BACKGROUND AND OBJECTIVE: Color change of composite resin restorations is one the most common causes for replacing these restorations, which might occur due to internal and external factors. This research was carried out to study and compare color change value of three types of composite resins in distilled water during the first 24 hours after exposure to light.

METHODS: In this laboratory research, 120 samples were prepared from three types of composites (Z350, Z250 and Heliomolar) and were divided into 3 groups of 40. Samples with 2 mm thickness and 7 mm diameter were prepared. After assessing the initial color by spectrophotometer, samples were exposed to distilled water for 1, 6, 12 and 24 hours, respectively. Then, the final color was assessed by EasyShade device and the color change value (ΔE) was calculated for all samples. Moreover, ΔE<3.3 was clinically acceptable.

FINDINGS: In 12h group, Heliomolar composite showed lowest color change value compared with two other composites (Z350=1.385, Z250=1.179 and Heliomolar=0.854) (p<0.05), while no significant difference was observed in other groups. Furthermore, lowest color change value in each composite was observed 1 hour after curing (Z350=0.352, Z250=0.641 and Heliomolar=0.298) and color change value increased 24 hours after curing (Z350=1.888, Z250=1.903 and Heliomolar=1.929).

CONCLUSION: Results of the study revealed that color change value of all three composites in distilled water was less than 3.3 after 24 hours and it was clinically acceptable