Hsa-miRNA-143-3p regulates the odontogenic differentiation of human stem cells from the apical papilla by targeting NFIC.

AIM: To evaluate the effects of hsa-miRNA-143-3p on the cytodifferentiation of human stem cells from the apical papilla (hSCAPs) and the post-transcriptional regulation of Nuclear factor I-C (NFIC). METHODOLOGY: miRNA expression profiles in human immature permanent teeth and during hSCAP differentiation were examined. hSCAPs were treated with miR-143-3p overexpression or silencing viruses, and the proliferation and odontogenic and osteogenic differentiation of these stem cells, and the involvement of the NFIC pathway, were investigated. Luciferase reporter and NFIC mutant plasmids were used to confirm NFIC mRNA as a direct target of miR-143-3p. NFIC expression analysis in the miR-143-3p overexpressing hSCAPs was used to investigate whether miR-143-3p functioned by targeting NFIC. Student's t-test and chi-square tests were used for statistical analysis. RESULTS: miR-143-3p expression was screened by microarray profiling and was found to be significantly reduced during hSCAP differentiation (p < .05). Overexpression of miR-143-3p inhibited the mineralization of hSCAPs significantly (p < .05) and downregulated the levels of odontogenic differentiation markers (NFIC [p < .05], DSP [p < .01] and KLF4 [p < .01]), whereas silencing of miR-143-3p had the opposite effect. The luciferase reporter gene detection and bioinformatic approaches identified NFIC mRNA as a potential target of miR-143-3p. NFIC overexpression reversed the inhibitory effect of miR-143-3p on the odontogenic differentiation of hSCAPs. CONCLUSIONS: miR-143-3p maintained the stemness of hSCAPs and modulated their differentiation negatively by directly targeting NFIC. Thus, inhibition of this miRNA represents a potential strategy to promote the regeneration of damaged tooth roots.

[Effects of stromal cell-derived factor-1 on proliferation, migration, and odontoblastic differentiation of human dental pulp stem cells].

OBJECTIVE: To compare the effects of stromal cell-derived factor-1 (SDF-1) and granulocyte colony-stimulating factor (G-CSF) on proliferation, migration, and odontoblastic differentiation of human dental pulp stem cell (DPSC) in vitro. METHODS: DPSCs were cultured in vitro and treated with either 100 µg/L SDF-1 or 100 µg/L G-CSF. Cell counting kit-8 (CCK-8) and colony-forming unit (CFU) were used to detect the effect of SDF-1 and G -CSF on the proliferation ability of DPSC. Cell migration of DPSC was determined by wound healing assay and Transwell migration assay. The effects of SDF-1 and G-CSF on odontoblastic differentiation of DPSC were evaluated by alkaline phosphatase (ALP) staining, ALP activity and alizarin red S staining. The expression of odontoblastic-related genes such as dentin matrix protein 1 (DMP-1) and dentin sialophosphoprotein (DSPP) were quantified by real-time RT-PCR. RESULTS: SDF-1 and G-CSF promoted the proliferation of DPSC slightly, but the difference was not statistically significant. Wound healing assay showed that SDF-1 and G-CSF promoted cell migration of DPSC significantly (P<0.01), but there was no significant difference between the two factors. In Transwell migration assay, the number of migrated cells of the control group was 5.0 ± 1.4 per sight, while the SDF-1 group was 24.3 ± 6.8 per sight and the G-CSF group was 11.8 ± 3.3 per sight, suggesting that cell migration of DPSC was improved significantly after being treated with SDF-1 or G-CSF, and SDF-1 was more effective than G-CSF (P<0.05). Significantly greater odontoblastic differentiation potential was found in SDF-1 group and G-CSF group based on the ALP staining. Higher ALP activity, more mineralization nodule formation and higher expressions of DMP-1 and DSPP were also found after SDF-1 or G-CSF treatment. CONCLUSION: SDF-1 had no significant effect on the proliferation of DPSC, but could significantly promote cell migration and odontoblastic differentiation of DPSC. Its effect on DPSC was better than G-CSF.

