State of the art of self-etch adhesives

Bonding efficiency and durability: current possibilities

“…4,6 Conversely, self-etch adhesives contain monomer molecules with carboxylate or phosphate acidic groups which concurrently etch and infiltrate dental substrates in such a manner that smear layer is not removed, but incorporated into the adhesive interface. 5,15,16 Even if the thickness of demineralization/impregnation area is smaller than that promoted by etch-and-rinse adhesives, this does not necessarily reflect on lower bond strength. 16 Self-etch adhesives differ from each other in the amount of intrinsic water and potential of hydrogen (pH).…”

“…Both presentations can be subdivided according to their acidity into 'strong' (pH≤1), 'intermediate' (pH ≈ 1.5), 'mild' (pH ≈ 2) and 'ultra-mild' (pH ≥ 2.5). 5 Those having a pH lower than or near to 1.5, contain functional monomers which mainly demineralize dental hard tissues instead of chemically bonding to hydroxyapatite; those having a pH greater than 1.5, only demineralize the dental substrate partially, chemically interacting with the remaining hydroxyapatite. 5 The latter thus only exposes dentin collagen very superficially, creating a nanoscaled hybrid layer also referred to as nano-interdiffusion zone.…”

“…3 Basically, the adhesive procedure consists of removing minerals from the dental substrate by acid etching it to create micro-retentive porosities, where resin monomers infiltrate and polymerize. 4,5,6 Specifically, on dentin, the acid etching procedure not only removes possible superficial debris, the so-called smear layer, but also exposes a net of collagen fibers besides opening the dentin tubules. By penetrating this collagen mesh and dentin tubules, the infiltrating resin will form two welldefined structures which are known as hybrid layer and resin tags, respectively.…”

“…7 Contemporary adhesives are formally categorized into two main types according to their mechanism of action, namely etch-and-rinse and self-etch systems. 4,5,8 The first requires prior application of phosphoric acid as an initial step. After mandatory rinsing, smear layer is completely removed and the tooth substrate is demineralized, resulting in profound pores in the highly-mineralized enamel and exposed collagen mesh in dentin in a depth that may range from 5 µm to 10 µm.…”

“…After mandatory rinsing, smear layer is completely removed and the tooth substrate is demineralized, resulting in profound pores in the highly-mineralized enamel and exposed collagen mesh in dentin in a depth that may range from 5 µm to 10 µm. 4,5,9,10 When using etch-and-rinse systems, proper hybrid layer is classically achieved through the infiltration of resin monomers into the exposed collagen mesh by using the so-called wet-bonding technique. In this protocol, water remaining from the rinsing step maintains the collagen network expanded, allowing resin monomers to properly infiltrate it; excessive dehydration would cause fibrils to collapse, impairing resin penetration and hybrid layer formation.…”