Self-etching primers

Self-etching primers are blends that can both etch and prime the surface in one step. They contain at least one acidic monomer, in order to allow them to undertake the etching process. They also eliminate the need to rinse away the solubilized products to the etching step. Instead, these substances become incorporated into the primer layer. This has the advantage of reducing the technique sensitivity associated with the process of bonding [4]. However, there is some evidence that the resulting adhesive bonds are weaker than those with substances that do not incorporate any mineral components of the smear layer [24]. 

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]. 

Weak self-etch primers (sometimes described as mild ) have pH values around 2, and as a result only partially attack the surface of the dentine and hence only solubilize a fraction of the available mineral phase. The hybrid layer formed with such primers is therefore relatively rich in mineral content, with bonding occurring by the interaction of carboxylic or phosphoric acid functional groups with the dentine surface. 

On the other hand, strong self-etch primers have a pH of around 1, and hence contain strong acids based on phosphoric acid groups only. They interact more aggressively with the smear layer of the freshly cut tooth, removing more of it from the surface. Though these substances nonetheless include the components of the mineral phase, the resulting bonded surface closely resembles that created by the etch-and-rinse technique. 

M. Ogata, N. Harada, S. Yamaguchi, M. Nakajima, P.N. Periera, J. Tagami, Effect of different burs on bond strengths of self-etching primer bonding systems. Open Dent. 26 (2001)375-382. 

H. Koibuchi, N. Yashuda, N. Nakabayashi, Bonding to dentin with a self-etching primer the effect of smear layers. Dent. Mater. 17 (2001) 122-126. 

F.R. Tay, H. Sano, R. Carvalho, E.L. Pashley, D.H. Pashley, An ultrastructural study of the influence of acidity of self-etching primers and smear layer thickness on bonding to intact dentin, J. Adhes. Dent. 2 (2000) 83-98. 

B. Van Meerbeek, Y. Yoshida, J. De Munck, S. Inoue, M. Vargas, P. Lambrechts, G. Vanherle, in J. Tagami (Ed.), Self-etching Primer Current Status and Its Evolution, Proceedings of the International Symposium 01 in Tokyo, Dental Materials Department, Kuraray Medical Inc., Tokyo, 2003, pp. 41-55. 

Group B Self-etching primer +Bonding immediately (positive control)... 

M. Hannig, K.-J. Reinhardt, B. Bott, Self-etching primer vs phosphoric acid An alternative concept for composite-to-enamel bonding, Open Dent., 24,172-180,1999. 

S. Kubo, H. Yokota, Y. Sata, Y. Hayashi, Microleakage of self-etching primers after thermal and flexural load cycling. Am. J. Dent., 14,163-169, 2001. 

Yamada, M., Miyazaki, M., and Moore, B.K. (2004) Influence of interchanging adhesive resins and self-etching primers on the mechanical properties of adhesive resins. Open Dent, 29 (5), 532-537. 

Modern formulations combine primer and adhesive components in a single blend, in order to reduce the number of steps involved in the bonding process and simplify the procedure for clinicians. Despite the widespread use of this approach, some sort of separate acid-etch process is required as the first step of bonding. This may be as a separate etching step, or through using so-called self-etching primers. 

Self-etching formulations are acidic because they contain acid-functional monomers, such as maleic acid. Because of their acidity, these self-etching primers are able to penetrate the smear layer and form a hybrid layer with the underlying dentin. This process causes the components of the smear layer to become incorporated into the bonding layers. There is no way to avoid this, as there is no rinse step to wash away the acid treated smear layer. However, there is evidence that retention of the smear layer components compromises the bond strength of self-etching primers (Pashley and Carvalho 1997). 

Hayakawa T, Kikutake K, Nemoto K. Influence of self-etching primer treatment on the adhesion of resin composite to polished dentin and enamel. Dent Mater. 1998 14 (2) 99-105. 

Torii Y, Itou K, Nishitani Y, Yoshiyama M, Ishikawa K, Suzuki K. Effect of self-etching primer containing A-acryloyl aspartic acid on enamel adhesion. Dent Mater. 2003 19 (4) 253-258. 

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