The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.for more details please visit www.indiandentalacademy.com

2. The American Society for Testing and
Materials (ASTM; Specification D907)
defines adhesion as “the state in which
two surfaces are held together by
Interfacial forces which may consist of
valence forces or Interlocking forces or
both.”
The word adhesion comes from the Latin
word ‘adhaerere’ (“to stick to”).

3. An important pre-requisite for adhesion
is an intimate contact between the
adhesive & adherend. The factors that
affect this phenomenon are:
1.Surface energy- surface tension of the
adhesive must be lower than the
surface energy of the adherend.
2.Wetting- ability of the liquid to flow
over the entire surface and adhere to
the solid.

4. The angle formed by the adhesive & the
adherend at their interface, the contact
angle determines the extent to which the
adhesive wets the adherend.
If the liquid spreads out completely on
the solid surface, this indicates complete
wetting or a contact angle of 0 degree
and no wetting occur at an angle of 180
degree.

5. A: When contact angle is 0, the liquid
contacts the surface completely and
spreads freely.
B: small contact angle on slightly
contaminated surface.
C: large angle formed by poor wetting

6. Early bonding systems consisted of
brackets welded onto bands bonded to
enamel with cements.
The introduction of an acid-etch
technique in the 1950s to bond dental
restorations to tooth structure was a
breakthrough point in the history of
orthodontic bonding.
In the mid 1960s, Bis-GMA resin
composites were introduced for this
purpose.

7. Dental composite is “A highly cross-
linked polymeric material reinforced by a
dispersion of amorphous silica, glass,
crystalline or organic resin filler particles
and/or short fibers bonded to the matrix
by a coupling agent.
Dental composite is a three dimensional
structure of two chemically different
materials with a single interface between
them.

8. COMPOSITION
• Resin matrix-
The resin is the chemically active
component of the composite. It is
initially a fluid monomer. It is
converted into a rigid polymer by a
radical addition reaction.
Monomers that are aromatic or
aliphatic diacrylates. Most commonly
bis-GMA, UEDMA or TEGDMA.

9. 2. Filler particles-
Inorganic filler particles generally
account for between 30 and 70 vol%
or 50 to 85 wt% of the composite.
Reduces polymerization shrinkage,
water sorption & coefficient of
thermal expansion.
Improves the mechanical
properties. Most commonly used are
Quartz, colloidal silica & glasses
containing heavy metals.

10. Classification based on filler
particle size
1.Macrofiller - 10-100um
2.Midifiller - 1 to 10um
3.Minifiller - 0.1 to 1um
4.Microfillers- 0.01 to 0.1um
5.Nanofillers - 0.005 to 0.01um

11. Classification based on the filler
particles, shape & density
1.Unfilled resins- not used any more.
2.Conventional filled resins- macrofillers.
3.Hybrid composites- macro & micro
fillers

12. 3. Coupling agent-
The coupling agent imparts improved
physical and mechanical properties and
provides hydrolytic stability by
preventing water from penetrating along
the filler-resin interface.
Titanates
Zirconates
Organosilanes such as GAMA –
methacryloxypropyl-trimethoxy silane

13. 3. Inhibitors-
to minimize or prevent spontaneous
polymerization. Butylated
hydroxytoluene, 0.01%. Hydroquinone
0.006% or less.
4. Optical modifiers-
Opacifiers- titanium dioxide &
aluminium oxide.
Pigments- different metal oxides in
minute amounts.

14. 5. UV absorbers:-
To prevent discolouration with age of
composites, compounds are incorporated
which absorb electromagnetic radiation.
Clinical evidence suggests that this
improves colour stability. Eg:- 2 hydroxy
4 methoxy benzo phenone.
Other additives such as wax may be added
to improve the polishability and
influence the abrasion behaviour of
composites.

15. 6. Activator – Initiator system:-
Methyl methacrylates and dimethyl
methacrylate monomers polymerize by
the addition polymerization mechanism
initiated by free radicals generated by
chemical activation or external energy
activation (heat/light).

