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1. Sree Ganeshaya Namaha
ADHESION IN DENTISTRY
1. INTRODUCTION
2. PRINCIPLES OF ADHESION
• THEORIES
• FACTORS AFFECTING ADHESION
• SURFACE ENERGY
• WETTING
• CONTACT ANGLE
3. ADVANTAGES OF ADHESIVE TECHNIQUES
4. BASIC CLINICAL APPLICATIONS OF ADHESION IN
DENTISTRY
• MECHANISMS OF BONDING
• MICROMECHANICAL
• PHYSICAL
• CHEMICAL
• MECHANICAL INTERLOCKING
5. FACTORS AFFECTING ADHESION
• CLINICAL FACTORS
• FACTORS AFFECTING ADHESION TO MINERALISED
TISSUES
• FACTORS RELATED TO ADHEREND
• FACTOR RELATED TO ADHESIVE RESINS
6. ADHESION TO ENAMEL
• EFFECT OF ACID ETCHING ON ENAMEL
• TECHNIQUE
• ETCHANTS USED
• PHOSPHORIC ACID
• ALTERNATIVE ENAMEL ETCHANTS
7. ADHESION TO DENTIN
• IN BRIEF ABOUT DENTIN
• CHEMISTRY OF BONDING AGENTS
• BONDING TO DENTIN
• TO INORGANIC PORTION OF DENTIN
• TO ORGANIC PORTION OF DENTIN
• DENTAL ADHESIVE SYSTEM
• CRITERIA FOR IDEAL DENTIN BONDING SYSTEM
• CLASSIFICATION OF DENTIN BONDING AGENTS -
VARIOUS AUTHORS
• CLINICAL PROCEDURE
• VARIOUS GENERATIONS OF DENTIN BONDING AGENTS
• ADVANCEMENTS IN DENTIN ADHESIVES
8. REFERENCES
9. CONCLUSION

3. ADHESION IN DENTISTRY
INTRODUCTION:
After observing the industrial use of phosphoric acid to improve
adhesion of paints and resin coatings to metal surfaces, Buonocore, in 1955,
applied acid to teeth to “render the tooth surface more receptive to adhesion”.
Buonocore’s pioneering work led to major changes in the practice of dentistry.
Today we are in the age of the adhesive dentistry. Traditional mechanical
methods of retaining restorative materials have been replaced, to a large extent,
by tooth conserving adhesive methods. The concepts of large preparations and
extension and prevention, proposed by Black in 1917, have gradually been
replaced by smaller preparations and more conservative techniques.
One major problem in restorative dentistry is the lack of proper union
between the restorative material and the tooth surface. The process of
inventions over a period of time have led to the development of arioso
technique and modalities which help in adhesion and thereby reducing the
tooth restoration gaps.
Bonding / adhesion which was introduced into dentistry by the concept
of acid etching by Buonocore in 1955 has changed the term to esthetic
dentistry.
Bonding in dentistry has improved stabilization and retention of
restoration / excessive removal of sound tooth structure and the restorations are
better able to transmit and distribute functional stresses across the bonding
interface.
ADVANTAGES OF ADHESIVE TECHNIQUES :
Bonded restorations have a number of advantages over traditional, non
adhesive methods.
1) Traditionally, retention and stabilization of restorations often required
the removal of sound tooth structure. This is not necessary in many
cases, when adhesive techniques are used.
2) Adhesion also reduces micro leakage at the restoration – tooth interface.
So by preventing the micro leakage or the ingress of oral fluids and
bacteria along the cavity wall – reduces the clinical problems such as
post-operative sensitivity, marginal staining and recurrent caries - all of
which may jeopardize the clinical longevity of restorative efforts.
3) Adhesive restorations better transmit and distribute functional stresses
across the bonding interface to the tooth and have the potential to
reinforce weakened tooth structure.
4) In contrast, a traditional metal intracoronal rest may act as a wedge
between the buccal and lingual cusps and increase the risk of cuspal
fracture. Adhesive techniques allow deteriorating restorations to be
repaired and debonded restorations to be replaced with minimal or no
additional loss of tooth material.
5) Last but not the least, these adhesive techniques have expanded the
range of possibilities for esthetic restorative dentistry. As today’s patient

4. pays more attention to cosmetics than ever before, and teeth are a key
consideration in personal appearance. Tooth colored materials are used
to cosmetically restore and/or recountour teeth with little or no tooth
preparation. Advances in dental adhesive technology have allowed the
dentist to improve facial esthetics in a relatively simple and economic
way.
BASIC CLINICAL APPLICATIONS OF ADHESION IN DENTISTRY:
To appreciate fully, the clinical application of adhesive techniques, the
clinician must have a thorough (1) Understanding of adhesive mechanisms, (2)
the materials to be bonded, the (3) dental adhesive systems available and (4)
how these are applied to the clinical situation.
An adhesive bond between two any two structures can be created by one
or more of the following mechanisms (Van Naart 1994).
1) Micromechanical adhesion
2) Physical adhesion
3) Chemical adhesion
4) Molecular entanglement
More usually, a combination of some or all of these is active in creating a
adhesive bond. So the different bonding mechanisms with dental examples, are
presented below. Along with that the adhesion promotes like primers and
coupling agents is also given.
a) Micro Mechanical Adhesion :
Micromechanical adhesion results from the presence of surface
irregularities, such as pits and fissure that give rise to microscopic undercuts.
The liquid adhesive when applied can penetrate the pits and once set, is
locked in the microscopic undercuts.
A prerequisite for this form of adhesion is that the adhesive can readily
adapt to the surface of the substrate  the adaptation is determined by the
wettability of the adhesive on the substrate, the ideal situation being that of
perfect wetting when the adhesive spreads spontaneously over the surface.
Any air / vapour in the pits must be able to escape infront of the
advancing liquid. The degree of penetration ay also depend on the pressure
used during the application of the adhesive, which helps to force the adhesive
into the surface irregularities.
In Micromechanical Retention Macro mechanical Retention
- Here the adhesive is only able
to disengage from substrate by
fracturing.
- Good wettability is of
paramount importance.
- Good wettability for macroretention
is not a requisite.
PRIMERS:
Most materials do not normally have surface irregularities ideal for
micromechanical bonding. However, the surface may be modified to make it
more micromechanically retentive. This can be done either mechanically, for
example by grit blasting ceramic and metal surfaces with small aluminum

5. oxide particles or chemically, with a primer. Primers are defined as substances
which alter the surface morphology of the substrate but do not themselves play
a part in bonding process – Wake 1976.
These primers are applied to the surface before the adhesive. Eg. Of
dental primers  H3PO4 acidic primers are also employed – by many of recent
DBA’s.
Eg. Resin to Enamel bonding.
Methacrylate – based resins, such as BisGMA, do not band to enamel,
however the surface of enamel can be modified by the application of acidic
primes. Here  H3PO4 is used  it helps by modifying the surface
characteristics in enamel in two ways.
a) Increases the surface roughness of enamel at the microscopic level,
making it possible to bond to this surface by the process of micro
mechanical bonding.
b) This acid  also raises the surface surgery of the enamel – which
improves the ability of the resin to adapt closely to the etched enamel
surface but only if the surface is thoroughly dried after etching (Baier
1992). Thus, the resin – to enamel bond is essentially micromechanical.
2) Other Forms of Micromechanical Bonding :
The resin ceramic bond for veneers and inlays and the resin metal bond
for resin bonded fixed partial dentures also relay on primers to modify the
surfaces of the restorative material.
PHYSICAL ADHESION:
When two surfaces come in close proximity to one another, secondary
forces of attraction can be generated through dipole-dipole interactions. The
molecules must be polar so that they become oriented in a specific way at the
interface.
This bond polarity is a consequence of asymmetric electronic
distribution in the bond. Polar reactions occur as a result of attractive forces
between the positive and negative charges on the molecules. The magnitude of
the interaction energy is dependent on the mutual alignment of the dipoles, but
is usually less than 0.2 eV. This is considerably less than the bond energy of
the primary bonds, such a ionic or covalent bonds, which is typically 2.0 to 6.0
eV.
This type of bonding is a rapid and reversible process, because the
molecules remain chemically intact on the surfaces. Therefore, this weak
physical adsorption is also easily overcome by thermal energy and is not
suitable if a permanent bond is desired.
It following that non polar liquids will not readily bond to polar solids
and vice versa, because there is no interaction between the two substances at
the molecular level, even if there is a good adaptation
Familiar Example of this Problem :
Inability of hydrophobic (water-repellent) silicon rubber impression
materials to adapt to the hydrophic (water loving) moist surfaces of the soft

