Introduction
Many of the restorative material used in
dentistry will not adhere chemically to
enamel / dentin thus increasing the chances
of micro leakage.
 An BONDING AGENT permits the placement
of a more conservative restoration
(composite), reduces microleakage and
dentin sensitivity.

Dental adhesives / bonding agents
Are solutions of resin monomer that join a
restorative material with a dental substrate
( enamel ,dentin ,rarely cementum) after
the monomer sets by polymerization
OR
 Material of low viscosity ,when applied on
the tooth surface ,can form thin layer (after
setting ) , strongly bond to tooth surface ,on
which composite resin is applied

 Advantages of adhesive in
dentistry
Retention of restoration
 No need to use undercut or mechanical
lock , so less tooth structure is removed
 More conservation of natural tooth
structure
 Reduction in microleakage- ↓post
operative sensitivity, ↓ staining
 Reduction in recurrent caries
 Reinforcement of tooth structure

Classification of bonding agent

1. According to the bonding mechanism
◦ Mechanical bonding through acid etching –
(composite resins , Bis GMA, TEGDMA,
Cyanoacrylates )
◦ Chemical bonding – zinc polycarboxylate
cements , GIC

2. According to the application
◦ Enamel bonding agents – thin composite
resins , TEGDMA , Cyanoacrylates , GIC
◦ Dentin bonding agents – several
dimethacrylate systems, NPG-GMA,
Cyanoacrylates, Bis GMA, Polyurethanes ,
4-META, Ferric oxalate systems
 REQUIREMENTS OF BONDING
AGENTS
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Bond strength – Adhesive should have strong bond to
withstand the stresses caused by polymerization
contraction of composites. Optimum bond strength
17Mpa – 20Mpa.
Should form long-term durable bond
Adhesive used should be biocompatible
Low viscosity to flow easily on the surface of
adherend
Wet the tooth structure easily – low S.T & C.A
Similar COTE as tooth (11.4 ppm/*c), Prevents
microleakage by reduced gap formation between tooth
structure and restorative material.

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Prevents recurrent caries and marginal staining.
Be easy to use and minimally technique
sensitive.
Have a reasonable shelf-life.
Low film thickness
Good dimensional stability
Should have both hydrophilic & hydrophobic
reactive groups
Low thermal conductivity
Mechanism of adhesion
Adhesion to tooth structure is by exchange of
inorganic tooth material (Hydroxyapatite) by
synthetic resins by the process of
1. Removing the Hydroxyapatite to create
more micropores
2. Infiltration of resin monomer (bonding
agent) into the micropores & subsequent
polymerization
 As a result ,resin tags are formed that forms
micromechanical interlocking with the
tooth structure

Resin -tags
Micro-pores

Obstacles to bonding are
1. Un-homogenous composition of enamel
and dentin.
2. Variation in the composition of enamel
& dentin it self.
3. Inherent wetness of the surface of
dentin.
4. Tenacious (adherent) microscopic debris
in the prepared cavity (called Smear
Layer)

Smear Layer:
Thin tenacious adherent layer (1-5 microns
thickness) develops during cutting or grinding of
tooth structure (both enamel & dentin ) after
cavity preparation .
 It is formed of:
a. Dentin chips.
b. Saliva.
c. Bacteria.
d. Collagen.
e. blood.


a.
Left smear layer on the tooth surface prevents
strong bonding .
So acid is used to remove smear layer from
both enamel & dentin
ADHESION TO
ENAMEL AND DENTINE
Bonding to enamel
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Enamel has a complex surface structure with
enamel rods inside & more organic components on
the surface
Low Surface energy 84 erg/cm2 (less than many
restorative materials) ,which do not help for
wetting
Surface has moisture & other contamination is also
decreases the wetting & proper bonding
So
◦ Mechanical bonding is achieved by acid etching
◦ Chemical bonding is achieved by the use of adhesive
cements like polycarboxylate & GIC
Acid etch technique

