This study suggests that sealers with different chemical compositions initiate different histological reactions. It also emphasizes the importance of confining root filling to the canal system because all sealers initiate inflammatory reactions when they are present in the apical tissues

The objective of this study was to evaluate the shaping characteristics of different root canal instruments in teeth with different root canal 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 angle and the length of the radius of arc of the curvature of the root canals. Each of the three groups containing 140 roots were randomly divided into seven subgroups prior to preparation. The canals were enlarged manually with traditional and flexible hand instruments, three different engine driven instruments and sonically and ultrasonically powered instruments. The shortcomings of the seven preparation methods were assessed by superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after preparation. Results showed that observation of perforation, incidence of elbow and of asymmetrical preparation of the root canals depended on root canal configuration. It was striking that the coronal transposition of the apical stop, uneven wall contour, ledge formation and incidence of zip were independent of root canal morphology. Evaluation of data of asymmetry of preparation (canal transposition) revealed significant differences (p < 0.05). Asymmetry of preparation was the most frequent aberration of the prepared root canals and it was possible to study it with precision. It was concluded that this measurement should be a priority for future instrument testing. The shaping characteristics of hand and engine driven instruments was modified by root canal morphology, but that of sonic and ultrasonic instruments was less dependent on the original anatomical form of root canals.

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The objective of this study was to evaluate the shaping characteristics of various root canal instruments using human teeth. 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, (ii) apically curved, and (iii) whole-length curved canals according to the Schneider's angle and the length of the radius of arc fitting the curvature of root canals. Each of the three groups containing 140 roots were randomly divided into seven subgroups prior to preparation. The canals were prepared manually with traditional and flexible instruments, engine driven Racer-type, Giro-type, randomly vibrating instruments and with sonic and ultrasonic instruments. The shortcomings of the seven preparation methods were assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after the preparation. The prepared straight canals showed a high percentage (75.7%) of apical asymmetry. Coronal transposition of the apical stop was graded with higher scores in all canal forms prepared with Racer-type and Giro-type instruments, which could have occurred through packing of debris towards the apical constriction. The majority of the prepared curved canals were asymmetrical in shape. The location of the aberrations depended on the original shape of the canal but the method of shaping also had a decisive effect on the post-operative form of the canal. Large differences were found between the incidence of elbow (11.7-40.0%) and zip (75.7-80.0%). K-Flex files produced minor canal aberrations and significantly less asymmetry (P < 0.05) than the conventional hand instruments. The MM 1400 handpiece and ultrasonic instruments were associated with less aberration and significantly less asymmetry than the other instruments tested. The Excalibur appeared to be superior to the conventional hand instruments in straight canals, but its shaping characteristics were similar to conventional instruments in curved canals. Under the conditions of this study, canal shaping with Cavi Endo, MM 1400 and K-Flex files appeared to be superior to that achieved with conventional hand instruments Excalibur, Intra Lux Endo Kopf 3LDSY, and 3LD instruments.