Bonding to Intact Dentin

Abstract

It has been reported that the presence of a smear layer on dentinal substrates can compromise bonding. Typically, smear layers are removed by acidic agents that selectively extract calcium salts from dentin surfaces to leave a collagen-rich substrate. Acid-conditioned dentin (i.e., demineralized) is then primed and an adhesive agent applied. In the present study, we removed smear layers by "polishing" dentin specimens with a hydroxyapatite paste and ultrasonication. Bonding procedures were carried out by means of an aqueous solution of 20% 2-methacryloyloxyethyl phenyl phosphoric acid (phenyl-P) and 30% 2-hydroxyethyl methacrylate, referred to as 2OP-30H, a "self-etching primer". The 20P-30H solution was applied to "intact" dentin (i.e., non-demineralized) for either 30 or 60 s. Control samples received no application (O s) of the self-etching primer. Mean tensile bond strengths (10 MPa) were similar in both the 30-second- and 60-second-primed groups. The widths of formed hybrid layers varied from 0.3 +/- 0.2 micron at O s application (control) to 2.1 +/- 0.3 micron for the 30-second group and 4.1 +/- 0.2 micron for the 60-second group. SEM and TEM observations revealed that the 20P-30H self-etching primer created diffusion channels into "intact" calcium-rich dentin which permitted monomer to infiltrate dentin substrates. Hybrid layers identified under microscopic examination demonstrated resistance to both HCI and NaOCI treatments, suggesting that the hybrid layer was not defective, and that bonding was stable.

Bonding efficiency and durability: current possibilities

“…5,59 Such chemical bond is mostly observed in mild and ultra-mild SE adhesives (pH < 2) that partially demineralizes dentin producing sub-micrometer hybrid layers 14 in which substantial HAp-crystals remain around partially exposed collagen fibers. 3,18,60,61 Besides protecting collagen fibers against degradation, such remaining mineral content also serves as receptor for additional chemical bonding with the respective functional monomer, 14,18 by which their two-fold bonding mechanism (i.e. micro-mechanical and chemical adhesion) closely resembles that of glass-ionomers.…”

“…This procedure, however, always requires an intermediate bonding agent which penetrates enamel and/or dentin, primarily establishing what is called micromechanical bonding. 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.…”

Effect of Thermal Cycling on Enamel Bond Strength of Single-step Self-etch Systems

“…The use of single-step self-etch adhesives may eliminate possible discrepancies between depth of etching and resin monomer penetration. 6 Single-step self-etch adhesive systems form a continuous layer by simultaneous demineralization with acidic monomers followed by resin monomer penetration into the enamel surface. Penetration of these acidic monomers into etched enamel creates resin tags.…”

Microleakage and interfacial morphology of self‐etching adhesives in class V resin composite restorations

“…When the depth of dentin demineralization exceeds the depth of dentin diffusion/impregnation, an area of hydroxyapatite-depleted collagen fibers is left exposed; that is, it is not resin infiltrated or hybridised. 7,8 This zone of exposed collagen may be unstable and subjected to hydrolysis. 9 -11 To avoid this, self-etching dentin bonding systems that do not require smear-layer removal by acidic conditioners are being developed.…”