Oral hygiene and caries experience in children with down syndrome and autism spectrum disorder: a systematic review and meta-analysis

Introduction Children with Down syndrome (DS) and autism spectrum disorder (ASD) are at increased risk for oral health problems due to anatomical, behavioral, and socioeconomic factors. However, evidence on their caries experience and oral hygiene remains inconsistent. This study systematically reviewed and meta-analyzed case–control and cross-sectional studies comparing oral health indices in children with DS or ASD to neurotypical peers. Methods A systematic search was conducted in PubMed, Web of Science, Science Direct, and Google Scholar using a standardized strategy. Eligible studies included children aged 0–18 years. Pooled mean differences (MD) in Plaque Index (PI), Gingival Index (GI), DMFT (decayed, missing, and filled permanent teeth), dmft (primary teeth), and Simplified Oral Hygiene Index (OHI-S) with 95% confidence intervals (CI) were calculated in R using meta and metafor packages. Results Twenty-four studies were included (527 children with DS, 1,221 with ASD, 1,875 controls). For PI, children with DS had MD = 0.53 (95% CI: −0.13–1.18; I 2 = 90%) and children with ASD 0.28 (95% CI: −0.05–0.61; I 2 = 93.3%) compared to controls. GI was MD = 12.10 (95% CI: −0.14–162.92; I 2 = 99.7%) for DS and 0.33 (95% CI: −0.13–0.78; I 2 = 93.1%) for ASD. DMFT showed MD = –0.29 (95% CI: −0.97–0.39; I 2 = 54.7%) for DS and 0.29 (95% CI: −0.53–1.11; I 2 = 97.6%) for ASD. dmft was MD = –0.14 (95% CI: −0.61–0.33; I 2 = 0%) for DS and −0.33 (95% CI: −1.49–0.82; I 2 = 94.6%) for ASD. OHI-S was MD = 0.28 (95% CI: −0.92–1.47; I 2 = 92.2%) for DS and 0.31 (95% CI: −1.37–1.98; I 2 = 65.7%) for ASD. Most differences were not significant due to high heterogeneity. Sensitivity analysis identified one influential study affecting PI; excluding it strengthened the effect (MD = 0.43; 95% CI: 0.17–0.70; p = 0.0047). No publication bias was detected for DMFT and dmft indices. Overall certainty of evidence was low. Conclusions Children with DS and ASD showed no consistent differences in PI, GI, DMFT, dmft, or OHI-S scores compared to neurotypical peers. Public health strategies should focus on inclusive oral health education, provider training, and equitable access to dental services to improve outcomes for children with neurodevelopmental disorders. Systematic Review Registration https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD420251155866 , identifier: CRD420251155866.