DENTIN BONDING AGENTS

KIRANPREET KAUR GREWALFINAL YEAR

GURU NANAK DEV DENTAL COLLEGE AND RESEARCH INSTIUTE, SUNAM.

DEFINATIONS Adhesion: It is the force or intermolecular

attraction that exists between molecules of two unlike substances when placed in intimate contact with each other.

Adhesive: the substance added to produce the adhesion.

Adherend: the material to which adhesive is applied .

Etchant: Chemicals such as phosphoric acid etc. are used for improving the reactivity of the substrate and to remove smear layer or demineralization of the superficial enamel and dentin.

Primer: These are the monomer dissolved in solvent such as water , acetone or alcohol. These agents are applied over the etched surface facilitating the easy flow of resin.

Bonding agent: It is an unfilled resin that consist of both hydrophilic monomer and hydrophobic monomer.

REQUIREMENTS OF IDEAL BONDING AGENT Should be biocompatible. Should bond effectively to both enamel and

dentin. Should be resistant to degradation in oral

environment. Should be Non toxic. Should be Non irritant. Should have Good dimensional stability. Should be easy to use.

ENAMEL BONDING Enamel is the hardest tissue of human body

consists of 95% mineralized inorganic substance i.e. hydroxyapatite crystals.

Due to high mineral content the bonding in enamel is good as compared to dentin.

Enamel is etched using 37% phosphoric acid applied for 15-30 seconds.

Etching creates 5-50 microns deep microporous layer into which adhesive resin flow.

This results in long lasting enamel bond achieved via micromechanical interlocking between resin and enamel.

Bond strength: 15-25 Mpa.

DENTIN BONDING Bonding to dentin presents a greater challenge as

compared to enamel bonding. In dentin inorganic part is only 50%. Hydroxyapatite crystals are arranged randomly in

organic matrix. Dentin contains dentinal tubules which contains

processes of the pulp. These makes the dentin sensitive. Fluid present in the dentinal tubules constantly flows

outwards which reduces the adhesion of composite resin to dentin.

Relative area offered by dentin tubules decreases with increasing distance from pulp. Since the tubules are more numerous and wider near the pulp, there is more fluid and less dentin, this makes dentin bonding less effective in deeper dentin than superficial dentin.

The presence of smear layer makes the wetting of dentin by adhesive more difficult.

ROLE OF SMEAR LAYER IN DENTIN BONDING Smear layer: Residues of dentin which adheres

tightly to dentin & fills the tubules after cavity cutting.

The smear layer fills the orifices if the dentinal tubules by forming smear plugs & decreases the permeability of dentin up to 86%.

Smear layer is composed basically of hydroxyapatite and altered denatured collagen.

The removal of smear layer and smear plugs with acidic solution may result in increase of the fluid flow onto exposed dentin surfaces.

MECHANISM OF DENTIN BONDING Composite resins do not show microscopic

contact with dentin when placed directly into the cavity.

In order to overcome this, an intermediate layer of fluid is used which combines with composite resins and components of dentin.

Dentin adhesives should be both hydrophobic as well as hydrophilic.

It is required to be hydrophilic so as to be able to displace dentinal fluids and thereby permitting penetration into porosities in dentin.

Hydrophobic properties are needed to allow bonding to composite resin.

DEVELOPMENT OF DENTIN BONDING SYSTEMSFIRST GENERATION DENTIN ADHESIVE:

Given by S.S White. There is development of surface active

copolymer NPG-GMA (N-phenylglycine glycidyl methacrylate)

This copolymer could bond on the tooth surface to generate water resistant chemical bonds of resin to dentinal tubules.

It bonds to the calcium component of dentin. Since they could bond with calcium ions in

tooth structure, they form stronger bonds with enamel then dentin.

Smear layer is ignored. Example: Cervident.

LIMITATIONS OF FIRST GENERATION BONDING AGENT:

Low bond strength: 2-3Mpa. Loss of bond strength over time. Lack of stability of individual

component during storage.

