Apicoectomy with retrograde amalgam is an accepted procedure for treating teeth that cannot be treated by nonsurgical methods. Some of these fail to heal for no apparent reason. Evidence is presented that indicates that some of these failures are caused by corrosion of the apical amalgam. Two cases are described in which the sinus tract that was associated with the failing retrograde amalgam was resolved without further surgery. To bring about the resolution, a zinc-enriched amalgam was placed in the crown that through an intervening conductor, reduced the rate of corrosion at the apex.