Subunit compartments of secretory stage enamel matrix.

Three quarters of the micro-environment of early secretory stage enamel consist of protein and water. The physical arrangement of this enamel matrix is closely related to enamel crystal growth and habit. In the present study, structural components of developing enamel were analyzed using atomic force microscopy, transmission electron microscopy, immuno-ultracryotomy, and electron diffraction. Atomic force images revealed spherical subunits measuring between 108 nm and 124 nm in diameter. Transmission electron micrographs indicated that developing crystals were surrounded by an electron dense coat which may be rich in proteins. Transmission electron micrographs and electron diffraction studies supported a concept in which initial enamel crystals consist of amorphous calcium phosphate and later fuse to hydroxyapatite. Cryo-immuno electron microscopy demonstrated homogeneous distribution of amelogenin epitopes within the entire enamel matrix. The current study suggests an intricate role of protein aggregation phenomena involved in initial enamel crystal growth and habit.