6. tissues. In the impression materials this problems is overcome by the
incorporation of surfactants (Pratten and Craig 1989).
CHEMICAL ADHESION:
If an adsorbed molecule dissociates on contact with a surface and the
constituent atoms rearrange themselves in such a way as to form covalent or
ionic bonds, a strong adhesive bond can result. This form of adhesion is known
as chemisorption. The feature that distinguishes the chemical bond from the
physical type of chemically to their surface of application to form strong bonds
and require identifiable reactive groups on both surfaces. Covalent bonding
occurs for an isocyanate adhesive, which can bond to soft tissues via surface
hydroxyl and amino group. An ionic bond is believed to form between the
carboxyl groups of the glass polyalkenoate cements and calcium ions in the
enamel and dentin (Wilson 1991).
Glass – Polyalkenoate Cement :
These form an ionic bond to enamel and dentin, that is so strong that it
exceeds the tensile strength of the cement. So, consequently the cohesive
fracture of the cement frequently takes place rather than fracture of the
adhesive interface.
Coupling Agents :
As we know, the incompatibility between polar and non polar
substances was obvious. Such is the situation when hydrophobic resins such as
BisGMA, are to be bonded to dentin or ceramic surfaces. The incompatibility
between the adhesive and the substrate can be overcome by the use of a
coupling agent.
Coupling agent and primer as said before are commonly referred to as
adhesion promoters. The difference between the primer is that, coupling agent
is integral to the creation of adhesive bond whereas primer helps in adhesion
but not an integral part of bonding.
Function of coupling agent is to provide a strong link between two
materials that would otherwise form an adhesive bond. A coupling agent can
be considered as having the general formulae.
M-S-R
Where H represents – Non polar organo functional gel methacrylate.
S spacer – ethyl (-CH2-CH2) / Oxypropyl (-O-CH2-CH2-CH2)
R represents a polar functional group such as hydroxyl, carboxyl /
silanol.
PRINCIPLES OF ADHESION:
Word adhesion is derived from the Latin word adharrere  which is
compound of ad, or to and hoerere or to stick. In adhesive terminology,
adhesion or bonding is the attachment of one substance to another.
The surface / substrate that is adhered to is termed the ADHEREND.
The adhesive / adherent, or in the dental terminology the bonding agent or
adhesive system ; defined as the material that, when applied to surfaces of

7. substances can join them together, resist separation and transmit loads across
the bond.
The adhesive strength /bond strength is the measure of the load, bearing
capability of the adhesive. The time period during which the bond remains
effective is referred to as durability. Adhesion refers to the forces or energies
between atoms / molecules at an interface that hold two phases together. In
dental literature, adhesion is often subjected to tensile / shear forces in
debonding tests and the mode of failure is quantified.
If the bond fails at the interface between two substrates, the modes of
failures is referred to as adhesive. It is referred to as cohesive if failure occurs
in one of the substrates, but not at the interface. But the mode of failure is
often mixed.
Four Different Theories have been advanced to account for the observed
phenomena of adhesion.
a. Mechanical Theories : Solidified adhesive interlocks micromechanically
with the roughness and irregularities of the surface of the adherend.
b. Absorption Theories : All kinds of chemical bonds between the adhesive
and adherend, including primary (ionic and covalent) and secondary
(hydrogen, dipole interaction and London dispersion) valence forces.
c. Diffusion Theories : Adhesion is the result of bonding between mobile
molecules. Polymers from each side of an interface can cross over and
react with molecules on other side. Eventually, the interface will
disappear and the two parts will become one.
d. Electrostatic Theories : Electrical double layer forms at the interface
between a meal and a polymer making a certain, yet obscure,
contribution to the bond strength.
The phenomenon of adhesion depends on certain factors, the main factors are ;
1) Surface energy
2) Wetting
3) Contact angle
When two substances re bought into intimate contact with each other, the
molecules of one substance adhere or are attracted to molecules of another.
This force is called adhesion while unlike molecules are attracted, and cohesion
when molecules of the same kind are attracted. The material film added to
produce the adhesion is known as adhesive, and the material to which it is
applied is called the adherend.
The principle of adhesion and the factors associated with this
phenomenon.
Surface Energy: For adhesion to exist, the surfaces must be attracted to one
anther at their interface. Concerned to dental structures, enamel which contains
primarily hydroxyapatite – has high surface free energy.
Wetting:
It is difficult to force two solid surfaces to adhere. Regardless of who
smooth these surfaces may appear, they are likely to be extremely rough when
viewed on an atomic / microscopic scale. Consequently when they are placed
in apposition, only the peaks in contact. Because these areas usually constitute

8. only a small percentage of total surface area, no perceptible adhesion takes
pale. One method of overcoming this difficulty is to use a fluid that flows into
these irregularities to provide contact over a greatest part of the surface of the
solid.
For example : When two polished glass plates are placed one on to of the other
and are pressed together, they exhibit little tendency to adhere for reasons
previously described. However, if a film of water is introduced between them,
considered difficulty is encountered in separating the two plates. The surface
energy of the glass is sufficiently great to atleast the molecules of water.
To produce adhesion in this manner, the liquid must flow easily over the
entire surface and adhere to solid. This characteristic is known as wetting. IF
the liquid does not wet the surface of the adherend, adhesion between the liquid
and adherend will be negligible or non existent. When surface energy is more
wetting is proper.
Contact Angle:
The extent to which an adhesive wets the surface of an adherend may be
determined by measuring the contact angle between the adhesive and the
adherend. The contact angle is the angle formed by the adhesive with the
adherend at their interface.
If the molecules of the adhesive are attracted to the molecules of the
adherend as much as or more than they are to themselves, the liquid adhesive
will spread completely over the surface of the solid, and no angle will be
formed.
Thus, smaller the contact angle between the adhesive and an adherend,
the better the ability of the adhesive to fill in irregularities on the surface of the
adhered. Complete wetting occurs at a contact angle of 0o
and no wetting
occurs at an angel of 180o
.
According to this theory of wetting and surface free energy, adhesion to
enamel is much easier to achieve than is adhesion to dentin. Enamel contains
hydroxyapatite, which ahs high surface free energy whereas dentin is
composed of two distinct substrates hydroxyl apatite and collagen, which has
low surface energy. In the oral environment, the tooth surface is
contraindicated by an organic saliva pellicle and low critical surface tension of
approximately 28 dynes/cm. Likewise, instrumentation of the tooth substrate
during cavity preparation produces a smear layer with a low surface free
energy. Therefore the neural tooth surface should be thoroughly claimed and
pretreated prior to bonding procedures to increase its surface free energy and
hence to render it more receptive to bonding.
FACTORS EFFECTING ADHESION:
1) Clinical factors
2) Factors effecting adhesion to mineralized tissue
I. Clinical Factors
a) Saliva and Blood Contamination

9. These contaminants act in a negative manner for adhesion. Although
dentin is a net substance, the constituents of saliva and blood create an
environment that can destroy dentin bonding.
b) Moisture Contamination From Hand Pieces :
Contamination from hand pieces can be due to lack of drying devices on
air lines leading from compressor, leakage of plumbing lines or due to
condensation of water in air lines. This will definitely effect the bonding
mechanism. This can be solved by blowing air from hand piece or syringe on
to a dry surface.
c) Oil Contamination from Hand Pieces / Air Water Syringes :
Oil contamination from airline occurs due to lack of maintenance of air
compressors. This can e prevented by using effective oil filters.
Oil and water contamination are the most potential and significant
factors present in tooth adhesion, because there presence is relatively unknown
and the result is unexpected.
Note : Bonding to dentin is compromised but the influence on adhesion to
etched enamel is less.
d) Surface Roughness of Tooth Structure :
Increase in surface area created by surface roughness may explain slightly
better bonds to dentin. It is possible that mechanical retention may be
increased slightly by microscopic roughness produced on dentin and enamel by
rotary cutting instruments.
e. Mechanical Undercuts in Tooth preparation :
f. Fluoride Content of Tooth
Increased fluoride content of enamel has shown to resist acid etching.
Clinicians generally need double the time to etch the fluoresced enamel.
Fluoride presence in dentin appears to influence bonding of adhesive agents
negatively (Nystrom Holtan and Douglas 1990).
g. Location and Size of Dentinal Tubules :
Dentinal canals at the external surfaces of the tooth or near the DEJ have
small diameters. As they approach the pulp, they become larger dentinal
canals. Such variations in the size o the dentinal tubules can affect adhesion.
Hence if canals are small, attachment is less and if canals are large, attachment
is enhanced.
h) Presence of Plaque, Calculus, Extrinsic Stains / Debris :
Presence of above said factors will impair effective bonding. Hence
before any bonding procedure the surfaces should be thoroughly cleaned with
scalers, abrasive prophy pastes using rubber cusp or with abrasive rotary
instruments.
i) Presence of Bases / Lines on Prepared Teeth :
Varnishes, copal cellulose or polyamide varnishes and resin liners affect the
bonding of the subsequently placed restorative material to the tooth surface.
Composite resins displaced over glass ionomer liner, the bond of resin to the
tooth is less than bond of the glass ionomer to the tooth or the bond resin to
glass ionomer.
j) Tooth Dehydration :

