Dr. lama khaled El Banna Faculty of Oral and Dental Medicine Al – Azhar University operative dentistry

2. College of DentistryCollege of Dentistry
Operative Dentistry IOperative Dentistry I
Fundamental of Cavity PreparationFundamental of Cavity Preparation
-2-2--
Dr. Hazem El AjramiDr. Hazem El Ajrami

3.  Other factors affecting the outline form ofOther factors affecting the outline form of
occlusalocclusal cavity preparations:cavity preparations:
A.A. Occlusal contacts:Occlusal contacts: Cavity margins must beCavity margins must be
placed atplaced at contact-freecontact-free areas of minimumareas of minimum
stress. If possible, the marginsstress. If possible, the margins should notshould not bebe
placed in centric holding areas. The marginsplaced in centric holding areas. The margins
must be defect-free, smooth, refined, runmust be defect-free, smooth, refined, run
symmetrically through anatomical defectssymmetrically through anatomical defects
and around cusps and ridges, and theirand around cusps and ridges, and their
junctions must be rounded.junctions must be rounded.

5. B.B. Occlusal table anatomy:Occlusal table anatomy: The occlusal tableThe occlusal table
of posterior teeth differs according toof posterior teeth differs according to
whether these teeth are in upper or lowerwhether these teeth are in upper or lower
jaw, and from one tooth to another in thejaw, and from one tooth to another in the
same jaw. Such difference affects the finalsame jaw. Such difference affects the final
shape of the obtained cavity preparation.shape of the obtained cavity preparation.
Unusual anatomy, mal-alignmentUnusual anatomy, mal-alignment andand steepsteep
cuspscusps will change the locations and extent ofwill change the locations and extent of
the outline form.the outline form.

6. Other factors affecting the outline form ofOther factors affecting the outline form of
proximaproximal cavity preparations:l cavity preparations:
The size and site of theThe size and site of the contactcontact area.area.
The width of theThe width of the embrasures.embrasures.
The position and health of the freeThe position and health of the free gingivalgingival
margin.margin.

7. • The outline form for proximal cavities demands:The outline form for proximal cavities demands:
Principal extension in the gingival, buccal andPrincipal extension in the gingival, buccal and
lingual directions which is just sufficient tolingual directions which is just sufficient to freefree
these marginsthese margins of the preparation from contactof the preparation from contact
with the adjacent tooth or restorationwith the adjacent tooth or restoration (flaring of(flaring of
the margins)the margins). This is done to make. This is done to make
them accessible forthem accessible for carving or finishingcarving or finishing of theof the
restoration and convenientrestoration and convenient for brushing andfor brushing and
oral hygiene measures.oral hygiene measures.

9. In proximal cavity preparation of posteriorIn proximal cavity preparation of posterior
teeth (Class II):teeth (Class II):
The buccal and lingual walls past theThe buccal and lingual walls past the
isthmus portion should approach the proximalisthmus portion should approach the proximal
surface at 90°surface at 90° (perpendicular to enamel rods),(perpendicular to enamel rods),
past the contact areapast the contact area and extend enough toand extend enough to
eliminate the carious lesion.eliminate the carious lesion.

10. • Other factors affecting the outline form ofOther factors affecting the outline form of
CervicalCervical cavity preparations:cavity preparations:
The outline form forThe outline form for Class V cervicalClass V cervical
cavitiescavities (Si/Sta(Si/Sta 3.1, 3.2, 3.3) is controlled3.1, 3.2, 3.3) is controlled
gingivally by the position of the gingival tissues.gingivally by the position of the gingival tissues.
In some occasions forIn some occasions for esthetic demands,esthetic demands, thethe
gingival margin should be hidden sub-gingival margin should be hidden sub-
gingivally. The outline form is just limited to thegingivally. The outline form is just limited to the
defect in case of tooth colored restorations in thedefect in case of tooth colored restorations in the
anterior region and the incisal wall is beveled foranterior region and the incisal wall is beveled for
maximizing the esthetics through colormaximizing the esthetics through color
degradation.degradation.

11. • For all cavities, theFor all cavities, the extent of cariesextent of caries in enamel asin enamel as
well as in lateral spread in dentin iswell as in lateral spread in dentin is the decidingthe deciding
factorfactor of extent and form of cavity outline. Itof extent and form of cavity outline. It
becomes evident that the main significance of abecomes evident that the main significance of a
correct outline form is primarily the removal ofcorrect outline form is primarily the removal of
actual defects. It must be stated that recentactual defects. It must be stated that recent
methods of preventive dentistry and improvementsmethods of preventive dentistry and improvements
of materials and manipulation techniques limitedof materials and manipulation techniques limited
the necessity for extensive extensions of cavitythe necessity for extensive extensions of cavity
margins. Sound bio-mechanical as well as estheticmargins. Sound bio-mechanical as well as esthetic
demands dictate conservation of tooth tissues.demands dictate conservation of tooth tissues.
• By knowing this, it should be very hard to acceptBy knowing this, it should be very hard to accept
over-cutting of tooth structures by any means.over-cutting of tooth structures by any means.

12. 2.2. Obtaining of the Resistance and RetentionObtaining of the Resistance and Retention
Forms:Forms:
These are two distinct but yet, inseparableThese are two distinct but yet, inseparable
and interrelated steps i.e., two faces for theand interrelated steps i.e., two faces for the
same coin. Thesame coin. The resistance formresistance form refers to therefers to the
design features in the cavity preparation whichdesign features in the cavity preparation which
allows both tooth and restoration to resist theallows both tooth and restoration to resist the
functional stresses of mastication withoutfunctional stresses of mastication without
fracture.fracture. The response of either the tooth or theThe response of either the tooth or the
restoration to the applied stress could be eitherrestoration to the applied stress could be either
favorable without fractures or un-favorablefavorable without fractures or un-favorable
with the fracture of either or both of them.with the fracture of either or both of them.

13. • Factors Influencing Stress Response of ToothFactors Influencing Stress Response of Tooth
and Restoration:and Restoration:
When a restored tooth is loaded duringWhen a restored tooth is loaded during
mastication, stresses will be induced in both themastication, stresses will be induced in both the
tooth and restoration. Whether they will sustaintooth and restoration. Whether they will sustain
such stresses without fracture will depend onsuch stresses without fracture will depend on
the following factors:the following factors:

14. 1)1) Occlusal loading in terms of:Occlusal loading in terms of:
 ItsIts magnitudemagnitude which differs from patient towhich differs from patient to
another (the action of the masticationanother (the action of the mastication
muscles, type of occlusion and inter-muscles, type of occlusion and inter-
cuspation, type of food, age and sex) andcuspation, type of food, age and sex) and
also varies from one location to another inalso varies from one location to another in
the same patient and also from one time tothe same patient and also from one time to
another.another.

