Physiological features of periodontal regeneration and approaches for periodontal tissue engineering utilizing periodontal ligament cells

Application of Biocompatible Scaffolds in Stem-Cell-Based Dental Tissue Engineering

Tissue engineering as an important field in regenerative medicine is a promising therapeutic approach to replace or regenerate injured tissues. It consists of three vital steps including the selection of suitable cells, formation of 3d scaffolds, and adding growth factors. Mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs) are mentioned as two main sources for this approach that have been used for the treatment of various types of disorders. However, the main focus of literature in the field of dental tissue engineering is on utilizing MSCs. On the other hand, biocompatible scaffolds play a notable role in this regenerative process which is mentioned to be harmless with acceptable osteoinductivity. Their ability in inhibiting inflammatory responses also makes them powerful tools. Indeed, stem cell functions should be supported by biomaterials acting as scaffolds incorporated with biological signals. Naturally derived polymeric scaffolds and synthetically engineered polymeric/ceramic scaffolds are two main types of scaffolds regarding their materials that are defined further in this review. Various strategies of tissue bioengineering can affect the regeneration of dentin-pulp complex, periodontium regeneration, and whole teeth bioengineering. In this regard, in vivo/ex vivo experimental models have been developed recently in order to perform preclinical studies of dental tissue engineering which make it more transferable to be used for clinic uses. This review summarizes dental tissue engineering through its different components. Also, strategies of tissue bioengineering and experimental models are introduced in order to provide a perspective of the potential roles of dental tissue engineering to be used for clinical aims.

Nano porous polycarbonate membranes stimulating cell adhesion and promoting osteogenic differentiation and differential mRNA expression

Tissue engineering is thought to be the ideal therapy for bone defect reconstructive treatment. In this study, we present a method of utilizing micro/nano porous polycarbonate membranes (PCMs) as the extracellular matrix to cultivate the human periodontal ligament cells (hPDLCs) and investigate the osteogenic differentiation of those cells. We also compared the osteogenic enhancing abilities of different pore size PCMs. The pore diameters of the candidate membranes are 200 nm, 800 nm, 1200 nm, and 10 μm respectively, and their physical properties are identified. After seeding and cultivating on the PCMs, hPDLCs can be stimulated to undergo osteogenic differentiation, in which the 200 nm PCM is proved to have the most optimal osteo-induction ability. The results of in vivo experiments provide strong evidence suggesting that the hPDLCs stimulated by 200 nm PCM greatly accelerates the healing of bone reconstruction in mice skull defects, as well as promote the process of ectopic osteogenesis. RNA-sequencing was conducted to determine the differential mRNA expression profile during the osteogenesis process of hPDLCs on PCMs. GO and KEGG enrichment analysis were conducted to study the regulatory mechanisms, in which osteogenic marker expression such as Hippo, TGF-β, and PI3K-Akt signaling pathways were significantly up-regulated. The up-regulation indicates the promising potential of nano porous PCMs for promoting osteogenesis for bone regeneration applications. Ultimately, signaling pathways that promote osteogenesis warrants further exploration.

The Structure and Function of Next-Generation Gingival Graft Substitutes-A Perspective on Multilayer Electrospun Constructs with Consideration of Vascularization

There is a shortage of suitable tissue-engineered solutions for gingival recession, a soft tissue defect of the oral cavity. Autologous tissue grafts lead to an increase in morbidity due to complications at the donor site. Although material substitutes are available on the market, their development is early, and work to produce more functional material substitutes is underway. The latter materials along with newly conceived tissue-engineered substitutes must maintain volumetric form over time and have advantageous mechanical and biological characteristics facilitating the regeneration of functional gingival tissue. This review conveys a comprehensive and timely perspective to provide insight towards future work in the field, by linking the structure (specifically multilayered systems) and function of electrospun material-based approaches for gingival tissue engineering and regeneration. Electrospun material composites are reviewed alongside existing commercial material substitutes', looking at current advantages and disadvantages. The importance of implementing physiologically relevant degradation profiles and mechanical properties into the design of material substitutes is presented and discussed. Further, given that the broader tissue engineering field has moved towards the use of pre-seeded scaffolds, a review of promising cell options, for generating tissue-engineered autologous gingival grafts from electrospun scaffolds is presented and their potential utility and limitations are discussed.

Biomimetic Aspects of Oral and Dentofacial Regeneration

Biomimetic materials for hard and soft tissues have advanced in the fields of tissue engineering and regenerative medicine in dentistry. To examine these recent advances, we searched Medline (OVID) with the key terms “biomimetics”, “biomaterials”, and “biomimicry” combined with MeSH terms for “dentistry” and limited the date of publication between 2010–2020. Over 500 articles were obtained under clinical trials, randomized clinical trials, metanalysis, and systematic reviews developed in the past 10 years in three major areas of dentistry: restorative, orofacial surgery, and periodontics. Clinical studies and systematic reviews along with hand-searched preclinical studies as potential therapies have been included. They support the proof-of-concept that novel treatments are in the pipeline towards ground-breaking clinical therapies for orofacial bone regeneration, tooth regeneration, repair of the oral mucosa, periodontal tissue engineering, and dental implants. Biomimicry enhances the clinical outcomes and calls for an interdisciplinary approach integrating medicine, bioengineering, biotechnology, and computational sciences to advance the current research to clinics. We conclude that dentistry has come a long way apropos of regenerative medicine; still, there are vast avenues to endeavour, seeking inspiration from other facets in biomedical research.

