Dental bonding agents seminar guide

BONDING AGENTSBONDING AGENTS
Seminar on
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
www.indiandentalacademy.comwww.indiandentalacademy.com

CONTENTSCONTENTS
 INTRODUCTIONINTRODUCTION
 HISTORICAL BACK GROUNDHISTORICAL BACK GROUND
 PRINCIPLES OF ADHESIONPRINCIPLES OF ADHESION
 REQUIREMENTS FOR ADHESIONREQUIREMENTS FOR ADHESION
 MECHANISMS OF ADHESIONMECHANISMS OF ADHESION
 COMPOSITION AND MICROMORPHOLOGYCOMPOSITION AND MICROMORPHOLOGY
OF ENAMELOF ENAMEL
 ENAMEL ADHESIONENAMEL ADHESION
 ENAMEL BONDING AGENTSENAMEL BONDING AGENTS
 COMPOSITION AND MICROMORPHOLOGYCOMPOSITION AND MICROMORPHOLOGY
OF DENTINOF DENTIN
 DENTIN ADHESIONDENTIN ADHESION

 FACTORS AFFECTING ADHESIONFACTORS AFFECTING ADHESION
 DENTIN SMEAR LAYERDENTIN SMEAR LAYER
 DENTIN CONDITIONERSDENTIN CONDITIONERS
 PRIMERSPRIMERS
 ROLE OF HYBRID LAYERROLE OF HYBRID LAYER
 REQUIREMENTS OF BONDING AGENTSREQUIREMENTS OF BONDING AGENTS
 CLASSIFICATION OF BONDING AGENTSCLASSIFICATION OF BONDING AGENTS
 MODREN CLASSIFICATION OF ADHESIVESMODREN CLASSIFICATION OF ADHESIVES
 MOIST VERSUS DRY DENTIN BONDINGMOIST VERSUS DRY DENTIN BONDING
 ROLE OF PROTIENS IN DENTIN BONDINGROLE OF PROTIENS IN DENTIN BONDING
 MICROLEAKAGEMICROLEAKAGE
 BIOCOMPATIBILITYBIOCOMPATIBILITY
 CONCLUSIONCONCLUSION
 BIBLOGRAPHYBIBLOGRAPHY

CLINICAL FACTORS AFFECTINGCLINICAL FACTORS AFFECTING
ADHESION:ADHESION:
1.1. Salivary and / or blood contaminationSalivary and / or blood contamination: -: -
Difficulty in controlling saliva or blood whileDifficulty in controlling saliva or blood while
accomplishing restorative therapy is aaccomplishing restorative therapy is a
significant challenge, these contaminants cansignificant challenge, these contaminants can
influence some adhesion concepts in ainfluence some adhesion concepts in a
negative manner. Although dentin is wetnegative manner. Although dentin is wet
substance, the constituents of saliva and bloodsubstance, the constituents of saliva and blood
create an environment that can destroy dentincreate an environment that can destroy dentin
bonding.bonding.

Thus for years both textbooks ofThus for years both textbooks of
operative dentistry and many adhesiveoperative dentistry and many adhesive
manufacturers have recommended themanufacturers have recommended the
use of rubber dam for proper isolationuse of rubber dam for proper isolation
and prevention of cavity contamination.and prevention of cavity contamination.

 Fritz et alFritz et al studied the effect of salivarystudied the effect of salivary
contamination during bonding procedures,contamination during bonding procedures,
on the bond strength. They stated thaton the bond strength. They stated that
any kind of contamination of the bondingany kind of contamination of the bonding
area should be avoided which is still bestarea should be avoided which is still best
accomplished with rubber dam. Oneaccomplished with rubber dam. One
bottle bonding agents have the advantagebottle bonding agents have the advantage
that in contrast to previous generationthat in contrast to previous generation
adhesives; they are less sensitive toadhesives; they are less sensitive to
salivary contamination of etched enamelsalivary contamination of etched enamel
and dentin.and dentin.

They concluded that:They concluded that:
 Air-drying of the contaminated area mustAir-drying of the contaminated area must
strictly be avoided.strictly be avoided.
 Contamination of the uncured adhesive isContamination of the uncured adhesive is
not critical because saliva and adhesive arenot critical because saliva and adhesive are
simply cleaned and the adhesive is reapplied.simply cleaned and the adhesive is reapplied.
 Any contamination of already cured adhesiveAny contamination of already cured adhesive
layer seriously compromises the bond, nolayer seriously compromises the bond, no
matter how carefully the contaminant ismatter how carefully the contaminant is
rinsed; this situation calls for resurfacing ofrinsed; this situation calls for resurfacing of
the cavity and repetition of the entirethe cavity and repetition of the entire
bonding procedure.bonding procedure.

 T Kaneshima et al, in 2001, conducted aT Kaneshima et al, in 2001, conducted a
study to evaluate the influence of bloodstudy to evaluate the influence of blood
contamination on bond strengths. Thecontamination on bond strengths. The
results obtained may be summarized asresults obtained may be summarized as
follows:follows:
If blood contamination occurred beforeIf blood contamination occurred before
collagen fibers were exposed by eithercollagen fibers were exposed by either
phosphoric acid etching or self-etchingphosphoric acid etching or self-etching
primer application, the contaminationprimer application, the contamination
had almost no influence on bondhad almost no influence on bond
strength.strength.

 Blood contamination of the dentin surfaceBlood contamination of the dentin surface
where collagen fibers had been exposedwhere collagen fibers had been exposed
decreased the bond strength even if thedecreased the bond strength even if the
blood was washed away with a stream ofblood was washed away with a stream of
water and air dried. However, when thewater and air dried. However, when the
contaminated collagen fibers werecontaminated collagen fibers were
dissolved or when blood contaminationdissolved or when blood contamination
occurred after the exposed collagen fibersoccurred after the exposed collagen fibers
were dissolved, the bond strength couldwere dissolved, the bond strength could
be maintained by rinsing the blood awaybe maintained by rinsing the blood away
and applying the self-etching dentinand applying the self-etching dentin
primer.primer.

The bond strength markedly decreasedThe bond strength markedly decreased
when blood contamination occurred afterwhen blood contamination occurred after
the self-etching primer application, butthe self-etching primer application, but
was restored by reapplying the primer.was restored by reapplying the primer.
 Based on these results, it is suggestedBased on these results, it is suggested
that if the contamination occurred on thethat if the contamination occurred on the
dentin where the self-etching dentin primerdentin where the self-etching dentin primer
had already been applied, thehad already been applied, the
contaminated surface should be rinsedcontaminated surface should be rinsed
with water, air dried, and recoated with thewith water, air dried, and recoated with the
dentin primer to restore the bond strengthdentin primer to restore the bond strength
potential.potential.

Moisture Contamination from AirMoisture Contamination from Air
syringessyringes::
 An unrecognized problem in most dentalAn unrecognized problem in most dental
offices is water leakage from air wateroffices is water leakage from air water
syringes. The source of leakage can besyringes. The source of leakage can be
lack of drying devices on airlines leadinglack of drying devices on airlines leading
from compressor, allowing wet air hasfrom compressor, allowing wet air has
carried to the syringe.carried to the syringe.

Oil contamination of hand piece or AirOil contamination of hand piece or Air
water syringewater syringe: -: -
 Adhesives combined with oilAdhesives combined with oil
contamination provided an unpredictablecontamination provided an unpredictable
clinical result and potential clinical failure.clinical result and potential clinical failure.
Observation of oil present in the airlines isObservation of oil present in the airlines is
not difficult.not difficult.

 A simple test may be conducted byA simple test may be conducted by
blowing air from air syringe or hand pieceblowing air from air syringe or hand piece
on to a dry impermeable surface such ason to a dry impermeable surface such as
glass slab or dry rubber glove andglass slab or dry rubber glove and
observing any residue that is present. Oilobserving any residue that is present. Oil
appears similar to water on dry surface butappears similar to water on dry surface but
will not evaporate. Water will evaporatewill not evaporate. Water will evaporate
from the test surface. Removing all oilfrom the test surface. Removing all oil
from dental airlines should be thefrom dental airlines should be the
immediate objective. Oil filters should beimmediate objective. Oil filters should be
placed after the air compressor and beforeplaced after the air compressor and before
the air syringe or hand piece.the air syringe or hand piece.

 However, Bruno T. Rosa et al conducted aHowever, Bruno T. Rosa et al conducted a
study to evaluate resin bond strength tostudy to evaluate resin bond strength to
enamel contaminated with handpiece oil.enamel contaminated with handpiece oil.
The result of this study showed that- allThe result of this study showed that- all
bonding systems tested in this study havebonding systems tested in this study have
a mean shear bond strength of at least 20a mean shear bond strength of at least 20
Mpa to dry, uncontaminated etchedMpa to dry, uncontaminated etched
enamel. In both situations ofenamel. In both situations of
contamination with oil, before or aftercontamination with oil, before or after
etching, the mean shear bond strengthetching, the mean shear bond strength
was atleast 18 MPa for all adhesives,was atleast 18 MPa for all adhesives,
which indicates that oil contamination hadwhich indicates that oil contamination had
little effect on bondinglittle effect on bonding

Surface roughness of tooth surfaceSurface roughness of tooth surface:: --
 Use of diamonds for tooth preparation isUse of diamonds for tooth preparation is
most common in clinical dentistry.most common in clinical dentistry.
Diamonds create irregularities in toothDiamonds create irregularities in tooth
structure that is related directly to the size ofstructure that is related directly to the size of
the diamond particles used on the diamondthe diamond particles used on the diamond
abrasive instrument. Increased surface areaabrasive instrument. Increased surface area
created by surface roughness explains thecreated by surface roughness explains the
slight better bonds. It is possible thatslight better bonds. It is possible that
mechanical retention may be increasedmechanical retention may be increased
slightly by the microscopic roughnessslightly by the microscopic roughness
produced on dentin or enamel by cuttingproduced on dentin or enamel by cutting
instruments .instruments .

