5 adhesion to dental tooth tissues 1 Operative dentistry Egypt Cairo University Palestine Gaza Al Azhar University Dr. Inas Alim Uploaded by Dr. Lama El Banna

1. ALPINE SKI HOUSE
Dr. Inas Ayoub Elalem
inas.alalem@gmail.com
00970599448344
1
Operative Dentistry V

2. Adhesion to dental
tooth tissue
2

3. Adhesive Dentistry is a, relatively, new field that has
totally revolutionized the face of dentistry.
It is based on the concept of adhesion and totally covers
the areas of anterior & posterior cosmetic restorations
3

4. Innovations in dentistry have always been related to the
development of new materials , techniques &equipments
and thus , were always subject to changing and
disappearing with the evolution of newer ones.
For the first time, the innovation related to adhesion is
concept related , whereas the materials & techniques are
revolving and changing around this concept to satisfy it
and improve it without changing it .
4

5. The dream of restorative dentistry has always been to
develop a material that would totally bond to tooth
structure in such a way that , both the tooth and
material, would act & react as being one single unit .
5

6. The concept of adhesion and its application in
dentistry has made this dream become, relatively
very close , but it has to be understood that , in
spite of all the advancements that were achieved in
this field, it still is in an infant stage .
Thus , in all adhesive dental systems , one should
still expect islands of attachments separated by
areas of non-attachment .
6

7. Historical breakthroughs in adhesive dentistry
1- Experiments on bonding acrylic resin to enamel & dentin
began in the early fifties with Dr. Oscar Hugger in
England who developed a monomer based on
glycerophosphoric acid .
7

8. Historical breakthroughs in adhesive dentistry
2- In 1955 , Dr.Michael Buonocore in usa, made the most
important advance in this field by identifying the
occurrence of micromechanical adhesion to enamel
through acid etching .
Buonocore is considered to be the father of adhesive
dentistry . This innovation was not fully recognized in our
profession until the early 70’s .
8

9. Historical breakthroughs in adhesive dentistry
3- In 1979 , Dr.Fusayama in Japan advocated etching and
conditioning of dentin using phosphoric acid , starting a
new era in this fascinating field .
9

10. Terminology
Adhesion is the bonding of dissimilar materials by the
attraction of atoms or molecules.
Adhesive is the material used to produce adhesion ,
and is always a liquid.
Adherend is the surface to which the adhesive is applied,
and is always a solid.
The components of an adhesive system are present in the
process of restoring teeth ,i.e, the tooth tissues ( enamel
& dentin ) represent the adherend while the adhesive
restorative material represents the adhesive .
10

11. Wetting
It is very difficult to make two solid surfaces to adhere
completely, Regardless of how smooth their surfaces
appear to be, they are likely to be rough when
considered on a microscopic level.
When they are placed in apposition, only the high spots
will be in contact.
One method to overcome this , is to place a fluid between
them which will flow into the irregularities and provide
for a wider area of contact between the two solid
surfaces.
11

12. So, wetting is the degree of spreading of one drop
of liquid on a solid surface, and is measured by
the contact angle.
12

13. Contact angle is the angle formed by the adhesive with the
adherend at their interface.
It may be 0 or 180 degrees = maximum adhesion
less than 90 degrees = moderate adhesion
more than 90 degrees = poor adhesion
13

14. Mechanisms of adhesion in restorative dentistry:
1- Chemical or true adhesion where there is bonding at
the atomic or molecular level.
2- Mechanical attachment based on the old mechanical
retention concept . The adhesive flows into the pores of
the adherend where it hardens and interlocks.
14

15.  Retention of adhesive restorations in cavities have not
shifted from the old Black's retention principle, which
relies on interlocking of restorative materials in
undercuts created inside the cavity .
 Retention of adhesive restorations relies upon the same
mechanical principle , but on a microscopic level
(micro-retention) , aided by some degree of chemical
attachment which is present with the new adhesive
systems.
 So , retention of adhesive restorations in our modern
 practice is mechanico-chemical in nature .
15

