The aspect of ultrastructural changes of the osteoblasts and surface areas of alveolar bone appearing in experimental tooth movement.

Molars of mature Wistar rats were moved experimentally by orthodontic elastic for four days. Then, the aspects of ultrastructural changes of the osteoblasts and structure of the alveolar bone surface which appeared in experimental tooth movement were studied. The following results were obtained. 1) These osteoblasts are classified into three groups according to their position. 2) The most active response to the orthodontic force is exhibited by the second group of cells with the ability of rapid production of abundant acid polysaccharide; i) Abundant rough surfaced endoplasmic reticulum with markedly dilated cisternae. ii) Well developed Golgi apparatus and electron opaque granules with a limiting membrane are found in the cytoplasm. Large granules are frequently seen to be secreted out of the cell. iii) The mitochondria are of large size and round shape with well developed cristae. 3) The surface of the new alveolar bone is covered with a belt-shaped structure consisting of small dense spherical-shaped structures. 4) Osteoclasts are rarely seen, but the original function of the cells appears to be almost inactive.