An 8 month old female child is brought to medical attention because her first four teeth show several discrete, discolored, circumferential bands that show very little enamel. Excessive levels of which of the following may have produced this defect?

Fluoride excess causes direct injury to ameloblasts, leading to inadequate production of tooth enamel. The resultant defect in enamel production causes recessed and discolored rings on the emerging teeth. Other conditions that cause enamel hypoplasia include inadequate levels of calcium, phosphorus, and vitamins A, C, or D, hypothyroidism, and hypoparathyroidism. Jaundice in the newborn period may cause bilirubin deposition in the developing teeth, resulting in pigmented, but otherwise normal teeth. Hyperparathyroidism, with resultant hypercalcemia, will result in osteoporosis, renal stones, and neuromuscular weakness, but no obvious dental changes. Enamel hypoplasia is associated with hypoparathyroidism. Hypehyroidism characteristically produces cardiac and nervous disturbances, weight loss, hypermetabolism, and proptosis, but does not cause enamel hypoplasia. Hypothyroidism, not hypehyroidism, produces enamel hypoplasia. Ref: Russell R.M., Suter P.M. (2012). Chapter 74. Vitamin and Trace Mineral Deficiency and Excess. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.