Purpose: To test the hypothesis that, in high caries-risk children, supervised toothbrushing (STB) reduces visible plaque levels and gingival bleeding to a greater extent than does unsupervised toothbrushing (USTB) in comparable children and in low caries-risk USTB children over 4 years. Materials and Methods: High caries-risk schoolchildren, ages 6 to 7, were allocated to three oral healthcare protocols using a cluster-randomised design: 1. Ultra-Conservative Treatment (UCT): small cavities in primary molars were restored using ART, while medium and large cavities were left open and cleaned under daily supervised toothbrushing together with the remaining dentition (UCT/STB); 2. Conventional Restorative Treatment (CRT): primary molars were restored with amalgam, while high caries-risk first permanent molars received resin sealants (CRT/USTB); 3. Atraumatic Restorative Treatment (ART): primary molars were restored using ART, while high caries-risk first permanent molars received ART sealants (ART/USTB). Low caries-risk children (dmft ≤ 1) formed the no-treatment/USTB group. 273 children were examined at baseline (T0) and after 4 years (T1) according to the VPI and GBI indices. Data were analysed using linear and logistic regression. Results: Mean VPI and mean GBI scores were statistically significantly lower at T1 than at T0. Reduction in mean VPI scores in UCT/STB children was statistically significantly higher than for CRT+ART/USTB children over 4 years (p = 0.03), but no difference was observed between UCT/STB and no-treatment/USTB children (p = 0.361). No statistically significant difference in the reduction of mean GBI scores was observed between UCT/STB and CRT+ART/USTB (p = 0.62) and no-treatment/USTB children (p = 0.74). Conclusion: In high caries-risk children, the protocol based on supervised toothbrushing presented greater reduction in visible plaque levels than did protocols based on restorations and sealants over 4 years. Keywords: caries prevention, dental caries, oral hygiene, toothbrushing