Single-File Technique Series
The introduction of nickel-titanium (NiTi) rotary file systems has resulted in a markedly progress on the mechanical preparation of the root canal space. NiTi instruments offer many advantages over conventional stainless steel files such as flexibility and cutting efficiency. Furthermore, NiTi instruments maintain the original canal shape during preparation and have reduced tendency to transport the apical foramen. However, the current technology for mechanical preparation - rotary NiTi files - have failed in debriding oval-shaped canals, leaving untouched fins or recesses on the buccal and/or lingual extensions. This untouched recesses may harbor unaffected residual bacterial biofilms and serve as a potential cause of persistent infection and poor treatment outcome. Besides, as these techniques also require the use of numerous instruments to enlarge the canal to an adequate size and taper, they are relatively time and cost consuming.
The newly developed reciprocating NiTi files are made of a special NiTi alloy (M-Wire) and are claimed to be able to mechanically prepare the root canal space with only one instrument. These files area available in different sizes, indicated to be used according to the initial canal diameter. Initial reports using these instruments in extracted teeth have shown that they can debride the root canal space similarly to conventional multi-instrument rotary systems.
Several methodologies were developed to evaluate the shaping ability of NiTi systems, including simulated root canal models, serial sectioning technique, and radiographic comparison. These methodologies have been successfully used for many years; however, some inherent limitations encouraging the search for new methods able to produce improved results. The development of X-ray micro-computed tomography (µCT) has gained increasing significance in the study of dental tissues. µCT offers a noninvasive reproducible technique for three-dimensional assessment of the root canal system and it can be applied both quantitatively and qualitatively.
The purpose of this single-file technique series is to provide some material for educational purposes which, in summary, shows that is the root canal anatomy that dictates the result of the instrumentation procedure and not the type of instrument or system used. Besides, it calls the attention to the importance of the irrigation during root canal preparation.
Click here to download an editable Power Point file with all pictures and movies 
Mesial root of mandibular molar - The 3D model in GREEN indicates the original root canal anatomy. The 3D model in RED indicates the root canal modified after preparation with a single-file system superimposed to the original canal.
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