BONDING IN OPERATIVE
ENAMEL AND DENTIN ADHESION
-Fundamentals of Operative Dentistry
(Schwartz, 2nd. Ed.)Chapter 8
-Art and Science 5th Ed chapter5
Indications and advantages of adhesive dentistry
Factors affecting adhesion
Adhesion to enamel VS adhesion to dentin
Wet Vs dry adhesion technique
Challenges facing an ideal adhesive bond
Requirements for an ideal bonding agent
Classification of bonding system
Clinical significance of bonding
Adhesion strategies and technique
Amalgam bonding and glass ionomer
1. Adhesion (or bonding) is defined in dentistry as The
forces or energies between atoms or molecules at
an interface that hold two surfaces together.
2. Adhesive strength = load bearing capacity
3. Durability = the time period of effect bond in
4. Adaptation: maximum degree of proximity
between two adjacent surface
5. Adhesive(adherent): the material or film added to
6. Adherend: the substrate to which the material
adhered e.g enamel ,dentin
7. Abhesive: a barrier against establishing adhesive
Adhesive failure: The bond that fails at the
interface between the two substrate
Cohesive failure: The bond fails within one of the
substrates, but not at the interface.
Adhesive joint; resin material ,tooth substrate and
hybrid layer in between
Hybridization : is the phenomenon of replacement of
the hydroxyapatite and the water in the surface
dentin by resin. This resin, in combination with the
collagen fibers, forms a hybrid layer.
In other words, hybridization is the process of resin
interlocking in the demineralized dentin surface .
This concept was given by Nakabayashi in 1982
The thickness of a hybrid layer is not a critical
requirement for success. Dentin bond strength is
probably proportional to the interlocking between
resin and collagen, as well as to the “quality” of the
hybrid layer, not to its thickness
1955 – Dr. M. G. Buonocore noted that
metal was treated with acid before painting to
provide a better bond between the
metal surface and the paint. He then
applied this procedure for the bonding of
composite resin to teeth.
ADVANTAGES OF ADHESIVE
1. Less tooth structure removed
2. Reduces microleakage at margins
3. Better distribution of stresses
4. Possible reinforcement of tooth structure
5. Easy to repair fillings with minimal tooth prep.
6. Tooth colored restorative material may be
added to teeth without preparations (veneers,
Debonded composite restoration
Tooth strength after restoration – amalgam vs C.R.
Strength of uncut tooth = 100%
MOD amalgam prep = 50%
MOD prep. + varnish + amalgam = 50%
MOD prep. + composite resin = 88%
Expanding Indications for Adhesive Dentistry
1. Restoration of carious teeth
2. Abraded and eroded surfaces
3. Veneers (esthetics)
4. Re-contouring (diastema)
5. Preventive sealants
6. Bonding orthodontic brackets
7. To treat dentinal hypersensitivity
Mechanism of adhesion
Four theories of adhesion (MADE):
Requirement of ideal adhesion:
Chemical affinity between the adhesive and the
Complete wettability of the substrate by the adhesive
-absolute substrate surface smoothness
-absolute substrate surface cleanliness
-complete substrate surface homogenecity
-strongly hydrophilic adhesive of minimal
Requirements for good adhesion/bonding
materials must be in contact
wetting of the tooth surface must occur with low
surface tension and low viscosity of the adhesive
Enamel = high surface-free energy +
Dentin = low surface-free energy –
Tooth surface must be clean to provide high surfacefree energy
Wetting is an expression of the attractive forces between
molecules of adhesive and adherent. In other words, it is
the process of obtaining molecular attraction .
Wetting ability of an adhesive depends upon two factors:
• Cleanliness of the adherend:
Cleaner is the surface, greater is the adhesion.
• Surface energy of the adherend:
More the surface energy, greater is adhesion.