16. Therefore, based on the mechanism of
generation of free radicals, composites
may be classified as:
1.Chemically activated/self cured.
2.Light cured.
3.Dual cured.
4.Thermal cured.

17. CHEMICALLY CURED
Most often supplied as a 2 paste system.
Each paste contains a blend of resin and
filler. One of the pastes contains a 1%
peroxide initiator such as benzoyl
peroxide. The other paste contains a
tertiary amine activator. N, N-dimethyl
toluidine was used as an activator. But
now, N, N-dihydroxy ethyl-toluidine is
widely used. Tolyl diethanolamine can
also be used as an activator.

18. LIGHT – ACTIVATED RESINS
The first light-activated systems used UV
light to initiate free radicals. Today, the
UV light cured composites have been
replaced by visible light activating
systems because of the many
disadvantages of UV light cured
composites.

19. These are:
1)Limited depth of polymerization.
2)Layering techniques attempting to
overcome this problem may cause
faults in the material.
3)Potential harmful effects such as
carcinoma of skin and eye damage.

20. Light curable dental composites are
supplied as a single paste which contains
the photo initiator molecule and an
amine activator. When these 2
components are left unexposed to light,
they do not interact. However, exposure
to light of the correct wavelength
(approx. 468 um) produces an excited
state of the photo initiator and an
interaction with the amine to form free
radicals that initiate addition
polymerization.

21. A commonly used photo initiator is
camphoroquinone, which has an
absorption range between 400 and 500
um that is in the blue region of the visible
light spectrum. The initiator is present in
the paste at levels of approximately 0.25
wt% or less.
Amine accelerators most commonly used
are dimethylaminoethyl methacrylate
(DMAEMA) in the concentration of 0.15
wt%.

22. Chemically Activated orthodontic
Adhesive systems
Chemically activated orthodontic
adhesives employ benzoyl peroxide as an
initiator, which is activated by a
tereitiary aromatic amine.
These are of 2 types:
1.Two-phase system.
2.One-phase (no-mix) syatem.

23. Two-phase adhesives-
•1st to appear in the market.
•Polymerization initiation- mixing of the
liquid & paste.
•Clinical handling- laborious & time
consuming.
•Properties-
Mixing introduces air entrapment & voids.
Increased exposure to
air induces oxygen inhibition.

24. No-mix adhesives-
•Succeeded the 2 phase adhesives
•Polymerization initiation- application of
liq on the enamel & bracket base. No
mixing.
•Clinical handling- efficient application,
limited time requirements.
•Properties-
limited data on degree of cure and bond
strength.

25. Inhomogenous polymerization pattern
due to sandwich technique involved in
diffusion of liquid component into paste
during application.
Enamel & bracket sides of adhesive are
more polymerized relative to the middle
zones.
May not be recommended in applications
where the adhesive thickness is increased
as in bonding molar tubes. Eg- System 1,
Rely-a-bond, Unite(3M).

26. Visible light-cured adhesives-
•Available since 1980s.
•Polymerization initiation-
exposure to light source.
•Clinical handling-
increased WT for optimal bracket
placement.
Ideal for educational purposes.
Time-consuming curing process.

27. •Photo-activation from the incisal &
cervical edges is recommended.
•Properties-
Bond strength & degree of cure have
been studied extensively and
support their use.

28. Dual cured adhesives-
•Polymerization initiation- initiation is
achieved through exposure to light.
Reaction proceeds following a
chemically cured pattern.
•Clinical handling-
combines advantages of handling of
both light-cured & chemically-cured
materials

29. •Properties-
Increased degree of cure
Increased bond strength.
Ideal for bonding molar tubes.

30. Thermal-cured adhesives-
•Polymerization initiation- through
exposure to heat.
•Clinical handling- not suitable for direct
bonding. Polymeriztion-initiator system
restricts their use to indirect bonding.
•Properties- superior.

