Light-polymerized compomers: Coefficient of thermal expansion and microhardness

Statement of problem. The relationship between the filler content, coefficient of thermal expansion, and microhardness of commercial light-polymerized compomers has not been fully investigated. Purpose. This study evaluated the effect of filler content on the coefficient of thermal expansion and microhardness of 3 commercially available light-polymerized compomers. Material and methods. Five specimens each from 3 commercially available compomers (Compoglass F, Elan and F2000) were evaluated. Linear thermal expansion (μm/°C) was measured with a thermomechanical analyzer in the temperature range 20° to 80°C with increments of 10°C. Standardized specimens were prepared in a metal die (1.5 x 2 x 12 mm) and polymerized for 40 seconds at 700 mW/cm² light intensity. The microhardness of 5 specimens from each of 3 compomers were measured with a Vickers hardness tester under a 15-second dwell time and 200-g load conditions. The specimens were polymerized at 700 mW/cm² intensity for 40 seconds after placing the compomers into a round aluminum mold. Differences in thermal expansion and microhardness among the compomers evaluated were statistically analyzed by use of one-way analysis of variance at P<.01 significance level, with differences assessed by use of Duncan's multiple range post hoc test. Results. The coefficients of thermal expansion of Compoglass F (54.17 ± 0.54 μm/°C), Elan (40.94 ± 0.78 μm/°C) and F2000 (24.43 ± 89 μm/°C) were almost linear in the temperature range 25° to 80μC for all 3 compomers (r >.99). Inverse correlations between die %wt of filler and the coefficient of thermal expansion (r = -0.98, P<.0001), as well as between the microhardness and the coefficient of thermal expansion (r = -0.98, P<.0001) were observed. On the other hand, a linear correlation between the %wt of filler and microhardness of compomers was exhibited (r = -0.96, P<.0001). The microhardness values for Compoglass F, Elan, and F2000 were 43.82 ± 1.62, 58.16 ± 1.90, and 72.94 ± 3.29, respectively. Conclusion. Within the limitations of this study, an inverse correlation between percent weight of filler and coefficient of thermal expansion, and a linear correlation between percent weight of filler and microhardness was observed for the evaluated compomers.