This study compared the shaping ability of nickel-titanium rotary files with different rake angle and radial land.

The nickel-titanium files used in this study were Profile(Dentsply, Maillefer, Ballaigues, Switzerland), Hero 642(Micromega, Besancon, France), and K3(SybronEndo, Glendora, Ca, USA) file. Resin blocks substituted for root canals. 36 resin blocks were divided into 3 groups with 12 canals each. The time for canal preparation was recorded. The images of pre- and postoperative resin canal were scanned and those were superimposed. Amounts of canal deviation, total canal widths, inner canal widths, and outer canal widths were measured at apical 1, 2, 3, 4, 5, 6, and 7mm levels.

The amount of canal deviation was the smallest in Profile group, and the time for canal preparation was the shortest in Hero 642 group. K3 group resulted in competent characteristics in both measurements. Positive rake angle seemed to result in fast shaping of root canal and radial land guide the instrument in center of the canals and around curvatures. Radial land also tended to reduce the sense of screwing into the root canal.

The proper selection of the nickel-titanium file based on the knowledge about file design is needed for the safer, simpler and faster root canal therapy.

Citations

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• Comparison of screw-in effect for several nickel-titanium rotary instruments in simulated resin root canal
  Jung-Hong Ha, Myoung-Uk Jin, Young-Kyung Kim, Sung-Kyo Kim
  Journal of Korean Academy of Conservative Dentistry.2010; 35(4): 267.     CrossRef
• Influence of root canal curvature on the screw-in effect of nickel-titanium rotary files in simulated resin root canal
  Ji-Young Son, Jung-Hong Ha, Young-Kyung Kim
  Journal of Korean Academy of Conservative Dentistry.2010; 35(5): 374.     CrossRef
• Comparison of shaping ability using various Nickel-Titanium rotary files and hybrid technique
  Jung-Won Kim, Jeong-Kil Park, Bock Hur, Hyeon-Cheol Kim
  Journal of Korean Academy of Conservative Dentistry.2007; 32(6): 530.     CrossRef
• Comparison of shaping ability of rotary Ni-Ti file systems used by undergraduates
  Mun-Seong Kang, Hyeon-Cheol Kim, Bock Hur, Jeong-Kil Park
  Journal of Korean Academy of Conservative Dentistry.2006; 31(1): 1.     CrossRef
• Comparative study on morphology of cross-section and cyclic fatigue test with different rotary NiTi files and handling methods
  Jae-Gwan Kim, Kee-Yeon Kum, Eui-Seong Kim
  Journal of Korean Academy of Conservative Dentistry.2006; 31(2): 96.     CrossRef
• Comparison of shaping ability between various hybrid instrumentation methods with ProTaper
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  Journal of Korean Academy of Conservative Dentistry.2006; 31(1): 11.     CrossRef

The purpose of this in vitro study was to compare the effects of root canal debridement following rotary Ni-Ti instruments with positive versus negative rake angle. Seventy sound, extracted human anterior teeth & premolars were randomly divided into four groups. The used rotary instruments were Ni-Ti HERO 642(Micro-Mega in France, 20 specimen), Ni-Ti ProFile(Maillefer, Ballaigues, Switzerland, 20 specimen), stainless steel engine reamer(Mani, Matsutani Seisakusho Co.,Japan, 20 specimen) and negative control group(10 specimen) was only extirpated with barbed broach(Mani, Matsutani Seisakusho Co.,Japan)

Group 1 & 2 teeth were prepared to a #40 at the apex followed by 1 mm using crown-down technique. Group 3 teeth were instrumented from a #15 to a #40 in sequential order. After preparation and final irrigation, the roots split longitudinally into a bucco-lingual direction. Root halves were cross-sectioned in apical third portion again. all root specimens were prepared for SEM investigation & photographed. Separate evaluations were undertaken for smear layer on prepared walls with a five score-index for each using reference photograph in root halves. the penetration depth of smear layer into dentinal tubules was also estimated in the other halves. the following results were obtained :

1. Smear layer was observed on all the prepared walls with three experimental groups except negative control group

2. Smear layer characteristics

1) HERO 642 groups showed snowy & dusty appearance & were observed only few some dentinal tubuli open on the prepared walls, and the penetration depth of it into dentinal tubules may be 1-2 µm thick.

2) ProFile groups showed shiny & burnished appearance & complete root canal wall covered by a homogenous smear layer with no open dentinal tubuli and penetration depth of it into dentinal tubules may be 1-2 µm thick.

3) Engine reamer groups showed obviously file's passed tracks on the prepared walls & were observed complete root canal wall covered by a homogenous smear layer with no open dentinal tubuli.

The results revealed that a completely clean root canal could not be achieved regardless of positive & negative rake angle, which is in accordance with the majority of studies on root canal cleanliness.

In conclusion, throughout irrigation with antibacterial solutions or chelating agents is recommended to remove the smear layer on prepared canal walls.

Citations

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• Comparative evaluation of dentin volume removal and centralization of the root canal after shaping with the ProTaper Universal, ProTaper Gold, and One-Curve instruments using micro-CT
  Hatice Yalniz, Mehrdad Koohnavard, Aysenur Oncu, Berkan Celikten, Ayse Isil Orhan, Kaan Orhan
  Journal of Dental Research, Dental Clinics, Dental Prospects.2021; 15(1): 47.     CrossRef
• Microorganism penetration in dentinal tubules of instrumented and retreated root canal walls.In vitroSEM study
  Saad Al-Nazhan, Alaa Al-Sulaiman, Fellwa Al-Rasheed, Fatimah Alnajjar, Bander Al-Abdulwahab, Abdulhakeem Al-Badah
  Restorative Dentistry & Endodontics.2014; 39(4): 258.     CrossRef
• Shaping characteristics of two different motions nickel titanium file: a preliminary comparative study of surface profile and dentin chip
  So-Ra Park, Se-Hee Park, Kyung-Mo Cho, Jin-Woo Kim
  Journal of Dental Rehabilitation and Applied Science.2014; 30(2): 121.     CrossRef