15. ItsIts direction,direction, i.e. compressive, tensile or sheari.e. compressive, tensile or shear
and this depend on the form of the loaded surfaceand this depend on the form of the loaded surface
as well as the inclination of the cavity areas atas well as the inclination of the cavity areas at
which the stresses are transmitted and analyzed.which the stresses are transmitted and analyzed.
ItsIts character,character, i.e., whether it is static, dynamic ori.e., whether it is static, dynamic or
cyclic since the repetitive cycles of dynamiccyclic since the repetitive cycles of dynamic
forces which occur during mastication canforces which occur during mastication can
damage the tooth and restoration due to thedamage the tooth and restoration due to the
possibility of fatigue and failure of the materialpossibility of fatigue and failure of the material
as a result of applied stresses even at stressesas a result of applied stresses even at stresses
below its bending or elastic limit.below its bending or elastic limit.

16. 2)2) Cavity design in terms of:Cavity design in terms of:
 Direction of walls;Direction of walls; which is recommended towhich is recommended to
be parallel or perpendicular to the direction ofbe parallel or perpendicular to the direction of
expected forces to get these forces balancedexpected forces to get these forces balanced
out and thus prevents unfavorable analysis ofout and thus prevents unfavorable analysis of
forces.forces.
 Smoothness and flatness of walls;Smoothness and flatness of walls; since thissince this
could prevent stress concentration.could prevent stress concentration.
 Line and point anglesLine and point angles which must bewhich must be roundedrounded
in brittle restorations to avoid stressin brittle restorations to avoid stress
concentration and initiation of cracks.concentration and initiation of cracks.

21. Amount ofAmount of bulkbulk provided which distributesprovided which distributes
stress. This is achieved throughstress. This is achieved through depth ratherdepth rather
than width.than width. If cavityIf cavity widthwidth is increased, this willis increased, this will
weaken the remaining tooth, increase area ofweaken the remaining tooth, increase area of
restoration subjected to forces and bring therestoration subjected to forces and bring the
criticalcritical marginsmargins to maximum tensile forcesto maximum tensile forces
towards the cusp tip.towards the cusp tip. Doubling the depthDoubling the depth
providesprovides 44 times increase in strength, whiletimes increase in strength, while
doubling the width provides only doubles thedoubling the width provides only doubles the
strength.strength.

22. TheThe cavo-surface angle inclinationcavo-surface angle inclination relative torelative to
the physical property of thethe physical property of the restorative materialrestorative material
as well as theas well as the direction of enamel rods.direction of enamel rods. ItIt
should be 90° in brittle restorations to provideshould be 90° in brittle restorations to provide
bulk for both the restoration and the tooth at thebulk for both the restoration and the tooth at the
margins. The gingival seat should be trimmedmargins. The gingival seat should be trimmed
to follow the cervical slanting of enamel rods atto follow the cervical slanting of enamel rods at
this area.this area.

24. TheThe isthmus portionisthmus portion should be provided withshould be provided with
appropriate width to avoid stress concentrationappropriate width to avoid stress concentration
at this critical area.at this critical area.
The amount ofThe amount of retention,retention, which provideswhich provides
stability for the restoration and secures thestability for the restoration and secures the
relation between the load and the loadedrelation between the load and the loaded
surfaces and prevents the development ofsurfaces and prevents the development of
excessiveexcessive tensile forcestensile forces within the restoration aswithin the restoration as
in compound Class II amalgam.in compound Class II amalgam.

25. 3)3) Strength characteristics of the restorativeStrength characteristics of the restorative
material;material; this influences the typethis influences the type
of major stresses developed within theof major stresses developed within the
restoration. Therestoration. The tensile and shear typestensile and shear types areare
crucial stresses for the brittle materials suchcrucial stresses for the brittle materials such
as amalgam, cements and ceramics becauseas amalgam, cements and ceramics because
they have high compressive but very lowthey have high compressive but very low
tensile and shear strength values, on thetensile and shear strength values, on the
contrary to the strong and ductile gold whichcontrary to the strong and ductile gold which
is utilized for protection of the weakenedis utilized for protection of the weakened
tooth structure.tooth structure.

26. • It is evident that resistance and retention formsIt is evident that resistance and retention forms
act together in a mutual manner to preventact together in a mutual manner to prevent
fracture of the tooth and the restoration and anyfracture of the tooth and the restoration and any
tendency for the restoration to get displaced outtendency for the restoration to get displaced out
of the cavity during mastication. Furthermore,of the cavity during mastication. Furthermore,
although both are explained separately, yet theyalthough both are explained separately, yet they
are usually obtained by the same technicalare usually obtained by the same technical
procedures.procedures.

27. • TheThe Retention formRetention form describes thedescribes the designdesign
features in the cavity which enables it to hold itfeatures in the cavity which enables it to hold it
or retain the restoration securely injunctionor retain the restoration securely injunction
preventing its displacement.preventing its displacement.
• Generally, restorations may be attached to teethGenerally, restorations may be attached to teeth
by chemical and/or mechanical mechanisms ofby chemical and/or mechanical mechanisms of
surface interactions:surface interactions:

28. A.A. Chemical retention:Chemical retention:
ChemicalChemical or true adhesion by primaryor true adhesion by primary
valence bonding is strong and stable. Retentionvalence bonding is strong and stable. Retention
or bonding byor bonding by physicalphysical or Van der Walls forcesor Van der Walls forces
is weak and clinically unstable. Chemical oris weak and clinically unstable. Chemical or
true adhesion is a function of surfacetrue adhesion is a function of surface
interaction of an adhesive (restoration) and ainteraction of an adhesive (restoration) and a
solid substrate phase (tooth). It is notsolid substrate phase (tooth). It is not
achievable except for the glass ionomerachievable except for the glass ionomer
restorations; due to inherent clinical problemsrestorations; due to inherent clinical problems
in the substrate hard tooth structures, andin the substrate hard tooth structures, and
limitations presented by oral environment.limitations presented by oral environment.

29. B.B. Mechanical retention:Mechanical retention:
This is theThis is the principle mechanismprinciple mechanism ofof
retention utilized inretention utilized in restorative dentistry,restorative dentistry,
although it may be enhanced by contributionalthough it may be enhanced by contribution
from chemical adhesion. Two distinctfrom chemical adhesion. Two distinct
mechanisms of mechanical retention aremechanisms of mechanical retention are
commonly used, i.e., macro- and micro-commonly used, i.e., macro- and micro-
mechanical retention.mechanical retention.

