A comparison of Flex-R files and K-type files for enlargement of severely curved molar root canals.

A double exposure radiographic technique is introduced and used to evaluate the magnitude of apical canal transportation that occurs during preparation procedures. The balanced force technique and a step-back method for cleaning and shaping root canals were evaluated in mesiobuccal root canals from 80 extracted human molar teeth with curvatures ranging from 30 to 73 degrees. Pre- and posttreatment file positions were examined from clinical and proximal radiographic views by computer digitization. Statistical analysis indicated significantly less apical transportation with the use of the balanced force technique when compared with a step-back technique in canals exhibiting both more and less than 45 degrees of curvature.