What differences exist between a dentist and an orthodontist?

The orthodontist is a dentist, but not all dentists are orthodontists.

Dentist diagnoses and treats problems in the cavity of the mouth.

Orthodontists treat misalignments in the mouth, called malocclusions, such as extra teeth, crowded teeth, congenitally missing teeth, and spacing problems.

Souce: https://www.mcdermottortho.com/whats-the-difference-between-a-dentist-endodontist-and-orthodontist/