O. A. Peters, C. I. Peters, K. Schonenberger & F. Barbakow
Endodontic Division, Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, USA.
Endodontic Department, University of The Pacific Dental School, San Francisco, USA.
Division of Endodontology, Department of Preventive Dentistry, Periodontology and Cariology, University of Zurich, Switzerland.

Introduction.
Modern engine-driven root canal preparation techniques claim to facilitate safe and efficient preparations. Such techniques have been evaluated in several studies using various experimental designs. Conventional analytical methods may employ reassembly techniques (Bramante et al. 1987) which evaluate cross-sections of root canals before and after preparation (Deplazes et al. 2001).
Recently, micro computed tomography (mCT) was introduced to evaluate not only cross-sections of roots, but also three-dimensional shapes of canals at resolutions as high as 36 mm (Peters et al. 2000, Rhodes et al. 2000, Bergmans et al. 2001, Gluskin et al. 2001). This innovation was achieved because new hardware and software was available to evaluate the metrical data created by mCT, thus allowing geometrical changes in prepared canals to be determined in more detail (Peters et al. 2000).
Evidence suggests that canal anatomy influences preparation outcomes: significantly more aberrations are recorded when preparing simulated canals with more acute curves in plastic blocks using various nickel-titanium (Ni-Ti) rotary instruments (Bryant et al. 1999). In addition, three-dimensional analysis using mCT indicated that canal transportation was more pronounced when shaping narrow curved canals than wider specimens (Peters et al. 2001a).
Nickel-Titanium rotary instruments such as ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) have a modified cross-sectional design that resembles a K-File configuration instead of the U-shape common to many other rotary instruments. Rotary instruments with this geometry are claimed to cut dentine more effectively, and may therefore reduce torsional loads (Ruddle 2002). However, more aggressive cutting could produce increased canal transportation and, aside from clinical guidelines (Ruddle 2001), little information exists about these instruments. Consequently, the aim of this study was to assess the shaping potential of ProTaper instruments, and to evaluate the effect of normal canal anatomy on the final outcome of the shaped canal using different variables.