bonding to enamel and dentin

1. V.NIVEDHA
V.NIVEDHA

2. • Intoduction
• History and evolution
• Classification by generation
• Classification by mechanism of adhesion /clinical step
• First generation
• Second generation
• Third generation
• Fourth generation
• Fifth generation
• Sixth generation
• Seventh generation
• Eigth generation
• Mechanism of adhesion to enamel and dentin
• Etch and rinse approach
• At enamel
• Smear layer of cut enamel
• Bonding of phosphoric acid etched un cut enamel

3. • At dentin
• Nano leakage phenomena
• Self etch
• Types
• Bonding to enamel and dentin
• Ph of varying adhesives
• Uncut enamel
• Cut enamel
• Bonding to dentin
• Smear layer
• Variables affecting bond strength
• Interaction of GIC with enamel
• Evaluation of bond strength
• Hybrid layer aging and interface stability
• Selective etching
• Universal adhesive system
• Referrences

4.  The development and regular use of adhesive materials has begun to
revolutionize many aspects of restorative and preventive dentistry.
 Attitudes towards cavity preparation are altering since, with adhesive
materials, it is no longer necessary to prepare the cavity to provide
mechanical retention through such features as dovetails, grooves,
undercuts, sharp internal angles in order to retain the filling .
 These techniques are, therefore, responsible for the conservation of
large quantities of sound tooth substance, which would otherwise be
victim to the dental bur.

6.  Microleakage a major dental problem, which is probably responsible for
many cases of secondary caries, may be reduced or eliminated.These
adhesive are therefore critical for the success of aesthetic materials
restorative in modern dentistry.

7.  Dental adhesives are solutions of resin monomers that make the resin
dental substrate interaction achievable .
 Adhesive systems are composed of monomers with both hydrophilic
groups and hydrophobic groups.
 The former enhance wettability
to the dental hard tissues, while
the latter allow the interaction
and co-polymerization with
the restorative material.
The chemical composition of
adhesives also includes curing
initiators, inhibitors or stabilizers,
solvents.

8. •.
 The mineralized part of the tooth is a complex structure made of
different hard tissues, which have a quite distinct ultra-morphology and
composition.
 Enamel is composed of a hard solid crystalline structure-hydroxyapatite
(HAp) with strong intermolecular forces, high-energy surface, besides
water and organic material.
 Dentin is a biological composite of HAp that envelops collagen. Dentin is
intrinsically humid, and less hard than enamel, with low intermolecular
forces and low-energy surfaces.The dentin is different from enamel, as it
has smear layer, organic contents and presence of fluid inside the
dentinal tubules. In addition, the density of dentinal tubules varies with
dentinal depth and, as well as the water content of dentin, is lowest in
superficial dentin and highest in deep dentin.

9.  In superficial dentin, which contains fewer tubules, the permeation of
resin into intertubular dentin will be responsible for most of the bond
strength.
 In deep dentin, dentinal tubules are more in number: the intratubular
permeability of resins will be responsible for higher bond strength .Dentin
is also a substrate that undergoes change with age in an asymmetrical
physiological aging process, leading to an increase of dentin thickness and
decrease in dentin permeability.
 Furthermore, sclerotic and carious dentin suffers
structural changes that result in a higher
mineralization and a consequently reduced
permeability .Unlike dentin, enamel can be
dried easily: so bonding process to enamel
is different from that of dentin.

10.  The history of dental adhesives started as early as 1949, when Dr. Hagger, a Swiss
chemist who worked for DeTrey/Amalgamated Dental Company, applied the
patent for the first dental adhesive.
 In 1952, it was postulated by Mclean and Kramer, that the material, “Sevriton
Cavity Seal”, chemically bonded to tooth structure .This was the first report of
changes in dentin promoted by an acidic monomer and may be considered to be
the precursor of the hybrid layer concept.
 In 1954, Buonocore conducted successfully his first experiments on adhesion to
enamel trough acid etching and he focused on altering the enamel surface to
obtain a bond with filling material. Besides his groundbreaking research, in 1955
he described using 85% phosphoric acid to alter the enamel surface that could
provide a surface suitable for bonding with risen and also to improve the
retention of acrylic resin to pit-and-fissures

12.  By the mid 1960S, the first commercially available pit-and-fissure sealants and
composite resin materials utilizing this new adhesive technology were used
clinically. Buonocore theorized that risen tags filling the defects created by the
etchant were responsible for enamel adhesion, and by the late 1960s, he also
proposed that bonding to dentin was possible.
 In the 1970s, for the first time, the concept of smear layer that blocked adhesion
to dentin, as identification by Eick, using the scanning electron microscope (SEM)
,and simultaneously, total-etch concept were being used. By the 1980s, etch-
and-rinse adhesive had gained widespread acceptability.
 Nakabayashi, in 1982, was the first to demonstrate true hybrid layer formation,
and also who named this new biocomposite by name of hybrid layer. Moreover,
he demonstrated that resin could infiltrate into acid-etched dentin to form a new
structure composed of a resin-matrix reinforced by collagen fibrils.

