Effect of adhesive-monomers and photoinitiator on C=C conversion and color stability of model self-adhesive flowable composites

The aim of this study was to determine the influence of the monomer type and photoinitiator systems on the degree of C=C conversion and color stability of model self-adhesive flowable composites (SAFCs). Three sets of flowable composites were formulated varying the monomer type: set 1 (control), with bisphenol-A glycidyl methacrylate and triethylene glycol dimethacrylate (BisGMA/TEGDMA) at 50/50 wt%; set 2, with BisGMA/TEGDMA/bis[2(methacryloyloxy)ethyl]phosphate (2MP) at 30/30/40 wt%; and set 3, with BisGMA/TEGDMA/4-ethyl-methacryloxy-trimetilato anhydride (4-META) at 30/30/40 wt%. For each set, different initiator systems were added: camphorquinone (CQ) + ethyl-4-dimethylamino benzoate (EDMAB); diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO); phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO); and the combinations CQ + EDMAB + TPO and CQ + EDMAB + BAPO. Degree of C=C conversion was determined by Fourier-transformed infrared spectroscopy with an attenuated total reflectance device (ATR-FTIR). The color stability was determined by CIE00 color difference formula (∆E*00), after water (T1) and coffee (T2) storages for 30 days. Data was submitted to two-way analysis of variance (ANOVA) followed by Student-Newman-Keuls test (α = 0.05). Degree of conversion and color stability were dependent on the resin matrix composition and the photoinitiator system. The 2MP-based set showed the highest DC, but also the poorest color stability. For the 4-META-base set, TPO and BAPO produced the highest degree of C=C conversion. The use of BAPO produced the best color stability for the acidic-monomer-based sets.