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DEPT. OF CONSERVATIVE DENTISTRY
Adhesion to Enamel
Bonding to Dentin and its problems faced
Ideal Requirements of DBA
Composition of DBA
Conditioning of Dentin
Primers, Mechanism of Action of Dentin Bonding
Classification of Dentin Bonding Agents
Clinical indications of Dentin Bonding Agents
Contra-indications of Dentin Bonding Agents
Bonding/ adhesion comprise a complex set of physical, chemical and
mechanical mechanisms that allow the attachment of one substance to
Bonding agents can be defined as material of low viscosity, when
applied on the tooth surface, forms thin film after setting.
This thin film strongly bonded to tooth surface, on which the viscous
composite restorative resin is applied. This sets forming an integrated
1. Provides resistance to separation of an adherend.
2. Distributes stress along bonded interface.
3. Seals the interface via adhesive bonding and hence reduces
• Development of epoxymolecule byCastan
• Glycerophosphoricaciddimethacrylatedeveloped by
• Buonocoredeveloped acid etchingtechniquewith
•Buonocoredeveloped the first dentinbondingagents.
•BowengaveBISGMA resin system
• Caustondescribedhowprimers work
•GwinnetandSilverstone described threepatternsof
• Bowen,CobbandRapsondeveloped multilayer
• Nakabayashireported thepresence of hybridlayer
• Fusayama gave theconcept of totaletchingand
• Kanca described the conceptof wetbonding
• Ferrari described about the bonding
mechanism ofone bottle adhesive system.1997
• Ferrari evaluated bonding abilityof6th
generation bonding systems.2000
• Ferrari developed the seventh generation
ADHESION – (Latin : to stick)
It is the force or the intermolecular attraction that exists between molecules of two
unlike substances when placedin intimate contact with eachother.
It is the substance that promotes adhesion of one substance or material to one
A material substrate that is bonded to anothermaterial by meansof anadhesive.
1. Physical - based on secondary forces
– Vander Waals forces, hydrogen bonds, dispersion forces(
speciallywhen surfaces are smooth and polished )
2. Chemical - based on primary forces
– covalent, ionic, metallic bonds.
3. Mechanical -based on penetration of one material into another at
microscopic level (when surfaces are rough).
1. Surface energy- Generally, the harder the surface is the higher the
surface energy willbe and so better willbe the adhesion.
2. Wetting- High surface energy , better wetting and better adhesion (
reduced irregularities ).
3. Contact angle- Lower the contact angle, better wetting and better
adhesion. For good adhesion, the contact angle should be < 900. The
zero contactangle is the best to obtain wetting.
4. Surface Contamination
Thesubstrate surface should be cleanas contamination prevents the adhesion.
Adhesive should be able to fill their irregularities making the surface smooth
allowing proper or intimate contact .
Thehigher the water content, the poorer is the adhesion.
Water can react with both materials by the high polar group and form hydrogen
bond which can hamper the adhesion.
The hardest tissuein the human body.
Consists of 95 percent mineralized inorganic substance.
To bond to enamel, it is very important to focus on the mineral
component (hydroxyapatite) of enamel.
• Adhesion to enamel is mainly by micromechanical methods. For this,
Effects of Conditioning / Etching:
1. Removes 10 µM of surface enamel & creates amicroporous layer.
2. Increases wettability.
3. Increases surface area.
4. Increases surface energy.
Bond strengthof composite to
etched enamel: 15-25 MPa.
[ENOUGH TO RESIST
was the first to reveal the adhesion of acrylic resin to acid etched
used 85 % phosphoric acid.
Silverstone revealed that the optimum concentration of phosphoric
acid should range between 30 – 40% to get a satisfactory adhesion to
Percentage of etchants used: 37%
If the concentration is greater than50 percent:
monocalcium phosphate monohydrate may get precipitated, that
can be rinsed off. (It prevent further dissolution).
If concentrations lower than 27% percent:
dicalcium phosphate monohydrate is precipitated, which cannotbe
removed easily and interferes with adhesion.
Originally,the etching time suggested was 60 sec.
Currently, it has been reduced to 15 sec as it produces same surface
roughness as a 60 sec etch time.