Factors Affecting Adhesion to Tooth Structure
I. Tooth-related factors
II. Material-related factors
III. Prepared cavity-related factors
IV. Technique of restoration
V. Oral environmental factors
I. Tooth-related factors
1. physiological effects:
- surface energy
- capillary attraction
- osmotic pressure
2. Compositional differences of tooth
3. Presence of smear layer
II. Material- related factors
1.Biodegradation in oral cavity
2. Thermal coefficient of expansion
3. Dimensional stability
4. Modulus of elasticity and transfer of stress at the
III. Prepared cavity-related factors:
1.Adhesive cavity designs should be prepared
2.The resistance and retention required should be
estimated and built in the preparation
3.All carious lesion must be removed
4.Adequate finishing, debridement and toilet of the
IV. Technique of restoration
1. avoid moisture contamination
2. use of liner and bases( must be restricted Rd less
3. constituents of temporary restorations
4.C-factor(bonded to free unbonded surface)
5.post operative and post restorative care
V. Oral environmental factors
1. Occlusal loads
2. Chemical degradation potentials
3. Oral microorganisms
5. Chewing habits
All these factors are all highly contributed
that affect the durability of the
Bonding to tooth structure
Compositional and Structural Aspects of Enamel and
Dentin “Because the composition of enamel and
dentin are different, adhesion to the two tooth
tissues is also different”
Problems (obstacles)with bonding to dentin
1. High organic and water content
2. Smear unit
3. heterogeneous of dentin structure
4. Vitality of the pulp (pulpal and dentinal fluid)
5. Difference in D.permeability
6. Intrapulpal pressure
7. Decreased percentage of hydroxyapatite
8. Divergence of dentinal tubules from the pulp
Dentin contains dentinal tubules which contain vital
processes of the pulp, odontoblasts. This makes the
dentin a sensitive structure.
• Dentin is a dynamic tissue which shows changes due
to aging, caries or operative procedures.
• Fluid present in dentinal tubules constantly flows
outwards which reduces the adhesion of the resin
composite to dentin .
Basically, when tooth surface is altered using hand or
rotary instruments, cutting debris are smeared on
enamel and dentin surface, this unit is called smear
unit (smear layer& smear plug)
Components of Smear Layer
Smear layer consists of both organic and inorganic
Components. The inorganic material in the smear layer
is made up of tooth structure and some nonspecific
The organic components may consist of heated
coagulated proteins (deteriorated collagen by cutting
temperature), necrotic or odontoblastic processes,
saliva, blood cells and microorganisms. Densely or
loosely packed to various depths into dentinal
Factors affecting dentin permeability
Amount of D.fluid
Intra pulpal pressure
Principles of dentin hybridization
1. Selective demineralization(conditioner)
2. Alteration of surface wettability(priming)
3. Resin impregnation(DBA)
Selective demineralization can be done
1. chemical conditioner )Acid)
2. physical conditioner (laser)
3. mechanical conditioner (micro abrasion)
1. Chemical conditioners
Acids used to prepare tooth surfaces
Maleic acid (10%)
Polyacrylic acid (10%)
Phosphoric acid (10 - 37%)
Acidic monomer(phenyl P)
It is the process of cleaning the surface and activating the
calcium ions, to make them more reactive.
It is the process of increasing the surface reactivity by
demineralizing the superficial calcium layer and thus creating
the enamel tags (5-50 micron) . These tags are responsible for
micromechanical bonding between tooth and restorative
Objectives of surface etching
-The acid-etching of a tooth surface allows for the
micro-mechanical adhesion of resin to the tooth
-Etching with acid removes a portion of the
superficial mineral component of enamel and
-Micro porosities (5-50 micron depth)left behind produce
a roughened surface, or open dentinal tubules,
into which resin will penetrate and mechanically
grip the tooth providing retention for an overlying
Pattern of etching
Type I etching pattern: preferential removal of
enamel prism core
Type II etching pattern: preferential removal of prism
Type III etching pattern: not related to prism
Effective etching of dentin does not require long times
to produce acceptable dentin bond strengths.
Usually, 15 seconds is employed. If etching time is
too long and the etched zone is too deep, the
decalcified dentin may not be fully impregnated.
The etched but not impregnated space may reside
as a mechanically weak zone and promote
Factors affecting successful acid
Time of etching
Cleaning of the surface
Primers are bonding-promoters e.g HEMA&TEGDMA
They are essentially composed of active bi-functional
hydrophilic/hydrophobic group of monomer molecules
[ in water, organic solvents such as ethanol or acetone
or a combination them].
The hydrophilic part increases substrate surface
wettability and permeability enhance resin diffusion
into de-mineralized dentin.
The hydrophobic part penetrates inside the created
pores where it polymerizes forming retentive tags
inside, and co-polymerizes with the applied
They are used to facilitate complete resin infiltration of de-mineralized
dentin with establishment of strong and gap-free resin-collagen
The primer may be transported and agitated onto the substrate
surface using a smooth brush. It is evenly spread, thinned out, and
Primers contain solvents to displace the water and carry the monomers
into the microporosities in the collagen network.