31. Moisture active adhesives-
•Made of cyanoacrylates
•Paste formulation only. No liquid.
•Polymerization intitation- through
exposure to water.
•Clinical handling- one step procedure.
Enamel surface must be intentionally
wetted.
•Properties- studies have shown

32. Moisture insensitive/resistant adhesives-
•Moisture insensitive primer is used with a
compatible adhesive. Eg- Transbond MIP
•Suitable in difficult moisture-control
situations such as 2nd
molar bonding and
bonding surgically uncovered impacted
canines.
•The hydrophillic primers polymerize in
the presence of a slight amount of water,
but they will not compensate routinely for
saliva contamination.

33. Light-cured adhesives are
particularly useful in situations in which
a quick set is required such as:
•Rebonding a single loose bracket.
•Placing an attachment on an impacted
canine after surgical uncovering
They are also advantageous when an
extra long working time is desirable.

34. Conventional & fast Halogen lights-
Most common method of delivering blue
light (470nm) until recently.
Halogen bulbs produce light when
electric energy heats up a small Tungsten
filament to high temperatures.

35. Despite their common use, halogen bulbs
have several disadvantages:
1.The light power output is <1% of the
consumed electric power.
2.Limited lifetime of about 100 hrs
because of degradation of the
components by the heat generated.
3.Prolonged curing time- composite
resins in 20secs & light- cured RMGIC
in 40secs/bracket.

36. Fast Halogens (e.g., Optilux 501) have
significantly higher intensity output than
conventional halogen lights. The light is
focused and concentrated into a smaller
area.
Curing times can be reduced to half the
time needed with conventional halogen
lights.

37. Argon lasers:
Introduced in the 1980s, Argon lasers
produce a highly concentrated beam of
light centered around the 480nm
wavelength. In addition the light is
collimated, which results in more
consistent density over distance.
Ability to protect lased enamel surface
around orthodontic brackets against
decalcification. (AJO-DO 2002, AO
2003)

38. Although the curing times could be
reduced to 5secs for unfilled & 10secs for
filled resins with Argon lasers, their use
in Orthodontics is not extensive,
probably because of:
•High cost.
•Poor portability.

39. Plasma arc lights-
The Xenon plasma arc lamps are high
intensity lamps introduced in the mid
1990s.
The lamp has a Tungsten anode & a
cathode in a quartz tube filled with
Xenon gas which emits an intense white
light. This light is filtered to the blue
wavelengths.

40. The advantage of using high-intensity
light is that the amount of light energy
needed for polymerization can be
delivered in a much shorter time.
Recent studies have shown exposure
times of 3 to 5 secs for metal brackets &
even shorter for ceramic brackets to yield
similar bond failure rates as for brackets
cured with conventional halogen light for
20secs ( AJO-DO2003, 2004).

41. An area of concern with the use of
plasma arc curing lights is the heat
generated by the high intensity lights &
the possibility of harming the pulp
tissue.
Studies have shown that the use of
these lights for curing orthodontic
adhesives for 5 to 10 secs should be safe
regarding the pulp temperature.

42. Light emitting diodes (LED)-
The most recent light source category.
Proposed by Mills et al in 1995 to
overcome the shortcomings of
conventional halogen lights.
Use junctions of doped semiconductors
to generate light.

43. Advantages:
•Lifetime of >10,000 hrs.
•Little degradation of output over time.
•Require no filters to produce blue light.
•Resist shock & vibration.
•Take little power to operate.
•Small size, cordless, are quiet
•Generate minimal heat.

44. Bonding agents

45. A bonding agent is usually an unfilled
resin that consists of hydrophobic
monomers (such as Bis-GMA, TEGDMA,
UDMA, and hydrophilic monomers
(such as HEMA).
Criteria for an “ideal” dentin bonding
system were enumerated in 1961 at a
workshop held at the University of
Indiana Dental School.

46. The criteria are:
•Provide a high bond strength.
•Show good biocompatibility to dental
tissue, including the pulp.
•Minimize microleakage at the margins
of restorations
•Prevent recurrent caries and marginal
staining.

47. •Be easy to use and minimally technique
sensitive.
•Possess a good shelf life.
•Be compatible with a wide range of
resins.
•Should not be toxic or sensitizing to the
operators or patients.
•Should seal tooth surfaces from oral
fluids.

