摘要： Background. Complete removal of existing composite restorations without unnecessary removal of tooth structure is challenging. The authors compared the amount of tooth structure removed and composite remaining in Class III preparations when using an erbium laser or a rotary instrument. Methods. Mesiolingual and distolingual preparations were prepared in 14 extracted anterior teeth, restored with shade-matched composite, ?nished, and polished. One restoration was removed with an erbium, chromium:yttrium-scandium-gallium-garnet laser and the other with a rotary instrument (handpiece and carbide burs). Gypsum models made from vinyl polysiloxane impressions of the preparation and removal stages were scanned. The 2 scans were precisely aligned to calculate the amount of tooth structure removed and residual composite, which were statistically compared (t test) between the bur and laser groups. Results. Rotary instruments removed signi?cantly more tooth structure than the laser in terms of mean depth (P ? .0017) but not maximum depth (P ? .0762). Although mean depth of tooth loss was smaller in the laser group, the area of tooth loss was signi?cantly larger (P ? .0004) because the rotary instrumentation left signi?cantly more composite than the laser in terms of volume (P ? .0104), mean depth (P ? .0375), maximum depth (P ? .0318), and area (P ? .0056). Conclusions and Practical Implications. The erbium, chromium:yttrium-scandium-gallium-garnet laser was more selective in removing existing composite restorations than a rotary instrument because it removed less tooth structure and left behind less composite. Unintentional loss of tooth structure and unnoticeable residual composite are inevitable when removing existing composites. Erbium lasers are alternative means of composite removal that may be more selective than a rotary instrument.