After work one day Elie is ordered to report to the dentist after he finishes his meal. Elie tells the guard that he "doesn't have a toothache." He has to report to the dentist anyway and when he arrives the dentist and asks him what the dentist intends to do. The dentist informs Elie that he is simply going to pull out his crown. Elie avoids this by telling the dentist that he is ill. He asks the dentist to wait a few days. The dentist says okay, but tells Elie to come back in a few days and "don't wait for me to call you!"
Elie actually went back a week later with the same excuse and the dentist once more granted him a reprive. Elie then learns that after the second visit the dentist's office has been closed and the dentist was arrested.
Elie manages to save his gold crown in Chapter Four of Night by feigning illness. After being forced to go to a medical checkup which is followed by a mandatory visit to the dentist, Elie realizes that this appointment is a smokescreen. The dentist is not checking teeth for decay, but rather to see if there are any gold fillings that can be removed.
Once he figures out that his tooth is going to be extracted, Elie quickly devises a plan to escape this fate. He tells his dentist that he has a fever and doesn't feel well, and he requests that the extraction be postponed a few days. The dentist agrees, but orders him to return when he feels better. Elie recycles this excuse when he has to return, buying himself just enough time. The dentist office is closed shortly thereafter, and the dentist himself is sentenced to hang.
Those are great answers!
Elie avoids this by telling the dentist that he is ill.