14.  In the early 1990s, the introduction of the three-step total-etch adhesive
system represented a revolution in adhesive dentistry. Once dentin is
etched with phosphoric acid and the etchant is rinsed off, hydrophilic
primers are used before applying a uniform layer of hydrophobic resin to
complete hybridization.
 However, two-step total-etch adhesive systems and two-step self-etch
adhesives were introduced into the market in the late 1990s.
 Whereas original simple bonding agents evolved to multi-step systems,
recent development focuses on simplification of the application
procedure in order to abate technique sensitivity and reduce
manipulation time

17.  At this stage it was proposed a classification of bonding systems, which
reflects their essential mode of use, rather than historical development:
 1.Three-steps: involving etch, prime and bond.
 These bonding systems are supplied as three bottles, one each from
etchant, primer and bonding agent.These are the most complicated to
use in the clinic, but result in highest bond strengths and greatest
durability.
 2.Two-steps
 1: here the steps are etch, then finally prime and bond in a single
coating. Bonding systems of this type employ substances in two bottles,
one consisting of etchant, and the other of the combined prime and
bond formulation.

18.  3. Two-steps
 2: for these systems, the two steps are etching and priming combined
followed by bonding. It uses two bottles of components, the first
containing a self-etching primer and the second the bonding agent.The
self-etching primer modifies the smear layer on the surface of the
dentine, and incorporates the products in the coating layer.
 4. One-step:
This uses a single bottle containing a formulation that blends a self-
etching primer and bonding agent. Clinically, this is the easiest to
use, and bond strengths are generally reported to be acceptable, despite
the simplicity of bonding operation

19.  NPG-GMA(N-phenyl glycine glycidyl methacrylate), a surface active
comonomer is considered as the first generation dentin bonding system.
 Both Invitro and invivo clinical study results were discouraging.
 Theoretically, the comonomer could chelate with calcium on the
tooth surface to generate water-resistant chemical bonds of resin to
dentin.
 Based on C-13 nuclear magnetic resonance analysis, It seems that
no ionic bonding develops between NPG-GMA and hydroxyapatite.
 Example : Cervident

20.  They are phosphate ester material (phenyl-P and hydroxyethyl
methacrylate in ethanol)
 Mechanism of action is based on polar interaction between phosphate
group and calcium in the smear layer.
 The smear layer was the weakest link in the system because of its loose
attachment with dentin.
 Bond strength was also poor (<10MPa). In addition
to this, the resins were relatively devoid of
hydrophilic groups.
 They show less wettability and penetration into
the dentin crossing the smear layer.
 • Example :Clearfil Bond, Scotchbond, Bondlite

21.  The third generation dentinal adhesives attempted to deal smear
layer in two ways.
 Either by modification of the smear layer to improve its properties or by the
removal of the smear layer by keeping the smear plugs intact.
 Fusayama et al in 1979 introduced the concept of phosphoric acid etching of
dentin prior to the use of phosphate-ester type bonding agent.
 Materials like phenyl-P or PENTA was used to achieve smear layer
modification by penetration of acidic monomers.
 Treatment of smear layer using acid primers were also attempted.
 2.5% maleic acid, 55% HEMA, and traces of methacrylic acid were used for this.

22.  The removal of smear layer using chelating agents such as EDTA was also
tried (GLUMA system).
 • Example : Clearfil New Bond, Scotchbond 2, GLUMA system

23.  They are; three step, total etch adhesive systems.
 Although smear layer acts as a ‘diffusion barrier’ that reduces the permeability
of dentin, it also can be considered as an obstacle to the bonding.
 Based on this consideration a fourth generation dentin adhesives was
introduced for use on acid etched dentin.
 This method is commonly known as the total-etch technique or the etch and
rinse technique.
 The acid will result in complete or partial removal of smear layer with
demineralization of underlying dentin.They also exposes the collagen.

