Background To assess the prevalence and severity of caries in 12- and 15-year-old schoolchildren, and to analyse the related risk factors. Methods We conducted a cross-sectional study on a random sample of 1843 schoolchildren aged 12 and 15 from Galicia (northwest of Spain). Self-administered questionnaire and dental clinical examination were performed to obtain information about oral health habits, dental caries and oral hygiene. A logistic regression model including dental-caries-related variables was generated for each age group. Results The respective findings for 12- and 15-years-old were as follows: decayed, missing, filled teeth index both for permanent and temporary dentition (DMFT/dmft) of 0.89 (95% CI, 0.87–0.91) and 1.38 (95% CI, 1.33–1.43), respectively; caries prevalence 39.6% (95% CI, 36.3–42.9) and 51.7% (95% CI, 48.0–55.4), respectively. In the 12-year-old group, individuals who occasionally, never or hardly ever brushed their teeth had higher values of caries (OR = 1.83, 95% CI 1.07–3.15, and OR = 9.14, 95% CI1.63–51.17, respectively). Also, the presence of plaque on more than 1/3 gingival was statistically associated with an increase of caries (OR = 2.03; 95% CI, 1.11–3.70), and living in a rural environment was a risk factor (OR = 1.3; 95% CI,1.02–1.80). In the 15-year-old group, higher caries risk was found when brushing was performed once a day (OR = 1.61; 95% CI,1.03–2.50), and among individuals who visited private clinics (OR = 1.77; 95% CI, 1.17–2.66), while electric toothbrush was associated with a lower caries risk (OR = 0.50; 95% CI, 0.29–0.86). Conclusions This study revealed that risk factors of dental caries showed differences in schoolchildren of 12- and 15-year-old. Strongest evidence related to caries in 12-year-old group were found in frequency of toothbrushing and dental plaque. In 15-year old group, electric toothbrush, time since the last visit to the dentist and type of dental care (public/private) had a stronger association with dental caries. Caries prevalence and mean DMFT/dmft increased from 12- to 15-year-old, in spite of improvement in oral hygiene at the age of 15. Electronic supplementary material The online version of this article (10.1186/s12903-019-0806-5) contains supplementary material, which is available to authorized users.

The Dental Aesthetic Index (DAI) was determined in 12- and 15-year-old schoolchildren to ascertain the prevalence of malocclusion and to assess its association with dental caries experience, dental plaque accumulation, and socio-demographic variables. We performed a cross-sectional study with a stratified two-stage sampling design. An oral health survey and oral examination were conducted, and socio-demographic data were recorded. The sample comprised 1453 schoolchildren aged 12 (868) and 15 (585). These two samples were analyzed separately because statistically significant differences were found: the 12-year-old age group displayed a higher frequency of schoolchildren who attended state-run public schools (p = 0.004) and belonged to a lower social class (p = 0.001); the 15-year-old age group registered higher levels of caries (p = 0.001) and lower levels of dental plaque (p < 0.001). The malocclusion was 9.5% higher (p = 0.001), and the global mean DAI score was likewise higher among the 12-year-olds (p < 0.001). The multivariate regression analysis not only showed that caries and dental plaque were the variables that were the most strongly associated with malocclusion, but that caries (OR = 1.5) and dental plaque (OR > 2) were also risk factors for malocclusion in both groups. In conclusion, this study revealed a higher prevalence of malocclusion and dental plaque at age 12. A higher risk of caries and dental plaque was found to be related to the presence of malocclusion in both age groups.