CONCERNING THE VITALITY OF THE CALCIFIED DENTAL TISSUES. II

THE PERMEABILITY OF ENAMEL

¹ Laboratory of Oral Histology and Embryology, School of Dental and Oral Surgery, Columbia University, New York City

Evidence has been advanced that stains can penetrate normal enamel from within, through the agency of the dental lymph but not from the surface of the tooth. Only as a result of certain changes such as incipient carious lesions in human teeth or the changes caused by the action of dental cement on the enamel of dogs does the enamel become permeable from without-inward. This may suggest that dental cements have a similar decalcifying effect on the enamel under orthodontic bands, crowns, etc.; a subject which is being investigated. The action of dental cement on the surface of the enamel in dogs appears to break down the surface impermeability, permitting stain particles to be carried into the enamel and dentin by the dental lymph. The stain was also demonstrated in cracks in human enamel but these are considered abnormal. It appears that enamel possesses the function of limiting the dental lymph to the tooth thus preventing its escape, just as the epidermis prevents the exudation of blood lymph.

Normal enamel seems to possess a protective function similar to that of skin; in teeth of dogs and young persons it is permeable from the dentino-enamel junction up to the outermost zone of the enamel but not from without-inward, thereby classifying enamel as a unidirectional permeable membrane. The establishment of the impermeability of enamel from without-inward seems to preclude the possibility of post-eruptive calcification of normal enamel by means of a deposition of mineral salts present in the saliva.