Ultrastructural study on human root caries.

Superficial root caries lesions of incisors and premolars of 24 patients aged 52-60 years were studied by scanning electron microscopy and transmission electron microscopy. In the predominantly gram-positive bacteria of the root dental plaque, a great number of corncob configurations were observed. Bacterial infiltration into cementum occurred without any gradient of demineralization and mainly followed the borders between calcified cementum bundles as well as incremental lines. The narrow channels which were filled initially by a single row of gram-positive bacteria broadened progressively with simultaneous destruction of the apatite minerals and the collagenous matrix. Root dentin invasion showed great similarities to coronal dentin with an important gradient of demineralization. In the deep layers, sclerosed tubules contained sometimes rhombohedral crystals. In more superficial layers, bacterial invasion occurred initially in still partially sclerosed tubules. Tubular lumens as well as lateral side branches which had lost their peritubular dentin were filled with gram-positive microorganisms. An important diffuse destruction of the apatite minerals was observed at this stage in the intertubular dentin which still presented typical cross-banded collagen fibrils. The confluence of enlarged dentinal tubules filled by numerous microorganisms led to large bacterial zones with complete destruction of root dentin.