Influence of Ferrule Design and Occlusal Thickness on the Fracture Resistance and Failure Patterns of Zirconia Endocrowns.

Abstract

Background and objective: Zirconia endocrowns are a popular restorative option due to their fracture resistance and aesthetic appeal, but the influence of different preparation designs on their performance remains underexplored. This study evaluated the effects of preparation design and the occlusal thickness on the fracture strength and failure modes of zirconia endocrowns in endodontically treated teeth.

Materials and methods: Thirty-two extracted human mandibular first molars were endodontically treated and divided into four groups (n = 8), based on margin design and occlusal thickness: Group A: 2 mm butt joint with 3 mm occlusal thickness, Group B: 1 mm butt joint with 4 mm occlusal thickness, Group C: 2 mm ferrule with 3 mm occlusal thickness, and Group D: 1 mm ferrule with 4 mm occlusal thickness. Zirconia endocrowns were fabricated using CAD/CAM technology and cemented with self-adhesive resin cement. The specimens were subjected to thermocycling and then tested for fracture strength using a universal testing machine. Failure modes were analyzed under a stereomicroscope. Data were statistically analyzed.

Results: Group B showed the highest mean fracture strength (6655.66 N), followed by Group D at 6091.00 N. Group C exhibited the lowest fracture strength (4867.41 N), although the differences were not statistically significant (P = 0.121). Type V failure was the most common failure mode across all groups, with 100% occurrence in both 2 mm margin groups (Groups A and C).

Conclusion: Margin design and occlusal thickness appeared to influence the fracture strength and failure modes of zirconia endocrowns; the differences were not significant.