Comparative Evaluation of Serum and Gingival Crevicular Fluid Periostin Levels in Periodontal Health and Disease: A Biochemical Study

Introduction

Periostin, a secreted adhesion molecule, is a matricellular protein secreted most in periodontal ligament and periosteum. This periostin is needed for integrity and maturation of periodontal tissue. The present study was conducted to estimate and compare the gingival crevicular fluid and serum periostin levels in subjects having chronic periodontitis, gingivitis and healthy periodontium.

Methods

Ninety patients belonging to both sexes were categorized into three groups, 30 patients each as healthy periodontium (Group I), chronic gingivitis (Group II) and generalised chronic periodontitis (Group III). The clinical parameters included assessment of plaque index (PI), gingival index (GI), probing pocket depth (PPD) and clinical attachment level (CAL). Gingival crevicular fluid (GCF) and serum samples were collected and the enzyme-linked immunosorbent assay was used to estimate periostin levels.

Results

Periostin levels in GCF were comparatively low in the chronic periodontitis than in the gingivitis and healthy periodontium groups and the difference was statistically significant. No statistical difference was found for serum periostin levels among Group I, Group II and Group III. On comparison of clinical parameters, significant difference was noticed among the three groups. GCF periostin levels were correlated inversely with the clinical parameters in chronic periodontitis patients.

Conclusion

GCF periostin levels were gradually reduced with the increase in severity of periodontal disease. This novel biomarker has role in maintaining normal periodontal tissue function and may be used as a potential marker in periodontal disease activity evaluation.

Chitosan-based double-faced barrier membrane coated with functional nanostructures and loaded with BMP-6

In the present study, a chitosan-based, multifunctional and double-faced barrier membrane was developed for the periodontitis therapy. The porous surface of the membrane was coated with bone-like hydroxyapatite (HA) produced by microwave-assisted biomimetic method and enriched with bone morphogenetic factor 6 (BMP-6) to enhance the bioactivity of chitosan. This surface of the membrane was designed to be in contact with the hard tissue that was damaged due to periodontitis. Otherwise the nonporous surface of membrane, which is in contact with the inflammatory soft tissue, was coated with electrospun polycaprolactone (PCL) fibers to prevent the migration of epithelial cells to the defect area. PrestoBlue, Scanning Electron Microscope (SEM) and real-time PCR results demonstrated that while porous surface of the membrane was enhancing the proliferation and differentiation of MC3T3-E1 preosteoblasts, nonporous surface of membrane did not allow migration of epithelial Madine Darby Bovine Kidney (MDBK) cells. The barrier membrane developed here is biodegradable and can be easily manipulated, has osteogenic activity and inactivity for epithelial cells. Thus, by implanting this membrane to the damaged periodontal tissue, bone regeneration will take place and integrity of periodontal tissues will be preserved.

Influence of Micropatterning on Human Periodontal Ligament Cells' Behavior

The periodontal ligament (PDL) is highly ordered connective tissue located between the alveolar bone and cementum. An aligned and organized architecture is required for its physiological function. We applied micropatterning technology to arrange PDL cells in 10- or 20-μm-wide extracellular protein patterns. Cell and nuclear morphology, cytoskeleton, proliferation, differentiation, and matrix metalloproteinase system expression were investigated. Micropatterning clearly elongated PDL cells with a low cell-shape index and low spreading area. The nucleus was also elongated as nuclear height increased, but the nuclear volume remained intact. The cytoskeleton was rearranged to form prominent bundles at cells' peripheral regions. Moreover, proliferation was promoted by 10- and 20-μm micropatterning. Osteogenesis and adipogenesis were each inhibited, but micropatterning increased PDL cells' stem cell markers. β-catenin was expelled to cytoplasm. YAP/TAZ nuclear localization and activity both decreased, which might indicate their role in micropatterning-regulated differentiation. Collagen Ι expression increased in micropatterned groups. It might be due to the decreased expression of matrix metalloproteinase-1, 2 and the tissue inhibitor of metalloproteinase-1 gene expression elevation in micropatterned groups. The findings of this study provide insight into the effects of a micropatterned surface on PDL cell behavior and may be applicable in periodontal tissue regeneration.

Human periodontal fibroblasts viability stored in Custodiol® , coconut water, and propolis. An ex vivo study

BACKGROUND/AIMS

Successful replantation of an avulsed tooth depends on the regeneration of periodontal ligament (PDL) attachment which is affected by the transport medium, dry time, and storage time. Various storage media have been studied but the search for the optimum storage medium is still needed to determine the ideal material and storage time to maintain PDL cells. The aim of this study was to determine the ability of Custodiol® , coconut water (CW) from different stages of maturity, and propolis as storage media for avulsed teeth by evaluating the viability of PDL cells for different time intervals.

