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 2wt% camphorquinone (CQ) and 2wt% ethyl-4-dimethylamino benzoate (EDMAB), an experimental 'SBU-TPO_2.1' version, containing 2.1wt% 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', 'LUB-TPO_0.35', 'LUB-TPO_0.7' and 'LUB-TPO_2.0', respectively containing 0.35wt% CQ and 0.35wt% EDMAB, 0.7wt% CQ and 0.7wt% EDMAB, 2.0wt% CQ and 2.0wt% EDMAB, 0.35wt% TPO, 0.7wt% TPO, and 2.0wt% TPO. DC was measured using micro-Raman spectroscopy. Additional specimens were immersed in ethanol for 24h 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 inverse photo-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/HEMA elution. TPO can be used as an alternative photo-initiator for CQ/amine.

Keywords: Bis-GMA; CQ/amine; Degree of conversion; HEMA; Monomer elution; TPO.