Was first used in 1955 by Michael Buonocore

Mechanism :-

Phosphoric acid is used to etch tooth enamel. It
reacts with hydroxyapatite of enamel or of the
enamel rods & cause selective dissolution. So that
micro porosities forms on the surface . To which
resin monomer (bonding agent) flows &
subsequently polymerize to form resin tags & bonds
mechanically to tooth structure
 ENAMEL
ETCHING :-
 Phosphoric acid as an etchant:
In 1955 Michael Buonocore etched with 85%
phosphoric acid for 30 sec
50 % phosphoric acid for 60 seconds - reacts with
enamel , results in formation of mono calcium
phosphate – monohydrate ,which will prevent
further etching .
Concentrations below 25% - dicalcium phosphate
monohydrate precipitate
Concentrations above 40% - Dissolve less calcium
and etch the patterns with poor definitions
Finally 37% for 15 sec is considered appropriate.
Enamel Etching
Dentin Etching
37% phosphoric acid.
Enamel surface
wash
15seconds
dry
bond
Etching of enamel with 37% orth - phosphoric
for 15-30 secs, removes smear layer & about
10mm of the enamel surface to expose
prisms of enamel rods to create a honeycomb
like appearance (micropores) .
 Then rinsed away with stream of water for 20
sec.
 Enamel is dried completely with warm air
until it takes a white frosted appearance
 This surface must be kept clean and dry until
the resin bonding agent is placed.

Surface of etched enamel
Mechanism of etching

Etchant phosphoric acid reacts with HAP of enamel or
of enamel rods & cause selective dissolution

Patterns of etching may be
1.
2.
3.

Type 1 etching ; dissolution of the enamel rods centers .
Type 2 etching ; dissolution of the enamel rod
peripheries,
Type 3 etching ; combination of both type 1 and type 2
Etching Produces a microporosities on the surface ,
has - 6 µm in diameter & 10-20 µm in length
Type I
Type II
Type III
When a low viscosity resin monomer is placed , it
wets ,flows & infiltrates into micropores &
polymerizes to form a RESIN TAGS (6 µm in
diameter & 10-20 µm in length), leading to
micromechanical interlocking
 Bond strength→20-25 Mpa ( after etching )
 Bond strength→ 5-10 Mpa ( without etching )

Etchant
Common etchant – phosphoric acid.conc.
37%
 About 30% - 50% aq solution ,also can be used
 Alternative acids was tried e.g. - pyruvic acid ,
sulphuric acid, maleic acid, nitric acid , citric
acid and oxalic acid .


Available as liquids (acid) in syringes or
gel form

Gel etchants are made by adding colloidal
silica or polymer beads to the H3PO4 &
applied with brush .
Steps :Cleaning – enamel surface by pumice slurry
& then washed with water
 Etching - phosphoric acid.conc 37% for 15
sec
 Washing – acid should be rinsed away
thoroughly with a stream of water for 20 sec
 Drying – with a mild stream of air
 Bonding agents are applied immediately
before the etched surface gets contaminated
with moisture ,saliva & blood

Precautions
1). Acid etchant should not come in contact with the
exposed dentin , acid ions penetrate through the
dentinal tubules , cause irritation . (So Ca(OH)2 is
placed over exposed dentin as a precautionary
measure )
2. Etched surface should not get contaminated with
blood ,saliva, moisture or oil of cutting instrument ,
before the bonding resin is applied
3. Delicate etched surface has thin fragile sections, this
should not be damaged by touching or contact with
instruments
Bonding to dentin
Bonding to dentin why difficult?
Dentin etching is more technique sensitive than
enamel etching because
1. Dentin is more humid & organic than enamel ,
hence bonding to this hard tissue extremely
difficult
2. Dentin surface has complex structure – dentin
consist of 50 vol% of inorganic HAP Crystal , 30
vol% of organic material (mainly type I collagen)
hence less calcium ions are available for chemical
bonding
3. Remaining is 20 vol% is fluid ,coming out of
exposed dentin tubule ,prevents the boding
4. Presence of smear layer on exposed dentin
tubules.

