Little attention has been given to the resistance to fracture of  teeth that have been endodontically treated  and  subsequently  restored. This study investigates the impact resistance of maxillary central incisors to simulated trauma. Untreated teeth, teeth treated endodontically, and teeth restored with the use of parallel stainless steel posts were subjected to identical impacts. The absorbed energy values recorded for each group were compared with changes in the size of the endodontic preparation and  the post diameter. Results of the study show that preservation of internal tooth structure and the use of smaller posts in teeth that have been endodontically treated provide maximum resistance to fracture