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 -1-
Dr. Hazem El Ajrami

3. Adhesion to tooth structure has been and is
still the daydream of the restorative dental
profession. Since the introduction of the acid
etch technique, by Buonocore in 1955, a new era
in dental practice based on the adhesion concept
has evolved. Today, we are in the age of
adhesive dentistry. Traditional mechanical
methods of retaining restorative materials have
been replaced, to a large extent, by tooth-
conserving adhesive methods. Most instances of
dental adhesion are also called dental bonding.

4. • Advantages and clinical significance of
adhesion:
1. Allow stabilization and long-term retention
of restorations.
2. Provides better resistance against fracture of
tooth or restoration by allowing better
transmission and distribution of functional
stresses across the bonded interface to the
tooth. Thus, the tooth and restoration will act
as one unit. This also gives the adhesive
restoration the potential to reinforce the
remaining weakened tooth structure.

5. 3. Maximize tooth conservation, compared to
non-bonded restorations which require
additional removal of sound tooth structure to
provide for the necessary resistance and
retention features.
4. Reduce micro leakage at the tooth/restoration
interface. This would minimize the ingress of
oral fluids and bacteria along the cavity wall,
thus reducing clinical problems such as
postoperative hypersensitivity, marginal
staining and recurrent caries, all of which may
jeopardize the clinical longevity of
restorations.

6. 5. Expand the range of possibilities for esthetic
restorative dentistry; including correcting
dimensions and color of teeth, bonding
indirect resin-based restorations, repairing
existing restorations in addition to producing
highly esthetic “invisible” direct restorations.

9.  The word Adhesion is derived from the Latin
word adhaerere, which is composed of ad = to
and haerere = stick (to stick to). When two
substances are brought into intimate contact
with each other, the molecules of one substance
adhere to or are attracted to the molecules of the
other. This force is called adhesion when unlike
molecules are attracted and cohesion when
molecules of the same kind are attracted.

10. It is very difficult to make 2 solid surfaces
adhere. Regardless of how smooth their surfaces
may appear, they are likely to be rough when
considered on microscopic level. When they are
placed in opposition, only the high spots will be
in contact. One way to overcome this is to place a
fluid between them which will flow into the
irregularities and provide for contact over a great
part of the solid. The material or film added to
produce adhesion is known as the adhesive, while
the surface to which it is applied is called the
adherent.

11. Glass ionomer cement is the only
restorative material that posses an intrinsic
self-adhesive capacity to tooth structure. Most
other situations involving dental adhesion
really involve adhesive joints. An adhesive
joint is the result of interactions of a layer of
intermediate material (adhesive) with two
surfaces (adherent) producing two adhesive
interfaces.

12. An example for an adhesive joint is
bonding resin composite to tooth structure
using a bonding agent, where the composite
and the tooth substrates are the adherents and
the bonding agent is the adhesive.

13. Mechanisms of adhesion:
1. Physical adhesion; involves electrostatic
interactions that are relatively weak. It may be
the only type of adhesion if surfaces are
smooth and chemically dissimilar.
2. Chemical adhesion; where there is bonding at
the atomic or molecular level formed across
the interface from the adhesive to the
adherent. The extent to which this type of
bonding is possible is limited.

14. Mechanisms of adhesion

15. 3. Mechanical adhesion; where the substrate
has undercuts or other irregularities that
produce interlocking of the materials.

16. Almost every case of dental adhesion is based
on mechanical retention. Retention of adhesive
restorations to cavities have not shifted far from
the old Black's retention principles, which relies
on the interlocking of restorative materials in
undercuts created in the cavities, now called
macro-mechanical means of retention. The
retention of adhesive restorations relies on the
same mechanical retention, but on a microscopic
level, where the adhesive flows into the pores of
the adherent where it hardens and interlocks,
producing micro-mechanical retention.

17. • Requirements for adhesion:
To produce good bonding, the adhesive
should be able to flow easily over the adherent
to produce good wetting. Wetting is the degree
of spreading of one drop of liquid on a solid
surface and is measured by the contact angle.
Contact angle is the angle formed by the
adhesive with the adherent at their interface it
may be:

18. 0 or 180 degrees → maximum adhesion
Less than 90 degrees → moderate adhesion
More than 90 degrees → poor adhesion

19. Principle of wetting measured by contact angle Ɵ

20. • In addition, sufficient wetting of the adhesive
will only occur if its surface tension is less than
the surface energy of the adherend. Surface
energy or surface tension is the increase in
energy per unit area of a surface.

21. Thus, the requirements for successful wetting of
adhesive are:
1.Intimate molecular contact between adhesive
and tooth tissues (adherent).
2.Cleanliness of the tooth tissues.
3.High surface energy of the tooth tissues to be
able to attract the atoms of the adhesive.
.4Low-surface tension of the adhesive material to
be able to properly wet the adherent.
5.Low viscosity of the adhesive to penetrate into
the microporosities.
6.To be able to displace air and moisture during
the bonding process.

22. A successful adhesive joint should be:
1. Gap free.
2. Of sufficient bond strength to resist
debonding under polymerization shrinkage
stresses of resin composite or under function.
The bond strength is the measure of the
bond-bearing capability of the adhesive and
is evaluated by the force needed to debond
the adhesive.

23. 3. Compatible to tooth tissues and restorative
material.
4. Dimensionally and hydrolytically stable in
the complex oral environment.
This would provide bond durability which is
the time period during which the bond
remains effective.

24. • History of adhesive dentistry:
Experiments on bonding acrylic resin to
enamel and dentin began in the 1950's in
England with Dr. Oscar Hugger who
developed a monomer based on
glycerophosphoric acid. In 1955, in the USA,
Dr. Michael Buonocore made the second, and
more important, advance in adhesive dentistry.
He identified the occurrence of
micromechanical adhesion to enamel via its
acid etching. Buonocore was regarded as the
Father of Adhesive Dentistry. His efforts
paved the way for development of bonding
agents that aimed enamel at the beginning, and
then shifted to dentin.

