1 INTRODUCTION

Despite considerable efforts, caries remains a highly prevalent oral disease in children and adolescents worldwide.^{1, 2} Caries experience varies considerably among countries, with declining rates reported from countries with a higher economic and social standard, whereas caries prevalence continues to increase in low- and middle-income countries.^{3, 4} Potential influencing factors discussed for these geographical differences in caries prevalence in children include a migrant background, socio-economic status, lifestyle factors, parental caring behaviours and birth order.^{5, 6}

Epidemiological surveys can help to assess the current status of oral health in a population and show whether changes have occurred, thus orientating the responsible authorities to the need for future action. This is of importance as dental caries can be controlled, when prevented or detected early and treated adequately, resulting in an improved quality of life and lower economic healthcare-related costs.

Switzerland has a long tradition of oral epidemiological surveys of children.⁷ Studies based on the World Health Organization (WHO) methodology are often conducted on schoolchildren, as most children in Switzerland attend public schools and are therefore easy to recruit.^{7, 8} In the canton of Basel-Landschaft, a region in the northern-western part of Switzerland, dental health examinations of schoolchildren must be, based on regional law, performed regularly.^{7, 9} Therefore, representative data on caries experience and prevalence in children aged 7, 12 and 15 years exist since 1992.⁷ During the first 10 years, a decline in caries prevalence could be observed in all age groups, whereas in 2011, this decline seemed to have levelled off.⁷

The aim of this study was to assess the prevalence of dental caries among schoolchildren in the canton of Basel-Landschaft, Switzerland, in 2021 and to describe possible changes in prevalence over a period of three decades. Secondary objectives were to evaluate the impact of various personal and demographic factors such as age group, place of residence or dental hygiene awareness on caries prevalence as well as the history of orthodontic treatment in the year 2021.

2 MATERIALS AND METHODS

3 RESULTS

In total, 1822 schoolchildren were selected to participate in this study. Four hundred and sixty-five children (25.5%), however, were either absent from class on the day of the dental examination or did not hand in the questionnaire. The rest (1357; 74.5%) were included in this study. Approximately three-quarters of the children examined were Swiss, and nearly equal numbers of male and female children were observed in the study population which were similar for all age categories. The detailed characteristics of the study population analysed in 2021 are shown in Table 1.

Table 2 shows the caries experience among the schoolchildren. In the year 2021, the youngest age group, that is the 7-year-olds, had an average of 0.68 primary teeth that needed treatment, whereas the two older study groups each had approximately 0.3 permanent teeth requiring treatment. About 60% of the children had a caries-free primary dentition, and about 70% had a caries-free permanent dentition. During a period of three decades, these caries indices either remained constant or even improved (Figure 1). In particular, the number of schoolchildren with a caries-free permanent dentition increased from 44% in the year 1992 to 73% in the year 2021 for 12-year-olds and from 29% in the year 1992 to 69% in the year 2021 for 15-year-olds.

Both the presence or absence of caries and of active carious lesions were not statistically significantly different for sex or the place of residence in the year 2021 (Table 3). Statistically significant differences, however, were found for the other socio-economic and confounding factors analysed. Specifically, younger children and children with a migrant background had a higher total caries experience and more active caries. Statistically significant associations were found between caries experience and the presence of MIH or the level of secondary school attended in ninth grade, as well as active carious lesions and self-described dental hygiene awareness (Table 3). Post hoc pairwise comparisons showed that children in the medium dental hygiene awareness group had a significantly higher caries prevalence (41.1%) than those in the high dental hygiene awareness group (34.1%). Similarly, children in the medium dental hygiene awareness group had a significantly higher active caries prevalence (29.0%) than those in the high dental hygiene awareness group (21.1%). When analysing the influence of the level at ninth grade using post hoc testing, children attending level P had a significantly lower caries prevalence (18.8%) than children attending level A (44.0%) and level E (33.8%) group, respectively. Likewise, children attending level P at ninth grade had a significantly lower caries prevalence (8.3%) than those attending level A (21.0%).

