Understanding tooth discolouration 
The aetiology of tooth discolouration is multifactorial. A number of factors such as dental trauma with blood contamination and also its management which usually involes regenerative endodontic or root canal therapy can cause teeth to discolour. It is well recognised that root treated teeth discolour and this leads to psychological distress for the person as well as further intervention which is at a cost. Tooth discolouration related to endodontic therapy has been associated with the use of bismuth oxide which is present in dental materials as it enhances the visibility on radiographs. Teeth undergoing root canal therapy are cleaned with bleaches such as sodium hypochlorite. The interaction of bismuth oxide with sodium hypochlorite leads to tooth discolouration. The current study investigates the chemical changes caused by this interaction.  
Bismuth oxide (monoclinic ??phase; C) was mixed with sodium hypochlorite at 20, 37, and 60?C (B20, B37, B60) for a period of 24 weeks. The products were imaged and characterised by thermographic assessment (TGA), phase analysis by X-ray diffraction (XRD) using Bragg Brentano geometry and Pilatus detector, infrared spectroscopy (FT-IR), and X-ray absorption fine structure (XAFS). 
This interaction of bismuth oxide with sodium hypochlorite resulted in a change in microstructure and colour. The thermographic assessment showed a change in mass and colour reversal to the yellow bismuth oxide at ~450?C. Phase changes dependent on temperature were demonstrated with ?-bismuth oxide, sodium bismuthate and bismuth oxychloride were formed as by-products at the different temperatures. This study identifies the phase changes that lead to tooth discolouration after endodontic procedures. 
Due to the phase changes, the material chemistry after the interaction is different to that of the material placed in the tooth. The by-products of the reaction have not been tested for use in patients. It is recommended to ban the use of bismuth oxide from dental materials and other clinical use due to its instability. The clinical guidance for endodontic therapy needs to be changed to reflect this. 

Grant Number: (N/A) 
Sponsor: N/A
Project title: Understanding tooth discolouration 
The following files have been archived:



