THE RATE OF OSTEOCLASTIC DESTRUCTION OF CALCIFIED TISSUES IS INVERSELY PROPORTIONAL TO MINERAL DENSITY

This study examined the relative ease with which three dissimilar mine ralized tissues from one individual organ were resorbed by osteoclasts in vitro. Cells released from the long bones of prehatch chicks by ag itating fragments of the chopped bones in medium were cultured for 24 hours on slices cut from an Elephas maximus molar so that enamel, dent ine, and coronal cementum were present in hands on the surface of the slice. The resultant pits were measured using a video-rate, line-confo cal reflection light microscope system. Variations in tissue mineraliz ation were characterized by analysis of digital backscattered electron images. The enamel pits were smaller than the dentine and the cementu m pits, but the dentine and cementum pits were not significantly diffe rent from each other. The sizes of the pits correlated with the relati ve mineral densities of the three tissues, showing that the rate of os teoclastic destruction of calcified tissues is inversely proportional to mineral density. This indicates that the initial step in osteoclasi s, the removal of the mineral phase, determines the volume removed and is the rate-limiting step.