10. Overdrying the dentinal surfaces will cause collapse of exposed collagen. Such
collapse may prevent resin infiltration and impair boding. So drying only until
the obvious shine of moisture is gone is necessary.
k) Presence of Residual Temporary Cements :
Dentin / enamel that has been in contact with eugenol – containing temporary
cements or state – containing non eugenol temporary cements disturb the
bonding of the resin to the tooth surfaces.
Parameters Affecting Adhesion to tooth Tissue / Mineralized Tissue :
The strength and durability of adhesive depends on several factors. Important
parameters may include ;
a. Physicochemical properties of adhesive and adherend.
b. Structural properties of the adherend.
c. Formation of surface contaminants during cavity preparation.
d. Development of external stresses that counteract the process of bonding
and their compensation mechanisms.
e. Mechanism of transmission and distribution of applied loads through the
bonded joint.
Furthermore:
- Oral environment
o Subject to moisture
o Physical stresses
o Changes in temperature and pH
o Dietary components
o Chewing habits
Also considerably influences adhesive interactions between materials and tooth
structures.
Factors Related to Adherend:
a. Physico Chemical Properties of Enamel and Effect of Acid Etching :
As the composition and structure of enamel and dentin are substantially
different, adhesion to the two tissues will also be quite different. Enamel
consists of 96.97% by weight of inorganic material mainly HA. The remaining
is 4% - 12% of water and organic material (1% to 2% weight).
In the oral environment, an organic pellicle covers the enamel surface
creating a chemically complex surface with low reactivity. This results in poor
bonding enamel surface. Here the critical surface tension is approximately 28
dynes/cm.
The cutting of enamel surface during cavity preparation removes this
organic biofilm but does not increase the enamel surface energy. Whereas
etching (40%) increases the critical surface energy to 72 dynes/cm. The
creation bonding area and surface roughness make bonding of hydrophobic
resin possible.
b) Physico Chemical Properties of Dentin
Composition of dentin by volume is ;
Organic : Collagen - Type I - 18%
Water 12%

11. Inorganic : HA - 70%
Dentin has low surface energy 44.8% dynes / cm owing to its high protein
content, so wetting of such a low energy surface is difficult and adhesion is
hard to achieve. So to achieve adequate wetting on this low surface energy,
dentin is conditioned to various treatments to increase the surface free energy
and thereby help in bonding properly.
Transformed Dentin Structure due to Physiologic and Pathological Process:
Dentin is a dynamic substrate subjected to continuous physiologic and
pathologic changes in composition and microstructure.Aging causes dentin
undergo physiologic dentinal sclerosis and relative sclerosis in response to slow
progressive or mild irritation. There is formation of reparative / reactive dentin
as a defense mechanism to any injury or caries etc. So this transformed dentin
structures due to these physiologic and pathologic process i.e. Sclerosed /
reparative dentin ahs areas of complete hypermineralization without tubular
exposure, even when etched with an acid. All these morphological and
structural changes, result in dentin substrate that is less receptive to adhesive
treatment than is normal dentin.
d) Smear Layer :
When the tooth surface is instrumented with rotary and manual
instrument during cavity preparations, cutting debris is smeared over the
enamel and dentinal surfaces forming what is termed as smear layer.
Definition:
Any debris, calcific in nature, produced by reduction or instrumentation
of dentin, enamel or cementum or as a ‘contaminant’ that precludes the
interaction with the underlying pure tooth tissue. This iatrogenically produced
layer of debris has a great influence on any adhesive bond formed between the
cut tooth and the restorative material.
The morphology, composition and thickness of the smear layer are
determined to a large extent by the type of instrument used, the method of
irrigation employed and by the site of dentin at which it is formed.Its
composition reflects the structure of the underlying dentin mainly containing
pulverized Ha and altered collagen, mixed with saliva, bacteria and other
grinding surface debris. The thickness of the smear layer has been reported to
vary from 0.5 – 5 µm.
Although smear layer occludes the dentinal tubules with the formation
of smear plugs, the smear layer is porous and penetrated by submicron
channels, which allows a small amount of dentinal fluid to pass through. Smear
layer is reported to reduce dentinal permeability by 86%.
e) Internal and External Dentinal Wetness :
The dentinal permeability and consequently, the internal dentinal
wetness depend on several factors, including the diameter and length of the
tubule, the viscosity of dentinal fluid and the molecular size of substances
dissolved in it, the pressure gradient, the surface area available for diffusion,
the patency of the tubules, and the rate of removal of substances by pulpal
circulation.

12. Occlusal dentin is more permeable over the pulp horns than at the centre
of the occlusal surface, proximal dentins more permeable than occlusal dentin,
and coronal dentin is more permeable than root dentin. High dentinal
permeability allows bacteria and their toxin to easily penetrate h dentinal
tubules to the pulp, if the tubules are not hermetically scaled.
The variability in dentinal permeability makes it a more difficult
substrate for bonding than enamel. Removal of the smear layer creates a wet
bonding surface on which dentinal fluid excludes from the dentinal tubules.
This aqueous environment effects adhesion, because water competes
effectively, by hydrolysis, for all adhesion sites on the hard tissue.
Early DBA failed primarily because their hydrophobic resins were not
capable of sufficiently wetting the hydrophilic substrate. IN addition, bond
strengths of several adhesive systems were shown to decrease as the depth of
the preparation increased, because dentinal wetness was greater.
No significant differences in bond strengths is observed between deep
and superficial dentin when smear layer is left intact. Bond strengths of more
recent adhesive systems that remove the smear layer appear to be less affected
by differences in dentinal depth, probably because of their increased
hydrophlicity provides better bonding to the wet dentinal surface.
Besides internal dentinal wetness, external wetness / environmental
humidity, has been demonstrated to negatively affect bond strengths to dentin.
For instance, environmental humidity is affected by rubber dam. The bond
strengths obtained with most adhesive systems decrease as the level of
humidity/ exte. Wetness in the air arises, but some systems appear to be more
sensitive than others.
FACTORS RELATED TO ADHESIVE:
1. Physical properties of adhesive – Wettability.
2. Polymerization contraction of restorative resins.
Methods of composition of polymerization shrinkage
a) Flow
b) Hygroscopic expansion
c) Elastic modulus
d) Cervical sealing
3. Thermal coefficient of expansion
4. Transmission of stress across the restorative tooth interface.
5. Biocompatibility.
ADHESION TO ENAMEL:
Adhesion to enamel is achieved through acid etching of highly
mineralized substrate which substantially enlarges its surface area for bonding.
This enamel bonding technique, known as acid-etch technique was introduced
by Buonocore in 1955.
Enamel etching transforms the smooth enamel surface into an irregular
surface with a high surface free energy of about 72 dynes/cm, more than twice
that of etched enamel. An unfilled liquid acrylic resin with low viscosity, the

