Introduction: Posts and cores are frequently used to enhance retention and mechanical performance in teeth with compromised coronal structure. Common strategies include gold cast post-and-cores and prefabricated fiber-reinforced composite (FRC) posts with composite resin cores. The elastic modulus of post materials influences stress distribution in root dentin. While some studies support high-modulus dowels, others advocate for materials with a modulus of elasticity closer to dentin. This study compared the biomechanical behavior of cast gold vs. FRC posts with composite cores using finite element analysis (FEA).

Methods: Two 3D models of a mandibular first molar were generated from micro-CT scans: (A) an intact molar (control) and (B) a structurally compromised molar restored with either (1) a cast gold post-and-core or (2) an FRC post and composite core, both restored with lithium disilicate crowns. FEA was performed on a fully dentate mandibular model, including bilateral occlusal contacts. Regular masticatory forces were applied, and stress distribution was evaluated. Major principal stresses were calculated for dentin (anisotropic behavior), while for the surrounding structures (isotropic behavior), the mvM analysis was applied. Validation was performed against experimental data.

Results: Both restored models showed maximum stress values in the crown and dentin similar to the control model. However, stress distribution differed significantly. Critical stress zones included the crown–core, core–dentin, and core–post interfaces and post preparation cavities. FRC posts and cores exhibited lower stresses, especially in the cervical dentin, more closely replicating a natural tooth’s biomechanics. Cast gold cores showed nearly double the stresses near the core–post interface and presented higher stresses within the dentin’s post preparation cavities. Stress and strain patterns in soft tissues (e.g., PDL) were similar across models.

Conclusions: While both systems restored biomechanical performance, FRC posts yielded a more favorable stress profile, particularly in critical areas of dentin, better resembling natural tooth behavior. Cast gold systems demonstrated higher stress concentrations in critical areas.