48. In an attempt to simplify the confusion
with variations in chemistries,
mechanisms, numbers of bottles,
application techniques, and effectiveness
of bonding agents, one common method
is to classify dental adhesives into a
series of “generations.”

49. BUONOCORE (1956) – Demonstrated
that the use of a Glycerophosphoric acid
dimethacrylate – containing resin, would
bond to acid etched dentine.
BOWEN (1965), tried N – phenylglycine
and glycidyl methacrylate. Bonding
occured due to the interaction of this
bifunctional resin with the calcium ions
of hydroxyapatite.
First Generation

50. Drawback – Poor bond strength (1 to 3
MPa ).
The first commercial system of this type
– Cervident, SS White

51. Second Generation
In the late 1970’s the second generation
system was introduced.
Incorporated halophosphorous esters of
unfilled resins such as bisphenol – A
glycidal methacrelate or bis – GMA, or
hydroxyethyl methacrylate, or HEMA.
Bonded to dentine through an ionic bond
to calcium by chlorophosphate groups.

52. Weak bond strength, but significant
improvement over first generation.
Scotch Bond (3M Dental ), Clearfil
(Kuraray Co. Japan)

53. The first- and second-generation
bonding agents used during the late
1960s and 1970s did not recommend
etching the dentin and relied on
adhesion to the attached smear layer.
The weak bond (2 MPa to 6 MPa) to the
smear layer still allowed dentin leakage
with clinical margin stain.

54. Third Generation
The third-generation systems of the
1980s introduced acid-etching of dentin
and a separate primer designed to
penetrate into the dentin tubules as a
method to increase bond strength.
The primer contains hydrophilic resin
monomers which include hydroxyethyl
trimellitate anhydride,(4–META), and
biphenyl dimethacrylate (BPDM).

55. The phosphate primer modifies the
smear layer by softening and cures,
forming a hard surface. Following this
the unfilled resin adhesive is applied,
attaching cured primer to the composite
resin.
Drawback – Bonding to smear layer -
covered dentine was not very successful.
Mirage bond, Scotch bond 2, Prisma
Universal bond 2 and 3.

56. The third generation systems increased
the bond strength to dentin to
approximately 12 MPa to 15 MPa and
decreased dentin margin failure.
However, with time, margin staining
caused clinical failure.

57. Fourth Generation
Of the early 1990s used chemistry that
penetrated both the etched and
decalcified dentin tubules and dentin
substrate, forming a “hybrid” layer of
collagen and resin.
The use of the total etch technique is one
of the main characteristics of fourth
generation bonding system, here
complete removal of the smear layer is
achieved.

58. The Total etch technique permits the
etching of enamel and dentine
simultaneously using 40% phosphoric
acid for 15 to 20 seconds. The surface
must be left moist to avoid collagen
collapse.
The application of hydrophilic primer
solution can infiltrate collagen network
forming the hybrid layer. According to
Nakabayashi (1982) the hybrid layer is
defined as “

59. “the structure formed in dental hard
tissues by demineralization of the surface
and subsurface, followed by infiltration
of monomer and subsequent
polymerization.”
All bound -2 (BISCO), Scotch bond
Multipurpose (3M).
The fourth generation adhesive systems
exhibited dentin bond strengths in the
low to mid 20-MPa range, and
significantly reduced margin leakage

60. These earlier systems required a very
exacting technique of controlled etching
with acid on both enamel and dentin, the
correct amount of water on the surface
of the dentin, and the placement of two
or more components on both enamel
and dentin. Because of the clinical
complexity with multiple bottles and
multiple application steps, dentists
began asking for a simplified adhesive
system.

61. Fifth Generation
The fifth-generation systems introduced
during the mid 1990s combined the
primer and adhesive while maintaining
high bond strengths.
Consist of the so called “one bottle”
systems.

