The influence of different radiopacifying agents on the radiopacity, compressive strength, setting time, and porosity of Portland cement

The aims of this study were to evaluate the radiopacity, compressive strength, setting time, and porosity of white Portland cement (PC) with the addition of bismuth oxide (Bi₂O₃), zirconium dioxide (ZrO₂), and ytterbium trifluoride (YbF₃) after immersion at 37 °C for 7 days in distilled water or phosphate buffer saline.

Specimens measuring 8 mm in diameter and 1 mm in thickness were fabricated from PC with the addition of 10, 20, and 30 wt% Bi₂O_3, ZrO₂ or YbF₃. ProRoot MTA (Dentsply, Tulsa, OK, USA) and pure PC were used as controls. For radiopacity assessments, specimens were radiographed alongside a tooth slices and an aluminum stepwedge on Extraspeed occlusal dental films (Insight Kodak, Rochester, New York). Mean optical density of each specimen was calculated and used to express radiopacity of the material as an equivalent thickness of aluminum. Compressive strength was measured by using 4-mm diameter and 6-mm high specimens and Universal testing machine. High-pressure mercury intrusion porosimeter (Carlo Erba Porosimeter 2000) was employed to measure the porosity of the specimens. The setting time was measured by using a needle of 100 g in weight. The morphology of specimens was evaluated using a scanning electron microscope (TESCAN Mira3 XMU, USA Inc.). Data were analyzed by one-way ANOVA and post hoc Tukey test (P < 0.05).

The PC with the addition of at least 10 wt% Bi₂O₃ and 20 wt% ZrO₂ or YbF₃ demonstrated greater radiopacity value than the recommended 3 mmAl cut-off. ZrO₂ and YbF₃ increased the compressive strength of PC, but it was not statistically significant (P > 0.05), while Bi₂O₃ decreased it (P < 0.05). All radiopacifiers significantly increased the porosity of the experimental cements (P < 0.05). Bi₂O₃ extended the setting time of PC (P < 0.05), whilst ZrO₂ and YbF₃ did not significantly affect it (P > 0.05).

ZrO₂ and YbF₃ may be used as a suitable alternative to replace Bi₂O₃ in MTA without influencing its physical properties.