THE EFFECT OF ROOT-CANAL MORPHOLOGY ON CANAL SHAPE FOLLOWING INSTRUMENTATION USING DIFFERENT TECHNIQUES

The objective of this study was to evaluate the shaping characteristic s of different root canal instruments in teeth with different root can al forms. A total of 420 extracted human roots were embedded in resin blocks, The embedded roots were divided into three groups, i.e., roots with (i) straight (I form), (ii) apically curved (J form), and (iii) entirely curved canals (C form) with reference to the Schneider's angl e and the length of the radius of are of the curvature of the root can als, Each of the three groups containing 140 roots were randomly divid ed into seven subgroups prior to preparation. The canals were enlarged manually with traditional and flexible hand instruments, three differ ent engine driven instruments and sonically and ultrasonically powered instruments, The shortcomings of the seven preparation methods were a ssessed by superimposition of projected radiographs taken in bucco-lin gual and mesio-distal views before and after preparation, Results show ed that observation of perforation, incidence of elbow and of asymmetr ical preparation of the root canals depended on root canal configurati on. It was striking that the coronal transposition of the apical stop, uneven wall contour, ledge formation and incidence of zip were indepe ndent of root canal morphology. Evaluation of data of asymmetry of pre paration (canal transposition) revealed significant differences (p<0.0 5). Asymmetry of preparation was the most frequent aberration of the p repared root canals and it was possible to study it with precision. It was concluded that this measurement should be a priority for future i nstrument testing. The shaping characteristics of hand and engine driv en instruments was modified by root canal morphology, but that of soni c and ultrasonic instruments was less dependent on the original anatom ical form of root canals.