1. The document discusses the fundamental concepts of enamel and dentin adhesion, including the mechanisms of adhesion and classifications of dental adhesives. 2. It describes Buonocore's acid etch technique for bonding to enamel and the challenges of bonding to dentin, such as its structure, the smear layer, and stresses at the resin-dentin interface. 3. Current strategies for resin-dentin bonding are discussed, including etch-and-rinse adhesives and self-etch adhesives. Etch-and-rinse adhesives involve removing the smear layer with acid before bonding, while self-etch adhesives combine etching and priming into one step.

1. FUNDAMENTAL CONCEPTS OF
ENAMEL AND DENTIN ADHESION
Dr. Richa Singh
Reader
Conservative dentistry and Endodontics

2. • The word adhesion comes from the latin
‘adhaere’ (‘to stick to’).
• Adhesion is defined as the state in which two
surfaces are held together by interfacial
forces, which may consist of valence forces, or
interlocking forces or both.

3. • Adhesive is a material, frequently a viscous
fluid that joins two substrates together by
solidifying, resisting separation and
transferring a load from one surface to the
other.
• Adhesive strength is the measure of the load-
bearing capacity of an adhesive joint.

4. Mechanisms of Dental Adhesion
1. Mechanical Adhesion:
Interlocking of the adhesive with
irregularities in the surface of the substrate,
or adherend. This would involve the
penetration of adhesive resin and formation
of resin tags within the tooth surface.

5. 2. Adsorption adhesion:
Chemical bonding between the adhesive and
adherend; the forces involved may be primary
valence forces (ionic and covalent) or secondary
valence forces (hydrogen bonds, dipole
interaction, or van der Waals). This would involve
the chemical bonding to the inorganic
component (hydroxyapatite) or organic
components (mainly type I collagen) of tooth
structure.

6. 3. Diffusion adhesion:
Interlocking between mobile molecules, such
as the adhesion of two polymers through
diffusion of polymer chain ends across an
interface. This would involve the precipitation
of substances on the tooth surfaces to which
resin monomers can bound mechanically or
chemically.

7. 4. A combination of the previous three
mechanisms.

9. Criteria for optimal adhesion
• For good adhesion to take place, five
fundamental attributes are:

10. Indications for Adhesive Dentistry
1. Restore class I, II, III, IV, V, and VI carious or
traumatic defects
2. Change the shape and color of anterior teeth.
3. Improve retention for porcelain fused to
metal or metallic crowns
4. Bond all ceramic restorations
5. Seal pits and fissures
6. Bond orthodontic brackets

11. 7. Bond periodontal splints and conservative tooth-
replacement prostheses
8. Repair existing restorations
9. Provide foundations for crown
10. Desensitize exposed root surfaces
11. Seal beneath or bond amalgam restorations to
tooth structure.
12. Impregnate dentin that has been exposed to the
oral fluids, making it less susceptible to caries.

12. 13. Bond fractured fragments of anterior teeth
14. Bond prefabricated fiber or metal posts and
cast posts
15. Reinforce fragile endodontically treated
roots internally
16. Seal root canals during endodontic therapy
17. Seal apical restorations placed during
endodontic surgery.

13. Enamel Adhesion: Buonocore’s Acid
Etch Technique
• Buonocore in 1955, envisioned the use of
acids to etch enamel for sealing pits and
fissures
• The formation of resin microtags within the
enamel surface is the fundamental
mechanism of resin-enamel adhesion.

15. Resin microtag mechanism of enamel adhesion:
Acid etching transforms the smooth enamel into
an irregular surface and increases its surface free
energy
Application of a fluid resin-based material to the
irregular etched surface, facilitates penetration of
the resin into the surface aided by capillary action
Monomers in the material are then polymerized,
and the material becomes interlocked with the
enamel surface.

16. Etch Pattern
3 different micromorphologic patterns:
1. Type I etch pattern involves the dissolution of prism
cores without dissolution of prism peripheries.
2. Type II etch pattern is the opposite of type I. The
peripheral enamel is dissolved, but the cores are left
intact.
3. Type III etch pattern is less distinct than the other two
patterns. It includes areas that resemble other
patterns and areas whose topography is not related to
enamel prism morphology.