[A retrospective study on pulpal tissue prognosis of avulsed permanent teeth in children].

OBJECTIVE: To analyze the pulpal prognosis of replanted permanent teeth in children and to examine the associated factors. METHODS: The samples consisted of 67 children with 81 avulsed permanent teeth treated in Peking University Hospital of Stomatology from 2000 to 2012. Their clinical data of the replanted teeth were collected, and the follow-up period was no less than 12 months. The pulpal prognosis was classified as pulp necrosis and pulp non-necrosis. RESULTS: The replantation within 30 minutes after avulsion led to the most significant increase in pulpal healing (P<0.05). The dental pulp of 80% (4/5) young permanent teeth replanted within 30 minutes remained vital, while all the teeth replanted after 30 minutes developed pulp necrosis within 60 days after replantation. CONCLUSION: The extra-alveolar period significantly affects the prognosis of pulp in immature permanent teeth after replantation. When the extra-alveolar period is more than 30 minutes, the chance of pulp revascularization after replantation is very low, therefore pulp extirpation should be performed.

[Spatiotemporal expression pattern of E-cadherin and P-cadherin during mouse tooth development].

OBJECTIVE: To investigate the expression patterns of E-cadherin and P-cadherin in murine-tooth germs at early developmental stages. METHODS: Mandible samples of CD1 mice from embryonic day 12.5 to postnatal day 3.5 were collected. The expressions of E-cadherin and P-cadherin in murine mandibular first molar germs were detected by immunofluorescence and observed under confocal fluorescence microscope. HE staining was performed for tissue morphology. RESULTS: Both E-cadherin and P-cadherin were widely expressed in the epithelial tissues through early developmental stages. The E-cadherin expression was increased in polarizing pre-ameloblasts, whereas the P-cadherin expression declined. The expression of the P-cadherin could be detected in epithelial tissues before bud stage, and expressed in mature ameloblasts at secretory stage. CONCLUSION: The E-cadherin and P-cadherin expressed in different spatiotemporal expression patterns, indicating their individual functions during tooth development. P-cadherin might function in the secretion and mineralization of enamel.

Nuclear factor I-C expression pattern in developing teeth and its important role in odontogenic differentiation of human molar stem cells from the apical papilla.

Nuclear factor I-C (NFIC) has an important role in the development of murine dental roots, but its role in human root formation is unreported. We thus elucidated the regulatory role of NFIC in the differentiation of human stem cells from the apical papilla (hSCAPs). The first step for this was to determine the expression of NFIC in human teeth, and it was found that NFIC expression was restricted to the odontoblasts and preodontoblasts of the developing molars of humans and mice. NFIC was found to be expressed in odontoblast-like cells after the subcutaneous transplantation of hSCAPs. NFIC expression was concomitant with dentin sialophosphoprotein (DSPP) in the mineralization of hSCAPs. NFIC knockdown in hSCAPs significantly inhibited expression of DSPP and promoted that of dentin matrix protein 1 (DMP1), meanwhile upregulated the expression of TGF-ß1 and downregulated SMAD3 and SMAD4. NFIC expression was significantly upregulated after TGF-ß1 treatment in hSCAPs. NFIC knockdown prolonged G1 phase of the cell cycle, but had no effect on cell proliferation and migration. These results suggest that NFIC is involved in the development of human root dentin and the regulation of odontoblastic differentiation of hSCAPs. NFIC may participate in the DMP1-DSPP signaling pathway and comprises a complex signaling cycle with TGF-ß1.

Msx1 regulates proliferation and differentiation of mouse dental mesenchymal cells in culture.

