Czech and Slovak Dental Students’ Oral Health-Related Knowledge, Attitudes, and Behaviours (KAB): Multi-Country Cross-Sectional Study

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.


Instrument
The SAQ comprised three main categories: (i) demographic characteristics including gender, university, and academic level, (ii) the original HU-DBI items (n = 20), and (iii) general health behaviours including tobacco smoking "I consume tobacco at least once a week", alcohol drinking "I drink alcohol at least once a week", problematic internet use "I find myself using my smartphone/compute longer than I planned", and regular dental check-ups "I go to the dentist/ hygienist for a regular check-up at least once a year" [45][46][47] (Appendix A).

Instrument
The SAQ comprised three main categories: (i) demographic characteristics including gender, university, and academic level, (ii) the original HU-DBI items (n = 20), and (iii) general health behaviours including tobacco smoking "I consume tobacco at least once a week", alcohol drinking "I drink alcohol at least once a week", problematic internet use "I find myself using my smartphone/compute longer than I planned", and regular dental check-ups "I go to the dentist/ hygienist for a regular check-up at least once a year" [45][46][47] (Appendix A).

Czech HU-DBI
The guidelines of Beaton et al. 2000 for translation and cross-cultural adaptation had been followed for producing a validated Czech version of HU-DBI [48]. Firstly, forward translation from English to Czech had been performed by two independent translators

Czech HU-DBI
The guidelines of Beaton et al. 2000 for translation and cross-cultural adaptation had been followed for producing a validated Czech version of HU-DBI [48]. Firstly, forward translation from English to Czech had been performed by two independent translators (FT1 and FT2) whose first language was Czech, and both of them had a dental background. Then, an experts' panel was formed to review the two Czech versions (FT1 and FT2) and produce a common version (FT-12) which was used in the third stage, "backward translation". Two translators (BT1 and BT2) whose first language was English had been invited to translate the FT-12 from Czech to English independently. In the fourth stage, another experts' panel comprising the four translators and the study investigators was formed to review BT1, BT2, FT-12, and original English HU-DBI versions in order to discuss all the linguistic and grammatical discrepancies with the intention of producing a pre-final Czech version.
The pre-final Czech version had undergone two phases of psychometric testing to verify its bi-lingual reliability (preliminary testing) and test-re-test reliability (final testing).
The preliminary testing phase involved a random sample of 20 young Czech individuals who had a good proficiency level of the English language who were invited to fill in the English version of HU-DBI primarily, and after 24 h, they filled in the pre-final Czech version. Cognitive debriefing (interviews) was conducted by asking 10 out of the 20 volunteers who participated in preliminary testing to share their feedback about the clarity and equivalence of the Czech translation and their suggestions to improve it. The minimum inter-rater agreement level was set to be 80%; therefore, any item rated as unclear by at least 20% of the volunteers, would have been referred back to the expert panel for further consultation and adaptation.
The final phase of psychometric testing (test-re-test reliability) was carried out by inviting a random sample of 40 Czech university students to fill in the pre-final Czech version twice with an interval of 48 h, recommended by Marx et al. 2003 [49]. The mean Cohen's kappa coefficient (κ) was 0.941 ± 0.070, and it ranged between 0.754 (item no. 1) and 1.000 (items no. 5, 6, 7, 15, 16, 18, 19, and 20). According to McHugh criteria for interpreting the Cohen's κ coefficient, the Czech HU-DBI version had an almost perfect level of reliability [50] (Supplementary Table S1).

Slovak HU-DBI
The WHO guidelines for translation and cross-cultural adaptation had been used in producing the Slovak HU-DBI version [51]. The WHO guidelines were pragmatic and involved forward translation by two Slovak native translators (from English to Slovak) and backward translation by a single translator (from Slovak to English). All translators were healthcare professionals. Then, an expert panel was formed to review the produced versions and compare them to the original English HU-DBI version in order to relieve linguistic and grammatical issues. Psychometric testing involved five students who were asked about their opinion about the clarity and equivalence of the Slovak translation to the English source.
Eventually, two items were found to be non-comparable between Czech and Slovak versions; therefore, cross-country comparison of those two items (no. 1 and no. 5) should be approached with caution. The verb "worry" in item no. 1 was translated as "fear" in the Czech version, while the Slovak version used its synonym "concern". The term "child-sized toothbrush" in item no. 5 was literally translated in the Slovak version, while the Czech version simplified it as "small-headed toothbrush" (Appendix A).