Mechanical under cuts in toothMechanical under cuts in tooth
preparationpreparation: -: -
 Since, the beginning of dentistry, mechanicalSince, the beginning of dentistry, mechanical
under cuts has been placed in toothunder cuts has been placed in tooth
preparation to provide retention forpreparation to provide retention for
subsequently used restorative materials. Ifsubsequently used restorative materials. If
undercuts are present in tooth structure, theyundercuts are present in tooth structure, they
hold restorative materials from bodilyhold restorative materials from bodily
dislodgment from the preparations, and theydislodgment from the preparations, and they
may also resist some microscopic movementmay also resist some microscopic movement
of the restorative material caused by thermalof the restorative material caused by thermal
or polymerization influences.or polymerization influences.

 Therefore, restorations with traditional dentinTherefore, restorations with traditional dentin
undercuts as well as chemical bonding, mayundercuts as well as chemical bonding, may
produce better results, such as less leakageproduce better results, such as less leakage
than those depending on adhesive alone.than those depending on adhesive alone.
(Clim 1990). Whereas in a recent review of(Clim 1990). Whereas in a recent review of
literature, Gordon J. Christensen hasliterature, Gordon J. Christensen has
suggested “It seems logical to bondsuggested “It seems logical to bond
restorative materials to tooth structures,restorative materials to tooth structures,
reducing or eliminating the need to cut awayreducing or eliminating the need to cut away
enamel or dentin to produce retentiveenamel or dentin to produce retentive
grooves and undercuts, and reducinggrooves and undercuts, and reducing
leakage around restorations.”leakage around restorations.”

6.6. Presence of plaque, calculus, andPresence of plaque, calculus, and
extrinsic stains / debrisextrinsic stains / debris:: --
 Any enamel / dentin surface that requiresAny enamel / dentin surface that requires
bonding must be cleaned thoroughly beforebonding must be cleaned thoroughly before
the bonding procedure begins. Plaquethe bonding procedure begins. Plaque
present on the tooth surface preventspresent on the tooth surface prevents
etching with 37% phosphoric acid. Toothetching with 37% phosphoric acid. Tooth
surface stains and dental calculus if notsurface stains and dental calculus if not
removed will not permit bonding. The toothremoved will not permit bonding. The tooth
surface should be cleaned thoroughly beforesurface should be cleaned thoroughly before
bonding either by use of scalers, abrasivebonding either by use of scalers, abrasive
prophylactic pastes, rubber cups or evenprophylactic pastes, rubber cups or even
abrasive rotary instruments.abrasive rotary instruments.

TOOTH RELATED FACTORS AFFECTINGTOOTH RELATED FACTORS AFFECTING
ADHESIONADHESION
 1.1. Physico chemical properties of dentin thatPhysico chemical properties of dentin that
complicate dentinal adhesioncomplicate dentinal adhesion: -: -

 Mineralized dentin is relatively stiff whichMineralized dentin is relatively stiff which
varies with dentinal depth. Following acidvaries with dentinal depth. Following acid
etching the de-mineralized dentin matrixetching the de-mineralized dentin matrix
becomes very soft and elastic. Infact, thebecomes very soft and elastic. Infact, the
modulus of elasticity of demineralizedmodulus of elasticity of demineralized
dentinal matrix is only about 5Mpadentinal matrix is only about 5Mpa (Macid(Macid
et al 1996et al 1996), which is 100 times lower than), which is 100 times lower than
that of mineralized dentin. The clinicalthat of mineralized dentin. The clinical
implication of this low stiffness is that theimplication of this low stiffness is that the
fibril network can easily collapse when air-fibril network can easily collapse when air-
dried, there by interfering with the up takedried, there by interfering with the up take
of adhesive monomers.of adhesive monomers.

 Further the permeability of bondingFurther the permeability of bonding
substrates to monomers and monomersubstrates to monomers and monomer
diffusability in to the substrates are essentialdiffusability in to the substrates are essential
factors for the hybridization of resins infactors for the hybridization of resins in
dental substrates. Mineralized dentinaldental substrates. Mineralized dentinal
matrix is relatively impermeable.matrix is relatively impermeable.
Permeability refers the ability of substance toPermeability refers the ability of substance to
move across diffusion Barrier (i.e. amove across diffusion Barrier (i.e. a
substrate). Two types of dentinalsubstrate). Two types of dentinal
permeability must be considered. Thepermeability must be considered. The
diffusion of substances through tubulesdiffusion of substances through tubules
filled with dentinal fluid to reach the pulp isfilled with dentinal fluid to reach the pulp is
intratubular dentinal permeability (Hansen etintratubular dentinal permeability (Hansen et
al. 1992; Hanks et al. 1994).al. 1992; Hanks et al. 1994).

 The second important type of dentinalThe second important type of dentinal
permeability is the diffusion of monomer intopermeability is the diffusion of monomer into
demineralized intertubular dentin, the dentindemineralized intertubular dentin, the dentin
between the tubules. This is referred to asbetween the tubules. This is referred to as
intertubular dentinal permeability. After theintertubular dentinal permeability. After the
surface is acid etched and rinsed with water,surface is acid etched and rinsed with water,
these spaces are filled with water. It isthese spaces are filled with water. It is
through these spaces that adhesivethrough these spaces that adhesive
monomer must diffuse if it has to infiltratemonomer must diffuse if it has to infiltrate
the demineralized dentinal matrix. Boththe demineralized dentinal matrix. Both
intratubular and intertubular dentinalintratubular and intertubular dentinal
permeability are important in dentin bonding.permeability are important in dentin bonding.

 Along with this dentinal permeability andAlong with this dentinal permeability and
consequent internal dentinal wetness,consequent internal dentinal wetness,
these depend on several factors like thethese depend on several factors like the
diameter and the length of the tubule, thediameter and the length of the tubule, the
viscosity of the dentinal fluid,the surfaceviscosity of the dentinal fluid,the surface
area available for diffusion, the patency ofarea available for diffusion, the patency of
the tubules and rate of removal ofthe tubules and rate of removal of
substances. The variability in dentinalsubstances. The variability in dentinal
permeability makes it a more difficultpermeability makes it a more difficult
substrate for bonding.substrate for bonding.

 Dentinal tubules permit adhesiveDentinal tubules permit adhesive
monomer to go down to the tubules formonomer to go down to the tubules for
varying distances. Most tubules containvarying distances. Most tubules contain
multiple lateral branches that radiate 2 to 6multiple lateral branches that radiate 2 to 6
um from the lumen and they provideum from the lumen and they provide
another route for monomer infiltration ofanother route for monomer infiltration of
hybrid layerhybrid layer (Mjor and Nardaul .1996.)(Mjor and Nardaul .1996.)

 The resin monomers penetrate acid etchedThe resin monomers penetrate acid etched
collagen fibrils through the spaces that cancollagen fibrils through the spaces that can
swell or shrink depending on the bondingswell or shrink depending on the bonding
conditions. Under some conditions (highconditions. Under some conditions (high
water concentration, acidic pH) the collagenwater concentration, acidic pH) the collagen
fibrils might swell slightly and reduce thefibrils might swell slightly and reduce the
width of the peri fibrillar spaces making itwidth of the peri fibrillar spaces making it
more difficult for primer monomers tomore difficult for primer monomers to
infiltrate the collagen network. Under otherinfiltrate the collagen network. Under other
conditions (air drying, dehydration by waterconditions (air drying, dehydration by water
miscible organic solvents) the collagenmiscible organic solvents) the collagen
fibrils may shrink (decreasing their diameter)fibrils may shrink (decreasing their diameter)
there by bringing the adjacent fibrils in to anthere by bringing the adjacent fibrils in to an
intimate contact with each other.intimate contact with each other.

 As a result the collagen peptides mayAs a result the collagen peptides may
form inter molecular hydrogen bonds withform inter molecular hydrogen bonds with
the nearest neighboring collagen peptides,the nearest neighboring collagen peptides,
which may contribute to further collapse ofwhich may contribute to further collapse of
the network by causing shortening of thethe network by causing shortening of the
fibrils and an increase in stiffnessfibrils and an increase in stiffness (Maciel(Maciel
et at 1996et at 1996). So over drying of collagen). So over drying of collagen
fibrils should be avoided.fibrils should be avoided.

2.2. Fluoride content of teethFluoride content of teeth
 Increased fluoride content of enamel hasIncreased fluoride content of enamel has
been shown to resist acid etching. Thisbeen shown to resist acid etching. This
reduction is not significant clinically if thereduction is not significant clinically if the
etching time is increased to allow moreetching time is increased to allow more
time for the acid to etch the enameltime for the acid to etch the enamel
surface and produce more roughness.surface and produce more roughness.
Clinicians are now etching apparentlyClinicians are now etching apparently
normal enamel for 15 sec and enamel thatnormal enamel for 15 sec and enamel that
shows signs of fluoridation for double thatshows signs of fluoridation for double that
time or more.time or more.

3.3. Dentinal canal characteristics: -Dentinal canal characteristics: -
 Dentinal canals at the external surface ofDentinal canals at the external surface of
roots or near the dentino enamel junctionroots or near the dentino enamel junction
have small diameters. Whereas dentinalhave small diameters. Whereas dentinal
canals close to the pulp are larger incanals close to the pulp are larger in
diameter. Old dentin has smaller dentinaldiameter. Old dentin has smaller dentinal
canals, while new dentin has largercanals, while new dentin has larger
dentinal canalsdentinal canals (pashley 1990).(pashley 1990).

4.4. Transformed dentin surface due toTransformed dentin surface due to
physiological and pathologicalphysiological and pathological process: -process: -
 Structural changes can occur in theStructural changes can occur in the
dentinal tubule due to carious, erosive anddentinal tubule due to carious, erosive and
abrasive processes and physiologicalabrasive processes and physiological
aging. In carious instances the lumen ofaging. In carious instances the lumen of
the dentinal tubules are very narrow orthe dentinal tubules are very narrow or
may even be obliterated by deposition ofmay even be obliterated by deposition of
intratubular crystals and apposition ofintratubular crystals and apposition of
irregular sclerotic dentin. Even repairativeirregular sclerotic dentin. Even repairative
dentin forms at the pulpal aspect of thedentin forms at the pulpal aspect of the
lesion.lesion.

