Biomechanical Behaviors of Molars Restored with Endocrowns Composed of Different Materials

To assess the biomechanical behaviors of endodontically treated molars (ETMs) restored with endocrowns composed of different materials, forty mandibular molars were assigned to five groups (n = 8 each). Untreated molars constituted the control group (group C); the rest of the teeth that underwent root canal therapy were restored with endocrowns composed of polycrystalline ceramics (ST zirconia^®, UPCERA) in group ZR, lithium disilicate glass ceramics (UP.CAD^®, UPCERA) in group LD, resin-based nanoceramics (Hyramic^®, UPCERA) in group NC, and feldspathic ceramics (CEREC Blocs^®, Sirona) in group FC. All teeth were axially loaded until fracture. The process was recorded using a high-speed camera system, and fractographic analysis was conducted. The results showed that fracture loads did not significantly differ among groups C, LD, and NC; the loads were significantly lower than the load in group ZR but higher than the load in group FC. The mean time from the initial crack to complete tooth fracture varied. Group C had the longest time, followed by group NC; groups ZR, LD, and FC had the shortest time. Similar failure patterns were observed in groups ZR and LD, which were more regular than the pattern in group NC; group FC exhibited the roughest fracture surfaces. Fracture resistance testing combined with a high-speed camera system and fractographic analysis provides a promising modality for studying the biomechanical behaviors of restored teeth. Endocrowns composed of lithium disilicate glass ceramics or resin-based nanoceramics offer alternative restorations for ETMs with extensive coronal loss.