24.  The fourth generation dentin bonding system consist of three essential
components.
 1. Phosphoric acid etching gel that is rinsed off
 2. A primer containing reactive hydrophilic monomers in ethanol,
acetone, or water
 3. An unfilled or filled resin bonding agent
 Acid treatment not only alters the mineral content of the dentin
substrate but also alters the surface free energy.
 When primer and bonding resins are applied to etched dentin, they
penetrate the intertubular dentin, forming a resin-dentin
interdiffusion zone, or ‘hybrid layer’.
 Examples : Scotch Bond Multi Purpose(3M),All Bond 2,
Panavia 21

25.  These adhesives are a simplified version of the fourth generation
adhesives.Also known as ‘one bottle’ system.
 The primer and adhesive is combined in one bottle. A separate etching
step is still required.
 Though they require fewer steps to achieve dentin
bonding, these agents are inferior to the
fourth generation bonding agents in terms
of bond strength.
 Example : Single Bond(3M), One-Step,Gluma
Comfort Bond

26.  Sixth generation dentin boding systems try to further simplify the
process of dentin adhesion by minimizing the clinical steps.
 Acids of lower concentration are generally used :10% Phosphoric, 2.5%nitric,
10% citric, 10% maleic acids.
 They are also known as SEP – Self Etching Primers.
 Commercially they are available in two forms :
 1. Self etching primers : etchant and primer is
in one bottle while adhesive is in a
separate bottle.
First the etchant and primer are applied on the tooth surface
which is then followed by application of adhesive agent.
 example : Clearfil SE bond, Xeno

27.  2. Self etching adhesives :
 In these, the etchant, primer and adhesive are all in one package but
require mixing before application on the tooth surface
 example : Prompt-L-Pop(3M)

28.  Also known as All-in-one adhesive system.
 These are the most recent generation of dentin bonding agents.
 They combine etchant, primer, and adhesive in one bottle.
 They do not require any mixing prior to application.
 Primarily these agents are intricate mixes of hydrophilic and
hydrophobic components in one bottle.
 Their bond strength is less than fourth and fifth generation adhesives
 Example : Cleaefil S3 Bond, G-Bond, Xeno IV

29.  Addition of nano fillers help in the penetration of resin monomers and
hybrid layer thickness which in turn improves the mechanical properties
of bonding systems
 They are from self etch generations and use acidic hydrophillic
monomers

30.  “etch & rinse”
 “self-etch” and
 “(resin-modified) glass-ionomer adhesives”

31.  This adhesion strategy involves at least two steps and, in its most
conventional form, three steps with successive application of the
conditioner or acid etchant, followed by the primer or adhesion promoting
agent, and eventually, application of the actual bonding agent or
adhesive resin.
 The simplified two-step version combines the second and third step but
still follows a separate “etch&rinse” phase.

32.  This etch&rinse technique is still the most effective approach to
achieving efficient and stable bonding to enamel and basically only
requires two steps.
 Selective dissolution of hydroxyapatite crystals through etching
(commonly with a 30-40% phosphoric-acid gel) is followed by in situ
polymerization of resin that is readily absorbed by capillary attraction
within the created etch pits, thereby, enveloping individually exposed
hydroxyapatite crystals .
 The goals of enamel etching are to clean the enamel of the surface
organic pellicle in uncut enamel, to remove the enamel smear layer in cut
enamel and to partially dissolve the mineral crystallites to create
retentive patterns for the infiltration and retention of resinous materials.

33. Gwinett and Silverstone, 1975.
 Type I:
Predominate dissolution of prism cores and peripheries left intact—
Honeycomb appearance most common.
 Type II:
Predominate dissolution of prism peripheries and core left intact—
Cobblestone appearance.
 Type III:
Surface loss without exposing underlying enamel prisms, more common.
On etching of enamel turns dull and appear Frosty white.

35.  The preservation of the smear layers and the smear plugs within dentinal
tubules was considered beneficial in reducing the hydraulic conductance
in bur-cut dentine, as dentine permeability increased rapidly during acid-
etching with even 6% citric acid, reaching a maximum value as early as 15
s of etching.
 The inclusion of bacteria in dentine smear layers also generated concerns
about their rapid propagation following dissolution of the smear plugs by
oral fluids that could result in their colonization within the dentinal
tubules and subsequent pulpal infection

36.  There is a general consensus that acid etching increases the surface
energy and lowers the contact angle of resins to enamel
 Two types of resin tags interlock within the etch-pits. “Macro”-tags fill
the space surrounding the enamel prisms.

37.  while numerous “micro”-tags result from resin infiltration/
polymerization within the tiny etch-pits at the cores of the etched
enamel prisms.The latter are especially thought to contribute the most
with regard to retention to enamel.