 In the normal dentin the odontoblasticIn the normal dentin the odontoblastic
process extend through out the entireprocess extend through out the entire
thickness of dentin but in the case ofthickness of dentin but in the case of
carious dentin, they disappear at thecarious dentin, they disappear at the
bottom of the carious lesions, collapsingbottom of the carious lesions, collapsing
with fringe like ends.with fringe like ends.
 This results in reduction of dentinThis results in reduction of dentin
permeability. Further permeability ispermeability. Further permeability is
reduced in aged sound dentin due toreduced in aged sound dentin due to
progressive deposition of peritubularprogressive deposition of peritubular
dentin and crystal formation in the tubules.dentin and crystal formation in the tubules.

 AR Yazici et al conducted a study in 2004AR Yazici et al conducted a study in 2004
to evaluate the bond strengths of soundto evaluate the bond strengths of sound
versus caries-effected dentin using a self-versus caries-effected dentin using a self-
etching adhesive system, Clearfil SEetching adhesive system, Clearfil SE
Bond. The results of this in vitro studyBond. The results of this in vitro study
indicated that the bond strength of theindicated that the bond strength of the
self-etching adhesive system, Clearfil SEself-etching adhesive system, Clearfil SE
Bond to sound dentin was greater than toBond to sound dentin was greater than to
caries affected dentin.caries affected dentin.

 Whereas a recent study by A. Sengun etWhereas a recent study by A. Sengun et
al has shown that the bond strengths ofal has shown that the bond strengths of
Clearfil SE was similar to both cariesClearfil SE was similar to both caries
affected and normal dentinaffected and normal dentin
 S. M. Kwong et al conducted a study toS. M. Kwong et al conducted a study to
evaluate the bond strengths to scleroticevaluate the bond strengths to sclerotic
dentin using a self-etching and a total-dentin using a self-etching and a total-
etching technique and they concluded thatetching technique and they concluded that
removal of the surface layers of scleroticremoval of the surface layers of sclerotic
dentin and/or conditioning with strongerdentin and/or conditioning with stronger
acids may be beneficial to obtain strongeracids may be beneficial to obtain stronger
bonding to sclerotic dentin.bonding to sclerotic dentin.

The dentin smear layer and permeability:The dentin smear layer and permeability:
 When the tooth surface is instrumentedWhen the tooth surface is instrumented
with rotary and manual instruments duringwith rotary and manual instruments during
cavity preparation, cutting debris iscavity preparation, cutting debris is
smeared over the enamel and dentinalsmeared over the enamel and dentinal
surfaces what is termed the smear layer.surfaces what is termed the smear layer.

 The burnishing action of cuttingThe burnishing action of cutting
instruments generate a considerableinstruments generate a considerable
amount of frictional heat locally, so thatamount of frictional heat locally, so that
the smear layer gets attached to thethe smear layer gets attached to the
underlying surface in a manner thatunderlying surface in a manner that
prevents it from being rinsed off orprevents it from being rinsed off or
scrubbed away. This smear debrisscrubbed away. This smear debris
occludes the dentinal tubules with theoccludes the dentinal tubules with the
formation of smear plugs which affect theformation of smear plugs which affect the
bonding negatively.bonding negatively.

DENTIN SMEAR LAYERDENTIN SMEAR LAYER
 Smear layerSmear layer - It is tenacious deposit of- It is tenacious deposit of
microscopic debris that covers enamelmicroscopic debris that covers enamel
and dentin surfaces and that have beenand dentin surfaces and that have been
created during the preparation of enamelcreated during the preparation of enamel
and dentin and its presence complicatesand dentin and its presence complicates
resin bonding.resin bonding. Eick and othersEick and others (1970)(1970)
first described this smear layer.first described this smear layer.

 When viewed under scanning electronWhen viewed under scanning electron
microscope the smear layer has anmicroscope the smear layer has an
amorphous, irregular and granularamorphous, irregular and granular
appearance that represents dentinalappearance that represents dentinal
shavings, hydroxy apatite, tissue debris,shavings, hydroxy apatite, tissue debris,
odontoblastic processes, obliteratedodontoblastic processes, obliterated
tubule orifices, bacteria, denaturedtubule orifices, bacteria, denatured
collagen etc.collagen etc.

Composition:Composition:
 The composition of smear layer reflects theThe composition of smear layer reflects the
composition of the dentin from which it iscomposition of the dentin from which it is
formed (Eick et al 1970). Thus the smearformed (Eick et al 1970). Thus the smear
layer in superficial normal dentin may have alayer in superficial normal dentin may have a
composition close to that of intertubularcomposition close to that of intertubular
dentin where as the composition of smeardentin where as the composition of smear
layer in deep dentin would reflect its degreelayer in deep dentin would reflect its degree
of mineralization. However smear layer foundof mineralization. However smear layer found
on deep dentin contains more organicon deep dentin contains more organic
component than those found on thecomponent than those found on the
superficial dentin.superficial dentin.

 Scanning electron microscopicScanning electron microscopic
examination has disclosed that itsexamination has disclosed that its
composition is both organic and inorganic.composition is both organic and inorganic.
The inorganic material in the smear layerThe inorganic material in the smear layer
is made up of tooth structures and someis made up of tooth structures and some
non specific inorganic contaminants. Thenon specific inorganic contaminants. The
organic components may consists oforganic components may consists of
heated coagulated proteins, odontoblastsheated coagulated proteins, odontoblasts
plus saliva, blood cells andplus saliva, blood cells and
microorganism.microorganism.

Morphology:Morphology:
 The smear layer consists of two separateThe smear layer consists of two separate
layers, a superficial layer, and a layerlayers, a superficial layer, and a layer
loosely attached to the underlying dentin.loosely attached to the underlying dentin.
 Dentin debris enters the orifice of theDentin debris enters the orifice of the
dentinal tubules and acts as smear plugs,dentinal tubules and acts as smear plugs,
which can decrease the dentinwhich can decrease the dentin
permeability by up to 86% (Meryon et al,permeability by up to 86% (Meryon et al,
1987).1987).

 The smear layer is neither always firmlyThe smear layer is neither always firmly
attached nor it is continuous over theattached nor it is continuous over the
substrate. Clinically produced smear layersubstrate. Clinically produced smear layer
have an average depth of 1-5 µmhave an average depth of 1-5 µm
(Goldman et at 1981, Madder et at 1984).(Goldman et at 1981, Madder et at 1984).
The depth entering the dentinal tubuleThe depth entering the dentinal tubule
may vary from a few um up to 40 µm.may vary from a few um up to 40 µm.

 Cengiz et at 1970 proposed that theCengiz et at 1970 proposed that the
penetration of smear layer into dentinalpenetration of smear layer into dentinal
tubules could be caused by capillarytubules could be caused by capillary
action as a result of adhesive forcesaction as a result of adhesive forces
between the dentinal tubules and thebetween the dentinal tubules and the
smear material. One can conclude that asmear material. One can conclude that a
smear layer is present on all tooth that aresmear layer is present on all tooth that are
prepared for restorative purpose unlessprepared for restorative purpose unless
the dentin surface was treated with anthe dentin surface was treated with an
acid or a chelating agent.acid or a chelating agent.

Several factors may cause the depth ofSeveral factors may cause the depth of
smear layer to varysmear layer to vary::
 dry or wet cutting of dentindry or wet cutting of dentin
 type of instrument usedtype of instrument used
 area and composition of dentinarea and composition of dentin

 Cutting the tooth without a water spray willCutting the tooth without a water spray will
produce a thicker layer of dentin debrisproduce a thicker layer of dentin debris
and the use of coarse diamond bursand the use of coarse diamond burs
produce a thicker smear layer than theproduce a thicker smear layer than the
use of carbide burs.use of carbide burs.
 Both steel and tungsten carbide burs showBoth steel and tungsten carbide burs show
a rapid detoriation of the cutting edges,a rapid detoriation of the cutting edges,
which significantly diminishes the cuttingwhich significantly diminishes the cutting
efficiency of the bur, probably increasesefficiency of the bur, probably increases
frictional heat and causes smearing.frictional heat and causes smearing.

 A significant difference exits when theA significant difference exits when the
burs are used with or without a coolant ofburs are used with or without a coolant of
water spray. In the absence of coolantwater spray. In the absence of coolant
smeared debris can be found commonlysmeared debris can be found commonly
on the surface. The smeared debris doeson the surface. The smeared debris does
not form a continuous layer but exists asnot form a continuous layer but exists as
localized islands with discontinuitieslocalized islands with discontinuities
exposing the underlying dentin. Coolant ofexposing the underlying dentin. Coolant of
water spray does not prevent smearingwater spray does not prevent smearing
but appears to significantly reduce thebut appears to significantly reduce the
amount and distribution of it.amount and distribution of it.

 In addition, its composition is influencedIn addition, its composition is influenced
by the area of dentin where it isby the area of dentin where it is
generated, because of varying organic togenerated, because of varying organic to
inorganic component ratios andinorganic component ratios and
percentage of dentinal tubules. All ofpercentage of dentinal tubules. All of
these variables can affect the integrity,these variables can affect the integrity,
morphology and composition of the smearmorphology and composition of the smear
layer and perhaps its potential to bondlayer and perhaps its potential to bond
with a dentin bonding agent.with a dentin bonding agent.

REMOVAL OF SMEAR LAYERREMOVAL OF SMEAR LAYER
 There are two divergent opinions aboutThere are two divergent opinions about
smear layer treatment. Some believe thatsmear layer treatment. Some believe that
the smear layer acts as an effectivethe smear layer acts as an effective
natural cavity liner that seals the dentinalnatural cavity liner that seals the dentinal
tubules and reduces permeability, makingtubules and reduces permeability, making
the smear a clinical asset. Other arguesthe smear a clinical asset. Other argues
that the smear layer interferes withthat the smear layer interferes with
adhesion of restorative materials, servingadhesion of restorative materials, serving
as focus of bacteria, and therefore itas focus of bacteria, and therefore it
should be removed.should be removed.

