yes it's true that root canals can be done in one visit but its not just because of the technology but more so because of the infection of the root, shape , calcification and number of the canals. Some teeth will be treated best in multiple visits . Either way , its best to build up the root canal treated tooth to seal off the canals and prevent bacteria from reinfecting the canals. And yes, the rate of success of root canals are very high nowadays.
Dr.Valerie P. De Leon