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.