Incidence of Deformation and Fracture of Twisted File Adaptive Instruments after Repeated Clinical Use.
OBJECTIVE
The aim of the present study was to investigate the incidence of deformation and fracture of twisted file adaptive nickel-titanium instruments after repeated clinical use and to identify and check whether the three instruments within the small/medium sequence showed similar or different visible signs of metal fatigue.


METHODS
One-hundred twenty twisted file adaptive (TFA) packs were collected after clinically used to prepare three molars and were inspected for deformations and fracture.


RESULTS
The overall incidence of deformation was 22.2%, which was not evenly distributed within the instruments: 15% for small/medium (SM)1 (n = 18), 38.33% for SM2 (n = 46) and 13.33% for the SM3 instruments (n = 16). The defect rate of SM2 instruments was statistically higher than the other two (P < 0.001). The fracture rate was 0.83% (n = 3), being two SM2 instruments and one SM3.


CONCLUSIONS
It was observed a very low defect rate after clinical use of twisted file adaptive rotary instruments. The untwisting of flutes was significantly more frequent than fracture, which might act as prevention for breakage. The results highlight the fact that clinicians should be aware that instruments within a sequence might be differently subjected to intracanal stress.
Department of Oral and Maxillo Facial Sciences, Sapienza University of Rome, Rome Italy.
Gianluca
G
Gambarini
Department of Periodontics and Endodontics, University at Buffalo School of Dental Medicine, Buffalo, New York USA.
Lucila
L
Piasecki
Department of Oral and Maxillo Facial Sciences, Sapienza University of Rome, Rome Italy.
Dario
D
Di Nardo
Department of Oral and Maxillo Facial Sciences, Sapienza University of Rome, Rome Italy.
Gabriele
G
Miccoli
Department of Oral and Maxillo Facial Sciences, Sapienza University of Rome, Rome Italy.
Gianni
G
Di Giorgio
Department of Endodontics, Pontifical Catholic University of Paranà, Curitiba, Paraná Brazil.
Everdan
E
Carneiro
Department of Restorative Dental Sciences, College of Dentistry, King Saud University, Riyadh Saudi Arabia.
Dina
D
Al-Sudani
Department of Oral and Maxillo Facial Sciences, Sapienza University of Rome, Rome Italy.
Luca
L
Testarelli
endodontics; nickel; root canal therapy; titanium