Material and methods: five premolars extracted for orthodontic reasons, with severe differences in their root morphology were selected. The teeth were sectioned at the cementun enamel junction. The canals were abnormally enlarged to a Nº 6 Largo (Maillefer). The roots were double coated with Solithane (Uniroyal Chemicals) and embedded in a 3X2 centimetres block of PL2 (Measurement Group). Cast Ag-Pd alloy (Ney-76) post and core were made for each root. After the insertion of the casts, the blocks were loaded vertically and with a 30 degree inclined load at 30 kilograms (Control samples). The blocks were subjected to stress analysis in a circular polariscope (Photolastic Inc.) and the fringe patterns were recorded with a camera (Olympus Co.) at insertion and at the loading conditions. Then the casts were removed, and a prefabricated post (Mooser system) was cemented in each root and the cores were build-up using the Compcore system (Bisco Inc.) (Experimental group) and the protocol of loading and photography was repeated.
Results: The cast post and core system showed higher stress for each root compared with their respective prefabricated post and resin core system. At inclined loading, the compressive side always registered higher stresses than the tensile side. For each root, no difference in the stress distribution was observed related to the post and core system used.
Conclusions: Stresses distribution in abnormally enlarge root canals is not related to the design features or fabrication material of the post and core system used, moreover, the stress distribution could be related to the root morphology.