Zero Inflated Binomial Model for Prognosis of the Risk Factors Associated with dmft Index in Children Aged 5 - 6 Years in Tehran

Background and Objective: The most common index in dental studies is the decayed, missing or filled teeth (dmft)/DMFT. Risk factor evaluation in order to investigate the significant factors that affected this dmft in children has an important role in dental epidemiological studies. This study aims to use a zero inflated binomial model for investigating the risk factors that affected the dmft in children aged 5 - 6 years in Tehran, Iran. Methods: This cross - sectional study was a part of a national survey for assessing the oral health status of Iranian citizens in 2012. The target population was children aged 5 - 6 years. The information and oral examination were collected by the WHO recommended clinical examination form and a trained calibrated dental team (dentists and hygienists). A binomial zero inflated model (ZIB) with random effect was used for evaluating the effect of all variables on dmft. Results: In general, 593 subjects were studied. From the entire subject in this study the frequency of zero was 1071 (45%). The result of ZIB model with random effect in zero part showed that brushing the teeth (OR = 3.5; P value = 0.012) and mothers with university education (OR = 11.24; P value = 0.016) had significant relation with zero dmft. The variance component of random intercept in zero part was significant too (σ 2 =4.68, P < 0.001). Conclusions: Zero inflated binomial model with random effect in zero part fitted better to this data. Brushing the teeth and high education of mothers had protective effect for dmft in children aged 5 - 6 years in Tehran.