Ethics
The Ethics Committee of the Faculty of Medicine, Masaryk University reviewed and approved the protocol of this study on 20 November 2019 (Ref no. 48/2019). The declaration of Helsinki for research involving human subjects and the European Union (EU) general data protection regulation (GDPR) guided the design and execution of the present study [52,53]. All participating students had to indicate their consent digitally prior to their participation, and those who failed to indicate their consent were disqualified from the study. No identifying personal data was collected; therefore, retrospective identification of the participants was not possible. Participation in this study was not encouraged by any means of incentives, and it was not coerced by any means of penalties.

Analyses
Initially, Shapiro-Wilk test had been performed to verify whether the overall HU-DBI score (0-12) and its subdomains, i.e., knowledge (0-5), attitudes (0-3), and behaviours (0-4) were normally distributed or not with a significance level (Sig.) < 0.05. The HU-DBI scores of Czech and Slovak dental students were not normally distributed; therefore, the non-parametric analytical tests were used.
Descriptive statistics for the nominal variables (gender and country), ordinal variables (academic level and HU-DBI items answers), and numerical variables (HU-DBI scores) had been executed using frequencies (n) and percentages (%) for qualitative variables, and mean and standard deviations (µ ± SD) for quantitative variables. Inferential statistics had been executed to test the association between HU-DBI responses and scores and sociodemographic and behavioural correlates. Chi-squared test (χ 2 ), Fisher's exact test, Mann-Whitney test (U), and Jonckheere-Terpstra test (JT) were used with a confidence level (CI) of 95% and a significance level (Sig.) < 0.05.
Binary logistic regression had been performed on the dependent variable (country); and it estimated the adjusted odds ratio (AOR) of the HU-DBI core items and the sociodemographic and behavioural predictors, which were found to be significant in the univariate analysis (Chi-squared test (χ 2 ) and Fisher's exact test). The Nagelkerke pseudo R 2 was used to explain the variability of group membership (country). Similarly, logistic regression analysis was used to evaluate the predictors of tobacco smoking behaviours.

Demographic Characteristics
Out of the 487 students who were included in the downstream analyses, 372 (76.4%) were females and represented 73.5% and 77.9% of Czech and Slovak samples, respectively, without a statistically significant difference (Sig. = 0.277). Over half of the participants (55.6%) were enrolled in preclinical years without a statistically significant difference (Sig. = 0.909) between Czech (55.3%) and Slovak (55.8%) samples (Table 1).

Health Behaviours
Tobacco smoking at least once a week was reported by 68 (14%) students, and it was significantly (Sig. = 0.008 and <0.001) more common among Slovak (17%) and male students (24.3%) than their Czech (8.2%) and female colleagues (10.8%), respectively. Drinking alcohol at least once a week was reported by more than one-third of the participants (35.5%), with males having a significantly (Sig. < 0.001) higher prevalence (50.4%) than females (30.9%) in both countries.
The majority of participants (88.3%) reported problematic internet use, which was more common (Sig. = 0.017) among Slovak (90.9%) than Czech (83.5%) students. Regular dental check-ups annually were also reported by the vast majority of our participants (93.6%) with no statistically significant differences based on country, gender, or clinical experience (Table 2).

HU-DBI Responses
Among Czech students, item no. 3 of worrying about teeth colour received the highest level of agreement (94.1%), followed by item no. 1 of dental anxiety (91.2%), and item no. 5 of using child-sized toothbrushes (90%). Contrarily, item no. 2 of bleeding gingiva had the lowest level of agreement (0.6%), followed by item no. 17 of using toothbrushes with hard bristles (1.8%), item no. 7 of dissatisfaction with gingival colour (2.4%), and item no. 6 of incapacity to maintain oral health in older age (2.9%).
The difference between Czech and Slovak students was statistically significant in fifteen items. Slovak students exhibited significantly higher agreement levels for items no. 2 of gingival bleeding (8.8% vs. 0.6%), no. 4 of noticing dental plaque (31.9% vs. 16.5%), no. 6 of incapacity to maintain oral health in older age (

Gender
On comparing HU-DBI responses across genders, item no. 3 of worrying about teeth colour was significantly more common among females (97.6%) than males (88.77%) in both countries. Czech female students had a significantly higher agreement level for item no. 5 of using child-sized toothbrushes (94.4% vs. 77.8%) and a lower agreement level for item no. 14 of preventing periodontal disease with brushing alone (12% vs. 24.4%) than Czech males. Slovak female students had a significantly higher agreement level for item no. 16 of using plaque-disclosing agents (40.1% vs. 27.1%) than Slovak males (Table 4).