38.  The surface aprismatic enamel is more resistant to etching due to the
parallel arrangement of the apatite crystallites which permit a high
packing density of these crystallites.
 There is also no interprismatic organic substance that acid can readily
diffuse through to effectuate subsurface etching.
 The bulk of the aprismatic enamel which demonstrates a less aggressive,
coral-like etching pattern that is characterized by the presence of
random-occurring surface pits on the surface of the etched aprismatic
enamel

39.  It is generally understood that the formation of resin tags are minimized
in phosphoric acid-etched uncut enamel, and that the predominant
mode of micromechanical retention is achieved via the creation of
surface and subsurface microporosities that result in an admixed zone of
enamel hybridization (ca. 8–10 mm thick) consisting of both aprismatic
and prismatic enamel
 Dissolution of the surface apatite crystallites results in preferential
dissolution of the carbonate- rich crystallite cores, forming central hole
regions that permit intra-crystallite resin infiltration

40.  At dentin, this phosphoric-acid treatment exposes a microporous
network of collagen that is nearly totally deprived of hydroxyapatite and
also removes the smear layer completely
Fe-SEM photomicrograph (image from M
Vargas) of dentin etched
for 15 seconds with 35% phosphoric acid
(Ultra-Etch, Ultradent). Note the
demineralization effect with exposure of
collagen up to a depth of 4-5 μm.
The transition of the exposed collagen
fibril network towards the underlying
unaffected dentin is very abrupt. Collagen
fibrils were nearly completely
deprived from hydroxyapatite

41.  The primary bonding mechanism of etch&rinse adhesives to dentin is
primarily diffusion-based and depends on hybridization or infiltration of
resin within the exposed collagen fibril scaffold, which should be as
complete as possible .
 True chemical bonding is rather unlikely, because the functional groups
of monomers may have only weak affinity to the
“hydroxyapatitedepleted’’ collagen.
 Such challenging monomer-collagen interaction might be the principle
reason for what has been documented as manifesting in the form of
“nanoleakage” phenomena

42.  Formation of gaps in the hybrid layer due to improper resin infiltration in
over etched or over demineralised dentin

43.  Perdigao et al advocated removal of demineralized collagen and
exposing hydrophilic underlying collagen for better penetration of
bonding agents.
 He advocated use of 2% sodium hypochloride. He suggested that
formation of hybrid layer is not essential for good bonding.This process
is called deproteinization.
 But others refuted this finding stating that hybrid layer as stress breaker
is necessary from preventing pulling away of composite during
polymerization shrinkage.
 Also partial dissolution of collagen fibrils and destabilization of molecules
that compose dentin structure during deproteinization, may compromise
reliable bonding interface.
 Oxygen released from sodium hypochloride also inhibits polymerization.

44.  “Dry-bonding” technique, involves air drying of dentin after acid etching,
and applying a water-based primer, capable of re-expanding the
collapsed collagen meshwork.
 An alternative approach is to leave dentin moist, thereby preventing any
collapse and using an acetone-based primer, known for its water-chasing
capacity.This technique is commonly referred to as “wet bonding” and
was introduced by Kanca, and by Gwinnett et al.,in the 1990s

45.  Most critical in the etch&rinse approach is the priming step.When an acetone-based
adhesive is used, the highly technique-sensitive “wet-bonding” technique is
mandatory.
 Otherwise, gentle post-conditioning air-drying of acid-etch dentin (and
enamel) following a “dry-bonding” technique still guarantees effective bonding when
a water/ethanol-based adhesive is used
 After the dentin surface is conditioned,it is recommended that it should be
maintained in a moist state prior to bonding, commonly referred to as wet bond-ing.
 Air drying of the conditioned dentin surface has been shown to cause the
unsupported collagen web to shrink and collapse, preventing monomers of the
adhesive resin from efficiently wetting and infiltrating the conditioned surface

46.  The dry bonding technique has been shown to cause a marked reduction in
the bond strengths to dentin with total-etch adhesive systems
 Adhesive systems that include water/ethanol as one of the solvents in the
mixture have been claimed to be able to promote re-expansion of collapsed
fibrils
 The bond strength to dry dentin was higher for water-/ethanol-based
than acetone-based systems.
 It was speculated that the higher concentration of volatile elements system
could result in a thin adhesive layer after solvent evap- oration. Acetone
content resulted in lower values of bond strength and thinner adhesive layers

47.  Probably, in regard to user-friendliness and techniquesensitivity,
clinically, the most promising approach is self-etch. It no longer needs an
“etch&rinse” phase, which not only lessens clinical application time, but
also significantly reduces technique-sensitivity or the risk of making
errors during application and manipulation.

48.  The concept of self-etching approach was created approximately 20
years ago, however, the first and second generations of bonding agents
can be considered self-etch materials because no acid etching/rinsing or
conditioning step were used.
 These early generations of dentin adhesives used glycerophosphoric acid
dimethacrylate, halophosporous ester-based primers of Bis-GMA or
HEMA, which were applied to unconditioned dentin .
 The first commercially system contained as main acidic monomer the 2-
(methacryloyloxyethyl)phenyl hydrogenphosphate (Phenyl-P)

49.  The basic composition of self-etch primers and selfetch adhesive
systems are an aqueous solution of acidic functional monomers, with a
pH relatively higher than that of phosphoric acid etchants.
 The role of water is to provide the medium for ionization and action of
these acidic resin monomers.

