Relationship between enamel formation and eruption rate in rat mandibular incisors

Summary The relationship between the formation of dental enamel and tooth eruption was investigated. Rat mandibular incisor eruption rate was accelerated by maintaining incisors out of occlusion. Rate of eruption, enamel thickness, secretory zone length and matrix breakdown were measured. Eruption rate increased by 120% in experimental teeth but enamel secretion increased by only 90%. There were no obvious differences between control and experimental teeth in final enamel thickness or in the molecular weight distribution of the enamel matrix proteins.     

Periostin is an extracellular matrix protein required for eruption of incisors in mice

A characteristic tooth of rodents, the incisor continuously grows throughout life by the constant formation of dentin and enamel. Continuous eruption of the incisor is accompanied with formation of shear zone, in which the periodontal ligament is remodeled. Although the shear zone plays a role in the remodeling, its molecular biological aspect is barely understood. Here, we show that periostin is essential for formation of the shear zone. Periostin-/- mice showed an eruption disturbance of incisors. Histological observation revealed that deletion of periostin led to disappearance of the shear zone. Electron microscopy revealed that the disappearance of the shear zone resulted from a failure in digestion of collagen fibers in the periostin-/- mice. Furthermore, immunohistochemical analysis using anti-periostin antibodies demonstrated the restricted localization of periostin protein in the shear zone. Periostin is an extracellular matrix protein, and immunoelectron microscopy showed a close association of periostin with collagen fibrils in vivo. These results suggest that periostin functions in the remodeling of collagen matrix in the shear zone.     

Osteogenic inhibition by rat periodontal ligament cells: modulation of bone morphogenic protein-7 activity in vivo

Periodontal ligament width is precisely maintained throughout the lifetime of adult mammals but the biological mechanisms that inhibit ingrowth of bone into this soft connective tissue are unknown. As bone morphogenic proteins strongly stimulate osteogenesis and can induce ectopic bone formation in vivo, we tested the hypothesis that topical application of this powerful osteogenic agent will overwhelm the osteogenic inhibitory mechanisms of periodontal ligament cells and induce ankylosis. Wounds through the alveolar bone and periodontal ligament were created in 45 male Wistar rats. Defects were filled with either a collagen implant or collagen plus bone morphogenic protein (BMP-7), or were left unfilled (controls). Three animals per time period were killed on days 2, 5, 10, 21 and 60 after surgery for each wound type. Cellular proliferation and clonal growth in periodontal tissues were assessed by ³H-thymidine labeling 1 h before death, followed by radioautography. Cellular differentiation of soft and mineralizing connective tissue cell populations was determined by immunohistochemical staining of α-smooth muscle actin, osteopontin and bone sialoprotein. In regenerating periodontium, BMP-7 induced abundant bone formation by 21 days (2.5-fold greater than controls or collagen implant only; P<0.001), but by day 60 the volume of the newly formed bone had returned to baseline levels and was similar for all groups. Independent of the type of treatment, periodontal ligament width was unchanged throughout the experimental period (P>0.05). Animals treated with BMP-7 implants showed greatly increased cellular proliferation in the periodontal ligament adjacent to the wound site and in the regenerating alveolar bone at days 5 and 10 after wounding compared to the other treatment groups (P<0.005). Animals in the BMP-7 group exhibited similar spatial and temporal staining patterns for α-smooth muscle actin, osteopontin and bone sialoprotein as controls. Collectively, these data show that BMP-7 promoted the proliferation of precursor cells in the periodontal ligament but did not induce osteogenic differentiation in this compartment. Consequently a powerful osteogenic stimulus like BMP-7 cannot significantly perturb the mechanisms that regulate periodontal ligament width and maintain periodontal homeostasis. Received: 2 March 1998 / Accepted: 16 June 1998     

