DENTIN BONDING AGENTS: A REVIEW OF THEIR EVOLUTION, MECHANISM AND CLINICAL APPLICATION

DENTIN
BONDING
AGENTS
2
DR JISNA

CONTENTS
Introduction Terminologies
Adhesion- Theories
•Requirements
•Clinical factors affecting
adhesion
Enamel-
Composition and
structure
Adhesion to enamel
Dentin- Composition
and structure of
dentin
Adhesion to dentin
Mechanism of
bonding to dentin
Generations of
dentin bonding
agents
Classification of
dentin bonding
agents
Challenges-bonding
procedure
RECENT ADVANCES Conclusion References
3

INTRODUCTION
• 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Black, have gradually been replaced by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 of4

BONDING IN DENTISTRY HAS
IMPROVED STABILIZATION AND
RETENTION OF RESTORATION
,ELIMINATED EXCESSIVE REMOVAL
OF SOUND TOOTH STRUCTURE
AND THE RESTORATIONS ARE
BETTER ABLE TO TRANSMIT AND
DISTRIBUTE FUNCTIONAL
STRESSES ACROSS THE BONDING
INTERFACE.
5

HISTORY
6
▸1949: Dr Hagger (De Trey/Amalgamated Dental Company)Sevriton Cavity Seal
▸1954: M Buonocore- Acid Etching
▸1968: Buonocore, Matsui and Gwinnet (Published report ) ‘Prism like Tags’
▸1960: Pit & fissure Sealants/ Composite introduced
▸1982: Nakabayashi : Hybrid layer formation
▸Fusayama: Total Etch sysytem
▸1992: Wet Bonding technique by Kanca
▸1990: 3 step Total Etch adhesive system
▸2000: SEA’s were developed
▸2011: Adhesion Decalcifictaion Concept by Van Meerberk et al
▸2011: Universal Adhesives developed

ADHESIVE
DENTISTRY
ADVANTAGES
• Preserves sound structure
• Esthetics
• Reduces microleakage
• Reduces postoperative sensitivity,
marginal staining and recurrent
caries.
• Transmits and distributes stress
7

IDEAL REQUIREMENTS OF DENTIN BONDING
AGENTS
• Provide high bond strength to dentin that should be present
immediately after placement and that should be permanent.
• Provide bond strength to dentin similar to that of enamel.
• Show biocompatibility to dental tissue including the pulp.
• Minimize microleakage at the margins of the restorations.
• Prevent recurrent caries and marginal staining
• Be easy to use and minimally technique sensitive.
• Possess a good shelf life.
• Be compatible with a wide range of resins.
• In addition it should be non toxic and non sensitizing to the
operators or patients.
• Bonding agents should seal the tooth surfaces from oral fluids.
8

ADHESIVE DENTISTRY
INDICATIONS
•Restore carious area
•Fractured tooth structure
•Correction of unesthetic shapes,
shades, positions- Close diastema,
add length, mask discoloration
•Bond ceramic restorations,
crowns, FPD, orthodontic brackets
•Treat dentinal hypersensitivity
•Repair fractured restorations
•Core built up foundations
9

TERMINOLOGIES
• DENTIN BONDING AGENT: The dentin
bonding agents are di or multifunctional
organic molecules that contain reactive
groups which interact with dentin and
the monomer of the restorative resin.
• INDIAN DENTAL ACADEMY
• Adhesion: is the force or the intermolecular
attraction that exists between molecules of
two unlike substances when placed in
intimate contact with each other
• Adhesive: The material that when applied
to surfaces of substances, can join them
together, resist separation & transmit loads
across the bond. i.e., Material that join
• ( Handbook of adhesion)
• Adherend: The surface / substrate that is
adhered to is termed the Adherend. 10

WORD ADHESION IS DERIVED FROM THE LATIN WORD
ADHAERERE  TO STICK
Attachment of one substance to another.
Forces or energies between atoms or molecules, at an interface that
hold two phases together
The substance added to produce the adhesion is known as ‘Adhesive’
and the material to which applied known as ‘Adherend’
11

DEFINITION
• “The mechanism that bonds two materials in
intimate contact across an interface” -
Davidson (1996).
• “ The state in which two surfaces are held
together by interfacial forces which may consist
of valence forces or interlocking forces or both.”
(The American Society for Testing and Materials)
12

The
adhesi
ve
strengt
h
/bond
strengt
h is
the
measu
The
time
perio
d
durin
g
which
the
13

ADHESION THEORIES
MECHANICAL ADSORPTION DIFFUSION ELECTROSTATIC
14

MechanicalTheory:
•Solidified
adhesive
interlocks
micromechanic
ally with the
roughness and
irregularities of
the surface of
the adherend.
AdsorptionTheory:
• All kinds of
chemical
bonds
between the
adhesive and
adherend,
including
primary (ionic
and covalent)
and secondary
(hydrogen
bond, dipole
interaction)
valence forces.
DiffusionTheory:
• 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
ElectrostaticTheory:
•Electrical
double layer
forms at the
interface
between a
metal and a
polymer
making a
certain, yet
obscure,
contribution
to the bond
strength
15

