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Dentin bonding agents
As we more through time, we are continuously faced with the opportunity to
change. This is true for our restorative materials, as it is for anything else. In order to
know whether or not we should change, we must have an understanding of where we
are currently. If the change mill not provide improvement is it wise to pursue?
How we determine improvement depends on our paradigm, our view of the
objectives of restorative dentistry. Traditionally, dentists have believed that slowing
down the restorative cycle as much as possible is the ideal persuit. We have in the time
that challenges that paradigm.
The earlier performance standard is centered on the concept of longevity. The
longer the restoration lasts, the fever the number of times a tooth will require restoration
in a lifetime. Therefore, pursuing a material that will withstand the rigors of oral
environment has long held our attention.
The materials commonly used for restorative purpose are amalgam, gold foil and
cast restorations.The main disadvantage of any of these restorations is ‘colour’.
Increasing environmental conserns and public awareness for tooth colored materials
have heralded patients to demand more esthetic, biocompatible materials such as
composites, glass inomer cements and porcelain.
Of all the innovative esthetic materials available today, the direct placement of
resin composite has assumed the current thrust in restorative dentistry .One of the
principle advantages in the use of these resin composites is the bondalility to the
enamel and dentin; which has been possible due to mostly improved bonding systems.
Dentin bonding agents have created a new in the field of dentistry, owing to its
property of adherence to the tooth structure by both micromechanical and chemical
means. This momentous change in dentistry is attributed to great scientists like Michal
Buonocore, Rafel Bomen, Nubo Nakabayashi, Fusyama.
Recent improvement in adhesive systems have generated a revolution in
dentistry, placing adhesive restorations on the front stage.Clinicians have been
confornted with this continuous and rapid turnover is adhesive materials. There has
been an ongoing process in developing more refined and diversified restorative
materials along with the production of steadily improving bonding agents creating
confusion as to which and is better.
This library dissertation discuses dentin bonding agents, with complete coverage
of the bonding systems, hoping that this would help dental professionals in
understanding bonding systems better.
HISTORY
DBA have developed over several decades. The various historical events, which
took place have led to our present day DBA.
1938 -Development of epoxy molecule by Castan
1951 -Development of glyerophosphoric acid dimetharylate molecule by
Dr.Oscar Hagger. This molecule permitted seen adhesion to dentin.
1952 -Usage of glyrerophosphoric acid dimethacrylate by Kramer and Mclean
(earliest description of hybrid layer)
1955 -Buonocore introduces etching of teeth any phosphoric acid; was he found
that an acrylic resin binds well with etched enamel.
1956 -Buonocore pioneers the work on adhesion to dentin. Initial DBA
developed was based on the glycerophospheric acid dimethacrylate
molecule and bonds to hydrochloric acid etched dentinal surfaces, but
bond strength diminishes greatly on immersion in water.
1957 -Bowen starts work on bis-phenol glycidyl methacrylate (BIS-GMA) resin
systems.
1962 -Bowen conducts first workshop on adhesive restorative dental materials.
1965 -Causton describes how primers work.
1982 -Bowen, Cobb, Rapson develop the multilayer adhesive system.
1982 -Nakabayashi reports the presence of hybrid layer.
1987 -Fusayama described the concept of total etching and bonding.
1991 -J.Kanca successfully promoted total etching
1997 -Ferrari et al establish the bonding mechanism of one bottle adhesive
system to condition dentin.
2000 -Evaluation of bonding ability of sixth generation bonding systems done by
Ferrari et al.
2003 -seventh generation by Ferrari et al.
1991 -J. Kanca successfully promoted total etching.
Enamel
Enamel is the hardest of the mineralized tissues of the body. It covers the
anatomical crown of the tooth. This tissue is very brittle in nature but protects the
underlying structure ie. dentin and pulp.
The inorganic component of enamel is principally appetite in its, hydroxyl, fluoro
carbonate forms. Calcium and phosphate are the two major inorganic elements
(Brudefold, steadmar and Smith 1960) minor narration occurs is composition is with
aluminum, barium, magnesium, strontium, radium and vanadium among others can be
found in the little.
Crystallites are embedded is as organic matrix with comprises less than 1% of
the nature of enamel (Estoe, 1963) less than one half of the organic component
contains protein high glycolic acid and sig anlt of proliferation and glucose contains
protein. During minimization of the crown, a significant shift occurs in the value of
organic material. The amenoblasts produce large amounts of organic matrix among
early phases of enamel development, then as crown saturation proceeds, the number of
organic matrix decreases while the number of inorganic material issues and
miniralization gradient (Chable and Darling 1960) exists in mature enamel, thus, the
outer portion of enamel is relatively more mineralized than the inner portions.
H2O exists in enamel in a significantly larger amt (up to 4% by value). About
25% of H2O is loosely bound to the crystallites.
A dynamic gradient anushing fluid exists b/w the pulp and oral environment
(Bergman 1963) in with enamel participates through its porous, permeable structures,
but enamel is selectively permeable (Darliag and Others 1961) allowing the passage of
H2O and cons but including large molecules (Poole, Fachy and Berry, 1963).
Histo-chemical studies have shown the complex nature of the surface
integument. This fully reacted low energy surface confers significance in the bonding
equations, as does the traumatically or operatively imposed tissue. An understanding of
the micro-morphological properties have been significant is remaining interactions b/w
enamel and bonding agents.
Dentin
Dentin forms the largest portion of the tooth structure. It is removed by the
enamel on the anatomical crowns and by root on the anatomical root internally it forms
the walls of the pulp cavity.
The dentin comprise of dentinal tubule that are small canals that extend across
the entire width of dentin, from DEJ/DCT to the pulp. Each tubule contains cytoplasmic
cell process (James Fiber) of an odontoblast. Each dentinal tubule is lined with a layer
of peri-tubular dentin that is much more mineralized than the surrounding inter-tubular
dentin. The number of tubules increases from DEJ (15000-20000/mn2) to the pulp (45-
65000/mn2). The dentinal tubules are filled with dentinal fluid which makes it a difficult
surface to bond.
The chemical composition of dentin comprises of 75% inorganic 20% organic
and 5% H2O and other materials. It is less mineralized than enamel but more
mineralized than cementum or bone. The minimal content of dentin increases with age.
This mineral phase is composed primarily of hydroxyapetite crystallites. The organic
phase is primarily collagen (Type I with traces of type IV of).
They consist of carboxyl, amino, hydroxyl surface groups. The other non-
collagerous constituents that can be found are dentin phospho-protein, sialoproteins of
ostecalcins. Dentin permeability is highly variable.Variation in permeability may arise
from tubular irregularities associated with mineral deposits, organic components of the
odontoblasts processes. An outward flow of dentinal fluid occurs because of a small but
positive pulpal pressure (10-15 mm Hg).
The permeability characteristics of dentin are of crucial importance in dentin
bonding because most of the current bonding systems rely on resin penetration or
infiltration into dentin(Transdentinal Permeation). Resin penetrates into tubules to form
tags that can contribute to resin adhesion. More important factor is permeation of resin
intointer-tubulardentin(Intra-dentinalPermeation).
Dentinal permeability is reduced with age and also in caries affected dentin as the
lumina becomes narrow or may get obliterated by deposition of intra-tubular crystals
and deposition of irregular sclerotic/reparative dentin.
ADHESION
Adhesion is definition by to “American society for testting and materials as “A
substrate capable of holding material together”.
The word adhesion is derived from the Latin word adherer, which means “ad”-to
and” hearer” to stuik. Adhesion refers to the attraction b/w the atoms and molecules at
the contacting surface of different materials (De Brayer et al 1951, Wake 1982).
In adhesive terminology ,adhesion or bonding is the attachment of one substrate
to another. The surface of the substrate that is adhered to is termed as adherent. The
adhesive /bonding agent may be defined as the material that when applied to the
surface of the substrate can join them together, resist separation and transmit loads
across the bond.
An important requirement for any of these interphase phenomenons to take place
is that two materials being joined must be sufficiently close and in an intimate contact
and besides this sufficient wetting of the adhesive only occurs if its surface tension is
less than the surface energy of the adherent. If the adhesive had a high surface
tension, then it would roll up into droplet and not wet the surface.
Based on this theory of melting and surface free energies, adhesion to enamel is
much easier to achieve than adhesion to dentin. This is because enamel is primarily
made up of hydroxyapetite without has a high free surface energy whereas dentin has
a low free surface energy because it is composed of two distinct materials
hydroxyapetite and collagen.
In the oral cavity, the tooth surface is normally covered by a pellicle. This
salivary pellicle is organic in nature and has a low critical surface tension that impairs
adequate wetting of the adhesive. Moreover, instrumentation of the tooth substrate
during tooth preparation produces a smear layer which has a low surface free energy.
Hence, the natural tooth surface should be thoroughly cleaned and pretreated prior to
bonding procedures to increase the free surface energy.
