This study uses data from the nationwide Finnish School Health Promotion study (SHP), which monitors the health, health behaviour, wellbeing and schooling of 14- to 20-year-olds in Finland. The SHP study is carried out nationwide every second year. Respondents include pupils in their eighth and ninth years of comprehensive school in mainland Finland and the Åland Islands, covering 80% of this target group in Finland . Every municipality in Finland receives the survey and decides whether the schools in their area will participate in it . The Ethics Committee of the National Institute for Health and Welfare, Finland, approved the study. Participation in the study was completely voluntary, and students consented to participate by answering the survey.
The data were collected in April 2013 with an anonymous, voluntary questionnaire administered in the classroom under a teacher’s supervision . In Finland, comprehensive school lasts nine years: from age 7 to age 16 years.
In 2013, the SHP study covered participants from the whole country and the participation rate was 84% among the adolescents in eight and ninth grades of comprehensive school . For the present cross-sectional study, we obtained data from 45,877 15-year-olds (excluding 830 participants who failed to report their tooth brushing frequency) who in the spring of 2013 were in their eighth (37%) or ninth (63%) year of comprehensive school. Males comprised 49.9% of our study sample.
The questionnaire enquired about factors related to the students’ health with several questions. The question ‘How often do you brush your teeth?’ enquired about tooth brushing frequency with the following answer options: ‘never’; ‘less than once a week’; ‘at least once a week but not daily’; ‘once daily’; or ‘more than once daily’. For our analyses, we formed three classes (‘less than once daily’, ‘once daily’, ‘twice or more daily’), and dichotomised (‘less than twice daily, ‘at least twice daily’) variables according to the international recommendation to brush one’s teeth twice daily . In the CF tooth brushing was seen as a behavioural determinant.
The questionnaire enquired about the participants’ gender and year in school (8th or 9th year of comprehensive school).
The question ‘What is the highest educational level your parents have achieved?’ enquired about the parents’ highest education level (separately for the mother and father) with the following answer options: ‘primary or comprehensive school’; ‘upper secondary school or vocational education’; ‘occupational studies in addition to upper secondary school or vocational education’; ‘university, university of applied sciences, or other higher education institution’; or ‘no education’. We further placed these alternatives into three categories by combining the first and last options (‘basic education or less’), as well as the second and third options (‘upper secondary school or vocational education with or without occupational studies’). For the logistic regression analyses, we dichotomised categories into two (‘secondary or tertiary education’, ‘basic education or less’). The question ‘Who are the adults you live with?’ aimed to determine the participants’ family structure with the following answer options: ‘my mother and my father’; ‘my mother and my father alternately, my parents don’t live together’; ‘only my mother’; ‘only my father’; ‘my father/mother and his/her partner’; ‘one or more other adults; or ‘none of the above’. We dichotomised these alternatives into ‘with both parents (mother and father)’ or ‘other’, assuming that living with both parents would stand out from other family structures in terms of health behaviour . In the CF parental education was considered as a material determinant and family structure as a material or social determinant.
The question ‘Which of the following alternatives best describes your current smoking habits?’ assessed the adolescents’ smoking habits among those who had ever smoked with the response alternatives: ‘I smoke once or more daily’; ‘I smoke once or more a week, but not every day’; ‘I smoke less than once a week’; or ‘I have quit smoking (temporarily or permanently)’. Respondents who answered the question ‘How many cigarettes, pipefuls of tobacco and cigars have you smoked altogether?’ with the answer option ‘none’ were identified as non-smokers. We then formed two categories for current smoking habits (‘daily or occasional smoker’, ‘non-smoker’). Smoking was seen as a behavioural determinant in the CF.
The question ‘How is your health in general?’ aimed to determine the respondents’ perceived overall health with the following four answer options: ‘very good’, ‘fairly good’, ‘moderate’, or ‘fairly or very bad’. We further dichotomised the alternatives for the regression analyses (‘very good, fairly good or moderate’; ‘fairly or very bad’). Since oral health and general health are interconnected in the CF, the question of general health was used as an indicator of health.
We assessed psychological distress with the Mini-Social Phobia Inventory (Mini-SPIN), a three-item self-rated scale used as a screening tool to help identify individuals at increased risk for SP . The Mini-SPIN has proved valid in identifying possible SP among adolescents, and a score of 6 points or greater was found optimal in predicting SP with a sensitivity of 86% and specificity of 84% . The Mini-SPIN includes the question ‘How much have the following problems bothered you during the past week?’ with three responses: (1) ‘Fear of embarrassment causes me to avoid doing things or speaking to people’, (2) ‘I avoid activities in which I am the centre of attention’ and (3) ‘Being embarrassed or looking stupid are among my worst fears’. The items are rated on a Likert scale: 0 = Not at all, 1 = A little bit, 2 = Somewhat, 3 = Very much and 4 = Extremely. The cut-off score for a possible SP diagnosis is six or more points [5, 7]. Based on this cut-off score, we formed two categories (0–5 points: no SP, 6–12 points: possible SP). The Mini-SPIN can serve as a primary assessment of one’s social anxiety; the results can help to identify any need for further examination.
The questionnaire also included the reliable and validated GAD-7 questionnaire [11, 12], which served in screening for Generalized Anxiety Disorder (GAD). GAD-7 has demonstrated good psychometric properties in adolescents in Finland, the internal consistency of GAD-7 has been good (Cronbach's α = 0.91); the associations of GAD-7 sum scores with self-report measures of depression and social anxiety have supported construct validity . The questionnaire contains seven items, including the question ‘During the past two weeks, how often have the following problems bothered you?” with the following answer options: (1) ‘Feeling nervous, anxious or on edge’, (2) ‘Inability to stop or control worrying’, (3) ‘Worrying too much about different things’, (4) ‘Trouble relaxing’, (5) ‘Being so restless that it’s hard to sit still’, (6) ‘Becoming easily annoyed or irritable’ and (7) ‘Feeling afraid, as if something awful might happen’, each rated on the following scale: 0 = Not at all, 1 = Several days, 2 = More than half the days, and 3 = Nearly every day. When screening for anxiety disorders, a cut-off score of ten or higher is recommended for further evaluation [11, 12]. We formed two categories for the regression analyses based on this cut-off score (0–9 points: no, slight or mild anxiety; 10–21 points: moderate to severe anxiety). Psychological distress was considered as a psychosocial determinant in the CF.
After checking the distribution of the data we used cross tabulation with Chi-squared test to analyse associations between background variables, social distress (measured with Mini-SPIN and GAD-7) and tooth brushing frequency. After checking correlations and multicollinearity, we conducted logistic regression analyses with tooth brushing as the dependent variable, and age, gender, family structure, parents’ educational level, adolescent’s smoking status, adolescent’s perceived general health and social distress (measured with Mini-SPIN) as covariates. Because gender strongly impacted tooth brushing, we conducted gender-specific logistic regression analyses as described above. We then repeated the logistic regression analyses using GAD-7 instead of Mini-SPIN as a measure of psychological distress. We presented the results with adjusted odds ratios (OR) and their 95% confidence intervals (95% CI). We used IBM SPSS Statistics 22 for all statistical analyses and considered p values < 0.05 statistically significant.