13. enamel bonding agent wets the high surface energy and is drawn into the
microporosities by capillary attraction.
Enamel bonding agents re commonly based on bisGMA/UDMA with
diluents such as TEDGDMA and HEMA. The bond between enamel and the
restorative material is established by polymerization of monomers inside the
microporosities and by copolymerization of remaining carbon – carbon double
bonds with the matrix phase of the resin composite, producing strong chemical
bonds.
Acid etching removes about 10 µm of enamel surface and creates a
microporous layer from 5-50 µm deep.
Three etching patterns have been described ;
Type I: Predominant dissolution of prism core and peripheries left intact – most
common.
Type II: Predominant dissolution of prism peripheries.
Type III: No prism structure is evident.
Mostly seen by action of strong chelating agents, but it is also seen with acids.
This shows there is no one specific pattern seen here. Different patterns may be
due to difference in chemical composition and crystalline orientation.
Variation may be seen from site to site or tooth to tooth.
Enamel bonding depends on resin tags becoming interlocked with
surface irregularities created by etching. Resin tags are formed circularly
between enamel prism peripheries (micotags are formed at the cores of enamel
primers). A much finer network of thousands of smaller tags is usually found
across the end of each rod, where individual HA crystals have been dissolved
leaving crypts of outlined by organic material. These fine tags are called
microtags. Macro and microtags are the basis of micromechanical bonding.
Microtags are more important because of their larger number and grater surface
content.
The effect of acid etching on enamel depends on several parameters :
1. Kind of acid used
2. Acid concentration
3. Etching time
4. Form of etchant – gel /semi gel / acquired solution gel is preferably –
better control.
5. Way in which wetting is activated (rubbing / irritating and or repeated
application of fresh acid). Etchant should always be applied in debbing
action. It should not be applied in subbringaction, because rubbing
action may fracture the thinned enamel rods thereby reducing the depths
of the created alleys and irregularities and obliterating what is left of
then with fractured enamel pieces.
6. Whether enamel is instrumented before etching.
7. The rinsing time
8. The chemical composition and condition of enamel.
9. Whether enamel is on primary or permanent teeth. Primary teeth –
prismless enamel and therefore require longer etching time.
10.Whether enamel is fluoridated, demineralised or stained.

14. Effects of acid Conditioning on the Surface Enamel:
Generally acid conditioning of enamel 935% - 40% of H3PO4 for 60
seconds) will cause the following changes.
1. Removes residual pellicle to expose the inorganic crystallite component
of enamel.
2. In the crystalline part – it causes preferential dissolution of
interprismatic enamel first, fooled by top of prisms themselves. The
east dissolvable are the sides of prisms.
3. Increases surface area upto 2000 times of its original unetched surface
and also increases wettabiliy.
4. It will create valleys and deepening. Valleys in place of interprismatic
enamel and top of prisms having circumscribed depressions. Depth of
these irregularities will range from 5 µ to 25 µ.
5. Acid etching will expose proteinaceous organic matrix substance of
enamel which can to restorations retention if it becomes inadequately
embedded within the restorative material.
6. Increases the surface energy with creation of reactive polar sites.
7. Mechanical cleansing and acid etching of enamel will assume removal
of substrate, enamel cuticles, salivary deposits, plaque composites and
any possible adhesives.
8. The enamel surface, thus exposing a cleanser lesser contaminated and
more wettable enamel.
9. Treatment with H3PO3 will add to enamel surface a highly polar
phosphate group which will increase the adhesive availability to the
enamel surface.
PHOSPHORIC ACID AS ETCHANT:
- Most commonly used etchant.
- Concentration – 30%, 40%  37% with etching time ≤ 15 seconds and
washing time of 10-20 seconds } Most acceptable and most receptive
enamel surface for bonding.
- Calcium dissolution and etching depth increase as the concentration of
H3PO4 increases until a concentration of 40% and at higher than this it
will start showing reverse effect.
- At concentration greater than 50%  There occurs a formation of
monocalcium phosphate monohydrate on the etched surface which
revents any further dissolution.
- At concentration less than 27%  There forms a precipitate of
dicalcium phosphate dehydrate that can not be easily removable.
- Etching time also has been reduced from traditional 60 seconds to 15
seconds and its shown that it has shown similar surface roughness and
etching pattern as that of 60 seconds.
- Currently it is recommended that enamel of teeth need not be etched for
more than 15-20 second except for the enamel which is acid resistant
because of high fluoride content. Primary teeth also require longer
etching time since the enamel is more aprismatic than that of permanent

15. teeth. Advantages of shorter etching time  it yields acceptable bond
strengths while conserving enamel and saving time.
- Rinsing time is important. R.T. of atleast 15 second is important to
remove dissolved CaPO4, which otherwise might impair infiltration of
monomers into the etched enamel microporosities, from the etched
surface.
- Recently rinse time of 1 second have been shown not to impair bond
strength/ promote microleakage at the enamel site.
- The use of ethanol to remove residual water from the etched pattern has
been reported to enhance the ability of resin monomers to penetrate the
surface irregularities (Gwinett 1992, Qusit V, Quist J 1985).
- Modern primers frequently contain drying agents such as ethanol /
acetone, with a similar effect.
ALTERNATIVE ENAMEL ETCHANTS:
As H3PO4 is said to be more aggressive, other alternatives have been
suggested like ;
1) EDTA
2) Pyruvic acid
3) Sulphuric acid
Ethylene diamine tetraacetic acid – is a strong decalcifying agent, promotes
only low bond strength to enamel, probably being EDTA does no etch
preferentially.
Pyruvic acid: 10% buffered with glycine to a pH of about 2.2, promotes high
bond strengths to enamel, but has been found to be in practical because of its
instability.
Sulphuric acid: 2% used for 30 seconds has shown to be as effective as H3PO4
whereas high H2SO4 concentration produce heavy crystal deposits which
interfere with bonding and cannot be washed away easily.
With the introduction of total-etch systems, in which enamel and dentin are
etched simultaneously, weaker acids re applied to enamel. With this total etch
concept, the term etching is often referred to as conditioning.
Etchant is referred to as conditioning agent:
The concentration and length of application of the conditioning agents
are adapted to provide a microporous etch pattern in enamel and causing
extreme demineralization of the dentinal surface.
Apart from H3PO4 acid – sued in concentration ranging from 10% to
40%  other inorganic acids such as nitric acid – 2.5% concentration.
Organic Acids :
- Citric acid
- Maleic acid
- Oxalic acid : 1.6% - 3.5%
Recent innovations : Candiprimers / SEP which serve simultaneously as
conditioner and primer. The rationale behind these acid monomer solution is
the formation of continuum between tooth surface and adhesive material by
simultaneous demineralization and resin penetration of enamel surface with the
10%

16. acidic monomers that can be polymerized in situ. The candiprimer is applied
and dispersed with air and rinsing.
Though acid conditioning remains the most popular method of bonding
composite resin to enamel, other methods have also been tried. One such
method which was tried was depositing CaSO4 crystals on the surface of
enamel by treatment with a solution of polyacrylic acid and potassium sulphate.
It was suggested that these crystals trapped resin to retain it mechanically.
New proposed method  by MAIJER and D.C. SMITH have proposed
a new method of bonding that involves crystal growth of enamel surface.
The system consists of treating a clean tooth surface with a 50% solution
of polyacrylic acid containing sulfate ions (SO4- ions). The liberated Ca ions
will react with these sulfate ions forming CaSO4. 2H2O in 1 or 2 minutes. As
these crystals nucleated with in the tooth and grow outwardly in a spherulic
habit, with irregular surfaces they are similar to an etched enamel with loss of
tooth substrate.
Lasers have been used for enamel / dentin preparation prior to the
restorative material placement.
Laser etching is a process of continuous vaporization and
microexplosion due to vapourisation of water trapped within the
hydroxyapatite matrix. In general, more material is removed by the micro
explosion of entrapped water than by direct vaporization of the HA crystals.
The amount of surface roughening is dependent upon the tupe and wavelength
of the laser.
CO2 and Nd:YAG proved most effective lasers for etching. However,
studies have shown that changes in surface morphology and bond strength after
laser etching are quite similar to acid etching.
KCP Technique: Kinetic cavity preparation – here both enamel and
dentin bombarded with aluminium oxide particles. Similar to sand blasting.
References :
- Critical Concepts on adhesion to Dentin. Crit Rev Oral Biol Med 1997 ;
8 (3) : 306-35.
- Principles of Adhesion. Oper Dent 1992 ; Suppl.5 : 1-19.
- Current Concepts in Dentin Bonding. JADA 1993 ; May 124 (5) : 26-
36.
- Dentin Bonding – Past and Present. Cur Dent 1996 ; Nov-Dec. 44 (6) :
498-507.
- New Trends in Dentin / enamel adhesion. JADA 2000 ; Nov.13 (Spec
No.) : 250-300.
BONDING TO DENTIN :
The classic concepts of operative dentistry have been challenged in the
last two decades by the introduction of new adhesive techniques first for
enamel and then for dentin. Nevertheless, adhesion to dentin still remains
difficult.
Adhesive materials can interact with dentin in different ways –
mechanically, chemically or both. The importance of micromechanical

