Several studies have been performed in order to assess the effect of different preparation designs for all-ceramic crowns, but the results are ambiguous. Most trials have found no or little effect of different design of the cervical finish line. The new method for clinically relevant testing of all-ceramic crowns developed at NIOM and the University of Bergen in 2012, and published in Dental Materials in 2013, has now been applied to assess one essential parameter of margin design: the curvature of the cervical margin over the gingival papilla.
The findings of this study were that the curvature of the cervical finish line affects the load at fracture for all-ceramic crowns with both zirconia and lithiumdisilicate-containing glass-ceramic (LS2) cores (Figure 1).
A moderate to low curvature of the crown margins increases crown strength compared with a high curvature. Most fractures originated from pre-existing microscopic margin flaws (Figure 2).
The results indicate that smooth and levelled finish lines improve crown strength. However, this has to be performed without jeopardizing the pulp or the gingival papilla for overall clinical success. The dentists need to emphasize on designing smooth and even finish lines on tooth preparations. Furthermore, the dental technicians need to ensure the production of all-ceramic crowns with flawless crown margins. Very thin knife-edge crown margins are more susceptible to margin flaws and should be avoided if possible.
More reading
The effects of margin curvature on load at fracture of ceramic crowns
Øilo M, Kvam K, Reisegg K, Gjerdet NR.
Int J prosthodontic, 2015, 28:357–359.
Download NIOM Newsletter October 2015
