Bonding agents2/ dental courses

BONDING
AGENTS
Its application in
prosthodonticsINDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
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TABLE OF CONTENTSTABLE OF CONTENTS
 Introduction
 Historical Perspective
 Terminologies
 Acid etching
 Requirements of Adhesion
 Chemistry of Adhesive Agents
 Factors affecting adhesion to mineralized tissue
 Classification of Dentin Bonding System
 Bonding Procedure
 Material Selection
 Surface treatments-Alloys, Ceramic
 Conclusion & Summarywww.indiandentalacademy.comwww.indiandentalacademy.com

Adhesion of restorative material to mineralized
tooth structure has been a goal of dental researchers
for many years.
Accomplishing such a bond has many principle
advantages like:
INTRODUCTION
1. Retention of restoration,
2. Conservation of tooth structure,
3. Elimination of marginal microleakage,
4. Reinforcement of remaining tooth structure
5. Increasing the clinical life time of
restorations.

Due to lack of adhesion between dental
restorative resins and tooth structure, microleakage of
salivary components and bacteria occur, which may
lead to:
Marginal staining.
Breakdown at the margins of the restoration
interface.
Secondary caries.
Post operative sensitivity.
Pulp pathology.

HISTORICAL PERSPECTIVEHISTORICAL PERSPECTIVE

Interest in esthetic restorations is definitely not
a modern concept. In 1856 prefabricated ceramic
inlays were used as an esthetic filling to be sealedsealed
with gold foilswith gold foils (Hoffman-Axthelm, 1973). Another
example is the development of fired ceramic inlays
in 1882 by Herbst in Germany, reported in the
dental literature for the first time by Bruce in1891.
The fabrication of fired ceramic inlays over platinumfired ceramic inlays over platinum
foilfoil was developed a few years later by Land, in
1888.

It is interesting to note that ceramic inlays
were introduced to the dental profession well
before amalgam (1895).
However, the absence of a satisfactory lutingabsence of a satisfactory luting
material was a serious obstacle to the clinical
success of these techniques (Nyman, 1905) until
recently, when resinous adhesives and porcelain
etching were combined to bond the restoration
efficiently to the tooth (Simonsen and
Calamia,1983)

The real development of direct esthetic materials
began with Silicate cementsSilicate cements 1871.
Unfilled resinsUnfilled resins in 1937, which have been
advocated for esthetic fillings since 1945
Epoxy moleculeEpoxy molecule developed by the Swiss chemist
Castan in 1938
Acid conditioningAcid conditioning of dental tissues by Hagger,
another Swiss chemist, in 1951.
First description of the so called "hybrid layer""hybrid layer"
(McLean and Kramer; 1952)

Enamel EtchingEnamel Etching
by
Michael BuonocoreMichael Buonocore
1955
Composite ResinComposite Resin
with
Bowen's BIS-GMA formulationBowen's BIS-GMA formulation
(Bowen, 1962).

TERMINOLOGIESTERMINOLOGIES

Acid-Etching-Acid-Etching- Process of roughening a solid surface by
exposing it to an acid and thoroughly rinsing the
residue to promote micromechanical bonding of an
adhesive to the surface.
Adhesion-Adhesion- A molecular or atomic attraction between
two contacting surfaces promoted by the interfacial
force of attraction between the molecules or atoms of
two different species; adhesion may occur as physical
adhesion, chemical adhesion, mechanical adhesion
(structural interlocking) or a combination of all types.
Adhesive-Adhesive- Substance that promotes adhesion of one
substance or material to another.
Adherend-Adherend- A material substrate that is bonded to
another material by means of an adhesive.

Adhesive Bonding-Adhesive Bonding- Process of joining two materials by
means of an adhesive agent that solidifies during the
bonding process.
Dentin Bonding-Dentin Bonding- The process of bonding a resin to
conditioned dentin.
Dentin Bonding Agent-Dentin Bonding Agent- A thin layer of resin between
conditioned dentin and the resin matrix of a
composite.
Dentin Conditioner-Dentin Conditioner- An acidic agent that dissolves the
inorganic structure in dentin, resulting in a collagen
mesh that allows infiltration of an adhesive resin.
Hybrid Layer-Hybrid Layer- An intermediate layer of resin, collagen,
and dentin produced by acid etching of dentin and
resin infiltration into the conditioned dentin.

Microleakage-Microleakage- Flow of oral fluid and bacteria into
the microscopic gap between a prepared tooth
surface and a restorative material.
Primer-Primer- A hydrophilic, low viscosity resin that
promotes bonding to a substrate, such as dentin.
Resin Tag-Resin Tag- Extension of resin that has penetrated
into etched enamel or dentin.
Smear Layer-Smear Layer- Poorly adherent layer of ground
dentin produced by cutting a dentin surface.

An adhesive joint is the result of interactions of a
layer of intermediate material (adhesive) with two
surfaces (adherends) producing two adhesive
interfaces.
CLASSIFICATIONCLASSIFICATION
The interactions which occur at the interface are
classified generally in terms of types of atomic
interactions which may be involved.
Adhesion is classified as: 1. Physical.
2. Chemical.
3. Mechanical. Micro
Macro

Physical bondingPhysical bonding involves Vander waals or other
electrostatic interactions that are relatively weak. It
may be the only type of bonding if surfaces are
smooth and chemically dissimilar.
Chemical bondingChemical bonding involves bonds between atoms
formed across the interface from the adhesive to
the adherend. Because the materials are often
dissimilar, the extent to which this bonding is
possible is limited and the overall contribution to
bond strength is normally quite low.
Mechanical bondingMechanical bonding is the result of an interface
that involves undercuts and other irregularities that
produce interlocking of the materials.

Almost every case of dental adhesion is based
primarily on mechanical bonding. Chemical bonding
may occur as well, but generally makes only a small
contribution to the overall bond strength. Common
method for producing surface roughness for better
mechanical bonding is to grind or etch the surface.
Grinding produces gross mechanical roughness but
leaves a smear layer of hydroxyapatite crystals and
denatured collagen that is approximately 1 to 3
microns thick.

Acid etching or conditioning dissolves this
layer and produces microscopic relief with
undercuts on the surface to create an opportunity
for mechanical bonding. If the interlocked adhesive
and adherend with dimensions less than about 10
microns, then the situation is described as micro-
mechanical bonding.

THE ACID ETCHINGTHE ACID ETCHING

Perhaps the most significant discovery in
dentistry during the last three decades is that of
Dr. Michael Buonocore in 1955Dr. Michael Buonocore in 1955. Working in New
York, he discovered that the bonding strength
between human enamel and acrylic resin could be
tremendously enhanced by exposing the tooth to
a mild acidic solution before applying resin to the
enamel surface.

