Cell-to-cell communication--periodontal regeneration

Single-cell and bulk RNA-sequencing reveal SPP1 and CXCL12 as cell-to-cell communication markers to predict prognosis in lung adenocarcinoma

Lung adenocarcinoma (LUAD) generally presents as an immunosuppressive microenvironment. The characteristics of cell-to-cell communication in the LUAD microenvironment has been unclear. In this study, the LUAD bulk RNA-seq data and single-cell RNA-seq data were retrieved from public dataset. Differential expression genes (DEGs) between LUAD tumor and adjacent non-tumor tissues were calculated by limma algorithm, and then detected by PPI, KEGG, and GO analysis. Cell-cell interactions were explored using the single-cell RNA-seq data. Finally, the first 15 CytoHubba genes were used to establish related pathways and these pathways were used to characterize the immune-related ligands and their receptors in LUAD. Our analyses showed that monocytes or macrophages interact with tissue stem cells and NK cells via SPP1 signaling pathway and tissue stem cells interact with T and B cells via CXCL signaling pathway in different states. Hub genes of SPP1 participated in SPP1 signaling pathway, which was negatively correlated with CD4+ T cell and CD8+ T cell. The expression of SPP1 in LUAD tumor tissues was negatively correlated with the prognosis. While CXCL12 participated in CXCL signaling pathway, which was positively correlated with CD4+ T cell and CD8+ T cell. The role of CXCL12 in LUAD tumor tissues exhibits an opposite effect to that of SPP1. This study reveals that tumor-associated monocytes or macrophages may affect tumor progression. Moreover, the SPP1 and CXCL12 may be the critic genes of cell-to-cell communication in LUAD, and targeting these pathways may provide a new molecular mechanism for the treatment of LUAD.

Induction of human stem cells into ameloblasts by reaggregation strategy

BACKGROUND

Human epithelium-derived stem cells and induced pluripotent stem cells (hiPSCs) possess the capability to support tooth formation and differentiate into functional enamel-secreting ameloblasts, making them promising epithelial-component substitutes for future human tooth regeneration. However, current tissue recombination approaches are not only technically challenging, requiring precise induction procedures and sophisticated microsurgery, but also exhibit low success rates in achieving tooth formation and ameloblastic differentiation.

METHODS

Suspended human keratinocyte stem cells (hKSCs) or cells from three hiPSC lines were directly mixed with dissociated embryonic mouse dental mesenchymal cells (mDMCs) that possess odontogenic potential in different proportions and reaggregated them to construct bioengineered tooth germs. The success rates of tooth formation and ameloblastic differentiation were confirmed after subrenal culture. The sorting capability, sequential development, and ameloblastic differentiation of stem cells were examined via GFP tracing, RT-PCR, and histological analysis, respectively.

RESULTS

Our reaggregation approach achieved an impressive success rate of more than 90% in tooth formation and 100% in ameloblastic differentiation when the chimeric tooth germs contained 1%~10% hKSCs or 5% hiPSCs. In addition, we observed that hiPSCs, upon exposure to mDMCs, initially transformed into epidermal cells, as indicated by KRT14 and CD29 expression, before progressing into dental epithelial cells, as indicated by SP6 and SHH expression. We also found that epithelial-derived hiPSCs, when reaggregated with mDMCs, were more favorable for tooth formation than their mesenchymal-derived counterparts.

CONCLUSIONS

This study establishes a simplified yet highly effective cell-cell reaggregation strategy for inducing stem cells to support tooth formation and differentiate into functional ameloblasts, paving the way for novel approaches for the development of stem cell-based tooth organoids and bioengineered tooth germs in vitro.

Weighted Gene Co-expression Network Analysis (WGCNA) of Wnt Signaling Related to Periodontal Ligament Formation: A Bioinformatics-Based Analysis

Introduction The Wnt signaling pathway is crucial for tooth development, odontoblast differentiation, and dentin formation. It interacts with epithelial cadherin (E-cadherin) and beta-catenin in tooth development and periodontal ligament (PDL) formation. Dysregulation of Wnt signaling is linked to periodontal diseases, requiring an understanding of therapeutic interventions. Weighted gene co-expression network analysis (WGCNA) can identify co-expressed gene modules. Our study aims to identify hub genes in WGCNA analysis of Wnt signaling-based PDL formation. Methods The study used a microarray dataset GSE201313 from the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus to analyze the impact of DMP1 expression on XLH dental pulp cell differentiation and PDL formation. The standardized dataset was used for WGCNA analysis, which generated a co-expression network by calculating pairwise correlations between genes and constructing an adjacency matrix. The topological overlap matrix (TOM) was transformed into a hierarchical clustering tree and then cut into modules or clusters of highly interconnected genes. The module eigengene (ME) was calculated for each module, and the genes within this module were identified as hub genes. Gene ontology (GO) and KEGG pathway enrichment analysis were performed to gain insights into the biological functions of the hub genes. The integrated Differential Expression and Pathway analysis (iDEP) tool (http://bioinformatics.sdstate.edu/idep/; South Dakota State University, Brookings, USA) was used for WGCNA analysis. Results The study used the WGCNA package to analyze 1,000 differentially expressed genes, constructing a gene co-expression network and generating a hierarchical clustering tree and TOM. The analysis reveals a scale-free topology fitting index R2 and mean connectivity for various soft threshold powers, with an R2 value of 5. COL6A1, MMP3, BGN, COL1A2, and FBN2 are hub genes implicated in PDL development. Conclusion The study identified key hub genes, including COL6A1, MMP3, BGN, and FBN2, crucial for PDL formation, tissue remodeling, and cell-matrix interactions, guiding future therapeutic strategies.

Nonsense-mediated mRNA decay affects hyperactive root formation in oculo-facio-cardio-dental syndrome via up-frameshift protein 1

OBJECTIVES

Oculo-facio-cardio-dental (OFCD) syndrome is a rare X-linked genetic disorder caused by mutations in the BCL6 co-repressor (BCOR) and is mainly characterized by radiculomegaly (elongated dental roots). All BCOR mutations reported to date have been associated with premature termination codons, indicating that nonsense-mediated mRNA decay (NMD) might play a vital role in the pathogenesis of OFCD syndrome. However, the molecular mechanisms underlying NMD remain unclear. In this study, we investigated the involvement of up-frameshift protein 1 (UPF1), which plays a central role in NMD, in the hyperactive root formation caused by BCOR mutations.

METHODS

Periodontal ligament cells, isolated from a Japanese woman with a c.3668delC frameshift mutation in BCOR, and primary human periodontal ligament fibroblasts (HPdLFs) were used for an RNA immunoprecipitation assay to confirm the binding of UPF1 to mutated BCOR. Additionally, the effects of UPF1 on the BCOR transcription levels and corresponding gene expression were determined by performing relative quantitative real-time polymerase chain reactions.

RESULTS

RNA immunoprecipitation revealed that UPF1 binds to exon 9 of mutated BCOR. Additionally, UPF1 knockdown via siRNA upregulated the transcription of BCOR, whereas overexpression of wild-type and mutated BCOR with the same frameshift mutation in HPdLFs altered bone morphogenetic protein 2 (BMP2) expression.

CONCLUSIONS

Our findings indicate that BCOR mutations regulate the transcription of BCOR via UPF1, which may in turn regulate the expression of BMP2. NMD, caused by a c.3668delC mutation, potentially leads to an OFCD syndrome phenotype, including elongated dental roots.

Hierarchically patterned triple-layered gelatin-based electrospun membrane functionalized by cell-specific extracellular matrix for periodontal regeneration

OBJECTIVES

Regenerating the periodontium poses a critical challenge in oral medicine. To repair various periodontal defects, it is necessary to adopt a bio-scaffold that provides both the architecture and bioactive cues for local stem cells to migrate, reside, proliferate, and differentiate. The objective of this study is to combine a cell-specific decellularized extracellular matrix (ECM) and a biomimetic electrospinning scaffold to regenerate severely destructed periodontium.

METHODS

SEM, water contact angle (WCA), live/dead staining, swelling ratio, tensile test and immune-fluorescent staining were used to define the suitable topography for certain dental stem cells seeding and culturing. Transwell assay, CCK-8, Alizarin Red staining and PCR immune-fluorescent staining were used to determine ideal cell-specific ECM for PDLSCs/BMSCs migration, viability, and oriented differentiation. A biodegradable triple-layered electrospun scaffold (TLS) was fabricated by electrospinning with aligned fibers on both surfaces and a polyporous structure in the middle. The morphology and inter-porous structure of the TLS were characterized by SEM and mercury intrusion porosimetry (MIP). The surface of the TLS was functionalized with cell-specific ECM (Bi-ECM-TLS) through decellularization of the cell sheets cultured on the scaffold. The regenerative outcome of Bi-ECM-TLS was assessed by an in-situ rat periodontal defect model. Micro-CT, HE-staining, Masson's trichome staining, Sirius Red staining and Immunofluorescent staining were used for histological analysis.

