Effect of tungsten as an alternative radiopacifier to bismuth oxide on the radiopacity, physical properties and microleakage resistance of mineral trioxide aggregate

Abstract

Radiopacity is one of the ideal properties of endodontic sealants. Bismuth oxide (Bi2O3) has been used to achieve that property. However, the addition of bismuth oxide as a radiopacifier agent has affected the material properties adversely. Objectives: The aim of this study is to expIore the effects of bismuth oxide replacement with tungsten on the radiopacity and the physical properties of experimental version of Mineral Trioxide Aggregate (EMTA). The properties tested were: setting time, biaxial flexural strength, microleakage, and pH levels. Furthemore, the effects of varying the tungsten particle size and amounts on the biaxial flexural strength and microleakage were evaluated. Methods: Experimental versions of Mineral Trioxide Aggregate, containing 3%, 6%, 11%, 16%, 20% tungsten (EMTA (W)) as study groups, and another containing 20% bismuth oxide (EMTA) as a control group, were used as testing materials. Digital radiographs were taken for both groups to ensure optimal radiopacity. Radiopacity was analyzed using UTHSCSA Image Tool software. Setting time was determined via a digital dial indicator. An Instron universal testing machine was utilized to verify the biaxial flexural strength after 1, and 7 days of setting. Microleakage was assessed using the fluid filtration method for 60 days. The pH level was measured after 2 hours, 1, 2, 7 and 21 days of setting. To explore the effects of varying the tungsten particle sizes and amounts on the biaxial flexural strength and microleakage, four different particle sizes of tungsten were tested (2-3.99, 4-5.66, 6-9.99, and 10-14 microns) at two different amounts (16% and 20%). Results: EMTA (W) group with 16% tungsten had a matching radiopacity to EMTA with 20% bismuth oxide with no significant difference in the optical density value. Statistical analysis showed no significant difference in the setting time of EMTA (W) and that of EMTA. The biaxial flexural strength of EMTA (W) is significantly higher than the biaxial flexural strength of EMTA at day 1 (p-value [less than]0.05), and significantly much higher after 7 days (p-value [less than] 0.05). The microleakage was not statistically different between both tested materials. There is no significant difference between the pH level of the EMTA and the pH of EMTA (W) after 2 hours, 1, 2, 7, and 21 days. The tungsten particle size had a significant effect on the biaxial flexural strength of EMTA (W) at day 1 and day 7 (p-value[less than]0.05). The amount of tungsten particles had no significant effect on the biaxial flexural strength at date 1 and day 7. The microleakage was not statistically different between EMTA (W) groups with different particles size and concentrations. Conlusion: Bismuth oxide substitution with tungsten as a radiopacifier agent in the experimental version of Mineral Trioxide Aggregate provided optimal radiopacity and further increased the biaxial flexural strength significantly with no effect on the setting time, microleakage, and pH-value. The tungsten particle size has a significant effect on the biaxial flexural strength, while varying the amount of tungsten has no significant effect on the biaxial flexural strength. The microleakage is neither affected by varying the size of tungsten particles nor amounts.