Effects of Initiators, Inhibitors and Cross-linking Density on Curing-Depth

Objectives: 3D printing based on Digital Light Processing (DLP) has been used for fabricating dental devices. The objective of this study was to investigate the effects of different levels of an initiator, inhibitor and cross-linking density on the DLP curing depths over various irradiation periods to better control the dimensions of 3D printed dental objects.
Methods: A DLP projector controlled by a computer was used to cast a circle image onto the bottom of a liquid resin vat over a specific time period (from 0.25, 0.5, 1, 2, 4 to 8sec) and then the heights of cured specimens were measured (at least 3 irradiations were collected and averaged for each data). 27 resin mixtures were prepared with different levels of initiator (Lucirin-TPO from 0.8wt%, 2wt% to 5wt%), inhibitor (BHT from 0.1wt%, 0.4wt% to 1.6wt%), and cross-linking density (3 levels with trimethylolpropane acrylate and tetrahydrofurfuryl acrylate).
Results: Curing speed increased with the increase of initiator, but the curing depth varied. Very high levels of initiator reduced the curing depth due to light absorption by initiator. Curing speed and curing depth reduced with the increases of inhibitor. The level of cross-linking density did not show significant effects on curing depth and curing rate. The results of the present study provide a basis for understanding the curing depth and the response of a DLP projector on various resin systems with different levels of initiator, inhibitor and cross-linking density. The curing depth data was statistically compared pair-wise.
Conclusions: The curing depth and curing rate of the selected resin system should be precisely controlled by adjusting the levels of initiator and inhibitor to accurately fabricate 3D dental objects and achieve desired details. Highly cross-linked resin systems are not needed to achieve fast curing and desired curing depth, which allows for a broader material selection.