RESULTS

Aligned Gelatin/PCL fibrous membrane (GPA) was most effective for both PDLSCs and BMSCs in culture with WCA around 50 degrees and better mechanical strength than the rest. MSCs favored the same type of ECM (cell-specific ECM), and their regenerative properties were effectively induced with better chemotaxis, proliferative and differentiating behaviors. TLS characterization showed that TLS possessed aligned-random-aligned structure and inter-porous structure. In a rat model of periodontal defects, the TLS functionalized by BMSC-specific ECM for bone regeneration and PDLSC-specific ECM demonstrated highest BV/TV ratio, best bone structure and ligament fiber orientation and blood vessel formation, suggesting optimal performance in regenerating both alveolar bone and periodontal ligaments over TLS, single-ECM loaded TLS and r-Bi-ECM-TLS.

SIGNIFICANCE

This study highlights the importance of combining a cell-specific decellularized ECM and a biomimetic electrospinning scaffold for targeted periodontal tissue regeneration, with potential implications for periodontal tissue engineering and improved patient outcomes.

Spatiotemporal cellular dynamics and molecular regulation of tooth root ontogeny

Tooth root development involves intricate spatiotemporal cellular dynamics and molecular regulation. The initiation of Hertwig's epithelial root sheath (HERS) induces odontoblast differentiation and the subsequent radicular dentin deposition. Precisely controlled signaling pathways modulate the behaviors of HERS and the fates of dental mesenchymal stem cells (DMSCs). Disruptions in these pathways lead to defects in root development, such as shortened roots and furcation abnormalities. Advances in dental stem cells, biomaterials, and bioprinting show immense promise for bioengineered tooth root regeneration. However, replicating the developmental intricacies of odontogenesis has not been resolved in clinical treatment and remains a major challenge in this field. Ongoing research focusing on the mechanisms of root development, advanced biomaterials, and manufacturing techniques will enable next-generation biological root regeneration that restores the physiological structure and function of the tooth root. This review summarizes recent discoveries in the underlying mechanisms governing root ontogeny and discusses some recent key findings in developing of new biologically based dental therapies.

Determination of the Sterilization Dose of Gamma-Ray Irradiation for Polyvinyl Alcohol-Collagen-Chitosan Composite Membrane as a Material for Periodontal Regenerative Surgery

OBJECTIVE

 Membrane sterility is very necessary considering its function as an implant material. Therefore, this research aims to determine the dose of gamma-ray irradiation for the sterilization of polyvinyl alcohol (PVA)-collagen-chitosan composite membranes used as regenerative surgery materials.

MATERIALS AND METHODS

 A total of 100 pieces of the composite membranes were prepared in a size of 2.0 × 1.5 cm by mixing 7.5% PVA, 3% collagen, and 2% chitosan using the film casting method in three batches. Furthermore, the bioburden test was performed to determine the initial microbial count in the sample by following ISO 11737-1. The results were used to ascertain the dose of gamma-ray irradiation on the sample according to ISO 11137-2. The dose verification test was then performed at the sterility assurance level 10-6.

RESULTS

 The average result of the bioburden test from three batches was 6.6 colony forming unit; hence, the verification dose was 4.8 kGy. In the verification dose test, since there was only one contaminated sample, the sterility dose test was continued.

CONCLUSION

 The sterile gamma-ray irradiation dose for PVA-collagen-chitosan composite membrane was 17.1 kGy.

Evaluation of the biological effects of amelogenin on human oral keratinocytes

OBJECTIVES

Amelogenins are clinically used in periodontal regeneration as main components of root surface modifying agents, even without specifically preventing the premature colonization of the healing tissue defect by means of a physical barrier membrane. The objective of this study was to investigate the effects of human amelogenin on the proliferation, migration, and morphology of Immortalized Human Oral Keratinocytes (iHOKs).

METHODS

Immortalized Human Oral Keratinocytes were expanded in Keratinocyte Growth Medium-2 (KGM-2). Full-length recombinant amelogenin protein was diluted in KGM-2 in five concentrations (10 ng/ml, 100 ng/ml, 1.000 ng/ml, 5.000 ng/ml and 10.000 ng/ml). iHOKs were cultured in medium supplemented with the amelogenin dilutions. Samples without amelogenin served as control. Cell metabolism and cell proliferation together with cell migration were evaluated at day 7, 14, 21.

RESULTS

At day 7, iHOKs treated with 10,000 ng/ml showed a significant decrease in keratinocytes´ proliferation. The metabolic activity at this timepoint was significantly lower for concentrations ≥ 1000 ng/ml. At days 14 and 21, both the addition of 5000 ng/ml and even more 10,000 ng/ml amelogenin reduced significantly the proliferation of keratinocytes. The effects on the metabolic activity for these timepoints were visible already with 100 ng/ml. Treatment of iHOKs with amelogenin of ≥ 1000 ng/ml led to inhibitory effects on cell migration already after 24 h.

CONCLUSIONS

The full-length recombinant amelogenin has a significant biological impact on iHOKs. The increasing dose dependent inhibitory effects of amelogenin shown on iHOKs might explain the disruption of the apical migration of the junctional epithelium during regenerative healing.

CLINICAL SIGNIFICANCE

Amelogenin, presents time- and dose-dependent inhibitory effects on the growth of keratinocytes, which might explain the biological rationale behind its application in periodontal regeneration.

BMP signaling in the development and regeneration of tooth roots: from mechanisms to applications

Short root anomaly (SRA), along with caries, periodontitis, and trauma, can cause tooth loss, affecting the physical and mental health of patients. Dental implants have become widely utilized for tooth restoration; however, they exhibit certain limitations compared to natural tooth roots. Tissue engineering-mediated root regeneration offers a strategy to sustain a tooth with a physiologically more natural function by regenerating the bioengineered tooth root (bio-root) based on the bionic principle. While the process of tooth root development has been reported in previous studies, the specific molecular mechanisms remain unclear. The Bone Morphogenetic Proteins (BMPs) family is an essential factor regulating cellular activities and is involved in almost all tissue development. Recent studies have focused on exploring the mechanism of BMP signaling in tooth root development by using transgenic animal models and developing better tissue engineering strategies for bio-root regeneration. This article reviews the unique roles of BMP signaling in tooth root development and regeneration.

Development, Establishment, and Validation of a Model for the Mineralization of Periodontium Remodelling Cells: Cementoblasts

Chronic kidney disease (CKD) patients undergoing dialysis are at high risk of bone fractures. CKD-induced mineral and bone disorder is extended to periodontal disease due to changes in the ionic composition of saliva in CKD patients, dysregulating mineralization, hindering regeneration and thereby promoting the progression of dental complications. Despite the importance of cementum for overall oral health, the mechanisms that regulate its development and regeneration are not well comprehended, and a lack of sufficient in vitro experimental models has hindered research progress. In this study, the impact of experimental conditions on the calcification of cementoblasts was systematically investigated, aimed at establishing a standardized and validated model for the calcification of cementoblasts. The effects of phosphate, calcium, ascorbic acid, β-glycerolphosphate, dexamethasone, and fetal calf serum on the calcification process of cementoblasts were analyzed over a wide range of concentrations and time points by investigating calcium content, cell viability, gene expression and kinase activity. Cementoblasts calcified in a concentration- and time-dependent manner with higher concentrations of supplements cause a higher degree of calcification but decreased cell viability. Phosphate and calcium have a significantly stronger effect on cementoblast calcification processes compared to osteogenic supplements: ascorbic acid, β-glycerolphosphate, and dexamethasone induce calcification over a wide range of osteogenic signalling pathways, with osteopontin being a central target of gene regulation. Conversely, treatment with ascorbic acid, β-glycerolphosphate, and dexamethasone leads to activating only selected pathways, especially promoting bone sialoprotein expression. The developed and validated cementoblast calcification protocol, incubating up to 60% confluent cementoblasts with 1.9 mmol L-1 of phosphate supplementation for a reasonable, multi-pathway calcification induction and 10 mmol L-1 β-glycerolphosphate, 75 µmol L-1 ascorbic acid and 10 nmol L-1 dexamethasone for a reasonable osteogenic differentiation-based calcification induction, provides standard in vitro experimental models for better understanding cementoblast function and regeneration.

