Quantitative analysis of human teeth by using LIBS technology with different calibration methods: in vitro study

The study utilized laser-induced breakdown spectroscopy (LIBS) to evaluate the quantitative and qualitative values of various tooth samples. LIBS is a sensitive elemental analysis method that measures the spectral emission lines of plasma that created by laser reactions with a material. A pulsed Nd: YAG laser with a wavelength of 1064 nm and 100 mJ energy/pulse, with pulse width of 9 ns was used to study all examined samples, recording their LIBS spectra in the (300–600) nm region. The study confirmed the potential of quantitative analysis using LIBS by comparing results with relevant inductively coupled plasma mass spectrometry (ICP-MS), energy dispersive X-ray (EDX), and standard data. Teeth samples were analyzed to find concentrations of Ca, Mg, C, and Zn, among other elements. The LIBS intensity of Ca (λ)396.82 nm, C(λ)426.7 nm, Mg(λ)518.36 nm, and Zn(λ)334.5 nm was plotted versus element concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS), energy dispersive X-ray (EDX), and standard analysis using linear correlation with high value of regressions (R²). The accuracy factor R² was stronger in inductively coupled plasma mass spectrometry (ICP-MS) measurements than in standard and energy dispersive X-ray (EDX) measurements. Inductively coupled plasma mass spectrometry (ICP-MS) measurements have the potential to improve the precision and stability of LIBS and Energy dispersive X-ray (EDX) measurements, but matching compact standards with teeth is difficult, potentially affecting the precision and stability of LIBS results. The calibration curve of LIBS with respect to Standard method has the highest percentage of error, the calibration curve of LIBS with respect to energy dispersive X-ray (EDX) technique have a slightly lower range of error, while the calibration curve of LIBS with respect to inductively coupled plasma mass spectrometry (ICP-MS) technique have the lowest range of error. The lack of availability of matrix-matched reference samples makes it very difficult to employ the existing calibration curves for accurate quantitative analysis. As a result, there are noticeable differences in plasma properties between tooth samples and reference samples prepared in a lab.