Abstract
This study aimed to evaluate and compare the dimensional accuracy (trueness and adaptation) and surface roughness ($R_a$) of cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks fabricated using Direct Metal Laser Sintering (DMLS), subtractive CAD/CAM milling, and conventional lost-wax casting. A standardized Partially Edentulous Maxillary Model (Kennedy Class II Modification 1) was digitized using an optical benchtop scanner. Thirty Co-Cr frameworks were fabricated across three equal groups ($n=10$): Group C (lost-wax casting), Group M (CAD/CAM milling), and Group D (DMLS). Dimensional accuracy was assessed by superimposing high-resolution 3D scan data of the frameworks onto the master digital model, calculating root mean square (RMS) deviation and measuring gap distance at designated rest seats and major connector regions using 3D inspection software. Surface roughness ($R_a$) was measured before and after a standardized polishing protocol using non-contact optical profilometry. Group M and Group D demonstrated significantly lower RMS deviation values ($36.1 \pm 4.2\, \mu\text{m}$ and $42.5 \pm 5.1\, \mu\text{m}$, respectively) compared to Group C ($78.3 \pm 9.4\, \mu\text{m}$, $p < 0.001$). DMLS frameworks exhibited superior fit consistency across complex geometry compared to cast frameworks. Prior to polishing, Group D presented the highest surface roughness ($6.42 \pm 0.58\, \mu\text{m}$), but post-polishing $R_a$ values dropped below the critical $0.2\, \mu\text{m}$ threshold ($0.16 \pm 0.03\, \mu\text{m}$) across all groups with no statistically significant differences ($p = 0.184$). DMLS Co-Cr RPD frameworks provide dimensional accuracy superior to conventional casting and comparable to CAD/CAM milling, while post-processing yields clinically acceptable surface smoothness.