MATERIALS AND METHODS

PDL cultures were subjected to Cutodiol® , immature, half mature, and mature coconut water, and different concentrations of propolis in Dulbecco's Modified Eagles Medium (DMEM). Culture plates with the tested media were incubated for 1, 2, 6, 24, 48, 72, and 168 hour. PDL fibroblast cell viability was assessed by MTT assay.

RESULTS

CW showed significantly higher viability of cells than other groups at 6 hour with half mature CW being superior. Propolis at 6.25 mg/mL in DMEM resulted in 138% viable PDL and it was able to preserve PDL cells for up to 168 hour.

CONCLUSIONS

Half mature and mature CW are superior storage media if replantation of avulsed teeth is within 6 hour. Propolis in DMEM could be a potential storage media for prolonged storage intervals up to 48 hour.

Damping ratio analysis of tooth stability under various simulated degrees of vertical alveolar bone loss and different root types

Background

The purpose of this study was to evaluate the feasibility of using damping ratio (DR) analysis combined with resonance frequency (RF) and periotest (PTV) analyses to provide additional information about natural tooth stability under various simulated degrees of alveolar vertical bone loss and various root types.

Methods

Three experimental tooth models, including upper central incisor, upper first premolar, and upper first molar were fabricated using Ti6Al4V alloy. In the tooth models, the periodontal ligament and alveolar bone were simulated using a soft lining material and gypsum, respectively. Various degrees of vertical bone loss were simulated by decreasing the surrounding bone level apically from the cementoenamel junction in 2-mm steps incrementally downward for 10 mm. A commercially available RF analyzer was used to measure the RF and DR of impulse-forced vibrations on the tooth models.

Results

The results showed that DRs increased as alveolar vertical bone height decreased and had high coefficients of determination in the linear regression analysis. The damping ratio of the central incisor model without a simulated periodontal ligament were 11.95 ± 1.92 and 27.50 ± 0.67% respectively when their bone levels were set at 2 and 10 mm apically from the cementoenamel junction. These values significantly changed to 28.85 ± 2.54% (p = 0.000) and 51.25 ± 4.78% (p = 0.003) when the tooth model was covered with simulated periodontal ligament. Moreover, teeth with different root types showed different DR and RF patterns. Teeth with multiple roots had lower DRs than teeth with single roots.

Conclusion

Damping ratio analysis combined with PTV and RF analysis provides more useful information on the assessment of changes in vertical alveolar bone loss than PTV or RF analysis alone.

In vitro comparison of the efficacy of TGF-β1 and PDGF-BB in combination with freeze-dried bone allografts for induction of osteogenic differentiation in MG-63 osteoblast-like cells

Predictable regeneration of alveolar bone defects has always been a challenge in implant dentistry. Bone allografts are widely used bone substitutes with controversial osteoinductive activity. This in vitro study aimed to assess the osteogenic potential of some commercially available freeze-dried bone allografts supplemented with human recombinant platelet-derived growth factor-BB and transforming growth factor beta-1. Cell viability, mineralization, and osteogenic gene expression of MG-63 osteoblast-like cells were compared among the allograft alone, allograft/platelet-derived growth factor-BB, allograft/transforming growth factor beta-1, and allograft/platelet-derived growth factor-BB/transforming growth factor beta-1 groups. The methyl thiazol tetrazolium assay, real-time quantitative reverse transcription polymerase chain reaction and alizarin red staining were performed, respectively, for assessment of cell viability, differentiation, and mineralization at 24-72 h post treatment. The allograft with greater cytotoxic effect on MG-63 cells caused the lowest differentiation among the groups. In comparison with allograft alone, allograft/transforming growth factor beta-1, and allograft/transforming growth factor beta-1/platelet-derived growth factor-BB caused significant upregulation of bone sialoprotein and osteocalcin osteogenic mid-late marker genes, and resulted in significantly higher amounts of calcified nodules especially in mineralized non-cytotoxic allograft group. Supplementation of platelet-derived growth factor-BB alone in 5 ng/mL concentration had no significant effect on differentiation or mineralization markers. According to the results, transforming growth factor beta-1 acts synergistically with bone allografts to enhance the osteogenic differentiation potential. Therefore, this combination may be useful for rapid transformation of undifferentiated cells into bone-forming cells for bone regeneration. However, platelet-derived growth factor-BB supplementation did not support this synergistic ability to enhance osteogenic differentiation and thus, further investigations are required.

Regenerative Applications Using Tooth Derived Stem Cells in Other Than Tooth Regeneration: A Literature Review

Tooth derived stem cells or dental stem cells are categorized according to the location from which they are isolated and represent a promising source of cells for regenerative medicine. Originally, as one kind of mesenchymal stem cells, they are considered an alternative of bone marrow stromal cells. They share many commonalties but maintain differences. Considering their original function in development and the homeostasis of tooth structures, many applications of these cells in dentistry have aimed at tooth structure regeneration; however, the application in other than tooth structures has been attempted extensively. The availability from discarded or removed teeth can be an innate benefit as a source of autologous cells. Their origin from the neural crest results in exploitation of neurological and numerous other applications. This review briefly highlights current and future perspectives of the regenerative applications of tooth derived stem cells in areas beyond tooth regeneration.

