牙髓幹細胞與牙齒神經發育的關係

Abstract

牙齒的神經發育是很重要的議題，由之前的研究可知牙齒神經隨著牙冠與牙根的形成而出現在牙髓腔之內。牙髓幹細胞來自牙髓組織，根據研究能在體外具有神經分化能力，可作為幹細胞的替代來源，具有表達 CD146的特徵，且是外胚層來源，起源於遷移的神經脊細胞和擁有間葉幹細胞的特性，有分化為成牙本質母細胞，骨細胞/骨細胞胚細胞，脂肪細胞，軟骨細胞和神經細胞的潛力。因此我們推測神經的生長可能與牙髓腔內的牙髓幹細胞有關係。所以，本研究的目的是探討和觀察牙髓幹細胞在牙齒神經支配中的角色。 本實驗方法是使用螢光染色和注射螢光染劑的方式，觀察牙髓幹細胞、神 經幹細胞、牙髓神經和神經生長椎在老鼠出生後第四天和第八天在牙胚中的位 置分佈和量，觀察這兩個不同時間點這些標記之間的關係。 實驗發現出生後四天的牙胚結果顯示神經纖維在牙胚外，並未進入牙髓中。出生後八天在牙胚內外都有神經纖維，且已進入牙髓中。 出生後四天和八天的牙胚中結果顯示神經幹細胞免疫反應陽性出現在成牙本質細胞和其突觸的位置。 出生後四天和八天的牙胚結果顯示牙髓幹細胞在牙胚中微血管內皮細胞和牙胚外微血管內皮細胞是免疫反應陽性。 出生後四天牙胚中結果顯示神經生長錐在牙囊外圍是免疫反應陽性。出生 後八天的牙胚在牙胚齒頸部免疫反應陽性的量較多且牙髓中有少量免疫反應陽 性。 經第四天至第八天的臼齒牙胚觀察到神經慢慢從牙胚外進入牙胚內。神經幹細胞一直出現在成牙本質細胞和其突觸的位置；此外，也一直有牙髓幹細胞出現在牙髓中。神經生長錐則由牙胚外慢慢往牙胚齒頸部移動。由實驗結果可以推測幹細胞和神經向牙髓內生長有相當大的關係，且牙髓內應具有神經分化潛力相關的類神經幹細胞。

The neurodevelopment of teeth is an important issue. It is known from previous studies that the growth of dental nerves occurs in the pulp cavity with the formation of crowns and roots. The dental pulp stem cells are derived from pulp tissue and can be studied in vitro. They have the abilities to be differentiated into nerve cells and can be used as an alternative source of stem cells. They have the characteristic of expressing CD146. These stem cells are derived from the ectoderm, which are originated from the migrating nerve ridge cells and possess the characteristics of mesenchymal stem cells. They can be differentiated into odontoblasts, osteocytes/osteocyte blasts, fat cells, chondrocytes and nerve cells. Therefore, we hypothesize that nerve growth may be related to dental pulp stem cells in the pulp cavity. The purpose of this study was to investigate and observe the relationship between dental pulp stem cells and teeth innervation. Immunofluorescence staining and injection of fluorescent dye were used to observe the distribution of dental pulp stem cells, neural stem cells, pulp nerves and nerve growth cone in the tooth germ of mice on the fourth and eighth day after birth. The relationship between these markers at these two different time points was observed. The results showed that in the tooth germ of mice at four days after birth showed that the nerve fibers were outside the tooth germ and did not enter the pulp. Eight days after birth, there are nerve fibers inside and outside the tooth germ, and they have entered the pulp. In both the four-day and eight-day tooth germs It was shown that the immunostaining of neural stem cell was positive in the odontoblasts and their processes we also found that dental pulp stem cells were positive for immunoreactivity in microvascular endothelial cells inside and outside of dental pulp in both the four-day and eight-day tooth germs. In the tooth germ four days after birth showed that the nerve growth cone was immunoreactive at the periphery of the tooth follicle. The tooth germs that were eight days after birth had more immunoreactive effects on the tooth germ and a small amount of immunoreactivity in the pulp. From the fourth to the eighth day, the nerve was observed to enter the pulp from the outside of the tooth germ slowly. Neural stem cells continue to appear in odontoblasts and their processes. Stem cells have also been found in the pulp. The nerve growth cone moves from the outside of the tooth germ to the cervical of the tooth germ. From the results, it can be inferred that stem cells have relationship with the growth of nerves in the pulp, and might have neural stem cells related properties with potential for neural differentiation in the pulp.