A Comparative Study Of Quantec- And Hero 642-Nickel-Titanium-Instruments M. Hülsmann*, M. Schade, J. Versümer (University Of Göttingen, Germany) The aim of this study was to compare several parameters of root canal preparation using two different nickel-titanium instruments: HERO 642 (Micro-Mega, Besancon, France) and Quantec (Tycom, Irvine, USA).   The following parameters were evaluated using a muffle system as described by Bramante et al. (1987) and Hülsmann et al. (1999): straightening of curved root canals, postoperative root canal diameter, working safety (file fractures, perforations, blockages, loss of working length), cleaning ability, and working time. 50 extracted mandibular molars with curvatures between 20° and 40° were distributed into two groups. All root canals were prepared to size 45 (Quantec), or 40 (HERO 642), respectively. Quantec was used with safe cutting (SC) files.   - Straightening: The mean degree of straightening was 2.3° for Quantec and 1.6° for HERO 642 (Wilcoxon-test, p<0.005).   - Working safety: Most procedural incidents occured with Quantec (5 fractures, 3 blockages, 8x loss of working length), followed by HERO 642 (3 blockages, 1 perforation).   - Cross section form: Following preparation with HERO 642 63% of the root canals showed a round, 24% an oval, and 17% an irregular diameter, whereas Quantec only in 24% of the cases produced round, in 29% oval, and in 47% irregular cross-sections. HERO performed significantly better in the coronal and apical part of the root canal (Fisher’s exact-test, p<0.005).   - Working time: Mean working time was shortest for HERO 642 (52 sec.), Quantec took 117 sec., the difference was statistically significant (Wilcoxon-test, p<0.005)   - Cleaning ability: Cleanliness of the root canal walls was investigated under the SEM using five-score indices for debris and smear layer. For debris HERO 642 achieved the best results (80% scores 1 and 2), followed by Quantec (76%). The results for smear layer were similar: preparation with HERO 642 resulted in 53% scores 1 and 2, followed by Quantec (41%). The results were not significantly different for debris and smear layer (Fisher’s exact-test, p>0.005).   Due to the high frequency of procedural incidents of Quantec SC files and the superior cleaning ability of HERO 642 instruments the latter seem better suited for automated root canal preparation.