18. Etchant Concentration:
Most current phosphoric acid gels have
concentrations of 30-40%, with 37% phosphoric
acid being the most common.
Etch Time:
Currently, an etching time of 15 sec is
recommended.
Bond Strength:
Shear bond strengths of composite to phosphoric
acid-etched enamel usually exceed 20 Mpa
depending on the test method used.

19. Dentin Adhesion: Mechanism and
Challenges
• Adhesive materials can interact with dentin in different
ways- mechanically, chemically or both.
• Dentin adhesion relies primarily on the penetration of
adhesive monomers into the network of collagen fibers
left exposed by acid etching.
• Dentinal adhesion is a clinical challenge due to the
following reasons:
i. Structure of dentin
ii. Smear layer
iii. Stresses at the resin-dentin interface

22. I. Structure of Dentin
• Bonding to enamel is a relatively simple
process where as bonding to dentin presents a
much greater challenge.
• Enamel is a highly mineralized tissue
composed of more than 90% (by vol)
hydroxyapatite, where as dentin is an
intrinsically hydrated tissue, penetrated by a
maze of fluid-filled tubules.

23. • Dentin also contains a dense network of dentinal
tubules that connect the pulp with the dentino
enamel junction. The relative area occupied by
dentin tubules decreases with increasing distance
from the pulp.
• A cuff of hyper mineralized dentin called
peritubular dentin lines the tubules. The less
mineralized intertubular dentin contains collagen
fibrils with the characteristic collagen banding.
• Adhesion can be affected by the RDT after tooth
preparation. Bond strengths are generally less in
deep dentin than in superficial dentin.

25. II. Smear Layer
• Whenever tooth structure is prepared with a bur
or other instrument, residual organic and
inorganic components form a layer of debris on
the surface of the substrate which is termed as
smear layer.
• The smear layer fills the orifices of dentin
tubules, forming smear plugs and decreases
dentin permeability by nearly 90%
• Thickness of smear layer- 0.5- 2um
• Thickness of smear plug- 1-10um

27. Composition:
Smear layer is predominantly made up of
hydroxyapatite and altered denatured collagen.
This altered collagen can acquire a gelatinized
consistency because of the friction and heat
created by the preparation procedure.
The factors determining the composition of the
smear layer include the following:
i. Type of cutting/abrading instrument used
ii. Type and method of chemicals/disinfectants
employed
iii. Composition of tooth structure, which would
vary according to the site
iv. Presence or absence of bacteria

28. Clinical Considerations
i. The presence of intact smear layer is
detrimental for optimal bonding to take place.
ii. Optimal dentin bonding can take place by:
a. Complete removal of the smear layer prior to
the bonding procedure by using etch and rinse
adhesives.
b. Incorporation of the smear layer into the
bonding layer by using self-etch adhesives
c. Complete removal of the smear layer
increases the permeability of dentinal tubules
by more than 90%

29. III. Stresses at the Resin-Dentin
Interface
• Composites shrink as they polymerize,
creating considerable stresses within the
composite mass, depending on the
configuration of the preparation.

30. i. Configuration Factor (C- Factor)
When the composite is bonded to one
surface only, stresses within the composite
are relieved by flow from the unbonded
surface.
Stress relief within a three-dimensional
bonded restoration is limited, however, by its
configuration factor.

31. ii. Coefficient of Thermal Expansion
Each time a restoration is exposed to wide
temperature variations in the oral
environment, the restoration undergoes
volumetric changes of different magnitude
compared with those of the tooth structure.
This occurs because the linear coefficient of
thermal expansion of the composite is about
four times greater than the tooth structure.

32. iii. Occlusal Loading
Loading and unloading of restored teeth can
result in transitional or permanent interfacial
gaps.
Additionally, the tooth substrate itself might
be weakened by cyclic loading.

