Cyclic fatigue resistance of Mtwo NiTi rotary instruments used by experienced and novice operators--an in vivo and in vitro study.
BACKGROUND
The aim of the present study was to evaluate the cyclic fatigue resistance of Mtwo NiTi rotary instruments after clinical use by 1 experienced and 1 novice operator.


METHODS
Cyclic fatigue testing of instruments was performed on tapered artiﬁcial canals with a 5 mm radius of curvature and 60° angle of curvature. Twenty Mtwo instruments for each size were selected and divided into 2 groups: group A consisted of 10 instruments of each size used for shaping 10 root canals in molar teeth of patients by an experienced operator; group B consisted of 10 instruments of each size used for shaping 10 root canals in molar teeth of patients by a novice operator. Instruments were rotated until fracture occurred and the numbers of cycles to failure (NCF) were recorded. Data obtained were subjected to an independent sample t-test to determine statistical differences. The signiﬁcance was determined at a 95% conﬁdence level.


RESULTS
No statistically signiﬁcant difference (P<0.05) was noted between the instruments of groups A and B for all sizes. More instruments with visible signs of plastic deformation were identified for the novice operator.


CONCLUSIONS
The clinical use of Mtwo NiTi rotary instruments by a novice operator did not signiﬁcantly affect the cyclic fatigue resistance when compared with the control group of the same instrument sizes used by an experienced operator. It can be concluded that novice operators can use these instruments safely under the recommended technical guidelines.
Department of Endodontics, Sapienza University of Rome, Rome, Italy. endo@gianlucaplotino.com
Gianluca
G
Plotino
Dina
D
Al-Sudani
Stefano
S
Pulino
Nicola M
NM
Grande
Piero Alessandro
PA
Marcoli
Silvia
S
Pizzi
Luca
L
Testarelli
Gianluca
G
Gambarini
D002983:Clinical Competence; D003762:Dental Instruments; D003799:Dental Stress Analysis / Q000295:instrumentation*; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation*; D009532:Nickel / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
C040654:titanium nickelide; D009532:Nickel; D014025:Titanium