My dentist says that 'sensitive' toothpastes build up layers of a dentine like substance which coat any exposed areas of dentine, nerve etc.
I don't know the name of the stuff - but it seems to work!
Thank you Millimole. That makes sense! More than does my first response here, which was directed to an answer from DawnDpt (who also indicated that the paste somehow plugs the holes), which now seems to have disappeared! Where has it gone????? And why???