16. A reliable and durable adhesive junction between the tooth
tissues and the adhesive restorative material is mandatory
for the successful clinical performance of the restoration,
in terms of retention, cosmetics and proper marginal seal .
Furthermore, the longevity of this reliable junction under
the destructive rigors which are present inside the oral
cavity represents the greatest challenge that faces our
adhesive practice .
16

17. Clinical significance of adhesion ( benefits )
1- Inhibition of marginal leakage which refers the ingress
of
saliva ,food debris , microorganisms and stains at the
tooth-restoration interface with its sequelae of recurrent
caries , hypersensitivity , discoloration , looseness of the
restoration and possible pulp involvement.
2- Re-inforcement of the tooth since adhesion bonds the
restorative material to the remaining tooth structure,
making them to behave clinically as one single structural
entity in sustaining and distributing the forces of
mastication . 17

18. 3- Solving the problem of retention especially in anterior
teeth, where trying to establish adequate mechanical
retentive features through undercutting would involve
more destruction & weakening of the tooth, if not
impossible at all &/or would not be sufficient to retain
the restorative material securely in place .
4- Adjusting esthetic defects without the need to grossly
reduce the teeth for crowning ( anterior cavities ,
minor discolorations , diastemas , malformed teeth ,
facings…)
5- Fulfilling the requisite of the modern esthetic practice
in placing successful posterior cosmetic restorations.
18

19. Requirements of a successful adhesive bond:
1- High bond strength values
- Bond strength to enamel should be equal or very close
to that to dentin, otherwise stresses might concentrate
at the interface with subsequent debonding and failure
- Bond strength values of 17-20 Mpa are required to
counteract the shrinkage stresses of composites during
polymerization , and even higher values are required
to resist mastication forces without failure .
- Recent adhesive systems have reached bond strength
values of 34-45 Mpa and even more as claimed by
some products.
19

20. 2- Elimination of voids at the interface
- The presence of voids at the interface, even in small &
separate areas, would disturb the structural continuity
of the tooth-restoration system, inviting leakage,
stress concentration, cracks formation and their
propagation with eventual debonding and failure.
- Voids are , unavoidably , present in all adhesive resin
systems, due to the polymerization shrinkage of the
material its incomplete polymerization , as well as
because of the inconsistent demineralization of the tooth
tissues.
20

21. 3- Stability and longevity
- The adhesive joint should be free from any dimensional
changes due to hardening or thermal changes, should
remain hydrolytically stable and should resist
biodegradation in the oral cavity.
- The long-term stability and longevity of an efficient
adhesive junction in the oral cavity is still very much
questionable and full of speculations because of the
complex interacting damaging rigors which are present
in the mouth ( stresses, temperature & PH fluctuations,
saliva, microorganisms as well as the heterogenicity of
the tooth tissues…) .
21

22. Properties that should be present in the tooth tissues
(adherend) and in the adhesive in order to provide for
a successful adhesive system
1- The tooth tissues should have a high surface energy to be
able to attract the atoms of the adhesive.
2- The tooth tissues should be clean and dry to provide for
direct apposition of the adhesive against these tissues.
3- The adhesive should have a low surface tension and low
viscosity to be able to properly wet the tooth tissues.
4- The adhesive should be biocompatible with the
dentin-pulp organ .
22

23. 5- The adhesive should contain both, hydrophilic
components to displace water and properly penetrate the
tooth surface ,and hydrophobic components to co-
polymerize with the composite resin material .
6- The adhesive should provide for some degree of
chemical bond with the tooth tissues , although the
longevity of this bond in the oral cavity is still not reliable
23

24. Bonding to tooth tissues
- Bonding to enamel & dentin is basically mechanical in
nature , and depends on the interlocking of an
intermediate adhesive layer ( bonding agent ) inside the
micro-pores created inside enamel and dentin through
etching and conditioning.
- An impregnated hybrid layer is thus formed from resin
and tooth tissues and co-polymerizes with the composite
material .
24

