3D-Printed Versus CAD/CAM-Milled Resin Restorations in Posterior Teeth.

Indirect resin restorations had become a well-established conservative alternative to direct composite restorations in posterior teeth, particularly in cases of significant loss of tooth structure requiring cuspal coverage (onlays/overlays). Compared with direct restorations, indirect techniques reduced the impact of polymerization shrinkage and shrinkage stress, generally achieving a higher degree of monomer conversion and greater resistance to marginal microleakage and wear, although at the cost of more extensive tooth preparation.

With the advancement of digital dentistry, indirect resin restorations could be fabricated using either subtractive manufacturing (CAD/CAM milling of prefabricated resin blocks) or, more recently, additive manufacturing (3D printing). Improvements in ceramic-filled resin formulations and in printing and post-processing protocols had expanded 3D printing from provisional to definitive restorations. Among printable materials, Crowntec (Saremco Dental AG) had demonstrated the most favorable mechanical properties reported in the literature, exceeding the minimum flexural strength threshold established by ISO 6872:2024 for monolithic single-unit restorations, although generally remaining below the values achieved by milled CAD/CAM resin blocks.

Despite the increasing clinical use of 3D-printed resins, evidence on their long-term clinical performance remained scarce, particularly in comparison with CAD/CAM-milled restorations. Existing data were derived mainly from in vitro studies with heterogeneous methodologies, limiting their extrapolation to real clinical conditions, where biological aging, occlusal loading, and patient-specific factors play a determining role.

Aim of the Study

The study aimed to evaluate and compare the following:

* The clinical performance of posterior indirect resin restorations fabricated by 3D printing (Crowntec, Saremco Dental AG) versus CAD/CAM milling (Brilliant Crios, Coltene), over a follow-up period of 36 months. * The volumetric wear of the restoration and of the antagonist tooth according to the manufacturing technique. * The effect of pulp status (vital vs. endodontically treated tooth) on the success and survival of the restorations.

Study Summary A prospective, randomized, parallel-group, double-blind (participant and outcomes assessor) clinical trial is being conducted at the Clínica Odontológica of the Universitat de València (Fundación Lluís Alcanyís). Each patient provides informed consent prior to participation, and ethical approval has been obtained from the Comité Ético de Investigación en Humanos of the Universitat de València.

Adult patients (≥18 years, ASA I or II) requiring a posterior indirect restoration with cuspal coverage, in either vital or endodontically treated teeth, are eligible for inclusion. Restorations are randomly assigned, in permuted blocks stratified by pulp status, to be fabricated by additive manufacturing (3D-printed resin) or subtractive manufacturing (CAD/CAM-milled resin).

Standardized tooth preparations are performed under local anesthesia using cuspal-coverage preparation principles, including immediate dentin sealing for vital teeth. Intraoral digital impressions are taken, and provisional restorations are placed. Final restorations are fabricated using either 3D printing or CAD/CAM milling techniques, depending on group assignment, and are cemented using resin cement following manufacturer instructions under rubber dam isolation.

Clinical evaluation is performed by a blinded outcomes assessor at baseline (1 week) and at 3, 6, 12, 18, 24, 30, and 36 months, using the revised FDI World Dental Federation criteria (Hickel et al., 2023), assessing functional, esthetic, and biological properties. Volumetric wear of the restoration and of the antagonist tooth is quantified by superimposition of successive intraoral digital scans, and restoration color change is assessed by standardized calibrated photography. An independent, blinded statistician performs the statistical analysis.