33. Classification of Dentinal adhesives
1. Historical strategies:
i. First generation (1965)
ii. Second generation (1978)
iii. Third generation (1984)
2. Current strategies:
i. Etch and rinse adhesives
a. Three step- etch and rinse adhesive (fourth
generation)
b. Two step- etch and rinse adhesive (fifth
generation)

34. ii. Self-etch adhesives
a. Two component- self-etch adhesive (sixth
generation)
- Two step- two component – self-etch
adhesive
- One step- two component – self-etch
adhesive
b. Single component- one step – self-etch
adhesive (seventh generation)

35. I. Historical Strategies
i. First Generation (1965)
Chemical- Surface-active co-monomer NPG-
GMA (N-phenylglycine glycidyl methacrylate)
This co-monomer could chelate with calcium
on the tooth surface to generate water-
resistant chemical bonds of resin to dentinal
calcium.

36. Brand name- Cervident (SS White)
Bond Strength- Only 2-3MPa
Clinical result- Poor

37. ii. Second Generation (1978)
Chemical- It was phosphate-ester material
(phenyl-P and hydroxyethyl methacrylate in
ethanol)
It was based on the polar interaction between
negatively charged phosphate groups in the
resin and positively charged calcium ions in
the smear layer.

38. Brand names
1. Clearfil Bond System F
2. Scotchbond
3. Bondlite
4. Prisma Universal Bond
Bond strength
Only 1-5 Mpa
Clinical result- unacceptable

39. iii. Third generation (1984)
Chemical- It was a phosphate-based material
containing HEMA and a 10-carbon molecule
known as 10-MDP (10- Methacryloyloxy decyl
dihydrogen phosphate)
The concept of phosphoric acid-etching of
dentin before application of a phosphate ster-
type bonding agent was introduced by
Fusayama et al in 1979. Clearfil New Bond was
the only third generation bonding agent to
follow the etched dentin philosophy.

40. Most of the other third-geneation materials were
designed not to remove the entire smear layer
but, rather, to modify it and allow the penetration
of acidic monomers, such as phenyl-P or PENTA
(Dipentaerythritol penta-acrylate
monophosphate).
Brand names-
1. Clearfil New Bond
2. Scotchbond 2
Clinical result- Results were mixed

41. II. Current Strategies for Resin- Dentin
Bonding
i. Etch and Rinse Adhesives
The smear layer is considered to be an obstacle that
must be removed to permit resin bonding to the
underlying dentin substrate. The next generation of
dentin adhesives was introduced for use on acid
etched dentin. The clinical technique involves
simultaneous application of an acid to enamel and
dentin, this method was originally known as the total-
etch technique. Now more commonly called etch-
and-rinse technique, it was the most popular strategy
for dentin bonding during the 1990s and remains
somewhat popular today.

42. Mechanism of action of etch and rinse adhesives:
Application of acid to dentin results in partial or
total removal of the smear layer and
demineralization of the underlying dentin
Acids demineralize intertubular and peritubular
dentin, open the dentin tubules, and expose the
collagen fibers, increasing the microporosity of the
intertubular dentin
Dentin is demineralized by up to appx 7.5um,
depending on the type of acid, application time,
and concentration.

43. The primer in the system is designed to increase
the critical surface tension of dentin, which gets
decreased after the acid etching step
Bonding mechanism
i. When primer and bonding resin are applied to
etched dentin, they penetrate the intertubular
dentin, forming a resin-dentin interdiffusion zone,
or hybrid layer
ii. They also penetrate and polymerize in the open
dentinal tubules, forming resin tags

45. Moist bonding technique
• Complete drying of dentin after completion of
the acid etching procedure is not clinically
recommended as vital dentin is inherently wet.
• Drying the dentin surface with air would cause
the dentinal collagen to collapse which would
prevent the monomers from penetrating the
nano channels formed by dissolution of
hydroxyapatite crystals between collagen fibers.
• The moist bonding technique used with etch-and-
rinse adhesives prevents the collagen collapse
that occurs on drying demineralized dentin.

46. • The use of etch-and-rinse adhesive systems on
moist dentin is made possible by
incorporation of the organic solvents acetone
or ethanol in the primers or adhesives.
• Because the solvent can displace water from
the dentin surface and the moist collagen
network, it promotes the infiltration of resin
monomers throughout the nanospaces of the
dense collagen web.

