Accuracy and Reproducibility of Digital Vertical Dimension Increase in Occlusal Splint Design: A Comparative In Vitro...

Background: Digital workflows based on computer-aided design and computer-aided manufacturing (CAD/CAM) enable the modification of the vertical dimension of occlusion (VDO) during occlusal splint design; however, the clinical reproducibility of these digital adjustments compared with conventional methods remains unclear. Objective: This in vitro study aimed to evaluate the accuracy and reproducibility of vertical dimension increase achieved with three different dental CAD software systems. Methods: A standardized STL dataset was used to design occlusal splints with three CAD software systems: ExoCAD DentalCAD (Exocad GmbH, Darmstadt, Germany), InLab SW 23 (Dentsply Sirona, Bensheim, Germany), and Medit Link (Medit Corp., Seoul, South Korea). A conventional articulator-derived condition served as the comparator. Splints were manufactured using Night Guard Firm 2 Midnight resin (SprintRay Inc., Los Angeles, CA, USA), and the vertical dimension was measured with a digital caliper (Mitutoyo Corp., Kanagawa, Japan). Representative STL superimposition was performed using OraCheck 5.0 (Dentsply Sirona, Bensheim, Germany), and biomechanical behavior was assessed using ANSYS Mechanical 2025 R2 (ANSYS Inc., Canonsburg, PA, USA). Data were analyzed using one-way ANOVA followed by Tukey's HSD post hoc tests, with the significance level set at α = 0.05. Results: The CAD systems showed variable accuracy in reproducing the reference vertical dimension; the Medit Link group yielded values closest to the reference (22.80 mm vs. 22.68 mm), the InLab group demonstrated marked overestimation (26.70 mm), and the ExoCAD group presented intermediate values (24.36 mm). One-way ANOVA confirmed statistically significant differences between the four groups for both sides (p < 0.001) with very large effect sizes (η² > 0.98). Three-dimensional superimposition revealed that the InLab splint presented the smallest mean surface deviation from the control (0.36 mm) and the highest proportion of points within 0.1 mm (59%), whereas Medit Link and ExoCAD showed larger mean global distances (0.83 mm and 0.70 mm, respectively). FEA revealed differences in biomechanical behavior, with the highest representative von Mises stress in the Medit Link geometry and the highest representative total deformation in the ExoCAD geometry. Conclusions: Digital modification of VDO is feasible, but its accuracy and reproducibility depend on the CAD system used. Careful verification of CAD design parameters against a conventional clinical reference is advisable before manufacturing occlusal splints involving vertical dimension modification, while representative 3D superimposition may provide complementary descriptive information.