A analysis of bone quality of growing rat mandible by a novel evaluation system

研究生长压力和咬伤压力对大鼠和小猎犬下颌骨质量和数量的影响。分析了咬伤动物和非咬伤动物牙根下咬应力的影响。不咬人动物是通过拔牙实现的。采用基于x射线衍射的新技术分析了生物磷灰石（BAp）中c轴作为骨质量参数的首选排列。体积和密度作为骨组织的常规参数也进行了评估。本研究结果如下：(1)大鼠和小猎犬皮质骨的横截面积均随生长单调增加。骨密度和磷灰石排列的增加比皮质区更早饱和。骨密度和Bap线的分布随位置的不同而有明显的变化。(2)在下颌骨中，通常可以发现沿中远端轴的单向BAp排列。然而，在牙根下方，由于施加的咬合力，Bap沿咬向排列。这一结果清楚地说明Bap取向是能灵敏地反映体内应力分布的参数。(3)无咬合比格犬下颌骨的骨密度分布和BAp对中存在较大差异。咬应力的缺乏导致骨密度分布更均匀，Bap排列更均匀。我们得出结论，骨密度和BAp排列的变化与咬合引起的生长程度和体内应力分布密切相关。BAp的结构可根据局部应力分布进行敏感控制，从而使骨组织在机械环境下表现出有效的机械功能。

We focused on the effect of growing and biting stress on the quality and quantity of rat and beagle mandible. The effect of the biting stress was analyzed just under the tooth root of biting and non-biting animal. The non-biting animal was achieved by tooth extraction. The preferred alignment of the c-axis in biological apatite (BAp) as a bone quality parameter was analyzed by means of the novel technique based on the X-ray diffraction.The volume and the density as conventional parameters for bone tissue were also evaluated. Following results were obtained from this research.(1) The cross-sectional area of cortical bone monotonically increased with growing in both in rat and in beagle. However,the increase in bone density and the apatite alignment saturated earlier than that in cortical area.The distribution of the bone density and Bap alignment showed significantly varied depending on the position.(2) In general in the mandible, the uni-directional BAp alignment along the mesiodistal axis could be found. However, just under the tooth root, Bap was aligned along the biting direction due to the applied biting stress. This result clearly represents Bap alignment is the parameter which can sensitively reflect the in vivo stress distribution.(3) In the case of non-biting beagle mandible, quite different distribution of the bone density and BAp alignment was found. The lack of biting stress induced more homogenous distribution of bone density and Bap alignment.We conclude that the change in the bone density and the BAp alignment is closely related to the degree of growing and in vivo stress distribution due to the biting. The BAp texture is sensitively controlled depending on the local stress distribution, as a result, bone tissue can exhibit effective mechanical function against the mechanical environment.