S1 Data -

Aim
According to the World Health Organization (WHO), early childhood caries (ECC) is still considered a major global health problem despite the general improvement in oral health practice. This study aimed to assess ECC’s prevalence, severity, and key social and behavioral determinants in Iranian children 1–5- years of age.
Method
This cross-sectional study recruited Iranian 1–5-year-olds with a three-stage stratified clustered sampling method. After providing consent, parents were interviewed using a validated questionnaire, including questions on child characteristics and behavioral factors. Each child underwent a dental examination by one of four trained and calibrated dentists. Associations between key covariates of interest and primary outcome measures were assessed by multivariable logistic regression modeling and multivariate generalized negative binomial regression modeling after weightings were applied. Statistical analysis was performed using SPSS V25 and Stata V14.2 software packages. A p-value ≤ 0.05 was considered significant.
Results
The mean age of 909 participants was 41.1±1.2 months, 48.6% were male, and 38.1% lived in rural areas. The overall prevalence of ECC was 53.2% and mean dmft score was 2.7± 0.3. Key determinants associated with ECC included living rurally (p = 0.009, OR = 2.13), consuming sweet drinks, sugary snacks, or both [p-value = 0.02 (OR = 2.53), and p-value<0.001 (OR = 4.96), respectively], and visible plaque (p<0.001, OR = 3.41). Covariates associated with dmft scores included residing in rural regions (p = 0.02, IRR = 1.31), having both sugary snacks and sweet drinks (p = 0.02, IRR = 1.85) compared to those had none, and visible dental plaque (p<0.001, IRR = 2.06).
Conclusions
The prevalence of dental caries in children is high in Iran. The increase of ECC prevalence and severity from toddlers to preschoolers emphasizes on the critical importance of early interventions in toddlers. Improving access to care for rural children is essential along with the need to change dietary and self-care behaviors through multilevel efforts.

## 研究目的
根据世界卫生组织（World Health Organization, WHO）的定义，尽管口腔卫生实践整体有所改善，但儿童早期龋病（early childhood caries, ECC）仍是全球主要公共卫生问题之一。本研究旨在评估伊朗1~5岁儿童儿童早期龋病的患病率、严重程度及主要社会与行为影响因素。

## 研究方法
本横断面研究采用三阶段分层整群抽样方法，招募伊朗1~5岁儿童作为研究对象。获得知情同意后，研究人员通过经过验证的调查问卷对家长进行访谈，问卷内容涵盖儿童自身特征与行为相关因素。随后，由4名经过培训且校准合格的牙医之一为每名儿童进行口腔检查。在完成权重校正后，本研究采用多变量logistic回归模型与多变量广义负二项回归模型，分析关键关注协变量与主要结局指标之间的关联。统计分析采用SPSS V25与Stata V14.2统计软件包完成，以P值≤0.05作为差异具有统计学意义的判定标准。

## 研究结果
本研究共纳入909名研究对象，其平均年龄为41.1±1.2个月，其中男性占比48.6%，38.1%的儿童居住于农村地区。儿童早期龋病总体患病率为53.2%，乳牙龋失补牙数（dmft）的平均得分为2.7±0.3。与儿童早期龋病相关的关键影响因素包括：居住于农村地区（P=0.009，比值比[odds ratio, OR]=2.13）、饮用甜饮料、食用含糖零食或二者兼具[分别对应P=0.02（OR=2.53）与P<0.001（OR=4.96）]，以及可见牙菌斑（P<0.001，OR=3.41）。与乳牙龋失补牙数评分相关的协变量包括：居住于农村地区（P=0.02，发生率比[incidence rate ratio, IRR]=1.31）、同时食用含糖零食与甜饮料（相较于无此类习惯者，P=0.02，IRR=1.85），以及可见牙菌斑（P<0.001，IRR=2.06）。

## 研究结论
伊朗儿童龋病患病率处于较高水平。从幼儿期到学龄前阶段，儿童早期龋病的患病率与严重程度均呈上升趋势，这凸显了对幼儿开展早期干预的关键重要性。需通过多维度干预手段改善农村儿童的口腔医疗可及性，同时纠正其不良饮食与自我口腔护理行为。