OBJECTIVE The clinical changes in roughness of resin-modified glass ionomer materials is relatively unknown. This study examined the in vivo wear of these materials using surface roughness as an indicator of wear patterns. METHODS Ten patients with four cervical abrasion lesions each were selected. The four cavities in each patient were restored with Fuji II LC (GC Corp., Japan), Vitremer (3M Dental, USA), Photac-Fil (ESPE, Germany) and Fuji Cap II (GC Corp., Japan). After light-curing, the restorations were polished and left uncoated. Silicone impressions were made of the surface of each restoration after polishing, and then at 3 monthly intervals up to 24 mon after restoration placement. Gold-coated resin replicas were made from the impressions for surface wear evaluation. Quantitative assessment of wear was performed by measuring surface roughness with a confocal microscope for topographical reconstruction of the specimen surface. The effect of material at each time period was analyzed using the Kruskal-Wallis test with exact non-parametric inference. Rugosity, as determined by the center line average, was determined by image analysis. SEM images of the same surfaces provided the qualitative analysis. RESULTS All restorations showed a cyclic distribution of rugosity with time as demonstrated by lowess plots. There were significant differences between materials at 6, 9 and 18 mon. The rugosity curves appeared to converge at 24 mon. CONCLUSIONS It was concluded that the in vivo surface changes in roughness of resin-modified glass ionomer materials is cyclic in nature over the first 2 y.