Periodontal and Peri-Implant Health Status in Traditional vs. Heat-Not-Burn Tobacco and Electronic Cigarettes Smokers: A Systematic Review

The aim of the present systematic review was to evaluate and possibly differentiate the effects of traditional cigarettes, heat-not-burn tobacco, and electronic cigarettes on periodontal and peri-implant health status. Electronic cigarettes and heat-not-burn tobacco have become very popular in recent years and have been proposed to consumers as a safer alternative to conventional tobacco smoke, although their effect on periodontal and peri-implant health remains unclear. The study protocol was developed according to PRISMA guidelines, and the focus question was formulated according to the PICO strategy. A literature search was conducted across PubMed/MEDLINE and the COCHRANE library from 2003 to April 2022. From the 1935 titles initially identified, 18 articles were finally included in the study and extracted data were qualitatively synthesized. It may be carefully concluded that e-cigarettes may cause attenuated clinical inflammatory signs of periodontitis and, hypothetically, of peri-implantitis when compared to conventional tobacco smoke. Both alternative smoking products, containing nicotine, may likewise exert negative effects on periodontal and peri-implant health, as demonstrated by in vitro studies. Further investigations are needed to assess the impact of electronic cigarettes and heat-not-burn tobacco products on periodontal and peri-implant health status.


Introduction
Periodontitis is a chronic inflammatory disease of bacterial etiology, affecting and progressively destroying the tissues supporting the teeth and eventually leading to bone and tooth loss [1][2][3][4][5]. Analogously, peri-implantitis is an inflammatory lesion of the soft tissues surrounding an endosseous implant, leading to progressive peri-implant bone loss until implant failure [1][2][3][4][5]. Both periodontal and peri-implant diseases most frequently occur in adulthood and have been found or proposed to be associated, mainly through systemic inflammation, to a variety of systemic inflammatory disorders, including cardiovascular and pulmonary ones, diabetes, obesity, preterm birth, Alzheimer disease, and benign and solid malignant tumors [6][7][8][9][10][11].
Electronic cigarettes (E-Cigs) were introduced in the United States of America in 2006 and, since 2014, have become the most widespread tobacco product among young people

Protocol Development
The study protocol was developed according to the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analyses) guidelines [29,30]. The research question was formulated according to the PICO (Population, Intervention, control or Comparison, Outcome) strategy [31]: The clinical question in "PICO" format was: Is there a significant difference in clinical, radiographic and inflammatory parameters of periodontal and peri-implant tissues from e-cigarette users and Heat-Not-Burn tobacco when compared to tobacco users and nonsmoking subjects?

Search Strategy and Study Selection
A literature search was independently conducted by two reviewers (F.D.A., S.M.) through PubMed/MEDLINE and the COCHRANE library. Only articles published after 1st January 2003 (when the electronic cigarette was introduced) till 24th April 2022, in the English language, were included.
A combination of the following keywords was employed for the electronic search: Periodontal disease OR periodontitis OR peri-implant disease OR peri-implantitis OR dental implant OR implant loss OR plaque index OR gingival index OR bleeding on probing OR probing depth OR tooth loss OR missing teeth OR marginal bone level OR IL-1b OR IL-8 OR IL-6 OR TNF-a OR MMP-1 OR MMP-8 OR IFN-y OR IL-4 OR IL-9 OR IL-10 OR IL-13 OR OPG OR RANK-LAND OR e-cigarette OR vaping cigarette OR electronic cigarette OR electronic nicotine delivery system OR Heat-Not-Burn Tobacco OR vape OR vaping.
Articles were included if they were published in the English language, after 1st January 2003, and described clinical trials and/or observational studies assessing clinical and/or radiographic periodontal and/or peri-implant parameters. Records were excluded if study participants were <18 years old and in case of missing data concerning clinical and/or radiographic periodontal and/or peri-implant parameters; systemic and narrative reviews and preclinical studies were also not considered in the current study.