Dentin etching :In 1979 Fusayama et al used 37%
phosphoric acid to etch both enamel and
dentin (“Total etch technique” )
 Showed that it did not damage pulp &
improved the bond strength.
 In 1984 Nakabayashi et al. discovered
formation of hybrid layer of resin infiltrated
resin.
 1990`s dentin etching gained world wide
acceptance.

HYBRID LAYER
Also known as interdiffusion zone, or resin
supported dentine layer.
 This is the zone where the adhesive resin of
the dentin bonding agent micromechanically
interlocks within the intertubular dentin and
surrounding collagen fibers
 The hybrid layer seals off the dentinal
tubules from the ingress of microorganisms
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Hybrid layer is formed in following manner:-

1.Etching removes smear layer and exposes
collagen fibers
It also removes hydroxyapatite with in the
intertubular dentin
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2. Primers penetrate the collagen network.
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3.Adhesive resins along with the primers form
resin micro tags within the intertubular dentin
34
Unfilled resin bonding agent
Hybrid layer
Unaltered dentine with dentinal
tubules
Steps of bonding to dentin
Etching
primer
bond
The aim of bonding to dentin is to obtain what’s called “ HYBRID
LAYER ” which is “Resin-reinforced dentin layer”.
Clinical Applications
1. Apply the conditioner ( is a type of acid used
to alter or remove smear layer) passively to the
prepared dentine not longer than 15 seconds
 2. Wash the conditioner with water and then
dry
 3. using a brush apply the primer immediately
to the dentine surface to minimize the seepage
of dentinal fluid to the dentine surface.
 4. Apply the adhesive resin, which penetrates
dentine to form hybrid layer
 5. Apply the restorative resin.

Dentin bonding agents

Designed to provide strong interface b/w
restorative composite & tooth structure to
withstand mechanical forces & shrinkage
stress
composition
Etchants
 Primer
 Resin monomers
 Solvents
 Initiators
 Inhibitors
 Fillers
 Antimicrobial agents (some times used)

ETCHANTS
Used to remove smear layer
 Phosphoric acid 37% used
 Conc. above 50% - Monocalcium phosphate
monohydrate forms on etched surface
 Available in liquid or acid (in a disposable
syringe ) or gel form
 Gel form - consist of adding colloidal silica
or polymer beads to the H3PO4
 Brushes are used to place acidic gels .

Primers
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Dentin etching is highly technique sensitive
because demineralized collagen network
readily collapses when dried
So a priming steps required to maintain a
hydrated collagen network.
Hence priming is necessary to maintain
collagen network for the infiltration of
hydrophobic adhesive monomer
Primers are solution containing hydrophilic
monomer HEMA (2- hydroxylethyl
methacrylate) dissolved in a solvent – acetone ,
ethanol, or water
primers defined as - a hydrophilic ,low
viscosity resin that promotes bonding to an
adherend substrate (dentin)
Self-etching primers
The primers that contain etchants are sometimes
referred to as self-etching primers.
OR
 If a primer has the ability to both etch & prime –
self etching primer
 Self –etching primers contains Acidic monomer
like – HEMA – phosphate , phenyl –P, 10-MDP
(10-metacryloxyethyle trimellitic acid, 4- META
(4-metacryloxyethyle trimellitic anhydride) , MAC
(11- methacryloyloxy -1,1-undecanedicarboxylic
acid)

Solvents
 Water ,ethanol, acetone
Solvent improves bond adhesion
 Water ionizes acidic monomer & as well as reexpand the collapsed collagen network
 Acetone or ethanol – volatile ,can displace water
from dentinal surface & keeps the collagen frame
work moist

