A 28-year-old female patient consulted a dentist about pain caused by thermal and chemical stimuli in the mandibular and maxillary teeth. Objectively: in the cervical zone of mandibular and maxillary incisors and canines there are irregularly shaped defects of hard dental tissues within the amelodentinal junction in form of tissue softening. In this clinical case a dentist will find it difficult to differentiate between the following diseases: