Two phases of the bone mineral as revealed by the high resolution scanning electron microscope on ion-etched bone surfaces and as seen on surfaces untreated and chemically etched.

Recently reported uses of the technique of high resolution scanning microscopy of polished and Argon ion-etched bone surfaces have revealed that, at the ultrastructural level, the bone mineral is spatially arranged in a network of twisted, closely packed segments containing globular and cylindrical components. The ion-etching technique, which preferentially removes organic and less dense material from the bone surface, has been subsequently used by the present authors for detailed screening of a quantity of human cortical and trabecular bone of different age and maturity during which it has been found that apart from this "structured bone' containing twisted segments, the mineral is also organised in another regular form, the "lining bone', which has the appearance of solid, smooth and dense slabs or sheets lining active bone surfaces and bone cell lacunae and canaliculi. In the present study, in order to exclude the possibility that these two newly described phases of the bone mineral microskeleton are results of an etching artifact, their SEM appearance in 14 Argon ion-etched human bone specimens from individuals aged 11 post-natal days to 79 years was compared in various compartments to that seen on surfaces which were untreated, just polished or etched by hot NaOCl. The results have shown that both the structured and lining bone are genuine features since although the best results for their clear and reliable distinction were achieved by the ion-etching technique, these images could also be recognised on bone surfaces which were untreated or treated in a different way.