Clinical Experience
On comparing the HU-DBI responses based on clinical experience, clinical students had significantly higher agreement levels for items no. 11 of toothbrushing without toothpaste (63.4% vs. 46.1%), no. 16 of plaque-disclosing agents use (55.6% vs. 43.2%), and no. 20 of positive feedback of treating dentist (84.3% vs. 76.8%) than their preclinical peers in both countries. Contrarily, clinical students had a significantly lower agreement level for item no. 17 of using toothbrushes with hard bristles (4.6% vs. 9.6%) than preclinical students. Additionally, clinical students had a significantly higher agreement level for item no. 5 of using child-sized toothbrushes (7.1% vs. 1.1%) than preclinical students in Slovakia only. (Table 4)

Tobacco Smoking
In both countries, the students who reported smoking tobacco at least once a week had a significantly lower agreement level for item no. 5 of using child-sized toothbrushes (22.1% vs. 35.8%) and higher agreement levels for items no. 14 of preventing periodontal disease through toothbrushing alone (42.6% vs. 25.1%), and no. 15 of delaying dental visits (14.7% vs. 6.4%) than non-smoking students (Table 4).

HU-DBI Scores
The mean HU-DBI score of the entire sample was 8.18 ± 1.80, with Czech students (9.34 ± 1.29) having a significantly higher score (Sig. < 0.001) than Slovak students (7.56 ± 1.73). Czech students had significantly higher knowledge (4.35 vs. 3.55) and attitudes scores (2.66 vs. 1.73) than their Slovak counterparts. The gender-based differences were not statistically significant (Sig. = 0.316); nevertheless, females exhibited slightly higher scores (Table 5). The highest HU-DBI score was recorded by the fifth-year students (8.87 ± 1.73), while the lowest score was recorded by the first-year students (7.38 ± 1.56). Similarly, the highest knowledge (4.15 ± 0.76) and attitude (2.35 ± 0.82) scores were achieved by the fifth-year students, while the lowest knowledge (3.49 ± 0.91) and attitude (1.68 ± 0.76) scores were achieved by the first-year students. The differences between the academic levels were statistically significant (Figure 2).
Clinical students from both countries had a significantly higher HU-DBI score (8.35 ± 1.86) than preclinical students (8.04 ± 1.75). The differences were in favour of clinical students in terms of knowledge and attitudes, even though these differences were not statistically significant (Figure 3).
The students who reported smoking at least once a week had a significantly lower HU-DBI score (7.63 ± 2.01) than non-smokers (8.27 ± 1.75). Similarly, the students who reported problematic internet use had a significantly lower HU-DBI score (8.11 ± 1.83) than those who did not report it (8.70 ± 1.50). Problematic internet use was associated with lower knowledge (3.79 vs. 4.11) and attitude (2.02 vs. 2.33) scores. Regular dental check-ups were significantly associated with higher HU-DBI (8.23 vs. 7.42) and behaviours (2.33 vs. 1.90) scores. Knowledge and behaviours scores were also higher among the students who reported regular dental check-ups without statistical significance (Figure 4).
The highest HU-DBI score was recorded by the fifth-year students (8.87 ± 1.73), while the lowest score was recorded by the first-year students (7.38 ± 1.56). Similarly, the highest knowledge (4.15 ± 0.76) and attitude (2.35 ± 0.82) scores were achieved by the fifth-year students, while the lowest knowledge (3.49 ± 0.91) and attitude (1.68 ± 0.76) scores were achieved by the first-year students. The differences between the academic levels were statistically significant (Figure 2). Clinical students from both countries had a significantly higher HU-DBI score (8.35 ± 1.86) than preclinical students (8.04 ± 1.75). The differences were in favour of clinical students in terms of knowledge and attitudes, even though these differences were not statistically significant (Figure 3).  The students who reported smoking at least once a week had a significantly lo HU-DBI score (7.63 ± 2.01) than non-smokers (8.27 ± 1.75). Similarly, the students reported problematic internet use had a significantly lower HU-DBI score (8.11 ± 1 than those who did not report it (8.70 ± 1.50). Problematic internet use was associated w lower knowledge (3.79 vs. 4.11) and attitude (2.02 vs. 2.33) scores. Regular dental ch ups were significantly associated with higher HU-DBI (8.23 vs. 7.42) and behaviours ( vs. 1.90) scores. Knowledge and behaviours scores were also higher among the stud who reported regular dental check-ups without statistical significance (Figure 4). than those who did not report it (8.70 ± 1.50). Problematic internet use was associated w lower knowledge (3.79 vs. 4.11) and attitude (2.02 vs. 2.33) scores. Regular dental che ups were significantly associated with higher HU-DBI (8.23 vs. 7.42) and behaviours ( vs. 1.90) scores. Knowledge and behaviours scores were also higher among the stude who reported regular dental check-ups without statistical significance (Figure 4).

