His teeth have been worn due to over-biting occlusion and habit of clenching. All of the lower front teeth have a similar length due to excessive wear. Instead of having gently rounded contours, their biting edges are frequently worn straight across.
His uppers is chipping, it is another phenomenon that’s often seen with teeth that have worn down. Enamel is a strong dental tissue but it is also brittle. They are worn down to very thin, sharp edge, tiny fragile bits of it will tend to chip off.
Full ceramic crowns are utilized to restore his teeth (re-establishing the normal thickness and length, function and appearance) and occlusion. Mr. Alan Berndt is very happy with the result: completely new smile. You can see the happiness on his face in the photo with Dr. Pham Thanh Cong.
Thanks Alan for the comment