Acid resistant teeth ( with high F content/ Fluorosis).
Primary teeth (More aprismatic).
smooth enamel converted into irregular surface [surface free energy ]
Resin monomer penetrate (b/c of low viscosity) into the irregular etched
surface [aided by capillary action].
Monomer polymerize, material become interlocked within the enamel
surface. [Microtag formation]
Macrotags–resin tags formed at periphery of enamelrods (between prisms )
Microtags - smaller tags formed at end of each rod where individual hydroxyapatite
crystal has been dissolved. More important because of greater number and surface
Various etchants used –
1. Phosphoric acid – as liquid or gel.
2. Sulphuric acid 2 %
3. Citric acid
4. Maleicacid 10 %
5. Nitric acid2.5 %
Depth of decalcification is
a)pH of the acid
Micromorphologic Patterns of etching of Enamel
A properly etched enamel surface gives a frosty white appearance on
Preferential removal of enamel prism cores & periphery intact.
Type2-Reverse of type 1.
Periphery removed andcores intact.
Type3–Etching pattern less distinct.
Both types 1 & 2 present.
After etching, the enamel surface should be throughly rinsed with a
continuous stream of water spray for 5-10 sec so that acid is completely
This should be followed by proper drying which will produce frosty, white
Contamination of the etched and dried enamel surface by saliva, moisture or
If anysortofcontaminationoccurs,repeat theprocedure.
Generally, enamel bonding agents contain Bis-GMA or UDMA with
TEGDMA added to lower the viscosity of the bonding agent.
Since, enamel can be kept dry, these hydrophobic resins worked well
when they were confined only to enamel.
Bonding to dentin has been proven more difficult and less reliable than to
This is basically because of difference in morphologic, histologic and
PROBLEMS IN BONDINGTO DENTIN
1) It has considerable amount of organic material & water (30% organic
2) Random arrangement of hydroxyapatite crystals in the organic matrix. (They
5) Dentin contains dentinal tubules which contain vital processes of the
odontoblasts. This makes the dentin a sensitive structure.
6) Cut dentin surface is covered by smear layer, that fills the orifice of
dental tubules, & blocks dentin permeability upto 86%.
6) Because of close proximity to pulp, various chemicals used for etching
& dentin bonding may irritate the pulp.
7) It’s a dynamic tissue, that shows changes due to ageing, caries or
Most of the bonding agents are unfilled.
May contain inorganic fillers 0. 5% to 40% by wt. microfillers, or
nanofillers,and submicron glass.
Advantages of nanofillers:
1. Provides radio opacity.
2. Better dissipation of forces.
3. Scatter of light isprevented.
4. Causes uniform thicknessof adhesive layer.
5. Better flexibilityto adhesives.
CONDITIONING OF DENTIN
Defined as removal or modification of the smear layer, to create a
surface, capable of micromechanical and chemical bonding to dentin
CHANGES AFTER CONDITIONING:
Removal or modification of smear layer.
Opening of dentinal tubule orifices.
Exposesthe microporous collagen network.
Decalcification of inorganic portion.
Conditioningcan be done by-
1. Phosphoric acid
2. Sulphuric acid: [2 % for 30 sec.]
As effective as phosphoric acid.
3. Nitric acid: [2.5% ]
Stronger than H3PO4
Removes only smear layer, not plugs.
10% citricacid+ 3% FeCl3 was recommended by Nakabayashi.
Lately, Kuraray proposed a combination of 10% citric acid and 20%
CaCl2 to stabilize collagen during etching.
5. Pyruvic acid:
Pyruvic acid buffered with glycine is used to facilitate polymerization
reactions and adjust the pH.
6. Polyacrylicacid: [40%]
A 10 second application opens up the dentinal tubules but does not
effect pulp as the particle size is greater than diameter of dentinal
7. Hydrochloric acid :
Causes violent surfacereactions.
2. CALCIUM CHELATORS:
Chelators are used to remove the smear layer without decalcification of
the underlying dentin as opposed to strong acid etchants.
Commercially availableas “Tublicid”.
It contains 0.1% EDTA and0.15% Benzalkonium chloride.
