Mechanical Response of Bone under Short-term Loading of a Dental Implant with an Internal Layer Simulating the Nonlinear Behaviour of the Periodontal Ligament

We consider a non-standard design for a fixed dental implant, incorporating a soft layer which simulates the presence of the periodontal ligament (PDL). Instead of being aimed at causing an a priori defined stress/strain field within the surrounding bone, upon loading, such a design simply tries to better reproduce the natural tooth–PDL configuration. To do this, the mechanical properties of the internal layer match those of the PDL, determined experimentally to be strongly nonlinear. Three-dimensional finite element analyses show that the presence of such a layer produces (i) a prosthesis mobility very similar to that of a healthy tooth, for several loading conditions, and (ii) a stress/strain distribution substantially different from that arising, upon loading, around a conventional implant. The lack of knowledge of the real mechanical fields existing, under loading, in the bone around a healthy tooth makes it very difficult to state that the stress distribution produced by the modified implant is “better” than that produced by the standard one. Nevertheless, the comparison of the results obtained here, with those of previous refined analyses of the tooth–PDL–bone system, indicates that the modified implant tends to produce a stress distribution in the bone, upon loading, closer to “natural” than that given by the standard one, within the limits imposed by the presence of threads coupling the implant with the bone.     

EGF体外诱导骨髓基质干细胞增殖分化为成纤维细胞的实验研究

目的:研究表皮生长因子(EGF)在体外诱导兔骨髓基质干细胞(BMSCs)向成纤维细胞增殖分化,为韧带组织工程种子细胞提供可能的来源。方法:以EGF对体外培养的BMsCs进行诱导分化培养,相差显微镜观察细胞生长,MTT检测细胞的增殖,免疫组化半定量细胞的分化。结果:诱导后7d、14d时,诱导组呈现更均一的纤维细胞样的带有长突起的纺锤形细胞,呈束状排列,并且具有更高的细胞密度;诱导组在7d、14d细胞增殖均比对照组快;第10d时,诱导组、对照组胶原Ⅰ、Ⅲ染色均为阳性,但诱导组有更高的染色密度;诱导组、对照组胶原Ⅱ染色阴性。结论:BMSCs经。EGF。诱导后细胞增殖,并且能刺激细胞外基质的表达,基本符合肌腱和韧带组织工程的要求。     

Preparation of Unfixed and Undecalcified Frozen Sections of Adult Rat Periodontal Ligament During Experimental Tooth Movement

The upper first molars of adult male rats were moved for 7 days and unfixed, undecalcified frozen sections of the molar periodontal ligament were prepared and observed. The upper jaws of the rats were immersed rapidly in liquid nitrogen and sectioned with a cryostat using a super hard knife. Five micrometer serial sections were cut, collected, freeze-dried and observed with both light and scanning electron microscopy. Electron probe microanalysis (EPMA) was also performed on the sections. On the tension side of the periodontal ligament, periodontal fibers were stretched and the osteoblasts were aligned on the osteoid, which showed metachro-masia with the toluidine blue stain. On the pressure side where the periodontal ligament was extremely compressed, tissue degeneration was caused by tooth movement and the osteoclasts were observed on the bone surface adjacent to the degenerating tissues. Scanning electron microscopy revealed a network arrangement of the collagen fiber bundles on the tension side, but not on the pressure side of the periodontal ligament. The spectrum obtained from EPMA of the osteoid demonstrated X-ray (Ka) peaks of Na, P, S, K and Ca.     

