Radiopacity and Cytotoxicity of Portland Cement Containing Zirconia Doped Bismuth Oxide Radiopacifiers Chiehfeng Chen, MD,* †‡§ Sung-Chih Hsieh, DDS, PhD, k Nai-Chia Teng, DDS, PhD, k Chih-Kuo Kao, MS, ¶ Sheng-Yang Lee, DDS, PhD, k# Chung-Kwei Lin, PhD, ¶ and Jen-Chang Yang, PhD ¶ Abstract Introduction: This study evaluates the radiopacity and cytotoxicity of Portland cements containing a radiopaci- fier of bismuth oxide (Bi 2 O 3 ) with yttria-stabilized zirconia (YSZ) dopant. Methods: Various radiopacifier powders of Bi 2 O 3 with 0%, 15%, 30%, and 100% YSZ dopant were prepared by solid-state reaction at 700  C for 12 hours and characterized by x-ray diffraction. Portland cement/radiopacifier/calcium sulfate (75/20/ 5) were mixed and set by deionized water. Changes in radiopacity and in vitro cell viability of the hydrated cements were assessed. An average of 6 measured equivalent thickness of aluminum (N = 6) capable of producing similar radiographic density was recorded. The cytotoxicity of each material was determined in MC3T3 E1 cell-based methyl-thiazol-tetrazolium assay. Results: The x-ray diffraction patterns of YSZ doped Bi 2 O 3 are different from those of pure Bi 2 O 3 and YSZ. The cement-containing radiopacifier of Bi 2 O 3 /YSZ (85/15) presented significantly greater radiopacity (P < .05) compared with pure Bi 2 O 3 . The mouse oste- oblastic cell (MC3T3-E1) viabilities of these 2 groups were statistically similar (P < .05). Conclusions: The radiopacifier of Bi 2 O 3 /YSZ (85/15) reveals higher radio- pacity but similar cell viability when compared with pure Bi 2 O 3 . It shows potential use as an alternative radiopacifier in root-end filling materials. (J Endod 2014;40:251–254) Key Words Biocompatibility, mineral trioxide aggregate-like cement, radiopacity P ortland cement (PC), a hydraulic material composed of mostly tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite, can be used as a safe pulp-capping material, which is evidenced by its biocompatibility and mineralization-related gene expression (1). An ideal root canal filling material should present sufficient radiopacity to distinguish filling material from surrounding anatomic structures (2). The radiopacity of PC associated with the various radiopacifying agents was evaluated (3, 4). Among the tested radiopacifiers, Bi 2 O 3 revealed the highest radiopacity. This explained why Bi 2 O 3 was widely used for many mineral trioxide aggregate (MTA)-type dental filling materials, because it can obtain acceptable radiopacity. Recent studies have shown that the cytotoxicity of Bi 2 O 3 -containing PC was statistically higher at 12 and 24 hours but later gradually decreased to the level of PC (5). A modified Bi 2 O 3 -based radiopacifier with improved radiopacity is desirable because its biocompatibility can be enhanced by reducing the dosage. The x-ray attenuation is attributed to 3 interactions between x-ray photons and traversed matter in the energy range meaningful for diagnostic imaging: coherent scat- tering, photoelectron effect, and Compton scattering (6). Among them, the photoelec- tron effect, which arises from the interaction of the x-ray photons with inner-shell electrons, dominates. Radiopaque fillers with high mass attenuation coefficients tend to absorb or scatter a large amount of photons at a given wavelength because of their high atomic number and high density (7). Commercially available contrast agents are usually metal salts from elements such as bismuth, tantalum, barium, zirconium, stron- tium, and titanium with individual atomic numbers of 83, 73, 56, 40, and 22. Among bismuth-based compounds, the radiopacity of bismuth oxide (D = 8.9 g/cm 3 ) contain- ing PC is larger than that of bismuth carbonate (D = 6.86 g/cm 3 ) and bismuth subni- trate (D = 4.93 g/cm 3 ) (3). This might be attributable to the density-related structure factor. Ionic crystal structure is determined on the basis of how positive and negative ions can be packed to maximize electrostatic attractive forces and minimize electrostatic repulsion (8). This study proposes that the close-packed structure is achieved by the structure factor enhancement of Bi 2 O 3 by another metal oxide dopant. In recent years, there has been a growing interest in using the principles of solid- state chemistry to design new materials (9). The solid-state reaction is the easiest way to prepare polycrystalline solids from a mixture of solid starting materials in direct reac- tion of their components at high temperatures (10). Many attempts have been made to synthesize ZrO 2 doped Bi 2 O 3 phase to achieve higher conductivity for solid oxide fuel cells (11). However, the preparation and properties of yttria-stabilized zirconia (YSZ) From the *Division of Plastic Surgery, Department of Surgery, Taipei Medical University - Wan Fang Hospital, Taipei; † Department of General Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei; ‡ Evidence-Based Medicine Center, Taipei Medical University - Wan Fang Hospital, Taipei; § Center for Evidence-Based Medicine, Taipei Medical University, Taipei; k School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei; ¶ School of Dental Tech- nology, College of Oral Medicine, Taipei Medical University, Taipei; and # Dental Department, of Wan-Fang Hospital, Taipei Medical University, Taipei, Taiwan. Chung-Kwei Lin and Jen-Chang Yang contributed equally to this work. Address requests for reprints to Dr Jen-Chang Yang, School of Dental Technology, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110-52, Taiwan, ROC. or Dr Chung-Kwei Lin, School of Dental Technology, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110-52, Taiwan, ROC. E-mail address: chungkweilin@gmail.com; Yang820065@tmu.edu.tw 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.07.006 Basic Research—Technology JOE — Volume 40, Number 2, February 2014 Novel Bi 2 O 3 /YSZ Radiopacifier 251