Removes smear layer, not plugs.
It is scrubbed on the surface of the smear layer for a few seconds, then
left passivelyfor another 60 seconds followed by additional scrubbing.
Nd:YAG laser used at 10 to 30 pulses per second.
The mechanism of action is through microscopic explosions caused by
The carbonized blackrot iseasily washed off with water.
C. MECHANICAL CONDITIONERS
Al2O3 is used for micro abrasion.
0.5 μparticles are used. 39
Amphiphilic bifunctional molecules i.e have both hydrophillic and
The priming step converts the hydrophillic dentin into a hydrophobic and
These solvents are volatile and displace water (water chasing ability) from the
This will allow the monomer of the primer to penetrate through the spaces in
For proper penetration, it is preferred to keep the dentin surface moist,
otherwise collagen fibers get collapsed in dry condition resisting the entry for
Primingisdoneafter etching.It shouldbeappliedinmultiplecoats.
2. Ethanolbased primers
Evaporates less quickly
Good surface energy and good penetration.
Optibond solo plus
3. Water based primers –
Have capacityto raise collapsed fibers.(9%-50%)
Long drying time.
Water caninterfere with adhesive if not removed.
Ex- Amalgabond plus
Prompt l pop
Scotch bond multipurpose
COMBINATION OF THE SOLVENTS THAT CAN BEUSED AS PRIMERS
1. Acetone & H2O
Eg: Tenure- quick
2. Acetone & ethanol
Eg: All bond 2 (Bisco)
3. Ethanol& water
Eg: Gluma comfort bond
By etching dentin, the smear layer and minerals from it are removed,
This water acts as a plasticizer for collagen, keeping it in an expanded soft
But these collagen fibers collapse when dry. This prevents the resin
Water removal also might permit additional hydrogen bonds to form
between collagen molecules, that previously were bonded to water
molecules, leaving no interfibrillar space.
During air drying, the volume of collagen network decrease to one third
of its original volume.
For this reason, presence of moist/wet dentin is needed to achieve
Introduced by Dr. JohnKanaandGwinnetin 1992.
So, it refers to bonding in which acid etched dentin is moist and hence,
acetone based primers are used.
acetone and ethanol based primer displace water and carry monomers in
b/w exposed collagen fibres. The primer solvents are then evaporated by
gentle air drying leaving the active primer monomer behind.
To get moist dentin after etching, do not dry the dentin with compressed
air after rinsing awayetchant.
Instead use high-volume evacuation to remove excess water and then
blot the remaining water present on the dentin surface using gauze or
cotton to leave dentin optimally moist.
Rewetting dentin after air drying to check for the enamel frosty aspect is
an acceptable clinicalprocedure.
Rewetting can be done by 35% HEMA, Chlorhexidine.
On rewetting, the collagen network assumes its original volume.
The re-expansion during rewetting occurs because the spaces between the
fibres are refilled with water. Also, type I collagen itself is capable of
undergoing expansion on rehydration.
Since water is lost gradually, the wet bonding technique has a better
bonding ability thanthe dry bonding technique.
In acetone containg primers, when acetone comes in contact with water,
the boiling point of acetone is raised &the boiling point of water is lowered
causingevaporation of both water and acetone and the resin is left behind.
Refers to the bonding in which the acid etched dentin is dry and so water-based
Water-based primers are not dependent on moist dentin because of their ability
to self-wet a dried dentin surface and thus separating the collapsed collagen
NOTE: Studies show that moist dentin is friendly with all primer types, it is
Hybridoid region/ Ghost hybrid layer is that area of demineralized
dentin into which resin fail to penetrate.
It is one of the disadvantages in dry bonding technique because of
ineffective resin penetration due to collagen collapse
It appears if surface air dried for more than 3 sec.
This zone inside the hybrid layer do not appear electron dense on
demineralized TEM sections.
Reduced bond strength.
If solvent of primer (acetone/ethanol) fails to remove water completely from
Dentinal tubules are more prone to show this phenomenon than the
In this the solubility of monomers is lowered as the excess moisture lowers
Monomerispresentasglobulesover thewater layer.
