Degree of conversion versus the depth of polymerization of an organically modified ceramic dental restoration composite by fourier transform infrared spectroscopy

Abstract

AbstractThe evaluation of the degree of conversion (DC) as a function of the depth (1–4 mm) of an organically modified ceramic (ormocer) dental restoration composite activated by a conventional light‐curing unit (450 nm, 21.2 J/cm2) was carried out. Fourier transform infrared spectroscopy was employed to measure DC at each depth with the ratio of the maximum height absorbance peaks at 1638 (variable band) and 1609 cm−1 (reference band) before and after the polymerization reaction. The formulation was reconstituted to understand better the composite behavior. The organic and inorganic fractions were characterized by thermogravimetric analysis, X‐ray fluorescence, proton nuclear magnetic resonance, and scanning electron microscopy. The DC values lay between 48 and 54%, seemed to be not sensitive to the depth of polymerization, and indicated a large amount of residual monomer. On the other hand, a continuous decrease in the Vickers microhardness (from 61 to 52) was observed with an increasing depth of polymerization. This behavior could be attributed to differences in the crosslinking degree on the top and bottom surfaces of the polymerized samples. The material was a conventional dental restoration composite containing 26% monomer mixture (bisphenol A/dimethacrylate and triethylene glycol dimethacrylate), a small amount (2%) of an ormocer as a compatibilizing agent, and 72% inorganic filler (barium sulfate and aluminum silicate). The low DC values could be ascribed to several factors, such as the monomer viscosities, amounts, and types, the average sizes and distributions of the fillers, and the large difference between the refractive indices of the organic and inorganic constituents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 325–330, 2007