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δ-Bismuth Oxide Responsible for Tooth Discolouration-A Laboratory Investigation.
J Camilleri1, P Zaslansky2, N Ramanan3
1Dentistry, School of Health Sciences, College of Medicine and Health, University of Birmingham, Birmingham, UK.
International Endodontic Journal
|December 1, 2025
Summary
Bismuth oxide reacts with sodium hypochlorite, causing phase changes and darkening, leading to tooth discolouration. This instability warrants banning bismuth oxide from dental materials.
Area of Science:
- Materials Science
- Biomaterials Science
- Dental Materials
Background:
- Bismuth oxide is used in dental materials.
- Tooth discolouration is a clinical concern.
- Understanding material interactions is crucial for safety.
Purpose of the Study:
- To investigate phase changes in bismuth oxide when exposed to sodium hypochlorite.
- To determine the cause of tooth discolouration linked to bismuth oxide.
Main Methods:
- Bismuth oxide was incubated with sodium hypochlorite at varying temperatures (20°C, 37°C, 60°C) for 24 weeks.
- Characterization included microscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and infrared spectroscopy (FT-IR).
Main Results:
- Interaction led to microstructural and color changes.
- Phase transformations resulted in the formation of δ-bismuth oxide, sodium bismuthate, and bismuth oxychloride.
- Thermogravimetric analysis indicated a 5%-10% weight change.
Conclusions:
- The formation of δ-phase bismuth oxide causes darkening and tooth discolouration.
- Bismuth oxide's chemical instability and reaction by-products raise safety concerns for clinical use.
- Recommendations include banning bismuth oxide from dental applications and updating clinical guidelines.
