PathFileTM: A New Rotary Nickel-Titanium Instrument for Mechanical Glide Path and Preflaring

NiTi instrument separation is a serious concern in endodontic therapy. The analysis of NiTi files after torsional fracture reveals that the majority of torsional separations occur in the last mm. of the files and in the files with lower taper and/ or diameter. Consequentely, the tip of the smaller files presents the higher risk of torsional fracture and should be protected using low torque motors, reducing axial pressure and avoiding the tip from engaging root dentin (“taper lock”). In contrast, flexural fractures occur after repeated subthreshold loads have led to metal fatigue. Numerous studies evaluated the causes of stress and separation of rotary NiTi files concluding that a significant reduction of rotary instrument separation could be obtained when use of rotary file was anticipated by an initial manual preflaring and glide path. A strong evidence supports the importance of manual preflaring and glide path to reduce the frequency of rotary file separation. The initial preflaring and glide-path are normally carried out using stainless steel hand files. Unfortunately these files presents several drawbacks because of their relative stiffness and aggressive tip that in curved and/or calcified canals can cause ledges or transportation. Consequently a new kit of three NiTi rotary instruments, the PathFileTM (Dentsply Maillefer) has been recently introduced for mechanical glide path and preflaring. The PathFileTM is the first instrument projected for and dedicated to mechanical glide path and preflaring. The low .02 taper, the robust square cross section and the four cutting angles create a good combination of flexibility, strength and efficacy that allow a safe and fast use even in severely curved and/or calcified canals. Preliminary investigation and clinical evaluations confirmed that PathFileTM instruments represent a significant help when shaping severely curved canals allowing the creation of a smooth glide path without transportation even in case of procedural errors (short or long working length determination). Introduction The use of Nickel-Titanium rotary files has changed radically the root canal instrumentation techniques and the prognosis of endodontic complex cases. Many “in vitro”(1-13) and “in vivo”(14-17) investigations demonstrate that rotary NiTi instruments are superior to stainless-steel ones with regard to their shaping ability and can shape even severely curved canals with lower risk of ledging and straightening. In an “in vivo” study by Schäfer (16) 110 Canals were prepared by NiTi Rotary Files and 84 canals were prepared using hand instruments. All canals were shaped by eight experienced dentists. Preoperative and postoperative (after obturation) radiographs were taken of each tooth. Straightening of the canal curvatures was determined with a computer image analysis software. Preparation with NiTi Rotary Instruments resulted in significantly less straightening and a shorter preparation time compared with hand instrumentation (16) (Fig.1). In another “in vivo”study, Sonntag et al. (17) compared the risk of complications during root canal preparation with manual stainless steel files and rotary NiTi files. All cases were performed by students. The results demonstrated that even inexperienced operators achieved better canal preparation with NiTi files than with hand stainless steel files with significantly less zips and elbows (17). Unfortunately, the use of NiTi rotary files has a serious limitation since it is associated with a significantly higher risk of intracanal separation in comparison with stainless steel files (17,18). Suter et al evaluated “in vivo” the probability of successfully removing fractured instruments from root canals reporting a success rate of 87%. The analysis of the removed fragment confirmed that NiTi Rotary Instruments fractured with a significant higher rate than stainless steel hand instruments (18). Comparable results were reported by Sonntag et al. (16). NiTi instrument separation is a serious concern in endodontic therapy. Several studies evaluated the influence of various factors on the fracture of nickel titanium (NiTi) endodontic rotary instruments and demonstrated that file separation mainly are caused by torsional (19-25) and fatigue stresses (21,23,26-28). Torsional stresses depend on the size of the contact area between root-canal dentin and the instrument, taper and diameter of the instrument, portion of the instrument subjected to torsion, intrinsic strength (cross sectional design) of the instrument, blade design and torsional forces applied to the instrument (27,28). The analysis of the NiTi files after torsional fracture reveals that the majority of torsional separations occurrs in the last mm. of the files and in the files with lower taper and/or diameter (24,25,27,28). Consequentely, the tip of the smaller files presents the higher risk of torsional fracture and should be protected using low torque motors, reducing axial pressure and avoiding the tip from engaging root dentin (“taper lock”) (27,28). In contrast, flexural fractures occur after repeated subthreshold loads have led to metal fatigue. 1,25 2,50 3,75 5,00