Osteogenic differentiation of dental pulp stem cells under the influence of three different materials

Background

Regeneration of periodontal tissues is a major goal of periodontal therapy. Dental pulp stem cells (DPSCs) show mesenchymal cell properties with the potential for dental tissue engineering. Enamel matrix derivative (EMD) and platelet-derived growth factor (PDGF) are examples of materials that act as signaling molecules to enhance periodontal regeneration. Mineral trioxide aggregate (MTA) has been proven to be biocompatible and appears to have some osteoconductive properties. The objective of this study was to evaluate the effects of EMD, MTA, and PDGF on DPSC osteogenic differentiation.

Methods

Human DPSCs were cultured in medium containing EMD, MTA, or PDGF. Control groups were also established. Evaluation of the achieved osteogenesis was carried out by computer analysis of alkaline phosphatase (ALP)-stained chambers, and spectrophotometric analysis of alizarin red S-stained mineralized nodules.

Results

EMD significantly increased the amounts of ALP expression and mineralization compared with all other groups (P < 0.05). Meanwhile, MTA gave variable results with slight increases in certain differentiation parameters, and PDGF showed no significant increase in the achieved differentiation.

Conclusions

EMD showed a very strong osteogenic ability compared with PDGF and MTA, and the present results provide support for its use in periodontal regeneration.

Periodontitis promotes the proliferation and suppresses the differentiation potential of human periodontal ligament stem cells

The aim of the present study was to investigate the periodontitis-associated changes in the number, proliferation and differentiation potential of human periodontal ligament stem cells (PDLSCs). Cultures of human periodontal ligament cells (PDLCs) were established from healthy donors and donors with periodontitis. The numbers of stem cell were characterized using flow cytometry. PDLSCs were isolated from the PDLCs by immunomagnetic bead selection. Colony-forming abilities, osteogenic and adipogenic potential, gene expression of cementoblast phenotype, alkaline phosphatase activity and in vivo differentiation capacities were then evaluated. Periodontitis caused an increase in the proliferation of PDLSCs and a decrease in the commitment to the osteoblast lineage. This is reflected by changes in the expression of osteoblast markers. When transplanted into immunocompromised mice, PDLSCs from the healthy donors exhibited the capacity to produce cementum PDL-like structures, whereas, the inflammatory PDLSCs transplants predominantly formed connective tissues. In conclusion, the data from the present study suggest that periodontitis affects the proliferation and differentiation potential of human PDLSCs in vitro and in vivo.

Tooth-derived stem cells: Update and perspectives

Tissue engineering is an emerging field of science that focuses on creating suitable conditions for the regeneration of tissues. The basic components for tissue engineering involve an interactive triad of scaffolds, signaling molecules, and cells. In this context, stem cells (SCs) present the characteristics of self-renewal and differentiation capacity, which make them promising candidates for tissue engineering. Although they present some common markers, such as cluster of differentiation (CD)105, CD146 and STRO-1, SCs derived from various tissues have different patterns in relation to proliferation, clonogenicity, and differentiation abilities in vitro and in vivo. Tooth-derived tissues have been proposed as an accessible source to obtain SCs with limited morbidity, and various tooth-derived SCs (TDSCs) have been isolated and characterized, such as dental pulp SCs, SCs from human exfoliated deciduous teeth, periodontal ligament SCs, dental follicle progenitor cells, SCs from apical papilla, and periodontal ligament of deciduous teeth SCs. However, heterogeneity among these populations has been observed, and the best method to select the most appropriate TDSCs for regeneration approaches has not yet been established. The objective of this review is to outline the current knowledge concerning the various types of TDSCs, and discuss the perspectives for their use in regenerative approaches.

Assessment of periostin levels in serum and gingival crevicular fluid of patients with periodontal disease

BACKGROUND AND OBJECTIVE

Periostin, a secreted adhesion molecule essential for periodontal tissue integrity, is highly expressed in the periodontal ligament and plays a critical role in tooth and bone development. The purpose of this study was to investigate periostin levels in the gingival crevicular fluid and serum of patients with periodontal disease and compare them with those of healthy individuals.

MATERIAL AND METHODS

Eighty individuals (41 males and 39 females; age range: 25-48 years) were enrolled in the study. Individuals were divided into three groups following clinical and radiographic examinations: the periodontal-healthy group (n = 20), gingivitis group (n = 30) and chronic periodontitis group (n = 30). Gingival crevicular fluid and serum samples were collected and periostin levels were determined using the enzyme-linked immunosorbent assay.