Data Extraction and Synthesis
Extracted data concerned: author(s) and year of publication; study design; total number, mean age, gender ratio and smoking habits of participants; periodontal status, number of implants, and periodontal and peri-implant clinical, radiographic and crevicular parameters, including clinical attachment loss (CAL) probing depth (PD), bleeding on probing (BOP), plaque index (PI), gingival index (GI), marginal bone levels (MBL), cytokines profile and periodontal treatment.

Risk of Bias Assessment
The risk of bias of the non-randomized clinical trials was evaluated through the ROBINS-I (Risk Of Bias In Non-randomized Studies of Interventions) tool, considering biases due to confounding, selection of participants, classification of interventions, deviations from intended interventions, missing data, selection of the reported result and biases in the measurement of outcomes and biases due to [32].
Risk assessment was conducted according to the following criteria [32]: • Low risk of bias: The study is judged to be at low risk of bias for all domains; • Moderate risk of bias: The study is judged to be at low or moderate risk of bias for all domains; • Serious risk of bias: The study is judged to be at serious risk of bias in at least one domain, but not at critical risk of bias in any domain; • Critical risk of bias: The study is judged to be at critical risk of bias in at least one domain.

Search Strategy and Study Selection
Electronic search and study selection were independently conducted by two reviewers (F.D.A., S.M.) and disagreements were discussed and solved.
Titles obtained through the electronic search were screened to eliminate duplicates. Abstracts of the pertinent records were screened according to eligibility criteria and related full texts were examined. In total, 1935 records were retrieved from PubMed/MEDLINE (1793 articles) and the COCHRANE library (142 articles). A total of 98 titles were removed because duplicates and 1796 titles were excluded as they were not pertinent to the topic of the present review; therefore, 41 articles were considered eligible and full texts were obtained. After the full-text evaluation according to the selection criteria, 23 studies were excluded (Table 1), specifically because: 11 did not describe clinical/radiographic parameters nor cytokine profile (11); 2 exclusively investigated the relationship between e-cigarettes and oral microbiome and 1 between e-cigarettes and alcohol, respectively; 2 studies involved former tobacco smokers who started using E-Cigs; 1 study assessed the effect of antimicrobial photodynamic therapy (aPDT) in E-Cigs smokers; and 6 articles were systematic reviews of the literature. Atuegwu, 2019 [37] No clinical/radiographic parameters Chrcanovic, 2015 [11] Systematic review Sancilio, 2015 [38] No clinical/radiographic parameters Ryder, 2018 [12] Relationship between e-cigarettes and alcohol Javed, 2019 [39] No clinical/radiographic parameters Ganesan, 2020 [40] Relationship between e-cigarettes and oral microbiome Andrikopoulos, 2019 [41] No clinical/radiographic parameters Nelson, 2019 [42] Relationship between e-cigarettes and oral microbiome Willershausen, 2014 [43] No clinical/radiographic parameters Rouabhia, 2018 [44] No clinical/radiographic parameters Finally, 18 articles were included in the present systematic review (Figure 1).  Table 2 illustrates the characteristics of the 18 included studies, concerning source, study design, aim(s), participants, periodontal and peri-implant parameters considered, main results and conclusions.

Study Characteristics
All included studies evaluated periodontal parameters and in 7 out of 18 peri-implants were also assessed. Extracted and analyzed periodontal and peri-implant parameters concerned traditional and electronic cigarettes smokers, whilst no study analyzed findings from HNB tobacco smokers; results from waterpipe smokers were also reported in the synthesis of the results and briefly discussed, although not relevant for the present study, since they could not be extrapolated from data comparison among study groups.
Due to the heterogeneity of the included studies and to the lack of randomized controlled trials, it was not possible to conduct a meta-analysis.  Table 2 illustrates the characteristics of the 18 included studies, concerning source, study design, aim(s), participants, periodontal and peri-implant parameters considered, main results and conclusions.