In his first experiments Dr. BuonocoreDr. Buonocore was
actually following the lead of industry. By the mid-
1950s it was already commonplace to pre-treat
surfaces, such as metals, with phosphoric acid before
applying resins or paint. In fact, his original trial used
85% phosphoric acid, which had by then become the
industrial standard.
The dramatic results obtained through this
technique were recognized instantly. Almost
immediately following Buonocore's initial discovery of
binding to human enamel, efforts intensified to
improve the process.www.indiandentalacademy.comwww.indiandentalacademy.com

It is fortunate that there is a difference
between the resistance of the enamel prisms and
the inter-prismatic enamel to acidic attack. Thus, as
Dr. BuonocoreDr. Buonocore discovered, placing a weak acidic
solution on the enamel surface causes a differential
etch rate between these two areas; this results in
an irregular and pitted surface.

In addition to the presence of the enamel
prisms, it has been discovered that the enamel
contains approximately 0.1 % to 0.2% space by
volume. Although this means that enamel is only
minutely porous, it is possible that these
porosities also play a role in the bonding process.
This results in augmentation of the bond strength
achieved by the differential etch.

Enamel Etching PatternsEnamel Etching Patterns
Four major etching patterns of enamel are
reported in the literature. The first, Type IType I, is created
when the center of the prisms erode more rapidly
than the inter-prismatic enamel. The average width
of the craters usually found in Type I etching pattern
is about 5 µ. This fact is of particular significance
when selecting the luting agent for the bonding and
fusing techniques. Any filler particle of greater
diameter would simply not penetrate the enamel
surface.

Type I

A second topography, Type IIType II, is created
when the inter-prismatic enamel erodes more
rapidly than the prism cores. Although Types ITypes I
and IIII patterns are complete reverses of each
other, both are suitable for mechanical retention.
Interestingly, both patterns are often found in
adjacent areas of the same tooth surface, even
in adjacent prisms

Type II
Type I & Type II

In the Type III etching pattern no rod
structures are evident. Type III pattern results when
the enamel being etched is composed of a
homogeneous mass instead of the more commonly
found prismed structure. Deciduous teeth often
exhibit just such a stratum in their outermost layer.
Since the outer layer is homogeneous in structure,
applying an acid etchant results only in a reduction
of enamel bulk, not the differential etch necessary
for bonding. The Type III pattern can be
troublesome for bonding because it does not allow
the resin to grip the enamel.

Type III

Unfortunately, recent reports show that areas
of prism-less enamel are not confined exclusively
to deciduous teeth as previously believed. In fact,
when surfaces of premolar and molar teeth are
divided into zones, the cervical two thirds of the
crown often exhibit enamel completely devoid of
rod patterns after etching. Fortunately, this
prismless enamel usually comprises only the outer
13 to 20 µ of the enamel. Since applying an acid
etchant not only roughens the outer surface, but
actually dissolves it, it is possible to etch past this
prismless layer using the etchant itself.

A 50 second application of 30%
orthophosphoric acid results in a loss of
approximately 10 µ in surface contour and
approximately 20 µ in depth of histologic change.
Once 20 µ of enamel have been removed from the
surface, the underlying structure usually exhibits
one of the other three etching patterns. Thus, the
time needed to etch an area of enamel displaying
prism-less outer structure is considerably greater
than an area of normal enamel.

COMPONENTS OF BOND STRENGTHCOMPONENTS OF BOND STRENGTH
Chemical, electronic, and van der Waals
forces play a critical role in keeping the filling
material in contact with the tooth over the first 48
hours. After 2 days of submersion, however,
simple mechanical gripping is the only major
component involved.

The currently accepted value for bond strength in
both the tensile and shear directions is
approximately 980 to 1400 psi.
Fourteen hundred psi is an extremely high bond
strength for this type of simple micro-mechanical
retention. This degree of tenacity can be explained
by the fact that once the enamel surface has been
roughened by the etchant, the enamel "pores" also
become enlarged.

Since these pores often interconnect
(Bergman and Hardwick hypothesized that they
are the pathways used for transport of ions and
tissue fluid), their increase in size not only allows
relatively large resin molecules to penetrate the
sub-surface of the enamel, but also allows these
resin tags to interconnect. This exceptional degree
of enamel and resin interlocking partly explains
the high bond strength afforded by the acid etch
technique.

ENAMEL PREPARATIONENAMEL PREPARATION
To create these exceptional bond strengths
consistently the enamel must be prepared
carefully before bonding. Enamel itself is a
reliable substrate for bonding, but in its usual
condition there are several mechanical barriers to
the development of a strong bond with composite
resin. Without meticulous attention to detail, the
bond strength can become significantly
diminished.

At the time of a tooth's eruption it is
completely covered with Nasmyth's membraneNasmyth's membrane.
This is the final stage of ameloblastic activity. If
present, this organic integument can prevent
adequate etching of the enamel surface, but it
measures only 1 µ to 2 µ in thickness when the
tooth first erupts, and some thickness is soon lost
owing to abrasion. By adulthood it is usually quite
worn down or even completely missing and,
therefore, is not usually of concern for most direct
bonded retainers.

Nasmyth's membraneNasmyth's membrane is not the only
barrier to preparing enamel properly. Since
proteins from saliva continually adsorb to the
enamel surface, even in areas of high abrasion,
the enamel retains a thin organic layer. This
further post eruptive integument is called pelliclepellicle,
and it is on this stratum that colonies of
microorganisms known as plaqueplaque form.

Plaque products, along with the fluid and
solid food constituents, become associated with
and integrated into this layer. They form a pellicle-
plaque complex containing fats and protein-
carbohydrate complexes. This layer serves as a
barrier to enamel etching by mild acids. For this
reason untreated enamel can be a poor substrate
for bonding.

Not only is the enamel in its natural state
contaminated with a layer of material that makes
it mechanically unsuitable for bonding, but its
surface is normally chemically fully reacted and
therefore of relatively low energy. Thus, the
enamel is normally chemically unsuitable for
bonding as well.

CLEANINGCLEANING
Obviously, then, the first step in preparing enamel for
bonding has to be to remove the surface layer of
contaminants. For a time it was felt that the acid
etchant itself might be sufficient for this purpose, but in
1973 Mura1973 Mura and his coworkers showed that maximum
bond strength could be achieved only if an oral
prophylaxis was performed before etching. Gwinnett
demonstrated that etched enamel that had not been
prepared with a prophylaxis was often contaminated
by remnants of the pellicle as well as by
microorganisms, even after acid treatment. Calculus
even further impedes proper preparation and must be
meticulously removed before etching.

