A total of 460 roots of extracted human teeth were divided into three groups i.e.
straight, apically curved and entirely curved groups. Each of the three groups were
divided into seven subgroups according to instrumentation by conventional hand, K-Flex
file, 3-LD, 3-LDSY, Excalibur. MM 1400 and Endo Sonic. Radiographs were taken both
clinical and proximal views before and after the enlargement of canals. An assessment
of shaping characteristic of instrumentation was made on the basis of overimposed
radiographs including perforation, ledge formation smoothness of wall contour incidence
of elbow and zip measurements at the elbow level and asymmetry measurements. The majority
of enlarged root canals were asymmetrical in shape. High differences were found between
the incidence of elbow and zip formation. Under laboratory conditions the K-Flex file
produced minor canal aberrations and significantly less asymmetry than the conventional
instruments. But both the above mentioned instruments caused perforations on curved
canals, such as the instrumentation by Excalibur. The loss of working distance was
significant in all canal forms prepared with 3-LD and 3-LDSY instruments, which could
have occurred through the packing of debris towards the apical constriction. The Excalibur
appeared to be superior to the conventional hand instrument in straight canals, but
its shaping characteristic was similar to conventional hand instrument in curved canals.
The MM 1400 handpiece and ultrasonic instruments resulted in less aberration and significantly
less asymmetry than the other tested instruments.