17. bonding, similar to what occurs in enamel bonding, ahs become accepted over
the last decade. Researchers now believe that dentin adhesion relies primarily
on the penetration of adhesion monomers into the filigree of collagen fibres left
exposed by acid etching.
CHALLENGES IN DENTIN ADHESION:
SUBSTRATE:
Bonding to enamel is a relatively simple process with major technical
requirements or difficulties. Bonding to dentin, on the other hand, presents a
much greater challenge. Severe factors account for this difference between
enamel and dentin bonding.
Enamel is highly mineralized tissue, composed of more than 90% (by volume)
hydroxyapatite. Dentin contains substantial proportion of water and organic
material primarily type I collagen.
Dentin contains a dense network of tubules that connect the pulp with
DEJ. The tubules are lined by a cuff of hypermineralized dentin called
peritubular dentin. The less mineralized intertubular dentin contains collagen
fibrils with the characteristic collagen banding.
The intertubular dentin is penetrated by submicron channels, which
allow the passage of tubular liquid and fibres between neighboring tubules,
forming intertubular anastomoses.
Dentin is intrinsically hydrated tissue, penetrated by a maze of 1 to 2.5
µm diameter fluid-filled dentin tubules. Movement of fluid from the pulp to
the DEJ is a result of a slight but constant pulpal pressure. Pulpal pressure has
a magnitude of 25-30 mm of Hg or 34-40 mm of H2O.
Dentin tubules enclose cellular extension from the odontoblasts and
therefore are in direct communication with the pulp. Inside the tubule lumen,
other fibrous organic structures (the lamina lamitans) can be observed, these
substantially decrease the functional radius of the tubule.
The relative area occupied by dentin tubules decreases with increasing distance
from the pulp. The number of tubules decreases from about 4,5000/mm3
close
to the pulp, to about 20,000/mm3
near the DEJ.
The tubules occupy an area of only 1% of the total surface near the DEJ,
whereas they compromise 22% of the surface close to the pulp. The average
tubule diameter ranges from 0.63 µm at the periphery to 2.37 µm near the pulp.
Adhesion can be affected by the remaining dentin thickness after tooth
preparation. Bond strengths are generally les sin deep dentin that in superficial
dentin. But some dentin adhesives like 4-META monomer, do not seem to be
affected by dentin depth.
Whenever tooth structure is prepared with a bur/other instrument
residual organic and inorganic components form a ‘smear layer’ of debris on
the surface. Smear layer fills the orifices of dentinal tubules (forming smear
plugs) and decreases dentinal permeability by upto 86%. Composition of smear
layer is basically HA and altered natural collagen. Its altered collagen may
even acquire a gelatinized consistency as a result of the friction and heat
created by preparation procedure.

18. Removal of smear layer and smear plugs with acidic solutions may
result in an increase of the fluid flow onto the exposed dentin surface. This
fluid may interfere with adhesion, because hydrophobic resins do not adhere to
hydrophilic substrate if the resin tags are formed in the dentinal tubules.
Additional factors affect dentin permeability
- Use of vasoconstrictors in local anaesthetics – decreased pulpal pressure
in a fluid flow in tubules.
- Radius and length of tubules
- Viscosity of dentin fluid
- Pressure gradient
- Molecular size of the substances dissolved in tubular fluid
- Rate of removal of substances by the blood vessel sin pulp affect
permeability.
All these variables make dentinal dynamic substrate and consequently a very
difficult substrate for bonding.
II. Stresses at Resin – Dentin Interface :
Composite shrink as they polymerize, creating stresses of upto 7 MPa
within the composite mass, depending on the configuration of the preparation.
When composite is bonded tone surface only, stresses within composite
are relieved by flow from the unbonded surface. However stress relief within a
3-D bonded restoration is limited by its configuration factor / C-factor.
Unrelieved stresses in the composite may cause internal bond disruption
as well as marginal gaps around the restoration that increase microleakage.
Immediate bond strengths of approximately 17 MPa may be necessary
to resist the contraction stresses that develop in composite during
polymerization to prevent marginal debonding.
Water sorption by the resin may composite for the effect the
polymerization shrinkage because resin may expand and seal off marginal
gaps, but this occurs only over a relatively long period of time. Water sorption
is directly proportional to the resin content.
Enamel bond strengths are usually sufficient to prevent formation of
marginal gaps by polymerization contraction stresses. These stresses may,
however be powerful enough to cause enamel defects at margins. Extension of
enamel cavosurface level may increase the enamel peripheral seal.
Microleakage around dentin margins is potentiated by this discrepancy
in linear coefficient of thermal expansion between the restoration and the
substrate.
Treatment of dentin for Optimal Bonding:
The characteristics of successful bonding of a resin composite to dentin
includes micromechanical attachment between resin and demineralized, primed
surface layer of intertubular dentin. This complex referred to as the hybrid
layer is best achieved by acidic conditioning agents which remove the smear
layer, produce a surface demineralization to a depth of 3-6 µm and expose the
dentinal collagen frame work.
In some cases smear layer is not removed but rather dissolved or
modified to include it within the bonding process. Application of hydrophilic

19. resin primers facilitates subsequent penetration of low viscosity adhesive resins
into microporous collagen scaffold and dentinal tubules. Polymerization of
this infiltrated resin stabilizes the surface hybrid layer. Meticulous application
of these steps effect a gap free bond.
Other areas of concern during dentinal bonding are complex histological
structure and variable composition of dentin at different locations.
It consists of 50% volume of in organic content, 30% of organic
material, 20% of water / fluid content.
The high protein content – respectively for low surface surgery of dentin
(44.8 dy/au2
), which differentiated from etched enamel. Wetting of such a low
surface energy – difficult.
Further H2O is an essential component of natural dentin and hence
surface drying is difficult to achieve than is generally realized. The acquired
environment is difficult to bond to since H2O competes effectively for all the
adhesion sites.
DENTAL ADHESIVE SYSTEM:
The dental adhesive system consists a conditioner (etchant), primer and
bonding agent (adhesive).
Criterial for Ideal Dental Adhesive System (Philips and Rage) 1961
- Provide a high bond strength to dentin that should be present
immediately after placement land that should be permanent.
- Provide a bond strength to dentin similar to that to enamel.
- Show good biocompatibility to dental tissue including pulp.
- Minimize microleakage at the margins of restorations.
- Prevent recurrent caries and marginal staining
- Be easy to use and minimally technique sensitive
- Possess good shelf life
- Be compatible with a wide range of resins
- System should not be toxic or sensitizing to the operators and patients.
- Should seal the tooth surface from oral fluids.
Etchants, Conditioners, Primers and Bonding Agents :
There is confusion regarding these terms because they are often used
interchangeably.
Etchants: Basically implies the dissolution of the etchant and reaction
substrate products are removed by rinsing.
Conditioning: Involves cleaning, structural alternation and increasing
adhesiveness of the substrate.
Primer: That is monomer dissolved in solvents such as water, acetone, or
alcohol are applied to the etched or conditioned dentin substrate but are not
rinsed off.
Primers are available in one bottle or two bottle version.
The 2 bottle version polymerized following mixing application and
solvent removal.
Bonding Agent: Usually an unfilled resin that consists of a hydrophilic
monomers such as BisGMA, UDMA, TEGDMA and hydrophilic monomers

20. such as HEMA. Some recent commercial products combined with primer and
bonding agent in one bottle (Prime and Bond).
Conditioner: Most commonly use din the initial stage of clinical application of
total etch system and are therefore applied simultaneously to enamel and
dentin.
CONDITIONER OF DENTIN:
Definition: Conditioning – Alteration of dentin surface including the smear
layer with the objective of producing a substrate capable of micromechanical
and possibly chemical bonding to a dentin adhesive.
Effects: Physical Effect
Chemical effect
Physical: Increase / decreases the thickness and morphology of smear layer.
Increase / decrease the morphology of dental tubules.
Chemical:
- Modifications of the fraction of organic matter.
- Decalcification of inorganic portion.
Performed by - Chemical
- Thermal
- Mechanical
CHEMICAL CONDITIONING:
Both acids and calcium chelators – rely on removing the smear layer are
used as chemical conditioners.
Acid Conditioners:
Earlier acid treatment was restricted to enamel and not used on dentin
with a fear of pulpal damage.
But with more of research and Fusayama’s pioneering research on total
etching with 37% H3PO4 – simultaneous etching is being accepted.
Acid conditioning are employed with the objective of not only removing
the smear layer but also simultaneously demineralizing superficial dentin of 3-7
µm to expose a microporous collagen scaffold into which therein will
punctuate.
On intertubular dentin, the exposed collagen fibres are often additionally
covered by an amorphous layer which is of variable thickness and has
microporosities which is attributed to combined effect of denaturation and
collapse of residual smear layer collagen. This collagen smear layer’ may
reduce the permeability of underlying dentin to resin monomers and is highly
cross linked and insoluble in acids.
At the tubule orifices, peritubular dentin is often completely dissolved to
form a funnel shape structure and expose circularly oriented collagen fibrils
which are often additional retentive sites at the tubule wall.
After conditioning, maintenance of a moist dentin surface is
recommended, following wet bonding technique to prevent collapse of
unsupported collagen and promote wetting and infiltration of subsequently
applied resin. Several acids are used for the purpose of conditioning. These