30. • Micro-mechanical retention:Micro-mechanical retention:
This is the most conservative mechanismThis is the most conservative mechanism
of retention or attachment. It is the mainof retention or attachment. It is the main
method of retention employed formethod of retention employed for resinresin
composite restorations.composite restorations. It depends on anIt depends on an
intermediary joint that interlocks theintermediary joint that interlocks the
restoration to tooth. It forms micro-scopicrestoration to tooth. It forms micro-scopic
resin tags created by resin impregnation ofresin tags created by resin impregnation of
pre-demineralized top layer of substratepre-demineralized top layer of substrate
enamel and dentin surfaces.enamel and dentin surfaces.

31. • This is achieved byThis is achieved by Acid etching of enamel andAcid etching of enamel and
dentindentin to achieveto achieve selective demineralizationselective demineralization ofof
the surface which serves for micromechanicalthe surface which serves for micromechanical
interlocking of the adhesive resin into the toothinterlocking of the adhesive resin into the tooth
substance, aiming to retain and improvesubstance, aiming to retain and improve
adaptation of the restoration as well as improveadaptation of the restoration as well as improve
its resistance to loading.its resistance to loading.
• However, this mechanism of retention isHowever, this mechanism of retention is
vulnerable to inconsistencies due to techniquevulnerable to inconsistencies due to technique
sensitivity, inevitable presence of stresssensitivity, inevitable presence of stress
concentration at different interfaces of variousconcentration at different interfaces of various
phases of restorative system, and instability ofphases of restorative system, and instability of
the resin bond in oral environment.the resin bond in oral environment.

32. • Macro-mechanical retention:Macro-mechanical retention:
This type of retention depends on certainThis type of retention depends on certain
retaining features that are incorporated in theretaining features that are incorporated in the
remaining tooth substance and serve to anchorremaining tooth substance and serve to anchor
the restoration mechanically in the preparation.the restoration mechanically in the preparation.
It is the main retention mechanism employed forIt is the main retention mechanism employed for
metallic restorations.metallic restorations.
This type of retention is generally classifiedThis type of retention is generally classified
according to the possible direction ofaccording to the possible direction of
displacement into:displacement into:

33. a)a) Axial retention:Axial retention:
This prevents displacement of restoration in aThis prevents displacement of restoration in a
direction parallel to the long axis of the toothdirection parallel to the long axis of the tooth
i.e. in occlusal or apical (pulpal or gingival)i.e. in occlusal or apical (pulpal or gingival)
directions.directions.
 ForFor direct restorationsdirect restorations,, the occlusalthe occlusal
displacement is prevented by,displacement is prevented by, through occlusalthrough occlusal
convergence of the cavity walls and theconvergence of the cavity walls and the
proximal locks (undercuts),proximal locks (undercuts), where the internalwhere the internal
outline of the preparation is made greater thanoutline of the preparation is made greater than
the external outline.the external outline.

35. Convergence of the wallsConvergence of the walls Divergence of the wallsDivergence of the walls

36. ForFor indirect restorations,indirect restorations, the retention againstthe retention against
occlusal displacement is provided by theocclusal displacement is provided by the
frictional parallelismfrictional parallelism of walls of the cavityof walls of the cavity
which increases by increasing the degree ofwhich increases by increasing the degree of
parallelism between walls, the length ofparallelism between walls, the length of
parallel walls and the roughness.parallel walls and the roughness.

37. Dentin ledgesDentin ledges which are flat seats performed inwhich are flat seats performed in
dentin withdentin with deep amalgam cavity preparationsdeep amalgam cavity preparations
to prevent pulpward movement of restorationto prevent pulpward movement of restoration
and also prevent fracture of the thin dentinand also prevent fracture of the thin dentin
bridge. Such preparation is performed with anbridge. Such preparation is performed with an
inverted cone bur to provide buccal and/orinverted cone bur to provide buccal and/or
lingual shelves for support.lingual shelves for support.

39. b)b) Lateral retention:Lateral retention:
The features provided to prevent displacementThe features provided to prevent displacement
in any other direction than the axial is consideredin any other direction than the axial is considered
lateral, e.g. proximal, buccal or linguallateral, e.g. proximal, buccal or lingual
directions.directions.
• The various retentive features are:The various retentive features are:
 Frictional opposing wall parallelism,Frictional opposing wall parallelism, the micro-the micro-
roughness of cavity walls aids in preventingroughness of cavity walls aids in preventing
displacement of restoration.displacement of restoration.
 Proximal axial grooves (locks):Proximal axial grooves (locks): it is done init is done in
compound or complex Class IIcompound or complex Class II cavitycavity
preparations at thepreparations at the axio-buccal and axio-lingualaxio-buccal and axio-lingual
line anglesline angles at the expense of buccal and lingualat the expense of buccal and lingual
walls and not on the expense of the axial wall.walls and not on the expense of the axial wall.

41. • They should extend either to the axio-pulpalThey should extend either to the axio-pulpal
line angle or fade to the occlusal margin. Theyline angle or fade to the occlusal margin. They
are made using a tapered fissure bur.are made using a tapered fissure bur.
Buccal or lingual extensionsBuccal or lingual extensions in molars andin molars and
extensions onto the other side inextensions onto the other side in
premolars or molars.premolars or molars.

42. Reverse bevelReverse bevel: This is a gingival lock: This is a gingival lock
performed in compound Class II cavity forperformed in compound Class II cavity for
cast gold restorationscast gold restorations inin dentin of the gingivaldentin of the gingival
floorfloor where an inward bevel (against thewhere an inward bevel (against the
direction of cavo-surface bevel) is cut using adirection of cavo-surface bevel) is cut using a
tapered fissure bur or gingival marginaltapered fissure bur or gingival marginal
trimmer of the opposite side.trimmer of the opposite side.

44.  The action of such reverse bevel is toThe action of such reverse bevel is to preventprevent
proximal displacementproximal displacement of the restoration, toof the restoration, to
produce favorable analysis of forces inwardsproduce favorable analysis of forces inwards
rather than outwards (favorable slope) and torather than outwards (favorable slope) and to
prevent rotation of the inlay along the axio-prevent rotation of the inlay along the axio-
pulpal line angle. Other forms of bevels arepulpal line angle. Other forms of bevels are
performed mainly in enamel and are used forperformed mainly in enamel and are used for
retention and other purposes.retention and other purposes.