Effect of interrupted eruption on the enamel organ of the rat incisor

The aim of this study was to investigate the behavior of rat incisor tissues during the inhibition of tooth eruption. Twenty Sprague-Dawley rats were used in this study, and incisor eruption was inhibited by a screw pin. Animals were sacrificed 1, 3, 7 and 14 days after the start of the experiment. Cross-sections at the mesial point of the mandibular first molar and sagittal sections of the mandibular tooth germ area were examined using immunohistochemical and immunofluorescence methods. For morphometric analysis, numbers of TRAP-positive cells were calculated against the total number of cells. In cross-sections from the experimental group, dentin was thickened and pulp tissue was constricted day by day. On days 1, 3 and 7, nestin-positive cells were observed in all odontoblast cell bodies and processes, while on day 14 fewer nestin-positive cells were seen than in the control group. On day 14, the mesial area of the periodontal ligament was constricted and the number of TRAP-positive cells in the mesial area was significantly higher than in the control group. In sagittal sections, enamel formation was found to be increased on days 7 and 14. Furthermore, in the enamel matrix amelogenin was expressed more strongly than in the control group. PCNA-positive cells were significantly increased in cells of the tooth germ compared with the control group. These results suggest that inhibition of tooth eruption accelerates the apical elongation with resorption of the mesial area of the alveolar bone and stimulates cell proliferation with thickened enamel towards the apical end.     

Inactivation of Fam20C in Cells Expressing Type I Collagen Causes Periodontal Disease in Mice

Background

FAM20C is a kinase that phosphorylates secretory proteins. Previous studies have shown that FAM20C plays an essential role in the formation and mineralization of bone, dentin and enamel. The present study analyzed the loss-of-function effects of FAM20C on the health of mouse periodontal tissues.

Methods

By crossbreeding 2.3 kb Col 1a1-Cre mice with Fam20C^fl/fl mice, we created 2.3 kb Col 1a1-Cre;Fam20C^fl/fl (cKO) mice, in which Fam20C was inactivated in the cells that express Type I collagen. We analyzed the periodontal tissues in the cKO mice using X-ray radiography, histology, scanning electron microscopy and immunohistochemistry approaches.

Results

The cKO mice underwent a remarkable loss of alveolar bone and cementum, along with inflammation of the periodontal ligament and formation of periodontal pockets. The osteocytes and lacuno-canalicular networks in the alveolar bone of the cKO mice showed dramatic abnormalities. The levels of bone sialoprotein, osteopontin, dentin matrix protein 1 and dentin sialoprotein were reduced in the Fam20C-deficient alveolar bone and/or cementum, while periostin and fibrillin-1 were decreased in the periodontal ligament of the cKO mice.

Conclusion

Loss of Fam20C function leads to periodontal disease in mice. The reduced levels of bone sialoprotein, osteopontin, dentin matrix protein 1, dentin sialoprotein, periostin and fibrillin-1 may contribute to the periodontal defects in the Fam20C-deficient mice.     

Periostin is required for matricellular localization of CCN3 in periodontal ligament of mice

CCN3 is a matricellular protein that belongs to the CCN family. CCN3 consists of 4 domains: insulin-like growth factor-binding protein-like domain (IGFBP), von Willebrand type C-like domain (VWC), thrombospondin type 1-like domain (TSP1), and the C-terminal domain (CT) having a cysteine knot motif. Periostin is a secretory protein that binds to extracellular matrix proteins such as fibronectin and collagen. In this study, we found that CCN3 interacted with periostin. Immunoprecipitation analysis revealed that the TSP1-CT interacted with the 4 repeats of the Fas 1 domain of periostin. Immunofluorescence analysis showed co-localization of CCN3 and periostin in the periodontal ligament of mice. In addition, targeted disruption of the periostin gene in mice decreased the matricellular localization of CCN3 in the periodontal ligament. Thus, these results indicate that periostin was required for the matricellular localization of CCN3 in the periodontal ligament, suggesting that periostin mediated an interaction between CCN3 and the extracellular matrix.     

