This is a spectacular case with Imperfect Amelogenesis, a genetic defect in enamel formation.
These defects are not rare, but it is true that they tend to occur locally (in molars and incisors) and with less intensity.
This is an orthodontic treatment (in which the two retained upper canines were placed in the mouth and space was opened for the two absent upper lateral incisors), but which also required the participation of the periodontist (gums), oral surgeon (to leave visible the 2 upper canines retained), endodontist and prosthetist (for crowns).
The treatment has changed the patient not only her teeth, but her life itself!
If for some reason you are especially interested in this case, you can consult it in an expanded way in the publication “Amelogenesis imperfecta: diagnosis and resolution of a case with hypoplasia and hypocalcification of enamel, dental agenesis and skeletal open bite” (Quintessence Int).