Degree of Conversion Composites Containing an Alternative Co-initiator

Objectives: To evaluate incorporation of Tris(trimethylsilyl)silane (TTMSS) as an alternative co-initiator in the dental composite resin matrix and its effect on the degree of conversion (DC).
Methods: A resin matrix was formulated with 10.2 wt% of BisGMA, 11.1 wt% of BisEMA, 11.1 wt% of UDMA, and 2.1 wt% of TEGDMA. Camphoroquinone (CQ) was used as photoinitiator. TTMSS, 2-(dimethylamino) ethyl methacrylate (DMAEMA) and diphenyliodonium hexafluorophosphate (DPIHP) were used as co-initiators. Six groups were formed: G1 (0.2 wt% - CQ/ 0.5 wt% -TTMSS/ 0.5 wt% DPIHP); G2 (0.2 wt% - CQ/ 1 wt% -TTMSS/ 0.5 wt% DPIHP); G3 (0.2 wt% - CQ/ 0.25 wt% -TTMS/ 0.25 wt% DMAEMA/ 0.5 wt% DPIHP); G4 (0.2 wt% - CQ/ 0.25 wt% TTMSS/ 0.25 wt% DMAEMA); GNegative (0.2 wt% - CQ/ 0.5 wt% -TTMSS); GPositive (0.2 wt% - CQ/ 0.5 wt% DMAEMA). Filler particles were added in 65 %wt. Degree of conversion (DC; n=3) was measured using a micro-Raman spectrophotometer (Xplora, Horiba JobinYvon, Paris, France). Uncured blends were scanned and then light cured with 24 J/cm² using ValoÒ (Ultradent Products Inc, South Jordan, UT, EUA). carbon double bonds were quantified by calculating the ratio derived from the aliphatic C=C (vinyl) absorption (1639 cm-1) to the aromatic C=C absorption (1609 cm-1).
Results: The results showed that G2 obtained the highest DC (%) (89.8 ± 2.55) and did not statistically differ from G4 (89.12 ± 1.8), G3 (85.6 ± 1.9) and GPositive (85.9 ± 2.4). G1 (73.2 ± 2.8) showed statistically lower DC mean value when compared to G2, G4, G3, and GPositive and higher than GNegative group (65.6 ± 2.4).
Conclusions: The use of TTMSS alone as a co-initiator (GNegative) decreased the DC. However, the DC can be improved by the addition of DPIHP. Increasing the percentage of TTMSS or its association with DMAEMA increased the DC.