A 35-year-old female patient has complaints of cosmetic defects of the front upper teeth crowns. The defects have been increasing for the last 10 years. The patient suffers from unpleasant sensations when brushing her teeth, and when chemical stimuli are applied. Objective examination revealed defects localised in the enamel of the front upper teeth vestibular surface. The defects are oval, saucershaped, and have clear margins. Probing and cold stimuli sensitivity test resulted in positive reaction. Make the diagnosis.