Proliferation of epithelial rests of Malassez during experimental tooth movement.

The epithelial rests of Malassez (ERM), remnants of Hertwig's epithelial root sheath, are found near the root surface in the periodontal ligament. The functional significance of the ERM is still unknown. The purpose of this study was to examine the behavior of the ERM during experimental tooth movement. Tooth movement was achieved in 12 male Sprague-Dawley rats (each, 120-200 g) by placing elastic bands between the maxillary right first and second molars. The left molars served as controls. The rats were killed after 6, 12, 18, 24, 60, and 72 hours. The mitotic activity of the ERM was assessed by injecting the animals with 5-bromo-2'-deoxyuridine (BrdU) 2 to 3 hours before killing by intracardial perfusion with 4% paraformaldehyde. The molar-bearing segments were dissected and processed for histological examination. The incorporated BrdU was detected by immunohistochemistry. The number of cells in each ERM cluster was counted in all groups. In the 18-, 24-, 60-, and 72-hour experimental groups, the cell numbers were significantly higher than in the controls. The surface areas of the ERM clusters were also measured in all groups, but only in the 18-, 24-, 60-, and 72-hour specimens were the areas significantly higher in the experimental than in the control groups. The ERM cells in the experimental specimens were labeled with anti-BrdU, while those in the controls were not. It was concluded that experimental tooth movement stimulates ERM cells to proliferate and increase in size. These increased activities of the ERM are consistent with a putative role for these cells in collagen turnover in the periodontal ligament that is accelerated during tooth movement.     

Apoptosis in epithelial cells of apical radicular cysts

AIM: To investigate the occurrence of apoptotic cell death in the epithelium of radicular cysts and to compare its frequency in lesions presenting a distinct functional state. METHODOLOGY: Twenty radicular cysts were selected and arranged into two groups with 10 lesions in each group: atrophic (quiescent) and hyperplastic (active) epithelium. Morphologic investigations of apoptosis were conducted by means of optic microscopy in haematoxylin and eosin slides. Immunohistochemical techniques to detect the bcl-2 protein were carried out by streptavidin-biotin-peroxidase assay. In both instances, 30 sequential high-power microscopic fields were observed to determine apoptotic (AI) and bcl-2 immunostaining (bcl-2I) indexes. The presence of AI and bcl-2I within the two groups was compared using the t-test. Correlation between the AI and the bcl-2I was investigated using the Spearman test. RESULTS: Apoptosis was detected in the epithelium of all cysts. Higher AI levels were found in lesions with an atrophic (0.17 +/- 0.19) rather than a hyperplastic (0.10 +/- 0.10) epithelium. The same was found for the bcl-2I levels (0.06 +/- 0.03 vs. 0.04 +/- 0.01, respectively). However, these differences were not statistically significant. A positive and significant correlation was found between AI and bcl-2I. CONCLUSIONS: Apoptosis was always present in the epithelium of the lesions and was more frequent in lesions with atrophic (quiescent) epithelium.     

Histatins,wound healing,and cell migration

Wounds in the oral mucosa heal faster and more efficiently than those in the skin, although the mechanisms underlying these differences are not completely clear. In the last 10 years, a group of salivary peptides, the histatins, has gained attention on behalf of their ability to improve several phases of the wound‐healing process. In addition to their roles as anti‐microbial agents and in enamel maintenance, histatins elicit other biological effects, namely by promoting the migration of different cell types contained in the oral mucosa and in non‐oral tissues. Histatins, and specifically histatin‐1, promote cell adhesion and migration in oral keratinocytes, gingival and dermal fibroblasts, non‐oral epithelial cells, and endothelial cells. This is particularly relevant, as histatin‐1 promotes the re‐epithelialization phase and the angiogenic responses by increasing epithelial and endothelial cell migration. Although the molecular mechanisms associated with histatin‐dependent cell migration remain poorly understood, recent studies have pointed to the control of signaling endosomes and the balance of small GTPases. This review aimed to update the literature on the effects of histatins in cell migration, with a focus on wound healing. We will also discuss the consequences that this increasing field will have in disease and therapy design.     