 Brannstrom et al reported that the smearBrannstrom et al reported that the smear
layer, which was firmly attached to thelayer, which was firmly attached to the
dentin initially, became loose and wasdentin initially, became loose and was
largely replaced by bacteria and fluid withlargely replaced by bacteria and fluid with
in a few weeks.in a few weeks. PashleyPashley and othersand others
found that smear layer was effective infound that smear layer was effective in
restricting dentin permeability. In addition,restricting dentin permeability. In addition,
they found that shear bond strength tothey found that shear bond strength to
dentin with smear layer intact were higherdentin with smear layer intact were higher
than to dentin with smear layer removed.than to dentin with smear layer removed.

 The removal of smear layer andThe removal of smear layer and
demineralization of the dentin matrixdemineralization of the dentin matrix
may facilitate bonding through amay facilitate bonding through a
number of mechanisms.number of mechanisms.
1.1. The exposed collagen may provideThe exposed collagen may provide
reactive groups that can chemicallyreactive groups that can chemically
interact with bonding primers.interact with bonding primers.
2.2. Exposure of collagen fibrils and theirExposure of collagen fibrils and their
epsilon-amino groups, which mayepsilon-amino groups, which may
catalyze HEMA polymerization.catalyze HEMA polymerization.
3.3. Exposure of intact collagen thatExposure of intact collagen that
serves as a scaffold for the creationserves as a scaffold for the creation
of resin collagen hybrid layer.of resin collagen hybrid layer.

 The retention of smear layer not onlyThe retention of smear layer not only
lowers dentin permeability but also maylowers dentin permeability but also may
prevent the decrease in bond strengthprevent the decrease in bond strength
seen with some bonding systems, asseen with some bonding systems, as
deeper dentin is prepared. It also greatlydeeper dentin is prepared. It also greatly
lowers the effects of pulpal pressure onlowers the effects of pulpal pressure on
bond strengths.bond strengths.

 Another approach to avoiding the intrinsicAnother approach to avoiding the intrinsic
weakness of the smear layer is to removeweakness of the smear layer is to remove
it, but use some of the mineral in theit, but use some of the mineral in the
smear layer to react with ions in thesmear layer to react with ions in the
etching to form insoluble precipitates thatetching to form insoluble precipitates that
adhere to each other and to underlyingadhere to each other and to underlying
dentin matrix more firmly than did thedentin matrix more firmly than did the
original smear layer particles.original smear layer particles. Bowen et alBowen et al
used ferric oxalate in 2.5% nitric acid forused ferric oxalate in 2.5% nitric acid for
this purpose.this purpose.

 In order to chemically attach a restorativeIn order to chemically attach a restorative
system to tooth structure, one of thesystem to tooth structure, one of the
several options must be considered for theseveral options must be considered for the
smear layer. For the currently availablesmear layer. For the currently available
dentin bonding agents, the smear layer isdentin bonding agents, the smear layer is
managed in one of the five ways:managed in one of the five ways:

1.1. No treatment at allNo treatment at all: The smear layer is left: The smear layer is left
in places with out modification, and thein places with out modification, and the
dentin bonding agent applied directly to it.dentin bonding agent applied directly to it.
2.2. Dissolution of smear layerDissolution of smear layer: The dissolved: The dissolved
smear layer plays a part in chemicalsmear layer plays a part in chemical
attachment of dentin bonding agent toattachment of dentin bonding agent to
dentin.dentin.
3.3. The smear layer is removedThe smear layer is removed: The dentin: The dentin
bonding agent develops chemicalbonding agent develops chemical
attachment directly to intact dentin.attachment directly to intact dentin.
4.4. The modification of the smear layerThe modification of the smear layer: This: This
process theoretically improves theprocess theoretically improves the
attachment of smear layer to dentin.attachment of smear layer to dentin.
5.5. Smear layer removal and its replacementSmear layer removal and its replacement byby
another mediating agent.another mediating agent.

System that work by removing the smearSystem that work by removing the smear
layer:layer:
 All bond all etch technique.All bond all etch technique.
 Gluma bond system.Gluma bond system.
 Denthesive.Denthesive.
 Clear fill liner bond system.Clear fill liner bond system.
 Scotch bond 2.Scotch bond 2.
 Syntac.Syntac.
 Tenure.Tenure.
 X-R bond.X-R bond.

 Systems that work by preserve the smearSystems that work by preserve the smear
layerlayer
 All bond 2All bond 2
 Prisma universal Bond 3Prisma universal Bond 3
 Tripton,Tripton,
 Tokuso light bond.Tokuso light bond.
 Systems that work by dissolve the smearSystems that work by dissolve the smear
layerlayer
 XR – BondXR – Bond
 Imperva BondImperva Bond
 Systems that work by modification of theSystems that work by modification of the
smear layersmear layer
 All bondAll bond
 Prisma universal Bond - 2.Prisma universal Bond - 2.

Methods of Removal of Smear LayerMethods of Removal of Smear Layer
 Brannstrom’s group has publishedBrannstrom’s group has published
several articles describing the use ofseveral articles describing the use of
water, hydrogen peroxide,water, hydrogen peroxide,
benzalkonuim chloride, EDTA(Ethylenebenzalkonuim chloride, EDTA(Ethylene
Diamine TetraAcetic Acid) and otherDiamine TetraAcetic Acid) and other
agents to remove the smear layer.agents to remove the smear layer.

 He has formulated severalHe has formulated several
commercially available products likecommercially available products like
Tublicid, that are designed to removeTublicid, that are designed to remove
most smear layer without removingmost smear layer without removing
smear debris that has fallen intosmear debris that has fallen into
orifices of the tubules of the dentin.orifices of the tubules of the dentin.
Though this concept is ideal, it isThough this concept is ideal, it is
difficult to achieve clinically because ofdifficult to achieve clinically because of
complex geometry of many cavitiescomplex geometry of many cavities
and difficulty in obtaining adequateand difficulty in obtaining adequate
access.access.

1.1. Remove the smear layer by etchingRemove the smear layer by etching
with acid.with acid.
 Etching dentin with 6% citric acid forEtching dentin with 6% citric acid for
60 sec removes the entire smear layer60 sec removes the entire smear layer
as does 15 sec of etching with 37%as does 15 sec of etching with 37%
phosphoric acid.phosphoric acid.

 The advantages are:The advantages are:
 The smear layer is essentially removedThe smear layer is essentially removed
 The tubules are open and available forThe tubules are open and available for
retentionretention
 The surface collagen is exposed for possibleThe surface collagen is exposed for possible
covalent linkages with new experimentalcovalent linkages with new experimental
primers.primers.
 When smear layer is removed, one does notWhen smear layer is removed, one does not
have to worry about its slow dissolutionhave to worry about its slow dissolution
under a restoration leaving a void betweenunder a restoration leaving a void between
the cavity wall and the restoration, whichthe cavity wall and the restoration, which
might permit bacterial colonization.might permit bacterial colonization.

 The disadvantage is:The disadvantage is:
 In the absence of smear layer there isIn the absence of smear layer there is
no physical barrier to bacterialno physical barrier to bacterial
penetration of dentinal tubules.penetration of dentinal tubules.
2. Another entirely different approach2. Another entirely different approach
would lie to use a resin that wouldwould lie to use a resin that would
infiltrate through the entire thicknessinfiltrate through the entire thickness
of smear layer and either bond toof smear layer and either bond to
underlying matrix or penetrate intounderlying matrix or penetrate into
the tubules.the tubules.

3.To try to fix the smear layer by3.To try to fix the smear layer by
gluteraldehyde or tanning agents such asgluteraldehyde or tanning agents such as
tannic acids or ferric chloride.tannic acids or ferric chloride. The idea is toThe idea is to
increase the cross linking of exposedincrease the cross linking of exposed
collagen within the smear layer and betweencollagen within the smear layer and between
it and the matrix of the underlying dentin toit and the matrix of the underlying dentin to
improve its cohesion.improve its cohesion.
4.A fourth and most recent approach4.A fourth and most recent approach to theto the
problem is to remove the smear layer byproblem is to remove the smear layer by
etching with acid and replace it with anetching with acid and replace it with an
artificial smear layer composed by aartificial smear layer composed by a
crystaline precipitate.crystaline precipitate.
 Bowen has used this approach by treatingBowen has used this approach by treating
dentin with 5% ferric oxalate which replaceddentin with 5% ferric oxalate which replaced
the original smear layers.the original smear layers.

DENTIN CONDITIONERS: -DENTIN CONDITIONERS: -
 There is confusion regarding two terms –There is confusion regarding two terms –
etchants and conditioners. Acids such asetchants and conditioners. Acids such as
phosphoric, maleic, nitric, or citric are usedphosphoric, maleic, nitric, or citric are used
for partial or total removal of the smear layerfor partial or total removal of the smear layer
and superficial demineralization of theand superficial demineralization of the
underlying dentin. Such liquids or gels areunderlying dentin. Such liquids or gels are
termed etchants and may also be calledtermed etchants and may also be called
conditioners by some dental manufacturers.conditioners by some dental manufacturers.
Etching implies the dissolution of theEtching implies the dissolution of the
substrate, whereas conditioning involvessubstrate, whereas conditioning involves
cleaning structural alteration, and increasingcleaning structural alteration, and increasing
the adhesiveness of the substratethe adhesiveness of the substrate
( Jendresen and Glantz, 1981).( Jendresen and Glantz, 1981).www.indiandentalacademy.comwww.indiandentalacademy.com

 Conditioning of the dentin will be definedConditioning of the dentin will be defined
as any alteration of dentin done after theas any alteration of dentin done after the
creation of dentin cutting debris, termedcreation of dentin cutting debris, termed
the smear layer. The objective of dentinthe smear layer. The objective of dentin
conditioning is to create a surface capableconditioning is to create a surface capable
of micro mechanical and possibleof micro mechanical and possible
chemical bonding to a dentin bondingchemical bonding to a dentin bonding
agent. The principal effects ofagent. The principal effects of
conditioning of dentin may be classifiedconditioning of dentin may be classified
as:as:
 Physical changes.Physical changes.
 Chemical changes.Chemical changes.

 Physical changesPhysical changes::
1. Increase or decrease in the thickness and1. Increase or decrease in the thickness and
morphology of the smear layer.morphology of the smear layer.
2. Changes in the shape of the dentinal2. Changes in the shape of the dentinal
tubules.tubules.
 Chemical changesChemical changes::
1. Modifications of organic matter.1. Modifications of organic matter.
2. Decalcification of the inorganic matter.2. Decalcification of the inorganic matter.

