Objective: The purpose of this in vitro study was to evaluate the change in cavity volume after removal of amalgam and resin composite restorations, based on the dental skills of the operators. Method and materials: A high-speed turbine and diamond burs were used to prepare Class II cavities in 60 acrylic resin mandibular first molar teeth. After the teeth were weighed with precision scales, the cavities were restored with amalgam or posterior resin composite. The restored teeth were then stored in distilled water at room temperature for 48 hours. Three undergraduate students with 2 years' practical experience on patients, and three postgraduate students with an additional 4 years' practical experience in the Department of Operative Dentistry, removed the restorations from the cavities with a high-speed turbine, and the teeth were all weighed again. After cavities were rerestored with the same materials, each restoration was removed once more by the same operator. The weighing procedure was repeated before and after the removal of the restorations. The data were subjected to paired and unpaired t tests. Results: Every time a restoration was removed from a tooth, the cavity preparation became significantly larger, but the postgraduate students caused significantly smaller increases in cavity volume. Conclusion: Increases in cavity volume are not based on the nature of the restorative material; however, the individual experience levels and dental skills of the operators lead to significant differences in the cavity volume increase.