25. Bonding to tooth tissues
- Recent adhesive systems provide for some degree of
chemical attachment to tooth substrate through chelation
of Ca ions of the tooth tissues ( bonding to Ca in the
hydroxyapatite crystals ), or through bonding to the
collagen of dentin trough cross-linking .
25

26. Hybrid
Layer
Resin
Tags
Dentin Hybrid Layer
Hybrid
Layer
Resin
Tags
Enamel Hybrid Layer
26

27. Bonding to dentin is more difficult,complicated and less
reliable than bonding to enamel due to the following
facts :
1- Dentin contains a much lower percentage of inorganic
components ( 65% as compared to 95% in enamel )
which provides for less micro-pores formation with
surface conditioning and decalcification.
2- The surface energy of conditioned dentin surface is
much lower than that of enamel, and hence its capability
to attract molecules of the adhesive is weaker.
3- The presence of the smear layer on the surface of cut
dentin significantly reduces adhesion, unless it is dealt
with and removed .
27

28. 4- The structure of dentin is heterogenous ( less
homogenous than that of enamel,) because it contains
a much more significant amount of water , which
requires a bonding agent than can compete with
water and remove it to properly wet the surface .
5- This is further complicated by the inter-tubular
dentinal fluid that runs inside the dentinal tubules
under a constant positive pressure of 25-30 mm Hg .
6- The dentinal tubules are not regular nor consistent in
their number nor sizes , as they vary with alterations
in location and depth within the same tooth as well as
from one tooth to the other .
28

29. Enamel Dentin
29

30. Development of dentin bonding agents
1-First generation bonding agents
- A co-monomer was used ( primer ) to react chemically
with the inorganic Ca hydroxyapatite &/ or with the
collagen of dentin , e.g. NPG-GMA
( N-phenylglycineglycidylmethacrtlate )
- This system was not successful as it provided for low
bond strength values ( 2-3 Mpa ) .
2-Second generation bonding systems ( phosphate
bonding agents )
- Phosphate esters were added to the BIS-GMA resins in
an attempt to bond chemically with the phosphate and
calcium of dentin .
- This system was hydrolytically unstable and provided
for low bond strength values ( 2-7 Mpa )
30

31. 3- Third generation bonding agents
- These are the first systems that advocated conditioning of
dentin with acids to modify or remove the smear layer .
- This generation represents one of the major breakthroughs
in adhesives and bonding. After the primer was added, an
unfilled resin was placed on both dentin and enamel.
- The weak link with this generation was the unfilled resins
that simply did not penetrate the smear layer effectively.
- 4- Fourth generation bonding agents
- This generation of bonding agents introduced the wet
bonding technique ( bonding to moist dentin.)
- It is considered to be the basis for all the recent dentin
bonding systems as it provided for much higher bond
strength values ( up to 27 Mpa ) and exhibited a fairly good
durability . 31

32. 5-Fifth generations dentin bonding agents
introduced to minimize the clinical steps of
bonding by amalgamating more than one step together,
e.g., etching followed by one single agent containing
both the primer and the adhesive .
6. sixth generation dentin bonding agents
sought to eliminate the etching step, or to include it
chemically in one of the other steps: (self-etching primer
+ adhesive) acidic primer applied to tooth first, followed
by adhesive or (self-etching adhesive) two bottles or unit
dose containing acidic primer and adhesive.
32

33. 7.The seventh generation or all-in-one-bottle:
It’s a self-etching system represents the latest simplification
of adhesive systems. With these systems, all the ingredients
required for bonding are placed in and delivered from a
single bottle
8. Eighth Generation dentine bonding agents:
Self etch which contains nanosized fillers by the addition
of nano-fillers with an average particle size of 12 nm that
increases the penetration of resin monomers and the hybrid
layer thickness, which in turn improves the mechanical
properties of the bonding systems.
Nano-bonding agents are solutions of nano-fillers, which
produce better enamel and dentin bond strength, stress
absorption, and longer shelf life
33

34. Classification of dental adhesives(according to clinical
application steps)
- Contemporary adhesives exhibit an common adhesion
mechanism of hybridization ( a process of micro-
mechanical interlocking occurring by the infiltration of
resin into demineralized substrate , creating a resin-
infiltrated hybrid layer) .
- This classification was described , in 2001 , by Van
Meerbeek and was based on the clinical steps of
application.
34

