Ho Sunita P, Sulyanto Rosalyn M, Marshall Sally J, Marshall Grayson W
Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, 707 Parnassus Avenue, University of California San Francisco, San Francisco, CA 94143-0758, USA.
J Struct Biol. 2005 Jul;151(1):69-78. doi: 10.1016/j.jsb.2005.05.003.
The presence of glycosaminoglycans (GAGs) and their contribution to mechanical properties of the cementum-dentin junction (CDJ) were investigated using nanometer scale characterization techniques. Five to two millimeter thick transverse sections from the apical ends of human molars were ultrasectioned at room temperature under wet conditions using a diamond knife and an ultramicrotome. The structure of the CDJ under dry and wet conditions before and after digestion of GAGs and collagen fibrils was studied using an atomic force microscope (AFM). The mechanical properties of the untreated and enzyme treated CDJ under wet conditions were studied using an AFM-based nanoindenter. GAG digestion was performed for 1, 3, and 5 h at 37 degrees C using chondroitinase-ABC. Collagen fibril digestion was performed for 24 and 48 h at 37 degrees C using collagenase. As reported previously, AFM scans of dry untreated CDJ (control) revealed a valley, which transformed into a peak under wet conditions. The height differences relative to cementum and dentin of untreated and treated CDJ were determined by measuring the CDJ profile under dry and wet conditions. The depth of the valley of GAG and collagen-digested CDJ was greater than that of undigested CDJ under dry conditions. The height of the peak of GAG-digested CDJ was significantly higher than that of the undigested CDJ under wet conditions. The collagen-digested CDJ under wet conditions is assumed to form a valley because of the removal of collagen fibrils from the CDJ. However, the depth of the valley was lower compared to the depth under dry conditions. Wet AFM-based nanoindentation showed that the elastic modulus and hardness of control (3.3+/-1.2 and 0.08+/-0.03 GPa) were significantly higher (ANOVA & SNK, P < 0.05) than chondroitinase-ABC treated CDJ (0.9+/-0.4 and 0.02+/-0.004 GPa) and collagenase treated CDJ (1.5+/-0.6 and 0.04+/-0.01 GPa). No significant difference in mechanical properties between chondroitinase-ABC and collagenase treated CDJ was observed. Based on the results it was concluded that the 10-50 microm wide CDJ is a composite that includes, chondroitin-4-sulfate, chondroitin-6-sulfate, and possibly dermatan sulfate, and collagen fibrils. The association of GAGs with the collagen fibrils provides the observed controlled hydration and partially contributes toward the stiffness of the CDJ under wet conditions.
利用纳米尺度表征技术研究了糖胺聚糖（GAGs）的存在及其对牙骨质-牙本质交界处（CDJ）力学性能的贡献。使用金刚石刀和超薄切片机在室温潮湿条件下对人磨牙根尖5至2毫米厚的横切片进行超薄切片。使用原子力显微镜（AFM）研究了GAGs和胶原纤维消化前后干湿条件下CDJ的结构。使用基于AFM的纳米压痕仪研究了潮湿条件下未处理和酶处理的CDJ的力学性能。使用软骨素酶ABC在37℃下进行1、3和5小时的GAG消化。使用胶原酶在37℃下进行24和48小时的胶原纤维消化。如先前报道，干燥未处理的CDJ（对照）的AFM扫描显示一个谷，在潮湿条件下转变为一个峰。通过测量干湿条件下的CDJ轮廓来确定未处理和处理后的CDJ相对于牙骨质和牙本质的高度差。在干燥条件下，GAG和胶原消化的CDJ的谷深度大于未消化的CDJ。在潮湿条件下，GAG消化的CDJ的峰高度显著高于未消化的CDJ。由于从CDJ中去除了胶原纤维，潮湿条件下胶原消化的CDJ被认为形成了一个谷。然而，与干燥条件下的深度相比，谷的深度较低。基于AFM的潮湿纳米压痕显示，对照（3.3±1.2和0.08±0.03 GPa）的弹性模量和硬度显著高于软骨素酶ABC处理过的CDJ（0.9±0.4和0.02±0.004 GPa）以及胶原酶处理过的CDJ（1.5±0.6和0.04±0.01 GPa）（方差分析和SNK检验，P<０.０５）。在软骨素酶ABC和胶原酶处理过的CDJ之间未观察到力学性能的显著差异。基于这些结果得出结论，10-50微米宽的CDJ是一种复合材料，包括硫酸软骨素-4、硫酸软骨素-6，可能还有硫酸皮肤素以及胶原纤维。GAGs与胶原纤维的结合提供了观察到的可控水合作用，并部分有助于潮湿条件下CDJ的硬度。