45. Dove-tail lockDove-tail lock (common in premolar): This is a(common in premolar): This is a
purposeful modification in the outline form inpurposeful modification in the outline form in
some cases, aiming to increase lateralsome cases, aiming to increase lateral
resistance of displacement of the restorations.resistance of displacement of the restorations.
SlotsSlots: This is an internal cavity within the floor: This is an internal cavity within the floor
of the preparation having a continuousof the preparation having a continuous
surrounding wall and floor. A slot is asurrounding wall and floor. A slot is a
retentive groove in dentin, whose length is in aretentive groove in dentin, whose length is in a
horizontal plane is approximately 0.6mm,horizontal plane is approximately 0.6mm,
depth 0.6mm and 0.5 to 1mm inside dentin-depth 0.6mm and 0.5 to 1mm inside dentin-
enamel junction. It is indicated in extensiveenamel junction. It is indicated in extensive
restorations requiring cusp building.restorations requiring cusp building.

46. Dove-tailDove-tail

49. Axial covesAxial coves: Prepared (with No 1/4 bur) in: Prepared (with No 1/4 bur) in
dentin in the vertical plane to provide additionaldentin in the vertical plane to provide additional
retention form in a preparation that uses pins orretention form in a preparation that uses pins or
in combination with grooves and slots.in combination with grooves and slots.

50. Dentin pinsDentin pins: they are additional retention: they are additional retention
feature, were considered at first both retentivefeature, were considered at first both retentive
and reinforcing to the amalgam restoration, butand reinforcing to the amalgam restoration, but
recently, it was found that if the pins wererecently, it was found that if the pins were
improperly located, increased in number orimproperly located, increased in number or
violating the bulk provided to the restorativeviolating the bulk provided to the restorative
material, they may act, on the contrary, asmaterial, they may act, on the contrary, as
inclusions in the restored mass and mayinclusions in the restored mass and may
adversely or negatively affect the resistance toadversely or negatively affect the resistance to
fracture of both the restoration and the toothfracture of both the restoration and the tooth
structure.structure.

51. PinsPins

52. • They can be cemented or threaded, parallel orThey can be cemented or threaded, parallel or
non parallel to each other. They could be usednon parallel to each other. They could be used
alone or with other additional means ofalone or with other additional means of
auxiliary retention. Pin retention is usedauxiliary retention. Pin retention is used
frequently in preparation with few or nofrequently in preparation with few or no
vertical walls.vertical walls.

53. Inter-radicular retention (posts):Inter-radicular retention (posts): it is indicated init is indicated in
endodontically treated teeth where retention isendodontically treated teeth where retention is
gained through the root portion of the tooth andgained through the root portion of the tooth and
not through the coronal portion which wasnot through the coronal portion which was
damaged either partially or totally. A dowel postdamaged either partially or totally. A dowel post
is inserted into the prepared root canal to serveis inserted into the prepared root canal to serve
for retaining the restoration in root canal treatedfor retaining the restoration in root canal treated
teeth. It could be specially fabricated or ready-teeth. It could be specially fabricated or ready-
made prefabricated. Like dentin pins, the postsmade prefabricated. Like dentin pins, the posts
may be retained into the canal by cementation,may be retained into the canal by cementation,
screwing or wedging.screwing or wedging.

54. PostPost

56. • Factors controlling the selection of retentionFactors controlling the selection of retention
features:features:
Size of the cavity and remaining amount of toothSize of the cavity and remaining amount of tooth
structure:structure: Increasing the cavity dimensions subjectsIncreasing the cavity dimensions subjects
the restoration to more displacing forces andthe restoration to more displacing forces and
provides little tooth structure for retaining theprovides little tooth structure for retaining the
restoration. Thus, the greater the size of the cavity,restoration. Thus, the greater the size of the cavity,
the greater the need for retentive means.the greater the need for retentive means.
Number of missing walls:Number of missing walls: This condition provideThis condition provide
additional multiple displacement directions whichadditional multiple displacement directions which
require more retention to serve for both axialrequire more retention to serve for both axial
and lateral directions, e.g., complex Class IVand lateral directions, e.g., complex Class IV
cavities present difficulty in retention.cavities present difficulty in retention.

57. Site of the cavity and occlusal stresses:Site of the cavity and occlusal stresses: In cavitiesIn cavities
with high stresses, there is an increase in thewith high stresses, there is an increase in the
displacing forces which necessitates additionaldisplacing forces which necessitates additional
means to secure retention, e.g., in compound ormeans to secure retention, e.g., in compound or
complex Class II cavity more retention featurescomplex Class II cavity more retention features
are needed than in cervical Class V cavity whichare needed than in cervical Class V cavity which
is not prone to excessive stresses.is not prone to excessive stresses.
Type of restoration:Type of restoration: Certain types of restorativeCertain types of restorative
materials dictate specific retention feature such asmaterials dictate specific retention feature such as
the acid etching for resins, undercuts forthe acid etching for resins, undercuts for
amalgam, frictional parallelism for inlays.amalgam, frictional parallelism for inlays.

58. Pulp vitality:Pulp vitality: Dowel post are only utilized inDowel post are only utilized in
root canal treated teeth and only cementedroot canal treated teeth and only cemented
posts can be used in non-vital teeth.posts can be used in non-vital teeth.
Esthetic requirements:Esthetic requirements: In certain cases, aIn certain cases, a
compromise could be made between retentioncompromise could be made between retention
versus esthetic requirements.versus esthetic requirements.

59. • It was agreed upon that the general shape ofIt was agreed upon that the general shape of
the cavity which provides resistance for boththe cavity which provides resistance for both
the tooth and restoration against fracture underthe tooth and restoration against fracture under
masticatory forces is themasticatory forces is the box (mortise)box (mortise) oror
modified box form.modified box form.

60. • The use of this box-like form is advocatedThe use of this box-like form is advocated
because:because:
1)1) TheThe seatseat of the restoration (pulpal andof the restoration (pulpal and
gingival wall) is placed at a distinctgingival wall) is placed at a distinct
right angle to the direction of functionalright angle to the direction of functional
stresses. This will favorstresses. This will favor neutralizationneutralization ofof
these stresses at the cavity seat and preventthese stresses at the cavity seat and prevent
them getting resolved into components ofthem getting resolved into components of
destructive tensile stresses which tend todestructive tensile stresses which tend to
fracture the tooth and/or the restoration.fracture the tooth and/or the restoration.

