Changes in oral fluid characteristics in smokers of electronic cigarettes and tobacco heating systems

Introduction 

Smoking is known to cause serious health problems in smokers: it is responsible for millions of deaths annually worldwide. It is estimated that by 2050, approximately 400 million adults will suffer from smoking-related diseases [1].

Previous studies confirmed a strong and steady association between smoking and poor dental health, including periodontal health, independent of plaque amount and other potential confounding factors such as age, gender, and socioeconomic status. Apparently, tobacco smoking diminishes the reparative capacity of periodontal cells, including fibroblasts, osteoblasts, and cementoblasts, thereby reducing their ability to form new tissue and potentially impairing the response to periodontal treatment. Cigarette smoking increases the risk of almost all oral mucosal diseases and reduces the success of many dental procedures, with evidence supporting a dose-response relationship. These associations were also confirmed by prospective studies demonstrating that cigarette smoking is a major risk factor for future tooth loss [2].

In addition to periodontal disease, an association was reported between cigarette smoking and dental caries, altered oral microbiome and reduced salivary secretion rate, which were proposed as potential mechanisms for the development of dental disease, but with less certainty regarding causality of these findings [3].

For many decades, it was believed that most of the harm from tobacco use was caused by the combustion process and the resulting complex cocktail of ingredients, rather than from the highly addictive nicotine [4]. Consequently, the last decade has witnessed an expansion in the assortment of nicotine products and their substitutes, primarily represented by electronic cigarettes (EC) and tobacco heating system (THS) [5]. ECs are sometimes thought of as a less harmful alternative for nicotine-dependent tobacco smokers who are unwilling or unable to quit nicotine use, as these products contain much lower levels of toxicants than cigarette smoke [6]. ECs are not the only recently introduced class of products that deliver nicotine without combustion. Newly formulated THS, also known as heat-not-burn tobacco products, create an inhalable aerosol by heating tobacco-containing material to a temperature below the ignition threshold, and their manufacturers report that they contain lower levels of harmful chemicals than conventional cigarettes [7].

Taking into account the well-known effects of tobacco smoke on the periodontium and oral mucosa, it is important to comprehend the effect of EC and THS aerosol, which also passes through immediate proximity to these tissues. The evidence base in Russia is virtually devoid of studies on the effects of EC and THS on changes in oral fluid characteristics, thereby making this study relevant.

The objective of this study was to evaluate the effects of e-cigarette smoking and THS use on changes in oral fluid characteristics.

Materials and Methods

We screened 150 individuals 18–55 years of age during routine dental procedures or when seeking dental care. Patients were divided into two equal groups of 50 individuals based on their EC/THS use history. Group 1 included EC smokers (the EC group), whereas Group 2 comprised THS smokers (the THS group). The control group (n=50) consisted of clinically healthy individuals who did not use either EC or THS (the control group). All patients signed informed consent to participate in the study.

Oral fluid samples were obtained during screening from patients in all comparison groups. The were analyzed for acid-base balance in the oral cavity (pH), natural salivary secretion rate (mL/min), and oral fluid viscosity (mPa·s). Besides that, we carried out a biochemical analysis of oral fluid to determine protein, calcium, phosphate, alkaline phosphatase, catalase, and malondialdehyde levels. This analysis was performed using ready-to-use reagent kits on a LabLine-100 automated biochemical and enzyme-linked immunosorbent assay analyzer (West Medica, Austria).

The Shapiro-Wilk W test was used to confirm normal distribution of collected measurements. The distribution was, in fact, normal (p=0.68). In this study, we calculated the sample mean (X) and standard deviation (SD). The Student’s t-test and the Kruskal-Wallis H test for independent samples were used to analyze and interpret the empirical data. All statistical calculations were performed at a significance level of 95% (p=0.05). Statistical analyses of the data were performed using Microsoft Excel and Statistica 64 v.20.0. (StatSoft, Inc).

Results

We discovered that patients in the THS group were characterized by a lower salivary secretion rate (0.48±0.02 mL/min) and higher oral fluid viscosity (1.87±0.04 mPa·sec) with a more neutral salivary pH level (7.1±0.04) vs. the control group. Contrariwise, patients in the EC group were characterized by a higher salivary secretion rate (0.56±0.03 mL/min) and lower oral fluid viscosity (1.68±0.05 mPa·sec) with a neutral salivary pH level (6.79±0.06), with no statistically significant differences between the EC and THS groups (Figures 1–3).

Besides that, the concentrations of total protein, calcium, phosphates, alkaline phosphatase, catalase, and malondialdehyde were analyzed among EC users, THS users, and nonsmokers. The total protein concentration in saliva was 2.3±1.2 g/L in EC group, 2.2±0.8 g/L in THS group, and 1.7±0.5 g/L in control group. Salivary calcium concentration was 0.8±0.5 mmol/L in EC smokers, 0.6±0.3 mmol/L in THS users, and 0.6±0.3 mmol/L in nonsmokers.

