This study was undertaken to determine the extent of in vitro penetration of E. coli endotoxin into the root cementum of periodontally healthy and diseased teeth. Freshly extracted teeth were washed in distilled water, scaled and divided into two groups of 16 teeth each. Nine diseased and five healthy teeth in the first group were immersed in various concentrations of E. coli endotoxin for 2 to 12 weeks. They were then prepared for indirect immunofluorescence examination after treatment with anti‐endotoxin antibody and rhodamine conjugated secondary antibody. Teeth in the second group were prepared for autoradiographic examination by immersing nine diseased and five healthy teeth in tritium labelled E. coli endotoxin for 2 to 12 weeks. The latter technique also allowed for semi‐quantitative study of the depth of endotoxin penetration by creating facets on the root at various depths after endotoxin exposure. This technique was also used to investigate the strength of endotoxin binding to the tooth surface by brushing for 1 minute and re‐examining the tooth for the presence of endotoxin. Controls included periodontally diseased and healthy teeth. Results of the study showed that (1) endotoxin adheres to the tooth surface without penetration into the root cementum of either periodontally healthy or diseased teeth, and (2) the binding of the endotoxin to the root surface appears to be weak.

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A correlated microradiographic-transmission electron microscopic study examined incipient caries in human enamel from the enamel surface through the body of the lesion. In sections parallel to enamel prisms in the body of the lesion, cross-striations are accentuated as 3–4 μm wide, light and dark bands. In the more radiolucent striations, crystals are reduced in number as well as in length with some showing longitudinal splitting. In sections with prisms cut in cross-section, most crystals exhibit central dissolution except for isometric hexagonal crystals bordering a gap at the prism periphery. Eventually a complete loss of crystals from prism cores occurs. Asymmetric widening of the gap at the prism borders may be associated with the striae of Retzius. Possible causes for differences in the rate of crystal dissolution in alternating striations are discussed.

The effect of a single injection of sodium fluoride (60 mg/kg) on the development of rat molar enamel beneath fluoride‐induced sub ameloblastic cysts was studied by transmission electron microscopy using un decalcified sections. Three bands of altered enamel were identified and defined as the cyst surface band, the hypo plastic band, and the hyper calcified band. The irregular cyst surface band, not previously described, was found to have two components: electron‐dense enamel globules and organic spherules. The electron‐dense globules consisted of small, randomly arranged crystals (confirmed by selected area electron diffraction) occurring within a stippled organic matrix. The organic spherules have staining properties similar to stippled material and lack a crystalline component. They may be a form of organic material being extruded from the underlying developing enamel. The critical role of normal matrix production and ameloblast Tomes’ process Structure on the development of the crystal orientation and rod pattern is discussed.