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An in vitro method for comparing the effects of different root canal preparation techniques on the shape of curved root canals.

This study introduced an in vitro model which was designed to observe the effects of instrumentation on the shape of curved root canals. The model may be accurately rotated through 90 degrees allowing reproducible radiographs to be taken from two different angles. The root canals were filled with a radiopaque contrast medium before radiographs were taken. Two-dimensional evaluation of the shape of the root canals, before and after preparation was made on enlarged photographic prints obtained from the radiographs. A custom-made grid was used as a guide for measurement and accurate transfer from the pre- to postpreparation prints. Reproducibility of measurement was within 4 per cent. This method is feasible for quantitative comparison of the effect of instrumentation on the shape of root canals.