35. 35

36. - Types of adhesives
1-Etch & rinse adhesives(smear layer removing)
a- three steps : etching , priming and bonding are done
in 3 separate steps.
b- two steps : etching is in one step and primer and
bonding in one step ( incorporated in
one bottle ) .
Etch& rinse adhesives represent the golden standards for
adhesives with proven long-term success.
2- Self-etch adhesives (smear layer dissolving)
No separate etching step.
a- two steps : acidic primer in one bottle and an
adhesive in another bottle .
b- all-in-one : acid , primer and adhesive in one
single bottle .
36

37. 37

38. 38

39. 39

40. 40

41. The nanoleakage
phenomenon, which is
basically the presence of
submicrometer-sized gaps
within the hybrid layer.
it is considered as a
manifestation of incomplete
resin infiltration of the
hybrid layer and of a
discrepancy between the
depth of demineralization
and the depth of resin
infiltration.
Or due to poor adaptation
and envelopment of the
resin to the collagen ,fibrils,
leaving microscopic gaps.
41

42. Self-etch adhesives are further classified according to their
acidity or aggressiveness into mild (pH more than 2),
intermediate (pH = 1.5) & strong (pH less than 1) .
Self-etch adhesives simplify the clinical steps , reduce post-
operative sensitivity( do not increase dentin permeability),
but exhibit lower bond strength values .
3-Glass ionomer adhesives (smear layer modifying)
Based on the glass ionomer self adhesive capacity technology.
Conditioning of dentin with weak acids ( 10-20% polyacrylic
acid) removes the smear layer and leaves the smear plugs.
These adhesives are simple to apply but exhibit low bond
strength values .
42

43. 43

44. 44

45. In particular, the high concentrations of water have
raised questions about potentially harmful effects
on polymerization, given that incomplete water
removal can cause water trees.
This also applies for the high concentrations of
solvent that may cause incomplete resin
polymerization in case of incomplete evaporation.
45

46. Resin modifies
glass inomer
adhesive
46

47. 47

48. 48

49. Universal adhesive
systems/“multi-mode″ or ″multi-
purpose″ adhesives:
they may be used as self-etch
(SE) adhesives, etch-and-rinse
(ER) adhesives, or as SE
adhesives on dentin and ER
adhesives on enamel (a technique
commonly referred to as
“selective enamel etching)
49

50. The composition of universal adhesive differs from the current
SE systems by the incorporation of monomers that are capable
of producing chemical and micromechanical bond adhesion to
the dental substrates
It contains specific carboxylate and/or phosphate monomers
that bond ionically to calcium found in hydroxyapatite. For
example, Methacryloyloxydecyl Dihydrogen phosphate (MDP)
is a functional monomer found in certain new adhesives that
helps promote strong adhesion to the tooth surface via
formation of non-soluble Ca2salts.
50

51. Steps of bonding
A- Selective acid demineralization (etching , conditioning)
- Aiming at decalcifying & removing part of the inorganic content in
order to create microscopic undercuts where the adhesive material
can flow & at cleaning the enamel and dentin walls from
any contaminants that might , adversely , affect bonding .
- In enamel , it selectively decalcifies the enamel rods ,creating
interprismatic pores. Properly etched enamel looks chalky white
in appearance.
- In dentin , it removes the smear layer , creates inter-tubular &
peri-tubular pores and exposes the dentin collagen , to chemically
aid in bonding .
- Both enamel & dentin are etched with the same etchant in one
single step “ whole-etch technique” .
51

