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| Effect of stress shelter for internal fixation of mandibular fractures in dogs |
| LIU Shijun1，LI Xiangli2，and WANG Lijun3. |
1.Department of Stomatology，Beijing Youwai Hospital，Beijing 100069，China；
2. Department of Stomatology， Hunan Provincial Corps Hospital，Chinese People’s Armed Police Forces, Changsha 410006，China；
3. Department of Stomatology，General Hospital of Chinese People’s Armed Police Forces， Beijing 100039，China |
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Abstract Objective To compare the stress-shielding effect before and after removal of the small bone plate for mandibular fracture fixation in order to provide a theoretical basis for long-term disposal of fixed materials after healing of mandibular fracture. Methods Eighteen adult male mongrel dogs with removal of the titanium bone plate after healing of mandibular fracture were divided into groups of 0, 1, 2, 3, 6-months according to the time of internal fixation removal. Two months after internal fixation, the plates were taken out in one group with bilateral plates (0 month group) and out of the right side in the remaining four groups (experimental side). After 1, 2, 3, 6 months of internal fixation removal, the left plates were taken out and bone density and tensile stress of the left and right mandibles were compared. Results Bone mineral density of experimental and control sides in the 1, 2, 3, 6-month groups were higher than that in 0-month group ( P <0.05), and there was no significant difference between experimental and control sides in each group. Bone density of the control side in 6-month group was lower than that in normal group, with significant difference ( P <0.05). The maximum breaking strength on experimental and control sides in 1, 2, 3, 6-month groups was higher than that in 0-month group ( P <0.05).When the experimental and control sides were compared, the maximum breaking strength between the groups was not significantly different. The maximum breaking strength in 6-month group on the control side was lower than that in normal group, with significant differerce ( P <0.05). Conclusions With the increasing duration of internal fixation, the effect of stress shelter will occur. After 3 months of internal fixation, bone density and the maximum breaking strength on experimental and control sides of mandibles will increase, indicating that the best time to remove the bone fracture plate fixation is 3 months.
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Received: 26 December 2011
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