Effect of glycerin gel application for post-curing process on the flexural strength, elastic modulus, and microhardness of 3D printing resins.

Purpose: To investigate the effect of the application of a glycerin gel on the surface of 3D printing resins (3DPRs) samples as a physical barrier, avoiding the inhibition layer formation caused by the presence of atmospheric oxygen during the post-curing process on their physical properties of 3DPRs.

Materials and methods: Two 3DPRs were tested: one for "provisional" restorations (Prizma 3D Bio Prov) and another for indirect "permanent" restorations (Prizma 3D Bio Crown). Samples of 3DPRs were printed for flexural strength, elastic modulus, and Knoop microhardness analysis (n = 10). Two post-curing treatments were investigated: a "Control" (without application of a glycerin gel on 3DPRs samples) and an "experimental" that included the glycerin gel application to cover the surfaces of the 3DPRs samples during the post-curing process (10 min). Generalized linear model analysis was applied to evaluate the data, followed by the Bonferroni test (α=0.05).

Results: The glycerin gel application significantly increased the flexural strength (15 - 26%) and elastic modulus (26 - 35%) of 3DPRs (p<0.05). The flexural strength and elastic modulus did not differ between 3DPRs, regardless of the glycerin gel application (p>0.05). The microhardness measured at different internal depths did not vary, regardless of the type of 3DPR and glycerin gel application (p>0.05).

Conclusions: The application of the glycerin gel on the surface of the 3D-printed samples positively impacted the flexural strength and elastic modulus results for both 3DPRs tested, but the glycerin gel application did not influence their internal microhardness.