63. 2)2) The tendency to split the buccal and lingualThe tendency to split the buccal and lingual
cusps of biscupids and molars by forcescusps of biscupids and molars by forces
transmitted through the restoration is greatlytransmitted through the restoration is greatly
diminished since the inverted truncated conediminished since the inverted truncated cone
shapeshape prevents the wedging actionprevents the wedging action of theof the
restoration inside the tooth.restoration inside the tooth.
3)3) It providesIt provides retentionretention by friction due toby friction due to
relative parallelism of the axial walls.relative parallelism of the axial walls.

64. • Thus, retention may partly be providedThus, retention may partly be provided
automatically during making the resistance formautomatically during making the resistance form
and vice versa. Therefore, they are consideredand vice versa. Therefore, they are considered
interrelated and inseparable forms, for instances:interrelated and inseparable forms, for instances:
AA boxbox form preparation, which is a form ofform preparation, which is a form of
resistance, will at the same time provideresistance, will at the same time provide
undercutundercut through the occlusal convergence ofthrough the occlusal convergence of
walls, thereby providing an occlusal lock.walls, thereby providing an occlusal lock.
When the walls are parallel they provideWhen the walls are parallel they provide
retention by friction.retention by friction.

65. TheThe inverted truncatedinverted truncated cone form preventscone form prevents
wedging actionwedging action of restoration (resistance form)of restoration (resistance form)
and meanwhile providesand meanwhile provides undercutsundercuts forfor
retention.retention.
TheThe bulkbulk provided for distribution of stressprovided for distribution of stress
and prevention of fracture of the brittleand prevention of fracture of the brittle
restoration also augments retention by morerestoration also augments retention by more
frictional retention and increasing thefrictional retention and increasing the
undercut area.undercut area.

66. The provision of ample independent retention inThe provision of ample independent retention in
compound proximal cavity for amalgam in thecompound proximal cavity for amalgam in the
form ofform of proximal axial locksproximal axial locks aids resistanceaids resistance
through preventing development of excessivethrough preventing development of excessive
tension at the isthmus which might cause isthmustension at the isthmus which might cause isthmus
fracture (resistance).fracture (resistance).
The liability of displacement of restoration fromThe liability of displacement of restoration from
corresponding preparation (lack of retention) iscorresponding preparation (lack of retention) is
accompanied by aaccompanied by a disturbance of relationdisturbance of relation
between the load, and the loaded surfacebetween the load, and the loaded surface withwith
eventual fracture (lack of resistance).eventual fracture (lack of resistance).

67. 3.3. Obtaining the Convenience Form:Obtaining the Convenience Form:
The convenience form describes thoseThe convenience form describes those
features in the prepared cavity, which arefeatures in the prepared cavity, which are
added for the specific purpose of making itadded for the specific purpose of making it
more conveniently seen, approached and/ormore conveniently seen, approached and/or
restored.restored. It refers to features which improvesIt refers to features which improves
visibility and accessibility during preparationvisibility and accessibility during preparation
and restoration.and restoration.

69. • These features include a slight moreThese features include a slight more extensionextension ofof
a cavity outline to enable better preparation anda cavity outline to enable better preparation and
manipulation,manipulation, accentuation of line or point angle;accentuation of line or point angle;
making the cavity outline inmaking the cavity outline in sweeping curvessweeping curves forfor
easier restoration of anatomy,easier restoration of anatomy, elimination ofelimination of
undermined enamelundermined enamel for convenient removal offor convenient removal of
decay. However, the advent of recent methodsdecay. However, the advent of recent methods
and instruments employed for the manipulation,and instruments employed for the manipulation,
condensation and finishing of the plasticcondensation and finishing of the plastic
restorations made most of these featuresrestorations made most of these features almostalmost
unnecessary.unnecessary.

71. • Another example for convenience form is theAnother example for convenience form is the
occlusal accessocclusal access to proximal lesions in Class IIto proximal lesions in Class II
and the palatal access to Class III.and the palatal access to Class III.
• It should be noted, however, thatIt should be noted, however, that simplesimple Class IIClass II
or III could be conveniently approached if theor III could be conveniently approached if the
adjacent tooth is missing or the embrasure isadjacent tooth is missing or the embrasure is
widened (as in case of senile gum recession).widened (as in case of senile gum recession).

72. • Modifications in the conventional cavityModifications in the conventional cavity
preparation to reach a conservative configurationpreparation to reach a conservative configuration
necessitated reconsideration of the appliednecessitated reconsideration of the applied
convenience form.convenience form.
• The smaller-sized cavity, the rounded andThe smaller-sized cavity, the rounded and
sweeping pear or tear-drop shaped cavitysweeping pear or tear-drop shaped cavity
preparations, need corresponding small-sizedpreparations, need corresponding small-sized
cutting burs and stones with newly designedcutting burs and stones with newly designed
shapes. These newly introduced cutting toolsshapes. These newly introduced cutting tools
allowed the operator to cut in one step the wholeallowed the operator to cut in one step the whole
cavity outline with the needed retention andcavity outline with the needed retention and
resistance features.resistance features.

73. • The finishing of the walls of the preparationThe finishing of the walls of the preparation
could now be performed using a single cuttingcould now be performed using a single cutting
tool with variable cutting efficiencies through thetool with variable cutting efficiencies through the
change in the abrasive grits of the different partschange in the abrasive grits of the different parts
of the same cutting stone.of the same cutting stone.

74. • Proper VisibilityProper Visibility inside the oral cavity duringinside the oral cavity during
each and every phase of the treatment iseach and every phase of the treatment is
mandatory. The use ofmandatory. The use of fiber-optic handpiecefiber-optic handpiece
with built-in light transmission improved thewith built-in light transmission improved the
visibility in the oral cavity. It was found to bevisibility in the oral cavity. It was found to be
of great help especially in case ofof great help especially in case of
ultraconservative cavity preparation that needsultraconservative cavity preparation that needs
precision and minimal cutting in the toothprecision and minimal cutting in the tooth
structure.structure.

76. 4.4. Removal of the Remaining Caries:Removal of the Remaining Caries:
The techniques for removal of dental cariesThe techniques for removal of dental caries
have evolved greatly due the technologicalhave evolved greatly due the technological
advances in the fields of laser applications,advances in the fields of laser applications,
microdentistry, bio-chemistry and debridement.microdentistry, bio-chemistry and debridement.

77. • Techniques for caries removal:Techniques for caries removal:
Manual excavationManual excavation by use ofby use of excavators.excavators.
Mechanical excavationMechanical excavation by use ofby use of burs.burs.
Air abrasion debridementAir abrasion debridement (microdentistry);(microdentistry);
which utilizes tiny aluminum oxide particleswhich utilizes tiny aluminum oxide particles
(20-50(20-50 µm)µm) under a stream of compressedunder a stream of compressed
air.air.

