Similar Marginal Precision of Zirconia- and Metal-Ceramic Posterior Fixed Dental Prostheses Objective: An increased gap between restoration and prepared tooth causes more luting material to be exposed to the oral environment resulting in increased deterioration, leading to bacterial accumulation which can cause marginal periodontitis and secondary caries. The purpose of this randomized clinical study was to compare the marginal precision of CAD/CAM Zirconia-ceramic (ZC) and cast gold alloy metal-ceramic (MC) posterior fixed dental prostheses. Methods: As part of an ongoing randomized controlled clinical trial, 34 patients were randomized into two groups to receive a 3-unit fixed dental prosthesis (FDP) replacing a second premolar or a first molar. 17 ZC FDPs (BeCe CAD Zirkon, BEGO with Vita VM9, VITA ) and 17 MC FDPs (Bio PontoStar, BEGO with Vita VM13, VITA). All FDPs were made in accordance with the manufacturer’s guidelines by one operator. Before and after veneering, the FDPs were placed on the abutment teeth with a light-body A-silicone impression material (Extrude Wash, Kerr) between the restoration and the abutment teeth. After setting, the FDPs were removed and the light-body material was stabilized with a heavy-body impression material (Extrude, Kerr). The impression specimens were segmented to allow measurements of the thickness of the light-body material corresponding to the marginal gap at 12 points for each abutment. The measurements were done under 32X magnification with SPOT Advanced. Statistical analysis was performed with Mann-Whitney Rank Sum Test and Wilcoxon Signed Rank Test (p<0.05). Results: The FDPs’ mean marginal gap was 82.5 µm (Range: 52.6-135.6 µm) and 71.5 µm (Range: 42.1-135.3 µm) for ZC and MC, respectively. The only statistically significant difference was observed at the lingual margins with median values of 94.5 µm for ZC and 61.6 µm for MC. Conclusion: Overall, posterior 3-unit FDPs of ZC and MC exhibited similar and acceptable marginal precision.