A 9-year-old boy requires complex dental care. Objective examination revealed chalky spots with lustrous surface on the vestibular surfaces of the 22, 21, 11, 12 teeth, as well as on the tubercles of the 26, 26, 46 teeth. The affected teeth are not sensitive to thermal and chemical stimuli. The child has a previous history of rickets. He lives in a locality where the fluoride concentration in drinking water is 0,5 mg/l. What is the most likely diagnosis?