1. Pindborg JJ (1947) Odontol Tidskr 55:443–446
2. Stein G, Boyle PE(1959)Arch Oral Biol 1:97–105
3. Reith EJ(1959)Anat Rec 133:75–89
4. Halse A, Selvig KA(1974)Scand J Dent Res 82:47–56
5. Ogura H, Ohya K, Mataki S, Hashimoto K, Kubota M(1984)Tooth Enamel IV, Elsevier, Amsterdam, pp256–260