Manual endodontic instruments. 1st Endodontic instruments class, on the basic definitions about the characteristics of instruments in general and the main ones about manual instruments.
In: Tavares et al. Fracture index of manual stainless steel and NiTi rotary instruments in a postgraduate Endodontic clinic. Arq Odontol, Belo Horizonte, 51(3): 152-157, Jul/Sept 2015
Introduction. Stainless steel (IA) hand instruments are widely used in endodontic practice. Due to the high modulus of elasticity, these instruments may predispose to operative errors such as transports, steps, zips and perforations. According to evaluation with scanning electron microscopy, fatigue was identified as the main cause of fracture of AI2 hand instruments. Rotatory instruments manufactured from nickel-titanium alloys (NiTi) were introduced in Endodontics to minimize procedural errors and increase safety during canal preparation.
NiTi alloy has two main properties: superelasticity and shape memory effect. These instruments have low modulus of elasticity, are flexible and have high mechanical strength. NiTi instruments, despite their desirable mechanical properties, can fracture. Torsional fracture occurs when the tip or other part of the instrument gets stuck inside the canal and its stem continues to rotate. Thus, the instrument undergoes plastic deformation, which can be followed by fracture. Fatigue fracture occurs without visible signs of previous deformation. When rotating within a curved canal, the instrument is subjected to tensile and compressive stresses, concentrated in the region of maximum root curvature. Fatigue of these instruments is directly proportional to the amplitude of deformation to which they are subjected, which depends on the canal geometry and the diameter of the instrument at the point of maximum bending.
The most severe fatigue conditions are associated with smaller canal curvature radii and larger calibrated instruments. The incidence of fracture of hand-held IA instruments has been reported to be between 0.25% and 6%7-10. On the other hand, power-driven NiTi instruments have been related to higher fracture rates, ranging from 1.3% to 10%8,11,12. However, there is little information in the literature regarding the moment of fracture of these instruments; whether it occurs in the initial phase of canal exploration or in later phases of instrumentation of the root canal system (RCS) Endodontic instruments. Basic and hand instruments.
Manual endodontic instruments.
