The influence of bis-EMA vs bis GMA on the degree of conversion and water susceptibility of experimental composite materials.

OBJECTIVE: The aim of this work was to assess the influence of the bis-EMA content on the degree of conversion (DC) and its effect on the water sorption and solubility. MATERIALS AND METHODS: In a polytetrafluorethylene (PTFE) mould, 30 samples (Ø = 5 mm, height = 2 mm) of four experimental dental composite resins were cured for 10 s, 20 s and 40 s. The DC was analysed by Fourier Transform (FT)-Raman spectroscopy. To analyse sorption and solubility, six samples (Ø = 15 mm and thickness = 1 mm) of each composite (n = 72) were stored in water at 37°C for different storage periods: 24 h, 7 days and 30 days. RESULTS: When cured for 20 or 40 s the DC increased with the increasing content of bis-EMA. However, the presence of 15 wt% of bis-GMA did not affect the DC, except when cured with 10 s irradiation time. This study also found a correlation between the content of bis-EMA and the reduced values for sorption and solubility, for all storage times used, when the materials were cured with 20 s. CONCLUSIONS: The DC of mixtures with higher content of bis-EMA is affected by the presence of bis-GMA at lower energy density delivered from the curing device, suggesting that the restrictions caused by the presence of hydrogen bonds is dependent of the irradiation time used.

Influence of different mould materials on the degree of conversion of dental composite resins

Aim: In this study, the degree of conversion (DC) was analyzed on the surfaces of dental composite resins cured in different mould materials with different irradiation times. Methods:Samples of three composite resins (Grandio®, Grandio Flow® [thickness = 2 mm; 4 mm; Ø = 5 mm] irradiated for 10 s, 20 s and 40 s and an experimental composite (EXPM) [thickness = 6 mm; Ø= 5 mm] irradiated for 40 s) were cured in moulds made of polytetrafluorethylene (PTFE), highdensity polyethylene (HDPE) and stainless steel (SS). The DC was analyzed by FT-Raman spectroscopy. Results: The DC was significantly lower for the 2-mm-thick samples of Grandio® cured with 20 s in the SS mould than in the PTFE mould. The same trend was found for the 4-mmthick samples of Grandio Flow® cured with 40 s. The main difference of the DC between Grandio® and Grandio Flow® occurred when 10 s irradiation was used, independently of the mould material and thickness of the samples. The analysis of the DC on the sites around the samples of EXPM showed no significant difference from those at the bottom when cured in each mould material with 40 s irradiation. Conclusions: The DC was not affected by the mould material, instead, the resin formulation and the irradiation times were the main factors affecting the degree of conversion.