Study Characteristics
All included studies evaluated periodontal parameters and in 7 out of 18 peri-implants were also assessed. Extracted and analyzed periodontal and peri-implant parameters concerned traditional and electronic cigarettes smokers, whilst no study analyzed findings from HNB tobacco smokers; results from waterpipe smokers were also reported in the synthesis of the results and briefly discussed, although not relevant for the present study, since they could not be extrapolated from data comparison among study groups.
Due to the heterogeneity of the included studies and to the lack of randomized controlled trials, it was not possible to conduct a meta-analysis. Table 2. Characteristics of the studies included in the present systematic review: author(s) and year of publication; study design; total number, mean age, gender ratio and smoking habits of participants; periodontal status, number of implants, and periodontal and peri-implant clinical, radiographic and crevicular parameters, including clinical attachment loss (CAL) probing depth (PD), bleeding on probing (BoP), plaque index (PI), gingival index (GI), marginal bone levels (MBL), cytokines profile and periodontal treatment. Electronic devices intended for "vaping" were heterogeneously defined by the authors of the included studies and are currently named as "electronic cigarettes". PI was significantly higher among CS and WS than E-Cigs (p < 0.05) and NS (p < 0.05).PI was significantly higher among E-Cigs than NS (p < 0.05). BOP were significantly higher among NS compared with CS (p < 0.05) and WS (p < 0.05) and E-Cigs (p < 0.05) PD (p < 0.05), CAL (p < 0.05) and MBL (p < 0.05) were significantly higher among CS and WS compared with E-Cigs and NS. There was no difference in PD, CAL, MBL, IL-1β and IL-6 levels among E-Cigs and NS IL-1β (p < 0.01) and IL-6 (p < 0.01) levels were significantly higher among CS, WS than E-Cigs and NS. Cotinine levels were significantly higher among CS (p < 0.001) and WS (p < 0.001) and E-Cigs (p < 0.001) than NS.

Authors, Year
CS and WS had worse radiographic parameters of periodontal inflammation than E-Cigs and NS.
Cotinine levels were similar in all groups. Salivary IL-1β and IL-6 levels were higher in CS and WS than E-Cigs and NS No significant differences were found between the groups for PD, PI, CAL. GI was significantly higher in group 2e 3 than group 1 and GI was significantly lower in group 2 than group 3. IL-8 level of Group I (70.47 ± 2.76) was significantly lower than in Groups II and III. TNF-a level of Group I (4.20 ± 0.14) was significantly higher than in Groups II and III.
Cigarette smoke and vaping have negative effects on the markers of oxidative stress and inflammatory cytokines. , PD (p < 0.05) and clinical AL (p < 0.05) were significantly higher among individuals in CS than NS. BOP was manifested more among NS than in CS (p < 0.05) and E-Cigs (p < 0.05). MBL was significantly higher in CS (p < 0.01) and E-Cigs (p < 0.01) than NS The concentrations of IL-1β, IL-6, IFN-γ, TNF-α and MMP-8 were significantly higher in the GCF samples of CS (p < 0.05) than E-Cigs and NS.
Periodontal status is worse and GCF levels of pro-inflammatory cytokines are higher in CS compared with E-Cigs and NS.  The scores of PI (p < 0.001), GI (p < 0.001), CAL (p < 0.001), PD (p < 0.001) and mesial (p < 0.001) and distal (p < 0.001) MBL were significantly higher among CS, E-Cigs, and NS with periodontitis compared with NS without periodontitis. There was no statistically significant difference in GI, PD, CAL, mesial and distal MBL and PI among CS, E-Cigs, and NS with periodontitis.
CS, WS and E-Cigs have higher levels of RANKL and OPG in the GCF than NS. BOP was significantly higher in NS compared with CS and E-Cigs (p < 0.01). PI (p < 0.01), PD (p < 0.01),MMP-9 (p < 0.001) and IL-1b levels (p < 0.01) were significantly higher in CS and E-Cigs than NS. MBL was significantly higher in CS compared with E-Cigs and NS (p < 0.01). Significant positive associations were found between MMP-9 (p = 0.0198) and IL-1b (p = 0.0047) levels and MBL in CS; and a significant positive association between IL-1b and MBL in E-Cigs (p = 0.0031).
Higher levels of cytokines in CS and E-Cigs suggest greater peri-implant inflammatory response and so worse clinical and radiographic peri-implant parameters. At baseline, there were no differences in PI, PD, CAL, MBL, and GCF IL-4, IL-9, IL-10, and IL-13 among E-Cigs and NS. At the 3-month follow-up, there were no significant differences in PI, GI, PD, CAL and MBL in E-Cigs compared to baseline, while there were significant reductions in PI, GI, and PD among NS.
Nicotine increases the expression of cotinine in the PISF. Periodontal and peri-implant assessment at baseline and after 12 weeks Photodynamic therapy at baseline + mechanical debridement (MD) Dental implants n. 111 implants (at least one in service for ≥1.5 years) PI BoP PD TNF-a MMP-8 PISF volume PI, PD, MMP-8 and TNF-a were higher in CS and E-Cigs than NS at baseline. BOP was higher in NS than other groups. A statistically significant reduction in PI and PD parameters was observed on baseline and at 12 weeks in all groups. BOP significantly increased in group 1 and 2 at 12 weeks. A statistically significant reduction from baseline to 12 weeks was reported in the biomarker levels for all the study groups.
PDT with adjunctive mechanical debridement reduced PI and PD and cytokines but increased BPO Vaping was found to be the most prevalent risk indicator for peri-implantitis.

