Introduction:
To decrease the amount of tooth structure loss a conservative access cavity (CAC) preparation was proposed where preserving peri-cervical dentin (PCD) would achieve that goal. The aim of this study was to evaluate the effect of the conservative access cavity on the surface changes of controlled memory Nickel titanium rotary files in comparison to the traditional access cavity.
Materials and Methods:
One hundred and forty-four extracted mandibular first molars were randomly divided into two treatment groups (n=72). The Traditional Access cavity (TAC) and the Conservative Access Cavity (CAC) groups. Forty-eight file sets of Endo-Edge X7 rotary files (Henry-Schein, USA) have been used to prepare the mesial canals of all the teeth. The edge 30/0.04 rotary files were scanned by the scanning Electron microscope to assess the surface topographic changes in the files after the preparation of three, six and nine canals.
Results:
The effect of the access cavity preparation design on the surface topographic changes in the edge files were non-significant in all the groups (p>0.05). The surface topographic changes were non-significant after preparation of the three and six canals in both the TAC and CAC groups, however after preparation of nine canals the changes were significant in both the TAC (3.25±0.50) and CAC (4.00±0.82) groups.
Conclusions:
1. As the number of prepared root canals increases, the rotary nickel titanium file defects also increases.

2. Both the TAC and CAC designs had no effect on the defects in the rotary NiTi files.