RESULTS

The total amount and concentration of periostin decreased in gingival crevicular fluid with the progression and severity of the disease from healthy controls to gingivitis and to chronic periodontitis groups and differed significantly (p < 0.05). However, there was no significant difference in serum periostin concentration within all groups (p > 0.05). Periostin in gingival crevicular fluid negatively correlated with the gingival index in the periodontal disease groups, whereas it is inversely correlated with the clinical attachment level only in the periodontitis group (p < 0.05). When all the clinical groups were examined together, the periostin concentration negatively correlated with clinical attachment level and gingival index; moreover, total periostin positively correlated with periostin concentration and clinical attachment level (p < 0.05).

CONCLUSIONS

The periostin levels in gingival crevicular fluid decreased proportionally with the progression and severity of periodontal disease, and negatively correlated with the clinical parameters. Within the limits of the study, the periostin level in gingival crevicular fluid can be considered a reliable marker in the evaluation of periodontal disease susceptibility and activity.

Co-culture with periodontal ligament stem cells enhances osteogenic gene expression in de-differentiated fat cells

In recent decades, de-differentiated fat cells (DFAT cells) have emerged in regenerative medicine because of their trans-differentiation capability and the fact that their characteristics are similar to bone marrow mesenchymal stem cells. Even so, there is no evidence to support the osteogenic induction using DFAT cells in periodontal regeneration and also the co-culture system. Consequently, this study sought to evaluate the DFAT cells co-culture with periodontal ligament stem cells (PDLSCs) in vitro in terms of gene expression by comparing runt-related transcription factor 2 (RUNX2) and Peroxisome proliferator-activated receptor gamma 2 (PPARγ2) genes. We isolated DFAT cells from mature adipocytes and compared proliferation with PDLSCs. After co-culture with PDLSCs, we analyzed transcriptional activity implying by DNA methylation in all adipogenic gene promoters using combined bisulfite restriction analysis. We compared gene expression in RUNX2 gene with the PPARγ2 gene using quantitative RT-PCR. After being sub-cultured, DFAT cells demonstrated morphology similar to fibroblast-like cells. At the same time, PDLSCs established all stem cell characteristics. Interestingly, the co-culture system attenuated proliferation while enhancing osteogenic gene expression in RUNX2 gene. Using the co-culture system, DFAT cells could trans-differentiate into osteogenic lineage enhancing, but conversely, their adipogenic characteristic diminished. Therefore, DFAT cells and the co-culture system might be a novel cell-based therapy for promoting osteogenic differentiation in periodontal regeneration.

Mechanotransduction in bone: Intervening in health and disease

Mechanotransduction has been proven to be one of the most significant variables in bone remodeling and its alterations have been shown to result in a variety of bone diseases. Osteoporosis, Paget’s disease, orthopedic disorders, osteopetrosis as well as hyperparathyroidism and hyperthyroidism all comprise conditions which have been linked with deregulated bone remodeling. Although the significance of mechanotransduction for bone health and disease is unquestionable, the mechanisms behind this important process have not been fully understood. This review will discuss the molecules that have been found to be implicated in mechanotransduction, as well as the mechanisms underlying bone health and disease, emphasizing on what is already known as well as new molecules potentially taking part in conveying mechanical signals from the cell surface towards the nucleus under physiological or pathologic conditions. It will also focus on the model systems currently used in mechanotransduction studies, like osteoblast-like cells as well as three-dimensional constructs and their applications among others. It will also examine the role of mechanostimulatory techniques in preventing and treating bone degenerative diseases and consider their applications in osteoporosis, craniofacial development, skeletal deregulations, fracture treatment, neurologic injuries following stroke or spinal cord injury, dentistry, hearing problems and bone implant integration in the near future.

An autologous platelet-rich plasma stimulates periodontal ligament regeneration

BACKGROUND

Regeneration of periodontal tissues is one of the most important goals for the treatment of periodontal disease. The technology of plasma rich in growth factors provides a biologic approach for the stimulation and acceleration of tissue healing. The purpose of this study is to evaluate the biologic effects of this technology on primary human periodontal ligament fibroblasts.

METHODS

The authors studied the response of periodontal ligament cells to this pool of growth factors on cell proliferation, cell migration, secretion of several biomolecules, cell adhesion, and expression of α2 integrin. Cell proliferation and adhesion were evaluated by means of a fluorescence-based method. Cell migration was performed on culture inserts. The release of different biomolecules by periodontal ligament fibroblasts was quantified through enzyme-linked immunosorbent assay. The α2 integrin expression was assessed through Western blot.

RESULTS

This autologous technology significantly stimulated cell proliferation, migration, adhesion, and synthesis of many growth factors from cells including vascular endothelial growth factor, thrombospondin 1, connective tissue growth factor, hepatocyte growth factor, and procollagen type I. The α2 integrin expression was lower in plasma rich in growth factor-treated cells compared to non-stimulated cells, although no statistically significant differences were observed.

