Redefining the role of custom post and core systems: Moving beyond retention to structural reinforcement of severely compromised teeth: An in vitro study

Abstract Purpose To evaluate the reinforcing potential of custom post and core restorations of varying materials and designs on the fracture resistance and failure modes of endodontically treated maxillary first premolars. Materials and Methods Fifty‐six extracted maxillary first premolars were divided into seven groups ( n = 8) based on custom post and core material and design. Three materials were investigated: lithium disilicate in classical (C) and modified (LM) designs, polyetherketoneketone (PEKK) in classical (PC) and modified (PM) designs, and zirconia in classical (ZC) and modified (ZM) designs, alongside a control group restored with zirconia crowns only. All experimental teeth underwent standardized tooth preparation and adhesive cementation and were subsequently restored with zirconia crowns. Following thermomechanical aging (10,000 thermal cycles and 240,000 cyclic loading cycles), fracture resistance was evaluated under compressive loading, failure modes were recorded, and the resulting data were statistically analyzed. Results A significant interaction was found between material and design. The LM group achieved the highest fracture resistance (2900.25 ± 325.36 N), closely approaching the control group (3213.12 ± 406.74 N) with predominantly favorable failure modes (62.5%–75%). The PEKK groups demonstrated comparably lower fracture resistance values (PC: 1287.63 ± 122.97 N; PM: 1132.75 ± 138.34 N) yet exhibited exclusively favorable failure modes (100%). The ZM group recorded the lowest fracture resistance (879 ± 170.35 N) with the highest prevalence of unfavorable failure modes (87.5%–100%). Conclusion All tested groups demonstrated clinically acceptable fracture resistance values. Lithium disilicate and PEKK custom post and core restorations each contributed to structural reinforcement in a distinct way‐lithium disilicate through superior load‐bearing capacity and PEKK through superior biomechanical protective capacity.