52. Resin Tags
Open D.T.
52

53. Conditioned Dentin
Open D.T.
Intertubular D.
Collagen Network
53

54. SEM micrograph of a resin-
dentin interface
A, Adhesive; D, residual dentin;
H, hybrid layer; T, resin tag.
54

55. - Types of acids most commonly used are phosphoric acid (10-37%)
and maleic acid (10%) .
- The acid is supplied in the liquid or gel forms with different colors.
- It is applied with a small brush, a small piece of sponge or with the
disposable tip of an injectable syringe for a length of time of approx.
15-30 sec.
- The etchant must be thoroughly washed away with water to remove
all the etched products , then enamel and dentin are dried with oil-free
compressed air .
B- Priming
- Aiming at increasing the wettability of enamel & dentin.
- Primers are adhesion promoting monomers (HEMA) containing
both hydrophilic & hydrophobic molecules.
- The hydrophilic part increases the wettability & permeability of the
demineralized enamel and dentin, while the hydrophobic part
55

56. penetrates inside the created pores where it polymerizes forming
retention tags inside them from the tooth-tissue side , and
co-polymerizes with the subsequently applied bonding agent from
the outer side .
- Acid- etched enamel has high surface energy , whereas etching of
dentin decreases its surface energy because of the high protein
content after etching (exposed collagen) , in addition to the fact
that its permeability and wetness increase, which hinder
adhesion furthermore.
- So , the primer is essential to ensure sufficient wetting of dentin,
displace residual water and carry the monomer inside the created
micro-porosities.
- The primer , usually, contains organic solvents (acetone or
ethanol) which act as water chasers , displacing water from
dentinal surfaces ,thus promoting the infiltration of monomers
through the exposed collagen .
56

57. - The primer is applied with small brushes or sponges ,is subjected
to a light stream of air to spread it(not the extent of removing it
or to cause collapse of the collagen bundles) , and is then left
undisturbed for at least 15 sec. ( enamel & dentin must appear
glossy after air spraying of the primer ) .
C- Bonding agent (adhesive resin)
- Is a solvent-free ,low viscosity filled or unfilled solution
containing mainly, hydrophobic monomers.
- It co-polymerizes with the primer that has penetrated the
undercuts from one side and with the subsequently applied
composite resin from the other side .
- It is applied with a brush or small sponge , gently air-thinned and
light cured .
- This is the final step in bonding , and is followed by the
application of the composite resin .
57

58. E. & D. etching Chalky white appearance
of Enamel
Priming
Glossy surface
58

59. Bonding Agent
Application Light curing
After
Curing
59

60. Smear layer
- Following cutting of dentin with rotary tools, a layer 2-5 microns
in thickness is formed on the surface of dentin . This layer is
loosely attached to dentin , but is burnished on the cut dentin
surface by the effect of heat and pressure during cutting and
cannot be removed by rinsing .
- It is formed of cut dentin chips , hydroxyapatite crystals,
collagen , saliva & blood and it incorporates microorganisms .
- Advantages of this layer is that it plugs the dentinal tubules and
reduces the flow of dentinal fluids(reduces dentin permeability),
thus providing for a drier surface for bonding and minimizing
post-operative hypersensitivity .
- Disadvantages of this layer is that it is loosely attached to the
underlying dentin providing for weak bonding and it
incorporates microorganisms .
60

61. - Adhesive systems should totally remove this smear layer ,or
penetrate through it to provide for efficient bonding .
- Etch-and-rinse adhesives totally remove the smear layer .
- Self-etch-adhesives dissolve the smear layer and incorporate it into
the hybrid layer .
- Glass ionomer-adhesives remove the smear layer and leaves the
smear plugs .
61

62. Wet bonding versus dry bonding
- Following etching & rinsing , enamel and dentin present different
conditions for priming & bonding .
- Whereas enamel should be dry to provide for good bonding ,
dentin should be a little wet to prevent collapse of its collagen
bundles , representing two totally opposing clinical conditions .
- Two approaches can be followed, depending on the type of
adhesive system used :
a- dry bonding technique which involves air drying of enamel
& dentin and applying a water-based primer capable of re-
expanding the collapsed collagen network .
b- wet bonding technique which leaves dentin a little moist to
prevent collapse of the collagen and use a solvent-containing
primer to chase water from both dentin and enamel .
- Wet bonding technique is more consistent and reliable .
62

63. Collapse of Etched Dentin by Air-drying
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