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INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

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Definitions
• Adhesion ~ the attraction between two atoms and
molecules at the contacting surfaces of different
materials; it can be chemical (ionic), physical (van der
Waals’), and/or mechanical (micro- or macro-
interlocking)
• Adhesive ~ monomer (or related) that penetrates and
establishes intimate contact with the conditioned tissue
substrate, polymerises, and forms a strong bond between
such substrate and the restorative material
• Priming ~ cleaning, structural alteration, and
increasing adhesiveness of the substrate.

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• Etching ~ dissolution of the substrate, removed by
rinsing to enhance intimate contact of adhesives
with collagen.
• Wetting ~ the ability of a liquid to come into
intimate contact with solid substrate; facilitates
bonding

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Evolution of the concept of “Acid etching”:

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Microstructure of enamel:
% by volume
3%
12%
85%
water
organic
mineral
• Inorganic component
is homogenous,
regular rods and
prisms

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Adhesion to enamel:
• Acid etching
removes approx 10
microns of enamel
• Creates microporous
layer 5-50 microns

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Microstructure of dentin:
• Human dentin is a heterogenous material composed
of a solid (circumpulpal) phase surrounding a
network of tubules.
• These tubules, measuring about 1 to 3 micrometer in
diameter, contain elongated cell bodies that radiate
from the the dental pulp organ throughout the entire
dentin.
• Their average density is about 30 000 tubules/square
mm..

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Microstructure of dentin:
• Structurally dentin is
composed of mineral crystals
deposited between a network
of protein fibrils.
• Approximately 90% of this
network is type I collagen,
the balance consisting of a
sheath of phosphoproteins
surrounding the collagen,
and other proteins in small
amounts.

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Microstructure of dentin:
% by volume
22%33%
45%
water
organic
mineral
• Inorganic component is
heterogeneous,
peritubular and
intertubular dentin
• Low surface free energy
- wets less easily

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A, Peritubular dentin; B, Intertubular dentin; C, Dentinal tubule

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A, Intertubular dentin; B, Peritubular dentin; C, Dentinal tubule

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Dentinal tubules Pulp DEJ
• Diameter (microns) 2.5 0.8
• Number 45,000 20,000
• Tubular surface area 25% 3%

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Difficulties of bonding to dentin
• Complex histologic structure and variable composition of
the dentin.
• Whereas enamel is 92% inorganic hydroxyapatite by
volume, dentine is (on average) only 45% inorganic.
• Also dentinal hydroxyapatite is randomly arranged in an
organic matrix that consists primarily of collagen, which is
permeated throughout by tubules.
• These contain vital processes of the pulp odontoblasts.
Hence, vital dentine is a sensitive structure.
• The high water content provides competition with any
adhesive biomaterial for bonding to dentine.

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Smear Layer:
• Tooth surface instrumented with a rotary or manual
instrument
• Composed of:
– Pulverized hydroxyapatite
– Altered collagen
– Bacteria
– Saliva

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Smear Layer
• To achieve a strong bond, it is necessary to either
strengthen this smear-layer in situ or to remove it
entirely.
• In the latter, it is imperative to ensure an adequately
adhesive restorative otherwise the open tubules may
allow irritants or bacteria greater access to the pulp.

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Conditioning of dentin:
• Removes smear layer.
• Exposes a microporous scaffold of collagen fibrils
increasing the microporosity of intertubular dentin.

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Conditioning of dentin:
Various acids used
Phosphoric
Citric
Maleic
Nitric

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Concept of a Dentin Bonding Agent:
D
E
N
T
I
N
COMPOSITE
Dentin
Bonding
Agent
HYDROPHILIC
HYDROPHOBIC

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Classification of Bonding Agents based on their
shear bond strength: (Eick et al, 1991)
Three categories of dentinal adhesives are proposed:
• Category I includes adhesives with shear bond
strength values between 5 and 7 Mpa;
• Category II includes dentinal adhesives with shear
bond strengths between 8 and 14 Mpa; and
• Category III includes adhesives with shear bond
strength values above 20 Mpa .