21. include phosphoric acid, maleic acid, citric acid, nitric acid, oxalic acid,
pyruvic acid and hydrochloric acid.
Among these, H3PO4 was first acid to used as the conditioner at a
concentration of 37%. Recently acid concentration and etching times have
been refined. A 10% solution of H3PO4 appears to provide better bond strength
than the higher concentration. However, results of enamel bond strength
become questionable when these lower concentration acids are used.
Nitric acid is a stronger acid than the phosphoric acid. DBA (Eg.
Tenure, Mirage bond) that use nitric acid conditioners are highly adhesive and
provide good tubule seals.
10% citric acid continued with 3% Ferric chloride is used as smear layer
remover and etchant. Another combination etchant is 10% citric acid and 20%
CaCl2 (eg. Clearfil linear bond). Composite to H3PO4 etching, this combination
etchant decalcifies dentin to a lesser depth, and tubules do not open into a
funnel shape. Maleic acid (eg. Scotchbond) results in removal of smear layer
but not smear plugs.
CHELATORS:
Contrary to the strong acid etchants, chelators remove the smear layer of
decalcification or significant physical changes on the underlying dentin
substrate.
Also no funnel shaped changes are evident with the use of these agents;
instead a chelate is formed. A chelate refers to a compound with a central rectal
ion surrounded by covalently bonded atoms, ions or molecules called ligands
which possess additional bonds for chemical reaction.
The best known chelator conditioner is EDTA adjusted to a pH of 7.4.
It was developed for use in Gluma system when used for 30 seconds, the smear
plugs were not fully removed with this conditioner.
THERMAL CONDITIONING:
The recent trend to use lasers in conditioning of dentin. These may
serve as a potential alternative to acids for conditioning of dentin. It is
speculated that the lasers cause recrystlalization of dentin resulting in fungi
form appearance that contributes to increased microrelation or possible
chemical adhesion of a restorative material to the tooth structure.
Further, they remove the organic elements, leaving behind an apatite
substance in a new alpha form. The carbonized black spot that results after
hazing is easily washed off with water.
PRIMING:
Primers are the 2nd
step in bonding procedure are the actual adhesion
promoting agents that contain monomers with hydrophilic properties, which
have an affinity for the exposed collagen fibrils and hydrophobic properties for
copolymerization with adhesive resin.
These monomers, usually HEMA and 4-META are dissolved in
solutions of acetone / ethanol.

22. EFFECT OF CONDITIONING:
Three layers are seen.
1st
Layer : Presence of an upper diffuse black layer 7 any ultrastrucural
arrangement implies that, over this distance, the collagen fibrils might have
been denatured by acid conditioning.
Another explanation for this dark amorphous material might be that of
the residual, demineralised insoluble and perhaps denatured collage from
original smear layer has fallen down on the surface during etching. In a further
step this denatured collagen layer was probably incorporated by the resin
infiltrating the decalcified dentin surface layer creating the so called resin
impregnation base.
2nd
Layer :
Underneath this layer closely packed collagen fibrils with small
interfibrillar spaces were arranged parallel to the dentin surface presumably
restricting deep resin impregnation to the interfibrillar tunnel like spaces.
Induced the resin impregnation base frequently bulged out into the
underlying collagen network and appeared to be confined by obstructive,
parallel running collagen fibrils.
Consequently the resin impregnation would primarily occur at the upper
denatured collagen layer with increasing gradient of intensity to the underlying
collagen fibril arrangement. The presence of an amorphous substance in the
interfibrillar spaces might represent such confined resin interdiffusion into the
tunnel like structure.
3rd
Layer : Otherwise referred as HIATUS has fewer collagen fibers with
mineral inclusion. This hiatus was observed in all polymer thickened
specimens, in 90% of specimens etched with aqueous H3PO4 and 60% of
specimens etched with silica thickened gels.
Depth of Demineralization depends on :
1) Kind of acid
2) Application time
3) Acid concentration and pH
4) Surfactant thickness and modifiers.
PRIMING AND WETTING:
Uses of Primers: Promote resin promotion into the moist, demineralized
dentin with the aim of achieving complete resin penetration.
The dentin adhesive resin must wet the dentin if adhesion is to take
place liquids wet a surface when they spread across it readily rather than
remaining braded on the surface.
Critical surface tension of a liquid allows a drop to spread across the surface so
that its contact angle is reduced to zero. It is desirable that the adhesive liquid
have a surface tension equal to or some what less than the critical surface
tension for the solid substrate. Smear layer covered of dentin has critical
surface tension equal to 42 dynes/cm2
but that following demineralization by
EDTA has a surface tensions – 29 dynes / cm2
.
2.5% nitric acid 27 dynes /cm2

23. This unlike surface energy of enamel, the surface energy of dentin
decreases probably due to higher concentration of collagen.
When dentin required with an acidic conditioner is rinsed with water the
solubilized Ca++
and PO4 ions and reaction products should be extracted from
spaces between collagen fibrils. When the strategy of wet bonding is applied,
the collagen fibril network is effectively suspended in water. During the
priming phase resin monomers and solvents must diffuse through the long
narrow spaces between fibrils to reach the bottom of the demineralized zone.
The primer solvents should be either water or water inscrible.
The primer monomer should be hydrophilic because they must compete
with water, infact diffuse through water especially in the depth of
demineralized zone. Collagen fibrils contain both bound and unbound water. If
the collagen fibrils are to be enveloped by resin, the unbound water must
displaced by resin monomers during bonding process. So that a layer of
hydrophilic resin may coat each collagen fibrils.
ADHESIVE RESIN:
Also called the bonding agent
- Consist primarily of
o Hydrophilic monomers (BisGMA and UDMA)
o Hydrophilic monomers
o Viscosity regulator
o Wetting agent – HEMA
- Function – Major role in stabilization of hybrid layer by formation of
resin tags i.e. resin extension into tubules.
- Types – Auto cure – theoretically advanced because it polymerizes at
the interface by body heat. Disadvantages – It is slow.
o Light cure – It is polymerized prior to the application of
composite resin.
- In this way, the adhesive resin is not displaced and adequate light
intensity is available to sufficiently cure and stabilize the resin tooth
bond to counter act the polymerization shrinkage of the resin composite.
- Modes of application : Spreading of adhesive resin over the surface to
which it is bonded should be done preferentially by brush thinning
rather than air thinning.
- Adhesive should be copiously placed using a brush tip.
- Adhesive resin layer thickness of 100 µm.
- Blowing of adhesive resin layer may reduce its thickness too much,
decreasing its elastic buffer potential.
- The adhesive resin should always be used prior to application of
restorative resin composite. In this way adhere resin is not displaced
when the restorative resin composite is applied.
- Procuring the adhesive resin will stabilize the resin tooth bond and
consequently activate the elastic stress relaxation mechanism.