Ionizing radiation effects on the secretory-stage ameloblasts and enamel organic extracellular matrix

This study assessed the effects of high doses of ionizing radiation on eruption rate, odontogenic region morphology, secretory-stage ameloblasts, and enamel organic extracellular matrix (EOECM) of rat maxillary incisors. For the study, 30 male rats were divided into three experimental groups: control (non-irradiated), irradiated by 15 Gy, and irradiated by 25 Gy. Irradiated groups received a single dose of 15 or 25 Gy of X-rays in the head and neck region. The maxillary incisor eruption rate was measured. Sections of 5-µm thickness of the maxillary incisor odontogenic regions were evaluated using bright field light microscopy. Ultrathin sections of secretory ameloblasts and their EOECM were analyzed by transmission electron microscopy (TEM). Irradiated groups showed significantly diminished eruption rate values at the 4th and at the 6th day after irradiation. Reduced optical retardation values were observed in the irradiated groups. The odontogenic region of maxillary incisors from irradiated rats exhibited altered and poorly organized preameloblasts. TEM showed degeneration areas in the secretory-stage EOECM and several autophagosomes in the secretory ameloblasts from irradiated animals. In conclusion, high radiation doses delay eruption and induce disturbances in secretory ameloblasts and EOECM of rat maxillary incisors. These findings may be associated with structural defects of mature enamel.     

Fluorosed Mouse Ameloblasts Have Increased SATB1 Retention and Gαq Activity

Dental fluorosis is characterized by subsurface hypomineralization and increased porosity of enamel, associated with a delay in the removal of enamel matrix proteins. To investigate the effects of fluoride on ameloblasts, A/J mice were given 50 ppm sodium fluoride in drinking water for four weeks, resulting serum fluoride levels of 4.5 µM, a four-fold increase over control mice with no fluoride added to drinking water. MicroCT analyses showed delayed and incomplete mineralization of fluorosed incisor enamel as compared to control enamel. A microarray analysis of secretory and maturation stage ameloblasts microdissected from control and fluorosed mouse incisors showed that genes clustered with Mmp20 appeared to be less downregulated in maturation stage ameloblasts of fluorosed incisors as compared to control maturation ameloblasts. One of these Mmp20 co-regulated genes was the global chromatin organizer, special AT-rich sequence-binding protein-1 (SATB1). Immunohistochemical analysis showed increased SATB1 protein present in fluorosed ameloblasts compared to controls. In vitro, exposure of human ameloblast-lineage cells to micromolar levels of both NaF and AlF₃ led to a significantly increase in SATB1 protein content, but not levels of Satb1 mRNA, suggesting a fluoride-induced mechanism protecting SABT1 from degradation. Consistent with this possibility, we used immunohistochemistry and Western blot to show that fluoride exposed ameloblasts had increased phosphorylated PKCα both in vivo and in vitro. This kinase is known to phosphorylate SATB1, and phosphorylation is known to protect SATB1 from degradation by caspase-6. In addition, production of cellular diacylglycerol (DAG) was significantly increased in fluorosed ameloblasts, suggesting that the increased phosphorylation of SATB1 may be related to an effect of fluoride to enhance Gαq activity of secretory ameloblasts.     

Rat <Emphasis Type="Italic">wct</Emphasis> mutation prevents differentiation of maturation-stage ameloblasts resulting in hypo-mineralization in incisor teeth

A recent study provided genetic and morphological evidence that rat autosomal-recessive mutation, whitish chalk-like teeth (wct), induced tooth enamel defects resembling those of human amelogenesis imperfecta (AI). The wct locus maps to a specific interval of rat chromosome 14 corresponding to human chromosome 4q21 where the ameloblastin and enamelin genes exist, although these genes are not included in the wct locus. The effect of the wct gene mutation on the enamel matrix synthesis and calcification remains to be elucidated. This study clarifies how the wct gene mutation influences the synthesis of enamel matrix and its calcification by immunocytochemistry for amelogenin, ameloblastin and enamelin, and by electron probe micro-analysis (EPMA). The immunoreactivity for enamel proteins such as amelogenin, ameloblastin, and enamelin in the ameloblasts in the homozygous teeth was the same as that in the heterozygous teeth from secretory to transitional stages, although the homozygous ameloblasts became detached from the enamel matrix in the transitional stage. The flattened ameloblasts in the maturation stage of the homozygous samples contained enamel proteins in their cytoplasm. Thus, the wct mutation was found to prevent the morphological transition of ameloblasts from secretory to maturation stages without disturbing the synthesis of enamel matrix proteins, resulting in the hypo-mineralization of incisor enamel and cyst formation between the enamel organ and matrix. This mutation also prevents the transfer of iron into the enamel.     

