In our observational study, we investigated the oral health condition and obesity in children and adolescents aged 12 to 15 years. Overall, there was a high frequency of gingival bleeding on probing and caries experience among obese individuals, which is in agreement with the results presented in the reports of the 2008 NSPOD and in its last update published in 2015.
No significant differences in DMFT for any of the age groups were observed when compared to the 2008 NSPOD study. However, fewer teeth were lost (p = 0.001) at age 12 in obese adolescents, which was counterbalanced by a higher number of sealed teeth (p = 0.012) detected in this population. The same occurred in relation to the 2015 study report. Furthermore, at age 15, obese adolescents had fewer decayed teeth (p = 0.017), but no analytical comparison to the 2015 NSPOD data was possible as this nation-wide study did not encompass 15-year-old subjects.
The association between obesity and dental caries has been previously studied, considering that both conditions have common etiological factors such as excessive sugar intake. Recent studies have suggested that obese children are at increased risk for dental caries and have identified an association between the two conditions in childhood 6, 7.
The present study found no differences in the dental caries experience between the obese population and the Portuguese population of the same age group, suggesting that the increase in BMI is not necessarily associated with an increase in the prevalence of caries, which is in agreement with previous studies 18–20. Alves, Susin 18 carried out a cross-sectional study and found no association between obesity and caries in a sample of 12-year-old children from public and private schools in southern Brazil. In addition, the largest cross-sectional study 19 with Kuwaiti children revealed no significant association between caries and obesity, but rather an inverse relationship between obesity and dental caries. Likewise, no significant association between caries and weight gain was observed among children and adolescents in the United States based on the NHANES IV (National Health and Nutrition Examination Survey) data 20.
The studies reporting a decrease in caries experience and increased obesity have concluded that the relationship between overweight and dental caries in children is much more complex and cannot be explained solely by carbohydrate intake 18–20. These results corroborate our findings, where obese adolescents aged 15 years presented significantly (p = 0.017) fewer decayed teeth than those of the same age in the 2008 NSPOD study 16. Of note, the obese participants in our study underwent treatment for obesity as well as medical and nutritional follow-up, which may explain the fact that they presented fewer decayed teeth.
Here, the obese children and adolescents had a higher percentage of sealed teeth as compared to the data published in the reports of the national studies for both 12 and 15 age groups. This can be considered an indicator of improvement of the oral health services provided to the Portuguese population, implied in greater coverage of the service and greater investment in the prevention of oral diseases, namely through the National Program for the Promotion of Oral Health (NPPOH), established since 2005.
The relationship between obesity and oral health in childhood remains inconclusive. While in adults there is a clear association between obesity and periodontal disease, in children and adolescents no consensus has been reached 21, 22. This association is due to the fact that periodontal disease is an inflammatory condition dependent on host, pathogens and environmental factors, and also due to the possible influence of the oral condition on the serum levels of inflammatory mediators, since obese subjects present alterations in the levels of systemic inflammatory markers. Moreover, the literature points out that a systemic inflammatory condition may interfere with the oral inflammatory condition 23. Recently, Modeer, Blomberg 24 in a cross-sectional study with obese and normal-weight adolescents observed that the former had a higher incidence of bleeding on probing and higher levels of inflammatory markers measured in the gingival crevicular fluid than normal weight subjects.
Our results indicated that obese children had a high prevalence of bleeding on probing (71.1%), but because there was no control group with normal-weight children submitted to the same conditions, the analysis of the relationship between obesity and periodontal status was not practicable. The high frequency of bleeding may also be related to the low frequency of daily brushing and/or to the absence of other oral hygiene care products, such dental floss, by most individuals in the sample.
Reeves, Rees 25 investigated the correlation between obesity and periodontal disease in a group of American adolescents. The authors concluded that the onset of periodontitis may be associated with an increased waist circumference and weight gain in individuals aged 17 to 21 years; in contrast, the association was no longer seen between the age 13 and 16. Considering these findings, further studies are needed to clarify the association, if any, between obesity and periodontal disease in children.
The results of our study contribute to reinforce the fact that medical or nutritional follow-up of obese patients is also an opportunity for recommendations regarding hygiene and oral care 26. While there seems to be no direct causal relationship between obesity and poor oral condition, it is known that oral diseases have etiological factors similar to those of obesity and that other aspects can be considered as conditioning factors, such as low self-esteem. For a detailed investigation of the relationship between these morbidities, further studies should be carried out with a sample of obese patients who are not under medical supervision and with a control group of normal-weight children. It would also be beneficial to investigate a sample of adults who have a long history of obesity, since childhood obesity is considered a risk factor for the disease development in adulthood.