24. Functions:
- A sufficiently thick layer of adhesive resin – may be due to its relatively
high elasticity – acts as stress relaxation buffer (elastic bonding
concept).
- Polymerization content stresses generated during the placement of
composite resin was found to be significantly absorbed and relieved by
the application of an increased thickness of two stiffness adhesive.
- It also aids in – Absorbing masticatory forces, Tooth flexure effect,
thermal cycling shock.
- Because oxygen inhibits resin polymerization on oxygen inhibited layer
of about 15 µm will always be formed on top of adhesive resin even
after light curing. This O2 inhibited layer offers sufficient double MMA
bonds for copolymerization of the adhesive resin with the restorative
resin.
SMEAR LAYER AND ADHESIVE STRATEGIES:
What is smear layer?
When tooth surface is instrumented with rotary and manual instruments
during cavity preparation, cutting debris is smeared over the enamel and
dentinal surface forming what is termed – smear layer.
Definition:
Any debris, calcific in nature produced by reduction/ instrumentation of
enamel and dentin or contaminant that precludes the interaction with
underlying tissue.
Smear layer Treatment – 2 Options :
1) Clinical asset : Acts as effective natural cavity liner that seals dentinal
tubules and reduces permeability.
2) Disadvantages : Interferes with adhesion of restorative material
surviving as a focus for bacteria and it should be removed.
Techniques for smear layer treatment :
1) No Re at al. The smear layer is left place of modification and the DBA
indirectly applied to it.
Eg. Scotchbond and Prisma bond.
Resin would infiltrate there the entire thickness of the smear layer and
even bond to underlying matrix or penetrate into tubules.
2) Dissolution of smear layer : Dissolved smear layer plays an vital role in
chemical attachment of DBA to dentin.
Eg. Scotchbond and Mirage.
3) Removal of smear layer by acid etching : Acid etching agents are used
to remove smear layer and develops attachment directly to intact dentin
(then primer)
4) Modification of smear layer : This allows interaction of DBA with the
smear layer and improves the attachment of smear layer to dentin.
Eg. Bonding agent – Prisma 2, XR Bond, All Bond.
5) Removal and replacement of smear layer : Removal of smear layer by
acid etching and replacement with another mediating agent. Tenure

25. replaces smear layer with oxalate crystals which are deposited in
dentinal tubules.
MARBIDIZATION:
Hybridization / formation of a hybrid layer, occurs following an initial
demineralization of the dentinal surface with an acidic conditioner, exposing a
collagen fibril network with interfibrillar microporosities that subsequently
become interdiffused with low viscosity monomers. This zone in which resin
of the adhesive system micro mechanically interlocks with dentinal collagen –
is termed as hybrid layer / hybrid zone.
Three Layers of hybrid Layer :
1st
Layer – Top most – Amorphous electron – dense phase – which can be
attributed to denatured collagen – Clearfil.
Optibond and Super Bond D-liner : More loosely arranged collagen fibrils and
individual collagen fibrils are directed towards adhesive resin and the
interfibrillar spaces filled with resins.
Scotch bond multipurpose and single bond – hybrid layer is covered by
an amorphous phase, which may have originated in a chemical reaction of
polyalkenoic cid copolymer of the primer with residual calcium.
Middle Layer of Hybrid Layer: Contains c/s and longitudinally sectioned
collagen fibrils separated by electronucleant spaces. These interfibrillar
channels which have typical dimensions of 10-20 nm, represent the reason
wherein HA crystals had been deposited and have been replaced by resin as a
result of the hybridization process. Residual mineral crystals are sometimes
scattered between collagen fibrils.
Base of Hybrid Layer : Char. By gradual transition to the unaltered dentin, with
a partially demineralized zone of dentin containing HA crystals enveloped by
the resin or by a more abrupt transition.
RESIN TAG FORMATION:
The contribution of resin tag formation for bond strength has been a
matter of speculation. Bond strength values droop in deeper dentin where the
number of size of dentinal tubules is greater and intertubular occupies less of
total bonding area.
This indicates that presence of intertubular dentin is more important than
the development resin tags in the bonding process.
MECHANISM OF DENTIN BONDING:
Composite resins do not show an intimate microscopic contact with
dentin when placed directly into the cavity.
To overcome this, an intervening layer of fluid is used, which fills in the
microscopic space, polymerizes and combines with the composite resin and
components of dentin.
The basic chemical composition of these dentin bonding adhesives can
be conceived as ;
M-R-X CH3

26. M – Methacrylate group CH2 = C
R – Spacer CO – O –R – X
X – Reactive group capable of bonding to dentin surface
The bonding mechanisms for all the three are presented in Figure 16.11
(Sikri Pg.358).
Agents that use a phosphate group in their group in their bonding to
calcium ions are referred to as phosphate bonding systems and are most the
common ones employed. The constituent ‘Z’ in the phosphate based adhesives
may be chlorine, a hydroxyl or a phenyl group.
BONDING OF THE ORGANIC PORTION OF DENTIN:
Bonding to the organic part of dentin involves interaction with the
amino (-NH), amido (-CONH2), hydroxyl (-OH) or carboxylate (-COOH)
groups present in the collagen of dentin.
Removal of hydrogen from any of these groups allows combination with
chemicals present in DBA. Compounds that have a capacity to react with one
or more groups of collagen are isocyanates, carboxylic acid chlorides,
carboxylic acid anhydrides and aldehydes.
Eg. Adhesives that rely on bonding to org.
Part of dentin  Dentin atheist (Isocyanate based) gluma (Aldehyde based)
ROLE OF WATER IN BONDING PROCESS:
When prepared dentin is acid etched, the smear layer and plugs are
removed and the underlying 2-7 µm layer of dentin is demineralized.
Solutions used for etching are generally acidic and contain H2O to ionize
the acids and dissolve and extracted minerals. Post-etching rinsing with water
removes this dissolved mineral and leaves a demineralized dentins surface
covered with water. About 70% of the demineralized dentin is occupied with
water in areas from where the mineral has been removed.
Functions of Water:
It is responsible for maintaining the collagen in an expanded state and
thereby preserving the spaces needed for infiltration of resin. IT acts as
plasticizer for collagen and keeps in soft state.
If its dehydrated : Dentin is dried/ exposed to air.
Water evaporates leaves collagen in a collapsed stiffened state because
of surface tension forces. So this reduces the ability of the subsequently applied
agents to penetrate the collagen web.
Also when collagen fibrils are brought closer, 2o
forces start becoming
active between adjacent peptide chains in the collagen triple helix, which is not
possible when water is present – thereby increasing the stiffness or modulus of
elasticity for collagen.
REWETTING:
- Upon addition of water, the collagen net work re-expands to about 100%
of its original volume.

27. - It is believed that critical water concentration exists that prevents
collapse of the network or allow reexpansion of dried dentin over a
period of 10-30 seconds.
Non Aqueous Primers:
When such primers are applied to dry dentin, the collagen is not
rewetted by H2O  network continues to exist in a collapsed stiffened state
with little / no resin penetration because of reduced porosity around collagen
fibrils.
Water Based Primers :
When such primers are applied to air dried, shrunken and demineralized
dentin – 2 events occur depending upon the concentration of primers.
a) If the H2O concentration of pumice is low – H2O soluble resin monomer
and/or organic solvent will stiffen the collagen meshwork faster than water can
plasticize the collagen and it will not completely re-expand.
CLASSIFICATION OF DENTIN BONDING AGENT:
I. By Deggrange / Jean Roulet
Type 1: Those that bond directly to smear layer and the sue of an acidic primer.
Type 2: those that use acidic primer to alter the smear layer prior to or during
bonding subdivided to
a) Which are 3 separate identifiable components – essentially
consisting of asepexate primer, coupling agent and unfilled resin.
b) Those that have a reduced number of components i.e. usually 2.
i. Or the coupling agent and unfilled resin.
ii. Or the coupling agent and unfilled resin.
Eg. Scotch Bond 2  Combines primer and coupling agent 
SEP.
Here conditioner – Primer
Primer  Coupling agent
c) When the H2O content of primer is large enough to plasticize the
collagen faster than the resin / solvent stiffens it, the hydrophilic
resin monomers infiltrate the network as it is gradually
expanding. Excessive H2O in primer should be avoided as it
dilutes the monomer concentration drastically.
Dry Bonding Wet Bonding Over Wetting Bonding
Technique
Dry
↓
Collapse of collagen
↓
Lesser space available
for resin infiltration
Moist
↓
Collagen maintained
↓
Optimal hybrid layer
Over wet
↓
Swelling of collagen
↓
Lesser space available
for resin penetration