It is standard procedure for the prophylaxis to
be carried out with unflavoredunflavored and unfluoridatedunfluoridated
pumice. The reason for using an unflavored abrasive
is that most flavorings in dental paste come from
essential oils, often containing glycerin. These
substances can interfere with the work of the acid.
Further observations suggest that the fluoride should
be removed from the polishing agent because it
reacts with the calcium hydroxyapatite of the enamel
to form calcium fluorapatitecalcium fluorapatite, a substance much more
resistant to acidic attack.

Recently a new device has been designed
for the removal of plaque and stain during
prophylaxis (Prophy Jet, Dentsply). It uses a
stream of sodium bicarbonate and water under
pressure aimed at the teeth much like a
sandblaster. This has a potential advantage over
other methods of cleaning because it is able to
gain access to areas in which the contacts are
quite close.

ETCHINGETCHING
The teeth should be rinsed, dried, and properly
isolated from the saliva. Acid is then applied to the
enamel with a cotton pellet, mini-sponge, brush, or
other similar means. If the acid is in liquid form, it
must be agitated gently on the surface of the tooth
for optimal results. This agitation is usually
accomplished either by a dabbing or by a very light
swabbing motion. It is critical to avoid burnishing the
enamel during the application of the acid since the
enamel rod ends exposed during the etching process
are extremely fragile. Even a mild rubbing is
sufficient to di-minish substantially the final bond
strength.

The optimal application time for the acid is
generally believed to be 60 to 90 seconds,7 but
several factors can affect the ideal etching time.
One is the presence of prismless enamel. Such an
enamel morphology usually requires doubling the
normal etch time in order to erode past the
prismless layer. The presence of high levels of
fluoride in the teeth can similarly increase the time
necessary for an optimal etch because the free
fluoride ions in the enamel environment allow the
calcium hydroxyapatite to react with them, thus
producing calcium fluorapatite.

Clinically, this is accomplished by relying on
the appearance of the tooth after etching, rather
than on the clock, to measure the effectiveness of
the etching. When properly etched, the tooth
should exhibit a dull, frosted, matte finishdull, frosted, matte finish. Under-
etching results in a tooth that retains its glossgloss.
Over-etching results in a surface chalkychalky in
appearance due to the formation of an insoluble
salt during the etching process.

Many different acids have been suggested
for the etching process, and much investigation
has gone into determining the ideal etching
solution. The popular current choice is
orthophosphoric acidorthophosphoric acid, which is commercially
available in concentrations ranging from
approximately from 30% to 65%.

SilverstoneSilverstone did an interesting study. He tested
20%, 30%, 40%, 50%, 60%, and 70% concentrations
of orthophosphoric acid, 50% orthophosphoric acid
plus boric acid buffered with 7% zinc oxide by weight,
5% and 50% citric acid, 10% polyacrylic acid, and
5% and 50% neutral and acid solution of EDT A for
exposure times varying from 1 to 5 minutes. HisHis
conclusion was that 30% orthophosphoric acid wasconclusion was that 30% orthophosphoric acid was
the solution of choice.the solution of choice.

In addition to the wide range of concentrations
of the acid solutions, acids are available in gel as
well as liquid form.
The clinical decision to use an acid gel or an
acid solution is a matter of personal preference. The
clinical advantage of a gel over a liquid is the
increased control in placing the acid. This is of
particular help when the clinician has to etch in an
area that surrounds some exposed dentin.

The major objection to using etching gels is
that they require increased wash time after the
etching procedure is completed. Most brands of
etching gels have added colorants to help the
dentist visualize exactly where the etchant has
been placed.
Immediately after etching, the enamel
should be completely cleaned of any etching
material. The combination of 60 seconds of
etching time and 10 seconds wash time seemed
to create the most powerful bond strength.

SURFACE ENERGYSURFACE ENERGY
The removal of inert enamel surface structure
exposes a fresh reactive surface with an energy
level greatly increased over its unetched
counterpart. The resulting surface, which is much
more wettable in this state, must be protected. Both
the application of fluorides and contamination from
saliva should be carefully avoided, since these
would alter the surface energy of the enamel and
greatly reduce the bond strength.

If saliva does contaminate the etched enamel,
it is extremely important that the surface be re-
etched for at least 10 seconds with the phosphoric
acid. If the dentist fails to do this, he will
compromise the bond strengths. The reason that
etched enamel surfaces which have contacted
saliva must be retreated is due to the high degree
of chemical and electrical activity in those enamel
surfaces treated by the etching procedure. Once
etched, the exposed enamel is extremely reactive.

When saliva comes into contact with the
reactive enamel, even for a second, it adsorbs
chemicals to its surface and lowers the activity of the
enamel. This dramatically alters its wetting
characteristics, which, in turn, severely reduces the
bond strength.
Besides creation of a new topography,
perhaps the most profound result of the acid etching
is the greatly increased surface area of enamel
available for interaction with the resin.

RISKSRISKS
Almost immediately upon the discovery of the
potential benefits of the acid etch system, questions of
potential risks arose. These questions dealt primarily
with risks to the pulpal tissue, gingiva, and unbonded
enamel. It is now clearly accepted that there is no
danger of pulpal irritation from the etchants when they
are placed over sound enamel. When they are placed
over dentinal or cemental tissue, however, there is
danger of pulpal inflammation. This danger increases
with the proximity of the acid to the pulp, the
concentration of acid used, and the duration of its
application.


Gingival irritation resulted from exposure to
upto 50% orthophosphoric acid when the clinician
had allowed cotton rolls that were saturated with the
acid to remain in the buccal fold for 5 minutes or
longer.


From a practical standpoint, much concern
has been voiced about the possible consequences
of etching enamel, only to leave it exposed and
unbonded. After much investigation, there is no
evidence at present indicating any permanent
damage to the enamel tissue caused by the etching
technique. Several studies indicate that the clinical
appearance of enamel that has been etched, but
not subsequently bonded, is restored from 48 to 72
hours from etching.

REQUIREMENTS OF ADHESION

To develop good adhesion, it is necessary to form a
microscopically intimate interface. To produce good
bonding, there must be good wetting.
The ability of an adhesive to wet the surface of the
adherend is influenced by.
a) Cleanliness of the surface :a) Cleanliness of the surface : Surfaces being
joined must be clean. Surfaces are cleaned by
application of solvents or acids to dissolve or
dislodge contaminants.
Clean surfaces are at high-energy state and rapidly
absorb contaminants from the air such as moisture
and dust. www.indiandentalacademy.comwww.indiandentalacademy.com

b) Adsorbed moisture :b) Adsorbed moisture : The major factor that
limits spreading of organic phases on clean
inorganic surfaces is the presence of adsorbed
moisture. An increasing amount of water
adsorbed, the critical surface tension continues to
decrease and approaches that of a bulk water
surface. Therefore, liquid devoid of hydrophilic
groups in contact with moisture surface do not
spread but instead exhibit appreciable contact
angles.

