Effects of post-polymerization on stainability and surface roughness of 3D printed composite resin.

Statement Of Problem: Although the post-polymerization is a necessary step to attain the final properties and color of the 3-dimensionally (3D) printed composite resins, research on its effects on color change and surface roughness is lacking.

Purpose: The purpose of this in vitro study was to evaluate the effect of post-polymerization time and additional placement in boiling water on the color change and surface roughness of 3D printed composite resins after exposure to coffee for 30 days.

Material And Methods: Sixty disk-shaped specimens (Ø10×2 mm) were 3D printed with composite resin (Crowntec). The specimens were randomly divided into 6 groups (n=10), according to the post-polymerization process at 3 different times (2×5, 2×10, and 2×20 minutes) and depending on subsequent placement in boiling water. The color differences (ΔE) between the baseline and each aging period (1, 7, 15, and 30 days) were determined by using a spectrophotometer. After 30-day aging period, ΔL*, Δa*, and Δb* values were calculated. The surface roughness (Ra) was measured at various aging periods (initial, 7, 15, and 30 days) by a 3D noncontact optical profilometer. The data were analyzed using 2-way repeated measures ANOVA and 1-way ANOVA tests for each aging period followed by Tukey tests (α=.05).

Results: As the post-polymerization time increased, a significant decrease was found in ΔE values (P<.001), while no significant difference was found in Ra values (P=.554). The values of ΔE and Ra increased with the aging period (P<.001). Additional placement in boiling water resulted in a statistically significant decrease in both ΔE and Ra values (P<.001). As the post-polymerization time increased, the Δa* and Δb* values decreased, while the negative ΔL* values increased (P<.001), except for Δa* between 2×10 and 2×20 (P=.175). Additional placement in boiling water resulted in a significant decrease in Δa* and Δb* values and an increase in the negative ΔL* values (P<.001), except for Δa* in 2×20 (P=.379).

Conclusions: An increase in post-polymerization time resulted in reduced stainability, while additional placement in boiling water led to reduced stainability and roughness. When subsequently placed in boiling water, the post-polymerization time had no effect on either stainability or roughness.