To compare the clinical performance of glass ionomer (GI) versus resin composite. A total of 40 Class II restorations were placed in 12 patients aged 4–8-year-old. Patients had to have one or more pair of contralateral teeth indicated for Class II restorations. The two materials, GI (ChemFil™ Rock) and resin composite (Z350) were randomly placed in a split mouth design. The restorations were evaluated using foreign direct investment criteria after 3, 6, 9, and 12 months. Data were
subjected to statistical analysis. The result did not reflect any significant differences at the first 6 months evaluation. However, change appeared at 9 and 12 months evaluation regarding; anatomic form, fracture of material and retention, marginal adaptation, wear, proximal anatomical form, contact point, proximal contour, radiographic examination, recurrence of caries and periodontal response. Resin composite Z350 showed better clinical performance than ChemFil™ Rock after
1-year follow-up.