CONTACT ANGLE :CONTACT ANGLE : The extent to which the
adhesive will wet the surface of the adherend is
generally determined by measuring the “contact
angle” between the adhesive and the adherend.
Contact angle of Zero degree indicates that
spontaneous spreading of the liquid takes
place.
Contact angle between 0 and 180° indicate
poor or incomplete surface wetting by the
liquid.

CLINICAL FACTORS AFFECTING ADHESION
1. Salivary and Blood contamination1. Salivary and Blood contamination
These contaminants can influence some
dental adhesion concepts in a negativenegative manner.
Although dentin is a ‘wet’ substance, the
constituents of saliva and blood create an
environment that can destroy dentin bonding.
Use of a rubber dam or other dry-field aids is
necessary to avoid salivary or blood contamination
during placement of tooth adhesion materials. Over
use of dry field aids may produce another potential
problem related to adhesion / dehydration.www.indiandentalacademy.comwww.indiandentalacademy.com

2. Moisture contamination from Hand pieces or2. Moisture contamination from Hand pieces or
Air-water syringesAir-water syringes
This is got a negative influencenegative influence.
The source of leakage may be due to
a) Lack of drying devices on air lines leading from the
compressor, allowing wet air to be carried to the
syringe or hand piece.
b) Condensation of water in air lines.
c) Leakage of water through gaskets.

3. Oil contamination of hand pieces or Air water3. Oil contamination of hand pieces or Air water
syringesyringe :- negative influencenegative influence. Oil comes from air
compressor. Dentin bonding agent combined with oil
contamination provides an unpredictable clinical
result and potential clinical failure. Oil filters are
placed on the airlines after the air compressor and
before the air syringe or hand piece and should be
changed frequently. Water and Oil contamination are
the most significant negative factors present in tooth
adhesion.

4. Surface roughness of tooth structure4. Surface roughness of tooth structure
Positive influencePositive influence.
Tungsten carbide steel burs make scratches and
irregularities in tooth surfaces, diamonds cut
irregularities in tooth structure that are related
directly to the size of the diamond particles.
Increased surface area created by surface
roughness helps in increasing the bond to dentin.

5. Mechanical under cuts in Tooth preparations5. Mechanical under cuts in Tooth preparations
Mechanical undercuts when present helps in holding
restorative materials from bodily dislodgment from
the preparation, they also resist some microscopic
movement of the restorative material caused by
thermal or polymerization shrinkage. Therefore
restorations with traditional dentin-placed undercuts
as well as chemically produced bonding, may
produce better clinical resultsproduce better clinical results such as less leakage
and less sensitivity.

6. Fluoride content of teeth6. Fluoride content of teeth Fluoride presence in
dentin appears to influence bonding with dentin
adhesive agents negatively.negatively. Increased fluoride
content of enamel resist acid etching, hence
increasing the etching time to allow for acid to
degenerate the enamel surface and produce move
roughness.
7. Use of Fluoride after Restorations have been7. Use of Fluoride after Restorations have been
placedplaced Stannous fluoride gel (pH at 3.6) cause
degeneration of zinc-phosphate and glass-ionomer
cements. Influence of fluoride on bond of adhesive
agent needs additional research.

8. Dentinal Canal Characteristics8. Dentinal Canal Characteristics
Dentinal canals at the external surface of roots or
near dentinoenamel junction have small
diameters. Dentinal canals closer to the dental
pulp become larger, older dentin has small
dentinal canals. Dentinal bonding agents use
some form of mechanical attachment into dentinal
canals. In small canals attachment is less and in
larger canals attachment is enhanced.

9. Presence of plaque, calculus, extrinsic stain or9. Presence of plaque, calculus, extrinsic stain or
debrisdebris Negative influenceNegative influence. After etching, the plaque-
covered surface remains shiny and prevents an etch
with 37% phosphoric acid. Penetration of plaque by
acids used in dentin bonding agents is not possible
and clinical adhesive failure will result.
Tooth stains and calculus are easier to see and are
removed usually, if not the bonding agents will not
work. Enamel or dentin tooth surfaces that are
expected to bond to resin to other materials should be
cleaned thoroughly before attempting bonding.

10. Presence of bases or liners on prepared teeth10. Presence of bases or liners on prepared teeth
(a) Varnish:(a) Varnish: Although reduced tooth sensitivity, they
should not be used if bonding of subsequent
materials to tooth surface is expected.
(b) Glass-ionomer liners :(b) Glass-ionomer liners : Create a moderate bond
to dentin but it is lower than the bond created by
placing resin on acid-etched enamel. If resin is placed
over glass-ionomer liner, the bond of the resin to the
tooth can be no stronger than the bond of the glass
ionomer to dentin or the bond of the resin to the glass
ionomer.
(c) Resin Liners:(c) Resin Liners: Resin liners have little or no bond
to dentine and subsequent restorations placed over
the resin liners have no effect on bond to dentin.www.indiandentalacademy.comwww.indiandentalacademy.com

11. Tooth dehydration11. Tooth dehydration Bond strength could be
related to wetness of dentin (Prati, Pashley and
Montanari 1991). Overdrying can lead to increased
tooth sensitivity. Drying only until the obvious shine
of moisture is gone is a good clinical guide.

12. Constituents of Temporary Cements12. Constituents of Temporary Cements
Eugenol containing temporary cements or sterate-
containing noneugenol temporary cements may
have different bonding characteristics to resin.
Fresh liquid eugenol placed on dentin or enamel
just before attempted bonding could be a negative
factor in adhesion.

CHEMISTRYCHEMISTRY
OFOF
ADHESIVE AGENTSADHESIVE AGENTS

Adhesive agents must have the ability to wet and
then to adhere to hard dental tissues. Dental bonding
systems contain monomers that have hydrophilic and
hydrophobic groups.
Adhesion to tooth structure depends on several factors:Adhesion to tooth structure depends on several factors:
1) There must be intimate contact between the tooth
structure and the restorative material.
2) Cavity walls must be clean.
3) Liquid part of the restorative material must wet both
enamel and dentin.
4) The surface tension of the liquid must be less than
the surface free energy of the enamel and dentin.

A freshly acid-etched enamel surface
has a surface energy more than twice that of
an un-etched enamel surface and easily
wetted by the monomer. Good adhesion after
polymerization and good adaptation can only
be obtained if the polymerization shrinkage is
low.

A gap may be formed at the filling and dentin
interface due to:
1. Polymerization shrinkage of the filling material.
2. Adhesive strength to dentin being weaker than
the polymerization stress.
3. Stresses developed from the differences in
coefficient of thermal expansion of tooth and filling
material.
4. Functional occlusal forces
A dentin adhesive with an initial strong bond is
needed to resist polymerization shrinkage.