47. a. Three step: Etch and rinse adhesives (fourth
generation)
Components: Etchant gel + primer (bottle I) +
adhesive bottle (bottle II)
These include 3 essential components that are
applied separately and sequentially:
1. Phosphoric acid – etching gel that is rinsed off
2. Primer containing reactive hydrophilic
monomers in ethanol, acetone, or water
3. Unfilled or filled resin bonding agent –
adhesive. It contains hydrophobic monomers
such as Bis-GMA, frequently combined with
hydrophilic molecules such as HEMA.

48. • Step I- Application of etchant gel for 15 sec
• Step II- Rinse the etchant off thoroughly and
blot dry the substrate (moist bonding
technique)
• Step III- Application of primer (bottle I) on the
substrate
• Step IV- Application of adhesive (bottle II) on
the substrate
• Step V- Light cure

49. Brand names
1. All-Bond 2 and All-Bond 3
2. OptiBond FL
3. Adper Scotchbond multi-purpose
Bond Strength- 17-30MPa
Clinical result- successful

50. b. Two step: Etch and rinse adhesives (fifth
generation)
Concept- In order to simplify the clinical
procedure a number of dental materials
manufactures are marketing a simplified, two-
step etch-and-rinse adhesive system.
They are sometimes called one-bottle systems
because they combine the primer and
bonding agent into a single solution.
Components: Etchant gel + Primer and
adhesive present in a single bottle

51. • Step I: Application of etchant gel for 15 sec
• Step II: Rinse the etchant off thoroughly and blot dry
the substrate
• Step III: Application of primer and adhesive (single
bottle) on the substrate
• Step IV: Light cure
Brand names:
1. Prime and Bond NT
2. Adper Single Bond
3. ExciTE
4. One Coat Bond
5. XP Bond

53. ii. Self-Etch Adhesives
Concept
An alternative bonding strategy is the self-etch
approach that involves the omission of a
separate etching step.
The elimination of the etching procedure has
the following advantages:
1. Clinician friendly procedure
2. Less technique sensitive

55. Two types of self-etch adhesives are available:
1. Two component- self etch adhesives (sixth
generation)
i. Two step: two component- self-etch adhesives
These are also described as nonrinsing
conditioners or self-priming etchants.
Mechanism of action-
These acidic primers include a phosphonated
resin molecule that performs two functions
simutaneously (a) Etching and Priming of
enamel and dentin (b) Incorporating smear
plugs into the resin tags

56. • Step I: Bottle I (conditioner+primer) application
on the tooth surface
• Wait for 10 sec and no need to rinse the
substrate
• Step II: Bottle II (adhesive) application on the
tooth surface
• Step III: Light cure
Brand names
1. Clearfil SE Bond
2. AdheSE
3. Optibond Solo Plus Self-etch

58. ii. One step: Two component- self-etch adhesives
Concept
They comprise of a two bottle system containing
the conditioner, primer and adhesive resin which
has to be mixed before applying to the bonding
substrate.
Step I: Dispense and mix one drop each from bottle
I (conditioner + primer) and bottle II (adhesive)
Step II: Apply on the tooth surface (no need to rinse
the substrate)
Step III: Light cure

59. Brand names
1. Xeno III
2. One up Bond
3. Prompt L Pop

60. 2. One step: Single component-self-etch
adhesives (Seventh generation)
Concept
Continuing the trend toward simplification,
no-rinse, self-etching materials that
incorporate the fundamental steps of etching,
priming and bonding into one solution have
been introduced
Conditioner + Primer + Adhesive = Single
Bottle

61. • Step I: Dispense and apply on the tooth surface
(no need to rinse the substrate)
• Step II: Light cure
Mechanism of action
In contrast to conventional adhesive systems that
contain an intermediate light-cured, low-viscosity
bonding resin to join the composite restorative
material to the primed dentin-enamel substrate,
these one-step self-etch or ‘all-in-one’ adhesives
contain uncured ionic monomers that contact the
composite restorative material directly.

62. Brand names:
1. AdheSE One F
2. Adper Easy One
3. Clearfil S3 Bond
4. iBOND Self-Etch
5. Xeno V+

65. Clinical Factors in Dentin Adhesion
1. Sclerotic Dentin:
The dentin that undergoes compositional
changes in which the tubules become
obliterated with tricalcium phosphate
crystals is called sclerotic dentin and is much
more resistant to acid-etching than normal
dentin.
Consequently, the penetration of a dentin
adhesive is limited.

