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The joining or attaching of two substances together by means of a chemical reaction or an adhesive, now extensively used in restorative dentistry. A bonding agent is a chemical agent used to provide a bond between two layers. Bond strength is measured in mega pascals (MPa) as the force necessary to break the adhesive bond per unit area. Bonding in restorative dentistry has evolved considerably during the latter part of the 20th century and is broadly divided into seven generations.

The development of bonding systems

1st generation

Introduced in the 1960s to overcome polymerization shrinkage and excessive wear of restorative materials. Bond strength of about 1–3MPa.

2nd generation

Improved but still weak dentine adhesion by utilizing halophosphorous esters such as Bis-GMA and HEMA.

3rd generation

The introduction of acid etching of dentine to partially remove or modify the smear layer. These systems usually used a hydrophilic dentine-resin primer.

4th generation

Involved the complete removal of the smear layer. Enamel and dentine were etched simultaneously.

5th generation

Simplified techniques introduced using a one bottle system incorporating both primer and adhesive. The self-etching primer contained HEMA.

6th generation

An improved bond strength developed using a one-bottle etch and primer system.

7th generation

Further development of the 6th generation such that etching, priming, and adhesion are undertaken in one stage.

Subjects: Dentistry.

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