Czech Students
In the Czech Republic, gender-based differences were not statistically signific nevertheless, females scored slightly better. The fifth-year students had the highest DBI score (9.56 ± 1.29), while the first-year students had the lowest HU-DBI score (8. 1.55). Clinical students (9.50 ± 1.22) and the students who reported regular dental ch ups (9.39 ± 1.23) had higher HU-DBI scores than preclinical students (9.20 ± 1.34) and th who did not report regular dental check-ups (8.62 ± 1.76). HU-DBI scores of the stud who reported tobacco smoking and alcohol drinking were not significantly different f their counterparts (Table 6).

Czech Students
In the Czech Republic, gender-based differences were not statistically significant; nevertheless, females scored slightly better. The fifth-year students had the highest HU-DBI score (9.56 ± 1.29), while the first-year students had the lowest HU-DBI score (8.31 ± 1.55). Clinical students (9.50 ± 1.22) and the students who reported regular dental check-ups (9.39 ± 1.23) had higher HU-DBI scores than preclinical students (9.20 ± 1.34) and those who did not report regular dental check-ups (8.62 ± 1.76). HU-DBI scores of the students who reported tobacco smoking and alcohol drinking were not significantly different from their counterparts (Table 6).

Slovak Students
In Slovakia, gender-based differences were not statistically significant. The sixth-year students had the highest HU-DBI score (8.44 ± 1.22), while the first-year students had the lowest HU-DBI score (7.21 ± 1.51). Clinical students (7.73 ± 1.85) and the students who reported regular dental check-ups (7.62 ± 1.71) had significantly higher HU-DBI scores than preclinical students (7.43 ± 1.62) and those who did not report regular dental check-ups (6.56 ± 1.79). HU-DBI scores of the students who reported tobacco smoking, alcohol drinking, and problematic internet use were lower than their counterparts (Table 7).

Czech Students
The year-over-year (YOY) analysis for Czech students' HU-DBI scores revealed that the differences between first vs. second year were statistically significant for the knowledge score (Sig. = 0.042), attitudes score (Sig. = 0.002), and overall HU-DBI score (Sig. = 0.007). Additionally, the attitudes score significantly increased from each year to the following one; first vs. second year (Sig. = 0.002), second vs. third year (Sig. = 0.014), and third vs. fourth year (Sig. = 0.033). There were no other significant differences found between the consecutive academic years in terms of HU-DBI scores (Table 8).

Slovak Students
The year-over-year (YOY) analysis for Slovak students' HU-DBI scores revealed no significant differences between the consecutive academic years in terms of HU-DBI scores. Nevertheless, the largest differences were found between second vs. third year without statistical significance (Table 9).

