Degree of conversion and interfacial nanoleakage expression of three one-step self-etch adhesives

Suboptimally polymerized monomers may be responsible for the reduced material properties of simplified adhesives and their inherent bonded interface instability. This study was performed to determine the degree of cure within the hybrid layers produced by three one-step self-etch adhesives in situ using Raman microspectroscopy and to investigate nanoleakage expression. Dentin disks were bonded with AdheSE One, Adper Prompt L-Pop, or iBond. Composite layers of 2-mm thickness were built up in bulk on the polymerized adhesive surfaces and then the adhesive-dentin interfaces were exposed to a micro-Raman beam. Adhesive penetration was calculated using the relative intensities of bands associated with mineral and adhesive, and the degree of conversion (DC) was evaluated. Interfacial nanoleakage expression was evaluated on the same specimens. The DC values for the tested adhesives were found to increase in the following order: AdheSE One (48 +/- 16%) < Adper Prompt L-Pop (83 +/- 2%) = iBond (90 +/- 6%; P < 0.05). AdheSE One showed greater nanoleakage expression than iBond or Adper Prompt L-Pop. Increased nanoleakage expression was associated with AdheSE One that showed the lowest DC. This suggests that a low DC may affect the quality and the long-term stability of the adhesive interface owing to the elution of unreacted monomers forming a porous and highly permeable hybrid layer.