3D printed dental protheses using TPO-initiated photopolymerization. Effect of the photoinitiator concentration and the use of a UV-blocker

A DLP 3D printer was used to reproduce several objects (a trunk scaffold, a cube, and a dental crown) in order to ascertain the conditions to obtain the best resolution. The polymerizing solution was a mixture of BisGMA, TEGDMA, and UDMA monomers. The photoinitiator was triphenyl phosphinic oxide (TPO) at various concentrations in the presence and absence of the UV-light blocker 2.5-bis (5’-tert-butyl 2-benzoxazolyl)thiophene (Datilux OB). The printed objects were analyzed by Scanning Electron Microscopy. It was found that the best results were obtained using concentrations of 1 and 2% m/m of TPO in the presence of 0.1% of the UV-blocker. This blocker has an absorption spectrum similar to the photoinitiator and avoids secondary photoinitiations due to reflections that may cause imperfections in the printed objects. The effect of the UV-blocker was evaluated by thermal analysis of the obtained polymers showing that in the presence of the blocker 3–4 times more monomers remained unpolymerized, indicating that the more irregular objects were due to the excess of undesired polymerization. ShoreD hardness of the dental crown material was around 80, within the values reported for other dental materials.