A 27-year-old female patient consulted a dentist about pain in the 35 tooth. The pain is caused by cold stimuli and quickly abates after the stimulus is removed. Objectively: in the cervical region of the 35 tooth there is a dental tissue defect within the enamel. The defect has white crumbling edges. Electroexcitability of the pulp was 5 mkA. What is the most likely diagnosis?