The homeobox, msh-like 1 (MSX1) protein is essential for cell proliferation and differentiation. Tooth germ development of Msx1 knockout mouse is arrested at the bud stage, impeding an understanding of its role beyond this stage of tooth development. The aims of this study were to investigate the potential role of MSX1 in the regulation of proliferation and differentiation of dental mesenchymal cells in culture, and to preliminarily explore its underlying mechanism of action. Tooth germs were isolated from embryonic day (E)15.5 mice. The mesenchyme was separated and digested into a single-cell suspension, and then cultured in vitro. Isolated dental mesenchymal cells were transfected with MSX1 small interfering RNA, and the effects on cell proliferation, cell cycle distribution, and the expression of bone morphogenetic protein 2 (Bmp2) and bone morphogenetic protein 4 (Bmp4) were studied. We also compared the expression levels of alkaline phosphatase (Alp), type I collagen (Col1A), osteocalcin (Ocn), runt-related transcription factor 2 (Runx2), dentin sialophosphoprotein (Dspp) and dentin matrix protein 1 (Dmp1), and mineralized nodule formation, between control and MSX1 siRNA-transfected groups after the induction of odontoblast differentiation. Knockdown of Msx1 expression was associated with decreased cell proliferation, prolonged time in the S phase of the cell cycle, enhanced odontoblast differentiation, and elevated Bmp2 and Bmp4 expression. We conclude that MSX1 may promote proliferation and prevent the differentiation of dental mesenchymal cells by the inhibition of Bmp2 and Bmp4 expression.

[Corrigendum] Comparison of the biological characteristics of human mesenchymal stem cells derived from exfoliated deciduous teeth, bone marrow, gingival tissue, and umbilical cord.

Subsequently to the publication of this paper, an interested reader drew to the authors' attention that, in Fig. 3 on p. 4973, the data panels shown for the "Osteogenesis" row of data for the GMSC and BMSC experiments appeared to be overlapping, such the data may have been derived from the same original source. After having examined their original data, the authors have realized that the data panel selected for the GMSC "Osteogenesis" experiment was inadvertently chosen incorrectly. The corrected version of Fig. 3 is shown below. Note that this error did not significantly affect the results or the conclusions reported in this paper, and all the authors agree to this Corrigendum. The authors are grateful to the editor of Molecular Medicine Reports for allowing them the opportunity to publish this corrigendum, and apologize to the readership for any inconvenience caused.[Molecular Medicine Reports 18: 4969­4977, 2018; DOI: 10.3892/mmr.2018.9501].

Root resorption of primary molars without successor teeth. An experimental study in the beagle dog.

Tooth agenesis is a common craniofacial congenital malformation in humans, but little is known about the mechanisms of root resorption in this condition. The purpose of this study was to investigate the mechanisms of root resorption in primary molars without successors. An animal model without permanent tooth germs was established by surgery in beagles. The times of onset of primary molar root resorption, with and without successors, were compared. The distribution of immune cells, odontoclasts, and their activating factors were determined by histochemistry and immunohistochemistry. Root resorption of primary mandibular molars without successors began later than physiological resorption. In primary molars without permanent germs, odontoclasts and immune cells were present mainly in the apical pulp at the start of root resorption, whereas in control teeth receptor activator of nuclear factor-κB ligand (RANKL)-positive cells were found mainly in the region of the periodontal ligament. CD14(+) and CD3(+) cells were found in both the pulp and the periodontal ligament region. These results suggest that the dental pulp of primary molars, as well as immune cells, may play an important role in root resorption in primary molars without permanent tooth germs.

Identification of multipotent stem cells from adult dog periodontal ligament.

