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 Flo^® cured with 40 s. The main difference of the DC between Grandio^® and Grandio Flo^® 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.

Keywords
mould material, dental composite resin, degree of conversion, Raman spectroscopy