Resin dental adhesives are broadly classified

into an etch-and-rinse system, or self-etch system.

An etch-and-rinse adhesive system

requires a separate acid etching procedure,

which is usually done using 32% to 37% phosphoric acid.

A self-etch adhesive system does not require

a separate acid etching procedure

as it contains acidic resin monomer

that can etch and bond simultaneously.

An etch-and rinse dental adhesive system

can be a 3-step system or a 2-step system.

A 3-step etch-and-rinse system

consists of primer and bonding resin

that comes in two separate bottles.

Therefore, in clinical application

one has to perform three steps,

etching, priming and bonding of adhesive resin.

A 2-step etch-and-rinse system

consists of self-priming resin

that comes in a single bottle.

Therefore, in clinical application

one has to perform two steps,

etching and bonding of adhesive resin.

The 2-step etch-and-rinse system

is also popularly known as

one-bottle dental adhesive system.

An etch-and-rinse dental adhesive system

consists of resin monomers, solvents,

photoinitiator, inhibitors and filler.

Resin monomers in dental adhesive systems

are dimethacrylates.

The most common dimethacrylic monomer resin

that is incorporated in any etch-and-rise

dental adhesive system is Bis-GMA

which is Bisphenol-A glycidyl methacrylate.

The other dimethacrylate includes TEGDMA

which is Triethylene glycol dimethacrylate

and HEMA which is 2-Hydroxyethyl methacrylate.

Bis-GMA is also known as Bowen-resin.

It is a hydrophobic resin

and used in composites too.

It is highly viscous and has superior mechanical properties.

Additionally, it exhibits lower polymerization shrinkage

and rapid hardening.

In terms of water sorption,

Bis-GMA ranks inferior to TEGDMA.

TEGDMA is a less viscous resin monomer

and usually added as a diluent.

It is inferior to Bis-GMA in mechanical properties.

A resin mixture of Bis-GMA and TEGDMA

has an improved conversion rate.

HEMA is a hydrophilic monomer

that helps in priming the demineralized dentin,

it is also inferior to Bis-GMA in physical properties.

It is prone to hydrolysis.

Solvents are important ingredient

in any resin-based dental adhesive system.

It helps in carrying resin monomer

to the bond surfaces and subsequently

volatizes by which it also removes water

from the bonded surfaces.

The most commonly used solvents

in resin dental adhesive system

are water, ethanol and acetone.

Acetone has high vapour pressure

and low hydrogen bonding capacity.

In contrast, water has low vapour pressure

and high hydrogen bonding capacity.

Photoinitiator is essential for light-cured polymerization

of resin monomers in the dental adhesives.

Camphor quinone with a co-initiator system

is most commonly incorporated agent.

Camphor quinone absorbs over a wide spectrum of wavelength from 360 to 510 nm,

with peak absorbance around 460 nm

which lies in the blue light.

Inhibitors are added to dental resins

to scavenge free radicals originating from

prematurely reacted initiator.

Mostly useful in extreme storage conditions

such as high temperatures.

The most frequently used inhibitors in adhesives

are butylated hydroxytoluene.

A self-etch dental adhesive system

can be a two-step or a single-step system.

A two-step self-etch system

consists of self-etching primer

and bonding resin that comes in two separate bottles.

However, being a self-etch system,

in clinical applications, one has to perform only two steps,

application of self-etching primer

followed by application of adhesive resin.

A single-step self-etch system consists of

self-etch primer and bonding agent

that either comes in two bottles, or a single bottle.

In either forms, in clinical applications

one has to perform a single step.

Therefore, when it comes in two separate bottles

an operator should dispense equal amount

of required content from both the bottles and mix together

followed by its application.

A self-etch dental adhesive system

consists of resin monomers, solvents,

photoinitiator, inhibitors and filler.

The resin monomers in self-etch dental adhesive system

consists of acidic functional monomers

for dentine demineralization,

hydrophilic monomer for water solubility

and bi- or multi-functional monomers to provide strength.

The common acidic functional monomers are

10-MDP and 4-MET.

10-MDP is very hydrophobic and forms

a strong chemical bonding to hydroxyapatite of enamel and dentine.

It has been patented by Kuraray from Japan.

In recent years, 10-MDP is also introduced to

ceramic primers especially for

segmentation of zirconia restorations.

4-MET is an acidic monomer

frequently used together with methylmethacrylate.

It forms a weak bond with calcium in hydroxyapatite

when compared to 10-MDP.

Phenyl p is another acidic monomer

and was used as one of the first acidic monomers

in self-etching primers.

Phenyl p has only very little chemical bonding capacity

to hydroxyapatite.

This acidic monomer is not frequently used anymore

in contemporary adhesives.

Classification and Composition of Resin Dental Adhesives

Materials in Oral Health

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