Oral diseases are among the most common non-communicable diseases around the globe and become a public health challenge that considerably impact general health and well-being in all ages across the lifespan. Oral health is an integral part of general health, where poor oral health and other lifestyle-related chronic diseases have a common risk factor background. The underlying causes of oral health inequalities are often complex and related to country-specific historical, economic, cultural, social, or political factors. For more than a decade, data from the Health Behavior in School-aged Children (HBSC) survey showed that tooth brushing rates are very low in post-Soviet countries. The general aim of our study was to focus on a more detailed profile of schoolchildren from post-Soviet countries, who have poor habits of teeth brushing, in terms of their family, social support, physical activity, nutrition, and other health-related behaviors. Data for this study was extrapolated from the Health Behavior in School-aged Children study, a World Health Organization collaborative cross-national study, conducted every 4 years since 1983/1984. For this study, the post-Soviet countries from Eastern Europe and Central Asia were selected: Armenia, Azerbaijan, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Lithuania, Latvia, Moldova, Tajikistan, Ukraine, and Uzbekistan. Data from all countries (some exceptions for Kyrgyzstan, Tajikistan, and Uzbekistan) were collected within 2017–2018 HBSC study, following international research protocol. The sample consisted of 44,760 schoolchildren, aged 11, 13, and 15 years from 12 countries. Irregular tooth brushing is more common among boys, elder adolescents, and schoolchildren from less affluent families. Low own health measures, low life satisfaction, low physical activity, and low FAS relate to poorer adolescent dental hygiene in post-Soviet countries. Adolescents characterized by irregular tooth brushing were more likely to assess their health as fair or poor rather than excellent or good (OR = 1.22), and also had greater odds of reporting low life satisfaction (OR = 1.36). Individual mental health complaints—feeling low, being irritable, being nervous, and having sleep difficulties—were assessed as a possible outcome of irregular tooth brushing. However, irregular tooth brushing was not associated with poorer mental health outcomes (p > 0.05). Conclusions: Oral hygiene in post-Soviet countries is still a major public health challenge and have to be addressed properly.What is Known:• Oral health strongly affects the overall health of children and adolescents in the future.• Oral diseases often share common determinants and risk factors with other chronic diseases.• The underlying causes of oral health inequalities are often complex and related to country-specific historical, economic, cultural, social, or political factors.What is New:• Irregular tooth brushing was more common among adolescents with low life satisfaction and poor or fair health as well as in less affluent families.• Irregular tooth brushing was not found to be associated with poorer mental health among post-Soviet countries adolescents.