Mitochondrial toxicity and caspase activation in HIV pregnant women

To assess the impact of HIV‐infection and highly active anti‐retroviral treatment in mitochondria and apoptotic activation of caspases during pregnancy and their association with adverse perinatal outcome. Changes of mitochondrial parameters and apoptotic caspase activation in maternal peripheral blood mononuclear cells were compared at first trimester of pregnancy and delivery in 27 HIV‐infected and ‐treated pregnant women versus 24 uninfected pregnant controls. We correlated immunovirological, therapeutic and perinatal outcome with experimental findings: mitochondrial DNA (mtDNA) content, mitochondrial protein synthesis, mitochondrial function and apoptotic caspase activation. The HIV pregnancies showed increased adverse perinatal outcome (OR: 4.81 [1.14–20.16]; P < 0.05) and decreased mtDNA content (42.66 ± 5.94%, P < 0.01) compared to controls, even higher in naïve participants. This depletion caused a correlated decrease in mitochondrial protein synthesis (12.82 ± 5.73%, P < 0.01) and function (20.50 ± 10.14%, P < 0.001), not observed in controls. Along pregnancy, apoptotic caspase‐3 activation increased 63.64 ± 45.45% in controls (P < 0.001) and 100.00 ± 47.37% in HIV‐pregnancies (P < 0.001), in correlation with longer exposure to nucleoside analogues. HIV‐infected women showed increased obstetric problems and declined genetic and functional mitochondrial parameters during pregnancy, especially those firstly exposed to anti‐retrovirals. The apoptotic activation of caspases along pregnancy is emphasized in HIV pregnancies promoted by nucleoside analogues. However, we could not demonstrate direct mitochondrial or apoptotic implication in adverse obstetric outcome probably because of the reduced sample size.     

Serum p53 protein and anti-p53 antibodies are associated with increased cancer risk: a case–control study of 569 patients and 879 healthy controls

The aim of this study to determine whether serum p53 protein and antibodies are associated with malignant tumors. A case–control study was conduct in 569 patients with various types of malignant tumors and 879 healthy controls. Serum p53 protein and antibodies were analyzed by enzyme-linked immunosorbent assay (ELISA).The rate of positive p53 protein in patients with various malignant tumors was 4.22% compared with 0.34% in healthy controls (P < 0.001). The rate of anti-p53 antibodies in patients with various malignant tumors was 14.59% compared with 1.02% in healthy controls (P < 0.001). The adjusted odd ratio (OR) for p53 protein was 17.55 (95% CI = 4.98–61.94). The adjusted odd ratio for anti-p53 antibodies was 14.27 (95% CI = 6.75–30.16). The study strongly suggested that serum p53 protein and antibody are associated with increased cancer risk and can be used as early serological markers in the diagnosis of malignancies tumors.     

