Effect of Shade on the Polymerization of Dental Composite Resin

Objectives: Light-cured dental composite resin comes in various shades to match the color of teeth. However, to control the shades, pigments are used in conjunction with the yellow camphorquinone. The added pigments can modify the optical properties of the composite resin. The objective of the study was to test the effect of shade on the quality of the polymerization in a composite resin (Z250). Methods: Four different shades (A3, A3.5, B3, C3) were chosen for the study and absorbance, microhardness, and color change of specimens were evaluated. To test the baseline absorbance, cylindrical resin specimen (n=5, 2x7mm) was light cured (40s, 1100mW/cm²) and the number of the photons transmitted through the specimens was measured using the photodiode detector and spectrophotometer (UV-VIS-NIR). To measure the surface microhardness, the resin specimen (4x2x3mm) of different thickness (1, 2, 3mm) was stored (37°C, 24h in dark chamber) and measured using Vickers hardness tester (n=12, 200g, 10s). To evaluate color change, specimens for each shade (n=5) were immersed in distilled water (37°C, 10d) and the absorbance was measured again. The results from microhardness and color change were analyzed (ANOVA, Tukey's, p<0.05). Results: The number of the incident photons decreased exponentially as the specimens thickened. Specimens of shade A3 showed statistically different microhardenss values from the other shades (p<0.05). Color difference (ΔE*) of specimens were as follows; A3 (2.3±0.2), A3.5 (2.2±0.2), B3 (0.9±0.1), C3 (0.9±0.1). Specimens of different shades had different L*, a*, and b* values, especially A and B, C (p<0.05). Conclusions: Shades of Z250 may have an effect on the physical properties of polymerization and color changes.