28. CLASSIFICATION OF DBA – BASED ON CHRONOLOGICAL
ORDER:
I. First Generation Adhesives :
Initiating his enamel acid – etching technique, Buonocore et al in 1956
reported that glycerophosphoric acid dimethacrylate (GPDM) could bonding to
HCl acid etched dentinal surfaces. The bond strength attained was only 2-3
MPa. After failures of this early dentin acid etching technique, research efforts
fraussed primarily on developing chemical adhesion to dentin.
DBA’s were no longer unfilled resins composited which intended purely
to enhance wetting of the dentinal surface. The became big functional organic
monomers with specific reactive groups that were claimed to react chemically
with inorganic Calcium-HA and/or organic collagen components of dentin.
The traditional concept of chemical adhesive potential base don
bifunctional molecule.
 With a methacrylate group M
 Linked to reactive group – X
 By an intermediary group – R
Development of N-phenyl glycine glycidyl methacrylate (NPG-GMA) was the
basis of first commercially available DBA – Cervident (SS White).
This NPG GMA – acted as primer and adhesion promote between
enamel / dentin and resin materials by chelating with surface dentin. Since Ca+
+, ions of the tooth substructure area mediator in the bound formation, agents
of this type a expected to form stronger bonds to enamel than to dentin.
II. Second Generation DBA:
Developed for clinical use in early 1980. These products were base don
phosphorous esters of methacrylate derivatives such as BisGMA or HEA.
Bonding mechanism involved enhanced surface wetting and ionic interaction
between negatively charged phosphate groups and (+)vely charged calcium.
The primary chemical adhesion is not thought to play a major site in the
bonding process.
Clearfil (Kuraray, Japan) – 1st
agent in this series - composed of ethyl
alcohol solution content, tertiary amine as the activator catalyst liquid –
BisGMA monomer containing phosphate ester, benzyl peroxide.
Bond is by attraction between (-)ve changes of O2 on the phosphorous
group and (+)ve charged calcium ions in dentins surface.
Drawbacks in First and Second Generations:
- Lack of adequate bond strength that could over come contraction
stresses during stresses.
- Being hydrophobic nature – close adaptation to the hydrophilic dentin
could not be dentin.
III. Third Generation Dentin Bonding agent:
Basis for 3rd
generation of dentin adhesives was laid by Japnese
philosophy of etching dentin to remove the smear layer gained acceptance.

29. 3rd
generation adhesives unlike the 2nd
generation ones either modify or
completely remove the smear layer to allow resin penetration into underlying
dentin before the application of the actual adhesive.
The postulated bonding mechanism of the dentin – etching technique
was that etched dentin would provide micromechanical retention for the
restorative resin composite by allowing penetration of the resin bonding agent
into the opened dentinal tubules.
The extra step comprised of conditioning and primary of dentin but
made the procedure more complicated and time consuming.
The three steps – conditioning, priming and application of bonding agent – may
be done either separately or the components combined to reduce it to two steps.
Dentin conditioner is an acidic solution that removes the smear layer and is
rinsed off water application.
The primer solution usually contains an adhesion promotes in a solvent such as
water, ethanol or acetone. These are applied to the surface and dried,
presumably leaving the adhesion promotes on the dentin with its hydrophobic
groups exposed to create a favourable surface for the bonding agent. In some
systems, the conditioner and primer may be combined to form the “self etching
primer”.
First system of third generation – oxalate bonding system/ FNP system – Initial
system utilized a solution of acidic ferric oxalate.
IV. FOURTH GENERATION ADHESIVES:
Till now, the strategies for dentin adhesion were based upon the
formation of resin tags penetrating into tubules of conditioned dentin formation
of precipitate on pre treated dentins surface followed by chemical and
mechanical bonding to resin and chemical union to either inorganic / organic
components of dentin.
Recent concept by Nakabayashi (1991).
Classification – Sikri : Based on Mode of application.
a. In which adhesives modify the smear layer and incorporate into the
bonding process.
b. In which adhesives completely remove smear layer and are subdivided
into 2/3 step application.
2 step – conditioning + (Primer and adhesive)
3 step – conditioning + Priming + adhesive application.
Action of these agent principally based on combined effect of
hybridization and resin top formation.
c. In which the adhesives dissolve the smear layer rather than remove it – 2
steps.
1st
step – Combined conditioner and primer (SEP)
2nd
Step – Application of adhesive
Principal : Partially demineralize the smear layer and underlying dentin
surface with removing dissolved smear layer remnants and unplugging
the tubule orifices – Rationale – demineralize dentin  simultaneously
penetrate with monomers and polymerize in situ.

30. IV. Classification of Dentin Bonding Agent – based on mode of action
I. Those that bond with calcium ion (Base don phosphate esters of
BisGMA) Eg. Scotchbond 1 and Bondlite.
II. Those that bond with amine / hydroxyl group (Based on isocyanate /
aldehyde) Eg. Gluma.
III. Those that bond with repreciptiated smear layers. Eg. Scotchbond 2
and Tenure.
Clinical Factors in Dentin Bonding:
1. Isolation
2. Bond to enamel
3. Roughen sclerotic dentin
4. Use mechanical retention
5. Have dentin moist after etching
6. Apply and dry primers correctly
7. Do not over thin bonding resin
8. Use flexible restorative system
9. Fill incrementally
10.Delay finishing
11.Rebound Margins
12.Follow mean directions
BONDING IN OTHER CLINICAL SITUATIONS:
Spectrum of bonding is quite wide. Almost every material and technique
has tried to achieve bonding between two variables.
Bonding spectrum in dentistry :
Enamel (Etch) Silane (Etch)
Metal
GIC Etch Composite
Resin
Etch
Dentin bonding Ceramic
Agent
Dentin
BONDING OF GLASS IONOMER TO HARD TISSUE:
- Can adhere to enamel and dentin
- Also can bond to reactive polor substrate- base metals

31. - Primary mechanism of bonding – chemical mainly micro mechanical
also.
BONDING OF COMPOSITE TO GIC – MECHANICAL
GIC commonly sued under composite as a dentin substitute – sandwich
technique / bilayered technique.
- 37% H3PO4  used etch enamel and GIC
- Acid treatment – improves bond to composted by producing rough
surface in which glass particle stand out of matrix.
- Thin liquid (low viscosity) resin applied is able to penetrate into
micropores between particles – thereby providing mechanical
interlocking.
- Cement should be fully set before etching.
- Normally 20 minutes second but for fast set – 2-3 minutes, slow set 
for an hour / so. Light cure  no need for etching.
- Etching period  15-30 second.
- Above 30 seconds  prone to degradation by acid.
- Higher the strength of cement  better clinical results.
- Few authors suggests  layer of varnish over GIC with the rationale
that polyshrinkage of composite will not disturb underlying cement.
III. Bonding of Composite to Porcelain
Partly – Mechanical interlocking
Partly – Chemical union
Mechanical Retention: Etching the surface of porcelain with HF acid / grit
blasted with aluminia – increase surface roughness.
Time for etching depends – Etchant concentration and type of porcelain used.
To improve mechanical bonding – gap between bonding medium and porcelain
minimized using low viscosity resin which penetrates into pores by capillary
action.
Chemical Union: By rinsing etched surface with silane coupling agent.
Mechanical interlock is more important than chemical adhesion.
Silane coupling agents - shown to reduce gap between porcelain and
compressive presumably – improving upon wettability and hence promoting
mechanical interlocking.
IV. Bonding of Amalgam to Resin
- Relating new treatment modality and made bonding between amalgam
and tooth structure, amalgam and amalgam, amalgam and metal –
successful possibility.
- Advantages – Increases retention and increases fracture resistance.
- Reduces microleakage
- Decreases chances of recurrent caries

32. Agents:
- All Bond
- Linear Bond -2
- Amalgam Bond and
- Panavia
- They have dual characteristic – Hydrophilic, so that it wets the
hydrophilic enamel and hydrophobic – amalgam which is hyophobic.
- 4-META, MDP – used comonomers.
- Bond – Between resin and amalgam – micromechanical as amalgam
interlocks with fluid resin during condensation.
SUCCESS AND FAILURES OF ADHESIVES:
1) Material factors
- Like hydrophobic bonding agents
- Incomplete resin penetration
- No significant hybrid layer
2) Substrate – As said before
3) Size and shape of lesion
4) Maxillary vs mandibular arch because of – less chances of
contamination and – Lower tooth flexural effects in upper jaws.
5) Patients age : Increased age – dentin sclerosed – Decreased clonal
adhesiveness, increased tooth flexure.
6) Tooth flexure : Influencing factor on retention. Adhesives especially at
cervical restoration. Heavy centric occlusal and eccentric forces
respectively for general compressive and tensile force s- cervical area –
gradually dislodge and debond the resin restoration. So compressive
with adequate elastic capacity like micro filled are preferred in rich
lesion.
7) Dentinal wetness : Bonding agents with effective wetting capacity
ensure successful bonding.
8) Elastic bonding concept : Due to shrinkage during polymerization –
Debonding can occur.
- So intervening adhesive resin – sufficiently elastic to absorb the poly
stress.
- Can be achieved by using – relation thick layer of separately
polymerized unfilled / semi filled resins.