Scanning electron microscopy examination of resorbing enamel surfaces in unexfoliated primary molar teeth

We examined unexfoliated primary molar teeth by scanning electron microscopy to study the resorbing internal enamel surfaces. They were fixed in a cacodylate buffered glutaraldehyde-formaldehyde mixture, treated with 2 percent sodium hypochlorite, washed, dehydrated with ethanol and air-dried, before sputter-coating with a 40 nm layer of gold. The examination with a Jeol 6100 scanning electron microscope revealed large areas of enamel resorption, characterized by closely adjoining honeycomb-like lacunae (concavities). In higher magnification, lacunae show enamel with various patterns of resorption: whereas in some regions, only the central portions of prisms are removed; in others, the prism sheath regions are seen below the other enamel structures. Also, regions showing a random pattern of resorption are observed. In addition, lacunae showing resorbing enamel prisms in longitudinal and other orientations are also observed. The results of the present study reveal, therefore, that in unexfoliated primary teeth, the odontoclasts first remove the coronal dentin and then reach and resorb large areas of enamel. Furthermore, the various patterns of resorption support the idea that removal of enamel by odontoclasts depends upon the orientation of enamel structures, rather than of the different degrees of mineralization suggesting that enamel structures do not possess different inorganic/organic composition.