Furthermore, females, schoolchildren of Swiss nationality and children attending higher secondary schools at ninth grade were significantly more likely to have undergone or to be currently undergoing orthodontic treatment, while no differences were found for age group, place of residence or caries experience (Table 4). It was observed from the post hoc testing that schoolchildren attending level A at ninth grade had a significantly lower proportion of undergoing orthodontic treatment (45.0%) than that (63.2%) of level P group.

4 DISCUSSION

This study presents an overview of the caries experience among schoolchildren in the canton of Basel-Landschaft, Switzerland, over three decades. Particularly in the age groups of the 12- and 15-year-old children, most dental caries indices have improved over this time period. Ten years ago, the steady decline in dmft and DMFT appeared to level off⁷; per current data, however, the rate of caries experience did not increase again in 2021.

Globally, untreated carious lesions are a major health concern, with untreated caries in primary teeth being the most prevalent disease for children aged 0–14 years and untreated caries in permanent teeth being the predominant health condition in the year 2019.¹⁶ Its prevalence and incidence remain static. Additionally, caries is not evenly distributed across regions and countries; therefore, simple, cost-effective and sustainable interventions are needed that are adapted to the particular region.^{2, 4, 17} Switzerland is considered to be a country with a low prevalence of untreated carious lesions.¹⁶ Nevertheless, the average number of teeth with untreated carious lesions either in primary or in permanent teeth, that is dt and DT, respectively, did not decrease but remained constant over time for all three age groups examined. This is despite the fact that in the canton of Basel-Landschaft, as in the whole of Switzerland, comprehensive preventive measures such as regular toothbrushing instructions in schools and an annual dental check-up are offered free of charge to all schoolchildren.

In the present study, nationality was shown to be a risk factor as mean dmft/DMFT and dt/DT values were significantly higher in schoolchildren with a migrant background. This association has already been reported in a previous study in Switzerland.⁷ Socio-economic factors such as education or income are known to play an important role in explaining differences in dental caries.^{4, 18} These factors have not been analysed in detail in the present study as there are ethical boundaries in Switzerland to access certain socio-economic factors such as employment, education or income in each family.⁵ Therefore, the influence of education could be analysed only in 15-year-olds as they attend three different sections based on their school performance. Schoolchildren visiting a school with baccalaureate-level requirements had the lowest caries prevalence of all ninth graders, indicating an influence of school achievement on caries.

The correlation between MIH and caries is currently still discussed, as there are studies that show a positive correlation and others that show no significant correlation.¹⁹ Also in our study, a positive correlation could be noticed. It has been argued that, especially in severe MIH-associated hypersensitivity, children will maintain insufficient oral care, which may lead to more carious lesions.¹⁹ In the present study, the severity of MIH was not analysed. Therefore, more detailed studies are needed to identify possible interactions between these two diseases.

Successful caries prevention requires a multilevel intervention approach that includes both general public oral health measures and individual person-centred dental care. Population-based caries prevention programmes were initiated as early as the 1960s in Switzerland and thus have a long tradition. Accordingly, a decline in dental caries could be observed initially.⁷ As social, economic and environmental factors, however, also influence the disease, a more personalised approach is required to identify children in need of dental interventions, ideally as early as possible. One of the approaches discussed is that dental services should be more integrated into the overall healthcare system.^{20, 21} Furthermore, it has been shown that the caries status of the first-born child can be used as a predictor for caries in younger siblings of the same family. This allows families in need of dental treatment to be identified, ensuring that available resources are utilised carefully and in a targeted manner.⁵

A known risk factor for dental caries is the consumption of sugar. In 2015, the WHO published a guideline with the recommendations to limit the intake of free sugars in adults and children to less than 10% of total energy intake.²² One possibility is the taxing of sugar-sweetened beverages. It has been calculated that such a taxation could reduce the number of caries occurrence in children by 2.7%–2.9% over a 10-year period.²³ In Switzerland, only 44% of women and 45% of men had a free sugar intake below the recommended 10% of total energy intake, indicating a low adherence to the recommendations.²⁴ So far, there have been no corresponding data on Swiss children. As the negative health effects of dental caries, however, are cumulative, a reduction in free sugar intake in childhood may be of significance in adulthood.

