| Summary: | The mandible develops prenatally as left and right halves (hemimandibles) that meet at a suture in the anterior midline. This suture normally is obliterated in the first year of life. We describe a 4-year-old girl in whom (A) this suture (symphysis menti) is only partially fused, (B) the primary lower left central incisor is congenitally absent (and also its permanent successor), and (C) there is pronounced ankyloglossia. These midline problems share a common etiology, namely incomplete fusion of the halves of the first branchial arch. No cause is suggested, but the embryological problem seems to stem from inadequate streaming together of the mesodermal cores of the first branchial arches. Similar cases with the dental and bony aspects of this condition should be identifiable in skeletal remains.
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