Copyright © 1996 by The American Association of Endodontists
Printed in U.S.A. VOL. 22, NO. 8, AUGUST1996
Canal Transportation Caused by a New Instrumentation Technique and Three Standard Techniques
Benjamin Brisefio Marroquin, DDS, Alexander Pistorius, DDS, and Brita Willershausen-Z6nnchen, DDS
The ability of three differentenlarging techniques (balanced force concept, step-back, and recapitulation) and a prototype system to maintain the original canal path during root canal preparation were compared, in vitro, with a theoretical ideally prepared root canal. Measurements were made at the concave and convex sides of the canal at four different levels (1, 4, 5, and 7 mm from apical, respectively). Simulated root canalsembedded in clear casting resin and an enlarging computersupported device were used for this study. The results showed that none of the enlarging techniques used in this study was able to prepare a canal ideally. The prototype system, at level 1, showed an ideal amount of material removed from the concave side and less, in comparison with the other techniques, from the convex side of the canals. Thesame tendencies persisted at all levels, with the exception of the level 4 concave side.
developed the Flex-R files to be used with the balanced force concept technique. They recommend clockwise and counterclockwise movements in the root canal to avoid the formation of ledges and to attain suitable debris transportation in a coronal direction. Wildey and Senia (8) developed the Canal Master "U"System to be used with modifications of the step-down and step-back techniques. It is said that apical transportation is minimized through instrument cutting segment reduction. A new root canal preparation system, which seeks the avoidance of ledging of the apical third, was presented a short time ago (9). However, research evidence that supports the theory postulated in this study has not beenpublished. The aim of this study was to investigate the benefits of the prototype system, comparing its transportation characteristics with those of three different enlarging methods in a theoretical ideally prepared canal by means of a computer-supported device.
M A T E R I A L S AND M E T H O D S Manufactured root canals (n = 20/enlarging method) embedded in clear casting resins were used todemonstrate the transportation effects of four different enlarging methods. The computer-supported enlarging device used in this study has been described in a previous study (10). Penetrations of 0.5 ram/shaping sequence, master apical files size 30, and a sequential coronal tapering of 1 ram/instrument (until final coronal files size 80) were programmed for all shaping techniques (with theexception of the prototype system). Canals were considered to be completely prepared after the master apical file (1 mm from the apical foramen) and final coronal file preparations were done. For this study, a major software modification was made. The power of the step motor responsible for the apical penetrations (x axis) was set at an uncritical value, allowing an adjustment between the respectiveinstrument load capacity and canal wall resistance. This means that the instruments were able to "detect" a determinate canal wall resistance, thus avoiding excessive binding of the instruments. In case an instrument did not reach the preprogrammed length at a determinate sequence, the step motor repeated the programmed movements until the preprogrammed length was reached. However, the shapingmovements were repeated at least five times in case no penetration resistance was encountered. Canals were rinsed with 0.5 mm 2 of tap water immediately before each new apical pene-
Different authors advocate different root canal enlarging techniques and/or instruments to avoid the formation of undesirable shaping effects, such as zipping, elbowing, perforation at the furcation area, etc. Schilder...