The evolution of adhesivr technique

University of sulaimany
prepared by Azheen Mohamad

References:
 Sturdevant's Art and science of operative
dentistry.2013 Mosby Elsevier . Sixth Edition
chapter 4
 Contemporary esthetic dentistry .2012 Mosby
Elsevier. first Edition chapter8
 Introduction of dental material. 2007 Richard van
Noort . Third Edition chapter 1.10

INTRODUCTION
The introduction of adhesive technique ,the increasing
demand for restorative and non-restorative esthetic
treatment ,and the ubiquity of fluoride have combined
to transform the practice of operative dentistry .the
classic concepts of tooth preparation were advocated in
early 1900s,but these have changed drastically .this
transformation in philosophy has resulted in a more
conservative approach to tooth preparation ,with a
regard to not only the basic concepts of retention form
but also the resistance form of the remaining tooth
structure.

Bonding techniques allow more conservative tooth
preparations ,less reliance on micromechanical
retention , and less removal of unsupported enamel.
Two example of new , adhesive restorative procedures
that spring to mind readily are resin-bonded bridge and
porcelain veneers . these procedures have been possible
because of our improved knowledge and understanding
of the surface characteristics of enamel and dentin , and
of the requirements that need to be satisfied in order to
obtain good bonds to them.

DEFINITION
Adhesion can be defined as the force that binds two
dissimilar materials together when they are brought in
to intimate contact .
Bonding agents can be defined as material of low
viscosity, when applied on the tooth surface and forms
thin film after setting.
This thin film strongly bonded to tooth surface , on
which the viscous composite restorative resin is applied.
this sets forming an integrated resin
restoration.

BRIFE HISTORY OF CLINICAL DEVELOPMENT AND
EVOLATION OF THE PROCEDURE
The "generation" definitions help to identify the
chemistries involved , the strengths of the dental bond
,and the ease of use for the practitioner. Ultimately this
type of classification benefit the dentist and patient by
simplifying the clinicians chair side choice.

•GENERATION OF DENTAL ADHESIVES
*First Generation(1970s)
- 1 to 3 MPa adhesion to dentin.
- Bonded well to enamel through resin tags in to enamel.
- 50% failure at 6 months.
- Examples: N-phenyl glycine and glycidyl methacrylate, NPG-
GMA.

*Second generation(early 1980s)
2 to 8 MPa adhesion to dentin.
Phosphate –ester bonding agents.
Bonded to smear layer(organic debris).
Weak ionic bond to calcium undergoes hydrolysis.
Examples : scotch bond , dentin adhesit , bondlite

*Third generation(late 1980s)
- 8 to 15 MPa adhesion to dentin.
- Etching of dentin removed or modified smear layer.
- Spaghetti-like projections of resin into dentinal tubules.
- Examples : sotch bond 2,Gluma,Tenure,XR Bond.

*Fourth generation (early 1990s)
-17 to 25 MPa adhesion to dentin.
-Total etch : complete removal of smear layer and
collapse of exposed collagen fibers.
-Bonds to enamel ,"moist“ dentin ,metal , porcelain.
-Multibottle , multistep.
-Examples: scotchbond MP , Imperva , gluma
2000,syntac,Allbond 2,permagen.

*Fifth generation(mid-1990s)
-20 to 25MPa adhesion to dentin.
-Single component in a single bottle.
-Bonds to enamel ,moist dentin ,metal , porcelain.
-Etching required.
-Moist surface required (wet or moist bonding).
-Examples' : pulpdent UNO-DUO , prime and Bond NT ,
Gluma comfort bond , singleBond , one step, Bond
1,Excite.

*Sixth generation (2000)
-17 to 22 MPa adhesion to dentin.
-No separate etching step.
-Multibottle , multistep.
-Bonds to dentin , metal , porcelain.
-High incidence of enamel interface fructures.
-Example : Adh e SE, SE Bond , Tyrian ,Prompt L-
Pop , Xeno III.

*Seventh generation(2003)
-20 to 30+ MPa adhesion to dentin.
-Single bottle- no mixing.
-Bonds to enamel, dentin , porcelain , metal.
-Moisture independent.
-No technique sensitivity.
-Examples: BeatiBond , Bond force.
-the most innovation of seventh-generation adhesives is
the added advantage of moisture independence . the
acidbase reaction of the seventh-

The evolution of adhesivr technique

GENERATION OF DENTAL ADHESIVES

Seventh generatin
seventh generation bonding agents are ideal for
bonding indirect restorations, and for direct composite
resin (where bonding is mandatory regardless of the
material and technique being used).
The most innovation of seventh-generation adhesive
on the dentin surface is that of an acid acting on an
organic base. this chemical reaction generates organic
salt and water . Thus , seventh-generation adhesive
procedures effectively create their own moisture.

