THE PATTERNS OF GROWTH AND DEVELOPMENT OF THE HUMAN TEETH AND JAWS

¹ The Division of Oral Anatomy, Columbia University School of Dental and Oral Surgery, New York, N. Y.

1. The development of the crown of the tooth must be sharply differentiated from the development of its root. 2. The developing tooth, in its stages of development preceding the formation of its root, should be designated as the crown germ. 3. The locus of initiation of the crown germ varies with different teeth of the dentitions. 4. Wherever the locus of initiation of a particular tooth may be, the crown germ continues its development in that particular site without bodily shifting its location until the crown of the tooth is completed. 5. Instead of changing its position, the crown germ grows eccentrically in all directions, according to its pattern. Its vertical dimensions are increased largely by proliferation deeper within the jaw bone, and partly by apposition of enamel increments in the incisal or occlusal regions. 6. The dental follicle is a very important factor in the growth process of the crown germ. Surrounding the outer enamel epithelium, it grows eccentrically in all directions in anticipation of the growth of the crown germ. 7. Growth of the follicle continues until the maximum space for the completed crown of the tooth is attained. 8. As the follicle grows it steadily resorbs the bone directly adjacent to it. This occurs in all directions including the fundus. 9. The concept that the crown germ moves away from the fundus as it increases its vertical dimension during growth is therefore incorrect. 10. The body of the mandible and the dental process of the maxilla increase their dimensions largely by apposition of bone along the crest. 11. In the embryologic stages and even at the birth stage, there is no evidence of bone along the crest covering the incisal or occlusal surfaces of the crown germs. 12. At the 9 months old period bone is present all along the crest covering the occlusal surfaces of the developing crowns. The addition of bone along the crest, increasing the vertical dimension of the body of the mandible and the dental process of the maxilla, creates the illusion that the developing crowns migrate in the jaw bone. 13. The growth of the crowns of the teeth has its individual pattern as has the growth of bone. They are independent of each other. 14. A retardation of bone growth may influence the positional arrangement of teeth, but not the growth and development of teeth. 15. Synchronization of the growth of bone and tooth development is the important factor for the normal arrangement of teeth in the arch. 16. Migratory movement of teeth occurs only after the dental follicle surrounding the crown has been reduced, resorption of bone adjacent to the follicle has ceased, and the enamel of the crown appears in close proximation to the surrounding bone. The surrounding bone then becomes active, apposition being noted at the fundus as well as in the peripheral regions, simultaneously with the beginning of migratory movement. This may explain the eruption phenomenon. 17. The concept that sutural bone growth increases dimensions by spreading the bone adjacent to a suture, is untenable. 18. Apposition occurs on the outer surfaces of the bones adjacent to a suture. In this way the outer perimeter is steadily enlarged, maintaining the sutural space as growth occurs at the peripheral ends of the bones adjacent to the suture.

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