Assessment of the separation incidence of mtwo files used with preflaring: prospective clinical study.
BACKGROUND
The Mtwo rotary system was designed to be used at full length without performing previous cervical enlargement or creating a manual glide path. However, to our knowledge, no study has investigated whether preflaring influences instrument fatigue. The purpose of this clinical study was thus to evaluate the incidence of separation of Mtwo instruments during the preparation of mandibular and maxillary molars and bicuspids that was preceded by cervical preflaring.


METHODS
A total of 556 treatments were performed by 6 endodontists after calibration. Cervical enlargement and exploration with hand files were undertaken before using the rotary files. The canals were negotiated with small K-type hand files. Cervical and middle thirds were prepared with hand files and Gates-Glidden burs. Irrigation was performed with 2 mL of 2.5% NaOCl after each instrument. The working length was established, and the apical third was prepared with Flexofiles until a #15 file could reach the working length, establishing a glide path. The Mtwo instruments were used following manufacturer's recommendations and disposed of after being used in 5 teeth. Each file was examined under ×8 magnification after use. In cases of file deformation or separation, the entire file kit was no longer used, except when using the 10.04 file. Because of its high failure rate, which is well-established in the related literature, this instrument could be replaced at any time.


RESULTS
Separation and deformation rates were 1.98% and 28.78%, respectively. Ten of the total separations observed occurred with the 10.04 file (90.01%) and one with the 15.05 file (9.09%).


CONCLUSIONS
The use of Mtwo rotary instruments preceded by cervical preflaring with manual files and Gates-Glidden burs provides a low separation incidence.
Graduate Program in Endodontics, São Leopoldo Mandic Dental Research Center, Campinas, São Paulo, Brazil. iracabral@yahoo.com.br
Iracema C
IC
Ehrhardt
Mário L
ML
Zuolo
Rodrigo S
RS
Cunha
Alexandre S
AS
De Martin
Daniel
D
Kherlakian
Maria Cristina C de
MC
Carvalho
Carlos Eduardo da S
CE
Bueno
D001641:Bicuspid / Q000473:pathology; D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000473:pathology*; D004492:Edetic Acid / Q000627:therapeutic use; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008963:Molar / Q000473:pathology; D011446:Prospective Studies; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D019227:Tooth Apex / Q000473:pathology
D003722:Dental Alloys; D012388:Root Canal Irrigants; D013193:Stainless Steel; D004492:Edetic Acid; D012973:Sodium Hypochlorite