Inheritance factors play an important part in many developmental disturbances. In some instances symptoms may be present at birth; in others they may develop during childhood or adolescence. Those disturbances which have their onset in adolescence produce) in general, dental changes which are less severe than do those which are congenital. The dental disturbance may be manifested mainly by faulty dental structure, interference with normal eruption of the teeth, and malocclusion. Most of the developmental disturbances which have an effect upon dentition are those which involve the skeleton. More rarely the dental defects may be of ectodermal origin) of which the most common is probably ectodermal dysplasia. Osteogenesis Imperfecta (Fragilitas Ossium) Osteogenesis imperfecta, which is a disturbance of mesenchymal development, is primarily characterized by brittle bones and may be associated with blue sclerae and deafness. The disease may be hereditary or non-hereditary; the etiologic factor is probably some inherent defect in the germ plasm, which may be hereditary or sporadic. Any disturbance of dental development which might be present would depend largely upon the time of appearance of the symptoms, and would occur in the fetal or infantile cases. The dental abnormality most often seen is very similar to dentinogenesis imperfecta (hereditary opalescent dentin), a condition which may be peculiar to the teeth. It has been described by Hodge and co-workers (1), Roberts and Schour (2), and others, and is characterized by an amber color of the teeth, absence of pulp chambers and canals, and imperfectly formed dentin. Reference to the yellowish or amber color and translucency of the teeth in osteogenesis imperfecta has been made by Colyer and Sprawson (3) and by Mittelman (4). Becks (5), who made histologic studies of tooth structure in a case of osteogenesis imperfecta, found a poorly calcified granular dentin and absence of pulp canals and odontoblastic processes. The dental roentgenogram shown in Figure 1is that of an eight-year-old girl who at eleven days of age had experienced the first of many fractures of the bones, and also had blue sclerae. This case was included in a series of 40 cases of osteogenesis imperfecta reported by Bickel and coworkers (6), but the dental findings were not described. The anterior teeth had a translucent appearance and were of light amber color. The crowns of the teeth were of normal size, and the premolars present were undergoing premature eruption, probably as a result of early loss of the primary molars. The roentgenogram revealed congenital absence of the two upper left premolars. The bone of both jaws was slightly osteoporotic. The typical developmental pattern which is followed in dentinogenesis imperfecta is in evidence. In the incisor and first molar teeth, which are the earliest to undergo complete formation, the pulp chambers have been replaced completely by dentin, and the pulp canals, particularly of the lower incisors, are almost completely obliterated.