25. • The Japanese researcher Fusayama, in 1979,
advocated etching dentin using phosphoric acid.
His researches with other colleagues started a new
era in dentistry. At that time many scientists
refused the concept of dentin etching, fearing of
pulpal irritation. Later in the mid 80's, this
concept was internationalized and it was clear that
dentin could be etched if, and only if, dentin could
be sealed adequately with subsequently applied
bonding resins. It was indicated that pulpal
problems results from ingress of bacteria and not
from acid-etch application. Thereafter, there was a
shift from enamel etch to total etch technique
involving enamel and dentin. Current adhesives
bond to enamel and dentin simultaneously.

26. • Classification of contemporary dental
adhesives: Based on the adhesion strategy, Van
Meerbeek in 2001 has classified dental
adhesives into three main categories; etch-and-
rinse adhesives, self-etch adhesives and glass
ionomer adhesives. All three categories of
adhesives exhibit a common adhesion
mechanism of hybridization. This is the process
of micro-mechanical interlocking which occurs
by infiltration of resin into demineralized
substrate. The resultant resin-infiltrated hybrid
layer to dentin was first described by
Nakabayashi in 1982.

28. • According to clinical application steps, the
etch-and-rinse adhesives are currently
available as three-step, where etching, priming
and bonding to tooth substrates are done
individually or two-step where primer and
adhesive are simplified into one bottle. Self-
etch systems do not comprise a separate
etching step. They are applied in either two-
step; an acidic primer and an adhesive or all-
in-one adhesive where primer and adhesive are
simplified into one step.

29. • Self-etch adhesives are further classified
according to their aggressiveness or acidity
into: mild (PH ≥ 2), intermediate (PH ≈ 1.5)
and strong (PH ≤ 1).

30. • Bonding to enamel and dentin:
The composition and structure of enamel
and dentin is different, and thus adhesion to the
two tooth tissues is also different. Bonding to
enamel is easily achieved than bonding to
dentin. Enamel is almost homogenous in
composition and structure, irrespective of its
depth or location. It is composed of 96 wt%
inorganic content, mainly hydroxyapatite
crystals arranged as enamel rods. It also
possesses a high surface-free energy. Bonding
to dentin, on the other hand suffer from different
obstacles, and only recently have dentin
adhesive systems reached bond strengths
approaching that of enamel.

32. • Problems in bonding to dentin:
1. Heterogeneous composition: Unlike
enamel, dentin contains high percentage of
water and organic content, mainly
collagen, and only 70 %wt inorganic
hydroxyapatite. In addition, these
constituents are unevenly distributed in
intertubular and peritubular dentin.

34. 2. Complex histological structure: It is
composed of numerous dentinal tubules.
Each tubule is surrounded by a collar of
hyper-mineralized peritubular dentin. In
between the tubules there is intertubular
dentin which is less mineralized and contains
more organic collagen. The dentinal tubules
diverge from the dentin-enamel junction to
the pulp. Thus, the number and diameter of
dentinal tubules increases at pulpal dentin.

36. (OP) odontoblastic process.(OP) odontoblastic process.
(DTS) dentinal tubule space.(DTS) dentinal tubule space.
(LL) lamina limitans.(LL) lamina limitans.
(PTD) peritubular dentin.(PTD) peritubular dentin.
(ITD) intertubular dentin.(ITD) intertubular dentin.
ITDITD

37. 3. Inherent intrinsic wetness: the dentinal
tubules are filled with dentinal fluid which
renders dentin under constant wetness. Deep
dentin has more intrinsic wetness than
superficial dentin and is thus more difficult
to bond to. In addition, the dentinal fluid is
under a slight, but constant, outward pressure
from the pulp. The intrapulpal fluid pressure
is estimated to be 25 to 30 mmHg.

39. 4. Dentin is a dynamic tissue subject to
continuous physiologic and pathologic
changes in composition and microstructure.
Presence of more than one type of dentin
presents challenges in dentin bonding.
5. Presence of smear layer on the cut dentinal
surface.

40. • The Smear Layer:
Following cutting of dentin with manual
and rotary instrumentation, a layer 2-5 microns
thick is formed on the surface of dentin. This
layer of cutting debris, called the smear layer, is
burnished on the cut surface by the effect of heat
and pressure of cutting and cannot be removed
by rinsing. Its composition is derived from the
cut tissue from which it is produced. In dentin, it
is generally formed of chips, hydroxyapatite
crystals, collagen, saliva and blood and it
incorporates microorganisms.

42. • The smear layer becomes packed inside the
dentinal tubule forming a smear plug. In
enamel, it is composed of larger apatite
crystals tightly bound by salivary
glycoprotiens to form a crust over enamel
surface. It also contains microorganisms.

44. Longitudinal section in cut dentin showing the smear layer and the smear plug.

45. • Advantages of smear layer:
It reduces dentin permeability by about
86% through plugging the dentinal tubules and
reducing the flow of inter-tubular dentin
fluids, thus reducing the intratubular and
intertubular permeability, respectively. It thus
provides a drier surface for adhesion,
minimizes post-operative hypersensitivity and
preventing the ingress of irritants from the
restorative material to the tubules.

46. • Disadvantages of smear layer:
It incorporates microorganisms. In
addition, it is loosely attached to the
underlying dentin providing for a weak joint
between the tooth tissues and the restorative
material. Thus, current adhesive systems
should remove or penetrate through the smear
layer to ensure successful bonding.

47. Thank You