2. WHATAREBONDINGAGENTS?
Bonding agents can be defined as materialS
of low viscosity, when applied on the tooth
surface forms a thin film after setting.
This thin film strongly bonds to the tooth
surface, on which the viscous composite
restorative resin is applied. This after setting
forms an integrated resin restoration.
3. CHALLENGESINDENTINBONDING
Adhesive material interaction- mechanically,
chemically or both.
Mainly relies on the penetration of adhesive
monomer into the filigree of collagen fibers left
exposed by acid etch technique.
Greater challenge- water, organic material, type
one collagen , dense network of tubules that
connect the pulp with DEJ.
4. Tubules are lined by peritubular dentin.
Intertubular dentin penetrated by submicron
channels- allow passage of tubular fluid.
Intrinsically hydrated and movement of fluid
from pulp to DEJ due slight constant
pressure.ENAMEL
MINERAL 88%
WATER 10%
ORGANIC 2%
5. Tubules enclose cellular extensions from the
odontoblasts- in direct communication with pulp.
45,000/mm² tubules - closer to pulp
( 22%), 22,000/mm²- near DEJ ( 1%)
Bond strength less in deep dentin- 4- META
MONOMER( not affected by dentin depth).
Formation of smear layer leads to smear plugs
in dentinal tubules that decrease dentin
permeability by 86%.
6. Smear layer- hydroyapatite
and altered denatured
collagen, its removal by acidic
solutions results in increased
fluid flow onto the exposed
dentin surface( interference
with adhesion)
Additional factors-
vasoconstrictors in LA that
dec. fluid flow and pulpal
pressure, radius and length of
tubules, viscosity of dentinal
7. STRESSESAT RESINDENTININTERFACE
Polymerization shrinkage of composites creates
stress within composite mass-7MPa
Configuration factor influences stress relief.
number of bonded surfaces
number of un-bonded surfaces
Stress relief depends on the number of free
surfaces
Unrelieved stresses- internal bond disruption,
marginal gaps and microleakage
8. Immediate bond strengths of 17MPa- to
resist contraction stresses, water sorption by
resin compensates for the polymerization
shrinkage, directly proportional to resin
content.
Wide temp. variations- restoration undergoes
volumetric changes
Linear coefficient of thermal expansion- 4
times greater for resin
9. DEVELOPMENT
BEGINNING
1950- Resin containing glycerophosphoric
acid dimethacrylate (GPDM) could bond to
hydrochloric acid etched dentin surface.
Primitive technique, bond strength low.
10. FIRST GENERATION
‘CERVIDENT’ NPG- GMA, surface active
comonomer.
Comonomer could chelate with Ca on the
tooth surface to generate water resistant
chemical bonds of resin to dental Ca.
Bond strenths of 2-3 MPa , poor clinical
results
11. SECOND GENERATION
Clearfil bond system- Japan
First product, contained phosphate-ester
material( phenyl-P and HEMA in ethanol)
MOA: polar interaction between negatively
charged phosphate groups in the resin and
positively charged Ca ions in the smear layer.
12. In vitro bond strengths of 1-5 MPa
Did not wet dentin well and did not penetrate
the entire depth of smear layer and could not
reach the superficial dentin to establish ionic
bonding or resin extensions into dentinal
tubules.
Bonding material tended to peel from dentin
surface after water storage
Clinically unacceptable after two yrs of
placement.
13. THIRD GENERATION
Concept of phosphoric acid etching of dentin
before applying a phosphate ester- type
bonding agent, hydrophobic nature of
bonding resin resulted in no significant
increase of bond strength.
Pulpal inflammatory responses.
Clearfil New Bond- long hydrophobic and
short hydrophillic component.
14. Removal of entire smear layer not seen
butmodified and allowed penetration of acidic
monomers, such as phenyl-P or PENTA.
Treatment of smear layer with acidic primers-
using 2.5% maleic acid, 55% HEMA nad a
trace of methacrylic acid
Scotchbond 2- first dentin bonding agent to
recieve full acceptance from ADA.
17. ONE-BOTTLE
TOTAL-ETCH
(E+[PB])
ETCHANT (E)
Removes smear
layer.
Exposes
intertubuler and
peritubular
collagen.
Opens tubbules
in funnel
configuration
and decreases
surface energy.
PRIMER +
BONDING
AGENT (PB)
Penetrates into
dentin tubules
forming resin tags.
First coat applied
on etched dentin
works as a primer-
increases surface
free energy of
dentin.
Second coat acts
as bonding agent
used in three step
system-
Fills spaces
between the dense
18.
19. TWO-BOTTLE
SELF ETCH (
[EP]+ B)
ETCHANT
+PRIMER (EP)
Self etching primer
does not remove
smear layer , fixes
it and exposes
about 0.5-1µm of
intertubular
collagen because
of its acidity( pH-
1.2-2.0).
Smear plug
impregnated with
acidic monomer,
prepares pathway
for penetration
subsequently
placed fluid resin
BONDING
AGENT (B)
Same type of
bonding agent
included in three -
step, total-etch
systems.
The resin tags form
on resin
penetration onto
the microchannels
of the primer-
impregnated smear
plug.
20. ALL -IN -ONE SELF
ETCH (EPB)
Etches enamel.
Incorporates the smear
layer into the interface.
Being an aqueous
solution of a phosphated
monomer, it de-
mineralizes and
penetrates dentin
simultaneously, leaving a
precipitate on the hybrid
layer.
Forms a thin layer of
adhesive, leading to low
bond strengths; a multi-
coat approach is
recommended.
21.
22. HYBRIDLAYER
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, exposure of
collagen fibrils seen, hydroxyapatite within the
intertubular dentin removed.
B) Primers penetrate collagen network.
C) Resin microtags formed by adhesive resins and
primers within the intertubular dentin and
surround the collagen fibres upon cooling.
23.
24.
25. MOISTVERSUSDRYDENTINSURFACES
Vital dentin is inherently wet, water is
considered as an obstacle for attaining an
effective adhesion of resins to dentin.
“Moist bonding technique” ( combination of
hydrophillic and hydrophobic monomers in
same bottle dissolved in an organic solvent like
ethanol or acetone) prevents collagen
collapse.
The solvents help in displacing water from
dentin surface and the moist collagen network
and promotes infiltration of resin monomers.
26. Pooled moisture- excess water on tooth
renders dilution of primer making it less
effective.
Glistening hydrated surface preferred
Usually tooth preparation dried to check for
classic etched enamel appearance but,
dentin collagen collapses easily on air drying,
resulting in closing of the micropores in the
exposed intertubular collagen
27. Acetone- based, water free dentin bonding
systems require rewetting of etched dentin
surface with aqueous rewetting agents that
restore bond strength values and raise the
collapsed collagen network.
Collapse of collagen network due to change in
molecular arrangement. Extra-fibrillar spaces
being fewer in dried collagen, results in less
penetration of monomers.
Rewetting dentin after air drying to check for
frosty appearance is an acceptable procedure.
