A Comparative Evaluation of the Passivity of Screw-retained Interim Implant-supported Prostheses Fabricated by Additive Manufacturing, Subtractive Manufacturing, and Conventional Techniques

Abstract Purpose: This study aimed to evaluate and compare the passivity and vertical marginal misfit of short-span, screw-retained interim implant-supported prostheses fabricated using three different techniques: Additive manufacturing, subtractive manufacturing, and the conventional technique, to determine the most effective technique for achieving optimal passive fit. Materials and Methods: Thirty interim prostheses ( n = 30) were fabricated for ten patients requiring two implants for rehabilitation of a short edentulous span in the mandibular premolar-molar region. For each patient, three sets of prostheses were fabricated, which were divided into three groups: Group A (additive manufacturing via stereolithography), Group B (subtractive manufacturing via computer-aided designing/computer-aided manufacturing [CAD/CAM] milling), and Group C (conventional technique via heat-cured acrylic resin). A standardized prosthesis design was followed across all groups. Passivity was assessed intraorally through direct visual inspection and tactile perception on a 5-point scale by three blinded observers. Vertical marginal misfit was evaluated using a one-screw test under a stereomicroscope on definitive casts before prosthesis delivery. Data were statistically analyzed using one-way ANOVA and intergroup comparisons. Results: The study revealed a significant difference in passivity among the three groups. Subtractive manufacturing demonstrated the highest level of passivity, with significantly more prostheses receiving “excellent” scores compared to additive and conventional methods ( P = 0.027*). Vertical marginal misfit values were lowest and statistically comparable for additive (5.92 ± 4.59 μm) and subtractive (5.94 ± 5.19 μm) manufacturing, both significantly better than the conventional group (20.73 ± 4.24 μm, P = 0.001*). Passivity differed significantly between subtractive and additive ( P = 0.022*) and subtractive and conventional methods ( P = 0.011*), but showed no significant difference between additive and conventional manufacturing ( P = 0.796). Conclusion: Subtractive manufacturing is the most effective technique for achieving optimal passivity in interim implant-supported prostheses, outperforming both additive manufacturing and conventional techniques. However, both subtractive and additive manufacturing methods yielded comparable results for vertical marginal misfit, with the conventional method showing a greater discrepancy. Therefore, CAD/CAM technology, particularly subtractive manufacturing, should be the preferred approach for fabricating interim prostheses.