Three Dimensionally Printed Ceramic-Filled Photopolymer Resin Versus CAD/CAM Resin Composite Overlays for Restoration of Extensively Damaged Endodontically Treated Posterior Teeth. An 18-month Follow-up Randomized Controlled Trial

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 composite resins via subtractive milling or heat-pressing techniques. However, 3D printing has emerged as a transformative technology, enabling additive manufacturing of resin-based restorations with enhanced precision and reduced material waste. (Tribst et al., 2024)

Review of literature:

Extensively destructed endodontically treated molars may represent a high-risk restorative scenario due to loss of internal dentin support and undermined cusps leading to increased flexure, stress concentration and analysis, making failure more likely to occur due to cuspal fracture, bulk fracture, tooth splitting or adhesive debonding rather than simple marginal defects. Contemporary restorative concepts therefore emphasize preserving remaining tooth structure while providing cuspal coverage through adhesively bonded partial-coverage restorations like onlays, overlays and endocrowns, aiming to redistribute occlusal loads and reduce catastrophic tooth fracture. Clinical reviews of root-filled teeth consistently highlight that prognosis depends less on "endodontic status" itself and more on the quantity and quality of remaining coronal tissue, presence of ferrule, and the capacity of the definitive restoration to protect the tooth under function.

Among current treatment options, direct resin composite restorations remain attractive for being conservative, repairable, and cost-efficient. However, the effectiveness of this treatment modality decreases as cavity size leading to increased polymerization shrinkage stresses, reduced cuspal stiffness as a result of increased cavity depth, difficulty in achieving durable proximal anatomy in very large defects, and technique sensitivity under moisture compromised isolation, which can translate into higher risk of fracture or marginal breakdown over time. Indirect restorations including full crowns, partial-coverage ceramic restorations, and resin-based CAD/CAM restorations can provide better anatomic control and cuspal coverage, but has some drawbacks like added steps, cost, and may require more tooth reduction depending on design and material used.

Systematic review and meta-analysis evidence focusing specifically on endodontically treated posterior teeth suggests that outcomes between direct composite and indirect approaches can be broadly comparable in some settings, but there is a tendency for indirect restorations to be favored as defect severity increases and remaining walls decrease, while direct restorations may be more appropriate for smaller defects; importantly, the available evidence is heterogeneous and often limited by variation in preparation design, materials, and follow-up.