XRD Study of NiTi Endodontic Files Using Synchrotron Radiation

Endodontic rotary files are Ni-Ti instruments used for cleaning and shaping dental root canals and, thus, avoiding the spread of dental infections. Their unsurpassed elasticity allows for preparing severe curvatures that naturally occur in human teeth. Nevertheless, they also present a major drawback: fracture. If one of these files breaks inside a root canal, not only might it be impossible to remove it but also, and most significantly, clinical prognosis might be hindered.

In clinical conditions, Ni-Ti files work – and fracture – under flexion/rotation. Published data on fracture focus on two approaches to this problem:

• Mechanical bench assays of different files, either to compare different brands, or different test conditions, or even putative material treatments that may delay fracture. All these assays concentrate on the instruments’ life span generally measured as number of cycles until fracture.
• Numerical calculations based on finite element analysis for a theoretical study of mechanical properties of endodontic files.

Some authors have tried to correlate the above-mentioned approaches. Nevertheless, structural alterations as a consequence of file flexion under controlled rotation remain to be clearly identified and related to available published data.

The present study is focused on two different brand files comparable in geometry (same tip size of 0.35 mm and same taper of .04) but different in their constituent Ni-Ti alloy. ProFile .04(35) files are made of traditional Ni-Ti alloy, austenitic at body temperature, and M-Two .04(35) files, rich in R-phase at 37ºC. Although some published data may be found reporting XRD results, these were obtained with lab sources with limited spatial resolution. Here we present XRD data obtained using synchrotron radiation (beam spot of 0.1 x 0.1 mm) in a non-stress as-received condition and under flexion conditions comparable to the ones found in common clinical practice.