Figure 3. External root resorption after internal bleaching of teeth #11 and #21. Both teeth had been endodontically treated due to caries 14 yrs earlier. No history of trauma was reported. Two years after endodontic treatment, both teeth were internally bleached by sodium perborate and 3% hydrogen peroxide. Due to an unsatisfactory bleaching result after 3 wks, the treatment was supplemented with in-office bleaching with 30% hydrogen peroxide and heat two times for 30 min each, with an interval of one week. External root resorption was diagnosed 12 yrs later.