Data Extraction and Synthesis
Detailed findings related to periodontal clinical and radiographic, as well as inflammatory parameters, are synthesized in Table 3 and in Table 4, respectively; Table 5 describes  peri-implant clinical and radiographic parameters Table 6 reports inflammatory ones.       At baseline, there were no differences, and GCF IL-4 among E-Cigs and NS. At the 3-month follow-up, GCF IL-4 levels were significantly elevated in ES and in NS (p < 0.05) compared to baseline. After3-month, GCF IL-4, levels were significantly higher in NS (p < 0.05) than in E-Cigs Levels of GCF IL-4 increased after SRP in E-Cigs and NS with CP; however, the anti-inflammatory effect of SRP was more profound in NS than in E-Cigs Table 4. Cont.

IL-9
Al-Hamoudi, 2020 [61] Cross-sectional At baseline, there were no differences in IL-9, among E-Cigs and NS. At the 3-month follow-up, GCF IL-9 levels were significantly elevated in E-Cigs and in NS (p < 0.05) compared to baseline. After 3 months, GCF IL-9 levels were significantly higher in NS (p < 0.05) than in E-Cigs Levels of GCF IL-9 increased after SRP in E-Cigs and NS with CP; however, the anti-inflammatory effect of SRP was more profound in NS than in E-Cigs IL-10 Al-Hamoudi, 2020 [61] Cross-sectional At baseline, there were no differences in IL-10 among E-Cigs and NS. At the 3-month follow-up, GCFIL-10 levels were significantly elevated in E-Cigs and in NS (p < 0.05) compared to baseline.After3-month, GCF IL-10, was significantly higher in NS (p < 0.05) than in E-Cigs Levels of GCF IL-10 increased after SRP in E-Cigs and NS with CP; however, the anti-inflammatory effect of SRP was more profound in NS than in E-Cigs

IL-13
Al-Hamoudi, 2020 [61] Cross-sectional At baseline, there were no differences in IL-13 among E-Cigs and NS. At the 3-month follow-up, GCF IL-13 levels were significantly elevated in E-Cigs and in NS (p < 0.05) compared to baseline.After3-month, GCF IL-13 levels were significantly higher in NS (p < 0.05) than in E-Cigs Levels of GCF IL-13 increased after SRP in E-Cigs and NS with CP; however, the anti-inflammatory effect of SRP was more profound in NS than in E-Cigs CO Fangxi Xu, 2021 [66] Case-control CO levels was highest among CS CS have highest CO levels GSH-PX AND 8-OHdG Karaaslan, 2020 [52] Case-control Although the GSH-Px level of Group II was higher than Group I, this difference was not statistically significant, but the mean GSH-Px level of Group III was significantly higher than in Groups I and II.
There was no significant difference in RANKL among CS, WS and ES CS and WS and E-Cigs are associated with an increased expression of RANKL in the GCF The OPG levels were significantly higher among CS (95.9 ± 7.2 pg/mL) (p < 0.001) and WS (86.6 ± 5.8 pg/mL) (p < 0.01) and E-Cigs (77.5 ± 3.4 pg/mL) (p < 0.05) than NS (21.5 ± 10.7 pg/mL) CS and WS and E-Cigs are associated with an increased expression of OPG in the GCF     A statistically significant reduction was reported in the biomarker levels for all the study groups.