Periodontal diseases, which are characterized by destruction of the connective tissues responsible for restraining the teeth within the jaw, are the main cause of tooth loss. Periodontal regeneration mediated by human periodontal ligament stem cells (hPDLSCs) may offer an alternative strategy for the treatment of periodontal disease. Dogs are a widely used large-animal model for the study of periodontal-disease progression, tissue regeneration, and dental implants, but little attention has been paid to the identification of the cells involved in this species. This study aimed to characterize stem cells isolated from canine periodontal ligament (cPDLSCs). The cPDLSCs, like hPDLSCs, showed clonogenic capability and expressed the mesenchymal stem cell markers STRO-1, CD146, and CD105, but not CD34. After induction of osteogenesis, cPDLSCs showed calcium accumulation in vitro. Moreover, cPDLSCs also showed both adipogenic and chondrogenic potential. Compared with cell-free controls, more cementum/periodontal ligament-like structures were observed in CB-17/SCID mice into which cPDLSCs had been transplanted. These results suggest that cPDLSCs are clonogenic, highly proliferative, and have multidifferentiation potential, and that they could be used as a new cellular therapeutic approach to facilitate successful and more predictable regeneration of periodontal tissue using a canine model of periodontal disease.

[Isolation, culture and biological characterization of Beagle stem cells from apical papilla].

OBJECTIVE: To isolate and characterize the Beagle stem cells from apical papilla. METHODS: Apical papilla was severed from the end of freshly extracted Beagle's young permanent upper anterior teeth, and digested by collagenase type I and dispase for cell culture. The isolated cells were investigated for stem cell properties by analyzing their colony-forming efficiency, growth characteristics and the expression of mesenchymal stem cell markers; and evaluating their multidifferentiation potentials including osteogenic, adipogenic, and chondrogenic potentials. Additionally, the cells were transplanted subcutaneously into immunocompromised mice to observe the mineral tissue formation. RESULTS: Our study showed that a clonogenic, rapidly proliferative population of cells existed in Beagle's apical papilla, and these cells had a significantly higher colony-forming rate than the stem cells from apical papilla derived from humans (P<0.001). These cells had multilineage differentiation ability including osteogenic, adipogenic and chondrogenic potentials. Mineralized nodules were formed after osteogenic induction, lipid droplets were found after adipogenic induction, and the pellets showed positive immunohistochemical staining for collagen II after chondrogenic induction. These cells also expressed the mesenchymal stem cell markers including STRO-1 and CD146, while negative for CK. Moreover, these cells transplanted with hydroxyapatite in immunocompromised mice could form mineral tissue and pulp-dentin complex-like tissue. CONCLUSION: There are stem cells from the apical papilla which have high proliferation ability and multilineage differentiation potential existing in the Beagle's apical papilla.

Regeneration of Dental Pulp Tissue by Autologous Grafting Stem Cells Derived from Inflammatory Dental Pulp Tissue in Immature Premolars in a Beagle Dog.

OBJECTIVE: To compare the biological characteristics of dental pulp stem cells (DPSCs) and inflamed dental pulp derived stem cells (I-DPSCs) in vitro and their regeneration potential in Beagle immature premolars. METHODS: Pulpitis was induced in the premolars of one beagle dog by opening the pulp chamber for 2 weeks, and inflammation was histologically confirmed. DPSCs and I-DPSCs were isolated from normal and inflamed dental pulp, and cell morphology, expression of mesenchymal stem cell markers, clone formation ability, cell proliferation and osteogenic/odontogenic differentiation potential were compared. The dental pulp of 20 roots from 10 immature premolars was extracted and divided into two groups. DPSCs or I-DPSCs with scaffolds were transplanted into the root canals. The roots were extracted after 3 months, and pulp regeneration was evaluated by histological analysis. The data were statistically analysed using one-way ANOVA and a Student t test. RESULTS: Histological analyses showed lymphocyte infiltration and elevated TNF-α expression, which confirmed the diagnosis of pulpitis. I-DPSCs showed similar morphology, marker gene expression and clone formation ability but greater proliferation ability and osteogenic/odontogenic differentiation potential. Pulp-like tissue formation and bone- and dentine-like tissue deposition were observed in both DPSC- and I-DPSC-transplanted roots. CONCLUSION: DPSCs derived from inflammatory dental pulp tissue have similar biological characteristics to those from normal dental pulp and could mediate pulp and dentine regeneration in immature premolars.