79. Laser debridement;Laser debridement; which uses thermalwhich uses thermal
energy.energy.
Chemo-mechanical debridement: Carisolv;Chemo-mechanical debridement: Carisolv;
which uses a combination of amino acids andwhich uses a combination of amino acids and
weak solution of sodium hypochlorite in a gelweak solution of sodium hypochlorite in a gel
form which makes the caries easier to scrap byform which makes the caries easier to scrap by
specially designed instruments.specially designed instruments.
Enzymes:Enzymes: some enzymes such assome enzymes such as PronasePronase
enzyme are still under investigations for theirenzyme are still under investigations for their
efficacy in caries removal.efficacy in caries removal.

83. • The most common methods for caries removalThe most common methods for caries removal
are the excavators and burs.are the excavators and burs.
• HardHard caries is removed usingcaries is removed using suitable size roundsuitable size round
bur running at slow speed, at intermittentbur running at slow speed, at intermittent
strokes with light pressurestrokes with light pressure to avoid damage ofto avoid damage of
the pulp. On the other hand, deep soft caries isthe pulp. On the other hand, deep soft caries is
removed usingremoved using suitable size excavators movedsuitable size excavators moved
parallel to the recessional linesparallel to the recessional lines of the pulp toof the pulp to
avoid pulp exposure. The use of other methodsavoid pulp exposure. The use of other methods
requires costly equipment and materials and isrequires costly equipment and materials and is
thus less frequently used.thus less frequently used.

84. • In the average case, most of carious dentin isIn the average case, most of carious dentin is
removed during the previous procedures.removed during the previous procedures.
However, the cavity must then be thoroughlyHowever, the cavity must then be thoroughly
inspected for remaining caries using sharpinspected for remaining caries using sharp
explorers, aided by good illumination andexplorers, aided by good illumination and
dryness of the operative field.dryness of the operative field.

85. • This inspection may then reveal the cavity floorThis inspection may then reveal the cavity floor
to be composed of:to be composed of:
Hard sound viable dentinHard sound viable dentin free from lateralfree from lateral
spread of decay or discolorations. If thisspread of decay or discolorations. If this
cavity seat is 0.25cavity seat is 0.25 mm beyond the dentin-mm beyond the dentin-
enamel junction,enamel junction, this would be thethis would be the
conventional and most accepted cavity depth;conventional and most accepted cavity depth;
no more deepening should be made.no more deepening should be made.

86. Lateral spread of cariesLateral spread of caries

87. • In case of adhesiveIn case of adhesive direct resin compositedirect resin composite
restorations, it is allowed to have the cavity atrestorations, it is allowed to have the cavity at
the level of enamel depth provided that at leastthe level of enamel depth provided that at least
1.5 mm is available for the required bulk of the1.5 mm is available for the required bulk of the
material. However; in most cases, cavitymaterial. However; in most cases, cavity
prepared forprepared for amalgam restorationsamalgam restorations must bemust be
extended beyond the dentin-enamel junction to:extended beyond the dentin-enamel junction to:

88. Ensure that there is no moreEnsure that there is no more lateral spreadlateral spread ofof
caries along thecaries along the dentin-enamel junction,dentin-enamel junction, whichwhich
will otherwise undermine the overlying enamel.will otherwise undermine the overlying enamel.
Avoid lateral cutting and then placing aAvoid lateral cutting and then placing a
restoration against a mostrestoration against a most sensitivesensitive area ofarea of
dentin at thedentin at the dentin-enamel junctiondentin-enamel junction where thewhere the
dentinal tubules branch and anastomose.dentinal tubules branch and anastomose.
Provide the necessaryProvide the necessary bulkbulk required for therequired for the
restoration (l.5-2mm).restoration (l.5-2mm).
ProvideProvide retentionretention in dentin, if required.in dentin, if required.

89. Hard but discolored dentin;Hard but discolored dentin; which is notwhich is not
considered as carious dentin since theconsidered as carious dentin since the hardnesshardness
indicates that such dentin is stained from theindicates that such dentin is stained from the
pigments produced by chromogenic bacteria andpigments produced by chromogenic bacteria and
not demineralized. If such dentin is hard, even ifnot demineralized. If such dentin is hard, even if
the cavity seat lies at a correct depth, then therethe cavity seat lies at a correct depth, then there
is no harm in leaving this dentin, except in caseis no harm in leaving this dentin, except in case
ofof anterior teethanterior teeth where it must be carefullywhere it must be carefully
removed for esthetic reasons or masked byremoved for esthetic reasons or masked by
opaquers.opaquers.

90. Carious dentin;Carious dentin; this type of caries may bethis type of caries may be
discolored or not but it is soft, even to a minordiscolored or not but it is soft, even to a minor
degree, if compared to sound dentin. If thisdegree, if compared to sound dentin. If this
layer constitutes the floor of deep andlayer constitutes the floor of deep and
moderately deep cavities, it has to be carefullymoderately deep cavities, it has to be carefully
removed.removed.

91. • It was previously thought that, due to the fast rateIt was previously thought that, due to the fast rate
of acute caries, the acids precede the bacteria onof acute caries, the acids precede the bacteria on
the contrary to chronic caries. However, thethe contrary to chronic caries. However, the
general consensus is that, irrespective to cariesgeneral consensus is that, irrespective to caries
type, softening of dentin precedes the organismstype, softening of dentin precedes the organisms
responsible for it. However, few organisms areresponsible for it. However, few organisms are
liable to remain even if all soft dentin is removed.liable to remain even if all soft dentin is removed.
These organisms remain viable beneathThese organisms remain viable beneath
restorations without apparently causing anyrestorations without apparently causing any
detrimental effect.detrimental effect.

92. • Thus, it is important to distinguish betweenThus, it is important to distinguish between
affected dentin,affected dentin, which is demineralized by acidswhich is demineralized by acids
but remineralizable, andbut remineralizable, and infected dentininfected dentin that isthat is
demineralized, heavily infected bydemineralized, heavily infected by
microorganisms and cannot be remineralized. Themicroorganisms and cannot be remineralized. The
most commonly used approach for managing themost commonly used approach for managing the
remaining caries at the pulpal wall is to removeremaining caries at the pulpal wall is to remove
infected dentin using a bur or excavator and leaveinfected dentin using a bur or excavator and leave
the caries affected dentin (whether discolored orthe caries affected dentin (whether discolored or
not) which is reasonably firm, uninfected,not) which is reasonably firm, uninfected,
remineralizable and painful (denoting presence ofremineralizable and painful (denoting presence of
viable protoplasmic processes).viable protoplasmic processes).