During application of the primer, most of the solvent evaporates
quickly. Thus several layers usually must be applied to ensure a
complete impregnation. The rule of thumb is that one should apply
as many layers as necessary to produce a persisting glistening
appearance on dentin.
After acid is rinsed, drying of dentin must be done
cautiously. Even a short air blast from an air-water
spray can inadvertently dehydrate the outer surface
and cause the remaining collagen scaffold to
collapse onto itself. Once this happens, the collagen
mesh readily excludes the penetration of primer
and bonding will fail.
However, excess moisture tends to dilute the primer
and interfere with resin interpenetration. The ideal
dentin moisture level varies according to the solvent
present in the adhesive.
Self-etch systems have the great advantages of
eliminating the risk of incomplete primer/adhesive
penetration into the collagen scaffold and also
eliminating the subjectivity when determining the
amount of moisture on the dentin surface ideal for
primer diffusion. With these systems, the smear layer
is dissolved and incorporated into the hybrid layer.
Ethanol or acetone based bonding
Acetone or ethanol diffuses into the moist D while
water diffuses into acetone or ethanol (water
They occupy the spaces previously filled with water,
and then evaporate rapidly leaving sufficient room
to the coming infiltrated resin
Acetone and ethanol generate less surface tension
forces in collagen fibrils with ultimate increase in
Moist vs Dry Dentin
Collagen is one of the important factors in determining the dentin bonding. By
etching of dentin, removal of smear layer and minerals from dentin
structure occurs, exposing the collagen fibers . Areas from where minerals
are removed are filled with water. This water acts as a plasticizer for
collagen, keeping it in an expanded soft state. Thus, spaces for resin
infiltration are also preserved. But these collagen fibers collapse when
dry and if the organic matrix is denatured. This obstructs the resin from
reaching the dentin surface and forming a hybrid layer.
Reasons for better bonding in moist dentin
1. The acetone trails water and improves penetration of the monomers into the
dentin for better micromechanical bonding.
2. Water keeps collagen fibrils from collapsing, thus helping
in better penetration and bonding between resin and
Disadvantage of self etch
Strong self-etch adhesives produce a similar pattern
on enamel as that obtained with phosphoric acid.
Mild self-etch systems present lower bond strength
to enamel compared to etch-and-rinse systems,
probably because of a shallower etching pattern.
Enamel bonding system
Enamel bonding depends on resin tags
becoming interlocked with the surface
irregularities created by etching.
Macrotags: form between enamel rod
Microtags: smaller tags form across
the end of each rod.
Macrotags and microtags are the basis
for micro-mechanical bonding.
Microtags are much more numerous and contribute
to most of the micromechanical retention.
Requirements for an ideal D.B.A
Should be hydrophilic in order to bond to wet D
Should contain hydrophobic part to co-polymerize
with the applied resin
Should have low viscosity for better diffusion
Should posses minimum film thickness for better
Should be biocompatible
Should posses high bond strength to both E.D
Should have good shelf life
Should minimize micro to nanoleakage
The Development of DBA
Enamel etch (1955)
Dentine etch (1960)
Treatment of smear layer (1980)
Wet Bonding technique(1990)
Fourth generation: Total etch technique
Sixth generation: All in one,2000
1960s and 1970s First and Second Generation
Did not recommend dentin etching. Relied on
adhesion to smear layer.
Since dentin was not etched , the adhesion actually
was due to bonding to the smear layer weak bond
strength (2-3 Mpa(
1980s Third Generation
Acid etching of dentin.
Increased bond strength.
Margin staining caused clinical failure over time
Early 1990s Fourth Generation)Total etch technique)
Acid etching of dentin.
Increased bond strength.
Fourth generation (total etch technique; etch &rinse tech
;three step technique)
Concept complete removal of the smear layer
Etching of both enamel &dentin
Bonding agent (three step)
Concept of “wet bonding” also introduced in late 1990.
These system incorporated monomers with high diffusivity
and compatibility to wet dentin
Moist dentin improve the performance
Not to wet not to dry (the key factor)
Strong and stable bond reach up to 27MPa
Mid 1990s Fifth Generation (two steps )
Etch and rinse(total etch) (etch separately and then primer
&bonding in one bottle) Combined primer and
adhesive in one bottle.
Maintained high bond strengths .
Unit-dose packaging introduced
less technique sensitive
Post operative hypersensitivity
Late 1990s, Early 2000s Sixth Generation (self etch
approach) “Self-etching” primers.
Reduced incidience of post-treatment sensitivity.
Bond strengths lower than fourth- and fifthgenerations.