SURFACE
ENERGY
• “The increase in energy per unit area
of surface is referred to as the surface
energy or surface tension.”
(science of dental materials,
Anusavice)
• For adhesion to exist, the surfaces
must be attracted to one another at
their interface.
• The energy at the surface of a solid is
greater than that of its interior.
• The surface atoms of a solid tend to
form bonds to other atoms in close
proximity to the surface and reduce
the surface energy. This attraction
across the interface between unlike
molecules is called adhesion.
16

• When primary bonding is
involved, the adhesion is
termed chemisorption.
• In this a chemical bond is
formed in between the
adhesive and the adherend.
Eg., oxide film formed on the
surface of a metal.
• The surface energy and the
adhesive qualities of a given
solid can be reduced by any
surface impurity, such as
adsorbed gas, an oxide, or
human secretions.
17

The greater
the surface
energy, the
greater the
capacity for
adhesion.
Surface
energy of
the adhesive
should
always be
lower than
the surface
energy of
enamel of
dentin
Concerned
to dental
structures,
enamel
which
contains
primarily
hydroxyapat
ite – has
high surface
free energy. 18

WETTING :
• WETTING is the measure of the energy of
interaction of the materials.
• It is difficult to force two solid surfaces to
adhere. Regardless of how smooth these
surfaces may appear, they are likely to be
extremely rough when viewed on an atomic /
microscopic scale.
• The attraction is generally negligible when the
surface molecules of substrates are separated
by distance > 0.7 nm.
• One method of overcoming this difficulty is
to use a fluid that flows into these
irregularities to provide contact over a greater
19

• 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.
20

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.
21
θ

• 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.
• 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.
22

THEREFORE AN ADHESIVE WITH LOW VISCOSITY,
LOW SURFACE TENSION AND LOW CONTACT
ANGLE IS PREFERRED
23

B) MOISTURE CONTAMINATION
FROM HAND PIECES :
• Water leakage from aerotor hand-
piece / air water syringes is an
unrecognized problem in most
situations.
• The source of leakage could be due to:
• 1) Lack of drying devices on air lines
leading from the compressor, allowing
wet air to be carried out to the syringe /
hand pieces.
• 2) Due to leakage of plumbing lines /
due to the condensation of water in
24

C) OIL CONTAMINATION FROM
HAND PIECES / AIR WATER
SYRINGES :
• Oil contamination from airline occurs due
to lack of maintenance of air compressors.
This can be prevented by using effective oil
filters.
• Oil and water contamination are the most
potential and significant factors present in
tooth adhesion, because their presence is
relatively unknown and the result is
unexpected.
• Bonding to dentin is compromised but the
influence on adhesion to etched enamel is
25

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.
26

e) Mechanical Undercuts in Tooth preparation
The mechanical undercuts are placed in the tooth structure
to hold the restorative material from bodily displacement
from the preparation.
They also may resist some microscopic movement of the
restorative material caused by thermal / polymerization
influences.
This is further augmented with the current generation dentin
bonding agents (CLIM 1990).
27

f) Fluoride Content of Tooth
Increased fluoride content of enamel has shown
to resist acid etching. Clinicians generally need
double the time to etch this enamel.
Fluoride presence in dentin appears to influence
bonding of adhesive agents negatively (Nystrom
Holtan and Douglas 1990).
28

g.) Location and Size of Dentinal Tubules :
Dentinal canals at the external surface of roots or near the
dentino-enamel junction have small diameters.
Dentinal canals which are closer to the dentinal pulp are
larger.
Old dentin has smaller dentinal canals, while new dentin has
larger dentinal canals (Pashley 1990).
29

h) Presence of Plaque, Calculus, Extrinsic Stains / Debris :
• Plaque present on the tooth surface prevents etching with 37%
phosphoric acid. Penetration of plaque by the less aggressive
acids used in dentin bonding agents is not possible and so will
result in a clinical adhesive failure.
• Tooth surface stains and dental calculus if not removed will not
permit bonding.
Hence before any bonding procedure the surfaces should be
thoroughly cleaned with scalers, abrasive prophylactic pastes using
rubber cusp or with abrasive rotary instruments.
30

i) Presence of Bases / Liners on Prepared Teeth :
Varnishes and resin liners affect the bonding of
the subsequently placed restorative material to the
tooth surface.
When Composite resins are placed over glass
ionomer liner, it is seen that the bond of resin to the
tooth is less than bond of the glass ionomer to the
tooth.
31

j) Tooth Dehydration :
Overdrying the dentinal surfaces will cause
collapse of exposed collagen. Such collapse may
prevent resin infiltration and impair bonding. So drying
only until the obvious shine of moisture is lost is
necessary.
32

