Influence of Different Primer/Resin Cement Systems on Retention of Monolithic Zirconia Crowns

 Statement of problem: Zirconia is a polycrystalline non etchable ceramic material therefore, there are difficulties to achieve a stable and durable bond.
Objectives: The aim of this in vitro study was to determine the retention strength of zirconia crowns cemented using different MDP-containing primers and resin cements.
Materials and Methods: Thirty natural extracted molars were fixed in epoxy resin and prepared with a flat occlusal surface, 20^o degree angle of convergence, approximately 3 mm teeth preparation height, and with roundation of the axio-occlusal line angles. Zirconia crowns were fabricatedwith the aid of CAD/CAMwith an added occlusal bar to facilitate removal of the cemented crowns. The internal surfaces of crowns were abraded with 50 µm aluminum oxide particles at 2.5 bar pressure for 10 seconds. Zirconia crowns were divided into 3 groups (n=10) according to the different cements and primers into; Group M:Multilink Speed/Monobond N, Group P: Panavia V5/Clearfil ceramic primer plus, Group D: Duo-Link universal/Z-Prime plus. Crowns were cemented and then thermal cycled for 10,000 cycles of 5^oC to 55^o C with a dwelling time of 20 seconds. The crowns with its occlusal bar were adapted to gear wire hooks device and removed vertically along path of insertion with the aid of universal testing machine at 0.5 mm/min crosshead speed. Maximum load was recorded and retention strength was calculated. One-way ANOVA was used to analyze the data of maximum load and retention strength and Monte-Carlo test was used to analyze failure mode.
Results: Group D showed the lowest retention strength (1.42±0.23 MPa) and differed significantly (P=<0.001) from of Group M (2.71±0.45 MPa) and Group P (2.47±0.41MPa). Also, Group P showed a non-significant difference in retention strength compared to that of Group M (P=0.34). Modes of failure showed mainly cohesive failure for Group M and Group P, and adhesive failure for Group D.
Conclusions:MDP-containing primers enhanced retention strength of the resin cements to zirconia crowns,however, retention strength of Multilink Speed and Panavia V5 resin cements was significantly higherthan Duo-Link Universal resin cement.
. Key words:Primer; Resin cement; Retention test;Monolithic zirconia.