Types of Adhesion
Van Noort in 1994 suggested that one or more of the following mechanisms can
create an adhesive bond:
1. Mechanical Adhesion
Here, retention is by the interlocking of one phase into surface of another. This
type of adhesion can be due to
a. Geometrical effects
These are caused by microscopic porosity or roughness of the surface
ie.mechanical locking provided by undercuts, grooves etc.
b. Rheological effects
This is caused by flow of materials in both liquid and semisolid phase
Mechanical adhesion also referred to as micro mechanical adhesion ,results from
the presence of surface irregularities that give rise to microscopic undercuts. The liquid
adhesive can penetrate these undercuts and once set is locked in them. A prerequisite
for this form of adhesion is that the adhesive can readily adapt to the surface of the
substrate. The adaptation is determined by the wettability of the adhesive on the
substrate, the ideal situation being that of perfect wetting when the adhesive spreads
spontaneously over the surface. The degree of penetration of the adhesive may also
depend on the pressure used during application of the adhesive that helps to force the
adhesive into surface irregularities.
The adhesive disengages from the substrate by fracturing because it cannot be
withdrawn from the undercut. This is not unlike the concept of retention used for
placement of restorations except that it occurs at a microscopic level. However, one
important difference is that good wettability is not a perquisite for micro-retention
whereas for micro-mechanical interlocking it is of paramount importance. Examples of
micro-mechanical adhesion one:
a. Resin to enamel bond
b. Resin to ceramic bond for veeners and inlays
c. Resin metal bond for resin bonded fixed partial denture
II. Physical Adhesion
When two surfaces come in close proximity to one another secondary forces
of attraction can be generated through dipole-dipole interactions. The polar
reaction occurs as a result of attractive forces between the positive and
negative charges on the molecules. The magnitude of the interaction energy
is dependant on the mutual alignment of the dipoles.
This type of bonding is a rapid and reversible process because the molecules
remain chemically intact on the surface. Therefore, this weak physical
adsorption is also easily overcome by thermal energy and is not suitable is a
permanent bond is desired. It follows that non-polar liquids will not readily
bond to polar solids and vice-verse, because there is no interaction between
the two substances at the molecular level even if there is good adaptation. A
familiar example of this problem is the inability of hydrophobic silicone rubber
impression materials to adapt to the hydrophilic moist surfaces of the soft
tissue (This problem is overcome by the use of surfactant).
III. Chemical Adhesion
If an adsorbed molecule dissociates on contact with a surface and constituents
alone rearrange themselves in such a way that as for covalent, a strong adhesive bond
can result. This form of adhesion is called as chemisorption. The features that
distinguishe the chemical bond from the physical type of interaction described
previously is that a chemical reaction takes place between the molecules and the
surface molecules of the substrate. Adhesives must be strongly attracted chemically to
the surface of application to form strong bond and require identical reactive groups on
both surface.
Covalent bonding occurs for an isocyanate adhesive which can bond to soft
tissues via surface hydroxyl and amino groups. Another such bond is believed to occur
b/w the hydroxyl groups of the glass polyalkonate and the calcium ions in the enamel
and dentin.
In some instances the formation of a chemical bond will not take place
spontaneously. This is the case with the metal to metal bond where high temperatures
ellicited by soldering, brazing or welding are needed to encourage the formation of a
bond .Another example is the porcelain to metal bond with is formed when the ceramic
oxide fuses with the oxides on to the metal surface when the restoration is faces high
temperature.
IV Adhesion through molecular entanglement
So far it has been assumed that there is a distinct surface b/w the adhesive and
the substrate. In effect, the adhesive as adsorbed on the surface and can be
considered surface active. If the substrate is permissive to adhesive is able to
penetrate through the surface of the substrate and absorb into rather than adsorb oncto
the substrate. If the absorbing molecule is a long chain molecule or better still forms
polymers within the pretreated layer, the resultant enlargement b/w the adhesive and
the substrate is capable of producing very high bond strength.
This approach is being adopted for resin bonding system.
The coupling agent utilizes the concept of hydrophilic and hydrophobic groups
i.e. it consists of a bi-functional molecule one part of outers into a chemical union with
the tooth surface whilst the other attaches to resin.
The coupling agents have basically the formula.
M-R-X
M- Methacrylate group, which eventually becomes bound to the resin by
copolymers.
X- represents a reactive group with interacts with the tooth surface. The
reactive groups are end groups.
R- is the clearing and spacing group spacing group must be able to provide
the necessary flexibility to the coupling agent to enhance the potential for
bonding of the reactive group. If the molecule is excessively rigid, the
ability of the reactive group to find a satisfactory conformational
arrangement is jeopardized
Eg-etyl / oxypropyl.
In N- Phenyl, glyine glycidyl mehacrylate a shelate bond is found between the N-
phenyl glycine group is the calcium of the tooth, while the methacrylate group becomes
incorporated into the resin during polymerization. Another coupling agent with works by
chelating with adhesive is 4-META.
Bond strength of these coupling agents can be increased by pre px with certain
mordant sons such as ferric and aluminum cons in the form of aqueous solutions of
their chlorides/oxalate salts. A strongly bond surface layer concentrated in cons
capable of reacting with the chelating species is formed. Systems based on the
complied used of mordant cons and coupling agents are non-becoming available. The
exact mechanisms or role of these mordent cons is not known. But it is possible that
the ionic solutions are supplying acting as weak acid without solublize and re-precipitate
the dentin smear layer. In some cases the acid may etc the dentin, opening up the
dentinal tubules and encouraging mechanical attachment.
A procedure with can be classified as multiplayer system has been suggested.
This system enacts the Rx of the mechanically prepared cavity with a ferric oxalate
solution and an acetone solution of NPG-GMA or NTA-GMA. An acetone solution of
PMDM (the reaction product of promellitic diaxhydride and 2- hydroxyl
ethylmethacrylate) is placed and surface is air brown. Finally, the composite restorative
materials is inserted and polymerized.
The chemistry of such Rx is based on the assumption that the Rx with ferric
oxalate solution initiates several reaction with the smear layer, resulting is a process
layer cross-linked with metal ions. The layer constitution insoluble icon phosphospate
and calcium oxalate attached to a continuous structure.
During Rx with NPG-GMA these monomer are bonded to icon (III) ions by
coordinative bonds. A continuous film is formed by polymerization of the methacrylate
groups NPG-GMA contains benzers wings rin’s in II electrons. During Rx with PMDM
monomer, this monomer is bonded to NPG-DMA by II complex or change transfer
complex formation.
The disadvantage of this system is discolonathprine due to reaction products of
ferric oxalate. In “tenure” ferric oxalate has been replaced with aluminum oxalate.
Other coupling agents with primarily bond to the inorganic component of dentin
contain reactive phosphate groups. The interfaced bond is stabilized through
attractions b/w the negative changes of oxygen on the dentin surface.
The bond strength to9 dentin produced by this type of adhesive is typically
around 5MPA although it is not certain how double this bond is in moist environment.
This R-O-P bond is thought to becomes hydrolyzed leading to a gradual reduction in
strength M-R-X, here X= O-P
Coupling agents utilizing this concept of hydropholic and hydrophilic groups are
the monomers based on phosphates or phosphonates. The hydrophilic PO4 group is
thought to interact with the calcium cons of dentin.
All the systems are basically adhesive molecules with a potential for calcium
bonding.
It can be decided into 3 groups
1) Phosphate based adhesive
M-R1-POYZ
2) Adhesive based on amino acid
M-R2-NZ-R3-COOH
3) Adhesive based on dicarboxylic acid
M-R4-COOH
COOH
All these involve attraction between negative changes on the adhesive and
positive changes on the tooth calcium ions.
Chemistry of adhesive systems
Dentin bonding systems contain monomers that have hydrophilic and
hydrophobic groups these provide a stable back with the dentin and the restoration.
The chemistry of adhesive agents can be explained as.
Chemical adhesion.
Adhesion by coupling agents.
Adhesion by grafting reaction.
CHEMICAL ADHESION
There are two types of chemical adhesion
Primary valence Foxes
Covalent bonds
Co-ordinative bonds
Ionic bonds.
Secondary valence foxes
Intermolecular adhesion (Vander Waal’s foxes)
Hydrogen bonds.
ADHESION BY COUPLING AGENTS
Sampling agents utilizing the concept of hydrophobic and hydrophilic groups are
the monomers based on phosphate or phosphoxate.
The hydrophilic PO4 group interacts with Ca+ ions in dentin. This type of
adhesion us seen to occur with the non-electrolyte adhesion. Bonding can be
accomplished to the organic part of the dentin hydroxyapetite, or to the organic part else
of coupling agents for bonding leads to only minor improvement in the bond strength.
