Comparative evaluation of bilayered and monolithic endocrowns: Fracture resistance, failure mode, and stress distribution.

Abstract

To evaluate the load-to-fracture after mechanical cycling, failure mode, and stress distribution of mandibular first molars restored with monolithic lithium disilicate (LDS) endocrowns and bilayered endocrowns featuring resin-matrix ceramic endocores veneered with cemented LDS. Thirty-six mandibular first molars were divided into three groups (n = 12): Group ME (monolithic LDS), Group VE (bilayered VITA Enamic endocore with LDS veneer), and Group CE (bilayered Cerasmart endocore with LDS veneer). After endodontic treatment, standardized preparation, and CAD/CAM fabrication, restorations underwent 250,000 mechanical loading cycles under a 150 N load. Surviving specimens were tested for fracture resistance, and fracture modes were classified. Finite element analysis (FEA) assessed stress distribution. All samples survived the load of mechanical cycling. Group VE exhibited the highest mean fracture resistance (2774.2 N), significantly higher than Groups ME (2120.8 N) and CE (1949.6 N) (p ≤ 0.05), with no significant difference between ME and CE (p > 0.05). Failure mode analysis revealed reparable fracture rates of 0 %, 33 %, and 50 % for Groups ME, VE, and CE, respectively. Fisher's Exact Test showed significantly more reparable failures in CE compared to ME (p ≤ 0.05) and no significant difference between VE and ME (p > 0.05). FEA revealed lower stress concentration in the tested bilayered models compared to the monolithic LDS model, with VE exhibiting the lowest stress concentration across the restoration complex and tooth structure. The biomechanical performance and failure reparability of bilayered endocrowns depend on the endocore material. Endocrowns with VITA Enamic endocores exhibited the highest fracture resistance and favorable stress distribution, while Cerasmart endocores had fewer irreparable failures.