Three-dimensional-printed endocrowns: Does increasing intracoronal depth improve strength at the expense of fracture severity?

Aim: To evaluate fracture strength (FS) and failure mode (FM) of additively manufactured endocrowns fabricated from two three-dimensional-printed resin composites with distinct inorganic filler contents, tested at two intracoronal preparation depths following thermomechanical aging. Materials and Methods: Twenty-eight endodontically treated human mandibular molars were restored using additively manufactured endocrowns according to material (Bio Crown or Voxelprint) and preparation depth (3 mm or 5 mm). After adhesive cementation and thermomechanical aging (300,000 cycles; 5°C–55°C), FS was measured under axial loading (0.5 mm/min), and FM were classified into four categories. Data were analyzed by two-way analysis of variance and Tukey’s test (α = 0.05). Results: Restorative material significantly affected FS ( P = 0.0063), whereas preparation depth did not ( P = 0.403). Voxelprint showed higher FS than Bio Crown, independent of depth, with a significant difference between Voxelprint 5 mm and Bio Crown 5 mm ( P = 0.034). Preparations with greater depth were associated with a higher frequency of catastrophic vertical fractures. No interaction effect was observed. Conclusion: Resin composition influenced FS more than preparation depth. Increased depth did not improve load capacity but shifted failure toward more severe patterns.