Biophysical Analyses of Sequential Bands of Enamel Related to Ruffle-ended and Smooth-ended Maturation Ameloblasts

During amelogenesis in the rat incisor, modulating ruffle-ended (RA) and smooth-ended (SA) ameloblasts are distributed as bands in the enamel organ of the maturation zone. This distribution of the two cell types has been shown to be precisely correlated with a banding of the underlying enamel, as shown by staining and other cyclical indicators (Takano et aL, 1982a,b). Several biophysical approaches have been taken here to characterize the enamel bands sequentially and to determine whether the appearance of such bands is attributable to differences in inorganic composition possibly related to RA and SA. Sprague-Dawley rats were decapitated under ether anesthesia, lower incisors were dissected from surrounding alveolar bone, and enamel organs were wiped from the teeth with moistened gauze. Analyses were performed on either the surface of intact enamel or on individual strips of enamel dissected from the tooth surface, by use of the translucent bands that appear during drying as reference marks for the positions of the overlying cell type. X-ray diffraction (XRD), infrared spectroscopy (IR), x-ray photoelectron spectroscopy (XPS), and wavelength-dispersive electron probe x-ray micro-analysis (WDS) all failed to detect significant differences between analysis areas; data were characteristic of enamel apatite having typical XRD maxima (hkl = 002, 211, 112, 300), IR absorption bands (PO 4 3- and CO 3 2- ), XPS Ca and P binding energies (Ca 2p = 350.5, 346.9 eV; P 2p = 133.7, 132.7 eV), and WDS Ca/P molar ratios (1.33 - 1. 49). It is concluded that discernible differences in Ca and P chemistry in enamel related to RA and SA are extremely small, and that enamel banding may not be solely an intrinsic property of changes in the inorganic component of this tissue but may also be a function of organic matrix effects determined by cumulative cellular modulations during enamel maturation.