TOOTH AS A SUBSTRATE FOR BONDING
Etching Bonding
34
Enamel
▸Composed of hard Crystalline –HAp with strong
intermolecular forces
▸High surface energy
▸Water
▸Organic material

• In the oral environment, an organic pellicle covers the enamel surface
creating a chemically complex surface with low reactivity. This results
in poor bonding to 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.
• Enamel is more homogeneous in structure, composition irrespective
of its depth and location, unlike dentin.
35

ACID ETCHING
EFFECTS
Removes the residual pellicle to expose the inorganic
crystalline component
Creates a porous layer 5 to 10 um in depth
Increase the wettability & surface area
Raises the free surface energy ----72 dynes/ cm 36

• Bonding to enamel depends primarily on resin tags becoming
interlocked within enamel surface irregularities
• Acid etching transform smooth enamel into rough surface .
• So when resin based material is applied to irregular etched
enamel ,resin penentrates into surface aided by capillary
action.
• Monomers polymerise and material becomes interlocked with
enamel surface
37

THE EFFECT OF ACID ETCHING ON ENAMEL DEPENDS ON SEVERAL
PARAMETERS :
• Kind of acid used
• Acid concentration
• Etching time
• Form of etchant – gel /semi gel / acquired solution gel is preferably – better control.
• Way in which wetting is activated (rubbing / irritating and or repeated application of fresh acid).
• Whether enamel is instrumented before etching.
• The rinsing time
• The chemical composition and condition of enamel.
• Whether enamel is on primary or permanent teeth. Primary teeth – prismless enamel and therefore
require longer etching time.
• Whether enamel is fluoridated, demineralised or stained.
• Etchant should always be applied in dabbing action. It should not be applied in rubbing action,
because rubbing action may fracture the thinned enamel rods thereby reducing the depths of the
created valleys and irregularities and obliterating what is left of them with fractured enamel pieces.
38

CONDITIONING ENAMEL :
The 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
unetched enamel.
(Jendresen & Glantz.Microtopography and clinical adhesiveness of
an acid etched tooth surface-an invivo study) 39

40
Type I : Predominant dissolution of prism
core and peripheries left intact – most
common.
Three etching patterns have been described
;
(Silverstone LM. Variation in pattern of
etching of human dental enamel examined
by SEM. Caries Res 1975)
HONEYCOMB APPEARANCE

Type II : Predominant dissolution of prism peripheries.
41
Cobblestone appearance

Type III : No prism structure is evident/combination
Mostly seen by action of strong chelating agents, but it is also
seen with acids. 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.
42
Includes areas resembling Type I & II patterns-
presence of prism less enamel

ACID ETCHANTS
• Includes acids like
• Citric acid, tannic acid, maleic acid, polyacrylic acid.
• Most commonly used however is Phosphoric acid – 37% 15-20 secs.
• NEW CONCEPT OF ETCHING :
Combined action of different etchants i.e. phosphoric acid on enamel
and EDTA (24% pH 7) on dentin may be a better alternative than
etching the entire cavity with single etchant.
43

PHOSPHORIC ACID
• Most commonly used etchant.
• Concentration – 30%-40%
37% phosphoric acid with etching time not less than 15 seconds and washing
time of 5-10 seconds  Most receptive enamel surface for bonding.
(Gwinnett AJ and
Summitt JB)
• 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. 44

• At concentration 50% phosphoric acid  There occurs a
formation of monocalcium phosphate monohydrate on the
etched surface which can be rinsed off.
• At concentration less than 27%  There forms a precipitate of
dicalcium phosphate dihydrate that can not be easily removed.
(Chow & Brown)
• Etching time also has been reduced from traditional 60 seconds
to 15 seconds and it has demonstrated equivalent bonding
effectiveness.
45

• Rinsing is important to remove dissolved CaPO4 from the
etched surface, which otherwise might impair infiltration of
monomers into the etched enamel microporosities.
• Flat surfaces -1 to 3 sec
• Complex preparation forms – 5 to 10 sec
(Summitt,Chan,Dutton.Effect of air/water rinse v/s water only
and of five rinse times to resin to etched enamel shear bond
strength. )
46

• Phosphoric acid is often made thicker with →
 Silica thickening agents which increase ph
 Polymer beads which lower ph
• Aqueous preparation and polymer gelled acids have lower pH and thus etches
deeper.
(Perdigao et al 1996)
• In acidic gels - silica particles, precipitate on the surface of etched dentin which
decreases permeability
• Shear bond strength of composite to phospohoric acid-etched enamel usually
exceed 20MPa
• Such bond strength provide adequate retention for a broad variety of procedures
and prevent leakage around enamel margins of restorations.
47

