Effect of Selective Laser Melting Platform Placement Orientation on Removable Partial Denture Framework Fit

The purpose of this in vitro study was to determine the effects of three different framework orientation (FO) positions on a Selective Laser Melting (SLM) building platform and two different designs (with stabilizing bars [B] or not [NB]) on the fitting accuracy of digitally fabricated Co-Cr removable partial denture (RPD) frameworks. Materials and Methods. Custom RPD framework CAD was performed on a digitized (Trios-3 intraoral scanner, 3Shape™A/S, Copenhagen, Denmark) 3D printed single experimental prototype resin-model of an edentulous maxilla bearing three custom 3D geometric tooth-form shapes. Co-Cr fine powder alloy (Mediloy S-Co, Bego, Germany) was processed through SLM (TruPrint Series 1000, Trumpf, Germany) into framework specimens (n=24) by dividing into 3 building FO groups (N=8, Horizontal, H; Diagonal-45o, D45o; Diagonal-60o, D60o), further divided into 2 subgroups each (N=4, with stabilizing-bars, B; without bars, NB). Qualitative/quantitative fit-evaluation was then performed for all specimens following virtual framework-to-model seating, utilizing a previously developed custom digital protocol and a free inspection software (GOM Inspect, 2018-Hotfix5, Rev.115656, GOM GmbH, Braunschweig, Germany). Mean fitting distances were calculated from 220 equidistant vertical framework-to-model measuring locations per specimen and groups were statistically compared (p=0.05, ANOVA-on-ranks, Kruskall-Wallis multiple comparisons, Bonferroni adjustment).Results. FO Sub-Group medians (Q1, Q3: 25% and 75% Quartiles) (mm) were: H/NB 0.150 (0.140, 0.164), H/B: 0.136 (0.121, 0.152), D45o/NB: 0.230 (0.219, 0.241), D45o/NB: 0.144 (0.137, 0.154), D60o/NB:0.238(0.232, 0.247), D60o/B: 0.171 (0.166,0.176). Pairwise comparisons indicated the following statistically significant (p < 0.05) FO Sub-Group differences: H/B-D45o/NB, H/B-D60o/NB, D45o/B-D45o/NB, D45o/B-D60o/NB, H/NB-D45o/NB, H/NB- D60o/NB.

Key words: Removable Partial Denture, Co-Cr dental alloys, Selective Laser Melting, Platform Orientation, RPDs Fitting Accuracy, RPDs Dimensional Stability