Failure Load Resistance of Different Repaired CAD/ CAM Ceramic Crowns Following Endodontic Access Preparation

Aims: This study aimed to evaluate the fracture resistance of different CAD/CAM ceramic crowns following standardized endodontic access preparation and repair using two restorative protocols. Materials and Methods: Ninety extracted human maxillary premolars were prepared for full-coverage crowns and restored with lithium disilicate (LD), yttria-stabilized tetragonal zirconia polycrystal (ZR), or polymer-infiltrated ceramic (VE) (n=30 per group). Each group was subdivided into three subgroups (n=10): intact crowns, crowns with access preparation repaired using a porcelain repair kit (GC), and crowns repaired with composite resin (Filtek Z350 XT). Endodontic access cavities were standardized using a custom template and prepared with diamond burs under water cooling. Specimens underwent thermomechanical loading, followed by fracture testing in a universal testing machine. Data were analyzed using one-way ANOVA and Duncan multiple range tests (α=0.05). Results: ZR crowns exhibited the highest fracture resistance across all conditions (mean intact: 3887.3 N; GC repair: 3371.7 N; composite repair: 2955.3 N), followed by LD (2742 N; 2281.5 N; 1960.2 N) and VE (1849.4 N; 1397.8 N; 1281.2 N). Access preparation significantly reduced fracture resistance in all materials (p