Comparative Analysis of Fracture Resistance in Endodontically Treated Molars Using Lithium Disilicate and Composite Overlays Versus Endocrowns

Statement of Problem.
Restoring extensively damaged, endodontically treated molars with an indirect restoration that both preserves and protects the remaining tooth structure is a significant challenge. Overlays and endocrowns offer a less invasive alternative compared to conventional crowns.
Purpose.
The aim of this study was to evaluate the fracture resistance and fracture patterns of molars restored with different materials and designs.
Materials and Methods.
This study involved 40 extracted human molars, which underwent endodontic root canal treatment and were divided into four groups: composite core build-up with pressed lithium disilicate overlay (OL) (n = 10); composite core build-up with milled composite overlay (OC) (n = 10); pressed lithium disilicate endocrown (EL) (n = 10); milled composite endocrown (EC) (n = 10). The teeth were subjected to thermocyclic loading (10,000 cycles between 5 and 55°C), followed by chewing simulation (0–50 N at 1.6 Hz for 600,000 cycles with a 10° inclination), another round of thermocyclic loading (10,000 cycles between 5 and 55°C), and finally, a fracture strength test (5 mm steel ball at a 10° inclination with a load rate of 0.5 mm/min). Afterwards methylene blue was used to stain any cracks or fracture lines in the teeth for microscopic evaluation.
Results.
The findings suggest that while the material type may not significantly impact fracture resistance or catastrophic fracture likelihood, the type of restoration (endocrown vs., overlay) is a crucial factor to consider.
Conclusions.
Clinicians should weigh the higher risk of catastrophic fractures associated with endocrowns when selecting restorative options for endodontically treated teeth.
Clinical Implications.
Overlays and endocrowns offer similar overall tooth fracture resistance, making both viable options for restoring endodontically treated molars. However, OLs may better withstand chewing forces and posed no risk of catastrophic tooth fractures, unlike ECs, which carry a higher tooth fracture risk.