Mesiodistal gradient of mandibular precedence in the developing dentition.

Abstract

In postnatal dental development, there are clear-cut mandibular-maxillary eruption precedences; usually the mandibular incisors tend to precede their maxillary opponents. There is also a mesiodistal gradient of mandibularmaxillary precedence such that maxillary precedence becomes both relatively and absolutely more common in the posterior teeth (H. IsRAEL, A. DAHLBERG, S. M. GARN, and R. KEREWSKY, J Dent Res 46:456, 1967; and H. IsRAEL, S. M. GARN, and R. F. BENITEZ, Arch Oral Biol 13:239-241, 1968). It is not known, however, whether such precedent polymorphisms exist in prenatal dental development and whether they have their origins in the first trimester of existence. To test this possibility, the relative development of maxillary and mandibular deciduous opponents in a series of 52 human embryos, all below 58 mm in crown-rump length, was examined. The developmental status of each tooth was assessed individually and described by a numerical code; the results were incorporated on standard IBM 80-column punch cards. Then for each pair of opponents, dental development was categorized as (1) mandible