 Conditioning of dentin may be done inConditioning of dentin may be done in
several means.several means.
 1) Chemical:1) Chemical:
a) Acidsa) Acids
 2) Thermal:2) Thermal:
a) Lasersa) Lasers
 3) Mechanical:3) Mechanical:
a) Abrasiona) Abrasion

CHEMICALCHEMICAL
 Acid conditionersAcid conditioners::
These acidic conditioners demineralizeThese acidic conditioners demineralize
dentin to a depth of at least 2-5dentin to a depth of at least 2-5 µµm. Them. The
factors that limit the depth offactors that limit the depth of
demineralization are:demineralization are:
 Type of acidType of acid
 Etching timeEtching time
 Strengthening of acidStrengthening of acid
 Buffering capacity of the dentin.Buffering capacity of the dentin.

 Historically several acids have beenHistorically several acids have been
researched as dentin conditioners. Theseresearched as dentin conditioners. These
include hydrochloric acid, oxalic acid,include hydrochloric acid, oxalic acid,
pyruvic acid, maleic acid, phosphoric acid,pyruvic acid, maleic acid, phosphoric acid,
10% citric acid, and 10% citric acid with10% citric acid, and 10% citric acid with
3% ferric chloride, 10% citric acid with3% ferric chloride, 10% citric acid with
20% calcium chloride, 2.5% nitric acid and20% calcium chloride, 2.5% nitric acid and
chelators like EDTA.chelators like EDTA.

Phosphoric acid: -Phosphoric acid: -
 It was the first dentin conditioner that wasIt was the first dentin conditioner that was
successfully used to remove the smearsuccessfully used to remove the smear
layer, etch the dentin and restore it withlayer, etch the dentin and restore it with
adhesive composite resin (adhesive composite resin (Fusayama andFusayama and
other, 1979other, 1979))

Scanning electron micrograph of etched
dentin showing exposed collagen fibers.

 This helps by removing the surface dentin,This helps by removing the surface dentin,
leaving a clean, well-defined etchingleaving a clean, well-defined etching
pattern where the tubules are enlargedpattern where the tubules are enlarged
into funnel shape. Phosphoric acid is theinto funnel shape. Phosphoric acid is the
acid of choice currently for the etchingacid of choice currently for the etching
purpose.purpose.
 However, controversy remains about theHowever, controversy remains about the
optimal concentration of H3PO4. Theoptimal concentration of H3PO4. The
most widely used concentrations used inmost widely used concentrations used in
clinical practice exceed 30% phosphoricclinical practice exceed 30% phosphoric
acid.acid.

Total etch/all etch technique:Total etch/all etch technique:
 FusayamaFusayama pioneered the research of totalpioneered the research of total
etching establishing the protocol foretching establishing the protocol for
simultaneous etching of dentin andsimultaneous etching of dentin and
enamel with phosphoric acid in 1979.enamel with phosphoric acid in 1979.
 Kuraray’s original clearfil new bondKuraray’s original clearfil new bond
system accomplishes the total etch usingsystem accomplishes the total etch using
37% phosphoric acid for 60 seconds.37% phosphoric acid for 60 seconds.
Bisco system uses 10% phosphoric acidBisco system uses 10% phosphoric acid
for 15sec in all etch technique.for 15sec in all etch technique.

THERMAL MODIFICATIONSTHERMAL MODIFICATIONS
 Lasers: -Lasers: -
 Hard tissue lasers in dentistry are anHard tissue lasers in dentistry are an
emerging technology. A pulsed Nd-YAGemerging technology. A pulsed Nd-YAG
laser will not disturb the pulp, even whenlaser will not disturb the pulp, even when
the approach is as close as 1the approach is as close as 1µµm. Most ofm. Most of
the research has been conducted on drythe research has been conducted on dry
dentin, but laser will operate on dentindentin, but laser will operate on dentin
immersed in saliva/water.immersed in saliva/water.

 The mechanism of dentin removal is throughThe mechanism of dentin removal is through
microscopic explosions caused by themicroscopic explosions caused by the
thermal transients. The carbonized, blackthermal transients. The carbonized, black
soot that results is easily washed off withsoot that results is easily washed off with
water. The laser treatment results inwater. The laser treatment results in
desensitized dentin, presumably bydesensitized dentin, presumably by
occlusion of the open and permeableocclusion of the open and permeable
dentinal tubules. Microorganisms anddentinal tubules. Microorganisms and
organic debris are eliminated from the lasedorganic debris are eliminated from the lased
surfaces. The laser decreases the organicsurfaces. The laser decreases the organic
fraction and increases the inorganic fractionfraction and increases the inorganic fraction
of the dentin surface.of the dentin surface.
 The bond strength increased by 60% whenThe bond strength increased by 60% when
this was done presumably by increasing thethis was done presumably by increasing the
bondable inorganic fraction of the dentinbondable inorganic fraction of the dentin
surface. The laser may create microsurface. The laser may create micro
mechanical retention (white and othersmechanical retention (white and otherswww.indiandentalacademy.comwww.indiandentalacademy.com

MECHANICAL MODIFICATIONSMECHANICAL MODIFICATIONS
 Micro-abrasionsMicro-abrasions
It is a mechanical means of modification ofIt is a mechanical means of modification of
dentin. Aluminum oxide is used for the purposedentin. Aluminum oxide is used for the purpose
of micro abrasion. It removes healthy as well asof micro abrasion. It removes healthy as well as
diseased dentin and results in a smear layer. Itsdiseased dentin and results in a smear layer. Its
abrasion action depends on the particle size asabrasion action depends on the particle size as
well as the velocity. The 0.5-micron or largerwell as the velocity. The 0.5-micron or larger
particles create a smear on the dentin andparticles create a smear on the dentin and
increase the surface area (Blake 1991). Theincrease the surface area (Blake 1991). The
smear layer formed might be used to enhancesmear layer formed might be used to enhance
the bond strengths of smear-mediated dentinthe bond strengths of smear-mediated dentin
bonding agents.bonding agents.

 An in vitro investigation of a comparison ofAn in vitro investigation of a comparison of
bond strengths of composite to etchedbond strengths of composite to etched
and air abraded human enamel surfacesand air abraded human enamel surfaces
was done by G.B. Gray et al in 2006. Theywas done by G.B. Gray et al in 2006. They
concluded composite resin applied toconcluded composite resin applied to
enamel surfaces prepared using an acidenamel surfaces prepared using an acid
etch procedure exhibited higher bondetch procedure exhibited higher bond
strengths than those prepared with airstrengths than those prepared with air
abrasion technology.abrasion technology.

PRIMERS:PRIMERS:
 Primer is a hydrophilic, low-viscocityPrimer is a hydrophilic, low-viscocity
monomer dissolved in solvents such asmonomer dissolved in solvents such as
water, acetone, or alcohol – are applied towater, acetone, or alcohol – are applied to
the etched or conditioned dentin substratethe etched or conditioned dentin substrate
but are not rinsed off.but are not rinsed off.

 Nowadays major advances have beenNowadays major advances have been
achieved in adhesion by the introduction ofachieved in adhesion by the introduction of
primers, which promote wetting of the dentinprimers, which promote wetting of the dentin
with the bonding agent, and penetration ofwith the bonding agent, and penetration of
the bonding agent into the dentin. Primerthe bonding agent into the dentin. Primer
monomers are amphiphilic i.e. they containmonomers are amphiphilic i.e. they contain
hydrophilic groups. E.g.: -OH, -COOH forhydrophilic groups. E.g.: -OH, -COOH for
better compatibility of the resin monomersbetter compatibility of the resin monomers
with the moist dentin, and hydrophobicwith the moist dentin, and hydrophobic
methacrylate groups for the co-methacrylate groups for the co-
polymerization with the bonding resin. Thepolymerization with the bonding resin. The
objective of this step is to transform theobjective of this step is to transform the
hydrophilic dentin surface in to ahydrophilic dentin surface in to a
hydrophobic and spongy state. Nakabayashihydrophobic and spongy state. Nakabayashi
and Pashley summarized the function ofand Pashley summarized the function of
dentin primer as “to maintain or recover thedentin primer as “to maintain or recover the
porosity of the demineralized dentin”.porosity of the demineralized dentin”.

 Primers are monomers dissolved inPrimers are monomers dissolved in
solvents . Organic solvents aid insolvents . Organic solvents aid in
displacing water, expanding or re-displacing water, expanding or re-
expanding the collagen fiber network andexpanding the collagen fiber network and
thus promoting the infiltration of thethus promoting the infiltration of the
monomer into the sub-micron ormonomer into the sub-micron or
nanometer sized spaces within thenanometer sized spaces within the
collagen fiber network.collagen fiber network.
 Besides HEMA, most of the primersBesides HEMA, most of the primers
contain other monomers such as NPG-contain other monomers such as NPG-
GMA, PMDM, BPDM and PENTA. MoreGMA, PMDM, BPDM and PENTA. More
recent primers also include a chemical /recent primers also include a chemical /
photo polymerization initiator so that theirphoto polymerization initiator so that their
monomers can be polymerized inside.monomers can be polymerized inside.www.indiandentalacademy.comwww.indiandentalacademy.com

WET VERSUS DRY BONDING:WET VERSUS DRY BONDING:
 The concept of ‘Moist’ or ‘Wet’ bondingThe concept of ‘Moist’ or ‘Wet’ bonding
technique was proposed by Dr. Johntechnique was proposed by Dr. John
Kanka (1990). Vital dentin is inherentlyKanka (1990). Vital dentin is inherently
wet; therefore complete drying of dentin iswet; therefore complete drying of dentin is
difficult to achieve clinically. Water hasdifficult to achieve clinically. Water has
been considered an obstacle for attainingbeen considered an obstacle for attaining
an effective adhesion of resins to dentin.an effective adhesion of resins to dentin.
With that in mind, research has shiftedWith that in mind, research has shifted
towards development of dentin adhesivestowards development of dentin adhesives
compatible with humid environments.compatible with humid environments.

