent dislodgment in a proximal direction.
• With the proximal box thus becoming a “
self-locking device- occlusal dovetail obviated.
• Discussed the management of a weakened
cusp by a procedure called “onfilling”
”Shoeing a cusp ” with amalgam.
Bronner, F.J. Engineering principles applied to class II cavities. J Dent Res 10:115-119,1930.

Markley
1951
• Narrow occlusal preparation with slightly
convergent walls following direction of
enamel rods.
• Proximal preparation- narrow across the
marginal ridge
• Recommended proximal retentive grooves so
that each portion of restoration could be self-
retentive .
Markley, M.R. Restorations of silver amalgam.JADA 43(2):133-146,1951

1956
1959
VALE
EXPERIMENTS
• Two important features recognised in
conservative preparation.
• Concluded:
 reduction of occlusal width from a third to
fourth the intercuspal distance- greater
strength in the prepared tooth.
 Rounding of internal angle -better adaptation
of amalgam.
Vale, W.A. Cavity preparation. Irish Dent Rev 2:33-41,1956.
Vale, W.A. Cavity preparation and further thoughts on high speed. Br Dent J 107:333-340,1959.

1958
Mahler & Peyton
• Slightly round the axiopulpal line angle to
increase amalgam bulk in that area; decrease
the internal stress.
• Decrease width of isthmus,depth of isthmus,
depth of preparation to decrease the internal
stress within the tooth.- increases the resistance
of tooth structure to deformation and failure
• Rounded pulpal floor more suitable than a
plane.
• Occlusal convergence should be minimal so
that the restoration may receive the maximum
support of the cavity walls.
Mahler, D.B. An analysis o f stresses in a dental amalgam restoration. J Dent Res 37(3):516-525,1958.

1964
Gilmore
For the modern preparation:
isthmus width:
1 mm or less for first premolars
1.5 mm or less for molars
depth of 0.5 mm into dentin .
Mahler, D.B., and Peyton, F.A. Photoelasticity as a research technique for analyzing stresses in dental structures. J
Dent Res 34(6):831-838,1955.

1975
Galan
Deformation in proximal portion of the
Class II restoration could be decreased by
locating retention grooves above the axio-
pulpal line angle.”
Galan, J.; Gilmore, H.W.; and Lund, M.R. Retention for the proximal portion of the Class n amalgam restoration. J
Ind Dent Assoc 54(6):16-19,1975

1998
SUMMILT
AND
OSBORNE CONCEPT
• Do not extend for prevention in class I
preparations - only prepare in areas of
diagnosed caries.
• Keep preparation as narrow as caries
allows.
• Do not extend class 2 preparations into
occlusal grooves, if occlusal surface is not
involved by caries at all
• If occlusal extension is less than 1.2 mm
wide, augment retention of proximal box
with retention locks on facial/lingual walls.
Osborne JW, Summitt JB. Extension for prevention: is it relevant today? Am J Dent. 1998 Aug;11(4):189-96.

20th
Century
“PREVENTION OF
EXTENSION”
• “Minimally Invasive Dentistry”
• Aim- achieve as much conservation of dental tissue as
possible.
• Includes :
 early detection of dental caries
 assessment and management of caries-risk,
remineralisation of early caries lesions,
 only restoring cavitated lesions
 restriction of excavation to the caries-infected
areas
 using adhesive-based technologies
• Retentive features changed from macromechanical to
micro-mechanical (resin adhesives) and chemical (e.g.
resin-modified glass ionomer adhesives) retention.
Ericson D (2007) The concept of minimally invasive dentistry. Dent Update 34(1): 9-10.
Frencken JE, Peters MC, Manton DJ, Leal SC, Gordan VV, et al. (2012) Minimal intervention dentistry for managing dental caries - a review: report of a FDI task group. Int Dent J 62(5): 223-243

CURRENT
PERSPECTIVES
 Prevention of extension or as Sigurjons
states, constriction with conviction -
operative phrases in modern cavity
preparation
 Increased knowledge of:
 caries progression and prevention
 remineralisation of tooth structure
 improved amalgam alloys
 systemic and topical fluoridation
 precision instrumentation
 advanced diagnostic aids
 better oral hygiene

• Basic principles governing the design of cavities and steps in their preparation- 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.

