Many shaping techniques and instruments have been described and constructed in an attempt to minimize apical transportation, zipping and other problems found in root canals. Most root canals are still prepared using conventional finger instruments to ensure the hardness and sharpness required to prepare the dentine walls of the root canals. The recent introduction of nickel titanium alloy to endodontics has solved many of the problems that have been associated with the negative features of stainless steel instruments. Endodontic instruments made from this super-elastic alloy are significantly more flexible and are highly resistant to fracture and corrosion. The evolution of rotary instrumentation, using specially designed Ni-Ti files in gear reduction and high-torque hand pieces, has recently revolutionized endodontics because of their speed and efficacy in canal shaping and maintaining canal curvature. Improvements in rotary techniques resulted in the marketing of Lightspeed instruments from 1993. Basically, these engine-driven nickel titanium instruments have cutting tips which vary in length from 0.25mm for size 20 instruments to 1.75 mm for size 100. The cutting tips have three geometric forms which optimize efficient cutting of dentin. The remainder of the instrument shaft is thin and highly flexible which, with the pilot nose cutting tip, helps in maintaining optimal centricity in the prepared canals. However, as mentioned earlier, most root canals are still prepared using conventional hand instruments. That is because mastering any new endodontic method is always related to the individual’s learning curve. The use of Lightspeed instruments and the step-back technique involving stainless steel files in clinical trials has not been assessed before. The aims of the study were: • to compare the Lightspeed system with the step-back technique involving stainless steel files with respect to quality of the dentist’s work, patient comfort, length of treatment, and side-effects. • to assess the quality of root canal fillings and the healing of periapical tissue after six months in each group. Patients admitted to our out-patient clinic requiring endodontic treatment were constitutively included into the study. 75 root canals in 75 patients were qualified randomly into two groups. :37 in the Lightspeed group (method I) and 38 in the stainless steel group (method 2). The indications for endodontic treatment were similar in both groups: pulpitis irreversibilis, necrosis of the pulp, inflammation of the periapical tissues and fracture of the tooth crown. The periapical area of each root canal was attributed to a specific class according to the PAI Index. Endodontic treatments was performed according to the following procedures: • X-ray assessment of canal curvature using the Schneider scale. • Access opening of the tooth chamber • Measurement of the root canal length • Measurement of the working length. • Root canal cleaning and shaping according to method I or II • Root canal obturation using cold lateral gutta-percha condensation with AH PLUS sealer. Immediately after the treatment, a control X-ray was taken to assess root canal obturation and to assign it to the optimal or non-optimal group. The number and type of endodontic failures were noted as was the time needed for performing the endodontic treatment (cleaning and shaping). Both the dentist and the patient subsequently filled in a questionnaire assessing the treatment. A four-step descriptive scale was used by the dentist to describe the quality of his work. A five-step descriptive scale was employed by the patient to describe the time of the endodontic treatment and a further five-stage scale assessed pain levels. The patient was also required to assess how he felt during the treatment according to a ten-step numerical rating scale. After six months the healing of periapical region was assessed using PAI Index. ; Both groups were similar in the following respects : reason for treatment, kind of root canal, degree of root canal curvature and the periapical region status. After six months, the quality of root canal fillings and the healing of the periapical tissue was assessed. The percentage of properly obturated root canals was significantly higher in patients treated by method I as compared to method II (96,2% vs. 72,7%, p=0,02, respectively). Patients treated by method I had also the shorter treatment time ( 422±118 s vs. 532±118 s, respectively), better outcome (complete healing, i.e – PAI before treatment>1, PAI after treatment =1), method I= 32,1%, method II= 17,6%, p=n.s.), significantly better comfort of treatment in the dentist’ opinion (the best mark was given in 70.3% of patients treated by method I, and only 23.7% of patients treated by method II), and better assessment of treatment in the opinion of patients (shorter time of treatment, higher marks in numerical comfort scale). Both methods were similar in the quality of the obturation of the root canals and the percentage of complication during treatment and pain complaints The study shows for the first time in the clinical environment that endodontic treatment by means of the Lightspeed system as compared to the step-back technique is superior in subjective and objective markers of the effects of treatment.