Dimensional characterization and mechanical behaviour of K3 rotary instruments.
OBJECTIVE
To correlate the mechanical behaviour in torsion, bending and fatigue tests of K3 instruments with their dimensional characteristics.


METHODS
Instrument length, tip angle, distance between blades (pitch length) and the diameter at each millimetre from the tip of sizes 20, 25 and 30, 0.04 taper and sizes 20 and 25, 0.06 taper K3 rotary instruments were measured in an optical microscope equipped with digital micrometers. The cross-sectional area at 3 mm from the tip of the same instruments was determined using digital image analysis of scanning electron microscopy images. Maximum torque and angular deflection, as well as bending moment at 45 degrees were measured according to specification of ISO 3630-1. Fatigue resistance of instruments size 30, 0.04 taper, and sizes 20 and 25, 0.06 taper was determined in a fatigue test bench device.


RESULTS
The analysed instruments presented no uniformity in the distance between adjacent blades, but the measured diameters at each millimetre from the tip were regular, showing compliance with manufacturing standards. Torque and bending moment of the tested instruments increased significantly with diameter and cross-sectional area at 3 mm from the instrument tip. The fatigue resistance of the instruments showed a tendency to decrease as the diameter of the instruments increased.


CONCLUSIONS
The bending moment at 45 degrees and the torsional resistance of K3 instruments can be predicted using instrument diameter and cross-sectional area at 3 mm from the tip. Fatigue resistance decreased as the instrument diameter increased.
Melo
M C C
MC
Department of Restoration Dentistry, Faculty of Dentistry, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil.
Pereira
E S J
ES
Viana
A C D
AC
Fonseca
A M A
AM
Buono
V T L
VT
Bahia
M G A
MG
D000704:Analysis of Variance; D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004548:Elasticity; D004867:Equipment Design; D004868:Equipment Failure; D009532:Nickel; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium; D019415:Torque
D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium