Impact of increased UV curing time on the curing depth of photosensitive resins for 3D Printing

Background: 3D printing (3DP) photosensitive resins are commonly used to produce patient-specific solutions in the fields of medicine and dentistry. These resins are toxic in their liquid state. To ensure that all resin has solidified and parts are safe for use, post-processing must be carried out after printing. Parts are first washed in IPA, allowed to dry, and then post-cured under ultra-violet light (UV), and sometimes heat. As 3DP is commonly utilised for its ability to create custom and rapid solutions, it is expected that a different geometry will be produced almost every time. Currently, post-processing guidance is supplied specific to a material, with the caveat that post-curing times should be extended for larger or complex parts. The aim of this study was to assess the effect of extending post-curing times for photosensitive resin printed parts. Method Two commercially available vat-polymerisation 3DP systems were used to print hollow 60mm diameter spheres. Two opaque white, two opaque black, and two translucent amber resins were used. The spheres were filled with liquid resin, then UV post-cured at intervals of 100, 200, 300, 400 and 500% of the recommended guidance. The spheres were sectioned along the centreline and radial measurements taken of the cured depth. Results The results showed that both translucent amber materials cured to full depth at the 100% interval, whereas none of the white or black opaque materials cured to full depth, even at 500% of the recommended guidance. Conclusions This suggests opacity has a considerable effect on the depth of cure in photosensitive resins, and that the use of opaque resins increases the possibility of uncured resin remaining inside parts.