FRACTURE LOAD AND FAILURE MODES OF ZIRCONIA CROWNS ACCORDING TO FINISH LINES AND FRAMEWORK DESIGNS

Abstract

AIM:This study aimed to assess the fracture load of bilayered zirconia crowns with varying finish lines and framework designs.
METHODS: Three prefabricated mandibular right first molar teeth were prepared with distinct finish line designs: shoulder (S), Chamfer (C), and feather-edge (F). Each group was duplicated onto 22 cobalt-chromium dies. Zirconia copings were fabricated with either anatomic or non-anatomic framework designs, veneered, and then cemented using adhesive resin cement. All specimens underwent thermocycling and mechanical ageing. Fracture load testing was performed using a universal testing machine, and failure modes were analyzed using stereomicroscopy and scanning electron microscopy (SEM).
RESULTS: The type of finish line significantly influenced the fracture load of zirconia crowns (p < 0.05), with the chamfer group exhibiting the highest mean fracture load. However, no significant difference was observed between the shoulder and feather-edge groups (p > 0.05). Framework design (anatomic vs. non-anatomic) had no statistically significant effect on fracture load (p > 0.05). Most failures were cohesive, especially in the feather-edge group. Group C had a significantly greater fracture load value compared to the other groups (p < 0.05). However, the clinically recommended S and minimally invasive F groups had similar fracture loads (p> 0.05). The framework design did not significantly affect the fracture load.
CONCLUSION: The chamfer finish lines achieved the highest fracture load for bilayered zirconia crowns, while minimally invasive knife
edge finish lines were mechanically strong enough for clinical use. Although the vertical finish line involved less tissue destruction, it raises some concerns about failure.