3D Printed Ceramic-Filled Photopolymer Resin Vs. CAD/CAM Resin Composite Overlays for Restoration of Extensively Damaged Endodontically Treated Posterior Teeth. An 18-month Follow-up

II. Introduction: 6\. Background and rationale: Restoring badly mutilated teeth was and has always been a challenge in restorative dentistry. In order to solve this issue, different approaches have been proposed, including cuspal protection or cuspal coverage. This proved to increase the fracture resistance of remaining tooth structure and overall survivability of endodontically treated teeth. Different materials and techniques have been proposed to attain cuspal coverage, such as using indirect milled or pressed ceramics, indirect milled composite, and direct composite restorations(Abu-Awwad, 2019). The integration of 3D printing in dentistry has revolutionized the fabrication of permanent indirect restorations, including inlays, onlays, and overlays. Evaluation of whether the mechanical properties, clinical feasibility, and accuracy of 3D-printed resin restorations are compared to traditional milled and pressed alternatives. Key findings highlight superior marginal fit, cost-efficiency, and adaptability of 3D-printed resins, while addressing limitations such as stain susceptibility and long-term durability Research question: Does a 3D printed ceramic-filled photopolymer resin show any difference in clinical performance when compared to a CAD/CAM milled composite in restoring badly decayed endodontically treated posterior teeth? Statement of the problem: The problems of indirect milled composites include the initial cost of the milling machine, running cost of machine repairs, bur changes, and the cost of discs and blocks, not to mention that the concept of milling as a manufacturing process has an unavoidable loss of material. (Josic et al., 2023) Rationale for conducting the research: Indirect restorations, such as inlays (without cusp coverage), onlays (partial cusp coverage), and overlays (full cusp coverage), aim to preserve tooth structure while restoring function and esthetics. Historically, these restorations were fabricated using ceramics or compos