Microbiota Regulates Dentine Mineralisation and Differentiation of Dental Pulp Stem Cells.

OBJECTIVE: To investigate the role of microbiota in dentine formation and the characteristics of dental pulp stem cells (DPSCs) in mouse incisors. METHODS: The influence of microbiota on dentine was detected via microcomputed tomography (microCT), microhardness testing and haematoxylin-eosin (HE) staining in incisors from germ-free (GF), specific pathogen-free (SPF) and conventionalised (ConvD) mice. Cell Counting Kit-8 (CCK-8) assay, alizarin red staining and expression of dentine sialophosphoprotein (DSPP), alkaline phosphatase (ALP) and bone sialoprotein (BSP) via real-time polymerase chain reaction (PCR) were used to evaluate the biological characteristics of DPSCs derived from mice of different microbiota status. RESULTS: MicroCT showed that the incisors in the GF and ConvD groups had comparable dentine thickness to those in the SPF group. Microhardness testing showed a lower dentine hardness value in GF incisors compared to SPF, while HE staining showed that GF incisors exhibited thicker predentine than SPF incisors. There was no difference between the ConvD and SPF groups. DPSCs from GF mice showed no significant difference in proliferation rate to SPF and ConvD DPSCs. DPSCs from GF mice formed less mineral deposition and expressed lower levels of osteo-/odontogenic differentiation-related genes including ALP, BSP and DSPP than SPF and ConvD DPSCs. The absence of microbiota in GF mice resulted in a lower dentine hardness value, thicker predentine and impaired osteo-/odontogenic differentiation capacity. CONCLUSION: The absence of microbiota impaired the dentine mineralisation and osteo-/odontogenic differentiation abilities of DPSCs.

Mineralisation Influence of Betamethasone on Lipopolysaccharide-Stimulated Dental Pulp Cells.

OBJECTIVE: To evaluate the mineralisation response of lipopolysaccharide (LPS)-induced dental pulp cells (DPCs) to betamethasone and the potential benefit of betamethasone application on the recovery of injured dental pulp. METHODS: The proliferation influence of betamethasone on DPCs was analysed through the cell counting kit-8 assay. To assess the anti-inflammatory effects of betamethasone, the expression levels of inflammatory factors IL-6, IL-1ß and TNF-∂ were determined by real-time polymerase chain reaction (PCR). Mineralisation was investigated through the detection of the mineralisation-related biomarkers alkaline phosphatase (ALP), dentine sialophosphoprotein (DSPP) and osteocalcin (OCN) through the ALP activity assay, immunohistochemistry staining, Alizarin Red and tissue nonspecific alkaline phosphatase (TNAP) staining, the reverse transcriptase PCR technique and western blot. RESULTS: A low concentration of betamethasone (1 µ/mL) promoted the proliferation of DPCs. The real-time PCR results demonstrated that inflammatory cytokines were downregulated by betamethasone treatment. The mineralisation outcome in DPCs treated with betamethasone was better than in those treated without betamethasone. CONCLUSION: Betamethasone promoted the proliferation of DPCs. Betamethasone enhanced mineralisation in LPS-stimulated DPCs.

Treatment with Stem Cells from Human Exfoliated Deciduous Teeth and Their Derived Conditioned Medium Improves Retinal Visual Function and Delays the Degeneration of Photoreceptors.

