why does warm water with salt and pepper take away my tooth pain?

no idea

In water the salt ions split up and those tell the pain receptors to STFU (in this case, not sound the alarms there's salt in the wound) since it reminds it of its internal STFU signal, pepper has capsaicin, more of the same (shuts it up a different way but whatever).

Also time to pull that tooth when you can.

nothing will stop REAL tooth pain

Salt and pepper will kill the germs causing your infection and inflamation.

It's the work of LUCIFER!