Validation of the laser-induced fluorescence effect of aromatic amino acids, protoporphyrin IX, and tetracycline hydrochloride on hydroxyapatite

Changes in mineral content (mainly phosphate) are important for detecting primary dental caries. However, so far, there has not been a device that can provide detailed information on the changes in organic and inorganic content of dental caries during the caries development and sensitively found early dental caries. DIAGNOdent has been widely used as a laser device for detecting dental caries, but it does not provide information about dental inorganics. Our experiment synthesised hydroxyapatite-aromatic amino acids (HA-AAAs), protoporphyrin IX (HA-PPIX), and tetracycline hydrochloride (HA-TCN) complexes as a simple biological mineralization model related to teeth in vitro and achieved single-factor control to avoid impurity interference so that the test results are accurate. For the first time, Raman and DIAGNOdent were used to detect HA-AAAs, HA-PPIX, and HA-TCN and determine the fluorescence characteristics of each organic substance. Our results show that Raman results are consistent with DIAGNOdent readings when detecting complexes and that Raman relative intensity (RRI) calculated by Raman spectroscopy can directly reflect the phosphate content in the sample. This implies that Raman is possible to replace DIAGNOdent as a novel and more accurate caries detector after conversion of the spectrum results.