RESUMEN
AIM: The case of a lower molar with apical periodontitis, which had previous root canal treatment and a fractured instrument in the distal root beyond the foramen, is presented. BACKGROUND: The simultaneous presence of a foreign body (endodontic instrument or material) in periapical tissues and microorganisms in the root canal, are etiological factors in the formation or maintenance of a periapical lesion, and can lead to failure in endodontic treatment. CASE DESCRIPTION: This instrument was removed through the staging platform technique, by using ultrasound and an Instrument removal system (IRS) microtube under microscope visual amplification. All the canals were re-instrumented, irrigated with sodium hypochlorite and passive ultrasonic irrigation, removal of smear layer and intracanal medication with calcium hydroxide for 8 days, after which they were filled. The symptoms disappeared and clinical and radiograph 2-year follow-up shows healing of periapical tissues. CONCLUSION: The combined use of visual magnification microscope, ultrasound and the IRS system by staging platform technique, allowed the removal of an endodontic instrument beyond the foramen, which made it possible to apply a conventional disinfection protocol. CLINICAL SIGNIFICANCE: Endodontic re-treatment by conservative approach of complicated cases it is an option with good clinical prognosis, before apical surgery or extraction.