Cell survival and gene expression under compressive stress in a three-dimensional in vitro human periodontal ligament-like tissue model

This study investigated cell survival and gene expression under various compressive stress conditions mimicking orthodontic force by using a newly developed in vitro model of human periodontal ligament-like tissue (HPdLLT). The HPdLLT was developed by three-dimensional culturing of human periodontal ligament fibroblasts in a porous poly-l-lactide matrix with threefold increased culture media permeability due to hydrophilic modification. In vitro HPdLLTs in experimental groups were subjected to 5, 15, 25 and 35 g/cm² compressive stress for 1, 3, 7 or 14 days; controls were cultured over the same periods without compressive stress. Cell morphology and cell apoptosis in the experimental and control groups were investigated using scanning electron microscopy and caspase-3/7 detection. Real-time polymerase chain reaction was performed for seven osteogenic and osteoclastic genes. Similar extracellular matrix and spindle-shaped cells were observed inside or on the surface of in vitro HPdLLTs, with no relation to compressive stress duration or intensity. Similar caspase-3/7 activity indicating comparable apoptosis levels was observed in all samples. Receptor activator of nuclear factor kappa-B ligand and bone morphogenetic protein 2 genes showed characteristic “double-peak” expression at 15 and 35 g/cm² on day 14, and alkaline phosphatase and periodontal ligament-associated protein 1 expression peaked at 5 g/cm² on day 14; other genes also showed time-dependent and load-dependent expression patterns. The in vitro HPdLLT model system effectively mimicked the reaction and gene expression of the human periodontal ligament in response to orthodontic force. This work provides new information on the effects of compressive stress on human periodontal ligament tissue.     

Decreased levels of Cx43 gap junctions result in ameloblast dysregulation and enamel hypoplasia in Gja1Jrt/+ mice

Coordinated differentiation of the ameloblast cell layer is essential to enamel matrix protein deposition and subsequent mineralization. It has been hypothesized that this process is governed by Cx43‐based gap junctional intercellular communication as oculodentodigital dysplasia (ODDD) patients harboring autosomal‐dominant mutations in Cx43 exhibit enamel defects typically resulting in early adulthood tooth loss. To assess the role of Cx43 in tooth development we employ a mouse model of ODDD that harbors a G60S Cx43 mutant, Gja1^Jrt/+, and appears to exhibit tooth abnormalities that mimic the human disease. We found that total Cx43 plaques at all stages of ameloblast differentiation, as well as within the supporting cell layers, were greatly reduced in Gja1^Jrt/+ incisors compared to wild‐type littermate controls. To characterize the Gja1^Jrt/+ mouse tooth phenotype, mice were sacrificed prior to tooth eruption (postnatal day 7), weaning (postnatal day 21), and adulthood (2 months postnatal). A severely disorganized Gja1^Jrt/+ mouse ameloblast layer and abnormal accumulation of amelogenin were observed at stages when the cells were active in secretion and mineralization. Differences in enamel thickness became more apparent after tooth eruption and incisor exposure to the oral cavity suggesting that enamel integrity is compromised, leading to rapid erosion. Additional analysis of incisors from mutant mice revealed that they were longer with a thicker dentin layer than their wild‐type littermates, which may reflect a mechanical stress response to the depleted enamel layer. Together, these data show that reduced levels of Cx43 gap junctions result in ameloblast dysregulation, enamel hypoplasia, and secondary tissue responses. J. Cell. Physiol. 223:601–609, 2010. © 2010 Wiley‐Liss, Inc.     

Finite element analysis of stress distribution in intact and porcelain veneer restored teeth

The aim of this study was to investigate the stress distribution generated in a veneer restoration of an upper central incisor compared to intact teeth using the finite element analysis after applying a lingual buccal loading at the incisal edge. Methods: Two models were developed: one model contained enamel, dentine, cementum, periodontal ligament, cortical and trabecullar bones, and the other model was a veneer restoration; both models were developed using MSC/Nastran software (MacNeal-Schwendler Corporation, Los Angeles, CA, USA) as the pre- and post-processor. A 10-N load was applied at the incisal edge from the lingual to the buccal side to simulate oral conditions in this area (protrusion). Results: Von Mises stresses were then analysed for three different regions: A-B (enamel elements under the veneer or second enamel layer), A′-B′ (buccal enamel and/or veneer element layer) and C-D (lingual enamel elements layer). A higher stress mode was observed for both models at the lingual cervical region. Conclusions: The presence of a veneer restoration on the incisors is a good alternative to mimic the behaviour of enamel under protrusion loading conditions. The use of veneers to replace enamel during rehabilitations is recommended.     

