A study of localized curing of glass‐filled composites using microhardness measurements

Abstract

Extent of cure of hybrid composite systems is examined by conducting hardness measurements at different stages of the photopolymerization reaction and obtaining kinetic parameters that matched the experimental data. The materials are commercial dental composites based on bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane resins with different photoinitiator concentrations as well as filler particle sizes and combinations. Samples (five per group) were made using nylon molds (2.5 ϫ 5 mm) of the tested composites. The samples were light cured with a constant-power light source for durations up to 20 s. After curing, all samples underwent Vicker's hardness testing of top and bottom surfaces. While there are significant differences in the polymerization behavior between the top and bottom locations for the tested composites, the corresponding growth exponent n, a kinetic parameter in the kinetic theory, is very close in all cases. For the tested materials the coefficient factor k is much lower for the bottom surfaces compared with the top surfaces. This reduction in the value of k is more severe for the material with a higher concentration of the photoinitiator as well as a higher percentage of glass filler particles in the wavelength range affecting the photopolymerization. It is argued that a relationship between k and the irradiation intensity can be used to quantify the decay of irradiated light with its penetration into the composites. The comparisons can be used to draw preliminary conclusions on the parameters controlling the effective depth of cure in a hybrid composite.

Polymerization efficiency of bulk‐fill dental resin composites with different curing modes

“…Perhaps the filler composition of the materials reduced their translucency, and this led to lower energy density in the deeper layers. Moreover, it was reported that the coefficient factor ( k ) was much lower for the bottom surfaces compared with the top surfaces of the composite specimens. This reduction in the value of k was more severe for the material with a higher concentration of photoinitiator and a higher percentage of glass filler particles in the wavelength range affecting the photopolymerization.…”