Degree of conversion and monomer elution of CQ/amine and TPO adhesives

Abstract

Objective. To evaluate the effect of photo-initiator on the degree of conversion (DC) and elution of Bis-GMA and HEMA for 8 one-step adhesive formulations. Methods. We used Scotchbond Universal ('SBU-CQ/amine 4.0', 3M ESPE), containing about 2 wt% camphorquinone (CQ) and 2 wt% ethyl-4-dimethylamino benzoate( EDMAB), an experimental 'SBU-TPO 2.1' version, containing 2.1 wt% diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), and 6 experimental LUB adhesives (Kuraray Noritake), namely 'LUB-CQ/amine 0.7', 'LUB-CQ/amine 1.4', 'LUB-CQ/amine 4.0', 'LUBTPO 0.35', 'LUB-TPO 0.7' and 'LUB-TPO 2.0', respectively containing 0.35 wt% CQ and 0.35 wt% EDMAB, 0.7 wt% CQ and 0.7 wt% EDMAB, 2.0 wt% CQ and 2.0 wt% EDMAB, 0.35 wt% TPO, 0.7 wt% TPO, and 2.0 wt% TPO. DC was measured using micro-Raman spectroscopy. Additional specimens were immersed in ethanol for 24 h to determine the elution of Bis-GMA and HEMA using HPLC. Results. DC of the respective SBU and LUB adhesives was alike at high photo-initiator concentration. At low concentration, TPO was significantly more efficient than CQ/amine (LUB adhesives only). A statistically significant positive photo-initiator concentration effect on DC was noted for both CQ/amine and TPO (LUB adhesives only). A statistically significant inversephoto-initiator concentration effect on HEMA elution was noted for both the CQ/amine and TPO-containing LUB adhesives. A significantly strong correlation was found between DC and Bis-GMA elution (R-2 = 0.744, p = 0.026), and between DC and HEMA elution (R-2 = 0.913, p = 0.002) for the LUB adhesives. Significance. The photo-initiator kind and concentration affect DC and the Bis-GMA/HEMAelution. TPO can be used as an alternative photo-initiator for CQ/amine.