93. • Also, dentin-enamel junction should be renderedAlso, dentin-enamel junction should be rendered
hard and stain-free.hard and stain-free.
• When it comes to manageWhen it comes to manage deepdeep cavities wherecavities where
removal of infected dentin (discolored or not)removal of infected dentin (discolored or not)
would expose the pulp, step-wise excavation andwould expose the pulp, step-wise excavation and
indirect pulp capping is recommended.indirect pulp capping is recommended.

94. • Indirect pulp capping:Indirect pulp capping: is a conservativeis a conservative
technique that comprises incomplete removal oftechnique that comprises incomplete removal of
affected dentin, cover it with a compatibleaffected dentin, cover it with a compatible
capping materials or cavity liner e.g. calciumcapping materials or cavity liner e.g. calcium
hydroxide and sealing the cavity with ahydroxide and sealing the cavity with a
permanent or temporary control restoration. Thepermanent or temporary control restoration. The
affected dentin usually remineralizes in 8-10affected dentin usually remineralizes in 8-10
weeks and can be detected radiographicallyweeks and can be detected radiographically
after 12 weeks.after 12 weeks.

95. Zinc oxide-eugenolZinc oxide-eugenol

96. • Sealing the cavity mostly kills or inactivatesSealing the cavity mostly kills or inactivates
the bacteria, thus giving the healthy pulp athe bacteria, thus giving the healthy pulp a
chance to lay down a natural protective barrierchance to lay down a natural protective barrier
of reparative dentin that wall off the lesion.of reparative dentin that wall off the lesion.
The technique is easy and has high potentialThe technique is easy and has high potential
for success, particularly in young permanentfor success, particularly in young permanent
teeth of healthy patients, provided the tooth isteeth of healthy patients, provided the tooth is
symptom free.symptom free.

97. 5.5. Finishing of cavity walls and margins:Finishing of cavity walls and margins:
To obtain properly finished cavity walls,To obtain properly finished cavity walls,
the followingthe following objectivesobjectives should be satisfied:should be satisfied:
 Removal ofRemoval of underminedundermined enamel.enamel.
 AdjustAdjust cavo-surface angle inclinationcavo-surface angle inclination
according to the physical properties ofaccording to the physical properties of
restoration and the direction of enamelrestoration and the direction of enamel
rods.rods.

98. Give theGive the cavity wall correct inclination.cavity wall correct inclination.
Render the wallsRender the walls smoothsmooth for better adaptation.for better adaptation.
Make the cavity outline inMake the cavity outline in sweepingsweeping curves.curves.
RoundationRoundation of line and point angles.of line and point angles.

99. • This is essential for the marginal seal andThis is essential for the marginal seal and
integrity of the restoration. However, if the threeintegrity of the restoration. However, if the three
previous steps of cavity preparation areprevious steps of cavity preparation are
meticulously done, so, this step is donemeticulously done, so, this step is done
automatically or with minimum effort.automatically or with minimum effort.
• Finishing is performed either byFinishing is performed either by hand cuttinghand cutting
instrumentsinstruments which cleaves the underminedwhich cleaves the undermined
enamel asenamel as enamel hatchet, chisels, gingivalenamel hatchet, chisels, gingival
marginal trimmers and angle formermarginal trimmers and angle former or byor by rotaryrotary
instrumentsinstruments asas fissure burfissure bur andand abrasive stonesabrasive stones
which is used to plan the wall, give it properwhich is used to plan the wall, give it proper
inclination and bevel the cavo-surface margin.inclination and bevel the cavo-surface margin.

100. • According toAccording to Noyes principles,Noyes principles, the maintenance ofthe maintenance of
a stronger enamel wall at the cavo-surface anglea stronger enamel wall at the cavo-surface angle
demands that:demands that:
TheThe enamelenamel should rest upon sound dentin.should rest upon sound dentin.
The enamelThe enamel rodsrods forming the cavo-surface angleforming the cavo-surface angle
must have their inner ends resting on sound dentin.must have their inner ends resting on sound dentin.
The enamelThe enamel rodsrods forming the cavo-surface angleforming the cavo-surface angle
and must have their inner ends resting on soundand must have their inner ends resting on sound
dentin and the outer ends covered by a strongdentin and the outer ends covered by a strong
restorative material. This gives the strongestrestorative material. This gives the strongest
enamel wall possible. This is produced byenamel wall possible. This is produced by bevelingbeveling
the cavo-surface angle and using cast restoration.the cavo-surface angle and using cast restoration.

104. TheThe cava-surface anglecava-surface angle must be trimmed ormust be trimmed or
beveled so that the margins will not be exposedbeveled so that the margins will not be exposed
to injury in condensing the restorative materialto injury in condensing the restorative material
against it. This rule is applied particularly toagainst it. This rule is applied particularly to
Class I and to occlusal portions of Class II, i.e. inClass I and to occlusal portions of Class II, i.e. in
narrow occlusal cavities where the enamel rodsnarrow occlusal cavities where the enamel rods
are inclined inward so that the cavosurfaceare inclined inward so that the cavosurface
margin will be very sharp. The latter pattern canmargin will be very sharp. The latter pattern can
make the enamel rods extremely susceptible tomake the enamel rods extremely susceptible to
injury, so they have to be trimmed or beveled toinjury, so they have to be trimmed or beveled to
prevent this type of marginal failure.prevent this type of marginal failure.

105. • Factors affecting the cavo-surface angle:Factors affecting the cavo-surface angle:
The type ofThe type of restorative materialrestorative material and itsand its
physical properties.physical properties.
TheThe stressesstresses acting on the cavity margin andacting on the cavity margin and
the functional forces.the functional forces.
TheThe locationlocation of cavity margin and theof cavity margin and the
direction of the enamel rods at this site.direction of the enamel rods at this site.
The condition ofThe condition of enamelenamel (friability).(friability).
PulpPulp vitality,vitality, root canal treated teeth requireroot canal treated teeth require
reinforcement.reinforcement.
EstheticEsthetic demands, labial undermined enamel isdemands, labial undermined enamel is
left for esthetics.left for esthetics.

106. • Types of cavo-surface bevels:Types of cavo-surface bevels:
I.I. Short bevel:Short bevel: extends for only a part of theextends for only a part of the
thickness of enamel (outer part), it is indicatedthickness of enamel (outer part), it is indicated
withwith cast gold restorationcast gold restoration to protect enamelto protect enamel
rods and facilitate burnishing of the ductile goldrods and facilitate burnishing of the ductile gold
for protection of the cement line (indicated infor protection of the cement line (indicated in
shallowshallow cavity). It is also used withcavity). It is also used with resinresin
composite restorationcomposite restoration for convenient etching; itfor convenient etching; it
exposes ends of rods rather than sides, itexposes ends of rods rather than sides, it
refreshes the enamel surface and improvesrefreshes the enamel surface and improves
esthetics by degradation between the opticalesthetics by degradation between the optical
qualities of the restoration and the toothqualities of the restoration and the tooth
structure.structure.

