Evaluation of the properties of Mineral Trioxide Aggregate mixed with Zinc Oxide exposed to different environmental conditions

Addition of zinc oxide(ZnO)to Mineral Trioxide Aggregate(MTA)has been shown to rectify tooth discoloration caused by Angelus MTA.This study evaluated the microhardness,compressive strength,calcium ion release and crystalline structures of MTA mixed with ZnO in different environmental conditions.Molds with a diameter of 4 mm and a height of 6 mm were used for compressive strength,calcium ion release and X-ray diffraction(XRD)evaluations.Molds with 6 mm diameter and 4 mm height were used for surface microhardness evaluations.Cements evaluated include Angelus MTA(Angelus,Brail),Angelus MTA+ZnO,ProRoot MTA(Dentsply Tulsa Dental,OK),and ProRoot MTA+ZnO.Each group was divided into 3 subgroups according to exposure conditions:normal saline(NS),phosphate buffered saline(PBS)or blood.After 7 days incubation,surface microhardness,compressive strength and XRD analysis was performed.Calcium ion release was evaluated after 3,24 and 168h incubation using atomic absorption spectrophotometry.Data were analyzed by One Way Anova followed by the Tukey HSD Post hoc tests and T-Test.The significance level was set at 0.05.Addition of ZnO to Angelus and ProRoot MTA significantly decreased the compressive strength of these cements regardless of the environmental conditions(P<0.001);however,it had no significant effect on their microhardness or calcium ion release.In conclusion,adding ZnO to Angelus and ProRoot MTA can adversely affect the compressive strength of Angelus and ProRoot MTA.