Previous work has demonstrated the relevance of FT-IR investigation on gingival crevicular fluid (GCF) for monitoring orthodontic treatments [1]. Usually, FT-IR spectra are acquired in reflectance mode by dropping a few microliters of GCF on a reflecting support. A faster procedure for collecting GCF spectra can be obtained by exploiting a different acquisition geometry. The attenuated total reflection (ATR) approach allows the collection of good-quality infrared spectra from any solid or liquid sample with almost no sample preparation. The objective of this research is to validate the ATR approach for GCF investigation by comparing the spectra acquired using the GCF extracted by paper cones and examined using reflecting support compared to those collected employing the ATR accessory.

Patients aged between 13 and 21 years undergoing orthodontic treatment with fixed multibracket appliances were recruited. Two different paper supports were used: standard sterile absorbent paper cones and PerioPaper strips inserted 1 mm into the gingival crevice. GCF was extracted for the FT-IR measurements in reflection geometry, whereas PerioPaper supports were directly used for the ATR acquisition mode. A Perkin Elmer Spectrum One FT-IR spectrometer was used for FT-IR in specular-reflection mode and a Universal ATR accessory was used for the other type of measurements.

FT-IR spectra in the range of 4000 to 600 cm^-1 with 4 cm^-1 of the spectral resolution were obtained from GCF samples before starting the orthodontic treatments using the two different collection geometries. The characteristics of the spectra acquired in reflection and ATR mode were examined and the contribution of the different GCF components was clearly evidenced also in ATR mode spectra. This analysis confirmed that the ATR approach can allow a detailed biochemical characterization of GCF similar to the reflection acquisition mode. Using the ATR geometry, the measurement time is greatly shortened and there is no risk that the spectra can be affected by the extraction procedures. These findings are pivotal for future research in order to make the GCF analysis fast and easy for the monitoring of orthodontic tooth movement in complex cases.

[1] d’Apuzzo, F.; Nucci, L.; Delfino, I.; Portaccio, M.; Minervini, G.; Isola, G.; Serino, I.; Camerlingo, C.; Lepore, M. Application of vibrational spectroscopies in the qualitative analysis of gingival crevicular fluid and periodontal ligament during orthodontic tooth movement. J. Clin. Med. 2021, 10, 1405