That is the number of the last molar on the lower right side. Mine is now in whatever receptacle oral surgeons use for pulled teeth. On episodes of "The Deadliest Catch" I have seen men pull out their own teeth with pliers. I was not that ambitious, or brave. In retrospect, I put up with tooth pain far longer than made sense just to avoid the procedure.
Both Hippocrates and Aristotle wrote about bad teeth. There is evidence that teeth have been pulled out to relieve pain for 2000 years. My dentist's wall gave framed evidence of his training and license. Patients in an earlier time were not so lucky. Perhaps the barber, perhaps a quack with primitive forceps, perhaps simply mom or dad with steely nerves got a hold and pulled. I'm glad modern instruments and medication are available. RIP # 31.