Patterns of keratin-expression in rests of Malassez and periapical lesions

Using immunocytochemistry and a panel of monoclonal antibodies directed against various keratin polypeptides we examined specimens of normal periodontal ligament, periapical granulomas and inflammatory dental cysts. Epithelial elements with the appearance of rests of Malassez were identified in 6 specimens of normal periodontium and 10 periapical granulomas. Altered epithelium was present in 16 periapical granulomas and a lining epithelium in 10 inflammatory dental cysts. The patterns of binding of antibodies by these epithelia indicated that (a) keratin 19 was expressed by all epithelia, and (b) rests of Malassez also expressed keratin 5 but not large amounts of other keratins and (c) epithelial proliferation in periapical lesions was associated with increased expression of keratin 14, a marker of stratifying epithelia, new expression of keratins 4 and 13, differentiation markers for non-cornifying epithelia and variable, low levels of keratins 8 and 18, markers of simple epithelia. Proliferation of the epithelial rests of Malassez to form the lining of inflammatory dental cysts thus appears to be associated with a change from an unusual epithelial phenotype to that of a stratified non-cornifying epithelium in which some simple epithelial keratins are coexpressed.     

建期上皮剩余的形态学和细胞活性研究

目的追踪观察上皮剩余在牙齿萌出和建!过程中的形态分布和细胞活性改变。方法细胞角蛋白14（ CK14）标记小鼠上皮剩余细胞，光镜观察其分布和细胞形态，透射电镜观察上皮剩余细胞的超微结构。PV免疫组化两步法检测CK14和增殖细胞核抗原（ PCNA）在上皮剩余细胞中的表达。结果自牙齿萌出前到建!后期上皮剩余的外形和分布改变明显，建!后期上皮细胞簇更为规则，分布由牙根表面的较广泛分布向根分叉和牙颈等部位局限，与成熟期上皮剩余相似。建!阶段，上皮剩余沿牙根表面呈现类网格样布局，细胞数量较萌出前期明显增加，细胞增殖活性检测显示此时上皮剩余特别是根分叉水平细胞增殖活跃。建!后期上皮剩余细胞数量开始减少，透射电镜结果显示簇内出现细胞凋亡征象。结论上皮剩余不是仅仅作为无功能的剩余物，其可能是上皮根鞘功能的延伸或持续，在建!过程中发挥积极作用，从而完成牙周组织的发育和维持牙周内环境的稳定。     

Malassez上皮剩余细胞培养方法学研究

Malassez上皮剩余来自牙根发育中的Hertwig's上皮根鞘,是存在于牙周膜中唯一的牙源性上皮细胞.近期研究发现上皮剩余不只是存在于牙周膜中的"剩余",而是具有多种功能,如:预防牙根的吸收,炎症刺激下形成根尖囊肿,维持牙周膜宽度,并且参与成牙骨质细胞的分化.体外细胞培养体系能排除体内的一些影响因素而很好的分析细胞的功能,因此本文就体外培养上皮剩余细胞的方法作一综述.     

Patterns of keratin-expression in rests of Malassez and periapical lesions

Using immunocytochemistry and a panel of monoclonal antibodies directed against various keratin polypeptides we examined specimens of normal periodontal ligament, periapical granulomas and inflammatory dental cysts. Epithelial elements with the appearance of rests of Malassez were identified in 6 specimens of normal periodontium and 10 periapical granulomas. Altered epithelium was present in 16 periapical granulomas and a lining epithelium in 10 inflammatory dental cysts. The patterns of binding of antibodies by these epithelia indicated that (a) keratin 19 was expressed by all epithelia, and (b) rests of Malassez also expressed keratin 5 but not large amounts of other keratins and (c) epithelial proliferation in periapical lesions was associated with increased expression of keratin 14, a marker of stratifying epithelia, new expression of keratins 4 and 13, differentiation markers for non-cornifying epithelia and variable, low levels of keratins 8 and 18, markers of simple epithelia. Proliferation of the epithelial rests of Malassez to form the lining of inflammatory dental cysts thus appears to be associated with a change from an unusual epithelial phenotype to that of a stratified non-cornifying epithelium in which some simple epithelial keratins are coexpressed.     