Matrix metalloproteinase 2 activity decreases in human periodontal ligament fibroblast cultures submitted to simulated orthodontic force

Orthodontic force compresses the periodontal ligament promoting the expression of pro-inflammatory mediators and matrix metalloproteinases responsible for tooth movement. The extent in time while periodontal cells are being treated and the increment in the amount of mechanical stress caused by the orthodontic force is thought to regulate the levels of metalloproteinases in the periodontal tissue. To study the possible regulation in the activity of metalloproteinases 2, 3, 7, 9, and 10 by simulated orthodontic force, human periodontal ligament fibroblast cultures were centrifuged (141×g) for 30, 60, 90, and 120 min, simulating the orthodontic force. Cell viability, protein quantification, and activity of metalloproteinases by zymography were evaluated at 24, 48, and 72 h after centrifugation in both cell lysates and growth medium. The activity of the 72-kDa matrix metalloproteinase 2 was decreased at 24 h regardless of the duration of centrifugation and at 48 h in cells centrifuged for 30 min only. Decrease in the amount of total protein in lysates was seen at 48 and 72 h with no change in cell viability. The data seem to indicate that the amount of mechanical stress regulates the levels of secreted matrix metalloproteinase 2. In addition, the centrifugation as a model for simulated orthodontic force may be used as a simple and reliable method to study the role played by matrix metalloproteinases in periodontal ligament when submitted to mechanical force as occurring during tooth movement.     

Regeneration of bone and periodontal ligament induced by recombinant amelogenin after periodontitis

Regeneration of mineralized tissues affected by chronic diseases comprises a major scientific and clinical challenge. Periodontitis, one such prevalent disease, involves destruction of the tooth-supporting tissues, alveolar bone, periodontal-ligament and cementum, often leading to tooth loss. In 1997, it became clear that, in addition to their function in enamel formation, the hydrophobic ectodermal enamel matrix proteins (EMPs) play a role in the regeneration of these periodontal tissues. The epithelial EMPs are a heterogeneous mixture of polypeptides encoded by several genes. It was not clear, however, which of these many EMPs induces the regeneration and what mechanisms are involved. Here we show that a single recombinant human amelogenin protein (rHAM⁺), induced in vivo regeneration of all tooth-supporting tissues after creation of experimental periodontitis in a dog model. To further understand the regeneration process, amelogenin expression was detected in normal and regenerating cells of the alveolar bone (osteocytes, osteoblasts and osteoclasts), periodontal ligament, cementum and in bone marrow stromal cells. Amelogenin expression was highest in areas of high bone turnover and activity. Further studies showed that during the first 2 weeks after application, rHAM⁺ induced, directly or indirectly, significant recruitment of mesenchymal progenitor cells, which later differentiated to form the regenerated periodontal tissues. The ability of a single protein to bring about regeneration of all periodontal tissues, in the correct spatio-temporal order, through recruitment of mesenchymal progenitor cells, could pave the way for development of new therapeutic devices for treatment of periodontal, bone and ligament diseases based on rHAM⁺.     

High yield of biologically active recombinant human amelogenin using the baculovirus expression system

The amelogenins are secreted by the ameloblast cells of developing teeth; they constitute about 90% of the enamel matrix proteins and play an important role in enamel biomineralization. Recent evidence suggests that amelogenin may also be involved in the regeneration of the periodontal tissues and that different isoforms may have cell-signalling effects. During enamel development and mineralization, the amelogenins are lost from the tissue due to sequential degradation by specific proteases, making isolation of substantial purified quantities of full-length amelogenin challenging. The aim of the present study was to express and characterize a recombinant human amelogenin protein in the eukaryotic baculovirus system in quantities sufficient for structural and functional studies. Human cDNA coding for a 175 amino acid amelogenin protein was subcloned into the pFastBac HTb vector (Invitrogen), this system adds a hexa-histidine tag and an rTEV protease cleavage site to the amino terminus of the expressed protein, enabling effective one-step purification by Ni2+-NTA affinity chromatography. The recombinant protein was expressed in Spodoptera frugiperda (Sf9) insect cells and the yield of purified his-tagged human amelogenin (rHAM+) was up to 10 mg/L culture. Recombinant human amelogenin (rHAM+) was characterized by SDS-PAGE, Western blot, ESI-TOF spectrometry, peptide mapping, and MS/MS sequencing. Production of significant amounts of pure, full-length amelogenin opened up the possibility to investigate novel functions of amelogenin. Our recent in vivo regeneration studies reveal that the rHAM+ alone could bring about regeneration of the periodontal tissues; cementum, periodontal ligament, and bone.     

