Clinical Performance and Oral Safety of 3D-Printed Definitive Crowns Versus Milled Resin-Ceramic Restorations: A Multicenter Randomized Controlled Trial

Abstract

Additive manufacturing is increasingly used for definitive dental restorations, yet uncertainty remains regarding its long-term clinical performance, biological safety, and resistance to intraoral aging compared with established subtractive computer-aided manufacturing. This multicenter randomized controlled trial proposes to compare 3D-printed definitive resin-based crowns with milled resin-ceramic crowns over a three-year follow-up period. Adults requiring a single posterior tooth-supported crown will be randomly assigned to receive either a digitally fabricated 3D-printed definitive crown or a milled resin-ceramic restoration using standardized preparation, scanning, design, cementation, and finishing protocols. The primary outcome will be restoration survival without replacement or major intervention at 36 months. Secondary outcomes will include fracture, chipping, debonding, marginal integrity, anatomical form, occlusal wear, surface roughness, color stability, antagonist wear, plaque accumulation, gingival inflammation, and patient-reported esthetic and functional satisfaction. Intraoral digital scans will permit quantitative three-dimensional assessment of restoration and antagonist wear. Salivary and local gingival samples will be obtained at predefined intervals to evaluate inflammatory biomarkers and potential resin-derived leachable compounds using high-performance analytical techniques. Surface replicas from selected restorations will undergo microscopic characterization to assess degradation patterns over time. Cost-effectiveness will also be examined using fabrication time, laboratory expenses, chairside adjustments, complications, and retreatment requirements. Analyses will follow intention-to-treat principles, with survival analysis and mixed-effects longitudinal models accounting for repeated observations and center-level clustering. Particular attention will be given to whether aging-related material changes correspond with biological responses in adjacent oral tissues. This trial is intended to address the gap between promising laboratory performance and limited long-term clinical evidence for additively manufactured definitive restorations. Establishing comparative effectiveness, material safety, patient-centered outcomes, and economic implications within one investigation could provide clinically actionable evidence for selecting additive versus subtractive workflows in contemporary restorative dentistry.