• 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.
48

ALTERNATIVE ENAMEL ETCHANTS :
As phosphoric acid ( H3PO4) is said to be more aggressive, other
alternatives have been suggested like ;
• EDTA
• Pyruvic acid 10%
• Sulphuric acid 2%
• nitric acid – 2.5% concentration.
Organic Acids :
• 10% Citric acid
• Maleic acid 10%
• Oxalic acid: 1.6% - 3.5% 49

• Ethylene diamine tetraacetic acid (EDTA) – is a strong
decalcifying agent, promotes only low bond strength to
enamel, probably EDTA does not 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 impractical 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.
50

• With the introduction of total-etch systems, in which enamel and
dentin are etched simultaneously, weaker acids are 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.
51

• 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 penetration of
enamel surface with the acidic monomers that can be
polymerized in situ.
52

• 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 nucleate within the tooth and grow
outwardly in a spherulic habit, with irregular surfaces they
are similar to an etched enamel with loss of tooth substrate.
53

• Lasers have been used for enamel / dentin preparation prior to the
restorative material placement.
• Laser etching is a process of continuous vaporization and micro
explosion due to vaporization 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 type
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
55

Air Abrasive Technology
• In 1992 U.S. Food and Drug Administration granted
clearance to air abrasive cavity preparation system.
• Here, a high speed stream of purified Aluminium Oxide
particles (0.5 um) propelled by air-pressure.
• It can prepare enamel and dentin for bonding, similar to
chemical etching.
• Lawrell et al, observed that bond strength to air-abrasive
treated enamel surfaces similar to the values obtained
with acid etching.
57

ENAMEL BONDING AGENTS
• Consists of BIS-GMA or UDMA resins with dilutent like TEGDMA.
• They flow easily into the microporosities of enamel.
• In the last few years these bonding agents here been replaced by same
adhesives that are used on dentin -advantage of simultaneously bonding to
both enamel and dentin.
• Bonding of resin to Enamel is mainly of Micromechanical type where Resin
Tags gets interlocked with Enamel Tags or surface 59

RESIN TAGS
• Enamel Bonding depends on resin tags becoming interlocked with surface
irregularities created by etching
MACRO TAGS : (interprismatic)
• Formed circularly between enamel rod peripheries.
• Most macro tags are only 2-5microns in length
60

MICROTAGS : (intraprismatic)
• Formed at the cores of enamel prisms
• A much finer network of thousands of smaller tags
from across the end of each rod where individual
hydroxyapatite crystals have been dissolved, leaving
crypts outlined by residual organic material
• Length is 2-10 microns
Micro tags contribute most because of their larger
number and greater surface area.
61

• Regarding bonding to enamel, the rapid volatilization of the solvent
allows for the complete interdiffusion of the adhesive system through the
extension of the conditioning.
• It is not an easy procedure to keep dentin moist and dry only the
enamel.
• Hydrophilic primers work very well when enamel is dry.
• The presence of residual moisture and organic solvents interferes
negatively in the complete polymerization of monomers
• Is important after the application to properly dry with air spray of a triple
syringe
• Also, it has been theorized that the stability of bonding to enamel is also
compromised with time because of the formation o f adhesive layers
similar to semipermeable membranes.
62

• Viscosity of the Adhesive System
 Some adhesives have inorganic filler particles to increase their
film thickness and cohesive strength (filler loading ranges
between 8.5% and 25% weight).
This seems to be related to the high viscosity of these
adhesives, which makes it difficult to penetrate in interprismatic
areas as deeply as unfilled adhesives.
It has been reported that highly viscous sealants have greater
difficulty penetrating enamel as much as the conditioning depth.
63

• Cleaning Enamel
A relevant factor in bonding to enamel is the
cleaning of the substrate to be bonded.
This cleaning must be accomplished before etching
using cotton pellets soaked in agents such as
chlorhexidine gluconate and benzalkonium chloride.
• Use of air/water spray of a triple syringe in easy
access locations .
• Floss and gauze are recommended for proximal
surfaces. Prophylactic pastes are useful on
noninstrumented enamel surfaces. 64

Dentin adhesion
65
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.
Adhesion to dentine remain difficult.adhesive materials can
interact with dentin in different ways-mechanical,chemical,or
both.
Dentin adhesion relies primarily on the penetration of adhesive
monomers into the network of collagen fibers left exposed by
acidic etching.

