In vitro investigations into the etiology of mineral trioxide tooth staining

AIM: To investigate the role of bismuth oxide, a constituent of contemporary mineral trioxide aggregate (MTA) materials, and its response to various solutions that may contribute to the potential discoloration that occurs following MTA applications within the scope of endodontics. SETTING AND DESIGN: Laboratory assessment of chemical reactions with white ProRoot(®) MTA and white Portland cement (WPC). MATERIALS AND METHODS: Set specimens and freshly mixed specimens of white ProRoot(®) MTA and white ProRoot(®) MTA powder, along with specimens of WPC were exposed to distilled water, phosphate buffered saline (PBS), 10% formalin, hydroxyethylmethacrylate (HEMA), sodium hypochlorite, sodium hydroxide (NaOH) base, and hydrochloric acid (HCl) acid. Specimens were visually inspected periodically for color changes. RESULTS: All forms of ProRoot MTA showed discoloration when exposed to 10% formalin within 30 min, as opposed to WPC, and were completely blackened at 4 days. Bismuth oxide alone and with calcium oxide also turned black within 30 min after exposure to 10% formalin. No discoloration was seen when exposed to the other solutions. CONCLUSIONS: Exposing MTA in various forms to a variety of liquids has determined that bismuth oxidein combination with other chemical moieties is the prime cause of staining observed by clinicians.