Selected risk factors of dental caries in 11- to 13-years old schoolchildren in Slovakia

Background: Oral diseases, particularly dental caries, affect as much as 9 in 10 persons globally. Its development starts during childhood and among factors participating in its aetiology, behavioural ones play a particularly important role. The aim of the study was to examine the selected behavioural risk factors of dental caries in Slovak adolescents between 2006 and 2018. Methods: We analysed occurrence of the selected factors (teeth brushing less than once a day, eating sweets and drinking sweetened soft drinks daily and their combination) in 11 to 13 years old schoolchildren in Slovakia by gender and socio-economic status using data from Health Behaviour in School-Aged Children surveys carried out in 2005/2006, 2009/2010, 2013/2014 and 2017/2018. Results: Consumption of sweets and sweetened soft drinks, despite of decline, remains widespread (41.3% of boys and 39.6% of girls in 2017/2018). Absence of daily teeth brushing, similarly as co-occurrence of these two risk factors, were more frequent in boys (10.6% and 5.0% in 2017/2018, respectively) than in girls (5.1% and 2.3% in 2017/2018, respectively). Absence of daily teeth brushing was associated with lower socioeconomic situation. Conclusions: Behavioural risk factors of dental caries play significant role in oral health of adolescents in Slovakia. Despite positive development of the epidemiological situation, effective interventions focused on consumption of sweets and sweetened soft drinks as well as improvement of oral hygiene in lower socioeconomic groups are needed.