An Overview of the Systematic Evidence on the Adjunctive Use of Laser Therapy in Non-surgical Periodontal Treatment

This overview aimed to recapitulate the evidence related to laser application in non-surgical periodontal treatment along with conventional periodontal treatment for optimum clinical practice based on the available systematic reviews (SRs). An advanced literature search in the English language was conducted in the PubMed, Medical Literature Analysis and Retrieval System Online (MEDLINE), ScienceDirect, and Scopus databases from January 2000 to October 2022. Two independent reviewers screened all the databases and extracted the data in duplicate. The risk of bias in the selected studies was assessed with the Methodological Quality of Systematic Reviews 2 (AMSTAR 2) guideline for SRs. Cohen's kappa statistics were performed to assess the level of agreement for the assessment of the risk of bias. A total of 556 studies (PubMed = 115, Scopus = 66, ScienceDirect = 298, and MEDLINE = 77) were identified after the initial search using the keywords from different databases. After removing the duplicates and assessing the full manuscripts, a total of 24 studies were selected based on the inclusion criteria for the current overview. A total of three, four, 12, and five systematic reviews were classified as high, moderate, low, and critically low-quality SRs as per the AMSTAR 2 quality assessment tool. Cohen's Kappa statistics showed perfect (𝛋 =1.000) agreement between the two reviewers. Adjunctive laser therapy along with conventional non-surgical periodontal treatment might be effective in short-term treatment outcomes; however, evidence of long-term effects is still lacking.

Oridonin alleviates the inhibitory effect of lipopolysaccharide on the proliferation and osteogenic potential of periodontal ligament stem cells by inhibiting endoplasmic reticulum stress and NF-κB/NLRP3 inflammasome signaling

BACKGROUND

The aim of this study was to investigate the protective effect and mechanism of oridonin in an in vitro lipopolysaccharide (LPS)-induced human periodontal ligament stem cells (hPDLSCs) model of periodontitis.

METHODS

Primary hPDLSCs were isolated and cultured, and then the expression of surface antigens CD146, STRO-1 and CD45 of hPDLSCs was detected by flow cytometry. The mRNA expression level of Runx2, OPN, Col-1, GRP78, CHOP, ATF4 and ATF6 in the cells was tested by qRT-PCR. MTT was taken to determine the cytotoxicity of oridonin at different concentrations (0-4 μM) on hPDLSCs. Besides, ALP staining, alizarin red staining and Oil Red O staining were utilized to assess the osteogenic differentiation (ALP concentration, mineralized calcium nodule formation) and adipogenic differentiation abilities of the cells. The proinflammatory factors level in the cells was measured by ELISA. The protein expression level of NF-κB/NLRP3 pathway-related proteins and endoplasmic reticulum (ER) stress-related markers in the cells were detected by Western blot.

RESULTS

hPDLSCs with positive CD146 and STRO-1 expression and negative CD45 expression were successfully isolated in this study. 0.1-2 μM of oridonin had no significant cytotoxicity on the growth of hPDLSCs, while 2 μM of oridonin could not only greatly reduce the inhibitory effect of LPS on the proliferation and osteogenic differentiation of hPDLSCs cells, but also inhibit LPS-induced inflammation and ER stress in hPDLSCs cells. Moreover, further mechanism research showed that 2 μM of oridonin suppressed NF-κB/NLRP3 signaling pathway activity in LPS-induced hPDLSCs cells.

CONCLUSIONS

Oridonin promotes proliferation and osteogenic differentiation of LPS-induced hPDLSCs in an inflammatory environment, possibly by inhibiting ER stress and NF-κB/NLRP3 pathway. Oridonin may have a potential role in the repair and regeneration of hPDLSCs.

Periodontal regeneration: Lessons from the periodontal ligament-cementum junction in diverse animal models

The attachment of the roots of mammalian teeth of limited eruption to the jawbone is reliant in part on the mineralization of collagen fibrils of the periodontal ligament (PDL) at their entry into bone and cementum as Sharpey's fibers. In periodontitis, a high prevalence infection of periodontal tissues, the attachment apparatus of PDL to the tooth root is progressively destroyed. Despite the pervasiveness of periodontitis and its attendant health care costs, and regardless of decades of research into various possible treatments, reliable restoration of periodontal attachment after surgery is not achievable. Notably, treatment outcomes in animal studies have often demonstrated more positive regenerative outcomes than human clinical studies. Conceivably, defining how species diversity affects cementogenesis and cementum/PDL regeneration could be instructive for informing novel and more efficacious treatment strategies. Here we briefly review differences in cementum and PDL attachment in commonly used animal models to consider how species differences may lead to enhanced regenerative outcomes.

Amelogenin-Derived Peptide (ADP-5) Hydrogel for Periodontal Regeneration: An In Vitro Study on Periodontal Cells Cytocompatibility, Remineralization and Inflammatory Profile

A relevant alternative to enamel matrix derivatives from animal origin could be the use of synthetic amelogenin-derived peptides. This study aimed to assess the effect of a synthetic amelogenin-derived peptide (ADP-5), alone or included in an experimental gellan-xanthan hydrogel, on periodontal cell behavior (gingival fibroblasts, periodontal ligament cells, osteoblasts and cementoblasts). The effect of ADP-5 (50, 100, and 200 µg/mL) on cell metabolic activity was examined using Alamar blue assay, and cell morphology was assessed by confocal imaging. An experimental gellan-xanthan hydrogel was then designed as carrier for ADP-5 and compared to the commercial gel Emdogain^®. Alizarin Red was used to determine the periodontal ligament and cementoblasts cell mineralization. The inflammatory profile of these two cells was also quantified using ELISA (vascular endothelial growth factor A, tumor necrosis factor α, and interleukin 11) mediators. ADP-5 enhanced cell proliferation and remineralization; the 100 µg/mL concentration was more efficient than 50 and 200 µg/mL. The ADP-5 experimental hydrogel exhibited equivalent good biological behavior compared to Emdogain^® in terms of cell colonization, mineralization, and inflammatory profile. These findings revealed relevant insights regarding the ADP-5 biological behavior. From a clinical perspective, these outcomes could instigate the development of novel functionalized scaffold for periodontal regeneration.

Transcriptome landscape comparison of periodontium in developmental and renewal stages

OBJECTIVES

Periodontium regeneration remains a significant challenge in clinics and research, and it is essential to understand the stage-specific biological process in situ. However, differing findings have been reported, and the mechanism has yet to be elucidated. The periodontium of adult mice molars is considered to be stable remodeling tissue. At the same time, the continuously growing incisors and the developing dental follicle (DF) of postnatal mice highly represent fast remodeling tissue. In this study, we attempted to explore different clues of temporal and spatial comparisons to provide improved references for periodontal regeneration.

METHODS

Periodontal tissues from the developing periodontium (DeP) of postnatal mice, and continuously growing periodontium (CgP) and stable remodeling periodontium (ReP) of adult mice were isolated and compared using RNA sequencing. Based on the Dep and CgP separately compared with the ReP, differentially expressed genes and signaling pathways were analyzed using GO, KEGG databases, and Ingenuity Pathway Analysis (IPA). The results and validation were obtained by immunofluorescence staining and RT-PCR assays. Data were expressed as means ± standard deviation (SD) and analyzed by GraphPad Prism 8 software package, and one-way ANOVA was used to test multiple groups.

RESULTS

Principal component analysis showed that the three groups of periodontal tissue were successfully isolated and had distinct expression profiles. A total of 792 and 612 DEGs were identified in the DeP and CgP groups compared with the ReP. Upregulated DEGs in the DeP were closely related to developmental processes, while the CgP showed significantly enhanced cellular energy metabolism. The DeP and CgP showed a common downregulation of the immune response, with activation, migration, and recruitment of immune cells. IPA and further validation jointly suggested that the MyD88/p38 MAPK pathway played an essential regulatory role in periodontium remodeling.

CONCLUSION

Tissue development, energy metabolism, and immune response were critical regulatory processes during periodontal remodeling. Developmental and adult stages of periodontal remodeling showed different expression patterns. These results contribute to a deeper understanding of periodontal development and remodeling and may provide references for periodontal regeneration.