 Most newer adhesives combineMost newer adhesives combine
hydrophilic and hydrophobic monomers inhydrophilic and hydrophobic monomers in
the same bottle, dissolved in an organicthe same bottle, dissolved in an organic
solvent such as ethanol or acetone. Thesolvent such as ethanol or acetone. The
“wet – bonding” technique prevents the“wet – bonding” technique prevents the
spatial alternations (i.e. collagen collapse)spatial alternations (i.e. collagen collapse)
that occur upon drying demineralizedthat occur upon drying demineralized
dentin, such alterations may prevent thedentin, such alterations may prevent the
monomers from penetrating labyrinth ofmonomers from penetrating labyrinth of
nano channels formed by dissolution ofnano channels formed by dissolution of
hydroxyapatite crystals between collagenhydroxyapatite crystals between collagen
fibers (Maciel KT et al 1996).fibers (Maciel KT et al 1996).

 The use of adhesive systems on moist dentin isThe use of adhesive systems on moist dentin is
made possible by incorporation of the organicmade possible by incorporation of the organic
solvents acetone or ethanol in primers orsolvents acetone or ethanol in primers or
adhesives. Because the solvent can displaceadhesives. Because the solvent can displace
water from both the dentin surface and the moistwater from both the dentin surface and the moist
collagen network, it promotes the infiltration ofcollagen network, it promotes the infiltration of
resin monomers throughout the nano spaces ofresin monomers throughout the nano spaces of
the dense collagen web. The “Wet bonding”the dense collagen web. The “Wet bonding”
technique has been shown repeatedly totechnique has been shown repeatedly to
enhance bond strengths because waterenhance bond strengths because water
preserves the porosity of collagen networkpreserves the porosity of collagen network
available for monomer inter diffusion (Kanca Javailable for monomer inter diffusion (Kanca J
1992).1992).

 If the dentin surface is dried with air, theIf the dentin surface is dried with air, the
collagen undergoes immediate collapsecollagen undergoes immediate collapse
and prevents resin monomers fromand prevents resin monomers from
penetrating (Carvalho RM et al 1996).penetrating (Carvalho RM et al 1996).
Kanca and Gwinnett (1992) recommendedKanca and Gwinnett (1992) recommended
that etched dentin should not be driedthat etched dentin should not be dried
before application of the bonding primer.before application of the bonding primer.

 The clinician must be aware that pooledThe clinician must be aware that pooled
moisture should not remain on the tooth,moisture should not remain on the tooth,
because excess water can dilute thebecause excess water can dilute the
primer and render it less effective. (Tay etprimer and render it less effective. (Tay et
al 1996). A glistening hydrated surface isal 1996). A glistening hydrated surface is
preferred. Many clinicians, however, stillpreferred. Many clinicians, however, still
dry the tooth preparation after rinsingdry the tooth preparation after rinsing
away the etching gel to check for theaway the etching gel to check for the
classic etched enamel appearance.classic etched enamel appearance.

 Because it is clinically impossible to dry enamelBecause it is clinically impossible to dry enamel
without simultaneously drying dentin, the dentinwithout simultaneously drying dentin, the dentin
collagen collapses easily upon air dryingcollagen collapses easily upon air drying
resulting in the closing of the micropores in theresulting in the closing of the micropores in the
exposed intertubular collagen (Tay FR andexposed intertubular collagen (Tay FR and
Gwinett AJ 1996) For acetone based water –Gwinett AJ 1996) For acetone based water –
free dentin bonding systems, the etched dentinfree dentin bonding systems, the etched dentin
surface must be rewetted before applying thesurface must be rewetted before applying the
adhesives. Rewetting the dried etched dentinadhesives. Rewetting the dried etched dentin
with water or with aqueous rewetting agents haswith water or with aqueous rewetting agents has
been demonstrated to restore bond strengthbeen demonstrated to restore bond strength
values and to raise the collapsed collagenvalues and to raise the collapsed collagen
network to a level similar to a “wet bondingnetwork to a level similar to a “wet bonding
technique” (Gwinett AJ 1994).technique” (Gwinett AJ 1994).

 Some authors have suggested that theSome authors have suggested that the
inclusion of water in the composition ofinclusion of water in the composition of
some adhesives may result in rewettingsome adhesives may result in rewetting
the collagen fibers in areas that are notthe collagen fibers in areas that are not
fully moist, thus opening the interfibrillarfully moist, thus opening the interfibrillar
spaces to the infiltration of the primingspaces to the infiltration of the priming
resin. Therefore the simultaneousresin. Therefore the simultaneous
inclusion of both an organic solvent andinclusion of both an organic solvent and
water may be fundamental for the bestwater may be fundamental for the best
infiltration of some adhesives intoinfiltration of some adhesives into
demineralized dentin. This could result indemineralized dentin. This could result in
a less technique-sensitive procedure.a less technique-sensitive procedure.

 A review of literature has showed that moistA review of literature has showed that moist
bonding is only essential for particular bondingbonding is only essential for particular bonding
systems with low water content of primer suchsystems with low water content of primer such
as all bond 2. The primer of all bond 2 containsas all bond 2. The primer of all bond 2 contains
acetone as solvent with only 5% of water. Inacetone as solvent with only 5% of water. In
contrast with water content of 20% or more (e.g.contrast with water content of 20% or more (e.g.
opti -bond FL, scotch bond multipurpose) areopti -bond FL, scotch bond multipurpose) are
able to re-expand the collapsed collagen due toable to re-expand the collapsed collagen due to
their intrinsic rewetting capacity. Acetone basedtheir intrinsic rewetting capacity. Acetone based
primers adhesive (e.g. prime and bond 2.1, one-primers adhesive (e.g. prime and bond 2.1, one-
step) have shown higher bond strengths andstep) have shown higher bond strengths and
reduced micro-leakage when a moist bondingreduced micro-leakage when a moist bonding
protocol is followed.protocol is followed.

 So, moist bonding is only mandatory inSo, moist bonding is only mandatory in
bonding system with minimal waterbonding system with minimal water
content of the primer / primer adhesives,content of the primer / primer adhesives,
while water based primers / primerwhile water based primers / primer
adhesives have shown to be less sensitiveadhesives have shown to be less sensitive
to variations in the moisture of the etchedto variations in the moisture of the etched
dentin surface.dentin surface.
 When etched dentin is dried using an airWhen etched dentin is dried using an air
syringe bond strength decreasesyringe bond strength decrease
substantially, especially for acetone andsubstantially, especially for acetone and
ethanol – based dentin adhesive systemsethanol – based dentin adhesive systems
(Kanca J 1992).(Kanca J 1992).

 When water is removed the elasticWhen water is removed the elastic
characteristics of collagen may be lost. Thecharacteristics of collagen may be lost. The
collapse of the collagen fibers upon drying maycollapse of the collagen fibers upon drying may
therefore be a result of the changes in thetherefore be a result of the changes in the
molecular arrangement. While in a wet state,molecular arrangement. While in a wet state,
wide gaps separate the collagen molecules fromwide gaps separate the collagen molecules from
each other, in a dry state, the molecules areeach other, in a dry state, the molecules are
arranged more compactly like a heap of cookedarranged more compactly like a heap of cooked
noodles. This is because extrafibrillar space innoodles. This is because extrafibrillar space in
hydrated Type I collagen are filled with water,hydrated Type I collagen are filled with water,
while dried collagen has fewer extrafibrillarwhile dried collagen has fewer extrafibrillar
spaces open for the penetration of thespaces open for the penetration of the
monomers included in the adhesive systems.monomers included in the adhesive systems.

 Water removal also may permit additionalWater removal also may permit additional
hydrogen bonds to form between collagenhydrogen bonds to form between collagen
molecules that were previously bonded to watermolecules that were previously bonded to water
molecules, leaving no interfibrillar space. Duringmolecules, leaving no interfibrillar space. During
air drying, water that occupies the interfibrillarair drying, water that occupies the interfibrillar
spaces previously filled with hydroxyapatitespaces previously filled with hydroxyapatite
crystals is lost by evaporation, resulting in acrystals is lost by evaporation, resulting in a
decrease of the volume of a collagen network todecrease of the volume of a collagen network to
approximately one third of its original volume.approximately one third of its original volume.
When air -dried demineralized dentin is rewetWhen air -dried demineralized dentin is rewet
with water, the collagen matrix may re – expandwith water, the collagen matrix may re – expand
and recover its primary dimensions to the levelsand recover its primary dimensions to the levels
of the original hydrated state (Maciel et al 1996).of the original hydrated state (Maciel et al 1996).

 This spatial re – expansion occurs because theThis spatial re – expansion occurs because the
spaces between fibers are refilled with water andspaces between fibers are refilled with water and
because Type I collagen itself is capable tobecause Type I collagen itself is capable to
undergoing expansion upon rehydration. Theundergoing expansion upon rehydration. The
stiffness of decalcified dentin increases whenstiffness of decalcified dentin increases when
the tissue is dehydrated either chemically inthe tissue is dehydrated either chemically in
water – miscible solvents or physically in air. Thewater – miscible solvents or physically in air. The
increase in stiffness is reversed whenincrease in stiffness is reversed when
specimens are rehydrated in water. Thereforespecimens are rehydrated in water. Therefore
rewetting dentin after air – drying to check forrewetting dentin after air – drying to check for
the enamel frosty aspect may be an acceptablethe enamel frosty aspect may be an acceptable
clinical procedure.clinical procedure.

 Clinically, it is very difficult to either assess orClinically, it is very difficult to either assess or
standardize the ideal amount of moisture thatstandardize the ideal amount of moisture that
should be left on the dentin surface before theshould be left on the dentin surface before the
application of the adhesive system. The idealapplication of the adhesive system. The ideal
dentin surface for moist bonding is visibly moistdentin surface for moist bonding is visibly moist
but without an excess of water leading to abut without an excess of water leading to a
meniscus on the surface. Ideally, water shouldmeniscus on the surface. Ideally, water should
form a uniform layer with out pooling (over wet)form a uniform layer with out pooling (over wet)
and with our dry areas (over dried). Therefore airand with our dry areas (over dried). Therefore air
drying with an air – water syringe after rinsing offdrying with an air – water syringe after rinsing off
the etching gel is not recommended because itthe etching gel is not recommended because it
cannot produce a uniform layer of water on thecannot produce a uniform layer of water on the
surface.surface.