Regression Analysis of State
According to the univariate analysis for HU-DBI core items, items no. 2 (bleeding gingiva), no. 4 (noticing dental plaque), no. 6 (incapacity to maintain oral health in older age), no. 8 (perceived-efficacy of oral hygiene), no. 10 (receiving professional oral hygiene training), no. 11 (toothbrushing without toothpaste), no. 12 (post-brushing checking), no. 14 (preventing periodontal disease through brushing alone), no.16 (plaque-disclosing agents use), and no. 19 (spending too much time while brushing) were used in the binary logistic regression analysis to predict group membership "country" of the participants. In addition, tobacco smoking and problematic internet use were found significantly associated with students' country; therefore, they were suggested to be used in the regression model (Table 10). Logistic regression had been used with a significance level (Sig.) ≤ 0.05. The Czech Republic was coded as "0" and Slovakia was coded "1". All significant associations are in bold font.
The suggested model managed to predict the country of the participating students with 80.9% of accuracy. Nagelkerke pseudo R 2 indicated that the model could explain 52.7% of the variability in the dependent variable (country) ( Table 11). The cut-off value is 0.50. Nagelkerke R 2 = 0.527.

Regression Analysis of Tobacco Smoking
According to the univariate analysis for HU-DBI core items, items no. 14 (preventing periodontal disease through brushing alone) and no. 15 (delaying dental visits) were used in the binary logistic regression analysis to predict group membership "tobacco smoking" of the participants. In addition, Slovak nationality, male gender, and alcohol drinking were found significantly associated with students' smoking behaviour; therefore, they were suggested to be used in the regression model (Table 12). The suggested model managed to predict the country of the participating students with 85.6% of accuracy. Nagelkerke pseudo R 2 indicated that the model could explain 13.7% of the variability in the dependent variable (tobacco smoking) (Table 13). The cut-off value is 0.50. Nagelkerke R 2 = 0.137.
While twice-daily brushing with fluoride toothpaste is a universal recommendation for oral hygiene, multiple systematic reviews and meta-analyses revealed that toothpaste has no contribution to the mechanical removal of dental plaque [61][62][63]. Sälzer et al. 2020 confirmed that a reduction in plaque scores by 50% can be achieved by toothbrushing either with or without toothpaste [63]. Therefore, agreement with item no. 11 of toothbrushing without toothpaste and disagreement with item no. 14 of preventing periodontal disease by toothbrushing solely were depicted as indicators for excellent oral health-related awareness and attitudes. Our study found that Czech students were significantly more agreeable with item no. 11 (84.1% vs. 37.5%) and disagreeable with item no. 14 (84.7% vs. 65.9%) than their Slovak counterparts; nevertheless, final-year students had significantly higher agreement levels with item no. 11 than their first-year colleagues in both the Czech Republic (91.7% vs. 53.8%) and Slovakia (66.7% vs. 19.4%). Similar positive trend was previously reported in Romania (freshers: 26% vs. seniors: 58%), Poland (1.9% vs. 33.9%), Greece (11% vs. 64%), Japan (59% vs. 96%), South Korea (3% vs. 88%) [18,60,64,65]. In Croatia, final-year dental students (42.6%) reported using plaque-disclosing agents significantly more than their first-year colleagues (16.1%) [66]. On the other hand, Croatian nurses with completed secondary school (16.3%) and nurses with bachelor's or master's degrees (19.6%) did not have significant differences (Sig. = 0.671) in terms of plaque-disclosing agents use; thus, indicating the positive impact of dental curricula on dental students' oral health attitudes [67].
Plaque-disclosing agents use (item no. 16) indicates positive oral health behaviours; therefore, it was incorporated in the HU-DBI scoring system. Recent studies revealed that the vast majority of dental hygienists in the Czech Republic (88.2%) recommend their patients use plaque detectors at home in the form of tablets (78.3%) and mouthwashes (9.9%) due to the ease of their application; nevertheless, more than half of Czech adults reported that they had never visited a dental hygienist in their life [68,69]. The use of plaque-disclosing agents was significantly (Sig. < 0.001) higher among Czech (70%) stu-dents than their Slovak counterparts (37.2%), even though there was a significant and steady increase (+30%) of their use from the first year to the final year in both the Czech Republic (53.8% vs. 83.3%) and Slovakia (33.3% vs. 63%). In Turkey, several HU-DBI-based studies reported the same increasing pattern of plaque-disclosing agents use from the first year to the final year [70][71][72][73]. On comparing dental students to other healthcare students, e.g., general medicine and nursing students, the use of plaque-disclosing agents was significantly increasing through dental education, while it did not differ between freshers and seniors of other healthcare programs [73,74]. Therefore, it is evident that dental curricula, through their preventive elements, can help in increasing the use of plaque-disclosing agents.
