What is the most common type of dental abnormality and its cause?

Malocclusion. Poor alignment of one's teeth. From just a few teeth out of alignment to a problem where the patient only touches their last 4 molars (right side upper to right side lower and left side upper to left side lower). The rest of their teeth do not touch, no matter how they close their mouth. See photo enclosed.
Wisdom Teeth. In my office wisdom teeth seem to present with the most abnormalities. I have seen a wide variety of abnormalities from 7 roots (1-3 is normal) to obvious visual deformity of the visible part of the tooth and even growing in the wrong part of the jaw. They are also one of the most likely teeth to never form! for the most part, wisdom teeth are as useful as you appendix!.