Types of Chemical Adhesion :Types of Chemical Adhesion :
Two main types
1) Primary valence forces.
2) Secondary valence forces.
The strongest and most stable primary valenceprimary valence
bondsbonds are the covalent and coordinative bonds,
which are both electron pair bonds. Ionic bonds
may also give strong adhesion.
Secondary valence bondsSecondary valence bonds or intermolecular
bonds are classified as Vander waals forces and
hydrogen bonds.

Adhesion based on ionic polymers:Adhesion based on ionic polymers:
Adhesion of the poly (alkenoic-acid) based materials to
apatite can be achieved by ionic bonding with calcium
ions acting as bridges. Two types of dental materials
zinc carboxylate and glass ionomers are classified as
poly alkenoates.
Polyalkenoates are based on polyacrylic acid, maleic
acid or itaconic acid.
Ions diffusing from cement particles or from dentin
apaitite allow cationic bridges to be formed between
carboxylic groups of the poly (alkenoic acid) and
collagen (acidic groups). The ability of glass ionomer to
adhere to enamel and dentin, has led to use G.I. as a
base of composite resin (McLean 1985)www.indiandentalacademy.comwww.indiandentalacademy.com

Adhesion by coupling Agents:Adhesion by coupling Agents:
1) Silane – for Silanization of fillers 3 –
methacryloyloxypropyl – tri methoxysilane
2) Another coupling agent was butylacrylate – acrylic
acid copolymer with free carboxylic acid groups.
3) Coupling agents utilizing the concept of hydrophobic
and hydrophilic groups are the monomers based on
phosphates or phosphonates.
Scoth Bond (2nd gen)
Clearfil New Bond (2nd)
Adaptic Dentin Bond
Prisma universal Bond (2nd gen)
Examples:

Adhesion by Hybrid Zone/Layer:Adhesion by Hybrid Zone/Layer:
When the primer is applied to a properly treated
dentin surface, they form ‘micro-tags’‘micro-tags’ into the
dentin substrate, there by creating a zone ofzone of
primer/resin infiltrated dentinprimer/resin infiltrated dentin at the interface.
Eg: All Bond IIAll Bond II, ProBondProBond, SyntacSyntac, Scotch bondScotch bond
multipurposemultipurpose, prime and Bondprime and Bond.

FACTORS AFFECTINGFACTORS AFFECTING
ADHESIONADHESION
TOTO
MINERALIZED TISSUEMINERALIZED TISSUE

FACTORS RELATED TO THE ADHERENDFACTORS RELATED TO THE ADHEREND
Physiochemical properties of Enamel and the effectPhysiochemical properties of Enamel and the effect
of acid etching:of acid etching:
# Inorganic content : 96-97 % by weight
# Water : 4%
# Organic Content : 1% Collagen
Bonding to enamel is poor because organic pellicle
covers the enamel surface.
Etching raises the critical surface tension of
enamel.
The creation of such a high energy surface
together with the increase in bonding area and
surface roughness make the bonding of hydrophobic
resins possible. www.indiandentalacademy.comwww.indiandentalacademy.com

Physiochemical properties of dentin thatPhysiochemical properties of dentin that
complicate dentin adhesioncomplicate dentin adhesion
The ultrastructure and chemical composition of
dentin does not permit micromechanical
interlocking as occur with the enamel.
Dentin consists 70% hydroxyapatite, 18%70% hydroxyapatite, 18%
organic material (Collagen) and 12% water.organic material (Collagen) and 12% water.
Etching of dentin leaves a sponge-like structure
with little compression, tensile or shear strength
(Standford 1985 ) .

The high protein content is responsible for the low
surface energy of dentin compared to enamel.
Constituents are unevenly distributed in inter and
peritubular dentin so the tissue is heterogeneous.
The dentinal tubules lodge the odontoblast process
as a direct connection to the vital pulp (Yamada and
others 1983).
Near the pulp, peritubular dentin represents 66%
and intertubular dentin only 12% while 22% of the
surface area is occupied by water.

DentinalDentinal smear layer and dentin permeabilitysmear layer and dentin permeability
When the tooth structure is worked with rotary tools,
cutting debris is smeared over the enamel and dentin
surfaces. (Pashley 1984 and 1988).
EDTAEDTA was found to be the most potent conditioner
in removing the smear layer and opening up the
orifices of the dentinal tubules.
Other Conditioners include:- citric acid, poly acryliccitric acid, poly acrylic
acid, Lactic acid, Phosphoric acid.acid, Lactic acid, Phosphoric acid. (In vitro study).
The depth of the smear layer depends on the type of
instruments and the condition of irrigation employed
normally varying from 1 to 5 mm (Elick and others
1970 Pashley 1984).

Smear Layer

Transformed dentin structure due toTransformed dentin structure due to
physiological and pathological proceduresphysiological and pathological procedures
Transformed dentin structures like carious and
eroded dentin, exhibit dentinal tubules that are very
narrow and obliterated by deposition of sclerotic
dentin and dentin permeability is reduced.
Reduced permeability of aged sound dentin
attributed to a progressive deposition of peritubular
dentin and crystal formation in the tubules.
In hypersensitive areas of wedge-shaped erosive
cervical areas, 75% of the tubular orifices will be
open, where as in insensitive areas of same dentin
most of the dentinal tubules are obliterated.

FACTORS RELATED TO THE RESTORATIVEFACTORS RELATED TO THE RESTORATIVE
RESINS.RESINS.
a) Physical properties of Adhesivesa) Physical properties of Adhesives
Primer and adhesive must wet the solid
surface, have relatively low viscosity in order to
penetrate the microporosites, and be able to
displace air and moisture during the bonding
operation.
Primers contain hydrophilic monomers like
HEMAHEMA as surface active agents to enhance the
wettability of hydrophobic resins. In addition,
solvents like ethanol or acetone assure adequate
removal of air and liquid by evaporation.

b) Polymerization contraction of restorative resinsb) Polymerization contraction of restorative resins
Dimensional rearrangement of monomers into
polymer chains leads to volume shrinkage (Bream
1985, Feilzer 1989).
Higher filler loading considerably reduces
polymerization contraction. In clinical situations curing
contraction is not allowed to develop freely but is
restrained by the simultaneously developing bond of
the restorative material to the cavity walls (Kemp-
Scoholte 1989). This restriction of free contraction
induces polymerization contraction stress, which
counteracts the developing bond of the restorative
resin to the cavity walls.