The dentin surface may appear blister like with water being trapped
beneath the resin layer.
Since blisters gets compressed and causes flow of dentinal fluids, hence
this leads to Post-operative sensitivity.
DISADVANTAGES OF WET BONDING TECHNIQUE
1. Technique sensitivity
2. Evaporation of acetone
Decreasedpenetratiablity of monomers
To overcome this problem acetone based adhesive formulations are available in Pre-
dosed-single patient use capsules (primerbond NTQuix ).
3. Difficult in checkingthe frosted appearance of enamel
ADVANTAGES OF DRYSURFACE
1. Frosted appearance of etched enamel can be verified.
2. Reduce risk of over wetting. (Rewetting of tooth surface using wet
cotton pellet with water or chlorohexidine or 35% HEMA).
AIR DRIED MOIST OVERWET
COLLAPSE OF COLLAGEN SWELLING OF COLLAGEN
NO RESIN PENETRATION LESSER SPACE AVAILABLE
FOR RESIN PENETRATION
NO HYBRIDLAYER OPTIMAL HYBRIDLAYER
Ideally a dentin bonding agent should have both hydrophilic and
hydrophobic ends. The hydrophilic end displaces the dentinal fluid, to wet
MECHANISM OF ACTION OF DENTIN BONDING
M R X
This is a spacergroup that
provides flexibility &mobility to
M group, after the X group has
beenimmobilizes by reaction at
a surface (tooth surface).
Hence, it increases the reactivity.
INORGANIC PART OF
ORGANIC PARTOF DENTIN
2. Hydroxyl (-OH)
3. Carboxylate (-COOH)
4. Amide(-CONH) groups
3. carboxylic acid
5. carboxylic acid chlorides
from the below groups and
Whenever tooth surface is cut with hand or rotary instruments , it causes small
Smear layer is defined as any debris ,calcific in nature ,produced by reduction
The smear layer easily washedaway from the enamel, but remains adherent to
1. Thesuperficialsmear layer.
2. Smear plugsthatoccludethedentinaltubules.
Some researchers consider it a natural protective liner for the pulp, while
others consider it as a source of microorganisms which can cause pulp
It interferes with adhesion, and so it should be removed, dissolved or
Zone where the adhesive resin of the dentin bonding agent
micromechanically interlocks within the intertubular dentin and
surrounding collagen fibres. Formed in the following manner:
A) Etching removes the smear layer & minerals (hydroxyapatite) exposing
the collagen fibrils & demineralized dentin.
B) Primers penetrate collagen network & demineralized dentine.
C) Along with the primers, adhesive resins form resin microtags within the
intertubular dentin andsurround the collagen fibres upon curing.
Whenabonding agentis applied,partofitpenetrates intothe collagennetwork,
known as intertubular penetration and the rest of it penetrates into dentinal
Intratubular penetration or the formation of resin tags upto a limited depth of
CHARACTERISTICFEATURESDUETO HYBRIDIZATION :
3) Lateral tubuleHybridization 64
1. Shag Carpet Appearance :
Appears when dentin surface after being acid etched is actively
scrubbed with an acidicprimer solution.
The combined mechanical and chemical action of rubbing the acid
etched dentin with an acidicprimer results in:
1. Additional mineral saltsare dissolved.
2. Fraying and separation of the entangled collagen at the surface
2. Tubulewall hybridization:
Extensionof the hybrid layer into tubule wallarea.
Hermetically sealsthe pulpodentinal complex againstmicroleakage.
Specially protective when bond fails at top or bottom of the hybrid
The resin tags keep tubules sealed as they break off at the level of
hybrid layer. This is attributed to tubule wall hybridization which
ensures aleakage free seal of tubules.
3) Lateral Tubule Hybridization :
Formation of tiny hybrid layer into the wallsof lateraltubule branches.
This microversion of hybrid layer typically surrounds a central core of
resin and calledmicroresin tag.
After etching, silica remnants from the phosphoric acid present on the exposed
collagen fibres, cannot be removedby vigorous rinsing.
These particles will not bond to infiltrating resin and hence, increase nanoleakage and
lead to failure overtime.