Emerging roles of platelet concentrates and platelet-derived extracellular vesicles in regenerative periodontology and implant dentistry

Platelet concentrates (PCs) are easily obtained from autogenous whole blood after centrifugation and have evolved through three generations of development to include platelet-rich plasma, platelet-rich fibrin, and concentrated growth factor. Currently, PCs are widely used for sinus floor elevation, alveolar ridge preservation, periodontal bone defects, guided bone regeneration, and treatment of gingival recession. More recently, PCs have been leveraged for tissue regeneration to promote oral soft and hard tissue regeneration in implant dentistry and regenerative periodontology. PCs are ideal for this purpose because they have a high concentration of platelets, growth factors, and cytokines. Platelets have been shown to release extracellular vesicles (P-EVs), which are thought to be essential for PC-induced tissue regeneration. This study reviewed the clinical application of PCs and P-EVs for implant surgery and periodontal tissue regeneration.

Bmal1 promotes cementoblast differentiation and cementum mineralization via Wnt/β-catenin signaling

Remodeling of the cementum plays a crucial role in periodontal regenerative therapy, while the precise mechanism of cementogenesis has yet been adequately understood. Recent studies have indicated the connection between osteogenic differentiation and Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein-1 (Bmal1). Besides, Wnt/β-catenin signaling is proven to be an essential regulator in cementogenesis. In this study, we found a robust expression of Bmal1 in cementoblasts in the mandibular first molar of mice by immunohistochemical staining. To further explore the role of Bmal1 in cementogenesis, we examined the expression pattern of Bmal1 in OCCM-30, an immortalized murine cementoblast cell line by qRT-PCR and western blot. Our data demonstrated the upregulation of Bmal1 at both mRNA and protein levels during differentiation. Additionally, stable knockdown of Bmal1 in OCCM-30 cells resulted in downregulation of osteogenic markers such as alkaline phosphatase (Alp), osteopontin (Opn), and osteocalcin (Ocn), and reduced formation of mineralized nodules. Moreover, qRT-PCR and western blot results exhibited that the expression of β-catenin was attenuated by Bmal1 deficiency. We also found that the mRNA levels of Tcf1 and Lef1, the target transcription factors of β-catenin, were reduced by Bmal1 deficiency. In conclusion, this study preliminarily confirms that Bmal1 promotes cementoblast differentiation and cementum mineralization via Wnt/β-catenin signaling, which contributes to a potential strategy in periodontal regenerative therapy.

Integration of collagen fibers in connective tissue with dental implant in the transmucosal region

Dental implants have been widely accepted as an ideal therapy to replace the missing teeth for its good performance in aspects of mechanical properties and aesthetic outcomes. Its restorative success is contributed by not only the successful osseointegration of the implant but also the tight soft tissue integration, especially the collagen fibers, in the transmucosal region. Soft tissue attaching to the dental implant/abutment is overall similar, but in some aspects distinct with that seen around natural teeth and soft tissue integration can be enhanced via several surface modification methods. This review is going to focus on the current knowledge of the transmucosal zone around the dental implants (compared with natural teeth), and latest strategies in use to fine-tune the collagen fibers assembly in the connective tissue, in an attempt to enhance soft tissue integration.

Application of Chitosan and Hydroxyapatite in Periodontal Tissue Regeneration: A Review

Chronic periodontitis is an infection caused by bacteria in the gum tissue that supports the teeth. The current periodontal therapy manages or removes periodontal infections and repairs the periodontium destroyed due to periodontal disease. Due to its biodegradability and biocompatibility, chitosan (CH) and hydroxyapatite (HAP) are employed for bone tissue healing. The purpose of this study was to compare the utilization of CH and HAP in the regeneration of periodontal tissue. The presented study is a systematic review prepared from a collection of recent relevant published articles. This research was conducted by reviewing articles from 2016 to August 2021. The analysis found that CH/HAP is a therapeutic strategy for chronic periodontitis patients that allow low-cost bone regeneration, mHA/CH scaffolds may inhibit the growth of periodontal pathogens, and CH or HAP has the potential to be developed bone tissue engineering.

Periodontal Wound Healing and Regeneration: Insights for Engineering New Therapeutic Approaches

Periodontitis is a widespread inflammatory disease that leads to loss of the tooth supporting periodontal tissues. The few therapies available to regenerate periodontal tissues have high costs and inherent limitations, inspiring the development of new approaches. Studies have shown that periodontal tissues have an inherent capacity for regeneration, driven by multipotent cells residing in the periodontal ligament (PDL). The purpose of this review is to describe the current understanding of the mechanisms driving periodontal wound healing and regeneration that can inform the development of new treatment approaches. The biologic basis underlying established therapies such as guided tissue regeneration (GTR) and growth factor delivery are reviewed, along with examples of biomaterials that have been engineered to improve the effectiveness of these approaches. Emerging therapies such as those targeting Wnt signaling, periodontal cell delivery or recruitment, and tissue engineered scaffolds are described in the context of periodontal wound healing, using key in vivo studies to illustrate the impact these approaches can have on the formation of new cementum, alveolar bone, and PDL. Finally, design principles for engineering new therapies are suggested which build on current knowledge of periodontal wound healing and regeneration.

Immunohistochemical Evaluation of Periodontal Regeneration Using a Porous Collagen Scaffold

(1) Aim: To immunohistochemically evaluate the effect of a volume-stable collagen scaffold (VCMX) on periodontal regeneration. (2) Methods: In eight beagle dogs, acute two-wall intrabony defects were treated with open flap debridement either with VCMX (test) or without (control). After 12 weeks, eight defects out of four animals were processed for paraffin histology and immunohistochemistry. (3) Results: All defects (four test + four control) revealed periodontal regeneration with cementum and bone formation. VCMX remnants were integrated in bone, periodontal ligament (PDL), and cementum. No differences in immunohistochemical labeling patterns were observed between test and control sites. New bone and cementum were labeled for bone sialoprotein, while the regenerated PDL was labeled for periostin and collagen type 1. Cytokeratin-positive epithelial cell rests of Malassez were detected in 50% of the defects. The regenerated PDL demonstrated a larger blood vessel area at the test (14.48% ± 3.52%) than at control sites (8.04% ± 1.85%, p = 0.0007). The number of blood vessels was higher in the regenerated PDL (test + control) compared to the pristine one (p = 0.012). The cell proliferative index was not statistically significantly different in pristine and regenerated PDL. (4) Conclusions: The data suggest a positive effect of VCMX on angiogenesis and an equally high cell turnover in the regenerated and pristine PDL. This VCMX supported periodontal regeneration in intrabony defects.

Epithelial Bone Morphogenic Protein 2 and 4 Are Indispensable for Tooth Development

The Bmp2 and Bmp4 expressed in root mesenchyme were essential for the patterning and cellular differentiation of tooth root. The role of the epithelium-derived Bmps in tooth root development, however, had not been reported. In this study, we found that the double abrogation of Bmp2 and Bmp4 from mouse epithelium caused short root anomaly (SRA). The K14-cre;Bmp2^f/f;Bmp4^f/f mice exhibited a persistent Hertwig’s Epithelial Root Sheath (HERS) with the reduced cell death, and the down-regulated BMP-Smad4 and Erk signaling pathways. Moreover, the Shh expression in the HERS, the Shh-Gli1 signaling, and Nfic expression in the root mesenchyme of the K14-cre;Bmp2^f/f;Bmp4^f/f mice were also decreased, indicating a disrupted epithelium- mesenchyme interaction between HERS and root mesenchyme. Such disruption suppressed the Osx and Dspp expression in the root mesenchyme, indicating an impairment on the differentiation and maturation of root odontoblasts. The impaired differentiation and maturation of root odontoblasts could be rescued partially by transgenic Dspp. Therefore, although required in a low dosage and with a functional redundancy, the epithelial Bmp2 and Bmp4 were indispensable for the HERS degeneration, as well as the differentiation and maturation of root mesenchyme.

Adipose-Derived Stromal Cells and Mineralized Extracellular Matrix Delivery by a Human Decellularized Amniotic Membrane in Periodontal Tissue Engineering

Periodontitis is a prevalent disease characterized by the loss of periodontal supporting tissues, bone, periodontal ligament, and cementum. The application of a bone tissue engineering strategy with Decellularized Human Amniotic Membrane (DAM) with adipose-derived stromal cells (ASCs) has shown to be convenient and valuable. This study aims to investigate the treatments of a rat periodontal furcation defect model with DAM, ASCs, and a mineralized extracellular matrix (ECM). Rat ASCs were expanded, cultivated on DAM, and with a bone differentiation medium for four weeks, deposited ECM on DAM. Periodontal healing for four weeks was evaluated by micro-computed tomography and histological analysis after treatments with DAM, ASCs, and ECM and compared to untreated defects on five consecutive horizontal levels, from gingival to apical. The results demonstrate that DAM preserves its structure during cultivation and healing periods, supporting cell attachment, permeation, bone deposition on DAM, and periodontal regeneration. DAM and DAM+ASCs enhance bone healing compared to the control on the gingival level. In conclusion, DAM with ASC or without cells and the ECM ensures bone tissue healing. The membrane supported neovascularization and promoted osteoconduction.