CLINICAL FACTORS IN DENTIN
ADHESION
1. Structure of dentin
2. Smear layer
3. Stresses at the resin denin interface—C factor,COTE
4. Type of composite
5. Biocompatibility
6. Microleakage
7. Nanoleakage 66

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.
(J prosth. Dent.1989)
• The thickness of the smear layer has been reported to vary from 0.5 – 2
m.
• Thickness of smear plug : 1-10 m
67

• Smear layer is reported to reduce dentinal permeability by
86%.(Pashley 1982)
• 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.
• Factors determining of composition of smear layer
1. Type of cutting/abrading instrument used
2. Type and method of chemicals/disinfectants employed
68

SMEAR LAYER TREATMENT
• NO TREATMENT- Resin would infiltrate through the entire
thickness of smear layer and even bond to underlying matrix or
penetrate into tubules Eg. Scotch bond and prisma bond.
• REMOVAL AND REPLACEMENT OF SMEAR LAYER- Removal of
smear layer by acid etching and replacement with another
mediation agent. Here replaces smear layers with oxalate
crystals which are deposited in dentinal tubules.
69

• Dissolution of the smear layer- This dissolved smear layer plays
an vital role in chemical attachment of dentin bonding agent to
dentin. Eg. Scotchbond-2.
• Removal of smear layer by acid etching- Acid etching agents are
used to remove smear layer and develops attachment directly to
intact dentin (through primers).
• Modification of smear layer : Modification of smear layer allows
interaction of dentin bonding agent with the smear layer.
Eg. Bonding agent – Prisma 2, XR Bond, All bond.
70

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

NANOLEAKAGE
• The term Nanoleakage has been used to describe small
porosities in the hybrid layer or at the transmission between the
hybrid layer and the mineralized dentin that allow the
penetration of miniscule particle of a silver nitrate dye.
• If the bond fails at the interface between two substrates is
referred to as adhesive failure.
• cohesive failure, if occurs in one of the substrates, but not at the
interface.
• But the mode of failure is often mixed. 72

• DENTINAL PERMEABILITY
• It refers to the ease with which a substance can move into or
across a diffusion barrier.
• Variation in permeability affects the bonding mechanism of
dentin.
73
• MAINLY OF 2 TYPES-

INTERTUBULAR PERMEABILITY
• Diffusion of monomer into demineralized intertubular dentin,
the dentin between the tubules.
• Intertubular dentin must be demineralized to expose the
collagen fibrils of the dentinal matrix and to create diffusion
pathways for monomer into these long, continuous,
interconnected, narrow channels, or pores.
74

INTRATUBULAR PERMEABILITY
• The movement of fluid within dentinal tubules
• Responsible for dentinal sensitivity
• Formation of resin tags
75

e) Internal and External Dentinal Wetness :
The dentinal permeability and consequently, the
internal dentinal wetness depend on several factors,
• diameter and length of the tubule,
• the viscosity of dentinal fluid
• 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. 76

Two factors that determine the wetting behaviour & penetration are
1. polarity
2. solubility
• 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 dentinal tubules to the pulp, if the tubules are not
hermetically sealed.
77

• 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 differBond 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
hydrophilicity which provides better bonding to the wet dentinal
surface.
• ences in bond strengths is observed between deep and superficial
dentin when smear layer is left intact.
78

COMPONENTS OF DENTIN
BONDING AGENT
• Etchant or conditioner
• Primer
• Adhesive resin
79

BASIC MECHANISM OF ADHESION TO TOOTH
SUBSTRATE
80

ADHESION TO DENTIN
Etching Priming Bonding
81

CONDITIONING OF DENTIN
• It can be defined as any chemical alteration of the dentinal
surface by acids or less commonly a calcium chelator (EDTA)
with the objective to remove the smear layer and simultaneously
demineralize the dentinal surface.
• Etching of enamel and dentin together for 15sec called as Total
etch or Unietch is the most successful way of managing smear
layer.
• It was introduced by Fusayama et al in 1979 and is now
commonly practiced.
• Acid- 35-37% phosphoric acid.
82

• Removes smear layer and smear plugs
• Demineralizes intertubular dentin
- upto a depth of 1-5µ
- Exposes longitudinally / obliquely oriented collagen
fibres
- Interfibrillar spaces – 15 –20nm (nanochannels)
• Demineralizes peritubular dentin.
- Opens tubule orifices in a typical funnel shape
configuration
- Exposes a circularly oriented collagen fibril
arrangement.
• Decreases free surface energy 83

• In superficial dentin the surface of dentin changes from one in which
only 1% of surface area is porous before etching to a condition in
which 13.4% of the surface area consisting of water filling tubules
that can serve for infiltration of monomer
• Also demineralizes 3- 7 microns of superficial dentin.
• Exposes a micro-porous collagen scaffold which is permeable to
resin.
• Surface free energy of etched dentin-
44.8 dynes/cm
84

85
(Demineralized inter tubular
dentin )

PRIMERS
• These are monomers dissolved in solvents such as
water, acetone or alcohol , applied to the etched or
conditioned dentin substrate but are not rinsed off.
• After conditioning maintainence of a moist dentinal
surface is essential to optimal bonding with modern
hydrophilic adhesive system.
• Desiccation of the conditioned dentin can cause
collapse of the unsupported collagen web preventing
infiltration of the resin.
86

