Introduction: To minimize the loss of tooth structure, the conservative access cavity (CAC) preparation was suggested where preserving the peri-cervical dentin (PCD) would achieve this goal. The aim of the current study was to assess the impact of the conservative access cavity on the microhardness of controlled memory nickel titanium rotary files in comparison to the traditional access cavity (TAC).

Materials and Methods: Twenty- eight files sets of Elephant files (ElephantDent, China) and Twenty- eight sets of EdgeFile X7 (EdgeEndo, USA) have been used to prepare the mesial canals of 144 mandibular first molars. Four sets from each type were used as control groups and 12 sets were grouped according to the access cavity type into CAC and TAC then subgrouped equally according to the number of prepared canals into 3, 6 and 9 subgroups. The molars were randomly allocated into two treatment groups (n=72) TAC and CAC groups. The Elephant and Edge 30/0.04 rotary files were subjected to Vickers hardness test to assess the microhardness changes in the files.

Results: The effect of the access cavity designs on the microhardness in the edge and elephant files were non-significant in all the groups (p>0.05). The microhardness changes were non-significant after preparation of the three, six and nine canals in both the TAC and CAC groups. Elephant files presented a higher significant microhardness value in all groups.

Conclusions: The access cavity designs and the number of prepared canals had no significant effect on the microhardness of the rotary nickel titanium files.