This study aimed to evaluate the effect of nano calcium hydroxide application on the fracture resistance of endodontically treated teeth as compared to conventional calcium hyroxide and calcium hydroxide paste with iodoform. Seventy freshly human extracted single rooted teeth were selected. The samples were biomechanically prepared and classified according to the type of the calcium hydroxide dressing into four groups as follows; Group 1; (21 samples) dressed with nano calcium hydroxide( Nano streams company, Cairo, Egypt) , Group 2; (21 samples) dressed with conventional calcium hydroxide with saline (GAMA dental lab, Cairo, Egypt ). Group 3; (21 samples) dressed with calcium hydroxide paste with Iodoform (Metapex) (META, Chungcheongbuk-do, Korea) and Group 4; Control group (undressed). The samples were further classified according to the observation time into: Subgroup A; (7 samples) after one month. Subgroup B; (7 samples) after two months and Subgroup C; (7 samples) after three month. Samples were loaded vertically after the observation periods using Universal Testing Machine until fracture. The results showed that nano calcium hyroxide weakened the endodontically treated teeth more than conventional calcium hydroxide followed by Metapex paste and this weakness increased by time for all tested groups.
It was concluded that all formulations of calcium hydroxide weaken the endodontically treated teeth.