Structural variations in the surface zone of human tooth enamel observed by scanning electron microscopy

The surface zone of human deciduous and permanent enamel was examined following sectioning, polishing and etching. Three main types of surface were where prisms reached the surface, where the prisms were not discernible and those formed by a complex of both types. The aprismatic layers were measured and the percentage of teeth with varying thicknesses at different sample sites was calculated. Thickness of surface aprismatic enamel varied between different tooth types, tooth surfaces and between deciduous and permanent teeth. It is likely that variations in the structure of surface enamel affect caries susceptibility and results of etching and bonding techniques.     

Haemagglutinating activity of Bacteroides melaninogenicus

Haemagglutinating activity was found in 29 out of 59 strains of B. melaninogenicus isolated from human gingival crevices. Erythrocytes of sheep, horse, guinea-pig and rabbit as well as human erythrocytes were agglutinated by the cells. Ag-glutinating activity was destroyed by heat treatment (80 °C, 10 min). Fimbria-like structures were observed in all strains manifesting haemagglutinating activity.