The use of toothbrushes with hard bristles (item no. 17) can be associated with hard dental tissues loss and soft tissues injuries. A randomized controlled trial by Zimmer et al. 2011 revealed that hard bristles had higher efficiency for plaque removal; however, they also caused soft tissue injuries more frequently compared with soft bristles [75]. Other studies concluded that hard dental tissue loss (erosion) had been mediated by stiffness of toothbrushes bristles, and it was mainly caused by toothpaste and their chemical composition [76]. A recent population-based study from Brazil found that bristles stiffness was significantly associated with erosive tooth wear among adolescents [77]. In our study, Slovak students had significantly (Sig. < 0.001) higher agreement with item no. 17 of using toothbrushes with hard bristles than their Czech counterparts (10.4% vs. 1.8%, respectively); and in both countries first-year students had significantly higher agreement levels compared with their final-year colleagues. In agreement with our findings, a recent survey for oral health practices of medical and dental hygiene students at the Third Faculty of Medicine, Charles University (Prague, Czech Republic) reported that the vast majority of participating students were using either extra-soft or ultra-soft toothbrushes [78]. Nevertheless, population-based studies for oral hygiene behaviours of Czech adults are recommended to address bristles stiffness for a better understanding of consumption patterns.
Aggressive toothbrushing refers to applying excessive mechanical forces during brushing that may cause tooth surface abrasion [79][80][81][82][83]. Several studies recommended that the application of appropriate mechanical forces during toothbrushing should be an integral part of oral hygiene education in order to avoid the negative consequences of aggressive toothbrushing [79,82]. In our study, Slovak students had a significantly (Sig. < 0.001) higher rate of reported aggressive toothbrushing (item no. 18) compared with Czech students, 14.5% vs. 3.5%, respectively. Among Czech students, the rate of aggressive toothbrushing did not differ significantly between preclinical and clinical students, while in Slovakia, firstyear students (25%) had a higher rate than final-year students (7.4%). Similar to the Slovak trend, final-year dental students had significantly lower levels of aggressive toothbrushing than their first-year colleagues in Poland (0% vs. 13%), Greece (7% vs. 33%), and Japan (13% vs. 48%) [18,56,64].
Worrying about teeth colour (item no. 3) was one of the few items that were not significantly different between Czech vs. Slovak students or preclinical vs. clinical students, even though this issue was significantly more common among female students than their male peers in both the Czech Republic (97.6% vs. 84.4%) and Slovakia (97.6% vs. 91.4%). Interestingly enough, the responses to items no. 7 of dissatisfaction with gingival colour and no. 13 of worrying about halitosis were not significantly different across gender or clinical experience. Prior HU-DBI-based studies found that female dental students were more worried about their teeth colour (item no. 3) than male students, e.g., Poland (38.6% vs. 20.4%) and Romania (44% vs. 31%) [60,64]. In Brazil, a descriptive cross-sectional study concluded that female dental students were less satisfied with their smiles than their male peers, and the preclinical students were more interested in having brighter teeth than clinical students [84]. While multiple studies revealed no significant differences between female and male dental students in their skills of teeth shade matching, few studies found that female dental students had superior skills [85][86][87]. Another explanation could be based on the finding that females are more concerned with facial appearance; therefore, they are more sensitive to teeth shape and colour and more inclined to seek esthetic treatments [88][89][90][91][92][93].
Female students represented the majority of our sample (76.4%); thus reflecting the female dominance of the dental profession in both the Czech Republic (64.9%) and Slovakia (61.2%), according to the latest reports of the Czech Dental Chamber (ČSK) and the Slovak Chamber of Dentists (SKZL) [41,94]. According to the Council of European Dentists (CED), countries with well-established public oral healthcare systems, such as Nordic and Eastern European countries, used to have higher shares of female dentists, e.g., Poland (78%), and Finland (69%). Additionally, the recent CED report pointed out the rising trend of female dentists in Europe, which was clearly evident in Western countries such as the United Kingdom, which witnessed a significant increase in female dentists proportion from 34% in 2008 to 45% in 2015 and France (36% vs. 40%) [95].
Cepová et al. 2018 found that female adults in Slovakia were significantly more likely to visit dentist/dental hygienist for routine check-ups (59.9% vs. 49.1%), report twicedaily toothbrushing (83.5% vs. 72.3%), and use interdental cleaning devices (62.5% vs. 42.1%) than male adults [96]. Similarly, Samohyl et al. 2021 concluded that avoidance of preventive oral healthcare was significantly more common among male adolescents than females in Slovakia [97]. The Health Behaviour in School-aged Children (HBSC) study found a significant difference between female (71.7%) and male (54.8%) adolescents in Slovakia in terms of twice-daily toothbrushing [98]. In the Czech Republic, the HBSC indicated that 32-38% of male and 21% of female adolescents were not brushing their teeth twice a day, even though there was an observed positive trend towards the twice-daily brushing habit among males between 1994 and 2014 [99]. In our sample, the gender-based differences were not statistically significant in HU-DBI scores and the vast majority of items responses, which is in contrast to what was previously reported about oral health behaviours and awareness of general Czech and Slovak populations [96][97][98][99]. Consequently, one may put forward that dental education can contribute to squeezing or probably closing the gender gaps in oral health attitudes and behaviours, which might be a sound reasoning for population-level interventions that target oral health literacy of the public [100][101][102].
