# Comparative FT-IR Spectroscopy Salivary Profiles of University Students: E‑Cigarette Users vs Nonusers

## TL;DR

This study used infrared spectroscopy to compare saliva samples from e-cigarette users and nonusers, finding detectable biochemical differences that may affect oral health.

## Contribution

The study demonstrates that e-cigarette use is associated with measurable changes in salivary composition, particularly in protein and lipid profiles.

## Key findings

- E-cigarette users showed a unique spectral band at 3273 cm–1 and shifted peaks in the 3050–2800 cm–1 region.
- The amide region (1720–1490 cm–1) showed altered protein peaks in users with moderate classification accuracy.
- The fingerprint region (1200–900 cm–1) showed minor intensity differences but no clear separation between groups.

## Abstract

This study investigated whether the use of e-cigarettes
induces
detectable alterations in salivary composition through Fourier-transform
infrared spectroscopy (FT-IR). Saliva samples were collected from
60 young university students (30 e-cigarette users and 30 nonusers)
at the University of Taubaté (Taubaté-SP). A total of
181 spectra were acquired in triplicate, resulting in 90 spectra for
e-cigarette users and 91 for controls, because one control was measured
in quadruplicate. Data were preprocessed by baseline correction, Savitzky–Golay
smoothing, and vector normalization. Three spectral regions were examined
(3050–2800 cm–1, 1720–1490 cm–1, and 1200–900 cm–1), and
discriminatory analysis was performed using a Support Vector Machine
(SVM) classifier with repeated 10-fold cross-validation. In the 3050–2800
cm–1 region, controls exhibited five peaks (3290,
2962, 2925, 2874, and 2853 cm–1), while e-cigarette
users showed six, including a unique band at 3273 cm–1 and shifts at 3288 and 2851 cm–1. In the 1720–1490
cm–1 amide region, controls presented peaks at 1640
and 1546 cm–1, whereas users exhibited peaks at
1649 and 1544 cm–1, indicating possible protein
alterations. This region yielded the best classification performance
(accuracy ∼ 0.65; F1-score ∼ 0.72; AUC ∼ 0.73).
In the 1200–900 cm–1 fingerprint region,
both groups shared a coincident peak at 1077 cm–1 with only minor intensity differences. There was not a clear separation
between cigarette user and nonsmokers groups by PCA analysis. Within
the limitations of this study, the findings suggest that e-cigarette
use may induce measurable biochemical changes in saliva, particularly
in protein- and lipid-associated vibrational modes. These alterations
could impair salivary defense functions, underscoring the importance
of dental professionals in preventive counseling.