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Clinical significance of this classification:
• Polymerization shrinkage
– 2.9 to 7.1% by volume
– contraction gap
– 17-20 MPa bond strength to overcome (Davidson
et al)

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According to generations:
Evolution of bonding
agents from
No etch to
total etch
and self etch.

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Evolution of Dentin Bonding Agents:
• First Generation.
• Second Generation.
• Third Generation.
• Fourth Generation.
• Fifth Generation.
• Sixth Generation.
• Seventh Generation.

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Factors influencing the evolution of
bonding systems:
• Etching enamel
• Etching/conditioning Dentin
• Smear Layer Treatment
• Handling properties

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First Generation
• These contained N-phenylglycine and glycidyl
methacrylate or NPG-GMA.
• NPG-GMA is a bifunctional molecule or coupling
agent.
• This means that one end of this molecule bonds to
dentin while the other bonds (polymerizes) to
composite resin.
• The bond strengths of these early systems were only
1 to 3 MPa.

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Second Generation
• In the late1970s, the second-generation systems were
introduced.
• The majority of these incorporated halophosphorous
esters of unfilled resins such as bisphenol- A glycidyl
methacrylate, or bis-GMA, or hydroxyethyl
methacrylate, or HEMA.
• The mechanism by which these bonded to dentin
were postulated to be through an ionic bond to
calcium by chlorophosphate groups.
• These were weak bonds with a range of 2-7 MPa.

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Drawbacks:
• Since dentin was not etched in these early bonding
systems bonding was with the smear layer.
• Water immersion.

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Third Generation
• Three step systems.
• Dentin etching was introduced by Fusuyama.
• Followed by a primer application.
• Application of an unfilled resin.

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Dentin Primer:
• The primer contains hydrophilic resin monomers
which include hydroxyethyl trimellitate anhydride, or
4-META, and biphenyl dimethacrylate, or BPDM.
• The primers contain a hydrophilic group that
infiltrates the smear layer, modifying it and
promoting adhesion to dentin, and the hydrophobic
group of the primer creates adhesion to the resin.
• Dentin primers may be 6 % phosphate penta-
acrylate, (PENTA) ; 30 % HEMA; and 64 % ethanol.

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Examples:
Denthesive

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Fourth Generation
• The fourth generation bonding system contains two
or more bottles.
• One consists of the primer and the other the
adhesive.

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Etchant Primer Adhesive+ +
Etchant Primer AdhesivePrimer
and
adhesive
3 step total etch IV Generation
The conditioning step → priming step → Adhesive application.

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Here the complete removal of the smear layer is
achieved .

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Fourth Generation
• Fusayama and colleagues tried to simplify bonding to enamel
and dentin by total etching the preparation with 40 percent
phosphoric acid.
• The mineralized tissues of the peritubular and intertubular
dentin are dissolved by the acidic action; the initial surface
penetration exposes the collagen fibers.
• In this area, for a depth of 2 to 4 micrometers, hybridization
takes place, and resin tags can seal the tubule orifices firmly.

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Hybridisation Zone
• Results from the polymerized methacrylate and
dentin.
• The hybrid layer is defined as “the structure formed
in dental hard tissues (enamel, dentin, cementum) by
demineralization of the surface and subsurface,
followed by infiltration of monomers and subsequent
polymerization.”
Nakabayashi et al (1982)

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Hybrid zone
Hybrid zone

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• The formation of resin tags and adhesive lateral
branches complete the bonding mechanism between
the adhesive material and etched dentin substrate.

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Examples:
All Bond 2 Pro-Bond Liner Bond 2 Scotch Bond

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Fifth Generation
• Unique feature is the combination of the priming and
bond resin application steps, resulting in a one
component formula.
• Also rely heavily on wet bonding.
• Most commonly used and probably the most
successful system.

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Fifth Generation
• These bonding systems create a mechanical
interlocking with etched dentin by means of resin
tags, adhesive lateral branches and hybrid layer
formation..