c) Contraction stress relaxation by Flowc) Contraction stress relaxation by Flow
Throughout the entire polymerization process,
plastic deformation or flow of the composite resin
occurs and partially compensates for the shrinkage
stress. (Davidson and De Gee 1984)
Restriction of flow capacity by the configurationconfiguration
of the restoration enhances the contraction stresscontraction stress
(C-factor)(C-factor)..
The higher the ratio of free surfacefree surface over bondedbonded
resin surfaceresin surface, the more flow may compensate for
contraction stress. www.indiandentalacademy.comwww.indiandentalacademy.com

d) Young’s modulus of Elasticityd) Young’s modulus of Elasticity
Composites with higher filler content resulting a much
higher stiffness or young’s modulus, reduce
volumetric contraction but will cause higher
contraction stress, which effects the composite dentin
interface. Viscous adhesive resins like Scotchbond 2Scotchbond 2
and Visar sealVisar seal produce a thick bonding layer creating
artificial “elastic cavity wall” with a low young’s
modulus as a buffer between the shrinking restoration
and the cavity walls. Clearfil linear bond systemClearfil linear bond system
with this concept of an elastic buffer layer providing a
low viscosity composite resin as a liner underneath
the subsequently applied restorative resin.

e) Initial polymerization sitee) Initial polymerization site
Initial setting for chemical cure composite occur at
the center part of the bulk material.
Initial setting for light cure composite occur towards
the light source.
For both instances tensile stresses operate
across the composite-dentin interface, tearing the
material away from the cavity walls.

Fusayama argues that initial setting of
chemical – curing resins start at the bottom dentin
part of the cavity, due to the locally higher
temperature of body heat (1991).
By incorporating champhoroquinone in the
adhesive resin the polymerization is initiated at the
very surface of the dentin, this pretreatment is
highly effective in reducing the gap sizes in cavities
in both enamel and dentin.

f) Relaxation of contraction stress byf) Relaxation of contraction stress by
hygroscopic expansionhygroscopic expansion
Polymerization shrinkage is tempered by
fluid absorption, which may offset the residual
elastic stress. Microfilled composites absorb
more water than macrofills due to the greater
resin volume.
Hygroscopic expansion takes place during
the days and weeks immediately following the
placement of restoration.

CLASSIFICATION OFCLASSIFICATION OF
DENTIN BONDINGDENTIN BONDING
SYSTEMSSYSTEMS
Dentin bonding agents are often
grouped into generationsgenerations, based on their
bonding procedures and the relative bond
strength they could achieve.

First GenerationFirst Generation “bonding” materials were far
more useful for enamel than dentin. These
bonding agents were designed for ionic bonding
to hydroxyapite or for covalent bonding
(hydrogen bonding) to collagen. These materials
tended to be hydrophobic. With bond strength of
2 Mpa – 6 Mpa2 Mpa – 6 Mpa, they had a tendency to debond
within a short time. The bond strength, was
limited by strength of the bond of the smear layer
to the dentin.

Materials:Materials: A surface active comonomers, N-
phenylglycine glycidyl methacrylate (Bowen, 1965)
was developed that acted as a primer or adhesion
promoter between enamel / dentin and resin materials
by chelating with surface calcium. E.g. Cervident.
DisadvantagesDisadvantages
1. Poor bond to dentin familiar amalgam type retentive
cavities.
2. Used only for small class III and class V restorations
where there was adequate enamel in which to bond.
3. Post operative sensitivity in attempted posterior
occlusal restorations.

Second Generation Dentin Bonding SystemsSecond Generation Dentin Bonding Systems
Performed better than the 1st generation
products. The 2nd generation of dentin adhesives
primarily used polymerizable phosphates added to
BIS-GMA resins. Adhesives that used phosphate
group to promote bonding to the calcium in
mineralised tooth structure were referred as
phosphate bonding systems. These materials had a
weak bond to dentin (4 to 6 Mpa), hydrophobic. The
bond strength was limited by relative attachment
strength of the smear layer to dentin substrate.

Phosphate ester bonding agentsPhosphate ester bonding agents Based on halo
phosphorous esters of BIS-GMA and HEMA
commonly known as phhosphate bonding agents.
They bond to dentin as a result of interaction
between the bonding agent phosphate group and
calcium in the tooth structure.
Polymethane bonding agentsPolymethane bonding agents Based on
polymethane polymers with isocyanate groups
believed to bond chemically to amino, hydroxy and
carboxy groups on dentinal collagen.

MaterialsMaterials
a) Clearfil
b) Scotch Bond
c) Prisma Universal Bond
d) Dentin Adhesit
DisadvantagesDisadvantages
1. Weak bond to dentin
2. Mechanical retention form was still necessary
since bond strength alone was inadequate.
3. Margins on dentin were problematic since the low
dentinal bond strengths permitted extensive
marginal microleakage.
4. Restoration failure occurred most commonly due
to hydrolytic decomposition.www.indiandentalacademy.comwww.indiandentalacademy.com

Third Generation Bonding SystemsThird Generation Bonding Systems
A Newer – generation adhesive system have
been developed that use a conditioning step on
dentin in conjuction with a bonding agent.
Bowen (1982) developed a multistep adhesive
system. Importantly third generation adhesives
were the frist to bond to metal and ceramics.
Components are :Components are :
a) Dentin-conditioner
b) Dentine primers / adhesive
c) Bonding agent

Dentin Conditioners :-Dentin Conditioners :- Are agents that
either modify or remove the smear layer and
subsequently interact with superficial dentin and
rinsed off after application.
Brannstrom’s developed a conditioner containing
0.2% EDTAEDTA and 0.1% benzalkonium chloridebenzalkonium chloride as a
surface active disinfectant –
Eg. 1) 1.0% Nitric acidNitric acid + 2% Phosphoric acidPhosphoric acid +
2.5% Aluminium oxalateAluminium oxalate -eg Tenure.
2) 2.5% Nitric acidNitric acid –eg: Mirage bond.
3) 17% EDTAEDTA – eg Gluma

4) 2.5% maleic acidmaleic acid & 55% HEMAHEMA) eg Scotchbond –2.
5) 10% maleic acidmaleic acid – eg Scotchbond MP
6) 35% HH33POPO44 – eg a) Scotch bond Dual Cure b)
Prisma uni b-3 c) Optibond.
7) HEMAHEMA – eg. All bond
8) 10% HH33POPO44 – eg All bond 2.
9) 10% Citric acid 20% CaclCacl22 – eg Clearfil liner bond.

