The use of a dental microscope is a scientifically researched and recognised method of optimising root canal treatment. Its use results in improved diagnostic and therapeutic accuracy and considerably expands treatment options. Many therapeutic problems can be successfully managed or avoided entirely. Well-established endodontic treatment methods can be checked more effectively and improved by the use of magnification. New therapeutic methods, such as ultrasonic-abrasive micropreparation to manage and correct iatrogenically created ledges, can improve the prognosis of orthograde endodontic retreatment. Keywords: dental microscope, ledges, retreatment, ultrasonic-abrasive micropreparation