The legal guardians of the schoolchildren were asked to complete a questionnaire that addressed, among other things, various aspects of dental hygiene, resulting in an assessment of dental hygiene awareness. Dental hygiene awareness is another factor that is determined and shaped in children and adolescents mainly by the family environment, where not only family traditions but also socio-economic status and education play an important role. Indeed, respondents with high dental hygiene awareness levels were found to have statistically significantly lower caries experience and fewer active carious lesions.

In this context, it should be noted that questionnaires are prone to subjectivity and therefore present a limitation in this study. Only children with a complete data set, that is with both the clinical examination and a filled-in questionnaire, were included in the study. It was not possible to follow up on the missing schoolchildren due to the COVID-19 pandemic during the dental examination period, which has led to some restrictions in the clinical evaluation process. Moreover, it cannot be excluded that there were also children with increased caries activity among the dropouts and that this specific population group was thus not included in the study. Additionally, the dental examinations were performed as recommended by the WHO for clinical oral health surveys, which do not include bitewings or other X-ray examinations.⁸ Clinical analysis alone cannot detect approximal caries. Therefore, the actual caries activity might have been underestimated.

Statistically significantly more female than male schoolchildren received orthodontic treatment. Such sex-specific differences have been noted in previous studies.^25-27 Differences in attitudes towards orthodontic treatment were also attributed to age, socio-economic status and geographical context.²⁵ While no regional differences were found, statistically significant differences were also observed in the present study for socio-economic parameters such as nationality and the level of school achievement of the respective child.

Orthodontic therapy presents potential risks including periodontal damage, pain, root resorption, tooth devitalisation, temporomandibular disorder, caries, speech problems and enamel damage, with white spot lesions being one of the most common side effects.²⁸ In the present study, no differences were found between children with or without caries experience and orthodontic treatment. On the one hand, this may be due to the fact that only carious lesions at the D3 or D4 level were recorded in this study. Initial lesions, that is D1 and D2 lesions, can be generally managed using preventive measures such as the application of fluorides.^{8, 28, 29} On the other hand, orthodontic treatment in Switzerland should start only when the patient is caries-free and oral hygiene has reached a good level.³⁰

In conclusion, the caries experience of schoolchildren in the canton of Basel-Landschaft, Switzerland, has not increased since the last survey over a decade ago. However, the average number of teeth with untreated carious lesions either in primary or in permanent teeth, that is dt and DT, respectively, has not improved but remained constant over three decades for all three age groups examined. Risk factors for an increased level of caries activity were found to include migrant status and self-declared dental hygiene awareness.

AUTHOR CONTRIBUTIONS

Andreina Grieshaber, Tuomas Waltimo, Michael Marc Bornstein and Eva Maria Kulik conceived the idea and designed the study; Andreina Grieshaber and Asin Ahmad Haschemi collected the data; Eva Maria Kulik analysed the data; Andreina Grieshaber, Michael Marc Bornstein and Eva Maria Kulik interpreted the data and drafted the initial manuscript. All the authors revised and approved the final manuscript as submitted.

CONFLICT OF INTEREST STATEMENT

The authors declare that they have no conflict of interest.

FUNDING INFORMATION

The study was financially supported by the canton of Basel-Landschaft, Switzerland. The funders have no influence on the study design, data collection and analysis, and manuscript preparation.

ETHICS STATEMENT

A study protocol was submitted to the Ethical Committee Northwest and Central Switzerland (EKNZ 2021-00107), but the study was exempt from formal approval as the planned oral health check-ups were considered mandatory.