Comparison of Two Techniques for Assessing the Shaping Efficacy of Repeatedly Used Nickel-Titanium Rotary Instruments Hani F. Ounsi, DCD, DESE, MSc,* † Giovanni Franciosi,* Raffaele Paragliola,* Khalid Al Huzaimi, BDS, MSc, † Ziad Salameh, DDS, MSc, PhD, † Franklin R. Tay, BDS (Hons), PhD, ‡ Marco Ferrari, DDS, MD, PhD,* and Simone Grandini, DDS, PhD* Abstract Introduction: The shaping capacity of nickel-titanium (NiTi) rotary instruments is often assessed by photo- graphic or micro–computed tomography (micro-CT) measurements, and these instruments are often used more than once clinically. This study was conducted to compare photographic and micro-CT measurements and to assess if the repeated use of NiTi instruments affected the shape of canal preparation. Methods: Ten new sets of ProTaper Universal instruments (Dents- ply-Maillefer, Ballaigues, Switzerland) were used in 60 resin blocks simulating curved root canals. Groups 1 to 6 (n = 10) represented the first to sixth use of the instrument, respectively. Digitized images of the prepared blocks were taken in both mesiodistal (MD) and buccolingual (BL) directions and area measure- ments (mm 2 ) were calculated using AutoCAD (Autodesk Inc, San Rafael, CA). The volumes of the same prepared canals were measured using micro-CT (mm 3 ). Statistical analysis was performed to detect differences between photographic and volumetric measurements and differ- ences between uses. Results: Two-way repeated- measures analysis of variance revealed significant differences between groups (P < .001). Regarding measurement type, there were no significant differences between BL and MD measurements, but there were significant differences between micro-CT and BL measurements (P < .001) and micro-CT and MD measure- ments (P = .001). Significant differences were also noted between uses. Conclusions: Within the limitations of the present study, micro-CT scanning is more discriminative of the changes in canal space associated with repeated instrument use than photographic measurements. Canal preparations are significantly smaller after the third use of the same instrument. (J Endod 2011;37:847–850) Key Words Nickel-titanium, repeated use, root canal, shaping N ickel-titanium (NiTi) rotary instruments are frequently used in endodontics because of their superelastic properties that permit efficient canal preparation (1, 2). They differ in taper, tip size, cross-section, helix angle, and blade pitch (3, 4). The major disadvantage associated with their use has always been the tendency to separate during function without warning in inexperienced hands (5). Although the repeated clinical use of NiTi rotary instruments resulted in the reduction of their cyclic fatigue resistance (6–9), clinicians often reuse these instruments because of financial reasons (10). The number of times in which a NiTi rotary instrument can be reused remains uncertain (11). The shaping efficiency of these instruments is usually assessed by two-dimensional (2D) photographic techniques and three-dimensional (3D) techniques such as micro– computed tomography (micro-CT) scanning. 2D photographic techniques involve taking digitized images/radiographs in two perpendicular directions and using a soft- ware program (eg, AutoCAD; Autodesk Inc, San Rafael, CA) to perform calculations with or without superimposition. These techniques have been used to assess the shape of the preparation, canal transportation, residual dentin after shaping or post space prepara- tion, and the cutting efficiency of different instruments (12–14). They are easy-to-use, inexpensive, and potentially informative depending on the question to be investigated (15) but lack the capacity to disclose volumetric information. Improvements in micro-CT techniques enable noninvasive 3D sampling at rela- tively high resolution (16). Data generated using micro-CT scanning may be repre- sented as 2D- or 3D-rendered images that can be analyzed qualitatively and quantitatively (17). Previous studies that evaluated the shaping ability of rotary files (18–23) investigated changes in various parameters after canal preparation. These parameters include surface area and volume of the root canal, the amount of dentin volume removed, canal diameter, prepared surface, canal curvature, canal tran- sportation, transportation of the center of mass, canal straightening, proportion of unchanged canal surface, and canal centering ratio. To date, no study has compared results obtained by 2D versus 3D measurement techniques or the effect of repeated use of NiTi rotary instruments on the final shape of the canal preparation. Thus, the objective aim of the present study was to compare photographic (2D) and micro-CT (3D) measurements and to assess if the repeated use of NiTi instruments adversely affects the shape of the preparation. The null From the *Department of Endodontics and Restorative Dentistry, University of Siena, Policlinico Le Scotte, Viale Bracci, Siena, Italy; † Eng AB Chair for Growth Factors and Bone Regeneration, King Saud University, Riyadh, Saudi Arabia; and ‡ Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, Georgia. Address requests for reprints to Dr Hani F. Ounsi, Department of Endodontics and Restorative Dentistry, University of Siena, Policlinico Le Scotte, Viale Bracci, Siena, Italy. E-mail address: ounsih@gmail.com 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2011.02.030 Basic Research—Technology JOE — Volume 37, Number 6, June 2011 Shaping Efficacy of NiTi Rotary Instruments 847