Salivary phosphate concentrations in EC smokers were 4.3±2.0 mmol/L vs. 4.1±2.3 mmol/L in THS smokers and 3.4±1.5 mol/L among nonsmokers.

Salivary alkaline phosphatase concentrations in EC smokers were 50.2±25.14 IU/L vs. 49.58±23.33 IU/L in THS users and 55.11±27.85 IU/L in nonsmokers. The salivary concentration of catalase in EC smokers was 1.33±0.34 μkat/L, 1.2±0.12 μkat/L among THS smokers, and 10.2±0.45 μkat/L in control group. The concentration of malondialdehyde in saliva in ES smokers was 14.4±1.67 μmol/L vs. 15.51±1.95 μmol/L in the group of THS smokers and 3.23±0.29 μmol/L among nonsmokers.

Discussion

This study investigated the impact of EC and THS use on oral fluid biological profiles vs. those of nonsmokers. The study demonstrates that exposure to EC aerosols containing various ingredients, toxicants, and carcinogens can have harmful effects and alter oral health in humans. Measurements of salivary secretion rate, and oral fluid viscosity and acidity revealed the following changes in the studied parameters in EC smokers and THS users: salivary secretion rate was lower vs. the control group (p=0.002), while mean oral fluid viscosity was higher than in the control group (p=0.004).

The reference values of salivary pH range from 6.2 to 7.6. Maintaining oral pH is associated with both the buffering activity of saliva and a continuous flow of saliva, which helps eliminate acids produced by oral bacteria or ingested with food and beverages. Nicotine dependence is associated with nicotine absorption by the buccal mucosa, and salivary pH is the main factor determining nicotine absorption [8]. In a study by S. Baliga et al., salivary pH was lower in patients with periodontitis than in a group of patients without periodontal disease, leading to the conclusion that salivary pH is associated with periodontal disease and can be used as a diagnostic biomarker for periodontitis [9]. Tobacco use can affect salivary pH. According to C.N. Kumar et al. [10], salivary pH undergoes substantial variations and, therefore, is related to the severity of periodontal disease. When measuring the pH of oral fluid in individuals in the EC and THS study groups, a more neutral value was found vs. the values in the control group (p=0.009). 

Concentrations of total protein in saliva of smokers in the EС and THS groups were higher than in nonsmokers. Statistically significant difference in total protein concentration in oral fluid was observed between EС smokers and nonsmokers (p=0.001).

Calcium concentration was higher in the EC group than in the THS group and nonsmokers. Oral fluid calcium level differed between EC smokers and nonsmokers (p=0.005).

 Phosphate concentration was higher in the EC smokers and THS users than in the control group, but no statistically significant differences were established. Salivary alkaline phosphatase and catalase concentrations were lower in both EC and THS smokers than in the control group. Statistically significant differences were observed between EC and THS smokers vs. nonsmokers (p=0.004 and p=0.006, respectively). Salivary malondialdehyde concentration was also higher in EC and THS smokers than in the group of nonsmokers. Statistically significant differences were observed between EC and THS smokers compared with nonsmokers (p=0.007).

Our data supported the results of previous studies. For example, in a study by D. Cichońska et al., conducted among EC users, pH was lower, while total protein, calcium, and phosphate concentrations were higher than in the nonsmoker group. Statistically significant differences were observed for calcium. Among traditional smokers, pH was lower, and total protein and phosphate concentrations were higher vs. the nonsmoker group. Statistically significant differences were observed for total protein [11]. 

According to A. Fattahi Bafghi et al., tobacco smoking reduces concentrations of total protein, calcium, and lead in saliva, but does not affect levels of sodium, potassium, and magnesium in saliva [12]. In a study by D. Cichońska et al., EC smoking affected the antioxidant capacity of saliva to a similar extent as traditional cigarettes when comparing smokers and nonsmokers [13]. A study by A.K. Pandarathodiyil et al. demonstrated higher levels of the lactate dehydrogenase in the saliva of vapers vs. the control group, thereby confirming the cytotoxic and harmful effects of EC on the oral mucosa [14]. 

Based on emerging evidence regarding the potential harmful effects of vaping (EC) and THS, it is crucial that young people receive early education to avoid any misconceptions about EC and THS compared to smoking addiction and the potential health risks associated with these harmful habits.

Conclusion

Statistically significant differences in oral fluid characteristics such as pH, salivary secretion rate, oral fluid viscosity, along with concentrations of protein, calcium, phosphate, alkaline phosphatase, catalase, and malondialdehyde levels, were found between groups with different smoking statuses, as well as between smokers and nonsmokers. This finding implies that EC/THS smoking affects oral health differently. Furthermore, analysis of the collected data suggests that the periodontopathogenic effect of THS (which contains nicotine) is more pronounced than of EC smoking. However, in both groups, it is implemented via changes in oral fluid properties and affects oral hygiene in both EC and THS smokers. 

We believe that further clinical studies in this field will be promising for providing professional dental care to these patient groups.

Conflict of interest. None declared by the author.