66. 2. Occlusal Forces
Masticatory forces might not only cause
noncarious cervical lesions but also might
contribute to the failure of class V
restorations.
Although this stress may be of very low
magnitude, the fatigue caused by cyclic
stresses may cause failure of bonds between
resin and dentin.

67. 3. Solvent
The solvent used in the adhesive monomer
solution has been shown to influence the
clinical behavior of dentin adhesives.
An acetone-based adhesive resulted in lower
retention rate than an ethanol-based adhesive
as it is more technique sensitive.

68. 4. Type of Composite
Composites shrink as they polymerize, but the
amount of shrinkage depends on the inorganic
load of each specific composite.
Microfilled composites have a low elastic
modulus, which means that they are better
able to relieve stresses caused by
polymerization or by tooth flexure. Materials
that have a higher young’s modulus do not
relieve stresses by flow; they are unable to
compensate for the stresses and subsequently
get transferred to the adhesive interface and
cause debonding.

69. 5. Polymerization Shrinkage Stresses
Polymerization is initiated on the surface of
the restoration, close to the light source,
eliminating this surface as a potential stress
relief pathway.
The use of a flowable composite between the
composite and the tooth wall serve as a shock
absorber and simultaneously protect the
interface against fatigue stresses.

70. 6. Biocompatibility
Dentin adhesive system are well tolerated by
the pulp-dentin complex in the absence of
bacterial infection.
Adverse pulpal reactions after a restorative
procedure are not caused by the material
used in that procedure but by bacteria
remaining in, or penetrating, the preparation.

71. 7. Microleakage
Microleakage is defined as the passage of
bacteria and their toxins between restoration
margins and tooth preparation walls.
An adhesive restoration might not bond
sufficiently to etched dentin to prevent gap
formation at margins.
The occurrence of gaps at the resin-dentin
interface may not cause immediate debonding of
the restoration. However, if a dentin adhesive
system does not adhere intimately to the dentin
substrate, an interfacial gap eventually develops,
and bacteria are able to penetrate through this
gap.

72. 8. Nanoleakage
The term nanoleakage has been used to
describe small porosities in the hybrid layer or
at the transition between the hybrid layer and
the mineralized dentin that allow the
penetration of minuscule particles of a silver
nitrate dye.
When ammoniacal silver nitrate is used, silver
deposits penetrate the hybrid layer formed by
either etch-and-rinse or self-etch adhesive
materials.

73. Penetration of ammoniacal silver nitrate results
in two distinct patterns of nanoleakage:
1. A spotted pattern in the hybrid layer of self-
etch adhesives, which might be caused by
incomplete resin infiltration.
2. A reticular pattern that occurs in the
adhesive layer, most likely caused by areas
where water was not totally removed from
the bonding area.

75. Types of failure
Failures of adhesive joints occur in three
locations, which are generally combined when
an actual failure occur:
1. Cohesive failure in the substrate
2. Cohesive failure within the adhesive
3. Adhesive failure or failure at the interface of
substrate and adhesive.

76. Amalgam Bonding System
Amalgam bonding systems were introduced to
seal underlying tooth structure and bond
amalgam to enamel and dentin.
4-methyloxy ethyl trimellitic anhydride (4-
META) based systems were used frequently as
amalgam bonding agents. This monomer
molecule contains hydrophobic and
hydrophilic ends.

77. Bonding mechanism
1. Although good bonding to the tooth
structure occurs, micromechanical bonding
at the interface of amalgam and the bonding
system is poor.
2. Most debonding occurs by fracture along this
interface. As no chemical bonding occurs at
this interface, it is important to develop
micromechanical bonding.
3. To accomplish this, the bonding system is
applied in much thicker layers(10-50um) so
that amalgam being condensed against the

78. resin adhesive layer forces the fluid
components of amalgam to squeeze into the
unset bonding adhesive layer and produce
micromechanical laminations of the two
materials.
Bond Strength
Macroshear bond strengths for joining
amalgam to dentin are relatively low (2-6
Mpa).