This study focussed on the oral health of children and adolescents with or without attention deficit hyperactivity disorder (ADHD) living in residential care. The null hypothesis that oral health parameters of children and adolescents with or without ADHD, living in the same residential care setting under similar conditions, would not be different, was accepted. No statistically significant difference in oral health of children and adolescents with or without ADHD living in residential care was found regarding dmft, DMFT, DMFS, API, bruxism and oral hygiene habits. In spite of these findings, participants with ADHD tended to have higher DMFS/DMFT values than the control group, the ADHD group tended to consume cariogenic drinks and food more often than the controls, and dental and orthodontic treatment was performed less often than in the control group.
More boys than girls seemed to be affected with ADHD with a ratio of 4:1 (27 males, 7 females), which was close to Grooms et al.  with 31 males and 7 females, and Chau et al.  with 27 males and 4 females in their ADHD groups, and higher than Rowland et al. , who found a prevalence ratio of 3:1. A greater proportion of boys having ADHD than girls was observed by another study .
There was no statistically significant difference in the dmft/DMFT between the ADHD and non-ADHD groups, which is in agreement with the study by Hidas et al.  and Chau et al. . Our participants had a DMFT ≤ 5, which was, in contrast to the study by Broadbent et al. , below their chosen cut-point, where the vast majority of the children with ADHD had a DMFT ≥ 5. In our study, the DMFS was different between the two groups, but the difference was not significant. This was also found in earlier studies [9, 17]. However, when the DMFS and DMFT scores were analysed separately for the various age groups from 9 to 15 years, the ADHD group tended to have higher values, with the exception of the 13- and 14-year-old children. These results confirm studies by Blomqvist et al. [5, 13, 18]. We found that the 9- to 12-year-old children had a tendency of higher caries experience than those without ADHD. This is in accordance with the study by Blomqvist et al. , who also found higher caries experience in 11-year-old children with ADHD than in healthy children; however, the difference was statistically significant. In our study, the 13- to 14-year-old children had in both groups a similar caries experience, which confirms the results of another study by Blomqvist et al. . At the age of 15 the participants with ADHD from our study had again a higher caries experience than the control group. Blomqvist et al.  observed in another study with 17-year-old participants again a statistically significant higher caries experience in the ADHD group. According to Maupome  at the age of 13 ADHD might be a protective factor against dental caries in spite of bad self-care and dietary patterns. However, at that particular age the recently erupted teeth have not been long enough in situ for caries lesion to develop .
The percentages of API were high in both groups, although there was no statistically significant difference between the two groups. This is similar to the findings of Chau et al. . In contrast, earlier studies [8, 9] found statistically significant differences in plaque indices between ADHD and non-ADHD children. In spite of these statistically significant differences in plaque indices, only Chandra et al.  observed in addition statistically significantly poorer oral hygiene habits in ADHD children than in the control group, whereas Hidas et al.  found no statistically significant differences between ADHD and control group, which is in agreement with our study. Tooth brushing frequencies did not differ between the two groups in the present study, and was similar to other studies [8, 17]. In contrast, it was observed that ADHD children  or children who have a risk for conduct/oppositional disorders  brushed their teeth statistically significantly less often than children from the control group. The similar tooth brushing habits in our study can be explained by the fact that all children in residential care were supervised by their guardians. Although the majority of the participants reported that they brushed their teeth twice daily or more often, the high values for the API, reflecting only fair oral hygiene, show the need for considerable improvement, including better instructions of guardians and parents.
The percentage of participants consuming acidic/sugary beverages and sweet snacks was similar in the two groups. But regarding frequency of intake of acidic/sugary beverages and sweet snacks, a higher percentage of children from the ADHD group tended to consume these drinks and foods more often than those from the control group. Blomqvist et al.  reported also a trend for a higher percentage of children from the ADHD group to frequently eat snacks between meals than in the control group. Chandra et al.  found also a higher percentage of children from the ADHD group to frequently eat sweet snacks between meals than in the control group; however, the difference was statistically significant. The study of Dursun et al.  confirmed the positive correlation of hyperactivity/inattention scores with an increase in consumption of cariogenic food. The lack of statistical significance in the present study might be explained by the residential care setting, where the children of both groups consume their meals together supervised by guardians.
The presence of bruxism was similar in both groups, which is in agreement with Hidas et al. , whereas Chau et al.  found a statistically significant higher percentage of bruxism in children with ADHD. There was less ongoing orthodontic treatment and more orthodontic treatment needed in the ADHD group than in the control group. This might be explained by the therapeutic difficulties encountered with children affected by ADHD, as was reported in a study where children with ADHD, due to a short attention span and lack of cooperation, presented more challenges during an orthodontic treatment compared to control participants .
A higher percentage of children with ADHD reported only for a dental check-up or received prophylactic measures, whereas actual dental therapy was performed more often in the control participants. Aminabadi et al.  observed that children with oppositional defiant disorder (ODD)/ADHD displayed high values of dental anxiety and behaviour-management problems during dental treatment, which could explain the lack of adequate dental therapy in ADHD children.
Due to an unequal sample size the participants with ADHD in the present study were not divided into medicated and non-medicated patients, because the majority (76.5%) was under pharmacotherapy and only eight out of 34 ADHD children received no medication. However, this non-discrimination into medicated and non-medicated participants may have affected the results of the present study. Studies [6, 17, 23] have reported that children with ODD/ADHD had a higher risk of caries than healthy controls, with statistically significantly higher DMFT scores due to their medication  or with statistically significantly higher DMFS scores . In children with ODD/ADHD a higher caries risk was found in those under pharmacotherapy compared to those under neuro-feedback therapy with statistically significantly higher DMFT scores . In addition, the plaque index was statistically significantly higher in ODD/ADHD children taking medication than in ODD/ADHD children under neuro-feedback therapy . In the present study, high DMFT scores and high approximal plaque indices were found not only in the participants with ADHD, but also in the controls, all living in the same residential care.
One of the limitations of the present study is the relatively small sample size of 79 participants, but which is similar to the study of Chau et al. . Only simplified examinations were conducted on site in rooms of the residential care setting and no recent dental radiographs were available and no new ones could be taken; thus, it was not possible to reliably identify non-cavitated lesions. Moreover, only absence or presence of gingivitis could be recorded, but clinical examinations such as assessment of gingival bleeding index (GBI) and salivary flow rate could not be conducted due to low compliance and short attention span of the ADHD participants. Earlier studies [5, 6, 13] have shown no statistically significant differences in GBI [6, 13] and in saliva production  between ADHD and non-ADHD participants, whereas in other studies statistically significant higher gingival bleeding [7,18] and lower unstimulated salivary flow rates in children using methylphenidate  were found in children with ADHD.
The findings of the present study show the need for considerable improvement of oral hygiene and dietary habits in children and adolescents, who live in residential care. In children with ADHD, the most effective method of reducing dental caries seems to be more frequent dental visits with a) instructions for better oral hygiene at home and b) dietary counselling to reduce the consumption of sweet snacks and drinks, including parents as well as guardians . In particular, the guardians in this residential care center, who were specially trained to care for children and adolescents with ADHD, need to be further instructed in better supervision of oral hygiene practices. They also need to be alerted to paying more attention to healthier eating and drinking habits, possibly with the assistance of a dietician, from which in consequence all children would benefit. In addition, dental and orthodontic therapy was performed less often in the children and adolescents with ADHD. Referrals to specially trained dentists and orthodontists might help children with ADHD to get the appropriate dental treatment they actually need. More awareness among clinicians to facilitate better caries- and trauma-preventive management is also important .