Ceramic Crown Margin Curvatures’ Effect on Fracture Strength

Method: Thirty zirconia (Zerion HT, Straumann) and 30 glass ceramic (IPS e.max, Ivoclar Vivadent) full-contour crowns were produced for three different premolar preparations. The preparations were made with a chamfer of 0.6 mm 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.

Result: There were statistically significant differences both among margin design and material groups (Table 1, p<0.001 Mann Whitney U test). A moderate to low curvature of the approximal crown margins was associated with higher strength compared with a high curvature.

Table 1. The mean load at fracture in Newton (standard deviation) for the different test groups and materials.

 Conclusion: The curvature of the cervical crown margin affects the load at fracture for all-ceramic crowns.