• Concepts professed by Bronner, Markley, J Sturdevant, Sockwell, and C Sturdevant.
• Improvements in restorative materials, instruments, and techniques.
• Increased knowledge and application of preventive measures for caries.

FUNDAMENTALS OF TOOTH PREPARATION
1. No friable tooth structure can be left.
2. Fault, defect, or caries is removed.
3. Remaining tooth structure is left as strong as possible.
4. Underlying pulpal tissue is protected.
5. Restorative material is retained in a strong, esthetic (in some
cases), and functional manner.

TYPE
Conventional
Preparation
Modified
Preparation
 Reduced degree of precision
 May require only removal of defect (caries,
fracture, or defective restorative material)
and friable tooth structure without specific
uniform depths, wall designs, retentive
features or marginal forms.
 Adhesive restorations, primarily composites,
glass ionomers
 Precise procedures resulting in uniform
depths, particular wall forms, and specific
marginal configurations.
 Require specific wall forms, depths, and
marginal forms
 Amalgam, cast metal, and ceramic
restorations preparations

GENERAL PATIENT TOOTH
RESTORATIVE
MATERIAL
Factors Affecting Cavity Preparation

GENERAL
• DIAGNOSIS
• Assessment of pulpal, periodontal status of tooth
• Assessment of occlusal relationships.
• Deciduous/ permanent tooth.
• Type, location of tooth.
• Type of anomaly
• Knowledge of Dental Anatomy
• Direction of enamel rods
• Thickness of enamel,dentin
• Size and position of pulp
• Relationship of tooth to supporting tissues
PATIENT
• Age
• Concern for aesthetics
• Economic status
• Xerostomia
• Diet
• Caries index
• General health.
• Parafunctional habits
• Supplementary intake of fluorides

TOOTH
• To conserve the tooth structure.
• To repair the damage from dental
caries and prove the vitality of the
tooth
• Restorations should be as small as
possible
• Lesser the tooth structure removed,
lesser the chance for pulpal damage
RESTORATIVE MATERIAL
• Type
• Physical properties of restoration
• Moisture control
• Extensiveness of problem

Abbreviated Descriptions of Tooth Preparations
an occlusal tooth preparation = O
a preparation involving - mesial and occlusal surfaces = MO
a preparation involving the mesial, occlusal, and distal surfaces = MOD
Description of a tooth preparation is abbreviated by using the first
letter, capitalized, of each tooth surface involved

COMPONENTS OF A CAVITY PREPARATION
COMPONENTS
CAVITY WALL CAVITY
PREPARATION
ANGLE
Additional

CAVITY WALL
EXTERNALINTERNAL FLOOR ENAMEL
WALL
DENTIN
WALL
AXIAL
PULPAL
FACIAL
LINGUAL

INTERNAL WALL
An internal wall is a prepared (cut) surface that does
not extend to the external tooth surface
An axial wall is an internal wall parallel
with the long axis of the tooth.
A pulpal wall is an internal wall that is
perpendicular to the long axis of the
tooth and occlusal of the pulp

EXTERNAL WALL
An external wall is a prepared (cut) surface
that extends to the external tooth surface

FLOOR (OR SEAT)
A floor is a prepared (cut) wall that is reasonably flat
and perpendicular to the occlusal forces that are
directed occlusogingivally (generally parallel to the long
axis of the tooth).

ENAMEL/DENTIN WALL
The enamel wall is that portion of a prepared external
wall consisting of enamel
The dentinal wall is that portion of a prepared external wall consisting of
dentin, in which mechanical retention features may be located

CAVITY PREPARATION
ANGLE
A line angle is the junction of two planal
surfaces of different orientation along a line
A point angle is the junction of three planal
surfaces of different orientation

INTERNAL LINE ANGLE EXTERNAL LINE ANGLE

CAVOSURFACE ANGLE
The cavosurface angle is the angle of tooth
structure formed by the junction of a
prepared (cut) wall and the external surface
of the tooth

TOOTH PREPARATION CLASSIFICATION

• Placing the preparation margins in the position they will occupy in
the final tooth preparation except for finishing enamel walls and
margins
• Maintaining the initial depth of 0.2 to 0.8 mm into the dentin.
• Outline form defines the external boundaries of the preparations.
1. OUTLINE FORM AND INITIAL DEPTH

