**1. Introduction**

In general, "homeostasis" of the periodontal ligament tissues (PDL) is occurring in any times, due to the mechanical stress to the tissue including the physiological and pathological occlusal stress and/or orthodontic mechanical stress, and so on. Thus, in the above sentences, the word "homeostasis" was used in the chapter. From a view point of developmental biology, there are well-known facts that the main component of PDL fibroblasts is from neural crest-derived neuroectodermal cells. From the point of the fact, at the period of the maintenance of the PDL, there are numerous cell proliferations that occurred in the regional tissues. It is a very important problem. Thus, at first, we introduce the chosed GFP bone marrowtransplanted model mouse (Tsujigiwa's model [1, 2]) shown in **Figure 1** (GFP mouse model: upper).

homeostasis of the periodontal ligament. Therefore, the facts suggest that these proteins will act on this as molecular chaperone for activation of an osteoblast and maintenance

Bone Marrow Mesenchymal Cell Contribution in Maintenance of Periodontal Ligament…

http://dx.doi.org/10.5772/intechopen.80785

95

We have investigated using the GFP mouse, the cell dynamics of the periodontal ligament in the past decade. The following experiments have been carried out: (1) Orthodontic mechanical stress causing injury of the periodontal ligament tissues. (2) Occlusal trauma of the periodontal ligament. In the examinations, histopathological changes were observed at the course of the experiments. Furthermore, we used the GFP bone marrow-transplanted mouse for examination of the cell supplying source to the regional periodontal ligament tissues from bone marrow-derived cells (BMDCs). (3) Experimentally induced periodontal polyp-contained cells are mainly from migration of undifferentiated mesenchymal cells of the bone marrow and differentiate into the tissue-specified cells. (4) Furthermore, the cell differentiation is due to the expression of Notch signaling. The result also suggests that the PDL fibroblasts in granulation tissue are differentiated in the periodontal ligament-specified cells from bone

**2. GFP-BMDCs into the PDL-received orthodontic mechanical stress**

The periodontal ligament (PDL) is usually remodeling at physiological in condition. Furthermore, orthodontic treatment results to mechanical stress inducing reorganization of PDL collagen bundles. The examination results in "movement of an orthodontics tooth." The mechanical stress communicated to PDL causes a reaction of organization and causes "movement of a tooth." This reaction of PDL is the one for maintenance of a homeostasis. A histology-like reply and production of the copying factor which controls a cell differentiation and various morphogenesis phenomena are studied more widely in recent years [3, 4]. It becomes clear that it's able to bring manifestation of a remodeling of a periodontal tissue and the activated molecule which replies to various mechanical stress and inflammation to maintain a homeostasis [5–10]. Our experimental method was based on our previous reports [4, 5]. The Waldo method of inducing mechanical stress load in mouse periodontal tissues was followed. Under general anesthesia, the mouse was inserted between the maxillary molars to induce persistent mechanical stress. A separator was inserted between M1 and M2 of the right maxillary molars to ensure the mechanical stress due to pressure over a period of time. After each experimental time, the periodontal tissues of the left maxillary molar region (untreated side) were used as controls. In this experiment, the distal buccal root of the maxillary first molar was the observation part. The schematic

Therefore, we focused on the expression of various HSPs that maintain homeostasis during injury. HSPs are one of the factors recognized that is transiently enhanced by heat shock [11]. It is also called stress protein because it is not only enhanced by heat shock but also by ischemia; other pathological changes such as infections and inflammation and radiation; physical stress such as light; stress from enzymes, heavy metal ion, arsenic, arsenic acid, methanol, and active oxygen; and stress from chemical and various amino acid derivatives [12, 13]. When the chromosomes of the salivary gland of *Drosophila* were at high temperatures, HSP

later.

marrow-derived mesenchymal cells.

diagram, macro-view, and histology are shown in **Figure 2**.

I used the ddY mouse as an experimental animal and chosed a histopathology in a periodontal ligament of the mouse that received mechanical stress by Waldo methods. The immunohistochemistry manifestation situation of heat shock protein 27 (HSP27) and phosphorylated HSP27 (p-HSP27) was investigated until that and at most 24 hours later. A periodontal ligament fibroblast was both low in HSP27 and p-HSP27 in the control group. But HSP27 was manifested 10 minutes later after a PDL fibroblast caused mechanical loading on the tension side of experimental group. The strongest appearance was detected 9 hours later after mechanical load was led. p-HSP27 was also weaker than HSP27, but it was manifested in a time-depending way. These results suggest that HSP27 and p-HSP27 are manifested by activation of a PDL fibroblast on the tension side for maintenance of the

**Figure 1.** GFP-transplanted model mouse schematic diagram.

homeostasis of the periodontal ligament. Therefore, the facts suggest that these proteins will act on this as molecular chaperone for activation of an osteoblast and maintenance later.

**1. Introduction**

94 Histology

In general, "homeostasis" of the periodontal ligament tissues (PDL) is occurring in any times, due to the mechanical stress to the tissue including the physiological and pathological occlusal stress and/or orthodontic mechanical stress, and so on. Thus, in the above sentences, the word "homeostasis" was used in the chapter. From a view point of developmental biology, there are well-known facts that the main component of PDL fibroblasts is from neural crest-derived neuroectodermal cells. From the point of the fact, at the period of the maintenance of the PDL, there are numerous cell proliferations that occurred in the regional tissues. It is a very important problem. Thus, at first, we introduce the chosed GFP bone marrowtransplanted model

I used the ddY mouse as an experimental animal and chosed a histopathology in a periodontal ligament of the mouse that received mechanical stress by Waldo methods. The immunohistochemistry manifestation situation of heat shock protein 27 (HSP27) and phosphorylated HSP27 (p-HSP27) was investigated until that and at most 24 hours later. A periodontal ligament fibroblast was both low in HSP27 and p-HSP27 in the control group. But HSP27 was manifested 10 minutes later after a PDL fibroblast caused mechanical loading on the tension side of experimental group. The strongest appearance was detected 9 hours later after mechanical load was led. p-HSP27 was also weaker than HSP27, but it was manifested in a time-depending way. These results suggest that HSP27 and p-HSP27 are manifested by activation of a PDL fibroblast on the tension side for maintenance of the

mouse (Tsujigiwa's model [1, 2]) shown in **Figure 1** (GFP mouse model: upper).

**Figure 1.** GFP-transplanted model mouse schematic diagram.

We have investigated using the GFP mouse, the cell dynamics of the periodontal ligament in the past decade. The following experiments have been carried out: (1) Orthodontic mechanical stress causing injury of the periodontal ligament tissues. (2) Occlusal trauma of the periodontal ligament. In the examinations, histopathological changes were observed at the course of the experiments. Furthermore, we used the GFP bone marrow-transplanted mouse for examination of the cell supplying source to the regional periodontal ligament tissues from bone marrow-derived cells (BMDCs). (3) Experimentally induced periodontal polyp-contained cells are mainly from migration of undifferentiated mesenchymal cells of the bone marrow and differentiate into the tissue-specified cells. (4) Furthermore, the cell differentiation is due to the expression of Notch signaling. The result also suggests that the PDL fibroblasts in granulation tissue are differentiated in the periodontal ligament-specified cells from bone marrow-derived mesenchymal cells.