Retinitis pigmentosa (RP) is a hereditary disease characterized by degeneration and the loss of photoreceptors. Stem cell-based therapy has emerged as a promising strategy for treating RP. Stem cells from exfoliated deciduous teeth (SHEDs), a type of mesenchymal stem cell from human exfoliated deciduous teeth, have the potential to differentiate into photoreceptor-like cells under specific induction in vitro. It has been confirmed that through paracrine secreta, SHEDs exert neurotrophic, angiogenic, immunoregulatory, and antiapoptotic functions in injured tissues. This study was designed to determine whether retinal-differentiated SHEDs and the conditioned medium derived from SHEDs (SHEDs-CM) have therapeutic effects in a mouse model of RP. The results showed that both SHEDs and SHEDs-CM improved electroretinogram responses, ameliorated photoreceptor degeneration, and maintained the structure of the outer segments of photoreceptors. The therapeutic effects were related to antiapoptotic activity of SHEDs and SHEDs-CM. Thus, SHEDs may be a promising stem cell source for treating retinal degeneration.

[Establishment of permanent tooth germ missing animal model and study on root resorption of the corresponding deciduous teeth].

OBJECTIVE: To establish the permanent tooth germ missing animal model for future research on the root resorption of deciduous tooth in the absence of permanent tooth germ. METHODS: The permanent tooth germ missing animal model was established by surgical removal of the permanent tooth buds in a male 11-week-old Beagle dog. Root resorption of the deciduous teeth without permanent successors was observed by taking periapical films periodically,and compared with physiological root resorption. Once the sign of root resorption of the deciduous teeth without permanent successors was detected on radiographic films, the animal was sacrificed and the mandibular bone was collected for histological study. RESULTS: Root resorption of the deciduous teeth with the presence of permanent tooth germ started at 20 weeks after birth, while root resorption of deciduous teeth without permanent tooth germ started 26-27 weeks which was significantly delayed. Histological studies showed that a large number of multinucleated giant cells were present on the pulpal surface of the root, while only few of them were seen on the outer surface. CONCLUSION: The permanent tooth germ missing animal model was successfully established in this study which simulated the case of congenital absence of permanent tooth germ in human. Root resorption of deciduous tooth without permanent tooth germ was significantly delayed than the deciduous tooth with permanent tooth germ.

Comparison of the biological characteristics of human mesenchymal stem cells derived from exfoliated deciduous teeth, bone marrow, gingival tissue, and umbilical cord.

Different sources of mesenchymal stem cells (MSCs) may differ in their biological characteristics, which are important for their clinical application. In the present study, MSCs were isolated from human exfoliated deciduous teeth (SHED), bone marrow, gingival tissue and umbilical cord tissue, and their biological characteristics including surface markers, proliferation capacity, tumorigenicity and immunogenicity were analyzed by flow cytometric analysis, ELISA and co­culture with human lymphocytes, respectively. The results indicated that all four types of stem cells obtained from different sources expressed MSC surface markers, and they did not show tumorigenicity either in vivo or in vitro. Stem cells from SHED exhibited the strongest proliferation capacity. Umbilical cord­derived MSCs displayed the strongest immunomodulatory ability, while bone marrow MSCs exhibited the best antigen­presenting potential in response to interferon­Î³ stimulation. These results provide information on MSCs derived from different tissues, which may be helpful in their clinical application.

[Effect of TNF-alpha on murine osteoclast differentiation].

OBJECTIVE: The purpose of this study was to investigate the effect of TNF-alpha on osteoclast differentiation in primary murine bone marrow cell culture with and without RANKL. METHODS: M-CSF-dependent bone marrow cells were isolated from 5-6 weeks old mice, and cultured in the presence of M-CSF (25 microg/L) with different concentrations of TNF-alpha (0, 1, 10, 100 microg/L) for 5 days, the formation of TRAP(+) multinucleated cells was observed. These cells were also cultured in the presence of both RANKL (30 microg/L) and M-CSF (25 microg/L) with or without 10 microg/L TNF-alpha for 4, 5, 6 and 9 days. The number of TRAP(+) multinucleated cells and resorption pits on dentine slices were counted under light microscope. RESULTS: In the absence of RANKL, TNF-alpha was unable to induce osteoclast formation from murine bone marrow precursors. In the presence of RANKL, TNF-alpha augmented osteoclastogenesis and bone resorption, and this effect occurred only on the early stage. CONCLUSION: TNF-alpha enhances RANKL-induced osteoclast formation and function, but cannot substitute for RANKL. TNF-alpha stimulates osteoclast differentiation, but not survival.