Preparation of Unfixed and Undecalcified Frozen Sections of Adult Rat Periodontal Ligament During Experimental Tooth Movement

The upper first molars of adult male rats were moved for 7 days and unfixed, undecalcified frozen sections of the molar periodontal ligament were prepared and observed. The upper jaws of the rats were immersed rapidly in liquid nitrogen and sectioned with a cryostat using a super hard knife. Five micrometer serial sections were cut, collected, freeze-dried and observed with both light and scanning electron microscopy. Electron probe microanalysis (EPMA) was also performed on the sections. On the tension side of the periodontal ligament, periodontal fibers were stretched and the osteoblasts were aligned on the osteoid, which showed metachro-masia with the toluidine blue stain. On the pressure side where the periodontal ligament was extremely compressed, tissue degeneration was caused by tooth movement and the osteoclasts were observed on the bone surface adjacent to the degenerating tissues. Scanning electron microscopy revealed a network arrangement of the collagen fiber bundles on the tension side, but not on the pressure side of the periodontal ligament. The spectrum obtained from EPMA of the osteoid demonstrated X-ray (Ka) peaks of Na, P, S, K and Ca.     

人参皂苷Rg1促进人牙周膜干细胞增殖及骨向分化

人参皂苷Rg1 (GS Rg1) 是人参的主要药理活性成分. GS Rg1有刺激造血干细胞的形成和促进骨髓间充质干细胞增殖和分化的作用.而人牙周膜干细胞（human periodontal ligament stem cells, hPDLSCs）具有自我更新和多向分化的干细胞特性.但目前关于GS Rg1能否促进牙周膜干细胞增殖和分化的研究尚不多见.本研究证明,1×10-5 mol/L GS Rg1作用于hPDLSCs后,能明显促进牙周膜干细胞的增殖与分化.MTT检测细胞增殖显示,培养液中加入了GS Rg1实验组在第2,3,4,5 d增殖情况明显高于对照组,提示GS Rg1成分促进了牙周膜干细胞的增殖. 检测ALP表达量,RUNX2,Collagen I,OPN,OCN表达水平,加药实验组表达水平均高于未加药对照组,它们的表达量的增高提示成骨分化的增强. 牙周膜干细胞与纳米羟基磷灰石支架结合的电镜图片及其支架植入小鼠体内后的免疫组化检测显示,含有GS Rg1成分的细胞支架能促进形成更多的骨样组织.因此,GS Rg1能促进hPDLSCs体内体外的增殖及骨向分化,并在替代传统生长因子应用于牙周组织工程方面有较好前景.     

补肾益气活血方及其单味药对人牙周膜干细胞增殖分化的影响

摘要 目的：探讨自拟补肾益气活血方及其单味药当归、补骨脂对体外培养的人牙周膜干细胞（hPDLSCs）增殖和相关成骨基因表达的影响。方法：分离培养得到hPDLSCs,选取第3代hPDLSCs,细胞增殖试剂盒（CCK-8）检测不同浓度（0 g/mL、1×10^-7 g/mL、1×10^-5 g/mL、1×10^-3 g/mL）补肾益气活血方和当归、补骨脂对hPDLSCs增殖的影响,并确定最佳作用浓度和最佳作用时间;通过定量聚合酶链式反应（qPCR）检测Runt相关转录因子2（Runx2）、碱性磷酸酶（ALP）、骨桥蛋白（OPN）、骨钙蛋白（OCN）相关成骨基因的表达水平,通过茜素红染色观察细胞成骨分化情况。结果：与0 g/mL相比,补肾益气活血方各浓度在第一天和第三天时均能显著促进细胞增殖（P<0.05）,且浓度为1×10^-5 g/mL在第三天、第五天时效果均最为显著（P<0.05）;当归同样在浓度为1×10^-5 g/mL、第三天及第五天时效果均最为显著（P<0.05）;补骨脂则仅在第一天时能显著促进细胞增殖（P<0.05）。与空白对照组比较,1×10^-5 g/mL的补肾益气活血方、当归、补骨脂均能显著提升成骨相关Runx2、OCN、OPN、ALP的表达（P<0.05）,且补肾益气活血方的上调效果最为显著。茜素红染色检测显示,补肾益气活血方可增加矿化结节,促进作用最为显著。结论：补肾益气活血方可促进hPDLSCs的增殖和骨向分化,在治疗慢性牙周炎中有望发挥更大作用。