Fig 1.
Tooth discolouration attributed to the use of “MTA”.
Photo: Bill Kahler, University of Adelaide.
Table 1.
Treatment media.
Fig 2.
Experimental scheme outline.
Table 2.
Colour change at each exposure time with respect to initial (as-supplied, ‘unexposed’) Bi2O3 control material.
Fig 3.
(a) Appearance of bismuth(III) oxide as received. (b) Appearance of treated material at 24 weeks after exposure.
Fig 4.
Bi2O3 in NaOCl after 24 h, Light.
Fig 5.
L*a*b* colour coordinate time trajectory plots.
Data for all treated and exposed materials, with projections on each 2-axis plane. The control is for 24 weeks, dark and light, no added CO2. The L* axis (0,0,0) ~ (100,0,0) is drawn in for reference (+···+). ‘Initial’: as-supplied material.
Fig 6.
XRD patterns from treated powders exposed to added CO2.
Patterns for Dark and Light conditions were averaged for noise reduction, there being no detectable systematic difference between the two. (a) H2O: the subcarbonate is present (‘*’). “0 weeks” = unexposed control. (b) NaOH: subcarbonate formed more strongly. (c) NaCl: subcarbonate again present, along with an unidentified but transient substance (‘?’); a remnant of NaCl is present. (d) NaOCl: bismuthate formed; some oxide remains; unidentified peaks marked ‘?’; a remnant of NaCl is present. (e) HCl: only BiOCl present.
Fig 7.
FT-IR spectra for treated materials at 24 weeks after exposure.
Spectra for Dark and Light conditions were averaged for noise reduction, there being no detectable systematic difference between the two. Spectrum for Bi2O3 included for reference. Artefact marked ‘?’. Contribution from atmospheric CO2 incompletely cancelled. (a) H2O: oxide, with carbonate present. (b) NaOH: oxide still detected, but strong carbonate peaks found for added CO2. (c) NaCl: oxide remains, strong carbonate peaks for added CO2. (d) NaOCl: no oxide detectable, nor carbonate. Moderate broad peak with two satellites attributed to bismuthate. (e) HCl: only BiOCl detected. (f) Blanks: showing that KBr disc spectrum is clear after background subtraction except for the artefact at 419 cm-1 and unknown peaks at 1060 and 1205 cm-1.
Fig 8.
EPR spectra for treated materials at 24 weeks, exposed without added CO2.
(a) at room temperature (RT). The principal signal is broad, and with some variation, and due to Bi2O3, except for NaOCl which shows a different kind of response, but Light resulted in almost no signal in comparison with Dark. (b) at 12 K. The principal signal is all, with small variations, due to Bi2O3, except for NaOCl where the result is obscured by metallic-like conductivity, and more so for Light than Dark.
Fig 9.
Raman spectra for treated materials at 24 weeks.
Without added CO2, with untreated Bi2O3 for comparison. (a) For H2O, NaOH and NaCl. The only appreciable effect is for NaOH Dark at 130 cm-1. (b) For HCl and NaOCl. For NaOCl, the signal is weak and diffuse. Reference peak positions shown for BiOCl (above) and Bi2O3 (below).
Fig 10.
(a) bismuth oxide as-supplied, (b) reaction product for NaOCl at 24 weeks, Dark, no added CO2.