File name
File description (Short description of content, sample size, format, any linking between different types of data, i.e. survey and interviews/focus groups)
BO as received Ð 13kev-1.dat
Bismuth oxide control tested using Pilatus detector- sample 1
BO as received Ð 13kev-2.dat
Bismuth oxide control tested using Pilatus detector- sample 2
RT-RT Ð 13kev.dat
Bismuth oxide mixed with sodium hypochlorite at room temperature tested using Pilatus detector- sample 1
37-RT-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C tested using Pilatus detector- sample 1
37-RT - 13kev - 2.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C tested using Pilatus detector- sample 2
37-300-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C and heated to 300?C tested using Pilatus detector- sample 1
37-300 - 13kev - 2.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C and heated to 300?C tested using Pilatus detector- sample 2
37-500-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C and heated to 500?C tested using Pilatus detector- sample 1
37-500-13kev-2.dat
Bismuth oxide mixed with sodium hypochlorite at 37?C and heated to 500?C tested using Pilatus detector- sample 2
60-RT-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C tested using Pilatus detector- sample 1
60-RT-13kev-2.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C tested using Pilatus detector- sample 2
60-300-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C and heated to 300?C tested using Pilatus detector- sample 1
60-300-13kev-2.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C and heated to 300?C tested using Pilatus detector- sample 2
60-500-13kev-1.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C and heated to 500?C tested using Pilatus detector- sample 1
60-500-13kev-2.dat
Bismuth oxide mixed with sodium hypochlorite at 60?C and heated to 500?C tested using Pilatus detector- sample 2
Control.raw
Bismuth oxide control tested using Bragg-Brentano geometry for phase analyses
Control-300.raw
Bismuth oxide control heated at 300?C tested using Bragg-Brentano geometry for phase analyses
Control-500.raw
Bismuth oxide control heated at 500?C tested using Bragg-Brentano geometry for phase analyses
RT.raw
Bismuth oxide mixed with sodium hypochlorite at room temperature tested using Bragg-Brentano geometry for phase analyses
RT-300.raw
Bismuth oxide mixed with sodium hypochlorite at room temperature heated at 300?C tested using Bragg-Brentano geometry for phase analyses
RT-500.raw
Bismuth oxide mixed with sodium hypochlorite at room temperature heated at 500?C tested using Bragg-Brentano geometry for phase analyses
37.raw
Bismuth oxide mixed with sodium hypochlorite at 37?C tested using Bragg-Brentano geometry for phase analyses
37-300.raw
Bismuth oxide mixed with sodium hypochlorite at 37?C heated at 300?C tested using Bragg-Brentano geometry for phase analyses
37-500.raw
Bismuth oxide mixed with sodium hypochlorite at 37?C heated at 500?C tested using Bragg-Brentano geometry for phase analyses
60.raw
Bismuth oxide mixed with sodium hypochlorite at 60?C tested using Bragg-Brentano geometry for phase analyses
60-300.raw
Bismuth oxide mixed with sodium hypochlorite at 60?C heated at 300?C tested using Bragg-Brentano geometry for phase analyses
60-500.raw
Bismuth oxide mixed with sodium hypochlorite at 60?C heated at 500?C tested using Bragg-Brentano geometry for phase analyses
Control.sp
Bismuth oxide control tested using Fourier transform infrared spectroscopy
RT-RT.sp
Bismuth oxide mixed with sodium hypochlorite at room temperature tested using Fourier transform infrared spectroscopy
RT-300.sp
Bismuth oxide mixed with sodium hypochlorite at room temperature heated at 300?C tested using Fourier transform infrared spectroscopy
RT-500.sp
Bismuth oxide mixed with sodium hypochlorite at room temperature heated at 500?C tested using Fourier transform infrared spectroscopy
37-RT.sp
Bismuth oxide mixed with sodium hypochlorite at 37?C tested using Fourier transform infrared spectroscopy
37-300.sp
Bismuth oxide mixed with sodium hypochlorite at 37?C heated at 300?C tested using Fourier transform infrared spectroscopy
37-500.sp
Bismuth oxide mixed with sodium hypochlorite at 37?C heated at 500?C tested using Fourier transform infrared spectroscopy
60-RT.sp
Bismuth oxide mixed with sodium hypochlorite at 60?C tested using Fourier transform infrared spectroscopy
60-300.sp
Bismuth oxide mixed with sodium hypochlorite at 60?C heated at 300?C tested using Fourier transform infrared spectroscopy
60-500.sp
Bismuth oxide mixed with sodium hypochlorite at 60?C heated at 500?C tested using Fourier transform infrared spectroscopy
Control.tg1d
Bismuth oxide tested using differential scanning calorimeter
B RT.tg1d
Bismuth oxide mixed with sodium hypochlorite at room temperature tested using differential scanning calorimeter
B 37C.tg1d
Bismuth oxide mixed with sodium hypochlorite at 37?C tested using differential scanning calorimeter
B 60C.tg1d
Bismuth oxide mixed with sodium hypochlorite at 60?C tested using differential scanning calorimeter
Control 1
Bismuth oxide control tested using X-ray absorption fine structure Ð sample 1
Control 2
Bismuth oxide control tested using X-ray absorption fine structure Ð sample 2
Control 3
Bismuth oxide control tested using X-ray absorption fine structure Ð sample 3
XAF RT-1
Bismuth  oxide mixed with sodium hypochlorite at room temperature tested using X-ray absorption fine structure - sample 1
XAF RT-2
Bismuth  oxide mixed with sodium hypochlorite at room temperature tested using X-ray absorption fine structure - sample 2
XAF RT-3
Bismuth  oxide mixed with sodium hypochlorite at room temperature tested using X-ray absorption fine structure - sample 3
XAF RT-300-1
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 300?C tested using X-ray absorption fine structure - sample 1
XAF RT-300-2
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 300?C tested using X-ray absorption fine structure - sample 2
XAF RT-300-3
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 300?C tested using X-ray absorption fine structure - sample 3
XAF RT -500-1
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 500?C tested using X-ray absorption fine structure - sample 1
XAF RT-500-2
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 500?C tested using X-ray absorption fine structure - sample 2
XAF RT-500-3
Bismuth  oxide mixed with sodium hypochlorite at room temperature and heated to 500?C tested using X-ray absorption fine structure - sample 3
XAF 37-1
Bismuth  oxide mixed with sodium hypochlorite at 37?C tested using X-ray absorption fine structure - sample 1
XAF 37-2
Bismuth  oxide mixed with sodium hypochlorite at 37?C tested using X-ray absorption fine structure - sample 2
XAF 37-3
Bismuth  oxide mixed with sodium hypochlorite at 37?C tested using X-ray absorption fine structure - sample 3
XAF 37Ñ300-1
Bismuth  oxide mixed with sodium hypochlorite at 37?C and heated to 300?C tested using X-ray absorption fine structure - sample 1
XAF 37Ñ300-2
Bismuth  oxide mixed with sodium hypochlorite at 37?C and heated to 300?C tested using X-ray absorption fine structure - sample 2
XAF 37Ñ300-3
Bismuth  oxide mixed with sodium hypochlorite at 37?C and heated to 300?C tested using X-ray absorption fine structure - sample 3
XAF 60-1
Bismuth  oxide mixed with sodium hypochlorite at 60?C tested using X-ray absorption fine structure - sample 1
XAF 60-2
Bismuth  oxide mixed with sodium hypochlorite at 60?C tested using X-ray absorption fine structure - sample 2
XAF 60-3
Bismuth  oxide mixed with sodium hypochlorite at 60?C tested using X-ray absorption fine structure - sample 3
XAF 60Ñ300-1
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 300?C tested using X-ray absorption fine structure Ð sample 1
XAF 60Ñ300-2
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 300?C tested using X-ray absorption fine structure Ð sample 2
XAF 60Ñ300-3
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 300?C tested using X-ray absorption fine structure Ð sample 3
XAF 60Ñ500-1
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 500?C tested using X-ray absorption fine structure Ð sample 1
XAF 60Ñ500-2
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 500?C tested using X-ray absorption fine structure Ð sample 2
XAF 60Ñ500-3
Bismuth  oxide mixed with sodium hypochlorite at 60?C and heated to 500?C tested using X-ray absorption fine structure Ð sample 3





Publications: (based on this data, if any)