Post operative hypersensitivity
Late 2002 Seventh Generation
“All-in-One”. Combines etching, priming and bonding.
Good bond strength(18 to 25 Mpa)and margin sealing.
They achieve the same objective as the 6th
generation except that they simplified the multiple
sixth generation materials into a single component,
single bottle system, thus avoiding any mistake in
mixing. Seventh generation bonding agents also have
disinfecting and desensitizing properties.
Three steps (etching,priming,and resin impregnation)
Two steps( etching –priming)and resin
impregnation/or etching then priming and resin
One step, all together (etchant, primer and resin)
all in one step
Recent classification of bonding systems
1.Etch and Rinse approach
Three - step ;conditioner, primer, adhesive
Two step; conditioner, (primer adhesive)
2.Self –Etch approach
Two-step (conditioner primer),adhesive
Adhesive system based on etch and rinse (three
step) technique are more clinically reliable and
durable than the self etching adhesives
Recent adhesive systems
Bio-active adhesive system include anti-microbial
monomer MDPB e.g clearfil
HEMA free adhesive system e.g G-bond
POSS nano-filled adhesive system e.g nano-bond
Adhesive systems, filled adhesives, and resin
cements can be used in association with amalgam
in the so-called bonded amalgam restoration. The
purpose of this technique is to reduce the need for
macromechanical retention, which would save tooth
structure, and reinforce the remaining structure by
creating a bonded interface between the restorative
material and the cavity walls.
The bonding between the adhesive and the amalgam is
achieved by the establishment of an interpenetration
zone. Although laboratorial studies show better results
for bonded amalgams compared to conventional,
nonbonded amalgam in terms of bond strength,
microleakage, and retention, these findings are not
supported by clinical data, which show no difference
between bonded restorations and those retained by
Bonded Amalgam Restoration
Etch the enamel & dentin walls of the preparation with ~35%
phosphoric acid gel for 15-20seconds. Wash & dry the
Apply primer to the conditioned dentin.
Then evenly apply dentin bonding agent.
Before the bonding agent is dried, condense freshly triturated high
copper amalgam into the uncured bonding agent, forcing the two
materials to intermingle.
They harden together in an interlocking matrix which provides
tremendous adhesion of amalgam to dentin
Carve, finish & polish the final restoration as usual
Bonded Amalgam Restoration
Bonding to tooth structure:
Bonded amalgam restoration has advantages of:
Conservative tooth preparation.
Better marginal seal along with improved retention & resistance.
Decrease the micro-leakage so the postoperative sensitivity & recurrent
Strengthening of restored tooth.
Bonded amalgam restoration has disadvantages of:
It is time consuming.
It is technique sensitive.
It is expensive.
Glass ionomers are water-based, self-adhesive
restorative materials in which the filler is a reactive
glass called fluoroaluminosilicate glass and the matrix
is polymer or copolymer of carboxylic acids. The
setting reaction of these materials involves an acidbase reaction.
There are two main types of glass ionomers:
• Conventional glass ionomer
• Resin-modified glass ionomer
Glass ionomer materials have good clinical adhesion
to tooth structure. Unlike the resin-based composite
materials, etching of the enamel or dentin
surface by phosphoric acid is not needed. Hence
these materials are sometimes referred to as being
self-adhesive. Preconditioning of the tooth surface
One of the following procedures is used for
• The cavity surface is conditioned using 10% to
20% polyacrylic acid(identified by manufacturers as (primer or
self -conditioner) for 10 seconds, washed well and dried.
• For some resin-modified glass ionomer restoratives
a dilute polycarboxylic acid based solution is applied on the
cavity surface and set through light. This ensures good contact
of the viscous mix of the glass ionomer with the tooth while not
impeding ion exchange reactions.
The mechanism of adhesion to the tooth structure
is mostly chemical in nature and proceeds through
an exchange of ions arising from both the tooth
Laboratory measurements of bond strengths of
conventional and resin-modified glass ionomers to
tooth structure have generally yielded lower values
than with the combination of resin adhesives and
composites. The failure is usually cohesive in the
glass ionomer;and restoration.
Resin-modified glass ionomers have been recognized as one of
the best treatments for minimizing postoperative sensitivity in
restored teeth. There are two reasons for this. First, because
prior etching is not needed during placement, the collagen
fibrils are not demineralized and collapse of the denuded layers
Second, the dual setting mechanism and gradual build-up of
modulus allow the material to absorb a considerable amount
of shrinkage stresses, thus minimizing the effect of contraction
forces at the tooth-restoration interfaces