Cutting efficiency of conventional and martensitic nickel-titanium instruments for coronal flaring.
BACKGROUND
This study aimed at evaluating the influence of rotational speed and number of uses on the cutting efficiency of 4 nickel-titanium coronal flaring instruments against 2 substrates, bovine dentin and acrylic blocks.


METHODS
BioRaCe BR0, HyFlex CM1, ProFile OS#2, and ProTaper Sx were used in simulated lateral action against both substrates at 250 and 500 rpm up to 5 times, producing 5 notches in each block. Notch areas and lengths were measured under a stereomicroscope, and data were compared by using parametric tests (α = 0.05).


RESULTS
Against both substrates, HyFlex CM1 and ProFile OS#2 were the most and the least cutting efficient instruments, respectively (P < .05). Against acrylic, area and length values at 500 rpm were significantly higher than those at 250 rpm for all brands. Against dentin, significant differences were detected between 250 and 500 rpm for HyFlex CM1 and ProTaper Sx (area) and for BioRace BR0, HyFlex CM1, and ProTaper Sx (length). Regarding cutting efficiency loss, area and length for notches 1 and 2 (first notches) and 4 and 5 (last notches) were similar against acrylic. Against dentin, length values for notches 1 and 2 were significantly higher than those for notches 4 and 5 in ProFile OS#2 and ProTaper Sx. A strong correlation was detected between the overall results obtained on acrylic and dentin for area and length (P < .0001), although further analysis showed that data against acrylic were a poor predictor of data against dentin after repeated use.


CONCLUSIONS
HyFlex CM1 was the most cutting efficient instrument in lateral action. An increase in rotational speed improved the cutting efficiency. Results against acrylic showed a high correlation to data against dentin, but acrylic may not be a proper substrate when the intention is to assess cutting efficiency loss with repeated use.
Department of Endodontics, School of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil; Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California. Electronic address: remorgental@hotmail.com.
Renata Dornelles
RD
Morgental
Fabiana Vieira
FV
Vier-Pelisser
Patrícia Maria Poli
PM
Kopper
José Antonio Poli
JA
de Figueiredo
Ove A
OA
Peters
D000818:Animals; D002417:Cattle; D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000648:ultrastructure; D004867:Equipment Design; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D019904:Polymethyl Methacrylate / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D019415:Torque
D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; D009532:Nickel; D019904:Polymethyl Methacrylate; D014025:Titanium
Coronal flaring; cutting efficiency; martensitic nickel-titanium