The property of a root-extended Ti-6Al-4V endocrown utilizing 3D printing for a four-wall defect in endodontically treated molars: An in vitro study

Severely damaged molars pose significant challenges in restorative dentistry. Conventional methods, such as resin composite restorations, often fail to provide sufficient fracture resistance, marginal integrity, and sealing, leading to frequent failures and secondary caries. This study aims to compare the mechanical properties and marginal integrity of 3D-printed Ti-6Al-4V root-extended endocrowns with direct resin composite restorations in molars with 4-wall defects. Forty-two extracted third molars were randomly assigned to a 3D-printed Ti-6Al-4V root-extended endocrown group (n = 21) or a nanohybrid resin composite group (n = 21). All specimens underwent thermocycling. Fracture resistance was evaluated in eight specimens per group using vertical loading. Microleakage was assessed by methylene blue staining, and marginal integrity was evaluated by SEM. Micro-CT was performed on endocrown specimens without visible failure to detect internal microcracks. The endocrown group showed a significantly higher fracture resistance than the resin group (4682 ± 981 N vs. 1334 ± 615 N, P < 0.05). No catastrophic failures occurred in the endocrown group, whereas the resin group exhibited multiple failure modes. Lower microleakage scores and fewer marginal defects were observed in the endocrown group (P < 0.05). Micro-CT revealed limited microcracks in two endocrown specimens, and marginal gaps remained within clinically acceptable limits. The study innovatively designs a 3D-printed Ti-6Al-4V root-extended endocrown, combining the structural advantages of endocrowns and post-core restorations. In our study, the 3D-printed Ti-6Al-4V root-extended endocrowns exhibited markedly enhanced fracture resistance, diminished microleakage, improved marginal integrity in comparison to the direct resin restorations, hence endorsing their application for molars with severe defect.