Biological interactions between calcium silicate-based endodontic biomaterials and periodontal ligament stem cells: A systematic review of in vitro studies

BACKGROUND

Most recently, the biological interactions, that is cytocompatibility, cell differentiation and mineralization potential, between calcium silicate-based biomaterials and periodontal ligament stem cells (PDLSCs) have been studied at an in vitro level, in order to predict their clinical behaviour during endodontic procedures involving direct contact with periodontal tissues, namely root canal treatment, endodontic surgery and regenerative endodontic treatment.

OBJECTIVE

The aim of the present systematic review was to present a qualitative synthesis of available in vitro studies assessing the biological interaction of PDLSCs and calcium silicate-based biomaterials.

METHODOLOGY

The present review followed PRISMA 2020 guidelines. An advanced database search was performed in Medline, Scopus, Embase, Web of Science and SciELO on 1 July 2020 and last updated on 22 April 2021. Studies assessing the biological interactions of PDLSCs with calcium silicate-based sealers (CSSs) and/or cements (CSCs) at an in vitro level were considered for inclusion. The evaluation of the 'biological interaction' was defined as any assay or test on the cytotoxicity, cytocompatibility, cell plasticity or differentiation potential, and bioactive properties of PDLSCs cultured in CSC or CSS-conditioned media. Quality (risk of bias) was assessed using a modified CONSORT checklist for in vitro studies of dental materials.

RESULTS

A total of 20 studies were included for the qualitative synthesis. CSCs and CSSs, as a group of endodontic materials, exhibit adequate cytocompatibility and favour the osteo/cementogenic differentiation and mineralization potential of PDLSCs, as evidenced from the in vitro studies included in the present systematic review.

DISCUSSION

The influence of the compositional differences, inclusion of additives, sample preparation, and varying conditions and manipulations on the biological properties of calcium silicate-based materials remain a subject for future research.

CONCLUSIONS

Within the limitations of the in vitro nature of the included studies, this work supports the potential use of calcium silicate-based endodontic materials in stem cell therapy and biologically based regenerative endodontic procedures.

REGISTRATION

OSF Registries; https://doi.org/10.17605/OSF.IO/SQ9UY.

Engineered Chitosan-based Nanoparticles Modulate Macrophage-Periodontal Ligament Fibroblast Interactions in Biofilm-mediated Inflammation

INTRODUCTION

Crosstalk between immune cells and tissue-resident cells regulates the pathophysiology and posttreatment healing of apical periodontitis. This investigation aimed to understand the influence of residual root canal biofilm on macrophage (MQ)-periodontal ligament fibroblast (PdLF) interaction and evaluate the effect of engineered chitosan-based nanoparticles (CSnp) on MQ-PdLF interactions in residual biofilm-mediated inflammation.

METHODS

Six-week-old Enterococcus faecalis biofilms in root canal models were disinfected conventionally using sodium hypochlorite alone or followed by calcium hydroxide medication or CSnp dispersed in carboxymethylated chitosan (CMCS). The effect of the treated biofilms (n = 25/group) on the inflammatory response of THP-1-differentiated MQ monoculture versus coculture with PdLF was evaluated for cell viability, MQ morphometric characterization, inflammatory mediators (nitric oxide, tumor necrosis factor alpha, interleukin [IL]-1 beta, IL-1RA, IL-6, transforming growth factor beta 1 [TGF-β1], and IL-10), and the expression of transcription factors (pSTAT1/pSTAT6)/cluster of differentiation markers (CD80/206) after 24, 48, and 72 hours of interaction. PdLF transwell migration was evaluated after 8 and 24 hours. Unstimulated cells served as the negative control, whereas untreated biofilm was the positive control.

RESULTS

Biofilm increased nitric oxide and IL-1β but suppressed IL-10, IL-1RA, and PdLF migration with significant cytotoxic effects. CSnp/CMCS reduced nitric oxide and IL-1β (P < .01) while maintaining ≥90% cell survival up to 72 hours with evident M2-like MQ phenotypic changes in coculture. CSnp/CMCS also increased the IL-1RA/IL-1β ratio and enhanced TGF-β1 production over time (P < .05, 72 hours). In coculture, CSnp/CMCS showed the highest IL-10 level at 72 hours (P < .01), reduced the pSTAT1/pSTAT6 ratio, and enhanced PdLF migration (P < .01, 24 hours).

CONCLUSIONS

CSnp/CMCS medication facilitated MQ switch toward M2 (regulatory/anti-inflammatory) phenotype and PdLF migration via paracrine signaling.

Impact of Adjunctive Diode Laser Application to Non-Surgical Periodontal Therapy on Clinical, Microbiological and Immunological Outcomes in Management of Chronic Periodontitis: A Systematic Review of Human Randomized Controlled Clinical Trials

Background

Due to the limitations of scaling and root planing (SRP) in chronic periodontitis (CP) management, research has been focused on utilising additional therapies to enhance conventional treatment methods. The present systematic review is aimed to appraise the accessible scientific evidence of in vivo human studies to establish the effectiveness of adjunctive diode (λ 808- λ 980nm) laser treatment to SRP in CP.

Methodology

This systematic review was conducted following the PRISMA statement guidelines. The review protocol is registered in PROSPERO (CRD 42021227695). The search strategies were based on structured electronic and manual (with appropriate keywords) and were conducted to collect the applicable published data on RCTs studies (in vivo human), spanning over ten years between August 2010 and August 2020. The articles were selected to address the following research focus question: “Does diode laser (λ 808- λ 980nm) therapy have superior effects as an adjunct to SPR, compared to SRP alone, in terms of clinical or microbiological or immunological profiles in the management of CP?”

Results

Fifteen articles met the eligibility criteria and are included in this review. A wide range of discrepancies and inconsistencies were shown in the outcomes of the laser and SPR treatment modality, compared to SRP alone. The data on standardised study protocol, optimal laser parameters and outcome measurements were inconclusive, and a high risk of bias in the majority of the studies observed, which are crucial in establishing a homogenous and reproducible protocol.

Conclusion

In light of the confined evidence-based data and critical evaluation of this systematic review, the efficacy of adjunctive diode laser treatment ranging between 808 and 980nm to SRP remains debatable. The observational quality of the present systematic review was emphasised after scrutinising the available data, and an attempt to propose a laser protocol for future RCTs consideration was a great challenge due to an absence of clear and standardised recommendations in delivering a reliable laser protocol which can be replicable by future investigators. RCTs with robust methodology are warranted.

Rodent incisor and molar dental follicles show distinct characteristics in tooth eruption

OBJECTIVE

Rodent incisors and molars show different eruption patterns. Dental follicles and their interaction with dental epithelia play key roles in tooth eruption. However, little is known about the differences between incisor dental follicle (IF) and molar dental follicle (MF) during tooth eruption of rodents. This study aimed to investigate the differences between IF and MF during tooth eruption under induction with cervical-loop cells (CLC) and Hertwig's epithelial root sheath (HERS) cells of rats.

MATERIALS AND METHODS

CLC, HERS, IF, MF cells were isolated from 10 postnatal day 7 rats and identified by immunofluorescence staining. CLC or HERS cells-derived conditioned medium (CM) was obtained to induce IF and MF cells. Cell proliferation, mineralization, gene and protein expression related to tooth eruption were detected, and histological analysis was also performed.

RESULTS

The osteogenic differentiation and mineralization abilities of IF cells were stronger than those of MF cells. Both CLC and HERS cells-derived CM enhanced these abilities of IF cells, whereas they showed the opposite effect on MF cells. At 7, 10, and 15 d after birth, IF cells expressed more OPG and less RANKL than MF cells.

CONCLUSIONS

IF and MF cells present distinct characteristics in tooth eruption, CLC and HERS cells have significant inductive effects on them.

