Stress distortion of 3D printing dentures with different printing directions

Objectives: The purpose of this study was to evaluate the effect of printing direction on the stress distortion and trueness of dentures manufactured by 3D printer.

Methods: The upper dentures were designed with CAD software. The printing direction of the dentures was set to 0°, 45° and 90°. A photopolymer resin was printed by 3D printer (Form 2) with a layer thickness of 100 µm (N=6). The trueness was evaluated by superimposing the after 3D printed STL file on the original STL file for each denture. The acquired images were processed and analyzed using a 3D analysis software (CATIA V5). The root means square estimates (RMSEs), and color map data was acquired. Strain gauges (Kyowa Electronic Instruments) were cemented on the oral surface of each denture: above the labial frenum (LF), at the incisive papilla (IP), at the end point of the denture (EP), and at the mid-point of the IP and EP (MP). An occlusal load was applied by a testing machine at a loading rate of 20 N/s to 200 N. The strain were recorded, and the maximum principal strain (MPS) was calculated. Each average of RMSEs with 0°, 45° and 90° were statistically, respectively by one-way ANOVA and Tukey’s multiple comparison (α=0.05). Each average of MPS were statistically, respectively by Kruskal-Wallis and Steel-Dwass multiple comparison (α=0.05).

Results: The lowest RMSEs was obtained with 45° experimental dentures, followed by 0° and 90° groups. When the MPS ranking were 0°, EP was the largest, followed by MP, IP and LF. 45°, the IP was the largest, followed by LF, EP, and MP. 90°, IP was the largest, followed by EP, MP, and LF.
Conclusions: Within the limitation of this study, printing direction of 45° showed the least stress distortion and highest trueness of the dentures manufactured by 3D printer.