Aim: Glassionomer cements (GICs) have been used for many years as restorative materials, as luting cements or as temporary fillings. The aim of this study was to evaluate the clinical performances of a glassionomer-based restorative system for Class I, II and V permanent dental restorations. Methodology: 4 experienced operators performed 380 dental restorations using a resin-coated high-viscosity GIC (Equia Fil and Equia Coat, GC, Europe NV, Belgium). Both vital and non-vital teeth were included and the use of dental dam was registered to identify possible differences in survival rate. Follow-up was scheduled at 3, 6, 12, 18, 24, 36 and 48 months, during which restorations were assessed for survival, partial loss or failure, changes in color, texture and integrity of surface and margins. Results: 304 restorations in 202 patients were still included in the study and evaluated after 48 months: 82 class I, 150 class II and 72 class V. Twentysix restorations out of 304 were lost, broken or seriously altered. They were considered as “failures”, defining a General Success Rate (GSR) of 91,45%. Thirtysix restorations presented a damage of less than 1 mm at the marginal edge, and they were considered as “successful”. The General Integrity Rate (GIR) was 79,61%. No statistical differences were identified for using the glassionomer restorative material in vital or non-vital teeth, or using or not a dental dam. Conclusions: A restorative system based on a high-viscosity glassionomer cement coated with an acrylic light-cured resin showed excellent behavior in the medium-long term.