These acid exposed non infiltrated collagen fibres undergo hydrolytic degradation
when exposed to fluid for long periods.
Due to these limitations of the total etch technique, alternative dentin bonding
strategies havebeenproposed, like self etch adhesives and deproteinization.
Sodium hypochlorite is a non-specific proteolytic agent that effectively removes
Thus, NaOC1 a deproteinising agent is used to completely remove the collagen
SEM revealed the direct resin tag penetration into the underlying dentinal
The total absence of any resin infiltrated collagen layer, may prevent any
hydrolytic degradation from taking place, thus accounting for the overall increase
Because of polymerization shrinkage, there is detachment of the adhesive resin
If a layer of separately polymerized adhesive resin[thickness of 50 – 100 μ,
elastic unfilled or semi filled] is placed, below composite resin, a gap free intact
These act as a shock absorber by elastic elongation thereby preventing the
Superficial layers are unpolymerized which then provide double bonds to polymerize
with the composite.
Water can pass from dentin around resin tags & form water filled channels that
project from the hybrid layer into the overlying adhesives.
When these water filled channels are stained with silver, they often look like
These arecalled water trees by Tay & Pashley.
They suggested that they might act as potential sites for hydrolytic degradation of
resin &also may bethe causeof nanoleakage.
All marketed products permitted someamount of water tree formation.
1. According to generation.
2. According to adhesion strategy (number of clinicalapplications).
3. According to treatment of smear layer.
4. According to mode of curing.
5. According to pH.
6. According to bond strength.
CLASSIFICATIONBASED ONTHE NUMBEROFCLINICALAPPLICATONS
STEPS AND HOW THEY INTERACTWITHTOOTHSTRCTURE
1) Total etch adhesives:
2) Self etch adhesives:
3)Resin modified glass ionomer adhesives
ON THE BASIS OFTREATMENT OFSMEAR LAYER
Clearfil liner bond system
Scotch bond 2
Scotch bond dual cure
Prisma universal bond
ACCORDINGTOTHEIRMODE OF CURING
1) Chemical cure:
2) Light cure:
Gluma comfort bond
3) Dual cure:
Clearfil liner bond 2V
Prime and Bond NT dual cure.
C) DEPENDING ONTHE pH (VanMeerbecketal2003)
Mild ( pH ≥ 2 )
( pH of 1.5)
Are more acidic
interlocking at the
Strong ( pH ≤ 1 )
reaction may take
place, since the
Intermolecular bonding: Hydroxyapatite acts as a receptor for additional molecular
interactions with specific carboxyl orphosphate groups of monomers like 4 META.
1) Mild adhesives :
Panavia ED primer
2)Intermediary adhesives :
Optibond Solo Plus SE primer
3)Strong adhesives :
Developed in 1960s.
First generation adhesives started with the development of NPG-GMA (Comonomer).
It chelates with the Ca of the dentin and form a water –resistant chemical bond.
When nuclear magnetic resonance analysis was done, it was found that no ionic bond
exist between NPG-GMA &hydroxyapatite(Ca).
Low bond strength (2–3 MPa).
Developed in 1978.
Low bond strength (1–5 Mpa).
It consisted of a phospahate – ester material.
-velycharged Binds to Ca of smear layer.
Also the smear layer is loosely
attached, so the bond created
was not strong
These were hydrophobic [So,do not wet dentin]
Cannot penetrate to entire depth of smear layer
Unable to reach superficial dentin for ionic bond
For modification of smear layer, concept of phosphoric acid etching of dentin
before applicationof aphosphateester-typebonding agentwas introducedby
Acid etching causes flow of resin into open dentinal tubules, even then any
significant improvement in dentin bond strength was not found. This was
So, overall there is preservation of modified smear layer with slight
Pulpalinflammatory responses were thoughtto be triggeredby application
Based on removal of smearlayer to permitresin bonding to the underlying dentin.
