Background: Atraumatic restorative treatment (ART) using high-viscosity glass-ionomer cement (HVGIC) is a minimally invasive approach that may match or exceed the longevity of conventional restorations for selected lesions while reducing pain, cost, and aerosol generation. Evidence varies by dentition, surface type, and operator. Methods: Following PRISMA principles, we synthesized nine original clinical studies comparing ART/HVGIC with amalgam or resin composite in primary and permanent teeth. Outcomes include restoration survival/failure and reasons for failure at the longest available follow-up. Narrative synthesis was performed owing to clinical/methodologic heterogeneity. Results: In permanent teeth of children over 6.3 years, overall survival was higher for ART than amalgam (66.1% vs 57.0%), with single surface non-occlusal ART markedly outperforming amalgam (80.2% vs 62.8%); occlusal single-surface differences were smaller and non-significant. In primary dentition at 3 years, single-surface ART also exceeded amalgam (86.1% vs 79.6%); multi-surface survival remained lower in both groups. Over 1–2 years, several trials found no overall difference between ART and amalgam in primary molars, with clear inferiority for Class II/occlusoproximal ART in some clinic settings. A randomized trial in permanent Class II lesions showed similar 2-year success for ART/HVGIC vs resin composite. Conclusions: ART/HVGIC is a viable alternative to amalgam/composite for single-surface lesions in primary and posterior permanent teeth; multi-surface performance is lower and operator-sensitive.