The apical border plaque in severe periodontitis. An ultrastructural study

This study concerns the apical border (AB) plaque in relation to severe forms of periodontitis (SP), including juvenile, post-juvenile, and rapidly progressing periodontitis. Twenty-four (24) teeth from 16 patients with SP were examined by transmission electron microscopy (TEM). The AB was not discrete, with islands of bacteria in the so-called plaque-free zone (PFZ). Coronal to the AB the established plaque consisted of a layer of Gram-positive cocci and ghost cells and a superficial layer mainly of Gram-negative morphotypes, including cocci, rods, filaments, fusiforms, and spirochetes. The most apical apparently intact organisms in the PFZ were in bacterial islands or in isolation and were predominantly Gram-negative cocci and rods, with ghost cells in abundance. Ruthenium red, alcian blue-lanthanum nitrate, and safranin O were used to label matrix polyanionic macromolecules, and periodic acid (thiosemicarbazide) silver proteinate for intracellular polysaccharide (IPS). The matrix components were mainly fibrillar. Many intact bacteria exhibited extracellular polysaccharides or glycocalyces associated with their cell wall, and cytoplasmic IPS granules. The latter varied in distribution and were evident even in the most apically advanced intact microorganisms. The results indicate that IPS and some matrix features of the apical border plaque in severe periodontitis in certain aspects resemble those of sub-contact area plaque on children's teeth, in health or associated with early chronic gingivitis, and with those in chronic adult periodontitis. They also suggest the establishment of acidic regions in the microniche at the bottom of the periodontal pocket in the various forms of periodontitis differing in rate of progression. It was concluded that there was a limited range of intact bacterial morphotypes in the apical border plaque in severe periodontitis, similar to those in chronic adult periodontitis.