The goal of this clinical trial is to compare the clinical performance of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM)-milled and 3D-printed composite resin partial-coverage restorations in endodontically treated molars.

The main questions it aims to answer are:

• Do 3D-printed composite resin partial-coverage restorations show similar clinical performance compared with CAD/CAM-milled composite resin restorations?
• Are there differences in survival, success rates, and complications between the two types of restorations over a 3-year follow-up period?

Researchers will compare CAD/CAM-milled composite resin restorations with 3D-printed composite resin restorations to evaluate their clinical performance.

Participants will:

• Receive a partial-coverage restoration (onlay or overlay) in an endodontically treated molar.
• Be randomly assigned to receive either a CAD/CAM-milled or a 3D-printed composite resin restoration.
• Attend follow-up visits at 12, 24, and 36 months.
• Undergo clinical evaluations by two blinded evaluators using the revised FDI criteria and standardized photographic documentation.

This randomized controlled clinical trial evaluates the clinical performance of indirect composite resin partial-coverage restorations fabricated using subtractive and additive manufacturing technologies in endodontically treated molars.

The study investigates whether 3D-printed composite resin restorations can achieve clinical outcomes comparable to CAD/CAM-milled composite resin restorations when used for cuspal coverage of structurally compromised posterior teeth.

All restorations will be fabricated using a fully digital workflow. Tooth preparation, immediate dentin sealing, digital intraoral scanning, restoration fabrication, and adhesive cementation procedures will be standardized and performed according to a predefined clinical protocol.

The trial will be conducted at Hospital San José, Santiago, Chile, using commercially available restorative materials manufactured by subtractive and additive technologies. Clinical performance will be evaluated according to internationally accepted restorative assessment criteria.

The study aims to generate medium-term clinical evidence regarding the use of 3D-printed composite resin restorations as a potential alternative to conventional CAD/CAM-milled restorations in restorative dentistry.

Inclusion Criteria:

• Adults aged 18 to 70 years
• Absence of active periodontal disease
• Good oral hygiene (O'Leary plaque index <20%)
• Absence of parafunctional habits (e.g., bruxism, onychophagia)
• Endodontically treated first molars (maxillary or mandibular) with extensive Class II cavities and loss of at least one cusp, requiring onlay or overlay restoration
• Tooth with functional occlusal contact and at least one proximal contact
• Referred from the Endodontics Department of Hospital San José, with endodontic treatment completed at the same institution
• Ability to provide written informed consent
• Ability to attend follow-up visits at 12, 24, and 36 months

Exclusion Criteria:

• Untreated active periodontal disease
• Poor oral hygiene (O'Leary plaque index ≥20%)
• Generalized active caries
• Active parafunctional habits
• Teeth with complete circumferential structural destruction or insufficient coronal tooth structure for onlay/overlay restoration
• Subgingival margins compromising the biologic width
• Known allergy to study materials
• Pregnancy or breastfeeding

Individual participant data will not be shared with other researchers due to confidentiality and privacy considerations related to patient information.

Participants and outcome assessors are blinded to treatment allocation. Two independent calibrated evaluators assess the restorations during follow-up visits. The treating clinician is not blinded because of the nature of the interventions. Allocation concealment is maintained through stratified block randomization using sequentially numbered opaque sealed envelopes.