Objective: To identify if the presence of dental plaque, dental brushing frequency and preventive dental care are related to the high severity of dental caries. Methods: A case-control study was carried out on a sample of schoolchildren aged 6 to 12 years. We selected 677 children from public schools in the city of León Nicaragua, 283 cases y 394 controls. Using questionnaires addressed to mothers / guardians, a series of sociodemographic, socioeconomic and dental variables were collected. Through oral clinical examination, the dmft and DMFT caries indexes were determined for primary and permanent dentition. The dependent variable was the high severity of caries, which was coded as (1) "dmft + DMFT = 0" and (2) "dmft + DMFT ≥ 6". The chi-square test and the Mann-Whitney test were used in the statistical analysis. Results: In the bivariate analysis, we observed that the associated variables (p<0.05) to high caries severity (dmft + DMFT ≥ 6) were: younger age of the child, younger age of the mother, less brushing frequency, presence of dentobacterial plaque and the pattern of dental care. Conclusions: The results of the study show that the variables related to oral hygiene, both objective measurement (presence of dentobacterial plaque) and subjective measurement (selfreport of toothbrushing frequency), are associated with high severity of dental caries. In addition, according to the pattern of dental care showed association with the severity of caries.