• Primer monomers are amphiphilic i.e. they contain hydrophilic groups
(eg. –OH, -COOH) for better compatibility of the resin monomers with
the moist dentin, and hydrophobic methacrylate groups for the co-
polymerization with the bonding resin.
• Organic solvents aid in displacing water,
Expanding
Or re-expanding the collagen fiber network
• Promoting the infiltration of the monomer
Into the sub-micron sized spaces within the collagen fiber network
• The objective of this step is to transform the hydrophilic dentin
surface into a hydrophobic and spongy state. 87

POSSIBLE EXPLANATIONS FOR THE MAJOR SHRINKAGE OF
DEMINERALIZED DENTINAL MESHWORK WHEN IT IS AIR-DRIED
• DEMINERALIZED COLLAGEN FIBRIL NETWORK IS FLOATING / SUSPENDED IN
WATER.
• EACH FIBRIL IS SEPARATED FROM THE OTHER BY WATER FILLED SPACE, WHICH
OCCUPIES THE SPACE THAT WAS PREVIOUSLY OCCUPIED BY APATITE
CRYSTALLITES.
• As the water supported collagen network is air-dried, the amount of
water separating the fibrils disappears as the water evaporates and the
collagen fibrils come closer together in all three dimensions.
• This results in a passive collapse of the collagen network. 88

• This results in a loss of space between the fibrils.
The addition of water rapidly reverses these events
causing passive re-expansion of the collapsed
collagen network.
• If water or an aqueous primer is added to dried
dentin -The water reverses all of these events; water
molecules will bind with collagen peptide using
hydrogen bond
91

Acetone Acetone Water Acetone Ethanol Ethanol Ethanol Water Water
ABC Enhanced (Chemeleon) AQ Bond (Sun Medical) All Bond 2 (BISCO) Excite (Vivadent) Gluma Comfort Bond (Kulzer) Amalgam bond Plus (Parkell)
EG Bond (Sun Medical) Reactmer (Shofu) Optibond Solo Plus (Kerr) Optibond FL (Kerr) ART Bond (Coltene)
Gluma One Bond (Kulzer) Tenure Quick (Den-Mat) Pq1 (Ultra dent) Permaquik (Ultra dent) Clearfil SE Bond (Kuraray)
One Step (BISCO) Quadrant Unibond (Cavex) Denthesive II (Kulzer)
Permagen (Ultra dent) Scotch bond 1 (3M) EBS (ESPE)
Prime & Bond NT (Dentsply) Syntac sprint (Vivadent) Fuji Bond LC (GC)
Solid Bond (Kulzer) Single Bond (3M) One – Coat Bond (Coltene)
Solist (DMG) Prompt L-Pop 1,2 (ESPE)
Stae (SDI) Scotch Bond Multi-Purpose (3M)
Tenure Quick F (Den Mat) Syntac Single Comp (Vivadent)
93
Current adhesives are categorized following the type of solvent of the primer or combined primer / adhesive resin.

MOIST BONDING– KANCA TECHNIQUE :
• In order to avoid the collapse of the collagen network, a moist (wet)
bonding procedure has been proposed in which the primer is applied to the
moist or even wet dentin where the peri-fibrillar spaces are kept open with
water (Kanca 1992).
• Surface moisture is an important factor in optimal bonding.
• Moist bonding is only essential for particular bonding systems with a low
water content of primer such as All Bond 2.
• The primer of All Bond 2 contains acetone as solvent with only 5% of water.
• In contrast primers with water content of 20% or more (eg. Optibond FL,
Scotch bond Multipurpose) are able to re-expand the collapsed collagen
due to their intrinsic rewetting capacity.
94

• On enamel, a dry condition is theoretically preferred
• On dentin, certain amount of moisture is needed to avoid collapse
of the exposed collagen fibers.
• Acid etched dentin shrinks 65% vol.
• Stiffness of mineralized dentin is about 19,000 MPa
Stiffness of acid etched dentin matrix is about 1 Mpa.
• The resulting layer of imperfect bonding is known as HYBRIDOID
REGION.
• Residual water is left in the acid etched dentin, then bond strength
could be doubled. (Kanca )
95

98
WET BONDING (KANCA & GWINETT) 1990
Once etched dentin should be left moist
Primer (Acetone) vaporizes the water-leaving the space for resin topenetrate
Optimal wetting of exposed collagen achieving high bond strength
Wet bonding Technique – Kanca & Gwinett 1990
▸How wet or dry the dentin should be……
Substrate should be neither too Wet or too dry
Excess water should be blotted with a dry sponge/ tissue paper

Dry Bonding
• refers to the bonding in which the acid
etched dentin is dry and uses the adhesive
systems that provide water based primers.
These rehydrate and re expand the collagen
fibers , allowing the resin to infiltrate.
99

