Mineral Phases in Forming Enamel

Nascent enamel is a three dimensional network of tiny mineral particles, suspended in a protein gel which serves as a template for mature enamel formation.

Objectives: To identify mineral phases present in nascent enamel we have characterized the mineral using XANES microspectroscopy, TEM and polarized microscopy.

Methods: Apical portions of constantly growing murine mandibular incisors, containing the cervical loop, and forming secretory enamel were extracted from freshly sacrificed mice, plunge-frozen in liquid ethane, freeze-dried, embedded in LR-White and polymerized at 4°C. Ultra-thin and semi-thin sections of the incisors were cut longitudinally. Semi-thin sections were stained with toluidine blue and studied with a light microscope in brigth field and polarized light modes. Ultrathin sections were studied using TEM in bright field and SAED modes and using XANES microspectroscopy.

Results: The results of our study demonstrate that the newly formed enamel mineral lacks a long range order, i.e. amorphous, and eventually transforms into crystalline mineral similar to hydroxyapatite. Interestingly, the shape and organization of the nascent mineral particles in the newly formed enamel is the same as in the older layers, suggesting that the shape of the nascent mineral particles is determined prior to their crystallization.

Conclusion: Initial enamel mineral is transient amorphous calcium phosphate (ACP) which transforms into apatitic phase. Mineralization via transient amorphous phases has been reported in a number of biomineralization systems including bone. The discovery of transient ACP in forming enamel furthers the notion that this biomineralization strategy might be universal. These findings significantly improve our understanding of basic mechanisms of biominralization in enamel and can provide new insights for the development of novel nanostrucured bioinspired materials.

Supported by grants from NIH/DE016703 (EB), NSF/CHE-0613972 (PG) and DOE/DE-FG02-07ER15899 (PG).