For extension for prevention:
Advantages
• Prevents recurrence of decay in the tooth surface adjoining
restoration
• Results in self-cleaning embrasure areas
• Margins of the restoration are placed on line angles of the tooth
• Occlusal surface is extended through pits and fissures
• Proximal line angles extended buccally and lingually through embrasures and
cervically below the gingival margin

Principles Features for Establishing A Proper Outline form
• 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.
• 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

Outline form for Smooth Surface Lesions—Outline form
of Proximal Caries (Class II, III and IV lesions)
• Extend the preparation margins until sound tooth structure is reached
• Restrict the depth of axial wall 0.2 to 0.8 mm into dentin
• Axial wall should be parallel to external surface of the tooth
• In class II tooth preparation, place gingival seat apical to the contact but occlusal to
gingival margin and have the clearance of 0.5 mm from the adjacent tooth

Rules for Class V Cavities
• Outline form is limited by extent of the lesion.
• Extensions are made mesially, distally, occlusally and gingivally till sound tooth structure is reached.
• Axial depth is limited to 0.8–1.25 mm pulpally

Primary resistance form is that shape and placement of preparation
walls to best enable both the tooth and restoration to withstand,
without fracture, the stresses of masticatory forces delivered
principally along the long axis of the tooth.
2. Primary resistance form

Features of Resistance Form
• Box-shaped preparation with flat pulpal and gingival floor
• Adequate thickness of restorative material
• In case of class IV preparations, check the faciolingual width of anterior teeth, to establish
the resistance form.
• Restrict the extension of external walls
• Inclusion of weakened tooth structure
• Rounding of internal line angle
• Consideration to cusp capping depending upon the amount of remaining tooth
structure.

3. 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.

Features
Amalgam
 Providing occlusal convergence (about 2°–5°) of dentinal
walls towards the tooth surface
 Giving slight undercut in dentin near pulpal wall
 Conserving the marginal ridges
 Providing occlusal dovetail

Features
CAST METALS
• Close parallelism of the opposing walls with slight
occlusal divergence of 2°–5°
• 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

Features
COMPOSITES:
– Micromechanical bonding between the etched and
primed prepared tooth structure and the composite resin
– Providing enamel bevels.
DIRECT FILLING GOLD:
Elastic compression of dentin and starting point in dentin
provide retention in direct gold fillings by proper
condensation.

4. Convenience Form
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
• Sufficient extension of distal, mesial, facial or lingual walls to gain adequate
access to the deeper portion of the preparation.
• Cavosurface margin of the preparation should be related to the selected
restorative material
for the purpose of convenience and marginal adaptation.
• Class II preparations:
 Access is made through occlusal surface for convenience form.
 Proximal clearance provided from adjoining tooth
 Tunnel preparation: proximal caries in posterior teeth is approached
through a tunnel initiating from occlusal surface and ending on carious
lesion on proximal surface without cutting marginal ridge.
 Cast gold restorations: occlusal divergence

5. Removal of Any Remaining Enamel Pit or Fissure,
Infected Dentin and/or Old Restorative Material, if
Indicated
• If a small amount of carious lesion remains, only this lesion
should be removed, leaving concave, rounded area in the wall.
• Use low speed handpiece with the round bur or spoon
excavator with light force and a wiping motion.
• Start removal of caries from the lateral borders of the lesion.
• Remove only infected dentin, not the affected dentin

6. Pulp Protection
Pulp protection is achieved using liners, varnishes and bases depending
upon:
• The amount of remaining dentin thickness
• Type of the restorative material used
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.

7. Secondary Resistance and Retention Forms

8. Procedures for Finishing the External Walls of
Tooth Preparation
Finishing of a tooth preparation walls is further development of a
specific cavosurface design and degree of smoothness which
produces maximum effectiveness of the restorative material being
used.
• Better marginal seal between restoration and tooth structure
• 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.

9. Final Procedures: Cleaning, Inspecting and
Sealing
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 restorative materials
Degree of smoothness of walls
Location of the margins

NEWER ADVANCES
Minimally invasive cavity preparations:
1. Tunnel preparation
2. Box only/ slot preparation
Minimally invasive methods of cavity preparations
1. Fissurotomy
2. Use of Polymer burs
3. Air abrasion
4. LASERS

CONCLUSION
 Tooth 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 tooth preparation are followed, the success of any restoration is greatly
increased.
 The increasing bond strengths of enamel and dentin bonding are likely to result in significant
emphasis on adhesive restorations. Likewise, the improved ability to bond to tooth structure is
likely to continue to alter the entire tooth preparation procedure.
 When materials can be bonded effectively to a tooth while restoring the inherent strength of
the tooth, the need for refined tooth preparations is reduced or eliminated.
 Emphasis shifts away from traditional tooth preparation to knowledge of restorative
materials and dental anatomy.