50.  A self-etch approach involves either a two- or onestep application
procedure .
 The self-etch effect should be ascribed to monomers to which one or
more carboxylic or phosphate acid groups are grafted.
 Depending upon the acid dissociation constants (pKa values), the etching
aggressiveness of self-etch adhesive systems can also be classified into:
 “strong” (pH<1)
 “intermediately strong” (pH≈1.5),
 “mild” (pH≈2) and
 “ultra-mild” (pH≥2.5)

51.  Indeed, the more aggressive systems, deeper demineralization of the
tooth substrate occurs resembling that of phosphoric acid-etching
treatment.
 At enamel, “strong” self-etching shows good bonding performance,
while the bonding effectiveness of “mild” self-etching on enamel is not
efficient and can be improved by prior phosphoric acid etching

52.  On the other hand, at dentin, “strong self-etching” dissolves nearly all smear layer,
but does not remove the dissolved calcium phosphates.These embedded calcium
phosphates seem to have low hydrolytic stability, with non-stable chemical
interaction with the exposed collagen, thereby weakening the interfacial integrity,
especially in a long-term
 “Intermediate strong” self-etching shows a transition between “strong” and “mild”
etching characteristics of the hybrid layer formed. It has typically a hybrid layer with
demineralized top layer and partially demineralized base.
 “Mild” self-etching partially removes the smear layer, forming a thin hybrid layer. It
has the great advantage of leaving substantial amount of hydroxyapatite-crystals
around collagen fibrils, which may establish chemical bond with specific carboxylic
or phosphate groups of functional monomers.The ‘ultramild’ self-etching can only
expose superficially dentin collagen, producing a nanometer interaction zone

53.  The bonding mechanism of self-etch adhesive systems has been
intensely investigated and two-fold bonding mechanisms; micro-
mechanical interlocking and chemical bonding were described, which
seems to be advantageous in terms of restoration durability.
 The micro-mechanical bonding contributes to provide strength against
mechanical stress, while the chemical interaction reduces hydrolytic
degradation, keeping the marginal sealing of restorations for a longer
period.
 The functional acidic monomers are able to chemically interact with
hydroxyapatite and are composed by specific carboxylic, phosphonic or
phosphate groups, such as:

54.  Phenyl-P, 10-methacryloyloxydecyl dihydrogenphosphate (10-MDP)
 methacryloyloxydodecylpyridinium bromide (MDPB),
 4-methacryloyloxyethyl trimellitate anhydride (4-META),
 4-methacryloyloxyethyl trimellitic acid (4-MET),
 11-methacryloyloxy-1,1-undecanedicarboxylic acid (MAC-10),
 4-acryloyloxyethyl trimellitate anhydride (4-AETA),
 2-methacryloyloxyethyl dihydrogen phosphate (MEP),
 phosphate methacrylates,
 acrylic ether phosphonic acid
 and other phosphoric acid esters
 carboxylic groups are related to demineralizing properties and monomer
infiltration, while the aromatic group provides the hydrophobic characteristics,
which tends to reduce the acidity and the hydrophilicity from carboxyl groups

56.  For bonding to uncut enamel, the efficacy of self-etch adhesives is
dependent upon their ability to demineralize the more acid-resistant
aprismatic enamel layer.
 Yoshiyama et al and Hara et al reported that bonding of self-etching
adhesives to ground enamel was inferior when compared with single-
bottle and multiple-step, total-etch systems which utilize phosphoric
acid as a separate conditioner.
 Whereas some studies supported the manufacturers’ recommendations
that the adjunctive use of phosphoric acid etching is necessary when
bonding to this substrate
 Bonding to uncut enamel, the efficacy of self-etch adhesives is
dependent upon their ability to demineralize the more acid-resistant
aprismatic enamel layer

58.  Hybrid layer that was localized to aprismatic enamel was less than 200
nm thick

59.  Some of the less aggressive versions of self-etching primers failed to
etch through clinically relevant, thick smear layers produced by diamond
burs
 It all depends upon the PH of the acidic monomer present
 Highy acidic monomers are able to etch similar to phosphoric acid
etching
 Complete removal of smear layer also increases post operative
sensitivity
 The hybrid layer formed by mild ph monomer was thin compared to
strong acid monomer (1–2mm thick)

61.  General, bonding to dentin is more challenging than to enamel, because
of the complex and hydrated structure of dentin
 Dentin is a complex composite material with less than 50 vol% inorganic
material, and with high water content (21 vol%).

