Comparative Study of Three Rotary Instruments for root canal Preparation using Computed Tomography

Cleaning and shaping the root canal is a key to success in root canal treatment. This includes the removal of organic substrate from the root canal system by chemo mechanical methods, and the shaping of the root canal system into a continuously tapered preparation. This should be done while maintaining the original path of the root canal. Although instruments for root canal preparation have been progressively developed and optimized, a complete mechanical debridement of the root canal system is rarely achievable. One of the main reasons is the geometrical dis symmetry between the root canal and preparation instruments. Rotary instruments regardless of their type and form produce a preparation with a round outline if they are used in a simple linear filing motion, which in most of the cases do not coincide with the outline of the root canal. Root canal preparation in narrow, curved canals is a challenge even for experienced endodontists. Shaping of curved canals became more effective after the introduction of nickel-titanium (Ni-Ti) endodontic instruments. Despite the advantages of Ni-Ti rotary instruments, intra canal fracture is the most common procedural accident that occurs with these instruments during clinical use. It is a common experience between clinicians that Ni-Ti rotary instruments may undergo unexpected fracture without any visible warning, such as any previous permanent defect or deformation. Pro Taper Ni-Ti instruments were introduced with a unique design of variable taper within one instrument and continuously changing helical angles. Pro Taper rotary instruments are claimed to generate lower torque values during their use because of their modified nonradial landed cross-section that increases the cutting efficiency and reduces contact areas. On the other hand, the variable taper within one instrument is believed to reduce the 'taper lock' effect (torsional failure) in comparison with similarly tapered instruments. Nevertheless, Pro Taper instruments undergo fracture without warning that is difficult, if not impossible, to predict clinically. Recently, an innovative concept of mechanical root canal preparation, the Anatomic Endodontic Technology (AET) has been introduced. AET was specifically designed to maintain the natural shape of the root canal during preparation. The AET technique was performed with stainless steel instruments used in a 30°reciprocating side-to-side and up-and-down motion. These instruments are stiffer than nickel-titanium rotary instruments and can be easier and with less risk forced towards the root canal walls and the polar recesses during the side-to-side lifting motion. The use of stainless steel instruments in this motion was probably more efficient in following the natural shape of canals and in removing tooth structure. The manufacturer claims that this system is intended to minimize the number of steps and instruments required for effective preparation of root canals. The reciprocating motion of the endodontic instrument has been shown to decrease the impact of cyclic fatigue compared with rotational motion. A reciprocating instrumentation system, (SafeSiders) introduced by Essential Dental Systems was introduced for preparing curved canal to overcome the problem of file separation. It contains a series of non-circular instruments with D-shaped cross section, cutting tip, a patented non-interrupted flat-sided architecture.