Adhesive Resins
They penetrate the etched dentine and
copolymerize with the primer to form the Hybrid
layer & resin tags to provide micromechanical
retention
 Function
1. adhesive fills the interfibrillar space of collagen
network ,& creates a hybrid layer & resin tags to
provide micromechanical retention
2. prevent fluid leakage along the restorative
materials margin
 Adhesives are usually hydrophobic monomers
such as: BIS- GMA ,TEGDMA ,UDMA & small
amount of hydrophilic monomer HEMA

Initiators :Photosensitizer – Camphoroquinone
 Initiator – tertiary amine
 Chemical initiator- BP

Filler
Nanometer –sized silica particles
 Filler size- 40 nm
 Fillers modifies the adhesive viscosity to a
thicker , pastier consistency

Different generation dentin bonding
agents
Different generations of dentin bonding
agents are :Generation - I
-2
-3
-4
-5
-6
-7
First Generation
(1950-1970’s)
These products ignored the smear layer.
 Bonding to the enamel and dentin by chelation with
calcium on the tooth surface only, not to the
collagen of dentin .
 They included NPG-GMA (N- Phenylglycine Glycidyl
methacrylate), the polyurethanes and the
cyanoacrylates.
 Bond strengths was 2-3 Mpa.

 Hydrophobic monomers
 First commercial dentinal adhesive

◦
Cervident - SS White (1965)
Trade name – Cosmic bond
Limitations: Low bond strength of 2-3 MPa
 Loss in bond strength over time
 Lack of stability of individual components
during storage
 Based on carbon-13 NMR analysis – No
ionic bonding develops between NPGGMA and hydroxyapatite
2. Second generation (60’s - 80’s)
Here smear layer may play certain role in bonding to
dentin .
 Comprised of phosphate - esters material (Phenyl – P &
HEMA in ethanol).
 Bonding mechanism was based on polar interaction
between -vely charged phosphate group in resin & + ve
charged calcium in smear layer.
 Bond strength only – 5 to 6 Mpa & did not improve much
due to weak smear layer
 E.g. ScotchBond (3M dental),
Prisma,universal bond ,Bonolite
and Clearfil bond system.

Drawbacks
Loosely attached smear layer
 Hydrophobic resin, did not wet dentin
well nor penetrate the entire depth of the
smear layer & could not reach superficial
dentin to establish ionic bonding.
 Bond strength were less than 10 Mpa

Third Generation
(mid-80’s)
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Designed not to remove the entire smear layer, but
rather to modify it & allow penetration of acidic
monomer such as Phenyl – P or PENTA
(Dipentaerythritol penta-acrylate monophosphate)
Here, the conditioner, primer and adhesive resin are
applied in different steps
Conditioner – HEMA dissolved in maleic acid as in Scotch
Bond II ,& 2% Nitric acid in Tenure
Primer - bi-functional monomer in a volatile solvent
Adhesive is a unfilled or partially filled resin
Bond strength - 3-8 Mpa
E.g- ScotchBond 2, Tenure, universal bond 2,Coltene ART
Steps
1) Application of dentin conditioner ( is a
type of acid used to alter or remove
smear layer)
2) Application of Primer (dentin bonding
agent )
3) Application of adhesive - Unfilled resin
4) Composite restoration on it

Etch - & - Rinse Adhesives are
1) 4 th generation ( 3- step)
 conditioner, primer, adhesive
2) 5 th generation (2 – step)
conditioner, (primer & adhesive)
Fourth Generation
(early 1990’s)
 Consist of 3 -step
◦ Acid etching (TOTAL ETCHING IS
DONE ) gel, rinsed off
◦ Application of primer – consist of
hydrophilic monomer dissolved in an
organic solvent such as acetone ,
ethanol, or water
◦ Application of unfilled or filled fluid
bonding agent (consist of
hydrophobic Bis- GMA + hydrophilic
HEMA)

