ABSTRACT
One reason for endodontic failure is calcified canals. Canals may be calcified radiographically or clinically but are not often completely obliterated. The purpose of this study was to determine the microscopic size of open spaces in clinically and radiographically calcified canals. In this in-vitro descriptive study 18 human extracted teeth including 21 calcified canals were selected and transverse sections were prepared in 0.8-0.9mm thickness and studied using a stereomicroscope. After taking digital photographs of these sections, open spaces dimensions were measured in each section using Auto Cad 14 program. Computerized evaluation of samples revealed varying dimensions of open spaces. Open spaces were observed in most of the canals, specially those with closed orifices. According to varying dimensions of open spaces in calcified canals, practitioners are recommended to be more persistent when negotiating canals with calcified appearances