62. ONE BOTTLE SYSTEMS combined the
primer and adhesives into one solution to
be applied after etching. Total etching was
done with 35 - 37% phosphoric acid for 15
to 20 secs.
Adv – The combination of etching and
priming steps reduce the working time.
Single bond (3M), One step (BISCO)

63. Sixth Generation
Recently several bonding system were
developed and these systems are
characterised by the possibility to
achieve the proper bond to enamel and
dentine using only one solution. These
should really be one - step bonding.
Unfortunately, the first evaluations of
these new system showed a sufficient
bond to a conditioned dentin while the
bond with enamel was less effective.

64. This may be due to fact that the systems
are composed of an acidic solution that
could not be kept in place, they must be
refreshed continuously and have a ph that
is not enough to properly etch enamel.
SELF ETCHING PRIMER was developed
by Watanabe and Nakabayashi. It is an
aqueous solution of 20% phenyl – P in
30% HEMA.
Prompt - L - Pop (ESPE, Germany).

65. Seventh Generation
The trend in the latest generation of
dental bonding systems, introduced in
late 2002, is to reduce the number of
components and clinical placement
steps. The introduction of i Bond, a
single – bottle adhesive system, is the
latest to new generation materials and
combines etchant, adhesive and
desensitizer one component.

66. According to the manufacturers,
iBondTM is a seventh-generation, single-
component, no-mix, one-step application
dental adhesive with an etchant,
adhesive, desensitizer, and photoinitiator

69. Latest classification of dental
adhesives
Generation classification for bonding
agents no longer exist as it was officially
withdrawn by its introducer Dr. Vargas in
the year 2000 with the advent of Clearfil
SE bond.
The introducer Dr. Vargas has officially
accepted after introduction of Clearfil SE
bond that there are only 2-systems :

70. Total etch Self etch
2 step –
Etchant + primer
& adhesive.
3 step –
Etchant + primer
+ adhesive.
Mild – (ph 2.4)
Moderate – (ph 1.6)
Strong/Aggressive –
(ph 1.2)

71. Self etching primer
The main feature of SEPs is that no
separate etching of enamel & subsequent
rinsing with water & air spray is required;
the liquid itself has a component that
conditions the enamel surface.
The active ingredient of SEPs is a
methacrylated phosphoric acid ester that
dissolves calcium from hydroxyapatite.

72. Rather than being rinsed away, the
removed calcium forms a complex and
is incorporate into the network when
the primer polymerizes.
Three mechanisms act to stop the
etching process:
1.The acid groups attached to the
monomer are neutralized by forming a
complex with calcium from
hydrxyapatite.

73. 2.As the solvent is driven from the primer
during the airburst step, the viscosity
rises, slowing down the transport of
acid groups to the enamel interface.
3.As the primer is light cured & the
primer monomers are polymerized,
transport of acid groups to the interface
is stopped.

74. SEM examination of the impression of
SEP treated enamel shows different
surface characteristics from acid etched
enamel.
Instead of the well known distinct
honeycombed structure with microtag &
macrotag formation, one finds an
irregular but smooth hybrid layer, 3 to 4
um thick & irregular tag formation with
no apparent indentations of enamel
prism or core material.

75. The minimal etch obtained with SEPs
indicates that the majority of the bond
may be more of a chemical bond with the
calcium in the enamel than the
mechanical bond achieved with
conventional phosphoric acid etch.

76. Enamel loss (Hosein et al AJO 2004)
•After pumicing and conventional
etching, the enamel loss was 2.76µm
ranged from 1.11 – 4.57µm.
•With the SEPs, the median enamel loss
was significantly lower, at 0.27µ m the
range was 0.03 to 0.74µm.
•Scanning microscopy revealed that self –
etching primer produced less dissolution
of enamel surface compared with
phosphoric acid.

77. Polished Enamel
Phosphoric etched
enamel surface-
More dissolution &
finely roughened
enamel surface.
Self etching primed
surface; Less dissolution
& enamel surface almost
flat & presence of minute
holes

78. Bond strength-
Adequate and acceptable bond strength.
Varies from 8 – 20 MPa.
No statistically significant difference
with conventional composite resin
adhesive system.
A delay in bonding after SEP application
further increases the bond strength.