One coupling agent was 3-methacryloyloxy propyl trimethoxysilane. Another coupling
agent was a butylanylate acrylic and copolymer with free carboxylic acid groups. NPG-
GMA is another coupling agent used.
I. Clinical factors affecting Adhesion
Salivary or blood contamination
Difficulty in controlling saliva or blood while accomplishing restorative dental
therapy is a significant challenge. These contaminants act in a negative manner for
adhesion. Although dentin is a not substance, the constituents of saliva and blood
create an environment that can destroy dentin bonding.
It has been prove that if contamination soon after etching the bond will fail while if
contamination occurs after enamel and dentin surface are etched and a bonding agent
has been used over these surfaces, the bond will not be compressed. Rubber dam and
other dry field acids should be used to prevent contamination.
Moisture and Oil contamination from Handpiece
Water leakage fro ioroter hand piece or air H2O syringes is an unrecognized
problem in most situation. The moisture of H2O with restorative or bonding resin is
interferes with adhesion of bonding agent to the tooth stuitane.
The oil contamination may be due to oil coming from air compresses without not
maintained well, Contamination with oil provides compredictable with oil provides im-
predictable clinical results and potential clinical features.
Surface Roughness of tooth structure
Increased surface area created by surface roughness results in cutting bonds
with dentin mechanical retention may be increased by the microscopic roughness
produced on dentin or enamel by rotary cutting instrument tungsten carbide thus when
used create more irregular surface than diamond layers.
Mechanical undents in tooth preparation
The mechanical underints placed in the tooth structure hold the restorative
material from bodily displacement from the preparation, microscopic movement caused
by thermal/ polymerization influences. This type of retention is further argument with
the cement generation of DBA.
Dentinal canal characteristics
Dentinal canals at the external surface of tooth roots or near the DET have small
diameters. As dentinal canals are observed loser to the dentinal pulp, they become
larger. Older dentin has small dentinal canals, while younger dentin has larger
dentinal canals. Superficial abounded dentin may have included canals. If the
canals are small, attachment is less and vice versa.
Presence of plaque, calculus, extrinsic stains/debris
Any enamel/dentin surface that requires bonding must be scrupulously cleared
before the bonding procedure begins. Plaque present on the tooth surface prevents
etcher with 37% phosphoric acid. Penetration of plaque by the acids used in DBA is
not possible and will result in a clinical adhesive failure. Tooth surface stains and
dental calculus if not removed will not permit bonding.
Presence of basis on liners on F
The presence of varnish eliminates the potential to bond restorative material to
the tooth surface. Liners may result in creating moderate bonds with dentin but the
bond strength is significantly lower than that created by placing seen on acid etched
enamel surfaces.
Tooth dehydration
Ever drying the tooth preparation before placing bonding agents should be
considered to be a negative factor. Drying only till the obvious shine of moisture is a
good clinical guide.
Dentin Bonding Agents
The DBA are di or multifunctional organic molecules that contain reactive group,
which interact with dentin and the monomer of the restorative resin.
Co
+A D
A
Components of DBA Conditioner
Premier
Adhesive
Requirements of DBA
Ideally, dentin-bonding system should have
Sufficient bond strength, optimum 11-20 Mpa
Be compatible with dental tissues
Provide in immediate permanent high strength bond to dentin
Minimize micro-leakage at the margins of the restoration
Prevent recurrent caries and marginal staining
Easy to use and less technique sensitive
Reasonable shelf life
Compatable with all resins
No reduction in bond strength when applied to moist surface
No potential for sensitization of patient on gerator
Problems in Bonding to dentin
The developments of adhesives that adhere to dentin have still been and still
remain a challenge to researchers.
Dentin consists of 50% of volume inorganic HAP, 30% organic material and 20%
volume of fluid.
Dentinal HAP is randomly arranged in an organic matrix
The high fluid content of dentin places certain requirements on restorative dental
material (resin are hydropholic).
The tubular nature of dentin provides a valuable area through which the dentinal
fluid might flow to surface and adversely affect adhesion.
Sucrosed dentin if present is difficult to penetrate (results from aging or mild
irritation and causes a change in the structure of primary dentin is the peri-tubular
dentin becomes wider, gradually filling the tubular with calcified material. The
areas are harder, denser, less sensitive)
Presence of inter-tubular and peri-tubular dentin, each tubular is suspended by a
collar of gyper-mineralized dentin called peri-tubular dentin. The less mineralized
dentin between the tubules is called inter-tubular dentin.
The presence of smear layer complicates dentin bonding. The smear layer is
present on cut dentin surface and is of limited strength so it must be either
removed or penetrated by the resin.
Permeability of dentin differs at different sites variation is permeability may arise
due to tubular irregularities associated with mineral deposits. It also increases
resin the pulp and pulp horns than the adjacent areas.
CLASSIFICATION OF DBA
1. Depending on chemical composition
2. According to generation
3. According to treatment of linear layer
4. According to chronology, chemistry and sear bond strength
5. According to mode of curing
6. According to their adhesion strategy towards enamel/dentin or on the
basis of number of clinical application
7. According to type of solvent
1. According to their chemical composition (Craig)
Polymethanes
Polyacrylic
Organic phosphonates
Mellitic anhydride and methylmethanylate (M-META)
Hydroxyethyl methacrylate + Glutealdehyde (HEMA+GA)
Ferric oxalate + NGP-GMA (N-phenyl glycine and glycidyl methacrylate)
+PMDM pyromethalic dianhydride and 2HEMA)
2. On the basis of treatment of smear layer
The smear layer of limited strength, so it must be either removed or modified
before application of bonding agent
a. Removed
Example: -
Tenure (nitric acid)
Mirage bond
Clearfil liner bond systems
b. Preserved
Example: -
Scotch ond dualina
Prisma universal bond
c. Modified
Example: -
All bond
Scotch bond 2
XR bond
IV on the basis of shear bond strength (Elik et al.)
Included dentinal adhesives without produce shear bond strength of 5-7Mpa
Example: -
Dentin adhesit
Scotch bond dual cure
Glynia
Category 2
Included the experimental and commercial products derived from Bowers work
with ferric and aluminium onalalates and have produced shear bond strength between
8-14 Mpa
Example: -
Tenure
Mirage bond
Category 3
Included dentinal adhesives, without produced shear bond strength values of
about 17-20Mpa
Example: -
Super bond
Scotch bond 2
Scotch bond multipurpose
All bond
(Decreased failure was cohesive in nature)
V. According to their mode of curing
- Clinical sure
Example: -
Amalgabond plus
- Light cure
Example: -
One bond
Glunia comfort bond
- Dual cure
Example: -
Clearfil linear bond 2V
Prime and bond NT dual cure
Category III:
Included (dentinal adhesives, which produced shear bond strength values of
about. 17-20 MPa.
Ex: Super bond
Scotch bond 2
Scotch bond multipurpose
All Bond
The failure was mainly cohesive in nature
According to their mode of curing
1. Chemical cure
Ex: Amalgam bond plus
2. Light cure
Ex: One Bond
Gluma comfort Bond
3. Dual cure
Ex: Clearfil liner Bond 2V Prime and Bond NT Dual cure
On the basis of Generations:
1.1-Generation Dentin Bonding Agents
Developed by Bowen - 1965.
Agents used in this generation are:
a. Glycerophosphoric acid dimethacrylate,
b. Cyanoacrvlates
c. NPG - GMA
d. Polyurethanes
Buonocore four decades ago found that a resin containing GPA-MA could bond to
Hcl etched dentin surfaces. However, the bond strength was by water. To overcome
this problem Bowen synthesized NPG-GMA a surface-active comonomer that
theoretically produced water resistant bonds. NPG-C, MA acted as an adhesion
promoter b/n the toot-h structure and resin material by chelating with surface calcium.
Disadvantages:
Poor clinical results
Hydrolysis of GPA-DMA in oral environment
Difficulty - in bulk polymerization of cyanoacrylates
Instability of NPG-GMA in solution
Hydrophobic resin
Low bond strength (2.1 - 2.8 Mpa)
Ex: Cervident (S.S.White Co.)
First commercially available dentin bonding agent.
Cosmic bond (Amalgamated Dental)
Palakav (Kulzer, USA)
2. II Generation Dentin Bonding Agents:
In general, the second-generation dentin bonding agent was much improved
compared with the first generation. These were developed during the early 1980's.
Most of the agents were primarily - (polylmerizable phosphates in BIS-GMA)
resin
1. Halophosphorous esters of BIS-GMA. Hence they were called as phosphate-
bonding systems.
2. Polyurethane based compounds were also used.
The bonding mechanism involves a surface wetting
Phenomenon as well as ionic interaction b/n phosphate groups and dentinal calcium.
The 11-generation systems required a smear laver intact. This was to create a
Ca+ rich layer where the phosphate can combine with Ca+.
