Stress generation during self-adjusting file movement: minimally invasive instrumentation.
BACKGROUND
Although nickel-titanium (NiTi) rotary instruments may produce a well- tapered root canal with a low tendency of aberrations, these are generally perceived to have a high fracture risk during use and may produce significant forces on root dentin during instrumentation, which may induce a dentinal defect or crack in the apical part of the root. This study compared mathematically the stress generated by the Self-Adjusting File (ReDent-Nova, Ra'anana, Israel) with conventional rotary instruments during the movement of 3 NiTi endodontic file designs in a curved root canal.


METHODS
Stresses were calculated using finite element analysis. Three file designs with tip size ISO #20 were used in this study. Finite element models of ProFile #20/.06 (Dentsply Maillefer, Ballaigues, Switzerland) (a constant tapered shaft), ProTaper Universal F1 (Dentsply Maillefer) (a progressively changing taper shaft), and SAF 1.5 mm (a mesh shaft) were activated within a curved root canal model. The stress generations resulting from the simulated shaping movement were evaluated in the apical root dentin area.


RESULTS
The SAF induced the lowest von Mises stress concentration and the lowest tensile principal stress component in root dentin. The calculated stress values from ProTaper Universal F1 and ProFile #20/.06 were approximately 8 to 10 times bigger than that of the SAF.


CONCLUSIONS
Stress levels during shaping and the susceptibility to apical root cracks after shaping vary with instrument design. The design of the SAF may produce minimal stress concentrations in the apical root dentin during shaping of the curved canal, which may increase the chance of preservation of root dentin integrity with a reduced risk of dentinal defects and apical root cracking.
Department of Conservative Dentistry, School of Dentistry, Pusan National University, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
Hyeon-Cheol
HC
Kim
Sang Yup
SY
Sung
Jung-Hong
JH
Ha
Michael
M
Solomonov
Jung-Min
JM
Lee
Chan-Joo
CJ
Lee
Byung-Min
BM
Kim
D017076:Computer-Aided Design; D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D003804:Dentin / Q000033:anatomy & histology; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D009068:Movement; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry; D019227:Tooth Apex / Q000033:anatomy & histology; D055114:X-Ray Microtomography / Q000379:methods
D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
Finite element analysis; Self-Adjusting File; nickel-titanium rotary file; root integrity; stress generation; vertical root fracture