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Effect of the of Zeolite Containing Silver-Zinc Nanoparticles on the Push out Bond Strength of Mineral Trioxide Aggregate in Simulated Furcation Perforation

Statement of the Problem: Recently, zeolite has been regarded to improve the properties of dental materials such as mineral trioxide aggregate (MTA). Purpose: The aim of the present study was to evaluate the effect of incorporating zeolite/silver/zinc (Ze/Ag/Zn) composite at 2 wt% to MTA powder on the push-out bond strength in simulated furcation perforations. Materials and Method: Furcal perforations, measuring 1.3 mm in diameter and 2 mm in height, were simulated in 40 human mandibular first molars. The samples were allocated to two groups (n=20) based on the material used for the repair of perforations. In the group 1, MTA and in the group 2, MTA plus Ze/Ag/Zn (2%) was used. The samples were incubated at 37°C for 1 week. Then the universal testing machine was employed to measure bond strength. The resistance of materials to dislodgment was recorded in MPa. Data were analyzed using t-test. Statistical significance was set at p< 0.05. Results: The push-out bond strength in the group 1 (6.40±1.98 MPa) was significantly higher than that in the group 2 (2.1±0.6 MPa) with p= 0.001. Conclusion: Under the limitations of the present study, it can be concluded that incorporation of Ze/Ag/Zn at 2 wt% to MTA powder had a negative effect on the push-out bond strength.

physico-chemical properties of MTA is to incorporate materials into its power or liquid [7].
In recent studies, focus has been on zeolite concerning the improvement of dental materials properties [8][9][10][11]. Zeolite is the crystalline structure of aluminosilicate and it has porous molecular structure; several ions such as zinc and silver are embedded in these pores [10]. Incorporation of silver-zeolite into MTA increased its solubility, resulted in the release of calcium, and decreased its setting time. Apparently, mixing with a 2 wt% ratio yielded better results compared to mixing with 0.2 wt% ratio [10]. Furthermore, incorporation of silver-zeolite into MTA increased its antibacterial activity against E. faecalis, S. aureus, and C. albicans [11][12][13]. The study conducted by Samiei et al. [14] revealed that incorporation of 2% wt Ze/Ag/Zn to the MTA decreased the compressive strength but did not present any cytotoxic effect. The extra dentin in each sample with greater dentin thickness was removed by using a disk. All the samples were irrigated with normal saline to remove the subsequent debris.

Preparation of Ze/Ag/Zn
HZSM-5 zeolite was prepared in the laboratory. Zinc

Repair of perforations
The samples were assigned to two groups (n=20) based on the type of the material used for the repair of perfora-

Results
The push-out bond strength (6.40±1.98 MPa) in the group 1 was significantly higher than that in the group 2 (2.1±0.6 MPa) with p=0.001. The failure type was mixed type (cohesive and adhesive).

Discussion
The results showed a significant decrease in push-out bond strength in the presence of such a composite. Since no similar study was available in the literature, the results of the present study could not be compared with those of other studies. Evaluation of the structure of zeolite indicates the presences of voids in its framework, which can house water molecules and ions such as silver and zinc [10]. A possible mechanism for decreasing the dislodgment resistance, by considering the porous structure of zeolite, is a disturbance in the hydration and crystallization processes of MTA by the composite above, because it is possible for the water molecule to enter its structure and exit the hydration process.
In the present study, Ze/Ag/Zn composite was incorporated into MTA powder at 2 wt%. This weight percentage has the best effect on solubility, release of calcium ions, antimicrobial activity, and setting time of MTA based on the results yielded by previous studies [10,13]. A review of the literature in relation to the use of zeolite in combination with various elements such as silver and zinc in the dental field indicates its positive antimicrobials effect. The cytotoxicity of endodontic sealer with 2 wt% of silver-zeolite is similar to that of glass-ionomer and is less than that of AH26 [8][9]11].
In the present study, the push-out bond strength was used to evaluate resistance against displacement, which is a reliable test for such a purpose based on the results of previous studies [1,3,15]. The push-out test uses a shearing stress at dentin-material interfaces, with various variables that are considered as the confounding factors during the push-out test such as the ratio of the diameter of the plunger to the dimension of the prepared root canal. Based on the results of previous studies, the effect of this confounding factor is minimal when the diameter of the plunger is 70-90% that of the root canal [15][16]. In the present study, the 1. Moreover, the resistance of MTA to displacement is influenced by the presence of phosphate-buffered saline solution [17][18].
Evaluation of the structure of zeolite indicates the presence of voids in its framework, which can house water molecules and ions such as silver and zinc [10]. In the present study, incorporation of Ze/Ag/Zn composite to MTA resulted in a significant decrease in its push-out bond strength. Considering the porous structure of zeolite, a possible mechanism would be the disturbance in the hydration and crystallization processes of MTA by the composite above since it is possible for water molecules enter its structure and exit the hydration process. Under the clinical conditions, apart from the type of restoration material used to repair the furcal area, other factors such as the presence of hemorrhage, inflammation and the resulted acidic environment can affect the setting process and bonding of the material to the dentinal wall in the perforated area [3,[19][20]. These issues were not concerned in the present study, therefore, it might be considered as one of the limitations of the present study.
The condensation force for amalgam is 5. 5-9.17 MPa, depending on the type of amalgam [3]. The results of the present study showed that MTA resistance to displacement one week after being placed in the area was in this range; however, this did not happen when combination of MTA/composite was used.

Conclusion
Under the limitations of the present study, despite the favorable effect of incorporating Ze/Ag/Zn into MTA powder on the properties evaluated in previous studies, resistance to displacement is affected negatively and this combination is not recommended in the repair of furcal perforations.