with appropriate dental hygiene is very important for maintaining overall health [2].
Dental caries ranks among the most common oral diseases [3]. Nature of the caries is gradual and cumulative. With time it becomes more compound. Due to its prevalence, economic aspects and effect on quality of life it is a significant public health problem [4][5][6].
Untreated caries in children may negatively affect their quality of life in many ways.
Besides direct negative impact i.e. pain, troubles in eating, it is the most frequent cause of loss of teeth. Consequences of dental caries have a lifetime effects including decreased quality of life, impaired self-esteem, as well as can result in various chronic diseases [7].
According to official World Health Organization (WHO) data, prevalence of tooth decay among 6 years old children in European countries considerably varies between 20 to 90 per cent [1]. In general, relatively positive situation can be seen in Western and Northern Europe such as United Kingdom or Scandinavian countries. On the other hand, the highest prevalence is in Eastern Europe. To monitor dental health, DMFT index is widely used as an epidemiological tool indicating count of decayed (D), missing (M) and filled (F) teeth (T) [8,9]. Slovakia, together with Croatia ranks among countries with the highest average DMFT index (4.3 and 4.8, respectively) within the European Union member countries [8,[10][11][12][13]. However, we should keep in mind that above mentioned information is mostly based on data coming from dentists providing primary dental care. So, these estimations originate from population attending dentists for treatment or/and preventive check-up and there are insufficient epidemiologic data from those not attending dentists. Therefore, population representative data would bring light to better understand an extent of the issue.
There are numerous factors increasing a risk of the dental caries. Beside inherent and metabolic predisposition, behavioural risk factors are of a great importance. Among them, namely oral hygiene and diet play a significant role [1,8,14]. Teeth brushing applied at least once a day has been considered as a principal tool to maintain oral health and to prevent caries and periodontal diseases [15]. On the other hand, consumption of sweetened food, soft and energy drinks promote initiation and further development of dental caries [16].
Numerous recent studies indicate that a socioeconomic situation can be considered as an independent determinant of teeth decay. Higher consumption of soft drinks was detected in children from low socioeconomic families and whose teeth brushing was sporadic [17][18][19]. It is also confirmed that children with good oral hygiene have mothers with higher education level [20,21]. Significantly more cases of dental caries are present in children whose grow up in lower socioeconomic families, in combination with low income and low education level [22].
Age of 12 is internationally determined as an age for global monitoring of dental caries. It is mostly because in majority of children all the permanent teeth have already erupted (except third molars) [13]. Considering the long-term and even lifelong impact of the caries, age between 11 to 13 years is crucial. Therefore, factors triggering process of caries and its further development are of a particular importance during this period.
Understating of epidemiological aspects of risk factors of caries during childhood can considerably help to design and implement effective preventive intervention programs tailored for this target population.
In our study, we focused on selected indicators of insufficient dental hygiene (teeth brushing less than once a day) and eating habits associated with increased risk of caries In the first step, participating schools were randomly selected with probability proportional to size using an official list of all schools obtained from the Slovak Institute of Information and Prognosis for Education. The sample of schools was stratified by region (eight administrative self-governing regions) and type of school (elementary schools comprising the 1 st -9 th grades, and eight-year grammar schools comprising the 6 th -13 th grades). In the second step, within the participating schools, classes were randomly selected to collect data. Parents were informed in advance about the study via the school administration and using a written informed consent form could opt out if they disagreed with their child's participation. Participation in the study was fully voluntary and anonymous, with no explicit incentives provided for participation. This approach provided samples proportionally representing all areas and population subgroups on the nationwide level and thus eliminating possible bias caused by heterogeneity of the target population.
Pupils from the 5 th -9 th grades were considered as eligible, i.e. associated with 11-to 15-year-old adolescents. We included 11 to 13-years old respondents in our analysis.  Table 1 shows the basic characteristic of the samples obtained in four waves of the survey. Drop outs were caused mostly by the absence of children due to illness or other personal reasons and the refusal of a parent or the adolescent to be involved in the study.
Our study analyses prevalence of insufficient teeth brushing (less than once a day), eating of sweets and/or drinking of sweetened soft drinks, co-occurrence of the two above mentioned factors in relation to gender and socioeconomic status: Teeth brushing was measured by the question "How often do you brush your teeth? Possible responses were "More than once a day", "Once a day", "At least once a week but not daily", "Less than once a week" and "Never". After dichotomisation, we analysed proportion of answers "At least once a week but not daily", "Less than once a week" and "Never".
Consumption of sweets in schoolchildren was measured by the question "How many times a week do you usually eat sweets (candy or chocolate)?" Possible answers were "Never", "Less than once a week", "Once a week", "2-4 days a week", "5-6 days a week", "Once a day every day" and "Every day, more than once". After dichotomisation, we analysed proportion of answers "Once a day every day" and "Every day, more than once".
Consumption of sweetened soft drinks was measured by question "How many times a week do you usually drink coke or other soft drinks that contain sugar". Possible answers were "Never", "Less than once a week", "Once a week", "2-4 days a week", "5-6 days a week", "Once a day every day" and "Every day, more than once". We analysed proportion of answers "Once a day every day" and "Every day, more than once". The results are expressed as percentage (%) with the respective 95% confidence intervals.
Differences were statistically evaluated using Chi-square test. As a level of statistical significance, p<0.05 was considered. To test changes across time, Bonferroni correction was applied for post-hoc pairwise comparisons.    (Tables 3, Table 4). Moreover, we should keep in mind that we deal with subjective data, thus the underreporting can potentially present "a top of iceberg" effect making the problem even deeper [24]. Another problem to be considered is a quality of teeth brushing. As many studies showed, the problem is mostly in wrong technique (incorrect brushing movements, insufficient time of brushing, etc.), which may be in long term harmful to the oral health.
Therefore, it is necessary to teach children not only to brush their teeth, but to brush them properly. In this research we only analysed whether or not they brush their teeth.
For the future research it could be interesting to deeply analyse determinants of teeth brushing and the quality of teeth brushing techniques.
As already mentioned, the insufficient teeth brushing relates particularly to boys. One of the possible causes may be that women in general consider oral health as important with positive impact on quality of life. Also, it could be in the perception of health, which girls seem to receive differently than boys [30,31].
Our results also showed an association between insufficient teeth brushing and socioeconomic situation. Main problem was detected in families with low education of children's parents. Parent, especially mothers, showed up to be very influential in the problematics of creating habits in children [31,32]. However, parents with lower educational level do not place an importance to brushing teeth, probably because of lack of information/health literacy [5,20]. Lack of information about oral health in parents is therefore associated with lack of motivation to even teach a child how to brush the teeth or to control if he/she is brushing the teeth. Children are influenced through opinions and attitudes of their parents towards dentists, too. Parental fear and worries about dental care are transferred to children [33]. It is necessary for parents to be motivational factor in the subject of oral hygiene [31,34]. It presents a challenge for public health how to better focus educational and information activities on families with lower socioeconomic position.
As potential limitations of our study, we should consider that the HBSC data do not provide a comprehensive picture on a risk but only some aspects of it. We should consider our findings rather as an insight into the epidemiological situation and its changes over time and trends. These pieces of information, despite their limited scope, provide as important groundwork for population based preventive measures as well as relevant projections of the situation in future. The strongest point of our analysis is, that it uses representative data including the whole target population of the given age group. Most of studies dealing with oral health employ data from dentists [13,35,36]. According to the HBSC Slovakia report, as much as 15 % of boys and 12 % of girls aged 13 years reported not visiting the dentists during recent year [37]. Moreover, as the latest official data on dental care show, among children and adolescents (6 to 14 years old) as much as one quarter of them have not been registered to dental care [23,38], i.e. such pieces of information are limited to a population attending check-ups and undergoing dental care and can overlook a considerable proportion of the population. Therefore, our findings fulfil this information gap.

Conclusions
Eventually, despite of decline of the daily eating of sugar within recent years, it remains a widespread risk factor of dental caries in children. Its combination with insufficient teeth brushing is mostly a problem of boys and lower socioeconomic population groups where a particularly high risk can be expected. Therefore, there is a need to find out effective ways how to address these target groups in preventive programs with emphasis on youngsters when habits are still developing. The study was approved by the Ethics Committee of the Faculty of Medicine at the P.J.

List Of Abbreviations
Šafárik University in Košice. Parents were informed about the study via the school administration and using a written informed consent form could opt out if they disagreed with their child's participation. Participation in the study was fully voluntary and anonymous, with no explicit incentives provided for participation.

Consent for publication
Not applicable.

Availability of data and materials
The dataset supporting the conclusions of this article is available upon request.

Competing interests
The authors declare that they have no competing interests. Teeth brushing less than once a day. Significant differences are marked as *p<0.05 and **p<0.001.

Figure 2
Consumption of sweets or sweetened soft drinks. Significant differences are marked as *p<0.05 and **p<0.001.

Figure 3
Teeth brushing less than once a day and consumption of sweets or sweetened soft drinks. Significant differences are marked as *p<0.05 and **p<0.001.