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. 2021 Sep 7;2:729144. doi: 10.3389/froh.2021.729144

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Copyright © 2021 Xu, Aboseria, Janal, Pushalkar, Bederoff, Vasconcelos, Sapru, Paul, Queiroz, Makwana, Solarewicz, Guo, Aguallo, Gomez, Shelly, Aphinyanaphongs, Gordon, Corby, Kamer, Li and Saxena.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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(A) Levels of breath carbon monoxide (ppm) across the subjects in the cigarette smokers, e-cigarette smokers, and the non-smokers at base line and 6-month follow-up: 0–6 ppm, Borderline (BdL): 7–9 ppm, low addicted smoker (LAS): 10–15 ppm, moderate addicted smoker (MAS): 16–25 ppm, heavily addicted smoker (HAS): 26–35 ppm, and very heavily addicted smoker (VHAS): 36+ ppm. Group mean was used for ANOVA (p < 0.001) as no interaction of time and group was observed. (B) Saliva flow rate in three groups at base line and follow-up. Group mean was used for ANOVA (p = 0.02) as no interaction of time and group was observed. (C) Distribution of salivary cotinine levels in the participants of the three groups. Kruskal-Wallis test was used and p < 0.001 for both visits. Paired t-test (p = 0.002) was then used to evaluate the change over time in each group. P value less than 0.01 was summarized with 2 asterisks. (D) Prevalence of periodontal disease in all three groups from baseline to follow-up visit.