ABSTRACT
Objective: Prosthetic molar crowns in service are subjected to chewing loads, which cause a
shift or dislodgment. The objective of this study is to investigate whether the addition
of resistance grooves to the proximal surfaces of the abutment teeth would enhance
the fracture resistance of the zirconia crowns and to compare between the patterns
of cracks development on the zirconia crowns after the application of mono loading
versus cyclic loading forces. Materials and Methods: Thirty-six all-ceramic zirconia cored crowns were prepared on the same abutment.
Resistance grooves were added to the mesial and distal surfaces of 16 abutments. Before
testing, all specimens subjected to thermal aging. Two groups of crowns were then
subjected to cyclic axial and lateral forces for 1,250,000 cycles in aqueous conditions.
Two groups of samples were also tested in monoloading fashion. Results: The crack pattern between mono and cyclic loading were compared. The crown fracture
resistance was compared in the two types of abutments, with and without grooves. The
results confirmed that the grooves addition had no effect on critical conditions to
initiate failure in the case of mono loading. In cyclic loading, grooves addition
increased the critical loads in the order of two. Failure patterns and location were
obtained. Conclusions: The results showed that the location of retention grooves halted the failure in
the surfaces where it was located in all loading mechanisms used in this study.
Key words:
All ceramic crowns - chewing simulator - failure modes - thermal aging