Tissue Engineering for Periodontal Ligament Regeneration: Biomechanical Specifications

The periodontal biomechanical environment is very difficult to investigate. By the complex geometry and composition of the periodontal ligament (PDL), its mechanical behavior is very dependent on the type of loading (compressive versus tensile loading; static versus cyclic loading; uniaxial versus multiaxial) and the location around the root (cervical, middle, or apical). These different aspects of the PDL make it difficult to develop a functional biomaterial to treat periodontal attachment due to periodontal diseases. This review aims to describe the structural and biomechanical properties of the PDL. Particular importance is placed in the close interrelationship that exists between structure and biomechanics: the PDL structural organization is specific to its biomechanical environment, and its biomechanical properties are specific to its structural arrangement. This balance between structure and biomechanics can be explained by a mechanosensitive periodontal cellular activity. These specifications have to be considered in the further tissue engineering strategies for the development of an efficient biomaterial for periodontal tissues regeneration.

Technology-enhanced learning: a role for video animation

The last 20 years has seen a shift in medical education from printed analogue formats of knowledge transfer to digital knowledge transfer via media platforms and virtual learning environments. Traditional university medical teaching was characterised by lectures and printed textbooks, which to a degree still have an important role to play in knowledge acquisition, but which in isolation do not engage the modern learner, who has become reliant on digital platforms and 'soundbite' learning. Recently, however, traditional methods of teaching and learning have been augmented by, and indeed sometimes replaced by, the alternative learning methods such as: problem-based learning; a greater integration of basic science and clinical considerations; smaller teaching groups; the 'flipped classroom' concept; and various technological tools which promote an interactive learning style. The aim of these new teaching methods is to overcome the well-documented limitations of traditional lectures and printed material in the transfer of knowledge from expert to student, by better engaging the minds of more visual learners and encouraging the use of diverse resources for lifelong learning. In this commentary paper, we share the concept of video animation as an additional educational tool, and one that can help to integrate molecular, cellular and clinical processes that underpin our understanding of biology and pathology in modern education. Importantly, while they can provide focused and attractive formats for 'soundbite' learning, their aim as a tool within the broader educational toolbox is to direct the interested reader towards more traditional formats of learning, which permit a deeper dive into a particular field or concept. In this manner, carefully constructed video animations can serve to provide a broad overview of a particular field or concept and to facilitate deeper learning when desired by the student.

Teaching the knowledge explosion is a challenge.

Video animation plays a future role in teaching complex biological concepts and processes.

Video animation helps in educating professionals and the public.

Facilitation of Bone Healing Processes Based on the Developmental Function of Meox2 in Tooth Loss Lesion

In the present study, we examined the bone healing capacity of Meox2, a homeobox gene that plays essential roles in the differentiation of a range of developing tissues, and identified its putative function in palatogenesis. We applied the knocking down of Meox2 in human periodontal ligament fibroblasts to examine the osteogenic potential of Meox2. Additionally, we applied in vivo periodontitis induced experiment to reveal the possible application of Meox2 knockdown for 1 and 2 weeks in bone healing processes. We examined the detailed histomorphological changes using Masson’s trichrome staining and micro-computed tomography evaluation. Moreover, we observed the localization patterns of various signaling molecules, including α-SMA, CK14, IL-1β, and MPO to examine the altered bone healing processes. Furthermore, we investigated the process of bone formation using immunohistochemistry of Osteocalcin and Runx2. On the basis of the results, we suggest that the knocking down of Meox2 via the activation of osteoblast and modulation of inflammation would be a plausible answer for bone regeneration as a gene therapy. Additionally, we propose that the purpose-dependent selection and application of developmental regulation genes are important for the functional regeneration of specific tissues and organs, where the pathological condition of tooth loss lesion would be.

Isolation and characterization of dental follicle-derived Hertwig's epithelial root sheath cells

OBJECTIVES

The aim of this study was the isolation and characterization of dental follicle-derived Hertwig's epithelial root sheath cells (DF-HERSCs).

MATERIALS AND METHODS

DF-HERSCs were isolated from dental follicle (DF)-derived single-cell suspensions. Their epithelial phenotypes were analyzed by Western blotting, polymerase chain reaction (PCR), and quantitative polymerase chain reaction (qPCR). Epithelial-mesenchymal transition (EMT) was induced in DF-HERSCs by treatment with transforming growth factor-β (TGF-β) or fetal bovine serum (FBS)-added medium. Characteristics of DF-HERSCs were compared with normal human oral keratinocytes (NHOKs) and normal human epidermal keratinocytes (NHEKs). Osteogenic differentiation and mineralization of DF-HERSCs were analyzed by alkaline phosphatase (ALP) and Alizarin red staining. All experiments were conducted in triplicate.

RESULTS

Primary DF-HERSCs were isolated from DF. Epithelial phenotypes of DF-HERSCs were confirmed by morphological and Western blot analysis. PCR results demonstrated that the origin of DF-HERSCs was neither endothelial nor hematopoietic. Enamel matrix derivative (EMD)-associated genes were not expressed in DF-HERSCs. Treatment with TGF-β and FBS-added medium triggered the progression of EMT in DF-HERSCs. The acquired potency of differentiation and mineralization was shown in EMT-progressed DF-HERSCs.

CONCLUSIONS

DF contains putative populations of HERSC, named DF-HERSC. DF-HERSCs shared common characteristics with NHOKs and NHEKs.

Mesoporous Hydroxyapatite/Chitosan Loaded With Recombinant-Human Amelogenin Could Enhance Antibacterial Effect and Promote Periodontal Regeneration

The recovery of impaired periodontium is still a challenge to the treatment of periodontitis. This study was the first to apply the mesoporous hydroxyapatites/chitosan (mHA/CS) composite scaffold to periodontal regeneration. The aim of our study is to evaluate the biological effects of mesoporous hydroxyapatite/chitosan (mHA/CS) loaded with recombinant human amelogenin (rhAm) on periodontal regeneration. The physicochemical properties of mHA/CS scaffolds were examined by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. Then, the biological effects of the mHA/CS loaded with rhAm were evaluated, including antibacterial effect, controlled-release capacity, osteogenic and cementogenic effects in vitro and in vivo. The antibacterial effect was tested on 1.5 mg/mL CS; 3 mg/mL mHA; 2.25 mg/mL mHA/CS; 4.5 mg/mL mHA/CS and 20 μg/mL rhAm. Tryptic Soy Broth culture medium was used as a baseline control. Osteogenic effect of rhAm (20 μg/mL rhAm), mHA/CS (4.5 mg/mL mHA/CS), and mHA/CS-rhAm (4.5 mg/mL mHA/CS and 20 μg/mL rhAm) on human periodontal ligament cells (hPDLCs) was evaluated in osteogenic media. The hPDLCs treated either with osteogenic media or Dulbecco's modified Eagle's medium (DMEM) alone were used as the baseline control. In the animal model, 4-week-old nude mice (BALB/c) (n = 6) implanted with root slices subcutaneously were used to observe the cementogenic effect in vivo. The root slices were treated with rhAm (20 μg/mL rhAm), mHA/CS (4.5 mg/mL mHA/CS), and mHA/CS-rhAm (4.5 mg/mL mHA/CS and 20 μg/mL rhAm). The root slices treated with osteogenic medium alone were used as the baseline control. The analyses showed that the mHA/CS particles were 2 μm in diameter and had a uniform pore size. The mesoporous structure was 7 nm in diameter and its surface area was 33.95 m²/g. The scaffold exhibited antibacterial effects against Fusobacterium nucleatum and Porphyromonas gingivalis. The mHA/CS scaffold sustainably released rhAm. The mHA/CS loaded with 20 μg/mL rhAm upregulated ALP activity, the expression levels of osteogenesis-related genes and proteins in vitro. Additionally, it promoted the formation of cementum-like tissue in vivo. Our findings suggest that mHA/CS loaded with 20 μg/mL rhAm could inhibit the growth of periodontal pathogens and promote the formation of bone and cementum-like tissue.

