# Oral and Dental Spectral Image Database--ODSI-DB
## 3 Results and Discussion
### Spectral Profiles  
Due to the non-flat nature of the imaged samples, extracting and combining the segmented spectra from the spectral images will have wide variations. As a preprocessing step, the spectra have been \(L^{2}\)-normalized prior to calculating their mean and standard deviation in the spectral profile plots shown in Figures 9 and 10. The spectra acquired with Specim IQ spectral camera have a common feature at the beginning and at the end of the wavelength range--a slope. The specifications of the light bulb [23] show that the normalized intensity at 400-430 nm range is approximately 10% of the maximum at 925 nm. This slope, therefore, is likely caused by poor illumination. Additionally, the specification seems to suggest the light bulb is unstable in the 950-1000 nm wavelength range, possibly explaining the slope at the end of the spectrum.  
Figure 9: Means of \(L^{2}\)-normalized spectra acquired with Specim IQ spectral camera, and their standard deviations for (**a**) hard tissue, (**b**) soft tissue, (**c**) hard tissue lesions, and (**d**) soft tissue lesions.  
As might be expected, the enamel and plastic share exceedingly similar spectra in Figures 9a and 10a. Interestingly, prosthetics differ in large part (400-600 nm) of the visible range (400-780 nm), but then follow enamel and plastic closely in the red and infrared regions--the latter being invisible to human eyes. Exposed tooth roots, on the other hand, differ remarkably in the 400-600 nm and 700-800 nm regions.  
The initial caries spectrum calculated from Specim IQ -acquired spectra (Figure 9c) stands out and differs significantly from the one calculated from Nuance EX -acquired spectra (Figure 10c). The standard deviation is also larger than on the other Specim IQ-based spectra. A skewed result is expected as the number of Specim IQ-acquired spectra for initial caries is only 1138, with 891 coming from a single test subject (when the technical masks are applied). The number of spectra with Nuance EX is, in total, 20,862 spectra with a median of 1225 per test subject (12 test subjects).  
The soft tissue spectra in Figure 9b all seem to blend in within their error margins, with skin being more reflective in the 500-600 nm regions. While it may seems like some skin segmentation in spectral images acquired with Nuance EX has an issue--as suggested by Figure 10b, where the skin spectrum has a very large error margin in 600-800 nm region with a questionable spectrum shape--this is likely not the case. Our test subject pool included people of different skin colors, but this was not taken into account in segmentation labeling. The 685 nm band, in particular, seems to have anthropological significance [24] in relation to skin color. Another notable feature is that all soft-tissue spectra (Figures 9b,d and 10b,d) exhibit a dip in reflectance approximately at 540 and 575 nm wavelength bands. These dips match the absorption spikes of oxygenated hemoglobin [25].  
Figure 10: Means of \(L^{2}\)-normalized spectra acquired with Nuance EX spectral camera, and their standard deviations for (**a**) hard tissue, (**b**) soft tissue, (**c**) hard tissue lesions, and (**d**) soft tissue lesions.  
Like the initial caries earlier, the ulcer spectrum in Nuance EX -acquired spectra exhibits notable individualism in comparison to the other soft-tissue lesion spectra in Figure 10d. In this case, all 1030 spectra forming the normalized mean spectrum for ulcer originate from a single test subject. On the Specim IQ side, Figure 9d, the spectrum originates from three test subjects, each contributing a medium of 1656 spectra.