Figure 4. Increasing severity of degradation within hybrid layers. (a–e) A series of TEM micrographs, taken from demineralized, stained sections of the other parts of the control teeth of the three clinical subjects, showing an increasing severity in the degradation that occurred within the hybrid layers after 6 mos of intra-oral functioning. In (e), most of the collagen fibrils within the hybrid layer have degraded, and only loose strands of microfibrils remain (arrow). (f) An undemineralized, unstained, silver-impregnated section depicting, from a different part of the control tooth, the electronlucent (white), silver-free zone within the hybrid layer (open arrow). These white zones probably corresponded to the regions in Fig. 4e, in which the collagen fibrils have degraded into gelatin strands. Further degradation of the denatured gelatin into polypeptides and amino acid residues could have resulted in the leaching of these smaller molecules out of the hybrid layer, with the resultant empty spaces being infiltrated by the silver deposits.