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Etchant Primer Adhesive+ +
Etchant + Primer Adhesive
Primer
and
adhesive
3 step total etch
IV Generation
2 step
V Generation

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Examples:
Prime & Bond- NT
Adper Single Bond Optibond Solo
Gluma Comfort Bond

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Inter-comparison of V Generation:
Adhesive Mean Shear Bond Strength
( MPa )
Single Bond 30.0±5.5
Opti Bond Solo 23.4±3.4
One-Step 22.5±3.8
Prime & Bond 2.1 21.1±5.0

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Sixth Generation
• They are self etching adhesives ( Etch & prime
simultaneously).
• They involve a somewhat different mechanism in
that, as soon as the decalcification process is initiated,
the infusion of the evacuated spaces by dentin
bonding agent is begun.
• As a result, the potential for residual vacancies
amongst the collagenous fibers is dramatically
reduced or eliminated altogether.
• The bonding agent is either applied after the self
etching primer or mixed together before single
application.

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Etchant Primer Adhesive
Etchant Primer
Adhesive
+ +
+ +
Self
etching
primer
All in one
adhesive
Sixth Generation
Type I
Sixth Generation
Type II

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Examples:
Xeno IIIPrompt L Pop
Clearfil SE Bond

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Seventh Generation
Etchant Primer Adhesive+ +
Etchant Primer Adhesive
= All in one
adhesive

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Seventh Generation
I- Bond Xeno IVG Bond

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Classification of Bonding Agents based on
their effect on smear layer:
1. Modify the smear layer & incorporate it into the
bond.
• One step – Prime & Bond 2.1
• Two step – Pro Bond

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2. Completely removes the smear layer:
• Two step – Clearfil Liner Bond 2.
• Three step – Clearfil Liner Bond.

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3. Dissolves the smear layer than removing it.
• Prime & Bond 2.0.

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Differences between dentin in primary and
permanent teeth:
• Difference in the degree of mineralisation.
• Concentrations of both calcium and phosphorus in
both peritubular and intertubular dentin are lower in
primary teeth.
• The tubular diameter and density in dentin of primary
teeth is lesser than that in permanent teeth.

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Bonding to dentin in primary teeth:
• Dentin of primary teeth is more sensitive to the acid
etch/ conditioning procedure.
• This leads to an increased thickness of the hybrid
layer and the subsequent lack of complete penetration
of the adhesive resin into the demineralised dentin.
• Ideally the concentration and duration of etch/
conditioning has to be re-calculated for primary teeth.

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Bonding to carious dentin in primary teeth:
• Carious dentin is a combination of porous and non-
porous zones.
• The resultant deposition of Whitlockite may warrant
additional etching/ conditioning times compared to
sound dentin.

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Clinical requirements of a bonding system for
use in pediatric dentistry:
• Simple to use.
• Minimally irritating to the tissue.
• Less technique sensitive.
• Clinically satisfactory bond.

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The future of dentin bonding
• Chemically bonding the resin molecule to the
collagenous structure of dentin rather than by
means of micromechanical retention (as is
done now).
• Incidentally, another approach to dentinal
adhesion could center on the chemical bonding
of the resin to the hydroxyapatite .

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Celebrate the bond of Love!
Conclusion

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Enjoy!

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Thank You!............

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Differences:
• Prime & Bond 2.0 – Total etch
• Prime & Bond 2.1 – No etch
• Prime & Bond NT – Nano-Technology

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Wet Bonding Technique:
• Drying the dentin will produce a relatively
impermeable amorphous layer:
– Denatured collagen
– Collapse of collagen layer
• Must remain moist to resist this impermeable layer.
• Pooled moisture should be removed by blotting and
not with a blast of air.
• Dry dentin should be remoistened with a wet cotton
pledget.

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Etched dried dentin

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Etched moist dentin

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Selective etch v/s Total etch:
• The total-etch technique permits the etching of
enamel and dentin simultaneously using phosphoric
acid for 15 to 20 seconds.
• The surface must be left moist (“wet bonding”),
however, in order to avoid collagen collapse .
• The application of a hydrophilic primer solution
infiltrates the exposed collagen network forming the
hybrid layer .

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Smear layer not removed in second
generation adhesives
Bonding Agent
Smear Layer