A 1-minute application of ferric oxalate reduces dentin hypersensitivity by 97%. Jain et al. (1997) reported that the use of 6% ferric oxalate was the most effective agent in blocking the dentinal tubules. See http://www.islah-mihani.com/Scientific/Articles/Dentin_Sensiitivity...
My dentist/friend used ferric oxalate on one of mine over a decade ago and I remember well the effective relief it provided for the excruciating sensitivity I was experiencing.