Disadvantages:
1. Low bond strength (1-3 Mpa) (studies by Relief and others 1986 and Solomon &
Beech)
2. Hydrolysis of phosphate Ca+ bond.
A major reason for the poor performance of these bonding agents is the fact. that
these bond to the smear laver rather than to the dentin itself.
Ex: Scotch bond dual cure ('OM Dental)
Bond Lite, (Kerr)
Dentin Bonding Agent (Johnson &. Johnson) Prima Universal
Creation Dentin Bonding Agent
Clearfil (Kuraray)
3. III generation Dentin Bonding Agents
Developed in mid 1980s
The third generation dentin adhesives showed increased bond strength and
improved clinical performance.
These systems required either total or partial removal of the dentinal smear laver.
In addition they required a surface-conditioning step. They used a solution or a
series of solutions to increase the wettability of dentin (i.e. priming solution).
Their mechanism of bonding to dentin was by penetration of smear layer i.e. they
used micro mechanical means of adhesion rather than the unreliable chemical bonding
of previous material.
Disadvantages:
Time consuming (More of number of steps)
Technique sensitive
Ex:
Gluma (Bayer Dental)
Conditioner: EDTA 17%
Primer: 35% 1-iEMA (Adhesion Promoter)
5% Glutaraldehyde
Resin: 55% BISGMA 45% TEGDMA
Bonding was achieved by
Glutaraldehyde bonds to amino groups in collagen
Charge compounds
Reacts with
OH group of HEMA
And causes mechanical interlocking in the opened ends of dentinal tubules
2. Tenure:
Oxalate was the first available dentin-bonding agent developed by Bowen.
Conditioner: 2.5% nitric acid + ferric oxalate (stains the teeth).
SYSTEM CONDITIONER ADHESION
PROMOTER
BA
1 Gluma 17% ED'FA 35% HEMA
5% GA
55% BISGMA
TEGDMA
2 Scotchbond 55% HEMA
2.5% Maleic
acid
BIS-GMA
HEMA
3 TENURE
(10.2-18.2
Mpa)
1% Nitric acid
2% Phos. Acid
2.5% Aloxalate
5% NTG- GMA
PMDM
BIS-GMA
TEG- DMA
4 4. Prisma Univ.
Bond 2
30% HEMA
6% PENTA
50% UDMA
25%TEG- DMA
4.5% PENTA
0.5% GA
4. Fourth Generation Dentin Bonding agent:
In these systems there was complete removal of smear layer.
Consists of primer and adhesive.
These bonding systems involved the "Total etch" technique that is simultaneous
etching of enamel and dentin with phosphoric acid or other acids. An improvement in
dentinal bond strength by etching was first demonstrated by Fusayama in 1979 and
became common in Japan. This gained acceptance in US much later. This is because
etching of dentin has been traditionally discouraged because of pulpal inflammation but
it is found that very little acid actually penetrates dentin.
These systems were also known as Universal bonding systems as these bonds to
dentin, enamel, amalgam, porcelain and composite.
Mechanism of bonding
The mechanism of bonding offers for mild and strong etch adhesives
Mild Sea (PH- I2)
In this type of adhesive, 2 types of bonding are seen i.e. Hybridization +inter-
molecular bonding.
Here, the H.L is of such micron size and resin formation is less pronounced. In
the H.L, HAP is not removed completely because of the weak acid. So a second type of
bonding occurs, is a HAP act as a receptor for additional molecular interaction with
specific carbonyl or PO4 groups of the monomer.
Eg- The primary sonic bonding, potential of unifil bond GC., 2 carbonyl groups of
YMETA with HAP were conformed in XP5 &TEM this 2 fold bonding mechanism may be
advantage in terms of restoration longevity.
Strong SEA (PH 1)
This is regular to the total etch systems.
Mechanism of bonding is by hybrid layer. Formation he nearly all HAP is removed
from collagen and thus any chemical reaction between HAP and function of
monomers are excluded.
ADVANTAGES
Simplified bonding process (-no post condition panix simultaneous demineralized
and resin infiltration).
No etch and rinse phase.
Nano-leakage is reduced.
Dentin is covered at all times.
Reduced postoperative sensitivity.
Possibility of single dose packaging.
Consistent staple composition
Controlled solvent evaporation
Hygienic application (chances of noss infertum are less)
Possibility of particle filled adhesive carts as shock absorber).
Adequate monomer collagen infiltration.
Effective dentin desensitizer
Time saving.
DISADVANTAGES
Insufficient long-term clinical research.
Adhesion potential to enamel needs to the clinically proved yet.
GLASS IONOMER ADHESIVES
A third adhesion strategy differs from former approaches (perused by resin-
based systems), as it involves glass-ionomer based interaction with the tooth substrate
with the development of resin modified glass ionomer adhesives have that can bond
resin to the tissue. A two-fold mechanism of adhesion is predicted acid pre-Rx without
creases the tooth surface and exposes and surface collagen fluids to a depth of 0.5 to
1m depth.
Here, micro-mechanical bond (due to resin inter-diffusion) and a chemical bond
(due to ionic interaction of the carboxyl groups of polyalkenoic acid with ca of HAP that
reward attached to the collagen fibrils) take places. The underlying mechanism of glass
ionomer adhesives and is similar to that of mild etch adhesives.
A network of hydroxyapetite- coated” collagen fibrils interpenetrated by povers is
typically exposed to a depth no deeper than 1m. Up to 0.5 m thick layer, often
referred to, as “get-phase” remains attached to the tooth surface despite the conditioner
being rinsed off.
The basic difference with the
First (I) Generation Dentin Bonding Agents
This was developed by Bowen in 1965.
Agents used in this generation are
a) Gylycerophosphoric acid airrethacrylate.
b) Cyanoacrylates.
c) NPG-GMA.
d) Polymethanes.
Buonocore four decades ago found that a resin containing GPA-MA could bond
to HCL etched dentin surface. However, the bond strength was affected by the matter
content. To overcome this problem, Bowen synthesized NPG-GMA, a surface-active
ionomer that theoretically produced water resistant bonds, NPG-GMA acted as an
adhesion promoter between the tooth structure and resin material by relating with
surface calcium. (N-phenyl glycine and glycidyl methacylate).
Disadvantages
Poor clinical results
Hydrolysis of GPA-DMA in oral environment
Difficulty in bulk polymerization of cyaroarrylater
In stability of NGP-GMA in solution
Hydrophobic resin
Low bond strength (2.1-2.8 Mpa)
Example: -
1. Cervident (S. S. White Co) (first commercially available DBA)
2. Cosmic bond (Amalgamated dental)
3. Palakar (Kulzer, USA)
Second Generation Dentin Bonding Agents
In the late 1970’s, the second-generation systems were introduced. Majority of
these had halo phosphorous stress of unfilled resins such as bisphenol-A glycidyl
methacrylate (Bis-GMA), hydroxyethyl methacrylate (HEMA). These were weak bonds
seldom increasing 1-3 Mpa. But were an improvement over the first generation
systems. However, in these systems the phosphate bond to calcium in dentin was not
strong enough to resist the hydrolysis resulting from H2O immersion. This hydrolysis
resulting either from saliva exposure/moisture from the dentin caused micro-leakage. In
these systems dentin was not etched, hence much of the adhesion was due to bonding
to the smear layer.
The inethane / isocyanate groups from covalent bonds with hydroxyl groups in
both organic and inorganic part of dentin. The adhesive mechanism of these second
generations bonding agents involved enhanced surface wetting as well as ionic
interaction between negatively charged PO4 group and positively charged Ca. It was
speculated that the clinical failure was due to inadequate hydrolytes stability in the oral
environment and become then primary bonding was to SL rather than the underlying
dentin. The presence of an intermediate SL presented intimate resin contact without is
a prerequisite for a chemical reaction.
Disadvantages
Low bond strength (1-3 Mpa) (studies by relief and others 1986 and
Solomon and beech)
Hydrolysis of and PO4, Ca+ bond
Example: -
Scotch bond dual cure
Bond lite
Prima universal
Clearfil
Third Generation Bonding Agents
There were developed in the mid 1980’s. In this generation, the acid etching of
the dentin partially removed or modified the smear layer. The acid opens the dentin
tubules partially and increases their bonding permeability. The acid must be rinsed
completely before application of primer. The primer contains hydrophilic resin modifies
like hydroxyethyl trimellitate anhydride and bio-phenyl dineth arylite. The primers
contain a hydrophilic group that infiltrates the dentin and the hydrophilic group that
adheres to the resin. The dentin primers usually used in this generation system were
6% PO4 penta-acrylate (PENTA) 30% HEMA and 64% ethanol. After the application of
primer the unfilled resin adhesive is applied. The most of these systems, the PO4
primer modified the SL by softening it after penetration. The adhesive is then applied
attaching the cured primer to the composite resin. However, bonding was not the
successful decrease the resins did not resin penetration is superficial penetrates the SL
and SL was may weak.