79. Disadvantages-
The solution must be refreshed
continuously because its liquid
formulation cannot be controlled.
Residual smear layer may remain in
between adhesive material and dentine.
Leakage tests reveal that, the seal achieved
at the enamel margins with one – bottle
systems is superior to that resulting from
self etching primer.

80. Clearfil liner bond V (Kuraray)
Mega bond (Kuraray)
Prompt – L – Pop ( 3M UniteK )
First step (Reliance)
Transbond Plus ( Unitek 3m )
Ideal 1 (GAC )
One up Bond F ( Tokuyama)

81. Recent advances
RESIN-IONOMER HYBRIDS-
1.COMPOMERS- polyacid-modified
composites. These are supplied as
ahhydrous single paste that contain
some major components of both resin
2.RM-GIC- set by acid-base reaction &
free radical addition poltmerization.
Should set under conditions in which no
polymerization occurs.

82. Composites and GICs, except water.
Exclusion of water ensures that the initial
setting occurs only by polymerization. An
acid-base reaction may occur later as the
material absorbs water in-vivo.
3.Ionomer-modified composites- set only
by a polymerization reaction, but contain
ion-leachable glasses in an attempt to
achieve fluoride release.

83. Practitioners have been searching for an
adhesive that could overcome the
shortcomings of the acid-
etch/composite system and simplify the
procedures involved in bonding.
In this quest, Flowable Composite
Resins (AO-2005) merit great
attention because of two of their clinical
handling characteristics, which have not
existed for composites until very
recently.

84. These are:
• nonstickiness, so that materials could
be packed or condensed, and
(2) fluid injectability.
These characteristics are associated with
the low viscosity of the mixture.
Generally, all mechanical properties of a
composite resin improve with filler
loading.

85. Traditional dental composite resins are
densely loaded with reinforcing filler
particles for strength and wear
resistance. Wear resistance increases
when small filler particles are highly
packed to protect the polymer matrix in
the composite.

86. Flowable composites were created by
retaining the same small particle size of
traditional hybrid composites but
reducing the filler content and allowing
the increased resin to reduce the
viscosity of the mixture.
They were originally considered for
restorative procedures.

87. However, because flowable composites
were not as robust as conventional
composites, clinicians limited their use to
applications that benefited from better
flow and were not associated with high
stress.
A recently introduced flowable composite
that has been tested for orthodontic
purposes is the Denfil flow.

88. Several in-vitro studies (AO-2005) have
indicated that Denfil Flow can be used
for bonding orthodontic brackets that
reduces working time while
concomitantly maintaining adequate SBS
as compared with a traditional composite
resin.
Flowable composites have also shown
reduced incidence of enamel fracture on
debonding.

89. Leaching of orthodontic
adhesives
Elution of substances from cured
composite resins in the oral cavity can be
a matter of concern. Published studies
are contradictory with respect to the
qualitative & quantitative parameters of
elution because of varying
methodologies used.

90. The quantity & composition of the eluted
substances are key factors for the toxic
potential of a resin adhesive.
Eluted substances include fillers,
enzymatic hydrolysis-induced
methacrylic acid, benzoic acid resulting
from degradation of the benzoyl peroxide
initiator, etc.

91. Eliades et al have investigated the elution
of Bis-GMA & TEGDMA from orthodontic
adhesives bonded to ceramic & metallic
brackets.
The highest values for the unsaturated
TEGDMA concentrations in the light-
cured resin were obtained with the use of
a composite ceramic bracket with a
flexible plastic base, followed by the use of
a metallic bracket.

92. The chemically-cured adhesive used in
this study exhibited increased momomer
concentration values relative to the light-
cured adhesive.

93. Since the bis-phenol A glycidyl
methacrylate (BISGMA) resins were first
applied in clinical orthodontic practice as
adhesives, the acid etched/composite
technique has become the most widely
adopted bonding system in
contemporary orthodontic practice.
This field continues to remain an area of
active research. While bond strength is of
interest to orthodontists, caution should
be exercised while interpreting results of
in-vitro studies for better bonding.