Comparative Insights Into the Degree of Conversion of a 3D-Printed Photopolymer Occlusal Splint Resin Fabricated by Stereolithography and Masked Stereolithography Compared to Heat-Polymerized Acrylics

Abstract

The degree of conversion (DC) is a critical determinant of the biocompatibility and long-term performance of occlusal splints. However, limited evidence exists on how emerging three-dimensional printing technologies, particularly masked stereolithography (MSLA), affect polymerization efficiency compared to established methods. This study investigated the DC of a photopolymer-based occlusal splint resin fabricated using stereolithography (SLA) and MSLA technologies, compared to a conventional heat-polymerized acrylic resin. DC was assessed by Fourier Transform Infrared Spectroscopy (FTIR) at three stages for printed specimens: the unpolymerized resin, after printing and washing (DC Print), and after post-curing (final DC). The difference between DC Print and final DC (ΔDC) represented the contribution of the post-curing step. Conventional specimens were evaluated after mixing and after polymerization. The final DC of the conventional group was significantly higher than both SLA and MSLA groups (p < 0.001), although SLA and MSLA did not differ significantly (p > 0.05). Post-curing significantly enhanced polymerization in both printed groups. MSLA printing achieved comparable DC to SLA while reducing production time. These findings support MSLA as a promising and time-efficient method for splint fabrication, though further improvements in resin formulation and post-curing protocols are warranted to match the polymerization efficiency of conventional heat-polymerized acrylics.