CONCLUSION

This plasma rich in growth factors exerts positive effects on periodontal ligament fibroblasts, which could be positive for periodontal regeneration.

bFGF-induced human periodontal ligament fibroblasts proliferation through T-type voltage-dependent calcium channels

OBJECTIVE

To test the hypothesis that T-type voltage-dependent calcium channels (T-CaCNs) are involved in basic fibroblast growth factor (bFGF)-induced proliferation of human periodontal ligament fibroblasts (HPLFs).

MATERIALS AND METHODS

This study examined the expression of the T-type calcium channel sub-units Ca(V) 3.1, Ca(V) 3.2 and Ca(V) 3.3 in HPLFs by real-time PCR. Mibefradil, a T-CaCNs antagonist, was used to block the effect of T-CaCNs and the proliferation of HPLFs was evaluated by the water-soluble tetrazolium (WST) assay. The level of intracellular calcium was measured by laser confocal microscopy.

RESULTS

Expression of the three subunits of T-CaCNs in HPLFs was detected, which was strongly up-regulated upon stimulation by bFGF. The proliferation of HPLFs induced by bFGF was decreased significantly by treatment with Mibefradil. This effect was associated with the decreased expression of T-CaCNs and a decreased level of intracellular calcium.

CONCLUSIONS

Expression of the T-CaCNs affected the proliferation of HPLFs that was induced by bFGF, indicating that T-CaCNs could be important in mediating periodontal ligament (PDL) remodeling.

Effect of therapeutic ultrasound on human periodontal ligament cells for dental and periodontal tissue engineering

The objective of this study was to investigate whether low intensity pulsed ultrasound (LIPUS) has anabolic effects on human periodontal ligament (PDL) cells. The PDL cells were plated in 48-well plates and cultured at 37°C in an atmosphere of 5% CO2 in air, in a humidified incubator until confluent. The cells were divided into three groups including control, 5 min and 10 min ultrasound application. The LIPUS was applied using a 2.5 transducer that produces an incident intensity of 30 mW/cm2 of the transducer's surface area. The results from the quantitative polymerase chain reaction (PCR) indicates that expression levels of alkaline phosphatase (ALP),cyclin D1 (CYC), nucleostemin (NCT) were increased after four weeks of 10 minutes of daily ultrasound treatment. The increased ALP/DNA by LIPUS shows a time dependent pattern with the highest activity occurring after four weeks of treatment. These results demonstrate that LIPUS has an anabolic effect on PDL cells and suggest that LIPUS may enhance the pluripotent characteristics of PDL cells as indicated by the up-regulation of NCT, a stem marker. These results also may explain the potential role of LIPUS in periodontal tissue regeneration.

Mesenchymal stem cells isolated from adipose and other tissues: basic biological properties and clinical applications

Mesenchymal stem cells (MSCs) are adult stem cells that were initially isolated from bone marrow. However, subsequent research has shown that other adult tissues also contain MSCs. MSCs originate from mesenchyme, which is embryonic tissue derived from the mesoderm. These cells actively proliferate, giving rise to new cells in some tissues, but remain quiescent in others. MSCs are capable of differentiating into multiple cell types including adipocytes, chondrocytes, osteocytes, and cardiomyocytes. Isolation and induction of these cells could provide a new therapeutic tool for replacing damaged or lost adult tissues. However, the biological properties and use of stem cells in a clinical setting must be well established before significant clinical benefits are obtained. This paper summarizes data on the biological properties of MSCs and discusses current and potential clinical applications.

FGF-2 induces proliferation of human periodontal ligament cells and maintains differentiation potentials of STRO-1(+)/CD146(+) periodontal ligament cells

The presence of human STRO-1(+)/CD146(+) periodontal ligament (PDL) cells has been reported, but obtaining a large amount of these cells is difficult. The purpose of this study was to evaluate the percentages of STRO-1(+)/CD146(+) cells in PDL cells and determine the effects of FGF-2 on the proliferation and multilineage differentiation potency of these cells. Human PDL (HPDL) cells were individually prepared from 15 extracted teeth. HPDL cells were cultured with or without FGF-2, and the percentages of STRO-1(+)/CD146(+) cells in each HPDL cell culture was examined using FACSAria™. The STRO-1(+)/CD146(+) cells were sorted with FACSAria™, and the mRNA expression and differentiation potency of the sorted cells were subsequently examined. The numbers of the STRO-1(+)/CD146(+) cells in the FGF-2 cultures were significantly higher than those cultured in the absence of FGF-2. The sorted STRO-1(+)/CD146(+) cells expressed mRNA of PDL markers and differentiated into adipocytes and osteoblast-like cells. The present study shows that FGF-2 augmented the proliferation of the STRO-1(+)/CD146(+) cells in the HPDL cultures whilst retaining adipogenic and osteogenic differentiation potentials. Thus, it may be useful to culture HPDL cells with FGF-2 for the application of the human STRO-1(+)/CD146(+) PDL cells in periodontal tissue regeneration.