ChelatorsChelators
Chelators are used to remove the smear layer without
decalcification or significant physical changes to the
underlying substrate.
The best chelating conditioner is ethylene diamineethylene diamine
tetraacetic acidtetraacetic acid (pH about 7.4) used in GLUMA
system. The smear plug in dentinal tubules are not
fully removed by 30 second application of the
conditioner, this results in a significant hybrid layer
formation.
Maleic acid (Scotch bond 2) also results in removal of
the smear layer but not the smear plug. Although it is
quite acidic, it does not appear to decalcify deeply and
the hybrid layer is comparatively thin.www.indiandentalacademy.comwww.indiandentalacademy.com

LasersLasers
A pulsed Nd:YAG laser will not disturb the pulp,
even when the approach is as close as 1mm
(White & others 1990).
The mechanism of dentin removal is microscopic
explosions caused by the thermal transients.
The lased surface result in desensitized dentin by
occlusion of the open and permeable dentianal
tubules. Microorganisms and organic debris are
eliminated (white & cohen 1991).

White & others (1991) in their study with ScotchScotch
bond 2bond 2 concluded that the bond strength increased
about 60% after lasing, by increasing the bondable
inorganic fraction of the dentin surface.
Micromechanical retention may be created by the
laser, which is analogous to the effect seen on
laser-etched enamel.

MicroabrasionMicroabrasion
Microabrasion with aluminium oxide removes
healthy as well as diseased dentin and results in a
smear layer. The abrasion action depends on the
particle size as well as on the velocity.
Particle size 0.5 microns or less in diameter do
not affect the enamel except to cleanse it.
The 0.5 micron or larger particles create a
smear on the dentin and increased surface area
(Blake 1991)

Dentin Primer / AdhesiveDentin Primer / Adhesive (Adhesion promoters)(Adhesion promoters)
A primer is an agent which enhances the wettability of
a bonding agent onto the dentinal surface. The primer
usually contains an adhesion promoter in a solvent
such as water, ethanolwater, ethanol or acetoneacetone. Primers are applied
to the surface and dried, presumably leaving the
adhesion promoter absorbed on the dentin with
hydrophobic gourps exposed to create a favourable
surface for the bonding agent ( hydrophilic compatible
with dentin). The concept of a self-etching primer has
been discussed by Hasegawa and others (1989).

Examples for Dentin primers are :Examples for Dentin primers are :
1. 35% HEMA + 5% Glutaraldehyde –eg. Gluma
2. 55% HEMA + 2.5% maleic acid (self etching
primer) eg. Scotchbond 2
3. 5% NTG-GMA + PMDM eg. Tenure
4. Mirage Bond (self etching primers) – 4% NPG &
2.5% Nitric acid
5. 2% NTG-GMA + 16% BPDM – eg. All bond.
6. Prisma universal bond 3 – 30% HEMA; 6%
PENTA (Primer)

Fourth Generation Dentin Bonding SystemFourth Generation Dentin Bonding System
The fourth generation dentin bonding system are
characterized by hybrid zone formationhybrid zone formation in the dentin.
The concepts of total etchtotal etch and moist dentinalmoist dentinal
bondingbonding (for acetone containing primers) are also
hallmarks of the fourth generation materials.

Fifth Generation Bonding SystemFifth Generation Bonding System
The current state of the art in bonding materials is the
single component bonding systems. This system
provide entire priming and bonding sequence in a
single liquid and single bottle. Dentin adhesives are
based on combinations of conventional hydrophobic
resins such as BIS-GMA, together with hydrophilic
resins and solvents. HEMA (Hydroxyethyl
methacrylate) is often used as a hydrophilic monomer.
Acetone, alcoholAcetone, alcohol or a combination of both can be
used as hydrophilic solvents. Several systems include
water in various quantities to make the compound as
an aqueous solution.www.indiandentalacademy.comwww.indiandentalacademy.com

MaterialsMaterials
1) Prime & Bond
2) One Step Bond
3) Tenure Quick
4) Syntac single
5) Opti Bond

AdvantagesAdvantages
1) Dentin bond strength are well above 15mpa.
2) Post-operative sensitivity is extremely rare.
3) Some of the 5th generation systems have
incorporated fluoride release and elastomeric
components to improve marginal integrity.
4) Time saving, and simplicity of use.

BONDING PROCEDUREBONDING PROCEDURE

Cleaning of Cavity SurfacesCleaning of Cavity Surfaces
If interim restorations were placed, the
complete removal of temporary cement is the first
step. This is preferably performed with hand
instruments and pumice brushed over the cavity
surfaces, or with an air-powder abrasive device,
which proved to be the most effective final
cleansing method. Actually, further adhesive
procedures mandate that the tooth substrate be
perfectly cleaned and decontaminated.

Restoration Try-InRestoration Try-In
The influence of precision on the quality of
adhesively luted restorations is a confusing issue
in the related scientific literature. This problem
should be analyzed according to the following
different points:

1. Thickness of the cementing space.1. Thickness of the cementing space.
It is now recognized that in thin resin cement
layers, the polymerization shrinkage is mainly
directed uniaxially (Feilzer et al, 1989). The resulting
"wall-to-wall contraction""wall-to-wall contraction" of the composite is therefore
largely proportional to its thickness under usual
clinical conditions. The marginal fit of semidirect and
indirect restorations (composite or ceramic) should lie
within 100 microns (Ariyaratnam et al, 1990; Dietschi
et al, 1992).

Internal gaps may be greater (up to 300
microns) because of the use of dye spacers and
adjusting procedures. This means that well-fitting
restorations will reduce the polymerization strains
exerted on the adhesive interfaces and should
therefore provide better adaptation and seal.

2. Compensatory movements.2. Compensatory movements.
On the other hand, giving the restoration and tooth
the possibility to undergo micro movements during
the luting composite contraction partially
compensate for the polymerization stresses
(Dietschi et al, 1992, 1995; Sorensen and
Munksgaard, 1995). In that respect, it is probable
that perfectly fitting units will lock inside the cavity
during insertion and impede any compensatory
movements, such as restoration descent and
flexion of remaining walls.

3. Adhesion potential.3. Adhesion potential.
As already mentioned, numerous studies have
demonstrated the advantage of luted restorations
regarding adaptation and seal. However, it seems
that this benefit is under exploited in the case of
direct bonding to dentin when the usual procedures
of modern adhesives are applied. Actually, it was
shown that adhesive failures often occur between
the hybrid layer and luting composite (Dietschi et al,
1995)

This problem is supposedly related to the
compression of the frail collagen network
exposed by dentin-etching during restoration
insertion, while the hybrid layer structure is not
stabilized by cured bonding resin. The same
phenomenon and its detrimental consequences
on dentin adhesion were described previously in
relation to dentin dehydration (Pashley et al,
1994).

It therefore appears pertinent to apply an
adhesive lining in each possible case, so that all of
the advantages of modern adhesives can be
exploited. One has to be aware that traditional lining
materials, such as chemical and light-curing glass
ionomers, are not appropriate for this because of their
insufficient adhesion potential (Dietschi et al, 1995).
The combined application of a modern DBA and
a mechanically resistant base-lining material is
mandatory. For that purpose, only compomerscompomers and
filling composite resinsfilling composite resins should be considered.