107. • Finally, it is indicated forFinally, it is indicated for gold foilgold foil
restoration for protection of the marginalrestoration for protection of the marginal
enamel during using a mallet for forcefulenamel during using a mallet for forceful
condensation of the restoration.condensation of the restoration.

108. II.II. Long bevel:Long bevel: extends from cavo-surfaceextends from cavo-surface
angle to dentin-enamel junction taking theangle to dentin-enamel junction taking the
full enamel thickness. Itfull enamel thickness. It was indicatedwas indicated withwith
cast restorationcast restoration in deep cavities for furtherin deep cavities for further
protection of enamel. It is also used withprotection of enamel. It is also used with
resin compositeresin composite when the cavity preparationwhen the cavity preparation
details are not retaining enough for thedetails are not retaining enough for the
restorations.restorations.

109. III.III. Hollow ground bevel:Hollow ground bevel: it is ground in ait is ground in a
concave manner about two thirds of theconcave manner about two thirds of the
enamel wall thickness so the cavity marginenamel wall thickness so the cavity margin
will have a right-angled cavo-surface marginwill have a right-angled cavo-surface margin
(butt joint) between the restorative material(butt joint) between the restorative material
and the marginal enamel.and the marginal enamel.
IV.IV. Counter bevel:Counter bevel: it is indicated in an onlayit is indicated in an onlay
restoration (inlay with cusp overlay). Cuspalrestoration (inlay with cusp overlay). Cuspal
coverage is done to protect the weak cusps ofcoverage is done to protect the weak cusps of
teeth from fracture.teeth from fracture.

112. 6.6. Toilet of the cavity:Toilet of the cavity:
This is the final step in cavity preparationThis is the final step in cavity preparation
prior to the restoration. It comprises allprior to the restoration. It comprises all
procedures employed to prepare the cavity toprocedures employed to prepare the cavity to
receive the restorative material according to itsreceive the restorative material according to its
type. No medicaments should be used at thistype. No medicaments should be used at this
stage. The cavity should be perfectly clean andstage. The cavity should be perfectly clean and
dry before insertion of the restoration. Thedry before insertion of the restoration. The
cavity should be lined and/or sub-based andcavity should be lined and/or sub-based and
based to provide pulp protection and the tissuesbased to provide pulp protection and the tissues
of the tooth conditioned, if needed, to receiveof the tooth conditioned, if needed, to receive
the entitled restorative material.the entitled restorative material.

113. • Objectives:Objectives:
Elimination of bacteria, debris and saliva.Elimination of bacteria, debris and saliva.
Removal of remnants of dentin chips andRemoval of remnants of dentin chips and
temporary restoration.temporary restoration.
To improve adaptation and hinder theTo improve adaptation and hinder the
recurrence of decay around the restoration.recurrence of decay around the restoration.
Prepare and condition the tissues to receivePrepare and condition the tissues to receive
the entitled restorative material.the entitled restorative material.

114. • Technique:Technique:
The most accepted and safe way for toiletThe most accepted and safe way for toilet
of the cavity is to scrap the cavity walls andof the cavity is to scrap the cavity walls and
floors with a hand instrument, flush the cavityfloors with a hand instrument, flush the cavity
with water and dry it gently with air blowing.with water and dry it gently with air blowing.

116. • CContraindications:ontraindications:
A.A. Cavity sterilizersCavity sterilizers as phenol since they provedas phenol since they proved
to beto be invalidinvalid in decreasing the recurrence ofin decreasing the recurrence of
decay around the restorations and, especiallydecay around the restorations and, especially
if used with higher concentrations, they mayif used with higher concentrations, they may
irritateirritate the pulp especially in deep cavitiesthe pulp especially in deep cavities
and cause permanent irreversible damage.and cause permanent irreversible damage.

117. B.B. UsingUsing chemicalschemicals as alcoholic cavity cleansersas alcoholic cavity cleansers
may cause desiccation of dentin.may cause desiccation of dentin.
C.C. Excessive drynessExcessive dryness with air blast since it causeswith air blast since it causes
excessive dehydration of dentin (desiccation)excessive dehydration of dentin (desiccation)
and aspiration of odontoblastic nuclei withand aspiration of odontoblastic nuclei with
subsequent post restoration pain andsubsequent post restoration pain and
hypersensitivity.hypersensitivity.

118. • Special considerations:Special considerations:
After the discovery of the existence of theAfter the discovery of the existence of the
smear layersmear layer (Eik,(Eik, 1974) and the approval and1974) and the approval and
application of the concept of hybridizationapplication of the concept of hybridization
(Nakabayashi, 1984),(Nakabayashi, 1984), the step ofthe step of toilet of thetoilet of the
prepared cavityprepared cavity gained lots of attention andgained lots of attention and
importance. The microscopic smear layer hasimportance. The microscopic smear layer has
undergone lots of controversies concerning how toundergone lots of controversies concerning how to
deal with it for the sake of improving adaptabilitydeal with it for the sake of improving adaptability
and adhesion and pulpal protection. It was formerlyand adhesion and pulpal protection. It was formerly
thought that it has to be removed since it is athought that it has to be removed since it is a
contaminant and contains bacteria.contaminant and contains bacteria.

119. Smear layer on cut dentin surface

120. Longitudinal section in cut dentin showingLongitudinal section in cut dentin showing
smear layer (SL) and smear plug (SP)smear layer (SL) and smear plug (SP)

121. • However, its importance in pulpal protection,However, its importance in pulpal protection,
particularly the smear plugs obliterating theparticularly the smear plugs obliterating the
tubular apertures, cannot be overlooked.tubular apertures, cannot be overlooked.
• It is believed that the smear layer has to beIt is believed that the smear layer has to be
modifiedmodified for bonding resin restorationsfor bonding resin restorations
effectively to dentin. Conditioning of dentin iseffectively to dentin. Conditioning of dentin is
followed by resin impregnation which leads tofollowed by resin impregnation which leads to
hybridization, or the formation of the hybridhybridization, or the formation of the hybrid
layer, which is considered a successful protectivelayer, which is considered a successful protective
layer to the pulp.layer to the pulp.

122. Thank YouThank You