68 Evaluation and Management of Cleft Lip and Palate Disorders

Abstract

The palatal shelves are initially separated by the developing tongue. Growth of the mandible is associated with inferior displacement of the tongue, which allows the palatal shelves to migrate superiorly and assume a horizontal orientation. The "shelf elevating force" that causes the upward motion of the shelves is believed to be mediated by a process involving mesenchymal proliferation and growth factor-induced changes in local extracellular matrix, including hydration of hyaluronic acid in the tips of the shelves. 5,6 If fetal development and mandibular growth do not proceed normally, the tongue does not descend and the palatal shelves cannot migrate superiorly and medially, despite the shelf elevating force. The resulting malformation can result in the Pierre Robin sequence (micrognathia, relative macroglossia, and U-shaped cleft palate) (Fig. 68.3). 7 Fig. 68.1 The developing human face at 5.5 weeks of gestational age. The primary palate is formed by fusion of the paired medial nasal prominences (a). The lateral nasal prominence (b) becomes the nasal ala. The maxillary process (c) forms the upper lip segments lateral to the philtrum. The mandibular process (d) becomes the mandible.This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.