Dr. lama khaled El Banna Faculty of Oral and Dental Medicine Al – Azhar University operative dentistry part two

2. College of Dentistry
Operative Dentistry II
Introduction to Adhesive Dentistry -2-
Dr. Hazem El Ajrami

3. • Steps of bonding to enamel and dentin:
The steps of bonding to tooth substrate differ
to some extent depending on the category of
adhesive used. Adhesive systems generally aim
to remove, dissolve or modify smear layer and
create microporosities in enamel and dentin for
micromechanical interlocking. Manufacturer's
instructions for application of each adhesive
system should be strictly followed, and the use
of the adhesive system with its recommended
composite is mandatory.

4. 1. Etch-and-rinse adhesives: (smear layer
removing adhesives):
A. Selective acid demineralization
(conditioning, etching):
Conditioning is defined as any
chemical alteration on the substrate surface
by acids with the objective of removing the
smear layer and simultaneously
demineralizing the surface. Etching is a form
of conditioning usually termed if a strong
acid is used, particularly on enamel surface.

5. • Etch-and-rinse adhesives incorporate a
separate etching step which is used for total
etching of enamel and dentin, followed by
thorough rinsing. Generally, use of phosphoric
acid concentration between 30% and 40% and
an etching time of no less than 15 seconds are
recommended to achieve the most receptive
surface for bonding.

6. • Acid etchant is supplied in the form of a liquid
or colored gel. The gel form is preferred
because its application is easier to control. The
etchant must be thoroughly rinsed with water
for 5-10 seconds to remove the acid remnants
and the dissolved calcium phosphates.

7. • Enamel etching:
The goals of enamel etching are to remove
the organic pellicle and prismless enamel in
uncut enamel and to remove the smear layer in
cut enamel. Enamel etching partially dissolves
the mineral crystals transforming smooth enamel
surface into an irregular surface with numerous
microporosities, thus enlarging its surface area
for bonding, increasing its surface energy more
than twice that of unetched enamel and lowering
contact angle of wetting.

8. • Selective demineralization of enamel surface
produces dissolution and microporosities in
the interprismatic substance (interprism
etching) (black arrow) in addition to
microporosities in the enamel prism core
(intraprism etching) (white arrow).

10. • Dentin etching:
The goal of dentin etching in Etch-and-rinse
adhesives is the total removal of the smear
layer, including the smear plugs and to
demineralize the superficial dentin surface. This
removes the minerals from this superficial layer
and exposes a microporous layer of organic
collagen fibers, thus increasing the
microporosity of the intertubular dentin.

11. • When the acid etching unplugs the dentinal
tubules, it demineralizes the peritubular dentin
to a lesser extent producing more funneling of
the dentinal tubules. The exposed collagen
fibrils function as a microretentive network for
micromechanichal interlocking of the resin
polymers.

12. B. Primer:
Acid-etched enamel has high surface
energy and does not need a separate primer
application to achieve effective bonding. On
the contrary to enamel, etching of dentin
decreases its surface energy. This is due to
the high protein extent exposed after etching
(exposed collagen).

13. • In addition, the increased permeability and
wetness of dentin hinder adhesion. Thus, a
primer should be used to ensure sufficient
wetting to dentin, displace residual water and
sufficiently carry monomer into created
microporosities. Primers are thus called
adhesion-promoting monomers.

14. • Effective primers should contain hydrophilic
monomers, e.g. Hydroxyethyl Methacraylate
(HEMA), that have an affinity for wet dentin
and a hydrophobic part that co-polymerizes
with the subsequently applied adhesive resin.
The primer could contain organic solvents,
such as acetone or ethanol.

15. • Because of their volatile characteristics, these
solvents act as water-chaser; it displaces water
from the dentinal surface, promoting the
infiltration of monomers through the exposed
collagen. A primer application time of at least
15 seconds should be performed to allow
proper interdiffusion of monomers to full
depth of demineralized dentin.

16. C. Adhesive resin:
The adhesive resin, also called "Bonding
agent", is a solvent-free, filled (i.e. containing
filler particles) or unfilled solution containing
mainly hydrophobic monomers. It co-
polymerizes with the previously applied
primer and the subsequently applied resin
composite.

17. • When adhesive resin infiltrates the etched
enamel, two types of resin tags are
subsequently formed; Macro-tags at the prism
peripheries with the etched interprismatic
substance and Micro-tags at the cores of
enamel prisms (with intraprism etching).
Macro-tags probably contribute more to bond
strength because of their greater quantity and
larger surface area.

