The Pattern of the Mineralization of Enamel

Voluminous literature on the subject of enamel mineralization has been reviewed and published recently.1. 2 Therefore, the author will not attempt to cite again the numerous individual contributions of the many investigators in this area. An evaluation of the past studies leads the reader to the conclusion that at least two general concepts of enamel mineralization have been developed and appear in the literature today. One concept postulates that mineralization of the enamel follows the pattern of formation of the enamel matrix from the dentino-enamel junction peripherally.1-12 A second concept of enamel mineralization suggests that enamel matrix formation and final mineralization are separate processes, the latter not occurring until after the former is complete.'3-22 This latter concept indicates that calcification of enamel matrix begins at the cusp tips and proceeds cervically in a direction perpendicular to that of incremental deposition of the matrix. Textbooks23' 24 have adhered to the principles of the latter concept, stating that a primary influx of mineral salts occurs during matrix formation and that a secondary calcification process, in which three-quarters of the ultimate mineral content appears, occurs after matrix formation is complete. This secondary mineralization process, termed "maturation," is said to proceed non-incrementally from the tips of the cusps to the cervical region and at right angles to the long axis of the tooth. Recently extensive investigations utilizing fluorescence and polarizing microscopy,' electron microscopy,25' 26 isotopes,27' 28 and microradiography,2, 8-12 have revealed new and convincing evidence confirming the earlier beliefs3-5 that enamel is mineralized from the dentino-enamel junction peripherally in the same or a similar pattern as that of matrix production. A recent study of the birefringence of developing enamel29 has confirmed the microradiographic findings of a gradient of mineral concentration from the dentino-enamel junction peripherally. It is difficult, however, to evaluate the recent information in respect to whether or not total pre-eruptive mineralization has been accounted for. Whereas the autoradiographic and microradiographic techniques have shown clearly the relative distribution of mineral, they have not quantitatively assessed mineral content. These latest investigations have not, therefore, ruled out a secondary mineralization or maturation of enamel which has been postulated from quantitative chemical analysis of developing enamel.'8 The present studies were carried out in an effort to determine the amount and dis-