In vitro osteogenic induction of human gingival fibroblasts for bone regeneration

Background And Objective:

Periodontitis is an inflammatory disease causing bone loss, and is a primary cause of tooth loss. Gingival fibroblasts are readily available with minimal donor site morbidity and may be ideal for tissue engineering efforts in regenerating lost alveolar bone. Dexamethasone (Dex) is commonly employed for in vitro osteogenic induction of a variety of cells, but its effect on human gingival fibroblasts (HGF) is still controversial. Therefore, the aim of our study was to investigate the osteogenic differentiation of HGF following Dex treatment.

Methods:

Cultured HGFs were exposed to osteogenic medium containing a wide range of Dex concentrations (0.01-10 µM). The osteogenic phenotype was assessed based on changes in alkaline phosphatase (ALP) activity, the mRNA expression of selected extracellular matrix proteins critical for mineralization and the extent of extracellular mineralization (Von Kossa staining and Ca-content).

Results:

All assays showed a consistent and maximal osteogenic effect of Dex on HGF at 0.1 and 0.5 µM (weeks 3 and 4), as evidenced by significant osteopontin and osteocalcin expression and mineralization. Longer cultures (week 4) also yielded positive osteogenic effect of Dex at 0.01 µM. Moreover, ALP activity was significantly stimulated at 0.1 and 0.5 µM Dex initially after one week, but ALP was subsequently reduced under Dex. Higher Dex concentrations caused down regulation of osteogenic effects observed at the optimal (0.1-0.5 µM) concentrations.

Conclusion:

Under appropriate osteogenic conditioning, Dex treated HGFs could be a potential source of cells for cell-based therapy for periodontal bone regeneration.

Analysis of gene expression profile of periodontal ligament cells subjected to cyclic compressive force

Cyclic compressive force is an important mechanical stimulus on periodontal ligament (PDL). The differential expression of genes in PDL cells is thought to be involved in the remodeling of periodontal tissues subjected to mechanical stress. However, little is known about differentially expressed genes in PDL cells under cyclic compressive force. In our study, human PDL cells were subjected to 4000 μ strain compressive stress loading at 0.5 Hz for 2 h. The effect of mechanical stress on PDL cells proliferation was observed by flow cytometry. Microarray analysis was used to investigate the mechano-induced differential gene profile in PDL cells. Differential expression was confirmed by quantitative real-time polymerase chain reaction (RT-PCR) analysis on genes of interest and explored at two more force loading times (6 h, 12 h). After mechanical loading, cell proliferation was repressed. The microarray data showed that 217 out of 35,000 genes were differentially expressed; among the 217 genes, 207 were up-regulated whereas 10 were down-regulated (p < 0.05). Gene ontology analysis suggested that majority of differentially expressed genes were located in the nucleus and functioned as transcription factors involved in a variety of biological processes. Five genes of interest (IL6, IL8, ETS1, KLF10, and DLC1) were found to be closely related to negative regulation of cell proliferation. The PCR results showed increased expression after 2 h loading, then a decline with extended loading time. The signaling pathways involved were also identified. These findings expand understanding of molecular regulation in the mechano-response of PDL cells.

Novel regenerative strategies to enhance periodontal therapy outcome

BACKGROUND

Chronic periodontitis is a widely prevalent inflammatory condition of the supporting tissues of the teeth and is characterized by loss of teeth with an associated risk of systemic complications. Regenerative therapies such as guided tissue and bone regeneration form an important armamentarium in periodontics with a high degree of outcome predictability in certain ideal clinical scenarios.

OBJECTIVE/METHODS

This review elaborates novel tissue regenerative treatment modalities based on sound understanding of developmental biology, tissue engineering, inflammation and wound healing. We focus on the role of biological mediators such as growth factors, gene-based therapy, cell therapy and pro-resolution lipid mediators in the regeneration of lost bone or periodontium.

RESULTS/CONCLUSIONS

These therapies have the potential to regenerate both periodontium and bone, aiding in the treatment of even clinically challenging cases.

Three-dimensional stress distribution in the human periodontal ligament in masticatory, parafunctional, and trauma loads: finite element analysis

BACKGROUND

The presence of the periodontal ligament (PDL) makes it possible to absorb and distribute loads produced during masticatory function and other tooth contacts into the alveolar process via the alveolar bone proper. However, several factors affect the integrity of periodontal structures causing the destruction of the connective matrix and cells, the loss of fibrous attachment, and the resorption of alveolar bone.

METHODS

The purpose of this study was to evaluate the stress distribution by finite element analysis in a PDL in three-dimensional models of the upper central incisor under three different load conditions: 100 N occlusal loading at 45 degrees (model 1: masticatory load); 500 N at the incisal edge at 45 degrees (model 2: parafunctional habit); and 800 N at the buccal surface at 90 degrees (model 3: trauma case). The models were built from computed tomography scans.

RESULTS

The stress distribution was quite different among the models. The most significant values (harmful) of tensile and compressive stresses were observed in models 2 and 3, with similarly distinct patterns of stress distributions along the PDL. Tensile stresses were observed along the internal and external aspects of the PDL, mostly at the cervical and middle thirds.

CONCLUSIONS

The stress generation in these models may affect the integrity of periodontal structures. A better understanding of the biomechanical behavior of the PDL under physiologic and traumatic loading conditions might enhance the understanding of the biologic reaction of the PDL in health and disease.

