Contrary to what many people think, wisdom teeth do not usually cause the other teeth in the mouth to shift. But, if you feel like your teeth may be shifting, they probably are. Here’s why:
Genetics: Even if you are born with straight teeth, if your genes dictate that they will shift at some point, they will,” says New York orthodontist Jacqueline I. Fulop-Goodling, DMD.
Age and Mesial Drift: As we age, the area between the teeth starts to wear away. As this happens, the enamel thins out. The teeth that are affected most by mesial drifting are generally the lower front teeth. Over time, adults notice that these teeth tend to overlap and crowd when they once were straight.

Cavities: When cavities are filled, changes can occur to your teeth and occasionally your bite. However, left untreated, decay can affect the gums and bone, eating away the bone that holds the teeth in place, and loosening them.

Missing Teeth: If a tooth is missing on the bottom, the tooth above it will grow downward since there is nothing there to stop it, and vice versa. Likewise, the teeth next to it will start to move sideways, too

Sleeping on your face: This puts gentle, consistent pressure on the teeth, which can cause them to move.

Grinding: Grinding forces the lower jaw forward and puts tension on the upper teeth. The continual thrusting affects the position of the upper arch, pushing it out of alignment.

Gum Disease: When you lose bone, your teeth lose support. In addition to becoming loose, they are likely to shift.