There are double blind, cross-over studies of tDCS coming out of Europe that seem to show promise in reducing TN pain for extended periods. Specifically, in the studies I have reviewed (all in the last 6 years, with the latest being 2014) the reduction of pain occurs after 5 days or so of once a day, 20 minute treatments. More importantly the average pain reduction (29% to 38% on the pain VAS) seems to "stick" for at least 3 months after stopping the treatment. It reduces the Attack Rate, but not in a statistically different manner vs. sham treatment.
Here is this particular article for interested folks to Google:
Hagenacker et al. Patient-conducted anodal transcranial direct current stimulation of the motor cortex alleviates pain in trigeminal neuralgia, The Journal of Headache and Pain 2014, 15:78
NOTE: Transcranial Direct Current Stimulation (tDCS) should NOT be confused with TMS (magnetic stimulation) tCES (alternating current stimulation) or TENS.) Also, it is approved by the FDA only for exploratory purposes. Thus, you can buy the device, but you are on your own. The electronics are trivially simple, though, so it would be a very cost effective device.
Best regards,
SwedeP