Clinical students had a higher HU-DBI score than pre-clinical students in both countries (8.35 vs. 8.04); nevertheless, this difference was only statistically significant among Slovak (7.73 vs. 7.43; Sig. = 0.032) not Czech (9.50 vs. 9.20; Sig. = 0.166) students, which could be due to sample size differences. The superiority of clinical students in HU-DBI scores was observed in prior studies, e.g., Lithuania (6.81 vs. 5.96), Romania (7.35 vs. 6.60), and Turkey (7.47 vs. 6.00) [58,60,71]. The standard hypothesis for explaining this difference implies that improvement of oral health KAB is a collateral gain from the professional education on oral diseases and prevention, which is gradually received by dental students [59]. On comparing the undergraduate dental curricula of both countries, the courses of preventive dentistry and dental public health are administered earlier in Czech than Slovak universities. In the Czech Republic, the course of preventive dentistry and dental hygiene (B03033) is administered during the first semester (first year) at Charles University (Prague); and the course of preventive dentistry and cariology (ST1/ZUB01) is also administered during the second semester (first year) at Palacky University (Olomouc) [103,104]. On the other hand, the course of preventive dentistry (J-S-ZL-035) is administered during the sixth semester (third year) at Comenius University (Bratislava), and the course of preventive dentistry (SK/PreZL-ZL/15) is administered during the fifth semester (third year) in Pavol Jozef Šafárik University (Košice) [105,106]. The year-over-year analysis (YOY) indicated that the only significant improvement for HU-DBI score occurred among Czech students was between the first vs. second year (Sig. = 0.007); thus, it may be depicted as an immediate effect of preventive courses that were administered during the first year.
The reported prevalence of tobacco smoking in our sample was 14%, which is significantly lower than the prevalence of tobacco smoking in both Czech (31.5%) and Slovak (32.3%) general adult populations [107,108]. Tobacco smoking was more significantly common among male students (24.3%) than females (10.8%), which is in agreement with the current demographics of tobacco use in both the Czech Republic (35.4% vs. 22.6%) and Slovakia (39.2% vs. 23.2%) [109]. Notably, Slovak students were significantly more likely to report tobacco smoking (17%) than their Czech counterparts (8.2%). According to the latest European Tobacco Control Scale (ETCS) report of 2019, the rank of the Czech Republic (23rd) had improved by eight positions since the report of 2016 (31st) due to the fact that the country adopted comprehensive anti-smoking legislations since February 2017 and ratified the WHO FCTC Illicit Trade Protocol [110]. The ECTS report of 2019 also showed that the rank of Slovakia (32nd) had dropped by two positions since the 2016 report (30th) as no progress was made since 2010 in the fight against tobacco [110]. Anti-smoking education was first introduced to undergraduate dental curricula in the Czech Republic twenty years ago [111]. The rationale for this move was based on the prior findings on the underestimation of smoking risks by healthcare professionals, including physicians and dentists, who were not reimbursed for helping their patients quit smoking [111]. In our study, the students who reported smoking tobacco at least once a week had a significantly lower HU-DBI score (8.27 vs. 7.63) and a higher agreement level for item no. 15 of delaying dental visits (14.7% vs. 6.4%) compared with non-smoking students. Our findings suggest that tobacco smoking may be associated with poor oral health KAB among dental students; thus, calling for a re-evaluation of the currently implemented anti-smoking curricula in Czech dental schools.
Mravčík et al. 2019 concluded that although alcohol consumption and heavy episodic drinking levels in the Czech Republic are one of the highest worldwide, there was a recent declining trend for alcohol drinking among adolescents and children [112]. A total of 35.5% of our participants reported drinking alcohol at least once a week, with a significant (Sig. < 0.001) difference between males (50.4%) and females (30.9%). Longitudinal analysis for HBSC data of Czech adolescents pointed out this significant decline of alcohol drinking between 1994 and 2014, with an increased vulnerability of male adolescents [113]. The same trend was reported by HBSC in Slovakia with similar gender-based differences [114]. A recent large cross-sectional study for American adults revealed that alcohol consumption, especially heavy drinking, was significantly associated with alterations of oral microbiome that might explain the aetiology of multiple alcohol-related diseases [115]. While alcohol drinking was not associated with poor oral health KAB among our participants, it is still imperative to educate and motivate future dentists to perform screening for alcohol use, especially heavy drinking, among their patients as this can be a life-saving intervention for early detection of oral and oropharyngeal cancers [116].
The vast majority of our participants (88.3%) reported using their smartphones and laptops longer than they planned. Problematic internet use had been consistently found among all age groups of Czech society, while the 12-15-year-old adolescents exhibited the highest level of excessive internet use [117]. In our sample, problematic internet use was significantly associated with a lower oral health-related knowledge score (3.79 vs. 4.11), attitudes score (2.02 vs. 2.33), and HU-DBI score (8.11 vs. 8.70). Recently, a national surveybased study for Korean adolescents revealed that problematic internet use affected sleep quality directly and oral health indirectly [118]. Our results warrant further investigation for the potential association between oral health KAB and problematic internet use, especially among younger age groups.