62.  The smear layer is revealed by scanning electron microscopy (SEM) as a
1- to 2-mm layer of debris with a mainly granular substructure that entirely
covers the dentin

63.  There are basically two options to overcome low bond strengths due to
the limited strength of the smear layer, i.e. removal of the smear layer
prior to bonding, or the use of bonding agents that can penetrate beyond
the smear layer while incorporating it.
 Both techniques have been proven successful.
 Removal of the smear layer, however, increases the permeability of the
dentin tubules radically, thereby permitting fluid flow from outside the
pulp chamber, and vice versa.
 After removal of the smear layer by an acid, dentin permeability through
the dentin tubules increases by more than 90%

64.  Open dentin tubuli may also permit access of bacteria towards the pulp
and irritation of the pulp by toxic chemicals such as acids.
 The more acidic and aggressive the conditioner,the more completely the
smear layer and smear plugs will be removed.

66.  The thickness of the hybrid layer and the presence of resin tags do not
overly influence the bonding performance, chemical interaction between
the monomers and hydroxyapatite may be a plausible explanation for
the good performance of self-etch adhesives
 The carboxylic and phosphate groups that render these monomers
hydrophilic and that function as proton donors,have been proven to
bond ionically with calcium in hydroxyapatite.
 The ability to make chemical bonds is monomer specific and depends on
the hydrolytic stability of the calcium monomer bond

67.  10-MDP exceeds the bonding potential of 4-MET and phenyl-P
 While bonding to enamel remains a problem, especially for mild self-etch
adhesives ,bonding to dentin has yielded reasonable results.
Hydroxyapatite crystals are left available in the hybrid layer for possible
chemical bonding
 Potential postoperative sensitivity has been reported to be reduced

68.  Fluoride
 Teeth with a higher concentration of fluoride are generally considered
more resistant to acid etching than normal teeth and may require an
extended etching time.
 Caries-Like Lesions
 The highest bond strengths are achieved with sound enamel.A caries-
like lesion resulted in a reduction in bond strength of 38–58%

69.  Air Abrasion
 Air abrasion, also referred to as micro-etching, is a technique in which
particles of aluminum oxide are propelled against the surface of enamel
or other substrate by high air pressure, causing abrasion of the surface.
Some manufacturers of commercial units have suggested that air
abrasion could eliminate acid etching;
 However, bond strengths to air-abraded
enamel are only approximately 50% of
those to acid-etched enamel for resin
Composites and hybrid ionomers

70.  Laser Etching
 Bond strengths of enamel prepared with phosphoric acid etching are
higher than those of enamel prepared with an Erbium-YAG laser
 Bleaching
 Bond strength of resin composite to carbamide-peroxide-bleached teeth
treated with bonding agents is reduced, although this reduction
apparently can be reversed using sodium ascorbate

71.  SCLEROTIC DENTIN:
 Resin bond strengths to noncarious sclerotic cervical dentine are lower
than bonds made to normal dentine.
 This is thought to be due to tubule occlusion by mineral salts, preventing
resin tag formation.

72.  Light-cured, resin-modified glass ionomer cement (RM-GIC) and auto-
cured, conventional glass ionomer cement (GIC) with enamel
 Glass-ionomers remain as the only materials that are self-adhesive to
tooth tissue, in principle, without any surface pre-treatment .Although
this is certainly true, pre-treatment with a weak polyalkenoic-acid
conditioner significantly improves bonding efficiency .
 Hence, this glass-ionomer approach can be achieved following a one- or
two-step application procedure.The additional conditioning step
becomes more important, especially when coarse cutting diamonds are
used and, consequently, thicker and more compact smear layers are
produced.
 In general, such a polyalkenoic-acid conditioner is applied for 10-to-20
seconds and gently rinsed off, followed by gently air-drying without
dehydrating the surface

73.  The increase in bonding efficiency must be partially attributed to
 (1) a “cleaning” effect, by which loose cutting debris is removed,
 (2) a partial “demineralization” effect, by which the surface area is
increased and microporosities for micromechanical interlocking or
hybridization are exposed, but also in part to
 (3) chemical interaction of polyalkenoic acid with residual
hydroxyapatite

74.  A network of “hydroxyapatite-coated” collagen fibrils interspersed by
pores is typically exposed to a depth no deeper than 1 μm.
 TEM and XPS have demonstrated that (depending on the product) this
polyalkenoic acid conditioner cannot be completely rinsed off
 An up to 0.5 μm thick layer, often referred to as “gel phase,” remains
attached to the tooth surface despite the conditioner being rinsed off

75.  The actual auto-adhesion of glass ionomers to tooth tissue has recently
been determined to be twofold. Micromechanical interlocking is achieved
by shallow hybridization of the micro-porous, hydroxyapatite coated
collagen fibril network .
 In this respect, glass ionomers can be considered as adhering to tooth
tissue through a “mild” self-etch approach.
 The basic difference with the resin-based self-etch approach is that glass
ionomers are self-etching through the use of a relatively high molecular
weight (8,000-15,000) polycarboxyl-based polymer.
 Resin based self-etch adhesives make use of acidic low molecular
weight monomers.

