Self-etch bonding systems acidity

Kidd EAM (1976) Microleakage a review. J Dent 4 199 Kitayama S, Nikaido T, Ikeda M, Foxton RM, Tagami J (2007) Enamel bonding of self-etch and phosphoric acid-etch orthodontic adhesive systems. Dent Mater 126 135... 

The acidity of self-etching primers allows them not only to penetrate the smear layer and incorporate its component, but also to interact with the underlying intact dentine. In doing so, it forms a hybrid layer of the type previously identified with three-layer bonding systems [20,21], and which is essential in promoting adhesion. This acidity varies between formulations, and can be classified as either strong or weak, depending on the acid involved in the blend and also its concentration [25]. 

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