Disadvantages:
Time consuming
Technique sensitive
Example: -
Scotch bond and dentin bonding systems
XR bonding system
Gluma bonding system
Tenure dentin bonding system
4-META
Phenyl I-P
Mirage bond
Super bond
Prima universal bond 2 and 3
Clearfil liner bond
Fourth Generation Dentin Bonding Agents
This generation appeared in the early 1990’s. The complete removal of the SL
was achieved in this generation. Fusayama and colleagues tried to simplify bonding to
enamel and dentin by the preparation of 40% phosphate acid for etching of enamel and
dentin. Unfortunately, it was not understood that dentin and resulted in the collapse of
exposed collagen fibers due to over drying and acid. The use of total etch was one of
the main characteristics of this generation. This technique permits the etching of
enamel and dentin simultaneously using phosphate acid for 15-20seconds. The surface
must be left moist should not be over dried, however in order to avoid collagen collapse.
The application of a hydrophilic primer can infiltrate the exposed collagen network
forming the hybrid layer (Nakahayashi resin 1982). The formation of resin tags and
adhesive lateral branches complete the bonding mechanism between the adhesive
material and etched dentin substrate. The mineralized tissue of the peri-tubular and
inter-tubular dentin are dissolved by the acidic caution, the initial surface penetration
exposes the collagen fibulas. In this area, for a depth of 2-4 micrometer (Nakahayashi
1982) hybridization taken place and resin tags can seal the tubule orifice purely. This is
thought to be the primary boning mechanism of most of the current adhesive system.
There are bonding systems that use etching of denting with phosphoric acid or other
acids.
The fourth generation is commonly known as multi-purpose bonding systems as,
1. They can be used in cavities for both enamel and dentin
2. Same of their components can also be used for bonding to substrates such as
porcelain and alloys. In each case, the mechanism of bonding is micro-
mechanical into etched / grit blessed surfaces.
The components of this generation are a set of chemical agents that proceed in a
sequence from an initially hydrophilic component through to gradually more hydrophilic
components. The term bonding agent no longer covers this multi-step application,
procedure and has been replaced by adhesive system.
Fusiyama in 1979, but the concept of total etch gained would wide acceptance
only recently. It was mainly discouraged before became total acid etching was thought
to produce pulp inflammation. The bonding system of this generation is basically a 3-
step process. This was also called as a mineral binding system.
1. Conditioning
2. Primer
3. Adhesive
Example: -
Opti bond
Probond
Scotch bond multipurpose
Clearfil liner bond
Amalgam bond plus
Advantage
Mets better
Bonds to met surface
Disadvantages
Unless the primer and adhesive are applied consequently, the overlying
composite resin will not bond to the surface.
In the fourth generation system, the clinician had an option of converting the DBA from
a light curing to a dual curing one. This was carried out by a self-activating agent
(sulfuric acid derovative) to the bonding agent (I: 1 ratio).
Fifth Generation Dentin Bonding Agents
To simplify the clinical procedure by reducing the bonding steps and thus the
working time, a better system was needed. Also clinicians needed a better may to
prevent collagen collapse of demineralized dentin. So, the 5th generation bonding
systems were made.
It consists of different types of adhesive materials “One bottle system” (JIDA
Mason and Karca 1997).
One bottle system
These systems complained the primer and adhesives into one solution to be
applied after etching enamel and dentin simultaneously with 35 to 37% of phosphoric
acid for 15 to 20 seconds. These bonding systems create a mechanical interlocking
etched dentin by means of resin tags, adhesion lateral branches and hybrid layer
formation and show high bond strength values both to etched enamel and dentin.
Sixth Generation Dentin Bonding Agents
The sixth generation bonding systems are characterized by the possibility to
achieve a good to enamel and dentin using only one solution. The first evaluation bond
to conditioned dentin while bond to enamel was less effective. This may be due to the
fact that the sixth generation systems are composed of an acidic solution that cannot be
kept in place, must be refused continuously and have a PH that s not enough to
properly etch enamel.
Recently, a H2O based bonding has been introduced with centries with the
functions of a conditioner, the primer and the adhesive. The active solution is mixed
from two components resulting in the formation of an acidic (self conditioning)
Moreover, without superficially etches dentin and enamel. The dentin bond mediated by
this bonding agent seems to be adequate. However, the etching pattern that produced
by phosphoric acid etching
Example: - It has 3 compartments
Compartment 1: Containing methgcrylated phosphoric acid, enters, photo
initiators, stabilize
Compartment 2: Contains water, complex fluoride and stabilizes
Compartment 3: Has a micro brush
The blister is activated by squeezing comportment 1, they realizing its content
into compartment 2. The mixing ratio is 4:4.1 and the freshly mixed solution is released
on the micro brush into compartment 3.
On applying this to dentin, the SL well be dissolved. Then the demineralized
dentin is leading with group with prop monomers leading to the formation of a hybrid
layer.
Seventh generation Binding Agents
His example is the latest addition in the saves of bonding systems.
According to manufactures, it a fluoride releasing, self-etching type of bonding
agent. It has a color changing capacity.
The etching, priming and bonding is one simple application with no rending or
drying.
It is available in two bottles, which have to be mixed and filled in the cavity.
Manufactured by a company called J Monta (USA) and the product is ONE UP
BOND F.
This is the only bonding system, which provides visual confirmation of complete
polymerization by color charge.
YELLOW PINK WHITE
(Liquid A and B) (Liquid A & B mixed) (Completely cured)
Manufactures are claiming that this bonding system blocks postoperative
sensitivity.
Another manufacturing company H KULZAR have brought a product “BOND” in
the market this has a single bottle system having self etch priming and bonding along
with desensitizing capacity.
It has the advantage of single bottle system and no need of mixing of any liquids.
SMEAR LAYER
Introduction
Knowledge of the nature, structure and composition of the prepared surfaces of
the teeth is the key to the formulation and understanding of adhesive destructive
systems.
Smear layer was first suggested by Skinner (1961). It was first decreased in
detail and termed as “smear layer” by Boyde et al (1963)
The SL encompasses of any debris remaining on enamel, dentin or insertation
after instrumentation and conventional methods of cavity preparation.
The S.L can be discussed under the following:
Composition.
Formation.
Size.
Attachment to dentin.
Potential advantages/disadvantages.
Composition
Smear layer in composed of debris generated during cavity preparation. Eculian KD
lists the following as its components.
Inorganic tooth particles.
Bacteria and tissues
Saliva.
Blood.
Smear layer is rich in nitrogen sulphur, carhon. The organic component consists
of coagulated proteins denatured by functional heat during cavity preparation.
The presence of hydroxyapetite crystals in S.L is because of its breaking away
front the organic matrix and then resetting in the smeared at matrix.
Formation
Smearing occurs when hydroxyapetite within (the tissue) is either phuked out or
broken or swept along the resets in the smeared out matrix.
Studies have shown that temperature will rise up to 6000C in dentin when it is cut
without a coolant. This valve is significantly comer than the melting point of appetite
(15000C – 18000C) and has led to collude that smear layer formation is a
physiochemical phenomenon rather than a thermal transformation of appetite involving
mechanical shearing and thermal dehydration of the protein. Plastic flow of
hydroxyapetite is believed to occur at low temperatures that its melting point.
Size
The smear layer thickness is about 5-10 microns but according to some studies it
may range from 1-5.
The size of the smear layer is influenced by the type of bur used, it speed of
rotation and presence on absence of coolants.
The steel and tungsten carbide bur produce an undulating pattern there is a rapid
deterioration of the cutting edges. The cutting efficiency of these burs increases the
frictional heat resulting in the smear layer formation.
This smear layer formed is irregular in shape and non- uniform in size and
distribution, and remains on the prepared surface even after thought levage with mater.
The diamond burs produce relatively deep and uniform groves.
Significant difference exists between diamond burs used etch and without a
coolant (water spay). The smeared debris does not form a continuous layer but exists
as localized islands with discontinuities exposing the underlying dentin. The mater
spray does not prevent smearing but significantly reduced its amount and distribution.
The smear layer consists of two separate layers
Superficial layer (outer) loose debris
Layer loosely attached to underlying dentin (Inner) plug formation
Attachment to the underlying tissue
The smear layer is not always firmly attached to or continuous over the substrate.
It may lift free in come cases.
Potential Advantages & Disadvantages of the smear layer
The main advantages of the presence of smear layer on dentin.
Reduction of dentin permeability to toxins and oral fluids.
Reduction of diffusion (usually inwards) & connection (outwards by hydrostatic
pressure or inwards example by cementing restorations) of fluids prevents wetness
of but dentin surfaces all to Brannstorm et al (1974) and Johnson et al (1976).
Bacterial penetration of dentinal tubules is prevented (Vojinovic et al 1973, Michelich
et al 1980 Orgart et al 1974).