They can be applied to a "moist surface"(however that
may be defined)or a dried surface(much more easily
described).
Because seventh generation systems are supplied in a
single premixed container and require a single
application step , and no moist or wet surface , few
mistakes are possible and there is no technique
sensitivity. The process is simple ; apply the adhesive

to the tooth surface , agitate or scrub if required , and
then, after a brief wait ,simply air dry the surface . once
the bonded surface is dry(no longer moist with
bonding),it is light cured . there are no separate etching
or conditioning steps , and the smear layer is not
removed . there has been virtually no post –operative
sensitivity reported with seventh-generation bonding
agents . the hybrid layer is created by the chemistry of
the adhesive . the number of bottles is one ; the number
of steps is one . there is no post-operative sensitivity,
and dentin bonds of 23 to 30 MPa and higher have been
reported.

Total-Etch Procedure 
In total-etch systems the finalized cavity preparation is treated
with phosphoric acid gel, which is applied and left in place for
15 seconds. The acid gel is then vigorously washed away, followed
by air-dispersal drying for 2 seconds. An alternate method
for removing the water consists of wiping the preparation with
a dry cotton pledget. When the wiping is finished, the surface
should exhibit a slight sheen.
Once the etching process has been completed, the dentin
primer is applied. An applicator is saturated with the primer and
then rubbed or swabbed onto the surface of the preparation
continuously for 15 seconds. After air dispersing, the process
may be repeated if called for in the manufacturer instructions,
then the surface of the preparation is light cured for 15 seconds.
The preparation surface is now hybridized and ready for application of the
composite resin restorative material.


Total-Etch Procedure and Self-Etch
Dentinal Adhesive

The greatest advantage of the self-etching dentin
bonding system is a substantial reduction in the observed
post-operative sensitivity.
However, there are a number of disadvantages, with the
primary one being the incompatibility between the dentin
bonding agent and dual- and self-cured resins, including
luting agents and core materials.
Advantages and Disadvantages
of Self-Etch Dentinal Adhesive

MECHANISM OF ADHESION
Four different mechanisms of adhesion have been
described , as follows:-
1-Mechanical adhesion:-interlocking of the adhesive
with irregularities in the surface of the substrate , or
adhered.
2-Adsorption adhesion:-chemical bonding between the
adhesive and the adhered ; the involved may be
primary( ionic and forces covalent)or
secondary(hydrogen bonds , dipole interaction , or van
der Waals ) valence forces.

3-Diffusion adhesion:-interlocking between mobile
molecules , such as the adhesion of two polymers
through diffusion of polymer chain ends across an
interface.
4-Electrostatic adhesion:-an electrical double layer at
the interface of a metal with a polymer that is part of
the total bonding mechanism.
In dentistry , bonding of resin-based materials to tooth
structure is a result of four possible mechanisms , as
follows:_

1-Mechanical:-penetration of resin and formation of
resin tags within the tooth surface.
2-Adsorption:-chemical bonding to the inorganic
component(hydroxyapatite)or organic components
(mainly type I collagen) of tooth structure.
3-Diffusion:-precipitation of substances on the tooth
surfaces to which resin monomers can bond
mechanically or chemically.
4-A combination of the previous three mechanisms.

For good adhesion ,close contact must exist between the
adhesive and the substrate(enamel or dentine).The
surface tension of the adhesive must be lower than the
surface energy of the substrate.
Failure of adhesive joints occur in three locations , which
are generally combined when an actual failure occurs:-

1-Cohesive failure in substrate.
2-Cohesive failure within the adhesive.
3-Adhesive failure, or failure at the interface of
substrate and adhesive.
A major problem in bonding resins to tooth structure is
that all methacrylate-based dental resin shrink during
free-radical addition polymerization . Dental adhesives
must provide a strong initial bond to resist the stress of
resin shrinkage.