4. Wear of the luting cement.4. Wear of the luting cement.
Luting composites undergo more wear than
the restorative composites (Suzuki et al, 1995;
O'Neal et al, 1993) and that occlusal wear is
proportional to the interfacial gap (Noack et al,
1992; Leinfelder et al, 1993). Therefore, it seems
important to reduce the cementing gap, at least
occlusally.

Practical and clinical considerationsPractical and clinical considerations
In clinical conditions, the removal of luting
composite excesses is probably the most critical
step of the whole procedure. The difficult task is
to avoid over-hangs or under-hangs resulting
from cementation. Margins providing a
satisfactory continuity between the restoration
and the tooth will be obtained only in perfectly
fitting restorations

Considering all factors, it appears that precise
restorations are preferable because they will reduce
polymerization stresses within the interfacial gap,
limit wear of the cement, and facilitate the removal of
cement excesses, providing even restoration
margins
In larger spaces, satisfactory adaptation and
seal may also be obtained as compensatory
phenomena take place (Dietschi et al, 1992), but this
may result in faster margin degradation. Currently,
dentin adhesion is perhaps a perfectible aspect of
the technique and requires further research to define
the best protocol.

When marginal inaccuracy is found,
composite restorations allow corrections to be
made. This may be performed very easily after
cavity insulation and in situ polymerization of a
small amount of restorative composite.

Tightening of proximal contacts may be
performed in a similar manner if the surfaces to be
corrected are properly roughened and covered with
bonding resin, especially with lab-made or post-cured
restorations. The ability to perform chair-side
restoration corrections before and after luting is a
definite advantage of composite resins over ceramics.

MATERIAL SELECTIONMATERIAL SELECTION

Apart from their physicochemical properties,
the consistency and working time of the luting
cements are two of their basic properties.
Sufficient working time is critical to placing
the restoration in its correct position and
eliminating cement overflow before chemical
curing. Unfortunately, working time is inversely
related to the efficiency of chemical curing.

This means that the dual-curing materials
that provide complete polymerization in dark
conditions generally provide insufficient working
time! Practically, the working time necessary can
vary greatly according to the surface number,
general design, and margin accessibility of the
restorations. Although it is theoretically
contraindicated, changing the paste-catalyst ratio
to extend working time may occasionally be
mandatory.

The flow and removal of cement from the
cementing gap is problematic in proximal areas.
In this respect, high viscosity materials permit the
cement excesses to be cut rather than wiped off,
which generally spreads the luting composite and
contaminates larger surfaces.

Surface Treatments

The luting of semi-direct or indirect restorations
implies a double bond: one between the luting
composite and the tooth, the other between the
luting composite and the ceramic or composite
restoration.

Tooth SubstrateTooth Substrate
A successful marginal adaptation and seal can be
achieved when enamel completely surrounds the
preparation limits. Where free marginal dentin
surfaces exist, the application of a modern dentin
bonding agent and resin
base is advisable to
improve the restoration
seal and prevent
postoperative sensitivity.

Bonding to CeramicsBonding to Ceramics
The composite-ceramic bond generally relies on the
standard procedures of ceramic etching with
hydrofluoric-based acid and silanization (Simonsen
and Calamia, 1983 and 1984) (Fig 10-12). This
combination of micromechanical anchorage and
chemical coupling proved to be more efficient in vitro
than each single procedure (Stangel and Nathanson,
1987; Lacy et ai, 1988; FeU et ai, 1991). The heat
curing of the silane can improve the composite-to-
ceramic bond (Bailey and Bennet, 1988; Roulet et ai,
1994). Silanes that are activated chairside are
preferred to preactivated products. It is noted that,
there is a tendency for silanes to undergo hydrolytic
degradation. www.indiandentalacademy.comwww.indiandentalacademy.com

Bonding to CompositeBonding to Composite
Depending on the fabrication method, the
restoration interface is likely to be contaminated by
model silicone material, dental hard stone, or
insulating media. Consequently, roughening of the
internal surfaces is required not only to create
microretentions, but also to provide a clean ground
for a chemical bond of the luting composite with
remaining free radicals, if they still exist. This can be
achieved very simply by roughening with coarse
diamond burs or sand-blasting (Boyer et ai, 1984;
Latta and Barkmeier, 1994; Swift et ai, 1992)

Untreated
Treated

The application of a thin adhesive resin layer
over the inlay interface is still desirable for good
surface wettability. Some clinical and in vitro data
questioned the efficiency of these procedures
(Tam and Mc Comb, 1991; Scott et al, 1992; Kreci
et al, 1994) (Fig 10-14). However, the clinical and
SEM follow-up of semi-direct composite inlays
made with a modern restorative system did not
substantiate these observations, even after several
years of service (Gladys et, 1995; Spreafico et al,
1996).

Although the occurrence of partial debonding
between luting and restorative composites
presumably depends on the materials used, this
problem is unlikely to have major clinical
significance. Etching with hydrofluoric acidhydrofluoric acid and
silanizationsilanization (Matsumura et ai, 1995) of the
composite have been proposed to ameliorate this
bond

Actually, the etched surface may
subsequently be difficult to fully impregnate with
resin, which could result in the weakening of this
layer.

Clinical ApplicationClinical Application
Although it has been advocated, the placement of a
matrix prior to cementation is contraindicated
because it guides luting material excesses
subgingivally. The cement is preferably placed or
injected inside the cavity to facilitate manipulation
of the restoration. Insertion of the restoration has to
follow immediately, as polymerization activa-tion
will speed up at mouth temperature.

Clinically, the technique of two-phase
insertion (partial insertion-removal of main
cement excesses-complete insertion) is tricky
and, of course, contraindicated when using a fast-
curing dual cement. Overflows of luting composite
are removed, before polymerization, with a probe
and a brush damped in bonding resin, for
accessible margins; floss is best used
interproximally. A last consideration is that the
restoration has to remain held down during the
removal of cement excesses to avoid
unpropitious displacement.

Since these conditions are rarely encountered in
clinical reality, the use of dual-cure materials is once
more validated for the luting of adhesive restorations
(Uctasli et al, 1994). Because the efficiency of the
chemical activation of dual-cure composites is
insufficient, proper light activation remains essential to
ensure the optimal curing rate of the material
(Breeding et al 1991; Hase-gawa et al, 1991; Darr and
Jacobsen,1995; Peutzfeldt, 1995).

Therefore, powerful light-curing is mandatory.
It is also strongly recommended that each
restoration surface be exposed to the curing light
for at least one minute.
In this respect, it must be stressed that the
bulbs and light guides of the curing units have to be
regularly checked with a curing radiometer to make
sure they emit sufficient light energy.

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