The main disadvantages are:
It may harbour bacteria, either from the original various lesions or saliva without may
multiply taking nourishment from the S.L or dentinal fluid.
The S.L is permeable to bacterial toxins.
The S.L may prevent the adhesion of composite resin systems, bonding agents,
glass ionomer polycarboxylate cements all to Schullen (1988), Dahl (1978), Powis et
al (1982), Asmussen et al (1988) and Erickson (1989).
HYBRID LAYER
Sending to acid etched tooth surface requires an air-dried surface to allow the
photo-polymerizable hydraulic bonding agent to be drown by capillary attraction into the
pits created by acid etching. As a result, two kinds of tag- like resin extensions are
formed.
Macro-tags are formed at the cores of enamel primes where the resin curves into
a multitude of distinct hypts of dissolved hydroxyapetite crystals,
The underlying mechanism of adhesion to dentin is alike for three or two step
total etch adhesives the dentin smear layer produced during cavity preparation removed
by the etch and rinse phase which results in a 3-5m deep demineralization of the
dentin surface. Collagen fluids are nearly completely uncovered front hydroxyapetite
and form a macro-retentive network for micro-mechanical interlocking of monomers this
interlouh was first discussed by Nakabayashi, Kojima & Masuhma in 1982 and is
commonly referred to as Hybrid layer.
Concurrent etch hybridization, resin tags seal the implugged dentinal tubules and
offer additional retention through hybridization of the tubule orifice mall.
Three specific ultra morphologic features have been described as resulting from
this hybridization process.
Shag carpet appearance stands for the loose organization of collagen fibrils that
are detected towards the adhesive resin and often unrevealed into their micro-fibrils.
This feature typically appears when the dentin surface, after being acid-etched,
has been actively scrubbed with an acidic primer solution. The physical insuling action
combined with chemical action of the citric acid was found to enhance the removal of
acidically dissolved inorganic dentin material and surface debris. This resulted in a
deeply tufted collaged fibril surface topography similar to appearance of a shag carpet
thickness, the combined mechanical chemical action of mubling the acid etched dentin
with an acidic premier dissolves additional chemical while fluffing and separating the
entangled collage at the surface. This active rubbing application is thought to promote
infiltration of monomers into the loosened collaged scaffold by a kind of “massaging
effect”.
A second typical hybridization characteristic has been termed as tubule- wall
hybridization and represents the extension of the hybrid layer into the tubule wall area.
Resin tag formation in the opened tubules is circularly surrounded by a hybridized
tubule orifice wall that is thought to be farmable in hermetically sealing the pulp-dentinal
complex against micro leakage and the potential subsequent ingress of
microorganisms. This effect may be especially protective when the bond fails either at
the bottom or top of the hybrid layer, without are considered the two weak links in the
micro-mechanical attachment. Then, the resin tags usually break at the hybrid layer
surface keeping he dentin tubules and thus the direct connectors to the pulp sealed. In
particular the resin tag necks at the top 5-10m of the tubule orifice are thought or
contribute most to retention and sealing effectiveness.
Thirdly, lateral tubule hybridization has been descried as the formation of tiny
hybrid layer into the walls of lateral tubule branches. This micro-version of a hybrid
layer typically surends a central core of resin, called a micro-resin tag.
Reverse Hybrid layer
The acid etched surface of dentin is further sulyected to Rx with Naocl. This
results in dissolution of the collagen fibrils that are exposed. Further, the use of self-
etching primers results in superficial etching of the surface. Here, the hybrid layer is
surrounded by more of inorganic material unlike the normal hybrid layer where the
collagen fibers are encapsulated by resin, and so this layer thus formed is termed as
reverse hybrid layer.
Inter-tubular bonding
The hybrid layer has been considered to provide micro-mechanical bonding to
dentin but resin tag formation may also contribute to the bond strength. Penetration of
the bonding agent into the tubular may provide much retention, as there will be so path
of withdrawal until same tags fracture this mechanism plays an important role in areas
where dentinal tubules are large in number (i.e. in areas of dentin nearer to pulp).
The action of these mechanisms is by
The resin tags, which significantly increase the bonding width.
Hybrid layer, which creates an elastic layer between the restoration and dentinal
tissue (elastic bonding).
CONDITIONING OF DENTIN
Conditioning of dentin can be defined as only attention don after the creation of
dentin cutting debris, termed the smear layer the objective of this to create a surface
capable of micro-mechanical and possible chemical bonding to a DBA.
The principal effects of conditioning of dentin may be classified as
a) Physical changes.
b) Chemical changes.
Physical changes are principally
Increase or decrease in the thickness and morphology or the S.L.
Changes in the shape of dentinal tubules.
Chemical changes are principally
Modifications of the fraction of organic matter.
Decalcification of the inorganic portion.
Removal of S.L generally results in increased permeability of the dentin (Pashley,
Michelich, Kehl 1981). The small particles comprising of S.L have a large surface to
volume ratio. The particles dissolve more easily then the intact dentin. If the S.L and
smear plugs with in the tubules are last, the exposed dentin becomes more permeable
and sensitive. For chemical success the conditioned dentin must be scaled to prevent
sensitivity and pathology (Brannstrons 1981).
Conditioning of dentin same be done by
1) Chemical: a) Acids b) calcium chelators
2) Thermal: Lasers.
3) Mechanical: Abrasion.
Acid conditioners
Manufactures generally use the terms conditions or etchant to describe agents that
are mashed off the dentin.
Mode of action of chemical conditioners
It has been suggested that mineralized collagen matures have appetite crystallites
managed not only around collagen fibrils but also within them. The depth of
demineralization because of either hyper-miniralization or formation of more acid
resistant forms of calcium phosphate (Pashlkey 1992)
Effect of chemical conditioners
Chemical conditioners remove the S.L and expose a microspores scaffold of
collagen fibrils thus increasing the micro porosity of inter-tubular dentin. Because this
collagen matrix is normally supported by the inorganic dentinal fraction,
demineralization causes it to collapse. On inter-tubular dentin the exposed collagen
fibrils are randomly oriented and are often covered by an amorphous phase with
selectively few micro-porosities and variable thickness. Etcharts thickened with silica
leave residual silica particles deposited on the surface, but the silica does not appear to
plug the inter-tubular micro-porosities. Sometimes fibrous structures probably renarts of
odonto-blastic processes are pulled out of the tubules and smeared over the surface.
With aggressive acid etchants the acids may tend to pull the collagen fibers away from
the intact dentin/unaffected dentin leaving a submission space termed as hiatus with
increasing aggressiveness of the conditioning agent a circumferential groove may be
formed at the tubule orifice separating a cuff of mineralized peri-tubular dentin from the
demanding enter-tubular dentin. Alternatively, the mineralized peri-tubular dentin may
be completely dissolved to form a funnel shape structure.
Historically, several acids have been researched as dentin conditioners. These
include hydrochloric acid, pycrimer acid, and phosphoric, citric, nitric, acids.
The hydrogen ions from these acids diffuse into the dentin while etching. The
surface reactions are violent as carbonate is commented to carbon dioxide and as
calcium and phosphates are liberated. These products may be liberated faster than
they can diffuse from the site leading to formation of reaction product that may limit
further penetration of protons. Further, the hypertonic solutions when osmotically draw
the fluid from the dentin towards the surface could restrict the inward proton diffusion.
The removal of smear layer and demineralization of the dentin matrix may facilitate
bonding through a number of mechanisms they are:
Removal of loose smear layer debris and exposure of dentin matrix.
Exposure of collagen fibrils and their Epsilon- Amino groups that may catalyze
HEMA polymerization.
Exposure of intact collagen that serves as a scaffold for the creation of resin
collagen hybrid layer.
PHOSPHORIC ACID
It was the first dentin conditioner that was successfully used to remove the smear
layer, etch the dentin and restore with adhesive composite resin by Fuzayama and
Others (1979). This helps in removing the surface dentin, leaving a clean, well-defined
etching pattern where the tubules are enlarged into a funnel shape. Phosphoric acid is
the acid of choice recently for the etching purpose. However, the controversy remains
about the optimal concentration of H3 PO4. The most widely used concertinos in clinical
practice of H3 PO4 Chow and Brown (1973) demonstrated that the application of H3 PO4
solutions greater than 50% (10-20m) resulted in the formation of monocalcium
phosphate monohydrate that is not readily soluble and mould not be completely washed
away in the clinical situation.
If H3 PO4 is applied on dentin when 50 of dentin removal it resulted in pulpal
damage as and liberated gas that passed through the pulp producing thropulus and
hemorrhage (Kozam and Burnett).
Nitric Acid
It is stronger than phosphorus acid.
Easily removes the smear layer.
Used in concentration of 2.5% causes funneling of the orifice of dentin to a depth
of 5m in 40 seconds.