Exosome-like vesicles derived from Hertwig's epithelial root sheath cells promote the regeneration of dentin-pulp tissue

Background: The formation of dentin-pulp involves complex epithelial-mesenchymal interactions between Hertwig's epithelial root sheath cells (HERS) and dental papilla cells (DPCs). Earlier studies have identified some of the regulatory molecules participating in the crosstalk between HERS and DPCs and the formation of dentin-pulp. In the present study we focused on the role of HERS-secreted exosomes in DPCs and the formation of dentin-pulp. Specifically, we hypothesized that exosome-like vesicles (ELVs) might mediate the function of HERS and trigger lineage-specific differentiation of dental mesenchymal cells. To test our hypothesis, we evaluated the potential of ELVs derived from a HERS cell line (ELVs-H1) in inducing in vitro and in vivo differentiation of DPCs. Methods: ELVs-H1 were characterized using transmission electron microscopy and dynamic light scattering. The proliferation, migration, and odontoblast differentiation of DPCs after treatment with ELVs-H1, was detected by CCK8, transwell, ALP, and mineralization assays, respectively. Real time PCR and western blotting were used to detect gene and protein expression. For in vivo studies, DPC cells were mixed with collagen gel combined with or without ELVs and transplanted into the renal capsule of rats or subcutaneously into nude mice. HE staining and immunostaining were used to verify the regeneration of dentin-pulp and expression of odontoblast differentiation markers. Results: ELVs-H1 promoted the migration and proliferation of DPCs and also induced odontogenic differentiation and activation of Wnt/β-catenin signaling. ELVs-H1 also contributed to tube formation and neural differentiation in vitro. In addition, ELVs-H1 attached to the collagen gel, and were slowly released and endocytosed by DPCs, enhancing cell survival. ELVs-H1 together with DPCs triggered regeneration of dental pulp-dentin like tissue comprised of hard (reparative dentin-like tissue) and soft (blood vessels and neurons) tissue, in an in vivo tooth root slice model. Conclusion: Our data highlighted the potential of ELVs-H1 as biomimetic tools in providing a microenvironment for specific differentiation of dental mesenchymal stem cells. From a developmental perspective, these vesicles might be considered as novel mediators facilitating the epithelial-mesenchymal crosstalk. Their instructive potency might be exploited for the regeneration of dental pulp-dentin tissues.

The effect of CPNE7 on periodontal regeneration

Introduction: Preameloblast-conditioned medium (PA-CM), as a mixture of dental epithelium-derived factors, has been reported to regenerate dentin and periodontal tissues in vitro and in vivo. The aim of this study was to investigate the biological effect of Cpne7 on the proliferation, migration, and cementoblast differentiation of periodontal cells in vitro, and on the regeneration of periodontal tissue using periodontal defect model with canine in vivo. Materials and methods: The effect of Cpne7 on cell proliferation, migration, and cementoblast differentiation of periodontal cells were evaluated in vitro. A periodontal defect canine model was designed and the defects were divided into five groups: Group 1: No treatment (negative control), Group 2: Collagen carrier only, Group 3: PA-CM with collagen carrier (positive control), Group 4: PA-CM + CPNE7 Antibody (Ab) with collagen carrier, and Group 5: recombinant CPNE7 (rCPNE7) protein with collagen carrier. Results: Cpne7 was expressed in HERS cells and periodontal ligament (PDL) fibers. By real-time PCR, Cpne7 increased expression of Cap compared to the control. In the periodontal defect canine model, rCPNE7 or PA-CM regenerated periodontal complex, and the arrangement of the newly formed PDL-like fibers were perpendicular to the newly formed cementum and alveolar bone like Sharpey's fibers in natural teeth, while PA-CM + CPNE7 Ab showed irregular arrangement of the newly formed PDL-like fibers compared to the rCPNE7 or PA-CM group. Conclusion: These findings suggest that Cpne7 may have a functional role in periodontal regeneration by supporting periodontal cell attachment to cementum and facilitating physiological arrangement of PDL fibers.

TGF‑β induces periodontal ligament stem cell senescence through increase of ROS production

Periodontal ligament stem cells (PDLSCs) are vital for the regeneration of periodontal tissue. Transforming growth factor (TGF) β1, a potent stimulator of tissue regeneration, is extensive and abundant in the bone matrix. However, the effect of TGF‑β1 in periodontal differentiation remains to be elucidated. The present study aimed to evaluate the effect of TGF‑β1 on human PDLSCs. PDLSCs were isolated using CD146 microbeads, and characterized by flow cytometry. The present study demonstrated that treatment with TGF‑β1 induced PDLSC senescence, characterized by increases in senescence‑associated beta‑galactosidase activity and elevation of both p16 and p21 expression. Furthermore, TGF‑β1 treatment demonstrated the capacity to induce the production of reactive oxygen species (ROS). Of note, addition of a ROS scavenger successfully rescued the TGF‑β1‑induced PDLSC senescence. Thus, the present results indicated that TGF‑β1 may serve a vital role in PDLSC senescence, and thus represent a potential target involved in the fabrication and formation of hard tissue for clinical treatment.

In vivo effects of different orthodontic loading on root resorption and correlation with mechanobiological stimulus in periodontal ligament

Orthodontic root resorption is a common side effect of orthodontic therapy. It has been shown that high hydrostatic pressure in the periodontal ligament (PDL) generated by orthodontic forces will trigger recruitment of odontoclasts, leaving resorption craters on root surfaces. The patterns of resorption craters are the traces of odontoclast activity. This study aimed to investigate resorptive patterns by: (i) quantifying spatial root resorption under two different levels of in vivo orthodontic loadings using microCT imaging techniques and (ii) correlating the spatial distribution pattern of resorption craters with the induced mechanobiological stimulus field in PDL through nonlinear finite-element analysis (FEA) in silico. Results indicated that the heavy force led to a larger total resorption volume than the light force, mainly by presenting greater individual crater volumes ( p < 0.001) than increasing crater numbers, suggesting that increased mechano-stimulus predominantly boosted cellular resorption activity rather than recruiting more odontoclasts. Furthermore, buccal-cervical and lingual-apical regions in both groups were found to have significantly larger resorption volumes than other regions ( p < 0.005). These clinical observations are complemented by the FEA results, suggesting that root resorption was more likely to occur when the volume average compressive hydrostatic pressure exceeded the capillary blood pressure (4.7 kPa).

Peri-implantitis and its prevention

This perspective article on peri-implantitis and its prevention was produced as a supplement to a 3-D, computer-animated film aiming at presenting key characteristics of peri-implant health, the build-up of a biofilm and the ensuing host-response resulting in peri-implant mucositis and, subsequently, peri-implantitis. Treatment concepts for peri-implantitis were briefly reviewed, and prevention of the condition was brought to attention as a priority in implant dentistry. The overview also highlighted the 2017 World Workshop on Classification of Periodontal and Peri-implant diseases and Conditions, in which new disease definitions and case definitions were presented for peri-implant health, peri-implant mucositis, and peri-implantitis.

Are Hertwig's epithelial root sheath cells necessary for periodontal formation by dental follicle cells?

OBJECTIVE

The role of Hertwig's epithelial root sheath (HERS) cells in periodontal formation has been controversial. This study aimed to further clarify whether HERS cells participate in formation of the periodontium, and the necessity of HERS cells in differentiation of dental follicle cells (DFCs) for periodontal regeneration.

DESIGN

HERS cells and DFCs were isolated and identified from post-natal 7-day Sprauge-Dawley rats. In vitro, direct co-culture of HERS cells and DFCs as well as the individual culture of HERS and DFCs were performed and followed by alizarin red staining and the quantitative real-time polymerase chain reaction analysis. For in vivo evaluation, the inactivated dentin matrix (iTDM) was fabricated. HERS cells and DFCs were seeded in combination or alone on iTDM and then transplanted into the rat omentum. Scanning electron microscope and further histological analysis were carried out.

RESULTS

In vitro, mineral-like nodules were found in the culture of HERS cells alone or HERS + DFCs either by alizarin red staining or scanning electronic microscope. The mineralization and fiber-forming relevant mRNA expressions, such as bone sialoprotein, osteopontin, collagen I and collagen III in HERS + DFCs were significantly higher than that of the HERS or DFCs alone group. After transplantation in vivo, cementum and periodontal ligament-like tissues were formed in groups of HERS + DFCs and HERS alone, while no evident hard tissues and attached fibers were found in DFCs alone.

CONCLUSIONS

Hertwig's epithelial root sheath cells directly participate in the formation of the periodontium, and they are essential for the differentiation of dental follicle cells to form periodontal structures. The combination use of Hertwig's epithelial root sheath cells and dental follicle cells is a promising approach for periodontal regeneration.

Influence of autogenous platelet concentrate on combined GTR/graft therapy in intra-bony defects: A 13-year follow-up of a randomized controlled clinical split-mouth study

AIM

To investigate the clinical long-term outcomes 13 years following guided tissue regeneration (GTR) in deep intra-bony defects with and without additional application of autogenous platelet concentrate (APC).

METHODS

In 25 patients, two deep contra-lateral intra-bony defects were treated according to GTR using β-TCP and bio-resorbable membranes. In test defects, APC was applied additionally. After 13 years, clinical healing results were assessed and compared to results at baseline and after 1 year. Furthermore, a tooth survival analysis was carried out.

