Dentists play a key role in the primary prevention of oral diseases and related systemic complications; therefore, their views on behavioural interventions need to be aligned with the current agendas for oral health. Likewise, dental students’ oral health-related knowledge, attitudes, and behaviours (KAB) are of practical importance, as they are the future opinion leaders for oral health in their respective communities. A cross-sectional survey-based study was designed to evaluate the oral health KAB of dental students in both the Czech Republic and Slovakia. The study utilized translated versions of the Hiroshima University Dental Behavioural Inventory (HU-DBI), and it aimed to recruit students from all Czech and Slovak dental schools. A total of 487 students were included in this study, out of which 372 (76.4%) were females, 271 (55.6%) were enrolled in preclinical years, 68 (14%) reported smoking tobacco at least once a week, and 430 (88.3%) reported problematic internet use. The mean HU-DBI score of Czech and Slovak dental students (8.18 ± 1.80) was comparable with the previously reported scores of dental students in Nordic and Western European countries. Czech students (9.34 ± 1.29) had a significantly higher score than their Slovak counterparts (7.56 ± 1.73). In both countries, preclinical students (8.04 vs. 8.35), the students who reported tobacco smoking (7.63 vs. 8.27), and those who reported problematic internet use (8.11 vs. 8.70) had significantly lower HU-DBI scores than their counterparts, respectively. In the Czech Republic, the significant increases in HU-DBI scores occurred after the first academic year when the students received preventive dentistry courses; therefore, one can put forward that early implementation of preventive elements in undergraduate dental curricula may yield better and more sustainable oral health gains for the students. Future research on Czech and Slovak dental curricula need to re-evaluate the oral hygiene and anti-smoking components and their impact on students’ views and attitudes.