Quantification of monomer elution and carbon–carbon double bonds in dental adhesive systems using HPLC and micro-Raman spectroscopy

Abstract

Objectives To quantify monomer elution from different adhesive systems using reverse-phase high-performance liquid chromatography (HPLC) and correlate this elution with the ratio of carbon–carbon double bonds from monomer to polymer (RDB) obtained using micro-Raman spectroscopy. Methods Thirty dentine discs were cut from 30 human, intact, third molars and randomly allocated to five groups according to the adhesive applied: total-etch, Excite (Ivoclar Vivadent), two-bottle self-etch, Clearfil SE (Kuraray), one-bottle self-etch, Clearfil 3S (Kuraray), ormocer-based, Admira (Voco) and Filtek Silorane adhesive system (FS) (3M ESPE). Monomer elution was studied 1 h, 6 h, 24 h, 96 h and 7 days after immersion in 75% ethanol/water. The RDB was calculated immediately after light-curing and thereafter at 24 h and 7 days. The data were statistically analysed using one-way ANOVA and Pearson's correlation coefficient ( p < 0.05). Results More than 90% of the whole elution occurred during the first 1 h, except for BisGMA in FS, with the highest absolute amount from Clearfil SE and the highest wt% from Admira. Initial RDB was in the ascending order FS < Admira < Excite < Clearfil SE < Clearfil 3S. In all groups, the RDB was significantly higher after 24 h and 7 days than immediately after light-curing ( p < 0.05). Negative correlation was found only for the elution of HEMA and the RDB of Clearfil 3S. Conclusions Different adhesive systems showed different monomer elution kinetics. In all systems, the RDB increased after monomer elution. Overall, no direct correlation exists between the RDB of adhesives and the elution of unreacted monomers.