RESULTS

After 13 years, 22 patients were available for tooth survival analysis showing 81.8% of test and 86.4% of control teeth still in situ. Based on the 15 patients still available for split-mouth analysis, median CAL was 10.0 mm in test and 12.0 mm in control sites at baseline. After 1 year, both groups revealed significant CAL gains of 5.0 mm, followed by a new CAL loss of 1.0 mm in the following 12 years. There were no significant differences between test and control sites.

CONCLUSION

Within the limits of this study, the data show that most of the CAL gain following GTR can be maintained over 13 years. The additional use of APC had no positive influence on the long-term stability.

Signaling Pathways Critical for Tooth Root Formation

Tooth is made of an enamel-covered crown and a cementum-covered root. Studies on crown dentin formation have been a major focus in tooth development for several decades. Interestingly, the population prevalence for genetic short root anomaly (SRA) with no apparent defects in crown is close to 1.3%. Furthermore, people with SRA itself are predisposed to root resorption during orthodontic treatment. The discovery of the unique role of Nfic (nuclear factor I C; a transcriptional factor) in controlling root but not crown dentin formation points to a new concept: tooth crown and root have different control mechanisms. Further genetic mechanism studies have identified more key molecules (including Osterix, β-catenin, and sonic hedgehog) that play a critical role in root formation. Extensive studies have also revealed the critical role of Hertwig's epithelial root sheath in tooth root formation. In addition, Wnt10a has recently been found to be linked to multirooted tooth furcation formation. These exciting findings not only fill the critical gaps in our understanding about tooth root formation but will aid future research regarding the identifying factors controlling tooth root size and the generation of a whole "bio-tooth" for therapeutic purposes. This review starts with human SRA and mainly focuses on recent progress on the roles of NFIC-dependent and NFIC-independent signaling pathways in tooth root formation. Finally, this review includes a list of the various Cre transgenic mouse lines used to achieve tooth root formation-related gene deletion or overexpression, as well as strengths and limitations of each line.

Differences between inflammatory and catabolic mediators of peri-implantitis and periodontitis lesions following initial mechanical therapy: An exploratory study

BACKGROUND AND OBJECTIVE

The aim of this study was to analyze the differences in inflammatory and catabolic mediators expressed in peri-implantitis compared to periodontitis lesions after non-surgical therapy. Peri-implantitis is associated with a faster rate of bone loss when compared with periodontitis, and peri-implant non-surgical therapy is ineffective to cure peri-implantitis. This may be due to persistent inflammation in peri-implantitis tissues after initial mechanical treatment.

MATERIAL AND METHODS

Eleven patients with peri-implantitis and 10 with severe chronic periodontitis received non-surgical therapy. They were included at re-evaluation (8 weeks) if they presented pocket depth ≥6 mm with bleeding on probing, and the indication for open flap debridement surgery. Connective tissues were harvested during surgery from diseased sites. Healthy gingiva were harvested during third molar extraction in a third group of healthy patients (n=10). Explants were incubated for 24 hours in media culture and the release of cytokines, chemokines, growth factors, osteoprotegerin, receptor activator of nuclear factor kappa-B ligand (RANKL), matrix metalloproteinase and tissue inhibitors of matrix metalloproteinase (TIMP) in the conditioned media was analyzed by an exploratory multiplex immunoassay. When difference was found in the conditioned media, an immunohistochemistry was performed to compare expression in the tissues.

RESULTS

Connective tissues from non-stabilized peri-implantitis exhibited a distinct cytokine profile compared to periodontitis lesions that did not respond to initial therapy. Indeed, TIMP-2 was significantly increased in media from peri-implantitis (P≤.05). In addition, the in situ expression of TIMP-2, interleukin-10 and RANKL was also significantly increased in peri-implantitis tissues (P≤.05). However, the ratio of RANKL/osteoprotegerin-positive cells did not vary (P≥.05).

CONCLUSION

This study suggests that peri-implantitis and periodontitis connective tissues exhibit differences in response to non-surgical treatment, which may contribute to a different pattern of disease evolution.

Cellular and molecular mechanisms of tooth root development

The tooth root is an integral, functionally important part of our dentition. The formation of a functional root depends on epithelial-mesenchymal interactions and integration of the root with the jaw bone, blood supply and nerve innervations. The root development process therefore offers an attractive model for investigating organogenesis. Understanding how roots develop and how they can be bioengineered is also of great interest in the field of regenerative medicine. Here, we discuss recent advances in understanding the cellular and molecular mechanisms underlying tooth root formation. We review the function of cellular structure and components such as Hertwig's epithelial root sheath, cranial neural crest cells and stem cells residing in developing and adult teeth. We also highlight how complex signaling networks together with multiple transcription factors mediate tissue-tissue interactions that guide root development. Finally, we discuss the possible role of stem cells in establishing the crown-to-root transition, and provide an overview of root malformations and diseases in humans.

Healing of root and surrounding periodontium after root damage with miniscrew implants: a histomorphologic study in dogs

OBJECTIVES

The main purpose of this study was to investigate the detailed healing process of the roots and surrounding periodontium [cementum, periodontal ligament (PDL), and bone] at different time points after intentional root damage with miniscrew implants (MSIs).

MATERIALS AND METHODS

After cone-beam computed tomography examination and measurement, a total of 78 premolar and molar roots from five beagle dogs were intentionally damaged by implanting miniscrews in the interradicular region. MSIs were immediately removed, and the histological morphology was observed at days 0 and 3 and at weeks 1, 2, 3, 4, 6, 8, and 12 after root injury using haematoxylin and eosin and fluorescence stainings (fluorescence staining was performed at days 28 and 56).

RESULTS

An early new attachment of PDL adhering on to the damaged root surface was found at week 2 after root injury. Tissue differentiation of newly formed bone tissue, PDL, and cementum began at week 3. Moreover, the newly formed cementum and bone were constantly forming and mineralising at weeks 4, 6, 8, and 12, and the width of PDL gradually narrowed until close to the normal width at week 12.

CONCLUSIONS

This study demonstrated the complete healing process of the roots and surrounding periodontium after root damage with MSIs in dogs when the damage was limited to the cementum or dentin.

CLINICAL RELEVANCE

The findings of this study may help provide a better understanding of the detailed healing process in roots and PDLs damaged by MSIs.

From molecules to macrostructures: recent development of bioinspired hard tissue repair

This review summarizes the bioinspired strategies for hard tissue repair, ranging from molecule-induced mineralization, to microscale assembly to macroscaffold fabrication.

From restoration to regeneration: periodontal aging and opportunities for therapeutic intervention

With the march of time our bodies start to wear out: eyesight fades, skin loses its elasticity, teeth and bones become more brittle and injuries heal more slowly. These universal features of aging can be traced back to our stem cells. Aging has a profound effect on stem cells: DNA mutations naturally accumulate over time and our bodies have evolved highly specialized mechanisms to remove these damaged cells. Whilst obviously beneficial, this repair mechanism also reduces the pool of available stem cells and this, in turn, has a dramatic effect on tissue homeostasis and on our rate of healing. Simply put: fewer stem cells means a decline in tissue function and slower healing. Despite this seemingly intractable situation, research over the past decade now demonstrates that some of the effects of aging are reversible. Nobel prize-winning research demonstrates that old cells can become young again, and lessons learned from these experiments-in-a-dish are now being translated into human therapies. Scientists and clinicians around the world are identifying and characterizing methods to activate stem cells to reinvigorate the body's natural regenerative process. If this research in dental regenerative medicine pans out, the end result will be tissue homeostasis and healing back to the levels we appreciated when we were young.

Cell-to-cell communication in guided bone regeneration: molecular and cellular mechanisms

This overview provides insights into the molecular and cellular mechanisms involved in guided bone regeneration, in particular focusing on aspects presented in the 3D movie, Cell-To-Cell Communication in Guided Bone Regeneration. The information presented here is based almost exclusively on genetic mouse models in which single genes can be deleted or overexpressed, even in a specific cell type. This information needs to be extrapolated to humans and related to aspects relevant to graft consolidation under the clinical parameters of guided bone regeneration. The overview follows the ground tenor of the Cell-To-Cell Communication series and focuses on aspects of cell-to-cell communication in bone regeneration and guided bone regeneration. Here, we discuss (1) the role of inflammation during bone regeneration, including (2) the importance of the fibrin matrix, and (3) the pleiotropic functions of macrophages. We highlight (4) the origin of bone-forming osteoblasts and bone-resorbing osteoclasts as well as (5) what causes a progenitor cell to mature into an effector cell. (6) We touch on the complex bone adaptation and maintenance after graft consolidation and (7) how osteocytes control this process. Finally, we speculate on (8) how barrier membranes and the augmentation material can modulate graft consolidation.