SECOND GENERATION DENTIN ADHESIVE: Clearfil Bond system F was the first product of

second generation bonding agent which was introduced in Japan in year 1978.

It was a phosphate ester material. Its mechanism of action was based on the popular

interaction between the negatively charged phosphate group of resin & positively charged calcium in smear layer.

LIMITATIONS: Smear layer was the weakest link in the system

because of relatively loose attachment to dentin surface.

Bond Strength was low : 1-5MPa.

THIRD GENERATION DENTIN ADHESIVE: Introduced in 1979. These were designed not to remove the entire smear

layer, but rather to modify it and to allow penetration of acidic monomers.

Involves the concept of phosphoric acid etching before application of phosphate ester type of bonding agent.

LIMITATIONS: But because bonding agent have hydrophobic

nature, acid etching did not produce the significant improvement in dentin bond strength inspite of flow of resin into open dentinal tubules.

Pulpal inflammatory responses were thought to be triggered due to application of acid.

FOURTH GENERATION DENTIN ADHESIVE: These are introduced for the use on acid –etched dentin. Multiple bottle adhesive system. Smear layer is considered as an obstacle that must be

removed so that resin can be bonded to the underlying dentin substrate.

Fourth generation adhesives are basically composed of:I. An acid etching gel that is rinsed off.II. A solution of primers that are relatively hydrophilic

monomers in ethanol, acetone and/or water.III. Fluid bonding agent.

Acid open up the dentinal tubules, thus creating microporosity of intertubular dentin.

When primer and bonding resins are applied to etched dentin, they penetrate the intertubular dentin, forming resin dentin interdiffusion zone or “hybrid layer”.

Examples:1. All Bond-22. Scotch Bond Multipurpose3. Optioned FL4. Clearfil Liner Bond 2

Hybrid layer: Also known as resin-dentin

interpenetration/ interdiffusion zone. This is the zone where the adhesive resin

of the dentin bonding agent micromechanically interlocks within the intertubular dentin and surrounding collagen fibers.

FIFTH GENERATION DENTIN ADHESIVES: Commercially available adhesive proves to be

satisfactory but it contain several time consuming steps to be applied.

So “one bottle” adhesive system was introduced. In this there is combination of primer and bonding

agent steps, but a separate etching step. Total etch adhesive system: Simultaneous application of an acid to enamel and

dentin, known as the total etch technique. It was initiated in Japan . In this phosphoric acid etching of dentin is done

before applying phosphate ester type of bonding agent.

Bond strength: 17-30MPa.

Examples:1. Prime and bond2. Optibond solo3. Single Bond

SIXTH GENERATION DENTIN ADHESIVES: Introduced in 2000. These are single bottle adhesives combine

etching, priming & bonding in a single solution & as single step.

It consists of self etching primers which are used in place of separate etchant

Less effective bond with enamel as compared to dentin due to high acidic content.

These are further of 2 types: Self-etching primer & adhesive. Self-etching adhesive.

Self-etching primer & adhesive: Two bottles: Liquid 1(acidic primer) Liquid 2(adhesive) Acidic primer applied to the tooth followed by

adhesive. Light cure formulations. Solvent is water.

Self-etching adhesive: Two bottles consisting of acid primer and adhesive. A drop of each liquid is mixed and applied to the tooth. Light cure formulations.

Examples: Xeno III

SEVENTH GENERATION DENTIN ADHESIVE: The self etching primers was introduced in Japan. These acidic primers include a phosphonated resin

molecules that performs two functions simultaneously- Etching & Priming of dentin and enamel.

Unlike conventional etchants, self etching primers are not rinsed off.

In addition to simplifying the bonding technique, the elimination of rinsing and drying steps reduces the possibility of overwetting or overdrying.

They also have properties of disinfection & desensitization.

Bond strength: 20-28MPa. Example: I bond G bond

THANK YOU.