Fratura de instrumento endodôntico

Endodontic Instrument Fracture Fracture Prevention Guide 5th class in the endodontic preparation series www.ferrariendodontia.com.br In: Lopes et al. Fracture of Endodontic Instruments. Clinical Recommendations. Rev. bras. odontol., Rio de Janeiro, v. 68, n. 2, p. 152-6, Jul./Dec. 2011 Introduction Fracture resistance is one of the main mechanical properties of endodontic instruments that should be communicated to the user to guide them in clinical practice. During the chemical-mechanical preparation of a root canal, endodontic instruments undergo extremely adverse stresses that vary with the anatomy of the canal, the dimensions of the instruments, and the skill of the professional. These adverse stresses continuously modify the torsional and rotary bending resistance of endodontic instruments during root canal instrumentation. Instrument fracture can occur due to torsion, rotary bending (tensile and compressive stresses), and a combination thereof. Instrument Fracture Due to Torsion For torsional fracture to occur, the tip of the endodontic instrument must be immobilized and a torque greater than the instrument's fracture resistance limit must be applied to the other end (handle). This can occur with stainless steel and NiTi endodontic instruments, whether manually or mechanized. If the tip of the instrument is not immobilized during root canal instrumentation, regardless of the torque applied, torsional fracture of the endodontic instrument will not occur. Torsion (T) can be defined as the rotational effect created by a force (F) distant from the axis of rotation of an object. It is calculated by the equation: Torque = F.R where, R (radius) is the distance between the point of application of the force (F) and the axis of rotation of the object. Force in the International System of Units is expressed in Newtons (N), and torque is expressed by the unit of force multiplied by the unit of length of the radius (newton x meter). The units kilograms (kgf) and grams (gf) are also used for force, and centimeters and millimeters for length. The following relationships exist between the units: 1 kgf = 1000 gf = 9.807 N 1 cm = 10 mm Clinical Recommendations Immobilization of the Instrument Tip If the tip of an endodontic instrument is immobilized within a root canal and the rotation is to the right, there will initially be plastic deformation (distortion) of its helices. The presence of plastic deformation of the helices observed when removing an endodontic instrument from a root canal during instrumentation warns that a torsional fracture is imminent. Therefore, during root canal instrumentation, it is important for the practitioner to remove the instrument from the canal more frequently and examine it carefully. Deformed endodontic instruments should be discarded before failure (fracture) occurs. Plastic deformation also allows the practitioner to make corrections and adjustments to the advancement of the instrument within the canal and the torque applied to a new instrument used in root canal instrumentation. These measures aim to prevent immobilization and plastic deformation of the new endodontic instrument used in the instrumentation. Immobilization of an endodontic instrument driven manually or by mechanical devices (motors) within a root canal can be minimized by reducing the loading and advancement of the instrument in the apical direction. The cutting action of endodontic instruments, through a widening movement (alternating or continuous), is achieved by advancing the instrument apically (1 to 3 mm) interspersed with withdrawals. Greater advances increase the contact area and cutting resistance of the dentin wall, which may cause total or partial immobilization of the instrument tip and induce a load exceeding its fracture resistance limit due to torsion. For manually actuated instruments, advancement is controlled by the right-hand rotation angle applied to the endodontic instrument handle. For small-diameter instruments, the right-hand rotation angle should not exceed 45º. For larger-diameter instruments, the rotation angle can vary from 90 to 120º. The smaller the rotation angle applied to the endodontic instrument handle, the slower its advancement into the root canal. It's also important to emphasize that the advancement of an instrument within a root canal depends on the angle of inclination of the instrument's helix. The smaller the angle, the greater the advancement. Fracture of an endodontic instrument