Purpose: To evaluate the clinical usefulness of directly fabricated glass and polyethylene resin-bonded fiberreinforced composite (FRC) inlay-retained fixed dental prostheses (FDPs) in posterior single missing teeth over a short period of time. Materials and Methods: Fourteen inlay-retained FRC FDPs with tub-shaped or box-shaped retainers were directly constructed in patients of both genders. A baseline examination was performed and the patients were examined regularly at 6-month intervals. The sulcus bleeding index, Silness-Löe plaque index, and probing depths of the abutments were checked regularly. Modified US Public Health Service (USPHS) parameters were used to compare the restorations at baseline and final examination. The Kaplan-Meier survival estimation method was performed to detect the overall survival rates and mean survival times of the restorations at the end of the follow-up. Results: The length of the clinical observation was between 16 and 40 months for the FDPs still functioning after the end of the follow-up. No partial or total debonding of the prostheses or fracture of the frameworks was detected. Four veneering composite fractures at the veneer layer/fiber framework interface occurred in the pontic elements of 2 glass FRC FDPs and 2 polyethylene FRC FDPs after 6 and 10 months, and 20 and 22 months, respectively. Periodontal evaluation revealed clinically acceptable results, as did the USPHS evaluation. The overall survival curves of Kaplan-Meier at the end of the follow-up illustrated a 71% survival rate for the both glass and polyethylene FRC FDPs with mean survival times of 27 and 35 months, respectively. Conclusion: This study reported a mean period of service of 19 and 31 months for directly fabricated inlayretained glass and polyethylene FRC FDPs, respectively, with a 71% survival rate for the two framework constructions. Within the limitations of the study, these results can only be considered as preliminary. However, because of the lack of clinical data available for directly fabricated inlay-retained FRC FDPs, the results of this clinical observation may contribute to the still-evolving clinical knowledge of the FRC restorations. Keywords: fiber-reinforced composite FDPs, inlay-retained FRC FDPs, directly fabricated FRC FDPs, resin-bonded FRC FDPs, glass FRC, polyethylene FRC