REFERENCES
1. Roberson T. Sturdevant's Art And Science Of Operative Dentistry ( Fifth Edition). St. Louis : Mosby Elsevier; 2006.
2. Rodda, J.C. Modern class II amalgam cavity preparations. New Zealand Dent J 68:132-138,1972. 2.
Markley, M.R. Saving teeth for lifetime service. A presentation to the Academy of General
Dentistry, July 20,1981.
3. Welk, D.A., and Laswell, H.R. Rationale for design of cavity preparations. J Am Acad Gold Foil Oper
13(2):75-85, 1970.
4. SigurJons, H. Extension for prevention: current status. Oper Dent 8(2):57-62,1983.
5. Prime, J.M. A plea for conservatism in operative procedures. JADA 15(1}:1234-1246,1928.
6. Bronner, F.J. Engineering principles applied to class II cavities. J Dent Res 10:115-119,1930.
7. Bronner, F.J. Mechanical, physiological and pathological aspects of operative procedures. Dent
Cosmos 73:577-584,1931.
8. Romnes, A.F. Clinical aspects of amalgam restoration. JADA 28(l):54-63,1941.
9. Ingraham, R. Application of sound biomechanical principles in the design of inlay, amalgam, and
gold foil restorations. JADA 40(4J:402-413,1950.
10. Markley, M.R. Restorations of silver amalgam. JADA 43(2):133-146,1951.
11. Vale, W.A. Cavity preparation. Irish Dent Rev 2:33-41,1956.
12. Vale, W.A. Cavity preparation and further thoughts on high speed. Br Dent J 107:333-340,1959.

REFERENCES13. Nadal, R.; Phillips, R.W.; and Swartz, M.L. Clinical investigation on the relation of mercury to the amalgam
restoration. JADA 63(4}:488-496,1961.
14. Nadal, R. Amalgam restorations: cavity preparation, condensing and finishing. JADA 65(l):66-77, 1962.
15. Mahler, D.B., and Peyton, F.A. Photoelasticity as a research technique for analyzing stresses in dental
structures. J Dent Res 34(6):831-838,1955.
16. Mahler, D.B. An analysis o f stresses in a dental amalgam restoration. J Dent Res 37(3):516-525,1958.
17. G ra n a th , L.E. P h o to e la s tic s tu d ie s on occlusal-proximal sections of class II restorations Odontol
Revy 15:169-185,1964.
18. Granath, L.E. Further photoelastic studies on the relations between the cavity and the occlusal portion of
class II restorations. Odontol Revy 15:290-298, 1964.
19. Granath, L.E., and Edlund, J. The role of the pulpoaxial line angle in the origin of isthmus fracture. Odontol
Revy 19:317-334,1968.
20. Gilmore, H.W. New concepts for the amalgam restoration. Practical Dental Monographs. Chicago, Year Book
Medical Publishers, 1964, pp 5-31.
21. Terkla, L.G., and Mahler, D.B. Clinical evaluation of interproximal retentive grooves in class II amalgam cavity
design. J Prosthet Dent 17:596-602, 1967.
22. Rodda, J.C. Modem class n amalgam cavity preparations. New Zealand Dent J 68:132-138,1972.
23. Galan, J.; Phillips, R.W.; and Swartz, M.L. Plastic deformation of the amalgam restoration as related to cavity
design and alloy system. JADA 87(6):1395- 1400,1973.
24. Galan, J.; Gilmore, H.W.; and Lund, M.R. Retention for the proximal portion of the Class n amalgam
restoration. J Ind Dent Assoc 54(6):16-19,1975.
25. Crockett, W.D., and others. The influence of proximal retention grooves on the retention and resistance of
class II preparations for amalgams. JADA 91(5):1053-1056,1975.
26. Almquist, T.C.; Cowan, R.D.; and Lambert, R.L. Conservative amalgam restorations. J Prosthet Dent 29:524-
528,1973

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