Citric Acid
10% citric acid is used for the purpose of removing the smear layer. It has been
reported by Nakabayashi (1989) that such Rx tends to lower the porosity or permeability
of the demineralized surface possibly by denaturing the collagen.
Nakabayashi developed 10% citric acids plus 3% ferric chloride
combination. The divalent rather seems to stabilize the dentin matrix during its
demineralization by citric acid. This combination was found to be particularly
effective for methacrylate based adhesives containing 4-META.
Ferric appears to be necessary same the sitric acid alone yield poor results
with this system. The higher bond strengths of 4-META/ MMA- TBB products
conditioned by 10% citric acid and 3% ferric chloride solution can also be achieved by
substituting cupric chloride for the ferric ions example super bond C and B metabond
and amalgam bond.
Kuraray Introduced 10% citric acid and 20% calcium chloride in the latest
generation of smearfil linear bond system. This dough concentration of calcium may
stabilize collagen during surface etching. It also decreased the extent of the
demineralization of hydroxyapetite by a common ion effect. Here, the depth of
decalcification is about and microns compared to the phosphor acid etching with results
in 16- micron depth of decalcification (Inokshe and others 1989).
Pyrumic Acid
Pyrumic acid and prysumic acid suffered with glycine have been reposed to
satisfactory acid etch both enamel and dentin (Asanussen and Munksgaard, 1988)
when using the Gluma Bonding system Glyrine was used to adjust the PH and perhaps
to facilitate polymerization reactions.
Calcium chelators
Chelators are used to remove the S.L without decalcification or significant
physical changes to the underlying substrate as apposed to the strong acid etchants.
EDTA
Brannstrom’s concern that bacteria might be incorporated into S.L and infect the
dentin surfaces of cavities led bur to develop a dentin conditioner containing 0.1%
ethylene diamine tetracetic acid and 0.15% Benzalkomum chloride as a surface active
disinfectant (1980). This agent was marked under the name “Zubulicid”. It is scrubbed
on the surface of the S.L for a few seconds, then left passively for another 60 seconds
folled by additional scrubbing such Rx removes the S.L and generally leaves the smear
plug intact the dilute solution of EDTA removes some Ca that is thought to be important
in the mechanism of bonding. This was probably responsible for the fall in bond
strength. EDTA was developed for its use in the Gluma system by Murksgoard and
Asmussen in 1984. it removes the S.L but does not form significant surface concavity
nor is the funnel shape change associated with phosphoric acid avided. The smear
plugs in the dentinal tubules are not for removed completely by 30 sers of application of
the conditioner. A significant hybrid layer is formed by the application of the prior
containing both gluteraldhyold and EMA to the EDTA conditioned substrate.
Maleic Acid
It removes the smear layer but not the smear plugs. It is used in scotch bond 2
and Dexthessive as a conditioner. Although it is grate acidic, it does not appear to
decalcify deeply. The chybrid layer formed in this is comparatively thin.
Thermal Modifications
Lasers
Hard tissue lasers in dentistry are an emerging technology. A pulsed Nd-YAG
laser will not disturb the pulp, even the approached is as close as 1m. Heat is
dissipated b/w the 10 to 30 sers pubes per second. Most of the research has been
conducted on dry dentin, but the laser operates on dentin immersed in saliva/H2O. The
mechanism 9of dentin removal is through microscopic implosions caused by the thermal
trannents. The carboxyed, black root that results easily washed off with H 2O based
surface results in desensitized dentin, presumably by occlusion of the open and
permeable dentinal tubules. Microorganisms and organic debris are eliminated from the
lazed surfaces. The laser decreases the organic fraction of the dentin surface.
The bond strength is increased by about 60% when this was done presumably by
increasing the bondable inorganic fraction of the dentin surface. The laser may create
micro-mechanical retention.
Mechanical Modifications
It is a mechanical mean of modification of dentin aluminum oxide is used for the
purpose of micro-abrasion. It removes healthy as well as diseased dentin and results in
a smear layer. Its abrasion action depends on the particle size as well as the velouty.
The 0.5-micron or larger particles create a smear on the dentin and increase the surface
area (Blacke, 1991). The smear layer formed might be used to eliminate the bond
strengths of smear layer mediated dentin bonding agents.
Polyacrylic Acid
These acids are being used more recently. A 10 second application of durelon
liquid (40% polyacrylic acid) nanults in opening of d.t. There is no chance of potential
harm to the dental pulp here, due to the large molecular size without prevents the and to
more through the d.t.
PRIMERS
Major advances have been achieved by the introduction of primers that promote
meting of the dentin with the bonding agent, and penetration of the bonding agent into
the dentin.
Primer monomers are bifuntional molecules i.e they contain 1) hydrophilic groups
(eg- OH2-COOH) for better compatibility of the resin monomers with the moist dentin,
and 2) hydrophilic emthanylate groups for the co-polymerization with the bonding resin
primers are monomer dissolved in solvents such as 1) aretone, 2) alcohol 3) metal and
are capable applied to the etched/ conditioned dentin substrate last are not rinsed off
organic solvents aid in displacing mater, expanding or re-expanding the collagen
network and thus promoting the infiltration of the monomer into the sulucron or
monometer sized spaces with in the collagen fiber network. The first dentin bonding
mechanism that gave reliable, high bond strengths reported by Nakabayashi et al
(1982) was based on the use of 4- META/ methyl methacrylate tri-n- borane (MMM-
TBB) and 3% ferric chloride in 10% citric acid as a conditioner.
Effective primers contain monomers with hydrophilic properties that have an
affinity for the exposed collagen fibril and hydrophilic properties for co-polymerize with
adhesive resins. The objective of this step is to transform the hydrophilic dentin surface
into a hydrophilic state. Besides HEMA primers contain other monomers, such as NTG-
GMA, PMDM, BPDM an PENTA present day primers also underde a chemical/photo
polymerization initiator so that these monomers can be polymerized in sitic.
There are 2 types of bonding systems
Water Based Primers
The first approach to create a hybrid layer in wet dentin is the use of water-
soluble primers containing HEMA. Examples of this type of monomer are scotch bond
2, scotch bond multipurpose. After application of the water HEMA mixture, the surface
all devised to evaporate the H2O. As the H2O concentration falls, the HEMA
concentration rises, until theoretically there should be no H2O and 100% HEMA on the
surface water has a much higher napour pressure than does HEMA. In fact, at
atmospheric pressure, HEMA can be regarded as almost volatile. This permits its
retention as its solvent; water is evaporated during air-drying.
Use of water Miscible primer solvents
The second method of creating hybrid layers in this category of bonding is to
sequentially acid etch, rinse, leave moist on dry prime and them bond the HEMA will be
in 2 types
1) 35% HEMA in water
2) 13% polyalkenoic acid copolymer in 50% HEMA.
The intringic metness of dentin varies from about 1% in superficial to about 22%
in deep dentin Iay et al using all Bond 2, Besco, have described the consequences of
applying acetone based premiers to over net dentin; the authors found that small
globules were formed within dentinal tubules. These were formed when the first one or
two layers of primer were applied i.e. in the tubules filled with dentinal fluid there was
too much water available to dilute the acetone with result that the monomer came out of
the solution. As more globules funed, they accumulated on the walls of the tubule,
reducing the permeability of the tubules, permitting successive primer applications to
dehydrate the tubules enough to form normal resin tags.
If successive extrinsic H2O is left on to surface prior to the application of primer
(All Bond 2) without tends to bridge the excess H2O droplets to four a tiny insuster. This
prevents resin tag formation in those tubules beneath the H2O droplet, clinically if the
clinician sees a rough denture on the primed surface that might be caused by this
phenomenon , these droplets can be destroyed with the tip of brush, without can be
used to add more primer . The danger is that, this may occur somewhere in a complex
cavity design that is not easily visualized. This may result in a unbounded region,
without changing its dimensions under thermial / ouhcal stress and produce sufficient
fluid shifts to cause dentinal sensitivity (Brannstrom, 1992). It may also permit the
concentration of stress that may lead to bond failure in that portion of the restoration
(Watahe, 1992). Thus over drying /over wetting of dentin can have undisuable effects
(Tay et al).
The goal of priming is to replace all of the H2O/aretone monomer mixtures in the
inter-fibular spaces with the polymerizable monomers Manel et al demonstrated that
100% acetone; ethanol and HEMA all cause a time dependent stiffening of
demineralized dentinal matrix. Once stiffened, the matrix cannot collapse thus allowing
efficient hybrid layer formation.