Quality Assessment of the Included Studies
The risk of bias of the studies included in the present systematic review is detailed in Table 7. Table 7. Risk of bias of the studies included in the systematic review. Response options were: Yes (Y), Probably yes (PY), Probably no (PN), No (N) and No information (NI); "Y" indicates low risk of bias, "PY" indicates a moderate risk of bias; "PN" indicates a serious risk, "N" indicates a critical risk of bias and "NI" indicates no information, as per the ROBINS-I tool.

Discussion
Electronic cigarettes and Heat-Not-Burn tobacco products are becoming very popular among the population, especially as many people think they are less harmful than conventional tobacco; therefore, the aim of the present systematic review was to evaluate the effects of electronic cigarettes and heat-not-burn tobacco products on periodontal and peri-implant status compared to traditional tobacco use. Unfortunately, data from clinical studies on Heat-Not-Burn tobacco systems were lacking and retrieved data on electronic cigarettes were heterogeneous, thus precluding the possibility of conducting a meta-analysis and, therefore, representing the main limitation of the study. Analyzed and qualitatively synthesized data are discussed below.

Clinical Periodontal and Peri-Implant Parameters in Traditional vs. HNB and E-Cigs Smokers
Jeong et al. suggested that vaping may not be a safe alternative to cigarette smoke; indeed, periodontitis was more prevalent in E-Cigs and CS than NS [26]; this finding may be considered especially relevant since this study, based on community periodontal status (CPI), included more participants (5715 males and 7836 females) than other studies included in this review [26].
A typical feature of periodontal disease associated with tobacco smoking is a greater destruction of the supporting tissues of the teeth with clinical attachment loss [67]. Many studies, reported in this review, agreed with this; in fact, Mokeem [50,54]. Similar results were also reported by Al-Hamoudi before and after SRP [61].
Regarding Bleeding on Probing, which is a clinical sign of periodontal and periimplant tissues inflammation [1,2,[8][9][10], several studies included in the present systematic review [50,53,54,56,59,60,62,64] showed an increased BoP in NS compared to CS and E-Cigs, with no differences, instead, between CS and E-Cigs [50,54]. These findings suggest that nicotine-containing e-cigarettes may cause vasoconstriction within both outer periodontal and peri-implant tissues, similarly to traditional tobacco products [68], although such an effect may not be as strong as that that related to tobacco products. Tatullo et al. found that BoP decreased over a 4-month period in e-cigarette smokers who were former smokers, even if they had been smoking for more than 10 years [47]; nonetheless, a few authors did not find statistically significantly differences between smokers and those who had never smoked [51,58,64].
Regarding plaque accumulation, many authors reported higher PI values in CS and E-Cigs compared to NS [53,58,59,64]. In more detail, Vohra et al. reported that CS had the worst PI values compared to E-Cigs and NS [55]; conversely, AlJasser et al. found that NS had worse plaque conditions than E-Cigs and CS [65]. Mokeem et al. also found higher, although not significantly different, PI values around natural teeth in CS than E-Cigs and in E-Cigs than in, otherwise ArRejaie et al. did not find any differences in PI around dental implants between CS and E-Cigs [50,60]. Aldakeel et al. instead found that CS, E-Cigs and NS with periodontitis had a statistically significantly higher PI compared to NS, CS and E-Cigs without periodontitis [57]. However, nicotine appears to induce proliferation of suspected periodontal pathogens, as A. actinomycetemcomitans and P. gingivalis, which were more frequently detected in CS and E-Cigs gingival biofilm compared to NS smokers with periodontitis plaque [57]. Al-Aali et al., Sinha et al., BinShabaib et al. and Karaaslan et al. found no statistically significant differences in PI values between E-Cigs and NS [51,52,54,64]. Al-Hamoudi et al. also found no differences among PI in E-Cigs and NS at baseline, but after a 3-month follow-up, significant reductions in PI in NS were described [61].
Regarding the Probing Depth, several authors described overall worse PD in Cs and E-Cigs compared to NS [51,[53][54][55][56]58,60,62,63], despite the fact that E-Cigs showed less clinical signs related to periodontal and peri-implant inflammation and disruption to CS [55]. Al Qahtani et al. found significantly lower PD values in E-Cigs compared to CS and WS [53], supporting the hypothesis that cigarette smoke may be responsible for periodontal tissue destruction and cell death and may increase the production of matrix metalloproteinases involved in the inflammatory process [55]. Karaslaan et al. [52], as well as AlDakheel et al. [57], did not find significant differences in PD values among CS, E-Cigs and NS with and without periodontitis [57]. Although many authors found no differences in PD values among NS and E-Cigs [50,54,59], Alhamoudi et al. [61], who similarly reported similar findings at baseline between NS and E-Cigs, described, following mechanical periodontal treatment, a significant PD reduction in NS but not in E-Cigs.
As for GI, it was found to be significantly higher in E-Cigs compared to CS [52] and in CS, E-Cigs, and NS with periodontitis compared to NS without periodontitis (p < 0.001); no statistically significant difference among CS, E-Cigs, and NS with periodontitis was observed, but instead for GI [57]. Noteworthy, GI was reported to be significantly higher in NS than E-Cigs at baseline, but at the 3-month follow-up, a statistically significant improvement was observed in NS [61] but not in E-Cigs.
Many authors did not find statistically significant differences for MT among CS, E-Cigs and NS, probably because the follow-up period considered in the studies was too short [54][55][56]59,60].