• Ideally, water should form a uniform layer without pooling (overwet) & without dry
areas (overdried).
• Air drying with an air syringe after rinsing off the ecthing gel – not recommended
cannot form uniform layer of water on the surface.
WATER BASED PRIMERS:
• The first approach to creating a hybrid layer in wet dentin is the use of water-soluble
primers containing HEMA.
• Examples Scotch bond 2 and Scotch bond Multi-purpose.
• After application of the water HEMA mixture, the surface is air dried to evaporate the
water. As the water concentration falls, the HEMA concentration rises, until
theoretically, there should be near zero water and 100% HEMA on the surface.
• CONSEQUENCES OF APPLYING ACETONE BASED PRIMERS TO OVER-WET DENTIN
DESCRIBED BY TAY ET AL (1994) USING ALL BOND 2, BISCO.
• SMALL GLOBULES ARE FORMED WITHIN DENTINAL TUBULES.
100

• When the first one or two layers of primer were applied i.e. in the
tubules filled with dentinal fluid there was too much water
available to dilute the acetone with the result that the monomer
came out of the solution.
• As more globules formed, they accumulated on walls of the
tubules, reducing the permeability of the tubules, permitting
successive primer applications to dehydrate the tubules enough to
form normal resin tags.
101

HYBRID LAYER:
Dentin hybrid layer is a
• “TRANSITIONAL ZONE OF RESIN
REINFORCED DENTIN SANDWICHED
BETWEEN CURED RESIN AND THE
UNALTERED DENTINAL SUBSTRATE”
(nakabayashi 1982)
• hybrid layer is the resin infiltrated
surface layer of collagen fibers in
demineralized dentin.
The synonyms are:
• “Adhesion interface”,
• “resin-dentin inter-diffusion zone”,
• Inter penetration zone.
103

SHAG CARPET APPEARANCE:
• Appears when dentin surface after being acid etched is actively
scrubbed with an acidic primer solution.
• Mechanism of action:
The combined mechanical and chemical action of rubbing the acid
etched dentin with an acidic primer dissolves additional mineral salts
while fluffing and separating the entangled collagen at the surface.
TUBULE WALL HYBRIDIZATION:
• Extension of the hybrid layer into tubule wall area.
• Hermetically sealing the pulpodentinal complex against microleakage
• Especially protective when bond fails at top or bottom of the hybrid layer
• The resin tags keep tubules sealed as they break off at the level of hybrid
layer. This is attributed to tubule wall hybridization which ensures a
leakage free seal of tubules.
106

GHOST HYBRID LAYER:
• This layer is formed due to incorporation of air bubbles at the substrate
adhesive interface.
REVERSE HYBRID LAYER:
• The acid etched surface of dentin is further subjected to treatment with
NaOCl. This results in dissolution of the collagen fibrils that are exposed.
• Here the hybrid layer is surrounded by more of inorganic material
unlike the normal hybrid layer where the collagen fibers are encapsulated
by resin, and so this layer thus formed is termed reversed hybrid layer.
Reverse hybrid layers form when dentin-bonding agent comes in contact
with the pulp.
• Gentle drying of the dentin surface, has been shown to result in
INCOMPLETE INTERTUBULAR RESIN INFILTRATION.
• Incomplete resin penetration due to collagen collapse has been observed
as the formation of a hybridoid layer/zone.
107

108
WATER TREES’– TAY & PASHLEY
▸Water can pass from dentin around resin tags& form water
filled channels that project from the hybrid layer into the
overlying adhesives
• Water absorption character of HEMA, water is prone to
permeate into the dental resin composite completely
through the dental adhesive materials by forming water
blisters and “Water trees”. Thus leading to Nanoleakage
problem and failure of dental restorations.
 Bidirectional water current

SCIENTIFIC CLASSIFICATION BASED ON
ADHESION STRATEGY & CLINICAL
APPLICATION STEPS
• Etch and rinse adhesives
3 step :– All Bond 2 Bisco
clearfil liner Bond Kuraray
optibond DC Kerr
2 step :- prime & Bond 2.0 Dentsply
singlebond 3M ESPE
• Self etch adhesives
2 step :- Adhe SE ivoclar vivadent
Clearfil SE kuraray
1 step:- G Bond GC
Adper prompt L-Pop 3M ESPE
113

FIRST GENERATION
• In 1956, Buonocore and colleagues demonstrated that
use of a glycerophosphoric acid dimethacrylate (NPG-
GMA) containing resin would bond to acid-etched dentin.
• This bond was believed to be due to the interaction of this
bifunctional resin molecule with the calcium ions of
hydroxyapatite.
• immersion in water would greatly reduce this bond.
• The bond strengths of these early systems were only 1 to
3 MPa . The clinical results with these systems were poor.
115