18. Enamel Prism (rod)
Macro-tag
Micro-tag

19. • When the adhesive resin infiltrates primed
dentin, it fills up the interfibrillar spaces left
between the collagen fibrils leading to
hybridization with dentin. This hybrid layer or
hybrid zone occurs mainly with demineralized
intertubular dentin. It also forms with
demineralized peritubular dentin (tubule wall
hybridization).

21. • The adhesive also enters dentinal tubules
forming resin tags. It was found that
intertubular hybridization is more important
than resin tags in the bonding process. It
contributes more to the bond strength of an
adhesive system.

23. • In addition, peritubular or tubule wall
hybridization provides a firm attachment of the
resin tag necks to the tubule walls and more
importantly guarantees proper hermetic sealing
of the tubules. The resin also infiltrates lateral
tubule branches forming submicron lateral
resin tag formation.

25. • A commercial example for three-step etch-
and-rinse adhesive system is Scotchbond
Multipurpose (3M ESPE). In two-step etch-
and-rinse adhesives, primer and adhesive
bonding components are combined into one
solution that should fulfill both functions. An
example is Excite Bond (Ivoclar Viva-dent).

27. • Wet versus dry bonding:
Following etching and rinsing, enamel and
dentin present different conditions for priming
and bonding. Whereas enamel should be dry to
achieve good bonding, a certain amount of
water is needed in dentin to prevent the collagen
fibrils in dentin from shrinking.

28. • Conventionally, acid etched enamel was dried
with short intermittent blasts of air until the
enamel shows a chalky white appearance.
However, this was found to cause collapse of
dentinal unsupported collagen network
preventing proper infiltration of collagen with
monomers.

30. Dentin was kept moist
Dentin was air-dried

31. • To overcome this problem in dentin bonding,
two different approaches can be followed
depending on the primer of the adhesive system.
The first approach, known as the dry bonding
technique, involves air drying of enamel and
dentin and applying a water-based primer
capable of re-expanding the collapsed collagen
network.

32. • An alternative approach, wet bonding technique,
is to leave dentin moist, thereby preventing any
collapse of collagen, and use a solvent-
containing primer, known for its water-chasing
capacity. The solvent displaces dentinal water,
thereby carrying the monomers into the opened
dentinal tubules and through the nanospaces of
the collagen web. The solvents of the primer are
then evaporated by gentle air-drying, leaving the
active primer monomers behind.

33. • N.B.: Although enamel does not need a
separate priming step, it needs dry bonding for
effective wetting of the adhesive. Thus, when
using wet bonding technique, primers are
indicated to be applied on acid etched enamel
to displace residual water through solvent
evaporation.

34. • Advantages of Etch-and-rinse adhesives:
1. Proven effective bonding with enamel and
dentin with sufficient long-term clinical
results. Three-step adhesives are considered
the gold standard for adhesives.

35. 2. Three-step adhesives have low technique
sensitivity due to separate application of
primer and adhesive resin; each applied to
serve a specific function. Two-step etch-and-
rinse adhesives have more simplified
application but are more technique sensitive
than three-step adhesives.
3. Possibility for particle-filled adhesive. Filled
adhesives act as shock absorbers and increase
the bond strength of adhesives.

36. • Disadvantages of Etch-and-rinse adhesives:
1. Time consuming due to multi-steps
required.
2. Separate post-etching rinsing step is
required.

37. 3. Risk of over-etching dentin due to aggressive
etching of phosphoric acid. This will cause
demineralization to a depth that might be
inaccessible for complete resin impregnation,
leading to a porous zone in the hybrid layer.
This discrepancy between depth of
demineralization and the depth of resin
infiltration results in nanoleakage which is
basically the presence of submicrometer-sized
gaps within the hybrid layer. By time, this may
compromise the durability of the bond due to
hydrolysis of exposed collagen.

38. 4. Total removal of smear layer can cause post-
operative sensitivity due to dentinal fluid
movement. It also increases dentin
permeability leading increased wetness of
dentin.
5. Sensitive to over-wet or over-dry dentin
condition. When using wet bonding technique,
over-wetting of dentin should be avoided to
prevent dilution of the adhesive. Over-drying
dentin causes collapse of collagen fibers as
discussed before.

39. Thank You