Assessing the performance of 3D-printed resin composite posterior fixed dental prostheses: A 3-year prospective clinical trial

Objectives: This clinical trial aimed to assess the clinical performance of 3D-printed resin composite fixed dental prostheses (FDPs) for posterior restorations. Methods: From October 10, 2020, to August 5, 2022, a total of 49 patients (33 females and 16 males), aged 19 to 60, were treated with 68 three-unit 3D-printed resin composite posterior FDPs (ELS Even Stronger, Saremco, Switzerland). Two weeks after placement, the FDPs were evaluated by two independent observers using modified FDI criteria. Parameters assessed included anatomical form, secondary caries, marginal adaptation, surface roughness, color match, material fracture, surface staining, margin staining, anatomical form, retention, gingival health, and patient satisfaction. Failures were classified as either mechanical or biological. Results: The mean observation period was 22.36 months. At the final recall, of the 64 FDPs, 24 remained in clinical service without any complications, indicating limited long-term success. Almost all restorations maintained normal anatomical contours throughout the follow-up period. During the initial six-month period, 9 instances of fractures were identified, followed by 14 after 1 year, 11 after two-year a further 2 cases after a three-year period of clinical service. Of the 40 failed FDPs, 36 exhibited mechanical failures, while 6 showed biological failures (2 cases exhibited both and were counted in both categories). Thirty-four FDPs showed cohesive fractures. Two FDPs were re-bonded, four abutment teeth required endodontic treatment, and two presented periodontal issues. Additionally, 2 FDPs exhibited a loss of surface luster, 4 exhibited color mismatches, and 4 exhibited surface staining (all scored 4). Kaplan-Meier analysis revealed a 40.7 % survival rate for mechanical failures and a 36.2 % survival rate when biological complications were included. Conclusions: The results of a three-year follow-up study indicated that 3D-printed resin composite FDPs present failures mainly in the connector region, suggesting the need for further design improvements. Clinical Significance: Three-dimensionally printed resin composite FDPs offer certain advantages but current restorations could be considered as long-term provisional due to the incidence of mainly mechanical failures up to 3 years. Clinical Trial Registration: Clinical Trials.Gov, NCT04600297.