High bond strength – 13- 30 Mpa
4 th generation
conditioner
Primer
Adhesive
resin
Steps
1) Total etching- etch enamel & dentin simultaneously with
Conditioner (phosphoric acid) for 15 sec, removes smear
layer & exposes collagen network
2.Rinse to remove etchant
3. Dry with air , without desiccating the collagen mesh
4. Slightly moisten the surface
5. Absorb excess water with a cotton pellet
6. Apply primer ( 1-6 coats ) which infiltrates collagen & allow
it to polymerize
7. Dry thoroughly to remove primer solvent
8. Apply adhesive bonding agent (thickness 50 µm ) to
enamel & dentin .
9. Light cure – the primers & bonding agents
10. Apply composite resin over adhesive
11. Cure the matrix resin of composite resin
Examples
◦ All – Bond II , ScotchBond Multi-Purpose
◦ Optibond FL
Fifth Generation(late 1990’s)
One step or one bottle products.
 Misnomer as these products are applied
in 2 steps
Etchant
Combined Primer
Adhesive resin
First step
Second step
(One bottle)
5 th generation
conditioner
Combined
Primer
adhesive resin
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Consist of 2-step
Available as “one bottle” or “one –step” adhesive system (but
product applied in 2 –step)
 Separate etching/ conditioning step
 Consist of primer & adhesive resin into one application
 Etchant – 30-40% phosphoric gel , rinsed away ,promotes
the dissolution of enamel rods ,creating more porosities ,
filled by bonding agent followed by polymerization
 In case of dentin phosphoric acid exposes a collagen
network ,resin infiltrates the collagen mesh ,forming a
hybrid layer . On polymerization hybrid layer provides
micromechanical bonding
High bond strengths 3-25 Mpa
E.g - prime & bond ,Single bond, OptiBond Solo , OptiBond
Solo Plus
Self – etch Adhesives
1. Two – step (6 th generation )
 Self etching primer (conditioner + primer), adhesive
2. One – step (7 th generation )
Sixth Generation(late 1990’s)
2 step (self – etch PRIMER)
Does not involve a separate
etching step
 In this case acidic monomer is
used to condition & prime the
tooth at the same time
 2 types of self etch adhesive –
mild & strong
 Mild(PH=2),partially dissolves
dentin surface, so substantial
amount of HAC remain available
with in the hybrid layer
 Strong (low PH ˂1)

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These systems use self etching primers to
partially demineralize the smear layer and
the underlying dentin surface without
removing the dissolved smear layer.
 2- step

Self etch primer
Adhesive
Resin
First step
Second step
6th generation
Self –etching
Primer
Adhesive
resin
Seventh Generation
(most recent)
 Comprise of the one – step self
etch system (single solution)
 Also named “All-in-one” adhesives
 In this all primary component - conditioner, primer
& bonding resin are into a single solution
 No mixing
 Low bond strengths
 E.g –
- Promp L Pop (ESPE)
- Prime and Bond NT (Dentsply)
Self –etching
Adhesive
Single solution (all
in one )
Currently Available Generations

Fourth Generation

◦ Three-step:
◦ 1. Etch & rinse
2.Primer
◦ 3. adhesive

Fifth Generation
◦ Two-step: 1. Etch &
rinse, 2. primer &
adhesive
 Mix
Sixth Generation
◦ Two-step Self-etch
 No mix
◦ One-step Self-etch
 mix

Seventh
Generation
◦ One-step Self-etch
 no mix
Uses of bonding agents
1. Adhesion of restorative resin to GIC -base
 2. Bonding amalgam restorations to cavity
walls using amalgam bond. It should be used
to supplement mechanical retention.
 3. Repair amalgam restorations by
condensing new amalgam on a freshened
old amalgam after applying the adhesive of
amalgam bond.
 4. Luting of cast restorations e.g. panavia
 Management of dentine hypersensitivity.
