Despite the high fracture strength of modern dental core ceramics, fractures are a common cause of clinical failures. The aim of this study was to use a clinically relevant test method to evaluate the effect of the curvature of the cervical crown margins on load at fracture.

Materials and Methods
Thirty zirconia crowns and 30 glass-ceramic crowns were produced for three premolar preparations with variation in the approximal crown margin curvature: low curvature (r = 12 mm), moderate curvature (r = 2.5 mm), and high curvature (r = 1.5). The crowns were loaded until fracture with a method that mimics clinical fracture modes.

Statistically significant differences were found among both crown margin curvature and material groups (P < .001). Most fractures originated from pre-existing flaws.

A moderate to low curvature of the crown margins increases crown strength compared with a high curvature.

The effect of margin curvature on load at fracture of ceramic crowns
Øilo M, Kvam K, Reisegg K, Gjerdet NR.
International Journal of Prosthodontics 2015; 28(4): 357–9.