This is where the enamel is abnormal because of a failure in the deposition of the enamel matrix. This may affect a single tooth - or many. The lesions on the tooth may also be single, or there may be multiple lesions on the same tooth.
Damage to the enamel development occurs whilst the tooth is within the jaw, under the gum line. Sometimes the cause can be trauma. This might have been a bite from mum, or an accident during play. Sometimes, inadvertently, the damage might be caused during extraction of a temporary tooth. Another cause, often affecting many of the teeth, might be an episode of fever (or pyrexia) during the developmental phase. Any systemic illness might spark a fever in a puppy or kitten - this could then affect dental development. The classic example of this is Distemper in puppies.