大鼠咬合创伤牙周膜中MCP-1、ICAM-1的表达变化

目的:研究咬合创伤大鼠牙周组织中MCP-1、ICAM-1的表达情况。方法:12周龄雄性SD大鼠24只,随机分为4组(1个正常对照组和3个实验组),每组6只。正常对照组不作任何处理,实验组通过在大鼠左上颌第一磨牙颌面粘接树脂并内置不锈钢丝形成高出颌面0.6-0.8 mm的树脂层以建立同侧下颌咬合创伤实验动物模型,分别于建模后3、5、7 d处死各组大鼠,分离大鼠下颌组织,运用HE、Masson染色观察咬合创伤牙周组织形态变化,同时用免疫组织化学染色法检测MCP-1和ICAM-1的表达变化。结果:HE染色显示,正常组牙周膜纤维排列整齐,牙骨质表面较为平整,牙槽骨结构致密。实验组牙周膜纤维排列紊乱,牙周膜血管水肿充血、间隙改变,牙槽骨和牙骨质表面不平整,出现骨吸收。Masson染色显示,正常组牙周组织未见异常表现;实验组牙周膜纤维排列紊乱,可见水解断裂,局部有血流障碍和血管破裂。免疫组织化学显示,各实验组MCP-1和ICAM-1的表达变化均较正常对照组增多,差异有显著性(P0.05)。其中7 d组表达水平最高,与其他2组相比有统计学意义(P0.05)。结论:咬合创伤可引起大鼠牙周组织形态变化,MCP-1、ICAM-1的表达随时间呈现递增的趋势。     

ELABORATION OF THE MATRIX GLYCOPROTEIN OF ENAMEL BY THE SECRETORY AMELOBLASTS OF THE RAT INCISOR AS REVEALED BY RADIOAUTOGRAPHY AFTER GALACTOSE-3H INJECTION

The elaboration of enamel matrix glycoprotein was investigated in secretory ameloblasts of incisor teeth in 30–40-g rats. To this end, the distribution of glycoprotein was examined histochemically by the use of phosphotungstic acid at low pH, while the formation of glycoprotein was traced radioautographically in animals sacrificed 2.5–30 min after galactose-³H injection. Histochemically, the presence of glycoprotein is observed in ameloblasts as well as in the enamel matrix; in ameloblasts glycoprotein occurs within the Golgi apparatus in amounts increasing from the outer to the inner face of the stacks of saccules, and is concentrated in condensing vacuoles and secretory granules; in the enamel matrix, glycoprotein is observed within linear subunits. Radioautographs at 2.5 min after injection demonstrate the uptake of galactose-³H label by Golgi saccules, indicating that galactose-³H is incorporated into glycoprotein within this organelle. After 5–10 min, the label collects in the condensing vacuoles and secretory granules of the Golgi region. By 20–30 min, the label appears in the secretory granules of the apical (Tomes') processes, as well as in the enamel matrix (next to the distal end of the apical processes, and at the tips of matrix prongs). In conclusion, galactose contributes to the formation of glycoprotein within the Golgi apparatus. The innermost saccules then distribute the completed glycoprotein to condensing vacuoles, which later evolve into secretory granules. These granules rapidly migrate to the apical processes, where they discharge their glycoprotein content to the developing enamel.