Strengths
To the best of the authors' knowledge, this was the first study to evaluate the oral health KAB of dental students in the Czech Republic and Slovakia. The use of HU-DBI as a widely used instrument facilitated international comparison of the Czech and Slovak dental students' outcomes. Following a rigorous methodology for translation and cross-cultural adaptation of the HU-DBI, especially in producing the Czech version, ensured the validity of the translated versions. The identity of the participants was anonymous in order to limit the Hawthorne's effect and information bias that is predicted to occur with healthcare professionals and students.

Limitations
The first limitation of the present study is the cross-sectional design that did not allow for real-time evaluation of the year-over-year gains of oral health KAB during dental education. Secondly, cross-country comparison was limited in items no. 1 (dental anxiety) and no. 5 (use of child-sized toothbrushes) due to discrepancies of Czech vs. Slovak translations; nevertheless, gender-and academic-level-based comparisons were possible for each country. Thirdly, there was a lack of information on tobacco smoking and alcohol drinking because the investigators aimed to keep the questionnaire as short as possible in order to ensure a satisfactory response rate. Fourthly, the unequal sample sizes of Czech and Slovak students may have limited the cross-country comparison.

Implications
The findings of this study suggest 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 current anti-smoking components and their impact on students' views and attitudes. The potential association between problematic internet use and oral health KAB need further investigation, especially among young adult groups, including future healthcare professionals.

Conclusions
The present study found that the mean HU-DBI score of Czech and Slovak dental students (8.18 ± 1.80) is 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. 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 current anti-smoking components and their impact on students' views and attitudes.

Data Availability Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments:
The authors would like to thank all the participating students for their efforts and time invested in this study. Additionally, we would like to thank Simona Šarmírová (Slovak Association of Dental Students [Slovenský spolok študentov zubného Lekárstva]), Dana Kloudová (Czech Association of Dental Students [Sdružení studentů stomatologieČeské republiky]), and Martin Krobot (Department of Public Health, Masaryk University) for their help in instrument validation and data collection.

Conflicts of Interest:
The authors declare no conflict of interest.