Clinical Evaluation of Additive and Subtractive Onlay Restorations

The goal of this clinical trial is to learn whether onlay restorations produced by additive manufacturing \[three-dimensional (3D) printing\] and subtractive manufacturing \[Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) milling\] perform equally well in vital posterior teeth. The main questions it aims to answer are: * Do 3D printed onlay restorations show similar marginal adaptation and clinical performance compared to CAD/CAM milled onlays? * Are there any differences in biological compatibility, surface properties, or postoperative sensitivity between the two techniques over time? Researchers will compare onlay restorations fabricated with 3D printing and CAD/CAM milling using a split-mouth study design. Participants will: * Receive one onlay restoration produced by 3D printing and another produced by CAD/CAM milling, placed on opposite sides of the mouth * Have checkups at baseline (1st week), 6 months, 12 months, and 18 months after treatment * Be evaluated using the Fédération Dentaire Internationale (FDI) criteria for marginal adaptation, surface quality, anatomical form, and biological compatibility

This prospective, randomized, split-mouth clinical trial is designed to evaluate the clinical performance of onlay restorations fabricated by two different digital manufacturing techniques-additive manufacturing (3D printing) and subtractive manufacturing (CAD/CAM milling)-in vital posterior teeth. Each participant will receive two onlay restorations: one produced by CAD/CAM milling using hybrid ceramic blocks (GC Cerasmart 270) and one produced by 3D printing with a biocompatible permanent resin (Bego VarseoSmile TriniQ). The restorations will be placed in contralateral posterior teeth, allowing direct intra-individual comparison under identical oral conditions. Randomization will determine which tooth receives which manufacturing method. The primary outcome of the study is marginal adaptation, assessed according to the Fédération Dentaire Internationale (FDI) World Dental Federation criteria. Secondary outcomes include surface quality, anatomical form, functional stability, postoperative sensitivity, color match, and biological compatibility. Clinical evaluations will be performed at baseline (1 week) and at 6 months, 12 months, and 18 months. To minimize bias, participants and clinical evaluators will remain blinded to the type of restoration applied. Calibration sessions will be conducted for all evaluators to ensure consistency and reliability of outcome assessment. An independent statistician, blinded to group allocation, will perform the statistical analyses. A total of 29 participants are expected to be enrolled, based on power analysis using G\*Power software, which indicated that this sample size provides 85% power with a 95% confidence level. Inclusion criteria consist of adults aged 18-84 with vital posterior teeth requiring onlay restorations, without systemic disease or active periodontal pathology. Teeth with pulp vitality confirmed by thermal or electrical testing and with moderate structural loss suitable for onlay restorations will be included. Exclusion criteria include teeth with previous endodontic treatment, advanced periodontal disease, or a history of full-coverage prosthetic restoration. All procedures will follow standardized clinical protocols, including tooth preparation, digital intraoral scanning, design with CAD software, manufacturing with either milling or 3D printing, and adhesive cementation. Adverse events such as restoration failure, pulp complications, or allergic reactions to materials will be documented and reported according to regulatory requirements. This study is expected to provide robust, long-term clinical evidence comparing the performance of additively and subtractively manufactured onlay restorations, addressing a current gap in the literature. The results will contribute to evidence-based clinical decision-making in digital restorative dentistry and support the development of guidelines for material and technique selection.