Validation of a Hyperspectral Imaging System for Color Measurement of In-Vivo Dental Structures

Abstract

A full comprehension of colorimetric relationships within and between teeth is key for aesthetic success of a dental restoration. In this sense, hyperspectral imaging can provide point-wise reliable measurements of the tooth surface, which can serve for this purpose. The aim of this study was to use a hyperspectral imaging system for the colorimetric characterization of 4 in-vivo maxillary anterior teeth and to cross-check the results with similar studies carried out with other measuring systems in order to validate the proposed capturing protocol. Hyperspectral reflectance images (Specim IQ), of the upper central (UCI) and lateral incisors (ULI), were captured on 30 participants. CIE-L*a*b* values were calculated for the incisal (I), middle (M) and cervical (C) third of each target tooth. ΔEab* and ΔE00 total color differences were computed between different tooth areas and adjacent teeth, and evaluated according to the perceptibility (PT) and acceptability (AT) thresholds for dentistry. Non-perceptible color differences were found between UCIs and ULIs. Mean color differences between UCI and ULI exceeded AT (ΔEab* = 7.39-7.42; ΔE00 = 5.71-5.74) in all cases. Large chromatic variations between I, M and C areas of the same tooth were registered (ΔEab* = 5.01-6.07 and ΔE00 = 4.07-5.03; ΔEab* = 5.80-8.16 and ΔE00 = 4.37-5.15; and ΔEab* = 5.42-5.92 and ΔE00 = 3.87-4.16 between C and M, C and I and M and I, respectively). The use of a hyperspectral camera has proven to be a reliable and effective method for color evaluation of in-vivo natural teeth.

Keywords: color; dentistry; hyperspectral imaging.

Figure 1

Schematic representation of the measurement set-up used to measure the hyperspectral reflectance images of the four maxillary incisors.

Figure 2

Workflow scheme of the spectral image capturing protocol, data processing and CIE L*, a* and b* values extraction corresponding to the cervical, middle and incisal thirds.

Figure 3

$\Delta E_{ab}^{*}$ and $\Delta E_{00}$ color differences between the contralateral and adjacent incisors.

Figure 4

$\Delta E_{ab}^{*}$ and $\Delta E_{00}$ color differences between the cervical, middel and incisal thirds of contralateral and adjacent incisors.

Figure 5

$\Delta E_{ab}^{*}$ and $\Delta E_{00}$ color differences between the cervical, middle and incisal thirds of the same tooth.