The SMILE study cohort: Baseline comparison of oral health and dental aesthetics among smokers in Italy, Poland, Moldova, and Indonesia

Objectives: SMILE Study is an international multicenter randomized prospective controlled trial investigating oral health and dental aesthetic endpoints in smokers who switch to combustion-free nicotine alternatives (C-F NAs). This paper reports baseline characteristics of the smokers enrolled in the SMILE study cohort. Methods: Conducted across Italy, Poland, Republic of Moldova, and Indonesia, the SMILE study recruited 460 adult daily smokers. Eligible participants were randomly assigned to continue smoking or switch to a C-F NA. Baseline assessments included Modified Gingival Index (MGI), quantitative light-induced fluorescence (QLF) imaging of plaque, digital spectrophotometry for tooth shade, extrinsic stain indices, and oral health–related quality of life. Standardized calibration, centralized training, and electronic case report forms ensured methodological consistency across sites. Results: Significant cross-country differences were observed in age distribution, sex ratio, smoking intensity, Whitening Index for Dentistry (WID) values, and MGI gingival inflammation scores. Italians reported the highest WID values, while Indonesians showed the lowest MGI and plaque coverage, possibly reflecting cultural, behavioral, and product-specific factors. Multivariable regression identified age, sex, ethnicity, and cumulative smoking exposure as significant predictors of oral health outcomes. Conclusions: Characterization of participants in the SMILE study cohort reveals marked inter-country variability in oral health and dental aesthetics among smokers, reflecting demographic, behavioral, and unique cultural factors. Clinical Significance: This large multicenter study used standardized, objective technologies to assess smokers, providing essential benchmarks for evaluating smoking cessation and harm reduction strategies in future longitudinal analyses and supporting clinicians in tailoring personalized interventions.