RESUMEN
In a major design change LightSpeed Technologies Inc. has replaced the U-shape blade design with a spade-shape design in LightSpeed LSX root canal rotary instruments. A double-digital radiographic technique was used to compare apical transportation (AT) and length control (LC) between the two instrument designs. Thirty simulated plastic root canals were instrumented by each rotary system. Digital radiography and AutoCAD 2007 were used to determine the central axes of files at 20, 35, 50, and 70 ISO sizes. By superimposition of central axes with a baseline at size 20, the degree of AT was measured at 0, 1, and 3 mm from working length (WL). The distance from file tips to set WL indicated any loss of LC. ANOVA test showed no significant differences between groups with respect to the degree of AT or LC. No instrument separation was noted. The results indicate that newly designed Lightspeed LSX instruments maintain the same effectiveness regarding AT and LC as that of the LightSpeed LS1 instruments.