Effect of layer thickness and post-curing protocol on the trueness and precision of DLP-printed occlusal splints

Abstract Background This in vitro study evaluated the effects of layer thickness and post-curing protocol on the trueness, precision, and mean internal gap of digital light processing (DLP)-printed occlusal splints. Methods A maxillary occlusal splint was fabricated by digital light processing (DLP) at 30, 50, and 100 μm and post-cured using Form Cure/air (S30-F, S50-F, S100-F) or Dreve PCU LED/nitrogen (S30-D, S50-D, S100-D). Six printed groups and one milled polymethyl methacrylate (PMMA) control group (S-C) were evaluated ( n = 8 per group). Trueness was assessed by root mean square (RMS) deviations of external, overall, and intaglio surfaces from the reference standard tessellation language (STL) file. Mean internal gap was measured using a triple-scan protocol. Within-group RMS variability was assessed using absolute deviations from group medians. Data were analyzed using two-way and one-way analysis of variance (ANOVA) and post hoc tests; RMS variability was analyzed using the median-centered Levene test with the Brown–Forsythe modification and Holm-adjusted pairwise comparisons (α = 0.05). Results Layer thickness significantly affected RMS trueness and mean internal gap ( p < .05). The 50-µm groups showed the lowest RMS deviations, whereas the 100-µm groups showed the lowest mean internal gaps. Post-curing protocol did not significantly affect external or overall RMS deviations. Internal RMS differed between protocols at 30 μm, but not at 50–100 μm. Post-curing protocol significantly affected mean internal gap ( p < .001). External RMS variability differed among groups ( p = .023), but no pairwise comparison remained significant after Holm adjustment. Internal and overall RMS variability did not differ significantly ( p = .096 and p = .067, respectively). Conclusions Layer thickness influenced splint trueness and mean internal gap, with 50-µm printing yielding the lowest RMS deviations and 100-µm printing yielding the lowest mean internal gaps. No pairwise differences in RMS variability were established. Lower mean internal gap alone does not establish superior adaptation or clinical fit. The two post-curing protocols differed in both device and atmosphere; therefore, the independent effect of atmosphere could not be determined. RMS deviations and mean internal gaps provide complementary, not interchangeable, information. RMS variability does not directly measure surface-to-surface repeatability.