Micro-Raman spectroscopic analysis of the degree of conversion of composite resins containing different initiators cured by polywave or monowave LED units

Objectives: To determine the degree of conversion (DC) over 48 h post-curing of resin mixtures containing trimethylbenzoyl-diphenylphosphine oxide (TPO) initiator cured by a polywave or a monowave LED light-curing unit (LCU).

Methods: In resin mixtures based on equal weight percent (wt%) of BisGMA and TEGDMA the following initiators were added: 0.2 wt% camphorquinone (CQ) + 0.8 wt% ethyl-4-dimethylaminobenzoate (EDMAB) (Group 1); 1 wt% TPO (Group 2) and 0.1 wt% CQ + 0.4 wt% EDMAB + 0.5 wt% TPO (Group 3). Half of the samples in each group (n = 5) were cured using a polywave (bluephase (R) G2, Ivoclar Vivadent) or a monowave LED LCU (bluephase (R), Ivoclar Vivadent). The DC was measured using micro-Raman spectroscopy within 5 min and then 1, 3, 6, 24 and 48 h post-irradiation. The data were analysed using general linear model and two-way ANOVA for the factors 'time', 'material', 'surface' and 'LCU' at alpha = 0.05.

Results: The initial DC values obtained upon light curing remained similar over a 48 h period. bluephase (R) G2 produced the highest DC in Group 2 followed by Group 3, and Group 1. bluephase (R) resulted in the highest DC in Group 1, followed by Group 2 and Group 3 (p <0.05).

Conclusions: Unfilled resin materials containing both TPO- and CQ-amine initiators are effectively cured using bluephase (R) G2. Resin mixture with the same wt% of initiators is better cured when TPO is the only initiator, compared to CQ-amine only or combined TPO and CQ-amine system. After initial light cure, no additional conversion of uncured monomers was detected in an unfilled resin material over 48 h at 37 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.