Extaro 300

After approval by the institutional ethics committee of Saint Joseph University, Beirut, Lebanon (USJ-2017-55), 85 lower premolars, extracted for reasons unrelated to the study, were cleaned using an ultrasonic insert (1S, Satelec Acteon Group, Mérignac, France) and stored in 0.1% formocresol. Teeth were inspected under an operating microscope (Zeiss Extaro 300, Oberkochen, Germany) at x25 magnification to eliminate teeth with cracks or advanced external resorption. Mesiodistal and vestibulolingual X-rays were taken (Sopix, Satelec Acteon Group, Merignac, France) to discard teeth with treated canals, pulpal calcification, or internal resorption. Cone beam computed tomography (Newtom VGI, Verona, Italy) (CBCT) was performed, and only teeth with mature apices and a single oval canal with a moderate curvature of 15 to 22 degrees according to the Schneider technique, were included in the study [18 (link),19 (link),20 (link)]. Finally, 30 mandibular premolars were selected. Access cavity was prepared using an 856 diamond bur (Komet Italia SRL, Milan, Italy) with a high-speed handpiece under running water under an operating microscope, and a size #10 k-file (Dentsply Sirona, Ballaigues, Switzerland) was introduced to verify patency. This study followed the CRIS guidelines for in vitro studies, as discussed in the 2014 concept note [21 (link)].

The crown portion of each tooth specimen was cut off under a dental operating microscope (Extaro 300, Zeiss, Jena, Germany). Roots were sectioned perpendicularly to its long axis in equal proportions with a low-speed handpiece diamond disc into the coronal third, middle third, and apical third, respectively. After dehydrating and processing the root surface with gold palladium, the sectioned specimens were viewed under a scanning electron microscope (SU3500, Hitachi Ltd., Tokyo, Japan) in 500× and 2000× magnifications to examine the remaining smear layer. An evaluation was made to evaluate the smear layer removal effectiveness by recording the dentinal tubule exposure quantity as well as the presence, quantity, and distribution of the smear layer based on the score described by Hulsmann et al. [46 (link)]. The score was graded on a four-point scale as follows: score I = dentinal tubules completely opened, score II = more than 50% of dentinal tubules opened, score III = less than 50% of dentinal tubules opened, score IV = all of the dentinal tubules covered with smear layer. Two observers were calibrated, and a blind evaluation was performed by examining the images independently. The level of agreement between the two observers was assessed with the kappa test.