 A recent study demonstrated that the excessA recent study demonstrated that the excess
water after rinsing the etching gel can bewater after rinsing the etching gel can be
removed with a damp cotton pellet, a disposableremoved with a damp cotton pellet, a disposable
brush, or a tissue paper without adverselybrush, or a tissue paper without adversely
affecting bond strengths.affecting bond strengths.
 Research has demonstrated that moist bondingResearch has demonstrated that moist bonding
increases the bond strengths of many bondingincreases the bond strengths of many bonding
systems. However the water present in betweensystems. However the water present in between
the fibrils should be displaced completely and ifthe fibrils should be displaced completely and if
too much water is present, the resin monomerstoo much water is present, the resin monomers
may not be able to successfully compete for themay not be able to successfully compete for the
collages fibril surface there by leaving a void.collages fibril surface there by leaving a void.

 Jorge Perdigao et al conducted a study toJorge Perdigao et al conducted a study to
determine the effect of solvent anddetermine the effect of solvent and
rewetting time on dentin adhesion. Theyrewetting time on dentin adhesion. They
concluded that:concluded that:

 When dentin is left moist, all DBSs resultWhen dentin is left moist, all DBSs result
in similar bond strengths regardless ofin similar bond strengths regardless of
their solvent.their solvent.
 water-based adhesives are less sensitivewater-based adhesives are less sensitive
to variations in surface moisture thanto variations in surface moisture than
ethanol or acetone-based DBSs.ethanol or acetone-based DBSs.
 Rewetting dentin after air drying restoresRewetting dentin after air drying restores
the bond strengths to the level obtainedthe bond strengths to the level obtained
on moist dentin, if rewetting is performedon moist dentin, if rewetting is performed
for twice as long as the air drying.for twice as long as the air drying.

 L Hitme et al, in 2002, conducted a study toL Hitme et al, in 2002, conducted a study to
evaluate the influence of drying and HEMAevaluate the influence of drying and HEMA
treatment on dentin wettability. They havetreatment on dentin wettability. They have
concluded that air-drying acid-etched dentinconcluded that air-drying acid-etched dentin
significantly decreased the spreading/infiltrationsignificantly decreased the spreading/infiltration
of water in comparison with blot drying. Re-of water in comparison with blot drying. Re-
wetting with water only partly restores thewetting with water only partly restores the
spreading/infiltration on etched and air-driedspreading/infiltration on etched and air-dried
dentin. However, HEMA primer prevents thedentin. However, HEMA primer prevents the
collagen collapse and restores the collapsedcollagen collapse and restores the collapsed
collagen network. Although multi-step dentincollagen network. Although multi-step dentin
bonding systems can be routinely used inbonding systems can be routinely used in
clinical practice because of their primers, the soclinical practice because of their primers, the so
called “one bottle” systems must be used onlycalled “one bottle” systems must be used only
on blot-dried dentin surfaces.on blot-dried dentin surfaces.

Application of primerApplication of primer
 Bonding can be carried out by applying primer toBonding can be carried out by applying primer to
a collapsed matrix followed by application ofa collapsed matrix followed by application of
bonding agent or else a primer and bondingbonding agent or else a primer and bonding
agent may be directly applied to a non-collapsedagent may be directly applied to a non-collapsed
demineralized dentin without the intermediatedemineralized dentin without the intermediate
step of primer application. In Prime and bondstep of primer application. In Prime and bond
and Bisco one step dental adhesive theyand Bisco one step dental adhesive they
combine the priming and bonding step.combine the priming and bonding step.


 Bonding to the smear layer covered dentinBonding to the smear layer covered dentin
was not very successful before 1990 aswas not very successful before 1990 as
the resins did not penetrate through thethe resins did not penetrate through the
smear layer and the smear layer was verysmear layer and the smear layer was very
weakweak (Tao et al 1988).(Tao et al 1988). This led mostThis led most
manufactures to use acidic conditioners.manufactures to use acidic conditioners.
How ever the resulting soft collagen richHow ever the resulting soft collagen rich
surface can collapse and interfere withsurface can collapse and interfere with
monomer infiltration.monomer infiltration.

 So in order to prevent this and to simplifySo in order to prevent this and to simplify
the number of bonding steps,the number of bonding steps, WatanabeWatanabe
(1990(1990) developed a new bonding system) developed a new bonding system
which was an aqueous solution of 20%which was an aqueous solution of 20%
phenyl-p in 30% HEMA. This self-etchingphenyl-p in 30% HEMA. This self-etching
and self-priming system providedand self-priming system provided
important new information on smear layerimportant new information on smear layer
as bonding substrates. The ideal self-as bonding substrates. The ideal self-
etching, self-priming bonding system isetching, self-priming bonding system is
one that can penetrate 2.0one that can penetrate 2.0µµm of smearm of smear
layer and engage underlying of dentin to alayer and engage underlying of dentin to a
depth of 1depth of 1 µµm.m.

Microscopic examination of attachmentsMicroscopic examination of attachments
produced by primer has shownproduced by primer has shown
deficiencies like:deficiencies like:
 Incomplete surface coverageIncomplete surface coverage
 Incomplete inter-fibrillar saturation with inIncomplete inter-fibrillar saturation with in
the hybrid zone.the hybrid zone.
 Incomplete penetration to the full depth ofIncomplete penetration to the full depth of
demineralized dentin.demineralized dentin.

Steps for effective priming: -Steps for effective priming: -
 One method of improving surfaceOne method of improving surface
coverage and diffusion of the primer is bycoverage and diffusion of the primer is by
the application of multiple coats. Athe application of multiple coats. A
second coat of primer has shown tosecond coat of primer has shown to
increase the shear bond strengthincrease the shear bond strength
significantly.significantly.
JAJA
Platt et al conducted a study in 2001, toPlatt et al conducted a study in 2001, to
determine the effect of double adhesivedetermine the effect of double adhesive
application on the shear bond strength toapplication on the shear bond strength to
dentin using three one-bottle adhesivedentin using three one-bottle adhesive
systems.systems.

This study showed that:This study showed that:
 The dentin shear bond strength of Prime &The dentin shear bond strength of Prime &
Bond NT is improved by the use of a secondBond NT is improved by the use of a second
application, when following manufacturer’sapplication, when following manufacturer’s
instructions.instructions.
 The dentin shear bond strength of One StepThe dentin shear bond strength of One Step
and Optibond Solo are not improved by theand Optibond Solo are not improved by the
use of a second application, when followinguse of a second application, when following
manufacturer’s instructions.manufacturer’s instructions.
 The surface of dentin should not be over driedThe surface of dentin should not be over dried
or over-wet.or over-wet.
 The etching time should not exceed the timeThe etching time should not exceed the time
recommended by the manufacturers.recommended by the manufacturers.

SOLVENTS:SOLVENTS: --
 Three types of solvents are commonlyThree types of solvents are commonly
used in dentin adhesives, they include:used in dentin adhesives, they include:
 ACETONEACETONE
 ETHANOL.ETHANOL.
 WATER.WATER.

Basic characteristic of solvents:Basic characteristic of solvents: --
ACETONEACETONE
 Highly volatile, evaporates quicklyHighly volatile, evaporates quickly
 Excellent water – chaserExcellent water – chaser
 Strong drying agentStrong drying agent
 Storage and dispensing problems presentStorage and dispensing problems present

ETHANOLETHANOL
 Excellent penetration capabilityExcellent penetration capability
 Good comprise in respect of evaporationGood comprise in respect of evaporation
 Good surface energy for wetting exposedGood surface energy for wetting exposed
collagen fiber networkcollagen fiber network
WATERWATER
 Excellent penetration capabilityExcellent penetration capability
 Enables self – etching capability of acidEnables self – etching capability of acid
monomersmonomers
 Evaporates slowly consequently more difficult toEvaporates slowly consequently more difficult to
removeremove
 Remaining water may hamper resinRemaining water may hamper resin
penetration / polymerizationpenetration / polymerization

 Organic solvents aid in displacing water,Organic solvents aid in displacing water,
expanding or re-expanding the collagen network,expanding or re-expanding the collagen network,
and thus promoting the infiltration of theand thus promoting the infiltration of the
monomer into the submicron or nanometer sizedmonomer into the submicron or nanometer sized
spaces within the collagen fiber network.spaces within the collagen fiber network.
 AF Reis et al conducted a study to evaluate theAF Reis et al conducted a study to evaluate the
effect of organic solvents on one-bottleeffect of organic solvents on one-bottle
adhesives’ bond strength to enamel and dentin.adhesives’ bond strength to enamel and dentin.
The result of this study demonstrated thatThe result of this study demonstrated that
complete solvent elimination did not produce acomplete solvent elimination did not produce a
statistical decrease in enamel bond strengths.statistical decrease in enamel bond strengths.
However, the high viscocity adhesive solutionHowever, the high viscocity adhesive solution
that resulted from solvent evaporationthat resulted from solvent evaporation
significantly decreased bond strengths tosignificantly decreased bond strengths to
demineralized, moist dentin substrate.demineralized, moist dentin substrate.

 They concluded that this reductionThey concluded that this reduction
probably occurred as a function of twoprobably occurred as a function of two
factors : incomplete monomer infiltrationfactors : incomplete monomer infiltration
and incomplete water displacement. Theand incomplete water displacement. The
absence of a water-chaser monomer-absence of a water-chaser monomer-
carrier resulted in difficult resin infiltration.carrier resulted in difficult resin infiltration.

HYBRID LAYERHYBRID LAYER
 Hybrid layer in dentin was first describedHybrid layer in dentin was first described
in detail by Nakabayashi, 1992. A similarin detail by Nakabayashi, 1992. A similar
phenomenon was first described in vitrophenomenon was first described in vitro
for enamel by Gwinnett and Buonocore infor enamel by Gwinnett and Buonocore in
1965.1965.