SECOND GENERATION
• Introduced in the late 1970s
• Attempted to bond chemically to either the inorganic or organic
components of dentin.
• They contain phosphate group, amino acid group,isocyanate group or
carboxylic acid group to effect the bond to the calcium or collagen of
dentin.
• Clinical applications did not succeed due to their lack of hydrolytic
stability; also they primarily bonded to smear layer and not to underlying
dentin.
• Bond strength :5 to 6 MPa
• Eg: Clear fil Bond system, Scotch bond, bond lite, prisma 116

THIRD GENERATION
• 1979 –fusayama-total etch concept
• Deal with smear layer as well as the dentinal fluid
• They employed 2 approach
1. Modification of smear layer to improve properties
2. Removal of smear layer with out disturbing smear plug that occlude dentinal tubule
ie, required either removal,modification or dissolution of smear layer
• Idea was to avoid aggressive etching of dentin , beacause of concerns that acid etching of
dentin can cause pulpal inflammation.
• In this they used mild acids like 2% nitric acid, 2.5% maleic acid with HEMA ,10% phosphoric
acid etc..
• Bond strength : 3 -8 MPa
Eg: clearfil new bond , scotch bond 2, Tenure, gluma, C&B meta bond
117

FOURTH GENERATION
• Total etch concept/Moist bonding
• 1982 Nakabayashi- Hybrid layer
Enamel & dentin both simultaneously etch with 37% phosphoric
acid for 15 sec.
Tooth washed & gently dried to leave the dentin surface moist , so
as to prevent collapse of exposed collagen network.
Primer applied, final step involves application of adhesive resin
Bond strength : 7 -24 MPa
• Eg: Compobond LCM, Scotch bond MPa
118

FIFTH GENERATION
• To simplify the clinical procedure by reducing the bonding
steps and thus, the working time, a better system was
needed. Also, clinicians needed a better way to prevent
collagen collapse of demineralized dentin.
• Totally removes smear layer
• based on Total etch concept.
• Eg: single bond(3M), one step , Exite,gluma comfort bond
,opti bond solo (kerr)
120

• The fifth generation consists of two different types of adhesive materials:
the so-called "one-bottle systems" and the “self-etching primer”
bonding systems.
• One-bottle systems. To facilitate clinical use, "one-bottle" systems
combined the primer and adhesives into one solution to be applied after
etching enamel and dentin simultaneously (the total-etch wet-bonding
technique) with 35 to 37 percent phosphoric acid for 15 to 20 seconds.
These bonding systems create a mechanical interlocking with etched
dentin by means of resin tags, adhesive lateral branches and hybrid layer
formation and show high bond-strength values both to the etched
enamel and dentin.
• Self-etching primer. Watanabe and Nakabayashi developed a self-
etching primer that was an aqueous solution of 20 percent phenyl-P in
30 percent HEMA for bonding to enamel and dentin simultaneously.
• The combination of etching and priming steps reduce the working time,
eliminate the washing out of the acidic gel and also eliminate the risk of
122

SIXTH GENERATION
• These bonding systems are characterized by the possibility to
achieve a proper bond to enamel and dentin using only one solution.
• These materials should really be a one-step bonding system.
Unfortunately, the first evaluations of these new systems showed a
sufficient bond to conditioned dentin while the bond with enamel was
less effective.
• Primer and etchant are combined in one step( self etching primers)
• Mainly two type; 1-SEP , 2 -SEA
• Eg: Prompt L-Pop, Clearfil SE bond, Liner bond
123

128
Addition of nano fillers help in the penetration of resin monomers and hybrid layer
thickness .
It improves mechanical properties of bonding system.

SURPASS: A UNIVERSAL EIGHTH
GENERATION BONDING SYSTEM
129

ADHESION- DECALCIFICATION(AD)
CONCEPT
• Van Meerberk 2011
• Molecules interact with HAp
tissues
• Release of phosphate
• Hydroxide ions
130

CONCLUSION
• Various advances in bonding agents have
eliminated the need for sacrificing sound tooth
structure for establishing retention form.
• Understanding the composition of the tooth and
components, mechanism of bonding agents help to
overcome difficulties and aid in mastering the
bonding technique for success of restorative
procedures.
146

REFERENCES
Sturdevant’s Art and science of operative dentistry, 5th edition
Phillips science of dental materials
Fundamentals of operative dentistry , summitt
Text book of OperativeDentistry. Nisha Garg, IVEdition JPpublications
Materials used in Dentistry. S. Mahalakshmi 2nd Edition, Wolters Kluwer
Text book of Dental Materials.Arvind Shenoy.Elsevier
Textbook of OperativeDentistry. Vimal Sikri
Classification of review of dental adhesive systems:from the IV generation to the universal type,E
.Sofan,Annali et al
147

DENTIN BONDING AGENTS: A REVIEW OF THEIR EVOLUTION, MECHANISM AND CLINICAL APPLICATION

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