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ABSTRACT:The 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/cm 2 ) 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 Ϫ1 (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.

Chitosan (CH) decorated polystyrene (PS) particles were synthesized within complexes of CH, a polycation under acid conditions, and tiny amounts of sodium dodecylsulfate (SDS). Particle characterization was performed by means of dynamic light scattering, zeta potential measurements, and transmission electron microscopy. All dispersions were stable in the ionic strength of 2.0 mol L-1 NaCl during 2 months. The outstanding colloidal stability was attributed to the presence of a hydrated CH layer around the particles. CH decorated PS particles were attached to atomic force microscopy cantilevers and probed against Si wafers in water and in NaCl 0.01 mol/L. The mean thickness of CH layer amounted to 35 +/- 11 and 16 +/- 6 nm, when the medium was water and NaCl 0.01 mol/L, respectively. Adsorption isotherm of hexokinase (HK) onto PS/CH particles studied by means of spectrophotometry showed three regions: an initial step; adsorption plateau and multilayer formation. Enzymatic activity of free HK and immobilized HK was monitored by means of spectrophotometry as a function of storing time and reuse. After 3 days, storing HK free in solution dramatically lost its catalytic properties. On the contrary, HK-covered PS/CH particles retained enzymatic activity over 1 month. Moreover, HK-covered PS/CH particles could be reused in the determination of glucose two times consecutively, without losing activity. These interesting findings were discussed in light of the role of water in enzyme conformation.