Detection of tooth-colored composite restorations via optical analysis - hyperspectral imaging (400 nm–1000 nm) and near-infrared spectroscopy (1550 nm–1950 nm)

Objective

The proportion of teeth restored with tooth-colored composite restorations increased significantly in recent decades. Owing to improvements in their composition and processing technique, they visually appear almost indistinguishable from native tooth structure. This poses a challenge when establishing and comparing the postmortem dental status in order to identify an unknown body. This study investigated two different wavelength ranges using hyperspectral imaging and near-infrared-spectroscopy.

Methods

78 extracted teeth were restored with single and multi surface dental resin restorations. Nine different composites from seven different manufacturers were included. Hyperspectral imaging (400 nm – 1000 nm) and near-infrared spectroscopy (1550 nm – 1950 nm) were compared for their usability. The recorded spectra were evaluated via graphical plots, statistical comparison and by the use of a classification model.

Results

Dental composite and enamel are defined by different spectral characteristics above the range of visible light. Wavelength between 1550 nm and 1950 nm revealed a clear difference over the entire range. Statistically significant differences were found for the range of 1750 nm to 1800 nm (α= 0.01, p = 1.588e⁻¹⁴). In 400 nm to 1000 nm, a clear optical differentiation was not possible. For both ranges, the classification model achieved an accuracy of 84 % (400–1000 nm, HSI) and 99.8 % (1550–1950 nm, NIS) for the correct labeling of enamel and composite.

Conclusions

The two wavelength ranges connected to portable NIS and HSI devices differ in the accuracy with which native tooth structure and restorative material can be distinguished. The NIR-range, tested through NIS allows reliable detection of tooth colored restorations.