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Abstract
The aim of this study is to compare the shaping ability of two rotary Ni - Ti systems and manual stainless steel K - flexofile and also SEM evaluation of two rotary NiTi systems after instrumentation cycles. The mesiobuccal canals of human mandibular molars were preferred to plastic standardized blocks to simulate the clinical situation. root canals with angle of curvatures range between 20{u00BA} and 40{u00BA} degrees and radius of curvature between 4-10 mm were used in this study. The length of the curved part of the canal was considered a factor affecting the performance of the instrument inside the canal, as the stress acting on a canal instrument is highest in the curvature zone for that, the selected range of the length of the curvature was between 6 - 8 mm. Direct digital radiography (Digora system) was used for evaluation the degree of canal straightening by comparing pre and post instrumentation curvature. Although the advantages of high image quality, low radiation dose and precision linear measurements, it has limitation of showing two dimensions only of the root canal. CBCT was used in this study for measurement root dentin thicknesses