Evaluation of Shaping Ability of Different NiTi Systems "Using Cone-Beam Computed Tomography" : In Vitro Study /

Abstract

Mechanical root canal preparation is one of the most crucial stages in endodontic treatment that goes hand in hand with canal disinfection and successful obturation. The prepared root canal should have a continuously tapered funnel shape while maintaining the original canal curvature and apical foramen, these objectives are often difficult to achieve due to highly variable root canal anatomy and the metallurgy, design and physical characteristics of the instruments during instrumentation. Some of the procedural errors such as zipping, transportation and ledge formation can occur along with loss of working length; however various instruments along with different root canal preparation techniques have been introduced to reduce these problems. (1) Despite recent advances in the field of endodontic devices and instruments, the mechanical preparation of a curved root canal is still challenging even for very skilled and experienced clinicians. Different, well- described preparation errors may result during the instrumentation of these root canals, such as canal straightening, transportation deviation or even perforation. Since that most of the root canals are curved, a high incidence of preparation errors or canal aberrations has been statistically reported. In 1985, Lim proposed the idea that the more the flexible instrument the better negotiation of the curved root canal, helping to avoid procedural errors such as, apical transportation, zipping, perforation, or ledges. (2) Walia introduced nickel-titanium instruments in 1988, concluding that they were three times more flexible than traditional stainless steel instruments. (3) This increased flexibility found with nickel-titanium instruments made it easier for clinicians to instrument curved canals. On the other hand it had shown

that nickel-titanium instruments had less cutting efficiency than stainless steel instruments. (4) File manufacturers began introducing nickel-titanium files with larger taper to enhance the cutting efficiency and reduce torsional fracture to deal with these shortcomings. These greater taper instruments provide better efficiency, however increasing the stiffness of the instruments. As a result, clinicians observed canal transportation more towards the outer aspect of the curvature in the apically. (5) The recently introduced nickel-titanium files WaveOne and Reciproc are alleged by their ability to completely clean and prepare root canals with single instrument. These files are made of unique NiTi-alloy called M-Wire that is created by a particular feature of thermal-treatment process. The benefits of this M-Wire and recently the G-Wire NiTi are to increase flexibility of the instruments and improve resistance to cyclic fatigue. These files are used in a reciprocal motion that requires special devices, Due to the fact that the counterclockwise angle is greater than the clockwise one, it is claimed that the instrument continuously progresses towards the apex of the root canal therefore reduce canal transportation.(6)Now Gold Wire technology is a post-machining process that makes files significantly more flexible and resistant to fracture. Investigations of the shaping effect of these new NiTi systems with different design features and manufacturing process are important for understanding how differences and recent advances affect their performance.