Immunohistochemical characteristics of epithelial cell rests of Malassez during cementum repair

To clarify the roles of epithelial cell rests of Malassez (ECRM) during periodontal repair, experimental root resorption was induced in rats and then the ECRM that existed in periodontal ligament during cementum repair was investigated using morphological and immunohistochemical approaches. At day 7, after mechanical injury, root resorption was observed and ECRM were present adjacent to the site of resorption lacunae. They were observed in periodontal ligament adjacent to site of the resorption lacunae. These ECRM were immunoreactive for bone morphogenetic protein-2. During the stage of early cementum repair, the ECRM were immunoreactive for osteopontin and ameloblastin. They strongly reacted to proliferating cell nuclear antigen. In uninjured control sections, ECRM located in the periodontal ligament adjacent to cementum were not immunoreactive for any antibodies. These findings suggested that ECRM may be related to cementum repair by activating their potential to secrete matrix proteins which have been expressed in tooth development.     

Langerhans' cell histiocytosis in association with periapical granulomas and cysts.

This report describes a series of six cases of inflammatory periapical disease with small aggregates of Langerhans cells as a minor component. Immunohistochemical findings confirm that the cells are phenotypically related to Langerhans cells. Aggregates of these cells are not normally found in radicular cysts or periapical granulomas and have been interpreted to represent chronic localized Langerhans' cells histiocytosis. Whether these lesions, which arise within the context of chronic inflammatory periapical disease, represent incipient eosinophilic granulomas or are a more benign, minimally destructive form of Langerhans' cell histiocytosis is unknown. Clinical follow-up suggests that these lesions remain localized and that curettage is adequate treatment.     

Evaluation of mast cells in periapical cysts, dentigerous cysts, and keratocystic odontogenic tumors

J Oral Pathol Med (2012) 41 : 630–636 Background: Several cell types are associated with the development of cystic and tumoral odontogenic lesions. Among inflammatory cells, mast cells can be associated with their pathogenesis. The aim of this study was to analyze mast cells in periapical cysts, dentigerous cysts, and keratocystic odontogenic tumors. Methods: Tissue sections were submitted to toluidine blue staining and immunohistochemistry with antibody anti‐tryptase (clone G3). Mast cells were quantitated using Image‐Pro Plus software to obtain the mean number of mast cells in three regions: epithelial, superficial portion of the fibrous wall and deep portion of the fibrous wall from 20 periapical cysts, 20 dentigerous cysts (six non‐inflamed and 14 inflamed) and 20 keratocystic odontogenic tumors (four non‐inflamed and 16 inflamed). Results: The mean number of mast cells detected per lesion by immunohistochemistry (4.1) was higher than by histochemistry (1.5) (P < 0.0001). Inflamed dentigerous cysts and keratocystic odontogenic tumors showed a higher mean number of mast cells than non‐inflamed lesions in all regions. The deep region from all cysts showed the highest mean number of degranulated mast cells, except for non‐inflamed keratocystic odontogenic tumors analyzed by immunohistochemistry. Conclusions: Immunohistochemical staining detected higher number of mast cells than histochemistry. The higher number of mast cells observed in inflamed lesions could indicate the participation of these cells in the inflammatory response in odontogenic lesions. The prevalence of degranulated mast cells in the deep region suggests intense activity of these cells, possibly related to growth of cystic lesions.     

Collagen membranes prevent the apical migration of epithelium during periodontal wound healing

Collagen membranes were interposed between full thickness periodontal flaps and denuded root surfaces of right upper canines in 3 mongrel dogs; the left canines were sham-operated without the use of collagen membranes. Animals were killed 10 d after surgery. Tissue blocks were removed, and experimental and control sites were processed for histometric and histologic examination. The results indicate that collagen membranes: (i) prevent apical migration of the epithelium during initial stages of healing; and (ii) are colonized by connective tissue cells and incorporated within the healing connective tissue.     

The incidence of epithelium in periapical granulomas and the mechanism of cavitation in apical dental cysts in man

In two series of periapical granulomas, approximately one third contained proliferating epithelium, the highest incidence being in the third and fourth decades. Histological observations on the walls of radicular cysts suggest that the cyst wall may result from a three-dimensional proliferation of epithelium. The hypotheses of the mechanism whereby apical cysts undergo central cavitation were investigated histochemically. Proteolytic enzyme activity was detected (a) in the connective tissue within and around the loops of epithelium, suggesting that cavitation may occur owing to connective tissue breakdown, followed by epithelial proliferation and (b) within the epithelium, suggesting that cavitation may be caused by intra-epithelial breakdown.