Write a note for the tooth fairy explaining the problem and leave that wrapped in a tissue or envelope under the pillow. (Makes it easier to find and extract it in order to insert cash and put it back )
This happened to both of my DS (one of them swallowed his tooth). I used to get them to draw a picture of the tooth so the toothfairy would know what she was looking for (!)and they would put that under their pillow. Good idea Janh re the envelope / wrapping in tissue. I can remember spending about 20 mins fishing around under pillows, duvets etc for DS1's picture when he was 6 and a very light sleeper!
For future ref: tooth fairies don't come on the first Saturday of the month - because everyone knows that's when they have the tooth fairy party. Esp useful when babysitter forgets to tell you dd2 tooth had fallen out & she put it under her pillow.
DH is still amazed I thought that one up so quick at 6:30am after a night out
Actually, dd1 (9) lost her 9th tooth yesterday & the tooth fairy was watching the election results & forgot!!! Suddenly remembered at 6:00 this morning - luckily she was still asleep. As you can see, my fairy skills are not too good.
BTW ours also put tooth in little bag on bedside table - saves all that rooting around under pillows.