Abstract: Objective　To investigate the effect and histological analysis of using simple screws to pull the rabbit mandibles.　Methods　Eight New Zealand female rabbits were studied and randomly divided into the left side or the right side of the experimental side. The experimental sides of mandibles were implanted with two fixing screws and one traction screw respectively. When the traction screw was rotated downwards, the cutting bone end was moved into the opposite direction to increase the bone mass, while the control side was not treated. After 20 days of traction, the bone mass of the experimental side was measured. Then, the bone tissue of the experimental side and the control side were taken for histological examination. Histiocytic change of the two each sides was compared.　Results　The bone height of the experimental side increased by nearly 2.5 mm. HE staining showed that the number of osteoblasts on the experimental side (598.5±130.01) were significantly higher than that on the control side (80.75±14.29). Immunohistochemical staining showed that the IOD of the bone morphogenetic protein-2 of the experimental side (0.13±0.011) were significantly higher than that of the control side (0.061±0.013).　Conclusions　Screws could be minimally and effectively increase bone mass. The mechanical force generated by the rotation of the screws can increase the cells viability of the stressed area, and animate the bone formation .

Key words:  Simple screws;　 Traction osteogenesis, 　BMP-2;　Bone formation;　Histological examination