Application of primer to smear layer covered dentin followed by bonding agent
Bonding to the smear layer covered dentin was not very successful before 1990
as the resins aid not penetrate through the S.L. This led most manufacturers to use
acidic conditioners. However, the resulting soft collagen with surface can collapse an
interface with the number of bonding steps (Watenbe, 1992) developed a new bonding
system with out an aqueous solution of 20% phenyl –p in 30% HEMA .This self etching
and self priming system provided important new information on S.L as bonding
substrates. The ideal self-etching self-priming bonding system is one that can penetrate
2.0m of S.L and engage underlying dentin to a depth of 1m. However, as S.L are
made up of dentin they have a significant buffer capacity and tend to buffer the acidity of
the acidic monomer used as self-etching agent. This property in addition to the tight
packing of S.L particles limit the penetration of monomer is about 2m. So Toida et al
advised the removal of smear layer by a separating etching steps to produce more
reliable and durable bonds.
Steps for effective priming
Microscope examination of attachments reduced y primer has shown deficiencies
Like
Incomplete surface coverage.
Incomplete inter-fibullar saturation within the hybrid zone.
Incomplete penetration to a full depth of demineralized dentin.
A – One method of improving surface coverage and diffusion of the primer is by the
application of multiple coats. A second coat of primer of multiple coats. A second coat pf
primer is shown to increase the shear bond strength significantly.
B—The surface of dentin should not be over dried or over wet.
C—The etching time should not exceed the time recommended by the manufacturers.
The primer reacts with the side chain grouping of the amino acids in the collagen
structures especially –NH2, -OH2 and COOH Masuhara and coworkers developed
analysis bonding agents containing the polymerization initiator tributyl boron, without is
said to induce grafting of the monomers and polymers on to the collagen structure.
Latest developments
The latest developments in the field of self-etching bonding agents are self –
etching bonding agents are self-etching premier- adhesives for composers (example-
Promp L-pop, F-2000) (it has been shown that prompt L-prop showed higher bond
strength to enamel than to dentin)
Several concepts of the bonding mechanism of adhesive resins to dentin have been
proposed.
Bonding via tag formation in to dentinal tubules of etched dentin (Nardennall and
BRANNSTRON, 1980).
Formation of precipitates on pretreated dentinal substrate to with an adhesive resin
may be chemically or mechanically bonded (Bowen, Cohh and Rapsdin, 1982)
Chemical union to either inorganic or organic components of the substrate
(Nakalrayashi, Hayta and Maxchara, 1977)
Diffusion and impregnation of monomers into the sub surfaces of pretreated dentinal
substrates and their polymerization creating a hybrid layer of resin reinforced dentin.
There are two types of handing systems they are wet and dry bonding system.
Wet bonding where dentin fluid us not removed completely example acetone is
based in bonding where dentin fluid is removed by using air H2 O BASED and drying
method.
Wet Bonding
Earlier, placement of restoration on wet surface may have caused confliction b/w
the dentist his tracing. However, the picture has changed now.
When the etched dentin is air dried the collagen restoration will collapse L & the
micro channels opened by the removal of the appetite systems will be closed from a
compact coagulate that is imponderable to resin.
Resulting in a layer of imperfect bonding termed as “Hybridoid region” (Tay,
Guvett, 1995). This results in micro leakage at monometer level (1/1000 ton of a micron
called “Naroleakage”.
This type of bonding results with the bonding systems containing hydrophilic
resin such as HEMA, with tolerate moisture.
Methods without are being followed for wet bondigae. This chamical techneque
commonly refered o as wet-bonding has been introduced by Karea 1992) abd Grinnett
1992).
Keeping the substrate field dry and use adhesive systems that provide mater based
pumers example opti-bond FL, scotch bond multipurpose). There rehydrate and re-
expand the collagen fibers allowing the resin to infiltrate.
Keeping the acid etched dentin surface moist and use acetone based primers (All
bo9nd 2) prime and Bond 2) without have H2O chasing capacity. This technique
was introduced by Karca (1992) and Gwinett (1992).
In acetone containing primers, when the acetone covers in contact with H 2O; the
bonding patient of acetone is raised and boiling patient of H2O is lowered
(AZEOTROPHISM) without caused evaporation of both the acetone and H2O and resin
is left behind.
Alternatively conditioned dentin may be are dried and remoistened with H2O an
antibacterial collection such as chlohenidere (Garimett and Kanca)> Also an aqueous
collection of HEMA (35%) Gaquapup BISCO) are affective for compensating the
dryness induced on dentin surface by air drying.
Over wetting phenomenon
When amount of H2O is present on dentine surface, this may interfere with the
bonding because when primer is applied the solvent evaporates leaving the resin, if
water is not completely replaced by primer, polymerization is affected.
In such conditions excessive water causes phase separations of hydrophilic and
hydrophilic components resulting in blister and globule formation at the resin dentin
surface.
Advantages of wet bond
It is a technique sensitive procedure. Firstly, acetone quickly evaporates from
the primer bottle, so that bottle should be immediately closed and the dispensed
solution is should be applied immediately on the etched surface.
The evaporation of solvent will increase the ratio of monomers to the acetone
solvent that will in have an effect on the eventual permeability of moners in the exposed
collagen network.
To format this primers is be available in pre-dosed single patient use capsules is
primer and bond NT Quix (Deulply).
In contract to adhesive systems that provide acetone based primers and show a
restricted minnow of opportunity” as far as premise amount of H2O that should remain
post-condition a on the dentin surface for efficient bonding to be achieved, adhesive
systems that provide H2O-based primers appear less technique sensitive and bond
equally well to varying degree of surface dry and wetness. Bonding to dry dentin has
the advantage of being the clinically accepted and utilized standard used by most
clinician.
Sovents used in adhesives
ACETONE
Highly nolatile.
Excellent H2Ochaser.
Strong duping agents (risk of over-drying dentin).
Storage and dispense problems.
Example- one step (BISCO)
Prime and bond NT (Dentsply)
Guma one bond
Ethanol
Gold penetration capacity.
Enables self-etching of acid monomers.
Slow evaporation difficult to remove.
Remaining H2O may hamper the resin penetratum air polymerization.
Example -Amalgam bond plus (Parkell).
-Prompt-L-Pop.
-Etch bond multipurpose.
Water
Good penetration capacity.
Enables self-etching of acid monomers.
Slow evaporation difficult to remove.
Remaining H2O may hamper the resin penetratum air polymerization.
Example -Amalgam bond plus (Parkell).
-Prompt-L-Pop.
-Etch bond multipurpose.
Solvents may also be used in combination i.e. Acetone –H2O
Example- tenure-quick
Acetone-Ethanot.
Example-All Bond 2(BISCO)
Example-Guma comfort bond etch bond 1.
Adhesives
The resin component of a bonding system consists of a combination of resin
such as BISGMA, TEGDMA, UGDMA or other methamylate resins.
These penetrate the preimed dentin and co-polymerize with the preimer to form
the hybried layer some of these systems may contain fibers without may be silica or
glass or fillers of nano size.
A filled adhesive has
Greater film thickness.
Greater utility to flex.
Helpers dispate stress of polymerization.
Example- Prime and Bond NT 4%.
-Optibond solo plus 15%.
-Surfaces resin film that stabilizer the hybrid layer.
-Improved bond strength or bond stability.
This is the final step of bonding process; application of adhesive layer spreading
of the adhesive resin over the surface to without it is bonded should be done preferably
with a brush rather than are spray the adhesive is copiously placed and evenly spread
with a brush tip that can be separately squeezed out b/w a paper tissue. The when
placed in a sufficiently thick layer, the adhesive resin may, due to its relatively higher
elasticity, acts as a stress relaxation buffer. This will absorb by elastic elongation, in
part, the tensile stresses imposed by polymerization contraction of the resin composite
subsequently placed over the adhesive resin.
The polymerization contraction stress generated during the placement of
composite restoration was found to be absorbed and relived by the application of an
increasing thickness of low-stiffness adhesive. Blowing the adhesive resin layer may
reduce its thickness to much, decreasing its elasticity buffer potential to relieve
polymerization contraction stress.
Amalgam Bonding
Although retention and resistance forms were the hallmark of traditional amalgam
preparations, modern consentive philosophy and the desire to extend the use of
amalgam to more extensive restorations have stimulated a search for improved
methods for retaining amalgam restorations mechanical adjuncts, including timeaded
prims/ retentive groves placed in dentin have served well for years employing M-R-X
type coupling agent have achieved some clinical sources where,
M = a methacrylate molecule without bonds to the composite resin.
R = a linking molecule.
X = a molecule without interacts with the dentine surface or smear layer.
One system used y-methacryloxyethyl trimelliate anhydride (y-META). However,
the mechanism for responsible foe the bonding amalgam to resin is predominantly
mechanical is native. It is produced by condentensory the plastic amalgam mass into
an inset adhesive resin layer, there producing an intimate mechanical interlocking as
macro retentive areas are produced within the resin after the resin has polymerized.
The results of controlled clinical trials have been mixed, but namely amalgam-
bonding agents have placed an adjunct to comentional retentive areas if properly
employed.
Adhesive- there are unfilled resin components without is having low minority so that
they can penetrate in the tags created by acid etching.
-Example- BIS GMA.