This discoloration could be due to congenital hypothyroidism. Neonatal hyperbilirubinemia (in biliary atresia) is also possible. Other causes include hemolytic disease and cholestasis caused by severe neonatal sepsis. Tetracycline use is a less likely cause (usually affects all teeth equally).
I think the teeth are decalcified and the discoloration could be secondary to decay. Since the front teeth are predominantly involved, i have a strong suspicion of 'sweetened pacifiers' in the etiology. Even sodas ( and i think the child is old enough..since the primary dentition seems to be complete ) can do the same, in fact worse...becos all the acid from the sodas can cause the deminerelisation and then the sugars ( from the soda ), will run the show. Sodas won't have a predisposition for the front teeth. Also if the child has frequent vomiting ( for whatever reason ), then we can have this picture. Another differential would be - Dentogenesis Imperfecta ( seen in patients with Osteogenesis Imperfecta ) I gave tetracycline a thought as well, although this doesn't seem to be a textbook picture of the same. I second the 2 strong possibilities raised by Dr. J.P.C Peper as well.