76.  As the second component of the self-adhesion mechanism, true primary
chemical bonding occurs through forming ionic bonds between the
carboxyl groups of the polyalkenoic acid and calcium of hydroxyapatite
that remains around the exposed surface collagen

77.  There is a micromechanical component in the bonding mechanism of
RM-GICs due to the inclusion of resinous components that can
polymerize via free-radical polymerization
 The use of even short periods of conditioning with mild surface
conditioners, such as 10–20% polyacrylic acid, has been shown to
improve the bond strengths of RM-GICs to enamel when compared with
bonding performed without pre-treatment

78.  It was further speculated that the interaction layer was composed largely
of the resin-infiltrated smear layer, being fairly loose and slightly porous
in texture.
 Thus, the weakest link in the interface was between this resin infiltrated
smear layer and the underlying unetched enamel.
 However, when enamel was first conditioned with polyacrylic acid, the
smear layer could have been dissolved or dispersed, so that there was
better infiltration of the resinous component of the RM-GIC into the
microporosities created in the enamel.
 This resulted in a gap-free interface ,in which the RM-GIC was connected
to the enamel via a thin interaction layer that also exhibited short resin
tag formation

79.  Several studies have shown that bonding of RM-GICs to enamel may
further be improved by replacing the manufacturer-recommended
surface pre-treatment protocol with 10–37% phosphoric acid
 Micromorphologically, a shallow hybrid layer of 0.5–1mm in thickness is
formed

80.  MACRO SHEARTEST
 In macroshear tests, a composite cylinder of restorative material is fixed to a
flat enamel or dentinal surface after the application of adhesive
 Force is then applied parallel to the tooth surface until the bond fails.
 MACROTENSILETEST
 In macrotensile tests, tensile force is applied to a cylinder of restorative
material (typically composite) that has been polymerized onto a flat enamel
or dentinal surface after the application of adhesive
 they allow the evaluation of bond strength in luting agents used with hard
materials such as metal alloys and ceramics

81.  PUSH PULL OUTTEST
 In push-out tests, a specimen is embedded into a thin slice of material
with its long axis oriented in the plane of the slice.
 A compressive axial load is then applied to the upper surface of the
specimen, extruding it through the base of the slice until debonding
occurs.
 The retention of posts luted in root canals is typically assessed with
push-out tests

82.  MICRO SHEARTEST:
 Microshear tests evaluate bond strength using restorative material buildups
with small (≤ 1 mm2) cross sections of bonded areas. Specimen preparation
for these tests is relatively simple, and multiple specimens can be prepared
from a single tooth.
 MICROTENSILETESTS:
 Bond strengths to dentin are most frequently evaluated using microtensile
test (μTBS).
 In these tests, large restorative material buildups are placed on a flat dentin
surface after the application of adhesive. Multiple specimens may then be
obtained from each tooth by removing 1 × 1–mm or smaller sections (ie,
sticks) from the tooth-composite preparation.

83.  The specimens are then loaded to failure, and the tensile load at failure is
divided by the cross-sectional area of the bonded interface to determine
microtensile bond strength.
 Specimens may be prepared using trimming or nontrimming
procedures; the nontrimming technique is simpler and requires less
preparation time. Trimming procedures create dumbbell- or hourglass-
shaped specimens by trimming them at the interface

85.  Physical and chemical factors contribute to the clinical longevity of the hybrid
layer.
 Physical factors affecting interface stability include occlusal chewing forces
and repetitive expansion and contraction stresses produced by temperature
changes within the oral cavity.
 The interface is also affected by bacterial and acidic agents in dentinal fluid,
saliva, food, and beverages, which produce various patterns of collagen fibril
and resin degradation and resin-monomer elution.
 The hybrid layer is created by the combination of the dentinal organic matrix
with residual hydroxyapatite crystallites, resin monomers, and solvents;
individual components may be affected by aging, and degradation may result
from the synergistic combination of several components within the hybrid
layer

86.  After storage, the hybrid layer may exhibit two patterns of degradation
that compromise the strength of the resin-dentin bond:
collagen fibril disorganization and the hydrolysis of resin from
interfibrillar spaces within the hybrid layer
 Hydrolysis is a primary means of resin degradation within the hybrid
layer.This chemical process involves the disruption of covalent bonds
between polymers when water is added to ester bonds, resulting in the
loss of resin mass and contributing to the reduction in long-term bond
strength created by dentinal adhesives
 Water sorption significantly decreased the elastic modulus of resins, as
plasticization of the polymer contributes to reduced bond strength

