## 5 Conclusions  
The quantity of subgingival perio-pathogenic species was more affected by periodontitis than by exposure to tobacco smoke, regardless of whether tobacco was heated or burned. Conceptualization, I.M., J.P., A.P. and S.S.; methodology, S.S.; validation, S.S.; formal analysis, S.S.; investigation, I.M. and B.M.-V.; resources, S.S.; data curation, S.S.; writing--original draft preparation, I.M., J.P. and S.S.; writing--review and editing, D.K., S.S., J.P., A.P. and B.M.-V.; visualization, I.M., J.P. and S.S.; supervision, S.S. and J.P.; project administration, S.S.; funding acquisition, S.S. All authors have read and agreed to the published version of the manuscript. **Funding:** Croatian Science Foundation IP-2020-02-4027 (Environmental factors and microbial interactions in the structure of the dental biofilm); principle investigator [PERSON]. **Institutional Review Board Statement:** This study followed the Declaration of Helsinki guidelines regarding medical protocol and ethics, and the protocol was approved by the Ethics Committee of Faculty of Dental Medicine University of Rijeka (2170-137-006-01-23-60, 4 April 2022) and Clinical Hospital Center Rijeka, Croatia (2170-29-02/1-23-2, 6 March 2022). **Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patients to publish this paper. **Data Availability Statement:** The data sets used and/or analyzed during the current study are available from the Digital Academic Repository of the University of Rijeka, Faculty of Dental Medicine ([PERSON] Okolisi embencii i mikrobioloske interakcije u strukturi dentalnog biofilma: istrazivacki podaci. [Internet]. Fakultet dentalne medicine; 2023, Available from: [[https://urn.nsk.hr/urn:nbn:hr:271:843444](https://urn.nsk.hr/urn:nbn:hr:271:843444)]([https://urn.nsk.hr/urn:nbn:hr:271:843444](https://urn.nsk.hr/urn:nbn:hr:271:843444)), accessed on 4 January 2024). **Acknowledgments:** Preliminary results were presented at 10. International Congress of School of Dental Medicine University of Zagreb 9 May 2024, and were awarded first prize. **Conflicts of Interest:** The authors clearly declare no commercial interests with the manufacturer of the tobacco heating system IQOS(r), PMI International Inc.  
* (19) Phillip Morris Int., Stamford, Connecticut. About Us, Our Products. Available online: [[https://www.pmi.com/markets/croatia/hr/about-us/our-products](https://www.pmi.com/markets/croatia/hr/about-us/our-products)]([https://www.pmi.com/markets/croatia/hr/about-us/our-products](https://www.pmi.com/markets/croatia/hr/about-us/our-products)) (accessed on 24 December 2023). * (20) [PERSON]; [PERSON]; [PERSON] Influence of smoking heating up tobacco products and e-cigarettes on the microbiota of dental plaque. _Pol. Merkur. Lekarski_. **2022**, _50_, 16-20. [PubMed]
* (21) [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON] Effect of cigarette smoking on subgingival bacteria in healthy subjects and patients with chronic periodontitis. _BMC Oral Health_**2017**, _17_, 64. [CrossRef]
* (22) [PERSON] [PERSON]; [PERSON]; [PERSON] Subgingival microbial profiles of smokers with periodontitis. _J. Dent. Res._**2010**, _89_, 1247-1253. [CrossRef]
* (23) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] The effect of cigarette smoking on the oral and nasal microbiota. _Microbiome_**2017**, \(5\), 3. [CrossRef]
* (24) [PERSON] [PERSON]; [PERSON]; [PERSON] The prevalence of pathogenic periodontal microflora in healthy young adult smokers. _J. Periodontol._**2000**, _71_, 562-567. [CrossRef]
* (25) [PERSON]; [PERSON] The role of the oral microbiome in the development of diseases. _Int. J. Mol. Sci._**2023**, _24_, 5231. [CrossRef]
* (26) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Periodontal disease and periodontal bacteria as triggers for rheumatoid arthritis. _Best. Pract. Res. Clin. Rheumatol._**2017**, _31_, 19-30.