INDICATIONS FOR CLINICAL APPLICATION:-
-All direct composite resin restoration , both anterior and
posterior.
-For bonding indirect composite resin inlays , onlays and
veneers.
-For bonding indirect ceramic veneers , inlays and onlays.
-Bonded amalgam restorations.
-Management of dentin hypersensitivity.
-Luting post and core restorations.
-For the repair of fractured porcelain , amalgam and resin
restorations.

-For pit and fissure sealants.
-Bond orthodontic brackets.
-Bond periodontal splintand conservative tooth
replacement prosthesis( composite , amalgam , ceramic
, or ceramometal ).
-Bond fractured fragments of anterior teeth.

BOND FRUCTURE FRAGMENT (a) Pre-operative view, labial (b) pre-operative view,
occlusal (c) fractured fragment (d) teeth isolated with a rubber dam (e) pulp protection
with Dycal and GIC (f) recess created in fractured fragment using round bur (g) Mylar
strip placed interproximally before rebonding (h) post-operative view, labial

CONTRA INDICATIONS:-
-There are no contraindications to adhesions in clinical
dentistry .There have been no reports of allergy to
materials. Restorations that failed have done so only
when the adhesion was improperly implemented , or
early in the adhesive era when bond strengths were
simply too weak. It is very important that adhesion be
accomplished rigorously, following the instructions and
requirements of the materials involved.

ADVANTAGE OF BONDING TECHNIQUE:-
-Adhesion of composite resin restorations to enamel
and dentin.
-Minimizes removal of sound tooth structure.
-Management of dentin hypersensivity .
-Adhesion reduce microleakage at tooth restoration
interface.
-Adhesion expands the range of esthetic possibilities.

-Bonding of porcelain restorations , e.g.:
porcelain inlays , onlays and veneers.
-Reinforces weakened tooth structure.
-Reduction in marginal staining.

IDEAL REQUIRMENTS
-Biocompatible .
-Non toxic , non irritant , non poisonous.
-Low film thickness , low viscosity.
-Form strong permanent bond.
-Good dimensional stability.
-Low thermal conductivity.
-Good shelf life.
-Prevent micro leakage.

CONDITIONING OF DENTIN
*Conditioning of dentin is defined as an alteration of dentin
surface including the smear layer with the objective of producing
a substrate capable of micromechanical and possibly chemical
bonding to dentin adhesive.
1*Acid conditioners :-several acids like phosphoric acid , maleic
acid citric acid , nitric acid , oxalic acid and hydrochloric acid are
used.
-commonly used 37 percent phosphoric acid.
-not only remove smear layer but also exposes microporous
collagen network in to which monomer penetrates.

Exposes microporous collagen network
in to which monomer penetrates

-usually it forms exposed collagen fibrils which are
covered with an micro porous layer , a combination of
denatured collagen fibers and the collapsed residual
collagen layer.
2* Chelators :- remove the smear layer without
decalcification or significant physical changes on
underlying dentin substrate.
Best known chelator conditioner is EDTA
3*Thermal conditioning :-recent trend is to use lasers in
conditioning teeth ,these may serves as

potential alternative to acid for conditioning of
dentin.it is speculated that the laser cause
recrystalization of dentin resulting in fugi form
appearance that contributes to increased
microrelation or possible chemical adhesion of a
restorative material to the tooth structure.

PRIMIMING OF DENTIN
-Primers are agents which contain monomers having
ahydrophylic end with affinitly for exposed collagen fibrils and
hydrophilic end with affinitly for adhesive resin.
-Commonly used primers have HEMA and 4- META monomers ,
dissolved in organic solvents.
-Primers are used to increase diffusion of resin in to moist and
demineralized dentin and thus optimal micromechanical bonding
for optimal penetration of primer in to demineralized dentin , it
should be applied in multiple coats .
-It is preferred to keep the dentin surface moist , otherwise
collagen fibers get collapsed in dry condition resisting the entry
for primer and adhesive resin.

HYBRID LAYER
-This is zone where the adhesive resin of the dentin bonding
agent micromechanically interlocks within the inter tubular
dentin and surrounding collagen fibers.

-Hybrid layer is formed in following manner:-

Hybrid layer is formed in following manner:_
1-etching removes smear layer and exposes
collagen fibers.
It also removes hydroxyl apetite with in the
intertubular dentin.
2-primers penetrate the collagen network.
3-adhesive resins along with the primers form
resin microtags within the intertubular dentin.
-Hybrid layer also called resin-dentin
Interpenetration/ interdiffusion zone.