Removal of smear layer via acid etching leads to significant improvement in bond
Thethree essential components of this system are:
1. Etchant: Phosphoric acid gel. It is rinsed off
2. Primer: Hydrophillic monomers +Solvent [ethanol, acetone orwater]
3. Bonding agent resin: unfilled orfilled
All- Bond 2
DENTIN & ALSO
7.5 Micro M)/
As the technique involves simultaneous application of acid to
enamel & dentin, this method is commonly k/s TOTAL ETCH
TECHNIQUE / ETCH & RINSE TECHNIQUE / THREE STEP TOTAL
Concept of HYBRID LAYER comes in this generation.
This was done to reduce number of steps
As primer & bonding agent are combined
into a single solution, they are also called
Also known as NON RINSING
CONDITIONER [NRC]/ SELF
PRIMING ETCHANTS [SPE].
In contrast to conventional
etchants, SEPs arenot rinsed off.
This reduces the possibility of
overwetting & overdrying, both of
which affects the adhesion
Ex:Clearfil SE Bond
SELF ETCH PRIMER & ADHESIVE
2 bottle system.
Components of both the bottles
are applied separately. i.e self
etch primer applied first
followed by adhesive
Ex:Clearfil SE Bond
2 bottle system.
Components of both the bottles
are first mixed & then applied.
Ex:Xeno III adper prompt
SELF ETCH ADHESIVE
1. SEPs do not etch enamel as well as phosphoric acid, & so do not provide higher
2. Initial bond might deteriorate with ageing,which could leadto prematurefailures.
3. Bonding to sclerotic andcaries affected dentin might be problematic.
1. Less technique sensitive than total –etch adhesive.
2. SEPs demineralize &infiltrate dentin simultaneously.
So, they are less likely to cause discrepency between
depth ofdemineralization & depth if infiltration.
Introduced by Dr. JohnKanca.
Its film thickness is sufficiently thin, so can be used to bond posts to
endodontically treated teeth and to bond indirect resin inlays.
All in one
Both the sixth and seventh generation adhesives are self etching, self priming
adhesives, but the seventh generation bonding agents also have disinfecting and
Colour changing capacity (visual confirmation of complete curing).
Theseventh generation DBAs haveshown verylittle orno postoperative sensitivity.
Ex- G-Bond, iBond, XenoIV, Adper Easy Bond, AdheSE OneandClearfil S3Bond.
Single step, no mix bonding system.
Five in one solution:
Based on nano interaction technology.
G-BOND forms a non-conventional interface with the dentin “Nano
Interaction Zone” (NIZ) with minimal decalcification and almost no
exposure to collagen fibers.
This “nano” level reaction produces an insoluble calcium compound for
a better bond less likelyto deteriorate.
Creates a remarkably thin (less than300 um) bonding layer .
Completely coats allbonding surfaces with very few voids.
This new technology features a bonding agent which is contained
within the composite resin restorative material.
A self etching self adhering flowable composite technology eliminates
the need for separate bonding application step with composites for
direct restorative procedures.
In this there is a stablenanofiller that willnot settle out of dispersion.
Ex-Vertise flow (Kerr), Single Bond, Optic Bond Solo Plus, Adper Single
Bond 2 adhesive
4. Bondingofamalgam restorations.
Dentin bonding agents
should not be used if the
patient isknown to be allergic
to any of the ingredients used.
1) Sensitizing reaction (burning sensation) : Seen in patient with a
hypersensitivity to any of its ingredients. Its treatment is that the
material should be removed.
2) Gingival Tissue reaction : It is white in appearance ,but not painful, has
been reported after extended contact with these materials. The reaction
ceases within few days.
Materials containing Eugenol or Clove oil inhibits the polymerization of
DBA. These types of materials should not be used in conjunction with
CLINICAL SUCCESS OR FAILURES IN BONDING :
Can occur at various levels:
1. Between mineralized anddemineralized dentin.
2. Between demineralized dentin andbonding agent.
3. Within layer of bonding agent.
4. Between bonding agent and composite resin.
Factors affecting it are as follows:
1. Size And Shape Of Lesion:
Small sized cervical lesions show less adhesion as compared to deep,
wedge shaped lesions
Adhesion is better in case of maxillary arch than mandibular arch due to
With increasing age dentin gets sclerosed and thus adhesives show a greater
Apart from old age, the age of lesion and the time period for which dentin
Higher the wettability of bonding agents, higher will be the permeability /