A retrospective study of using removable occlusal splint in the treatment of condylar fracture in children.

BACKGROUND: Although the concept of conservative treatment for paediatric condylar fracture is well understood, there is still a lack of a recognized method for treating child patients with a condylar fracture. The purpose of this study was to investigate the effect of the removable occlusal splint in treating condylar fractures in children and adolescents. MATERIALS AND METHODS: Forty children and adolescents with condylar fracture, aged 3-16, were included in this study. A removable occlusal splint with varying thickness was fabricated according to the age, developmental stage of the mandible, and degree of condylar dislocation. This was worn for 1-3 months, accompanied by functional exercises. Follow-up was carried out by clinical observation and panoramic X-ray. RESULTS: Clinically satisfactory results with good occlusion were obtained in all the patients, along with unimpaired function and normal growth and development of the mandible. The panoramic image showed remodelling and reconstruction of the fractured condyles. CONCLUSIONS: Our results confirm that conservative treatment has a satisfactory clinical outcome in treating condylar fracture in children. The removable occlusal splint is a promising approach for treating condylar fracture in children and adolescents.

[Isolation and identification of Beagle dog dental pulp stem cells].

OBJECTIVE: To identify the existence of the dental pulp stem cells in Beagle's pulp tissue by using the same methods of isolating and culturing the human dental pulp stem cells. METHODS: Pulp tissue was extirpated from the crown and root of the Beagle's healthy permanent tooth, and digested by dispase for cell culture. Classical identification methods of mesenchymal stem cells including observation of biological characteristics, capacity of multilineage differentiation, and expression of specific markers associated with mesenchymal stem cells were applied to verify the existence of Beagle's dental pulp stem cells. RESULTS: A clonogenic, rapidly proliferative population of cells were isolated from Beagle' pulp tissue. Under the same culture condition, the Beagle's dental pulp stem cells had a significant higher colony-forming unit-fibroblast (CFU-F) formation rate (150 colony/10(4) cells) than the dental pulp cells derived from the human pulp tissue (60 colony/10(4) cells). These cells also had the multilineage differentiation ability. They could be induced to form mineralized nodules, lipid droplets and chondrocytes. Furthermore these cells expressed the mesenchymal stem cell markers including STRO-1, CD146, alkaline phosphatase, nestin, vimentin and cytokeratin-18. CONCLUSIONS: There are dental pulp stem cells in the Beagle's pulp tissue.

[The role of pulp in the root resorption of primary teeth without permanent tooth germs].

OBJECTIVE: To investigate the role of pulp in the root resorption of primary teeth without permanent tooth germs. METHODS: The animal model without permanent tooth germs was established by surgery in Beagle dog. The root resorption was observed by taking periapical radiographs periodically. The samples of mandibular bone and pulp at different resorption stages were collected. The distribution of odontoclasts and the activating factor was analyzed by histological staining and semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR). The role of pulp in the root resorption of primary teeth was tested by early pulpectomy. RESULTS: In the root resorption of primary molars without permanent teeth germs, a large number of odontoclasts were present on the pulpal surface of the root canal. Semi-quantification RT-PCR showed that the ratios of the expression of receptor activator of NF-κB ligand (RANKL) mRNA and ß-actin in the pulp of permanent teeth and primary teeth without permanent teeth germ during different periods of root resorption are 0.1314, 0.1901, 0.2111 and 0.6058 (P > 0.05). The root resorption of primary teeth without permanent teeth germs in test groups was about 5 weeks later than that of control group. CONCLUSIONS: The pulp of primary tooth played an important role in the root resorption of primary tooth without permanent tooth germ.