Autumn 2013; Vol. 25, No. 4 229 Original Article In-Vitro Evaluation of the Effect of MTA Setting on Apical Micro- leakage of Open Apex Canals with MTA Apical Plug S. Shahsiah 1 , M. Yazdizadeh 1 , S. Jalali 2 , M. Jafarzadeh 2 , P. Pourakbar Jahandideh 2 , Z. Buzarjomehri 3 1 Assistant Professor, Department of Endodontics, School of Dentistry, Ahwaz University of Medical Sciences, Ahwaz, Iran 2 Post graduate student, Department of, Endodontics, School of Dentistry, Ahwaz University of Medical Sciences, Ahwaz, Iran 3 Under graduate student, Department of Endodontics, School of Dentistry, Ahwaz University of Medical Sciences, Ahwaz, Iran  Corresponding author: S. Jalali, Post graduate student, Department of, Endodontics, School of Dentistry, Ahwaz University of Medical Sciences, Ahwaz, Iran drsaharjalali@gmail.com Received: 26 Nov 2012 Accepted: 2 Feb 2013 Abstract Background and Aim: Mineral Trioxide Aggregate (MTA) has a high clinical suc- cess rate when used as the apical plug. The conventional method of using MTA as an apical plug is doneduring two treatment sessions. This study aimed to evaluate the possibility of complete filling of root canal with gutta percha and AH26 sealer imme- diately after the placement of MTA plug. Materials and Methods: A total of 88 single-rooted teeth were selected for this expe- rimental study. The teeth were prepared and randomly divided into two groups of 40 each. Four teeth were considered as the positive control group and the remaining 4 as the negative controls. In group 1, MTA apical plug was placed, specimens were stored in saline solution for 24h and then filled with gutta percha and AH26 sealer. In the 2 nd group, the roots were filled immediately after the placement of MTA. In the positive control group, the root canals were left unfilled and in the negative control group, root canals were filled with gutta percha and sealer. The specimens were then immersed in 1% methylene blue, demineralized in 5% nitric acid and cleared in me- thyl salicylate. Dye penetration was measured by a stereomicroscope in micrometer. T-test was used for statistical analysis. Results: The mean dye penetration was 7813 μm in the first and 9152 μm in the second group. According to t-test, the 2 nd group had significantly greater microlea- kage than the first group (p<0.05). Conclusion: MTA needs to be exposed to moisture for final setting and root canal ob- turation must be delayed until complete setting of MTA. Key Words: Apexification, MTA, Microleakage Journal of Islamic Dental Association of IRAN (JIDAI) Autumn 2013 ;25, (4) Introduction Non-vital open-apex teeth have lost their pulp tis- sue before their complete development and closure of their apices. As the result, they have open apic- es. Such cases may also result from periapical trauma or surgery [1]. In such conditions, instru- mentation is difficult since there is no sufficient apical barrier stop. In such cases, formation of an apical calcified tissue barrier is necessary for con- densation of root canal filling material and achiev- ing an optimal apical seal [2]. Apexification is a treatment method for closure of root canal apices during which, a calcified barrier is formed separat- ing the root canal pulp tissue from the periapical tissue. This barrier is made of dentin, cementum, bone or osteodentin, blunting the root apex and sometimes slightly increasing the root length [3, 4]. Several materials have been successfully used to stimulate barrier formation at the apex. Mixture of water and calcium hydroxide is among the most