Association between periodontal changes and biomechanical factors from tooth movement

研究了牙周韧带（PDL）的组织学变化，并将其与应力分析结果相结合。使用带闭环的校准截面弓丝对成年犬的下第二前磨牙施加250 gf的远端定向力。在实验牙移动开始后2小时、4天和7天分别制备牙的中远端切片和支撑组织。此外，采用有限元分析方法分析了PDL内的应力水平。建立了用于分析的三维模型。该模型由3651个节点和2938个实体单元组成。对牙齿施加250 gf的远端定向力。在PDL中确定了三个主应力，并评估了体积主应力和剪应力分量。PDL主应力分布的性质与PDL部位特异性张力和压缩以及牙槽骨重塑的组织学结果高度一致。这些结果强烈强调主应力和PDL生物变化之间的关系，特别是骨重塑，因此其随后的牙齿运动。采用间接免疫荧光法观察了降钙素基因相关肽(CGRP)-和P物质(SP)-免疫反应性神经纤维（IR）在小鼠切牙PDL中的分布及其相关性。CGRP-IR和SP-IR细神经纤维在PDL的顶端和中间三分之一丰富。在舌部的切侧PDL中，这些神经纤维定位于牙槽区一半的PDL，并观察到自由神经末梢。未观察到CGRP-IR和SP-IR特化的神经末梢，如ruffini样小体。在唇部PDL中，CGRP-IR和SP-IR神经纤维沿切轴分布。CGRP-IR神经纤维的分布与SP-IR神经纤维的分布非常相似。

Histological changes in the periodontal ligement (PDL) from experimental tooth movements were investigated and integrated with analytical findings of stresses. A distally directed force of 250 gf was applied to the lower second premolars of adult dogs by use of a calibrated sectional arch wire with a closed loop. Mesiodistal sections of the tooth and supporting tissues were preparated at 2 hours and at 4 and 7 days after the beginning of experimental tooth movements. Further, stress levels in the PDL were analyzed by means of finite element analysis. A three-dimensional model for the analysis was constructed. The model consists of 3651 nodes and 2938 solid elements. A distally directed force of 250 gf was analytically applied to the tooth. Three principal stresses were determined in the PDL, and volumetric principal stress and shear stress component were evaluated. The nature of principal stress distributions in the PDL was highly coincident with histological findings in terms of site specific tension and compression of the PDL and alveolar bone remodeling. These results strongly emphasize the relationship between principal stresses and biological changes in the PDL, bone remodeling in particular, and hence its subsequent tooth movements.The distribution of calcitonin gene-related peptide (CGRP)- and substance P (SP)-immunoreactive (IR) nerve fibers and their correlation in the PDL of mouse incisors were examined by indirect immunofluorescence. Both CGRP-IR and SP-IR thin nerve fibers were abundant in the apical and middle third of the PDL. In the lingual protion of the incisal PDL, these nerve fibers were localized in the alveolar half of the PDL and were observed as free nerve endings. No CGRP-IR and SP-IR specialized nerve endings, such ans Ruffini-like corpuscles, were observed. In the labial PDL, CGRP-IR and SP-IR nerve fibers ran along the incisal axis. The distribution of CGRP-IR nerve fibers was very similar to that of SP-IR nerve fibers.