Abstract : It is reported that there is same difference in tenacity among the lots of even same production when the flow test of the root canal filling material of the gutta percha on the market is operated.

 We have operated the root canal filling by the meathod of the NT-condenser with the different lots of the obturation gutta-NT and have investigated the effect of the difference of tenacity on the sealing ability of the apex of root by the dye-stuff permeation test, and have the following results.

 The feeling of operation and the sealing ability of the apex of root among the three kind of lots on the market can not be acklowledged when the temperature control is accurate in the method of the NT-condenser.