87.  Hybrid layers created which lacks solvent free hydrophobic coating
behave as semipermeable membranes that permit the movement of
water throughout the bonded interface, even after adhesive
polymerization

88.  The degradation of collagen is caused primarily by the presence of water.
 Resin or collagen hydrolysis may degrade the hybrid layer, causing the
loss of resin from interfibrillar spaces and the disorganization of collagen
fibrils and physically weakening the resin-dentin bond
 Incomplete hybridization may leave exposed collagen fibrils and residual
adhesive solvent and/or surface water that increases vulnerability to
hydrolytic degradation.
 MMPs are zinc- and calcium-dependent endopeptidases that are
incorporated within the mineralized dentinal matrix during tooth
development.When released and activated during dentin bonding
procedures, these endogenous enzymes can degrade extracellular
matrix components

89.  The use of chlorhexidine, an antibacterial agent with MMP-inhibiting
properties, on acid-etched dentin during etch-and-rinse bonding
procedures can maintain hybrid layer collagen integrity.
 This effect confirms the indirect involvement of MMPs in collagen
degradation.
 Cysteine cathepsins, which can be activated in mildly acidic
environments, may also contribute to collagen degradation.
 The activation of dentin-bound cathepsins may also activate matrix-
bound MMPs, increasing long-term hybrid layer instability

90.  Self-etch adhesives do not etch enamel sufficiently, which results in
lower bond strength to enamel than total-etch adhesive materials.
 Therefore, a selective etch- ing technique has been proposed to
incorporate the advantages of the total-etch system on enamel with the
self-etch system on dentin

91.  Selective enamel etching is an additional step using phosphoric acid to
etch only the enamel margin of a cavity, followed by rinsing, prior to the
application of an acidic primer.
 Etching of enamel with phosphoric acid increases the surface area
available for bonding and improves the wettability of the enamel surface.

92.  These new products are known as “multi-mode″ or ″multi-purpose″
adhesives because 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”)

93.  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
 Most of these adhesive contain specific carboxylate and/or phosphate
monomers that bond ionically to calcium found in hydroxyapatite
 (MDP) is a functional monomer found in certain new adhesives, but not for
older-generation bonding agents.This is a hydrophilic monomer with
mild-etching properties. MDP is one of the monomers that enable a universal
adhesive to be used with any etching techniques. Stable MDP-calcium salts
are formed during this reaction and deposited in self-assembled nano-layers
of varying degrees and quality depending on the adhesive system.
 It also helps promote strong adhesion to the tooth surface via formation of
non-soluble Ca2 salts

94.  Some universal adhesives may contain silane in their formulation, potentially
eliminating the silanization step when bonding to glass ceramics or resin
composites, for instance
 This multi-approach capability enables the clinician to apply the adhesive
with the so-called selective enamel etching technique that combines the
advantages of the etch-and-rinse technique on enamel, with the simplified
self-etch approach on dentine with additional chemical bonding on remnant
carbonated apatite crystallites in those bonding substrates.
 Therefore, the universal adhesives have much broader applications than 7th
generation systems.Additionally, manufacturers typically state that
universal adhesives can be used for the placement of both direct and indirect
restorations and are compatible with self-cure, light-cure and dual-cure
resin-based cements and bonds to metals, zirconia, porcelain and composite.

95. Phosphoric acid conditioning of enamel yields a higher bond strength of a resin-
based composite restorative material when compared to acidic monomers.
Excellent bond strengths to dentin are achieved with both phosphoric acid and acid
monomer conditioning.
Extending the conditioning time of both etch-and-rinse and self-etch adhesive
systems on enamel and dentin does not greatly influence bond strengths

96.  Ann Stomatol (Roma). 2017 Jan-Mar; 8(1): 1–17. Classification review of
dental adhesive systems: from the IV generation to the universal
type Eshrak Sofan,
 Eur J Dent. 2016 Jan-Mar; 10(1): 155–159. A review of ethanol wet-
bonding: Principles and techniques
Muhamet kerim ayar
 Buonocore Memorial Lecture Adhesion to Enamel and Dentin:
Current Status and Future Challenges-BVan Meerbeek • J De Munck
Operative Dentistry, 2003, 28-3, 215-235
 Stability of wet versus dry bonding with different solvent-based
adhesives - Adriana P. Manso dental materials 24 (2008) 476–482

97.  Dental HardTissues and Bonding G. Eliades · D.C.Watts ·T. Eliades
(Eds.)
 Summitt’s Fundamentals of Operative Dentistry:A Contemporary
Approach Fourth Edition