Degree of conversion of 3D printing resins used for splints and orthodontic appliances under different post-polymerization conditions.

Objectives: To measure the degree of conversion (DC) of different 3D printing resins usable for splints or orthodontic appliances, manufacturing under different post-polymerization conditions. Materials: and Methods Five 3D printing photopolymer resins were studied. Each resin was analyzed in liquid form (n=15), then cylindrical specimens (n=135) were additively manufactured and post-cured with different times (10, 60 and 90 minutes) and temperatures (20°, 60° and 80°). The degree of conversion of each specimen was measured by Fourier Transformed Infrared Spectroscopy (FTIR). The data were statistically analyzed using a 3-way ANOVA followed by Tukey’s post hoc test. Results: Time and temperature of post-polymerization significantly influenced the DC of each resin: when time and/or temperature increased, the DC increased. For all resins tested, the lowest DC was obtained with a post-curing protocol at 10 min and 20° and the highest DC at 90 min 80°. However, at 80°, samples showed a yellowish color. Conclusions: The time and temperature of post-curing could have an impact on the DC of the 3D printing resins studied. DC of the 3D printing resins could be optimized by adjusting the post-polymerization protocol. Clinical Relevance Whatever the resin used, it seems that a post-curing at 60 min and 60° would be the minimal time and temperature conditions to obtain a proper polymerization. Beyond that, to boost the DC, it would be preferable to increase the post-curing time