The Origin and Development of the Upper Lateral Incisor and Premaxilla in Normal and Cleft Lip/Palate Monkeys Induced With Cyclophosphamide

Abstract Objective: Cleft lip/palate (CLP) is a common human congenital defect in which the maxillary lateral incisors are often absent, malformed, and malpositioned. The present study was designed to examine the origin of the upper primary lateral incisor relative to the medial nasal process (MNP) and maxillary process (MP) fusion area and to the premaxillary/maxillary (incisive) suture in monkeys. Method: Scanning electron microscopy, histology, skeletal staining, and drying techniques were used to study facial development in embryo and fetal monkey specimens. A teratogenic dose of cyclophosphamide was administered to pregnant monkeys prior to fusion of the MNP and MP and fetuses were examined for CLP. Results: Formation of the anterior maxilla involved fusion of the MNP and MP at stages 14–18. At stages 18–20, the palatal portion of the MNP had formed the medial and lateral incisive mounds. By stage 22, the upper primary lateral incisor has formed within the MP, lateral to the MNP/MP fusion area and to...