ROLES OF SMEAR LAYER
-Whenever tooth surface is cut with hand or rotary
instruments , it causes small particles of the cut tooth
surface to the tooth producing the smear layer.
-Smear layer is defined as any debris , calcific in nature,
produced by reduction or instrumentation of enamel , of
dentin or cementum.

-It has two phases:-
A*Solid phase:-made up of cutting debris primarily denaturated
collagen and mineral.
B*Liquid phases:-made up of tortuous fluid filled channels around
the cutting debris.
-Bacteria entrapped in smear layer can survive and multiply
beneath the restoration.
-Retention of smear layer:-
1-Lowers dentin permeability.
2-Prevent decrease in bond strength.
3-Lowers effect of pulpal pressure on bond strength.
-Recent generations adhesives involves modification of smear
layer to facilitate bonding.

ENAMEL BONDING
-To bond to enamel ,it is very important to focus on the
mineral component (hydroxyapatite)of enamel.
-Buonocore,1955
Was the first to reveal the adhesion of acrylic resin to
acid etched enamel.
Used 85 percent phosphoric acid for etching.
-Silverstone revealed that the optimum concentration of
phosphoric acid should range between 30 to 40 percent
to get a satisfactory adhesion the enamel.

-If concentration is greater than 50 percent
-monocalcium phosphate monohydrate may get
precipitated.
-Concentrations lower than 30 percent
-dicalcium phosphate monohydrate is precipitated
which interferes with adhesion.
-Percentage of etchants used %35
-Use of lower concentration of phosphoric acid and
reduced etching time has shown to give an adequate
etch of the enamel while avoiding excessive
demineralization of the dentine.

DENTIN BONDING
The classic concept of operative dentistry were
challenged in the 1980s and 1990s by the introduction
of new adhesive techniques, first for enamel and then
for dentine . nevertheless , adhesion to dentine remains
difficult . adhesive materials can interact with dentine in
different ways-mechanically , chemically , or both. The
importance of micromechanical bonding , similar to
what occurs in enamel bonding , has become accepted.

Dentine adhesion relies primarily on the penetration of
adhesive monomers in to network of collagen fibers left
exposed by acid etching. However ,for adhesive
materials that do not require etching ,such as glass
ionomer cements and some phosphate-based self etch
adhesives , chemical bonding between polycarboxylic or
phosphate monomers and hydroxyapatite has been
shown to be an important part of the bonding
mechanism.

CRITICAL STEPS IN BONDING
-Proper isolation:-by using rubber dam , saliva
contamination can block mechanical bonding.
-Pulp protection:-by using calcium hydroxide liner.
-Acid etching of enamel and dentin:-by using 37%
phosphoric acid for 15 second then wash.
-Dentin surface must be kept moist . if dentin is over
dried it would result in collapse of exposed collagen
fibers.
-Careful application and curing of bonding agents.
-Placing the composite resin.

FACTOR AFFECTING ADHESION
1.Wetting
-Wetting is an expression of the attractive force
between molecules of adhesive and adherent. In other
words, it is the process of obtaining molecular
attraction.
-Wetting ability of an adhesive depends up on two
factors :_
A-Cleanliness of the adherend :- cleaner surface ,
greater adhesion.
B-Surface energy of the adherend:-more surface
energy, greater adhesion.

2.Water
-The higher the water content ,the poorer is the
adhesion.
-Water can react with both materials by the high polar
group and hydrogen bond which can hamper the
adhesion.
3.Contact angle
-Refers to the angle formed between the surface of a
liquid drop and its adherent surface.
-The stronger the attraction of the adhesive for the
adherent ,the smaller will be the contact angle. The zero
contact angle is the best to obtain wetting.

4.Surface contamination
-The substrate surface should be clean as contamination
prevents the adhesion. Adhesive should be able to fill
their regularities making the surface smooth allowing
proper or intimate contact.
5.Acid application time : Ideally 10 seconds
-Studies show that enamel should not be etches for
more than 15 to 20 seconds.

 PROBLEMS IN BONDING TO DENTIN
-Dentin is a dynamic tissue that changes due to
ageing , caries or restorative procedures.
-Dentinal tubules are filled with dentinal fluid which
constantly flow outward from the pulp.
-Dentine has considerable amount of organic
material and water.
-Dentine is close to pulp , so different chemical used
for bonding and etching may irritate the pulp.

The evolution of adhesivr technique

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The evolution of adhesivr technique