What is the probability of having more than four wisdom teeth?

Although most people have four wisdom teeth, it is possible to have more or fewer. Absence of one or more wisdom teeth is an example of hypodontia. Any extra teeth are referred to as Supernumerary teeth.

In dentistry, hyperdontia is the condition of having supernumerary teeth, teeth which appear in addition to the regular number of teeth. The occurrence of hyperdontia ranges from 0.1% to 3.8% in various populations.

https://en.wikipedia.org/wiki/Supernumerary_teeth

My father (who majored in Physical Anthropology once upon a time) said that the trait of having more than four wisdom teeth is a trait that isn't very rare, but isn't very common either. He also said that it is most common in Australian Aboriginies. He said all of this when he found out that I have six - count 'em, six - wisdom teeth. Which the dentist said will probably all have to come out in one swell foop. *ouch!*

This is called Supernumerary teeth and while it is not common, it is possible. While it is uncommon, it is also possible for Wisdom teeth to grow back after they have been extracted.