59 Risk Factors and Oral Health-Related Quality of Life lated. Statistical significance was defined as p≤0.05 (α level= 5%) and a 95% CI was chosen. Statistical Package of the Social Sciences (SPSS, version 26) was used for these analyses (IBM, 2018). Ethical considerations The research protocol has been approved by The Medical Ethical Committee in Leeuwarden, the Netherlands (decision no. RTPO979a). Standard rules for good clinical practice and ethical principles that have their origin in the Declaration of Helsinki were followed by informing all participants about the study and their rights, and all subjects gave oral consent to participation (The World Medical Association, 2013). Results Table 1 shows the patient characteristics. The mean age of the participants in the case group (N=81) was 25.9 years. The mean age in the control group (N=166) was 25.0 years. There were no significant differences in case and control group in gender, age, and educational level, which demonstrates a successful matching process. Comparison of risk factors Table 2 shows the results of the Chi-square test, conducted to test the differences between case and control group on risk factors. First, regarding risk factors in general, we found that there was a statistically significant difference between the case and control group in smoking, χ2(1) = (20,51), p = <.001. The case group demonstrated to smoke more frequently than the control group. Second, regarding risk factors in dental health care behaviour, we found that there was a statistically significant difference between the case and control group in low frequency of brushing, χ2 (1) = (13.45), p = <.001. The case group brushed their teeth less often. Last, regarding financial risk factors, we found that there was a statistically significant difference between the case and control group in finances, χ2 (1) = (33.87), p = <.001. The case group reported more frequently a lack of finances to take care of their teeth compared to the control group. No significant differences were found on other risk factors. 3
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