Radiographic Periodontal and Peri-Implant Parameters in Traditional vs. HNB and E-Cigs Smokers
Marginal bone loss was generally higher in CS compared to NS [50,53,54,58,60]. Furthermore, cotinine, which is a nicotinic metabolite that remains in saliva and crevicular fluid for up to 1 week after using nicotine-containing products, has been found in higher concentrations in CS, WS and E-Cigs PISF compared to NS [62], as expected, although no significant differences were found by Alquantani et al. and Mookem et al. among individuals using nicotinic products [50,62]. Conversely, Fangxi Xu et al. described higher crevicular cotinine levels in CS compared to E-Cigs.
Further studies are needed to highlight the impact of electronic cigarettes and Heat-Not-Burn tobacco products on periodontal and peri-implant health status. Indeed, a better comprehension of the role of these alternative smoking habits, which may affect periodontitis and peri-implantitis onset differently from traditional tobacco use, may pave the way for multi-disciplinary personalized prevention strategies, especially in subjects considered at higher risk, such as those who are diabetic [79][80][81][82]. Moreover, the indirect effect of both E-Cigs and HNB tobacco products on periodontitis and peri-implant treatment outcomes may encourage the use of adjunctive therapies, also comprising antibiotics and oral antiseptics administration in non-conventional smokers [80,[83][84][85][86].

Conclusions
The presented results carefully support the hypothesis that e-cigarettes may cause attenuated clinical inflammatory signs of periodontitis, and, hypothetically, of peri-implantitis, when compared to conventional tobacco smoke. However, both electronic cigarettes and Heat-Not-Burn tobacco, considered as alternative smoking products, containing nicotine, may have negative effects on periodontal and peri-implant health, as demonstrated in vitro by the toxic effects at the cellular level detected.
Furthermore, a deeper insight into the existence and extent of the effect putatively exerted by E-Cigs and HNB tobacco products on periodontitis progression rate, as already estimated for traditional tobacco use, may guide in the optimal planning of active periodontal treatment sessions and, above all, of maintenance phase recall intervals.