A catenary analysis of the maxillary dental arch during human embryogenesis.

Human embryos aged six and one-half through 12 weeks were studied to determine the morphological changes in shape of the maxillary dental arch during this early developmental period. Age was determined by crown-rump lengths using the table of Patten ('53). When compared to a reference catenary curve, the embryonic dental arch exhibited several time-linked and directional changes in shape. First, 6.5 to 8 week embryos characteristically had upper dental arches which were wide and anteropos-teriorly flattened and did not conform to the catenary curve. At 7.5 to 9 weeks, the C-shaped dental arch showed more elongation and increasing depth. It was not until weeks 9.5 to 12 that the embryonic dental arch grew enough to conform to the cate-nary curve. It is suggested that the catenary curvature of the postnatal upper dental arch can be first recognized as early as 9.5 weeks of development. On the basis of qualitative observations, the general shape of the human postnatal maxillary dental arch has been described as semiellipsoid (Black, 1894), paraboloid (Angle, lS99), U-shaped, rotund, and horseshoe-shaped (Martin, '14; Hrdlicka, '20). Using occlusal contact points as specific landmarks, MacConaill and Scher ('49) quantitatively indicated the curvature of the " common occlusal line " was typically described by a catenary curve. The catenary is a geometric curve produced by a chain of many links suspended by its ends but otherwise allowed to hang freely and has been conveniently used as a reference standard. Scott ('57a) has suggested that both the embryonic dental lamina and later the dental organs of the human deciduous tooth germs were arranged in the form of a catenary curve. The aims of this study are (1) to determine if the shape of the human prenatal maxillary dental arch is indeed catenary, (2) to describe the temporal sequence in the morphogenesis of catenary arch shape, if it is present, and (3) to correlate arch shape with possible mechanisms in the dynamics of facial growth during early human prenatal development. (20 through 75 mm crown-rump length) were studied (table 1). This series represented stages in tooth development from the presence of the dental lamina to the presence of ten maxillary deciduous dental organs. After fixation in 10% neutral buffered formalin, each embryo was histologically prepared and frontally sectioned at 10 v. Sections were serially mounted and stained either with a Masson triple-stain or with hematoxylin and eosin. The maxillofacial region of each …