The validity of simulated root canals for the investigation of the prepared root canal shape.

Summary. Curved root canals from extracted human teeth were prepared using K-type files. The resultant shapes were compared both quantitatively and qualitatively with canals that were formed in polyester clear casting resin and similarly prepared. Moderately curved canals generally demonstrated a funnel-shaped canal preparation. Severely curved canals showed a high incidence of hour-glass shaped preparations. When the proportions of the hour-glass shaped canals from extracted teeth and simulated root canals were compared, there were no significant differences.