The effect of post preparation on the apical seal of endodontically treated specimens was studied. The canals prepared in bovine bone were instrumented and obturated using five obturation techniques: the silver point technique, the lateral condensation of gutta-percha technique, the warm vertical condensation of gutta-percha technique, the Hygenic Ultrafil injection system and the Obtura technique. In addition to these five control groups, the five experimental groups were also subjected to post preparation. In the latter group, the gutta-percha was removed with an engine-driven root canal reamer 48 hours after obturation. Both the control and experimental groups were suspended in a 0.5 per cent crystal violet solution for 48 hours. After dye penetration, the specimens were immersed in liquid nitrogen and then split longitudinally. Linear measurements of the resultant apical dye leakage were determined by image processing. For each obturation technique, all specimens in both the control and experimental groups were recorded if they showed leakage. Using Fisher's exact probability test, it was shown that there was no significant difference between the obturation techniques used.