## 2 Materials and Methods
### Unit-of-Analysis Issues
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Authors, Year** & **Cell line/Strain/Treuth/Sample** & **Outcome** & **Ain and Exposure** & **Conclusion** \\ \hline [PERSON] et al., 2016 & Human gangival epithelial cells & Cell modification and apoptotic activity & Effects on human gingival epithelial cells & Exposure to co-garette vapor induced cell shape modification and increased LDH activity and mediated cell activity by promoting apoptosis (esaspase-3). \\ \hline [PERSON] et al., 2016 & & & & \\ Italy [96] & HGF & HGF and ROS production & Effects on HGF & There is a role for EC fluids in the pathogenesis of oral diseases, such as periodontitis. \\ \hline [PERSON] et al., 2017 & & & & \\ Italy [97] & HGF & HGF cytotoxicity markers & Exper. EC liquids (with and without nicotine) & EC liquids (with and without nicotine) trigger molecular and morphologic responses in oral fibroblasts. \\ \hline [PERSON] et al., 2021 & & & & \\ Brasil [98] & Exfoliative cytology of the tongue & & & \\ Other & and the mouth from ECS, CS, NS, FS & Oral cells anomalies & To investigate cytogenetic and cytotoxic damage through the evaluation of micronucle in the oral mucosa compared to those who have not used ECS. \\ \hline [PERSON] et al., 2019 & & & & \\ UK [99] & Human gangival mucosa & Cell morphology alterations, healing process & Effects on the proliferation of normal and cancerous monolayer of cytotoxic effects on normal human radio fibrosis and keratinocytes. \\ Periodontology & & & & \\ \hline [PERSON] et al., 2016 & & & & \\ USA [100] & Human periodontal fibroblast & ROS presence & Mechanism of gingival epithelial inflammation and pro-escence in human and epithelial cells and periodontal ligament fibroblasts & There is a pathologic role of EC aerosol and its flavoring to cells and tissues of the oral cavity. \\ Periodontology & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Authors, Year Country, Sub-Section** & **Cell line/Strain/Teeth/Sample** & **Outcome** & **Aim and Exposure** & **Conclusion** \\ \hline [PERSON] et al., 2022 USA [101] & Subgraphical plaque & Bacterial composition/diversity & Evaluate the microbiome in subjects with mild periodontitis & FCS have a unique microbiome that seems healthier than CS, but not Exp: ECS, CS, NS & compared with NS. \\ \hline [PERSON] et al., 2022 Ukraine [102] & Plaque from cervical region & Bacterial growth & Evaluate the changes of dental & ECS promotes opportunistic \\ Oral Microbiome & Plaque from cervical region & Bacterial growth & microbiome across adolescents & transient streptropoc, while hindering resident plaque \\  & Oral Microbiome & Plaque from cervical region & bacterial growth & \\  & & & products and vaping & microflora. \\ \hline [PERSON] et al., 2019 & & & & There is a deregulation of critically \\ USA [103] & Oral epithelium & Gene transcript deregulation & Regulation of genes and associated molecular pathways, genome-wide, in oral cells & important genes and associated molecular pathways in the oral \\ Oral cancer & Oral epithelium & Gene transcript deregulation & in oral cells & epithelium of vapers that bears both resemblances and differences with that of smokers. \\ \hline [PERSON] et al., 2020 & & & impact on gingival squamous cell carcinoma invasion, RAGE & Electronic cigarette flavoring and carcinoma devastate the differential expression, and the elaboration of & regulation of oral squamous cell carcinoma (OSCC) cell invasion and inflammatory effects. \\ USA [104] & Gingival and tongue squamous cell & Cell invasion and gene expression & Cell invasion and gene expression & \\ Oral cancer & & & Exp: ECS with flavor and nicotine & inflammationy effects. \\ \hline [PERSON] et al., 2020 & & & & Compare the effects on HGF in terms of proliferation, metabolic \\ Germany [105] & HGF & Metabolic activity of HGF & activity, cell death, and formation of ROS. & Exposure of HGF to ECS does not