 Hybrid layer is an intermediate layer of resin,Hybrid layer is an intermediate layer of resin,
collagen, and dentin produced by acid etching ofcollagen, and dentin produced by acid etching of
dentin and resin infiltration into the conditioneddentin and resin infiltration into the conditioned
dentin.dentin.
 Basically it is a transitional zone of resinBasically it is a transitional zone of resin
reinforced dentin sandwiched between curedreinforced dentin sandwiched between cured
resin and unaltered dentinal substrate and isresin and unaltered dentinal substrate and is
generated by monomer impregnation of thegenerated by monomer impregnation of the
exposed collagen of demineralized superficialexposed collagen of demineralized superficial
dentin, after removal and/or modification of thedentin, after removal and/or modification of the
smear layer. The synonyms are “adhesionsmear layer. The synonyms are “adhesion
interface”, resin dentin “inter diffusion zone”,interface”, resin dentin “inter diffusion zone”,
inter penetration zone”.inter penetration zone”.

 The formation of hybrid zone depends onThe formation of hybrid zone depends on
several factorsseveral factors
 1) Type of conditioners.1) Type of conditioners.
 2) Depth of the cavity, hybrid layer appeared to2) Depth of the cavity, hybrid layer appeared to
be thinner at the deeper parts of the dentinbe thinner at the deeper parts of the dentin
compared with the middle and superficial parts.compared with the middle and superficial parts.
In the superficial dentin most of the hybrid layerIn the superficial dentin most of the hybrid layer
is composed of hybridized intertubular dentinis composed of hybridized intertubular dentin
with only occasional resin tag penetrating in towith only occasional resin tag penetrating in to
the tubules. In deep dentin the tubules are sothe tubules. In deep dentin the tubules are so
numerous and so large that there is less amountnumerous and so large that there is less amount
of hybridized intertubular dentin and large resinof hybridized intertubular dentin and large resin
tags are seen.tags are seen.

 3) Permeability of the dentin surface.3) Permeability of the dentin surface.
 4) The conditioning and priming pre4) The conditioning and priming pre
treatment procedures.treatment procedures.
 5) Diffusability and wettability of monomer5) Diffusability and wettability of monomer
resins.resins.
 In order to obtain an intimate associationIn order to obtain an intimate association
between the resin monomers and collagenbetween the resin monomers and collagen
fibrils, the primers and bonding agentsfibrils, the primers and bonding agents
must be able to wet the collagen fibrils.must be able to wet the collagen fibrils.

Role of the Hybrid LayerRole of the Hybrid Layer
 The role of the hybrid layer in dentinThe role of the hybrid layer in dentin
bonding is somewhat controversial.bonding is somewhat controversial.
Studies of various adhesive systemsStudies of various adhesive systems
report different results. In order to obtainreport different results. In order to obtain
proper adhesion, it is essential to create aproper adhesion, it is essential to create a
hybrid layer at the resin-dentin interfacehybrid layer at the resin-dentin interface
(Nakabayashi, 1985, Sugaizaki, 1991,(Nakabayashi, 1985, Sugaizaki, 1991,
Vanmeerbeek and others, 1992, 1993).Vanmeerbeek and others, 1992, 1993).

 A study with Prime & Bond (Dentsply) indicatedA study with Prime & Bond (Dentsply) indicated
that the removal of collagen fibers may actuallythat the removal of collagen fibers may actually
increase bond strengths of resin to dentin.increase bond strengths of resin to dentin.
Studies with One-Step(Bisco) indicated that theStudies with One-Step(Bisco) indicated that the
hybrid layer might not play any important role inhybrid layer might not play any important role in
the establishment of bond strengths. For athe establishment of bond strengths. For a
multibottle adhesive system, All-Bond 2(Bisco),multibottle adhesive system, All-Bond 2(Bisco),
one study reported that the presence or absenceone study reported that the presence or absence
of the hybrid layer did not affect fractureof the hybrid layer did not affect fracture
toughness of resin-dentin interfaces. Thereforetoughness of resin-dentin interfaces. Therefore
the presence of the collagen layer wouldthe presence of the collagen layer would
presumably allow for the establishment of apresumably allow for the establishment of a
stress-relieving layer at the interface.stress-relieving layer at the interface.

 A study using a self-etching primerA study using a self-etching primer
demonstrated that dentin bond strengths did notdemonstrated that dentin bond strengths did not
vary from 1 day to 6 months to 1 year in teethvary from 1 day to 6 months to 1 year in teeth
subjected to occlusal function. It also showedsubjected to occlusal function. It also showed
that porosity in the hybrid layer increasedthat porosity in the hybrid layer increased
significantly at 1 year, due to loss of resinsignificantly at 1 year, due to loss of resin
between the collagen fibers. Since these resultsbetween the collagen fibers. Since these results
were obtained with a hybrid layer being createdwere obtained with a hybrid layer being created
by a self-etching primer, they cannot beby a self-etching primer, they cannot be
generalized to total-etch adhesives. However,generalized to total-etch adhesives. However,
they do support the theory that collagen maythey do support the theory that collagen may
play an important role in the strength of theplay an important role in the strength of the
resin-dentin interface.resin-dentin interface.

 For most dentin adhesives, theFor most dentin adhesives, the
ultramorphological characterization of theultramorphological characterization of the
transition between the hybrid layer and thetransition between the hybrid layer and the
unaffected dentin suggests that there is anunaffected dentin suggests that there is an
abrupt shift from hybrid tissue toabrupt shift from hybrid tissue to
mineralized tissue, without any emptymineralized tissue, without any empty
space or pathway that could result inspace or pathway that could result in
leakage. The demarcation line seems toleakage. The demarcation line seems to
consist of hydroxyapatite crystalsconsist of hydroxyapatite crystals
embedded in the resin from the hybridembedded in the resin from the hybrid
layer.layer.

 According to Kanka, acid etched dentin cannotAccording to Kanka, acid etched dentin cannot
be dried without shrinking. It is literally floatingbe dried without shrinking. It is literally floating
in the rinsing water. If the water is evaporatedin the rinsing water. If the water is evaporated
by air-dryng, the collagen fibrillar networkby air-dryng, the collagen fibrillar network
collapses into a relatively impermeable organiccollapses into a relatively impermeable organic
film that interfares with resin infiltration. Resinfilm that interfares with resin infiltration. Resin
tags could still be formed and gave some resintags could still be formed and gave some resin
retention, but hybridization of the dentin betweenretention, but hybridization of the dentin between
tubules could not occur. This left much nakedtubules could not occur. This left much naked
collagen fibrils in the acid etched layer that couldcollagen fibrils in the acid etched layer that could
slowly hydrolyze and leads to gap formationslowly hydrolyze and leads to gap formation
between resin and dentin.between resin and dentin.

 Kanka discovered that if one left some residualKanka discovered that if one left some residual
water in acid etched dentin, bond strength couldwater in acid etched dentin, bond strength could
be doubled. Also it creates thicker hybrid layersbe doubled. Also it creates thicker hybrid layers
(i.e., more resin uptake in etched surfaces) than(i.e., more resin uptake in etched surfaces) than
did dry bonding.did dry bonding.
 Most adhesive interface studies by SEMMost adhesive interface studies by SEM
(Scanning Electron Microscope) have(Scanning Electron Microscope) have
demonstrated creation of hybrid layers. Medinademonstrated creation of hybrid layers. Medina
et al, in 2001, in his study had shown that acidet al, in 2001, in his study had shown that acid
etching of dentin and the application of Prime &etching of dentin and the application of Prime &
Bond are required for the formation of a distinctBond are required for the formation of a distinct
hybrid layer and resin tags. However, there washybrid layer and resin tags. However, there was
no significant correlation between shear bondno significant correlation between shear bond
strength and the thickness of the hybrid layer.strength and the thickness of the hybrid layer.

REQUIREMENTS OF A BONDINGREQUIREMENTS OF A BONDING
AGENT:AGENT:
A bonding agent is usually an unfilledA bonding agent is usually an unfilled
resin that consists of hydrophobicresin that consists of hydrophobic
monomers (such as Bis-GMA, TEGDMA,monomers (such as Bis-GMA, TEGDMA,
UDMA, and hydrophilic monomers, suchUDMA, and hydrophilic monomers, such
as HEMA).as HEMA).
 Criteria for an “ideal” dentin bondingCriteria for an “ideal” dentin bonding
system were enumerated in 1961 at asystem were enumerated in 1961 at a
workshop held at the University of Indianaworkshop held at the University of Indiana
Dental School.Dental School.

These criteria were:These criteria were:
1.1. Provide a high bond strength to dentinProvide a high bond strength to dentin
that should be present immediately afterthat should be present immediately after
placement and that should beplacement and that should be
permanent.permanent.
2.2. Provide a bond strength to dentin similarProvide a bond strength to dentin similar
to that to enamel.to that to enamel.
3.3. Show good biocompatibility to dentalShow good biocompatibility to dental
tissue, including the pulp.tissue, including the pulp.

4. Minimize microleakage at the margins of4. Minimize microleakage at the margins of
restorations.restorations.
5. Prevent recurrent caries and marginal staining.5. Prevent recurrent caries and marginal staining.
6. Be easy to use and minimally technique6. Be easy to use and minimally technique
sensitive.sensitive.
7. Possess a good shelf life.7. Possess a good shelf life.
8. Be compatible with a wide range of resins.8. Be compatible with a wide range of resins.
 In a current review of literature, J. D. Eick et alIn a current review of literature, J. D. Eick et al
had proposed to add the criterion that thehad proposed to add the criterion that the
systems should not be toxic or sensitizing tosystems should not be toxic or sensitizing to
the operators or patients. And, finally, Bondingthe operators or patients. And, finally, Bonding
agents should seal tooth surfaces from oralagents should seal tooth surfaces from oral
fluids.fluids. www.indiandentalacademy.comwww.indiandentalacademy.com

CLASSIFICATION OF DENTIN BONDINGCLASSIFICATION OF DENTIN BONDING
AGENTS:AGENTS:
 The BeginningThe Beginning : During the 1950s, the first: During the 1950s, the first
attempt to develop an adhesive system forattempt to develop an adhesive system for
bonding to dentin was made by Hagger, abonding to dentin was made by Hagger, a
Swiss researcher working forSwiss researcher working for
Amalgamated Dental Company, London.Amalgamated Dental Company, London.

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