Engineering craniofacial structures: facing the challenge

The human innate regenerative ability is known to be limited by the intensity of the insult together with the availability of progenitor cells, which may cause certain irreparable damage. It is only recently that the paradigm of tissue engineering found its way to the treatment of irreversibly affected body structures with the challenge of reconstructing the lost part. In the current review, we underline recent trials that target engineering of human craniofacial structures, mainly bone, cartilage, and teeth. We analyze the applied engineering strategies relative to the selection of cell types to lay down a specific targeted tissue, together with their association with an escorting scaffold for a particular engineered site, and discuss their necessity to be sustained by growth factors. Challenges and expectations for facial skeletal engineering are discussed in the context of future treatment.

Loss of proliferation and differentiation capacity of aged human periodontal ligament stem cells and rejuvenation by exposure to the young extrinsic environment

The application of periodontal ligament stem cells (PDLSCs) may be effective for periodontal regenerative therapy. As tissue regenerative potential may be negatively regulated by aging, whether aging and its microenvironment modify human PDLSCs remains a question. In this study, we compared the proliferation and differentiation capacity of PDLSCs obtained from young and aged donors. Then, we exposed aged PDLSCs to young periodontal ligament cell-conditioned medium (PLC-CM), and young PDLSCs were exposed to aged PLC-CM. Morphological appearance, colony-forming assay, cell cycle analysis, osteogenic and adipogenic induction media, gene expression of cementoblast phenotype, and in vivo differentiation capacities of PDLSCs were evaluated. PDLSCs obtained from aged donors exhibited decreased proliferation and differentiation capacity when compared with those from young donors. Young PLC-CM enhanced the proliferation and differentiation capacity of PDLSCs from aged donors. Aged PDLSCs induced by young PLC-CM showed enhanced tissue-regenerative capacity to produce cementum/periodontal ligament-like structures, whereas young PDLSCs induced by aged PLC-CM transplants mainly formed connective tissues. To our knowledge, this is the first study to mimic the developmental microenvironment of PDLSCs in vitro, and our data suggest that age influences the proliferation and differentiation potential of human PDLSCs, and that the activity of human PDLSCs can be modulated by the extrinsic microenvironment.

Periodontal ligament cellular structures engineered with electrospun poly(DL-lactide-co-glycolide) nanofibrous membrane scaffolds

Periodontal tissue engineering is expected to overcome the limitations associated with the existing regenerative techniques for the treatment of periodontal defects involving alveolar bone, cementum, and periodontal ligament. Cell-based tissue engineering approaches involve the utilization of in vitro expanded cells with regenerative capacity and their delivery to the appropriate sites via biomaterial scaffolds. The aim of this study was to establish living periodontal ligament cell-containing structures on electrospun poly(DL-lactic-co-glycolic acid) (PLGA) nanofiber membrane scaffolds, assess their viability and characteristics, and engineer multilayered structures amenable to easy handling. Human periodontal ligament (hPDL) cells were expanded in explant culture and then characterized morphologically and immunohistochemically. PLGA nanofiber membranes were prepared by the electrospinning process; mechanical tensile properties were determined, surface topography, nanofiber size, and porosity status were investigated with SEM. Cells were seeded on the membranes at approximately 50,000 cell/cm(2) and cultured for 21 days either in expansion or in osteogenic induction medium. Cell adhesion and viability were demonstrated using SEM and MTT, respectively, and osteogenic differentiation was determined with IHC and immunohistomorphometric evaluation of osteopontin, osteocalcin, and bone sialoprotein marker expression. At days 3, 6, 9, and 12 additional cell/membrane layers were deposited on the existing ones and multilayered hybrid structures were established. Results indicate the feasibility of periodontal ligament cell-containing tissue-like structures engineering with PDL cells and electrospun nanofiber PLGA scaffolds supporting cell adhesion, viability and osteogenic differentiation properties of cells in hybrid structures amenable to macroscopic handling.

Regional structural characteristics of bovine periodontal ligament samples and their suitability for biomechanical tests

Mechanical testing of the periodontal ligament requires a practical experimental model. Bovine teeth are advantageous in terms of size and availability, but information is lacking as to the anatomy and histology of their periodontium. The aim of this study, therefore, was to characterize the anatomy and histology of the attachment apparatus in fully erupted bovine mandibular first molars. A total of 13 teeth were processed for the production of undecalcified ground sections and decalcified semi-thin sections, for NaOH maceration, and for polarized light microscopy. Histomorphometric measurements relevant to the mechanical behavior of the periodontal ligament included width, number, size and area fraction of blood vessels and fractal analysis of the two hard-soft tissue interfaces. The histological and histomorphometric analyses were performed at four different root depths and at six circumferential locations around the distal and mesial roots. The variety of techniques applied provided a comprehensive view of the tissue architecture of the bovine periodontal ligament. Marked regional variations were observed in width, surface geometry of the two bordering hard tissues (cementum and alveolar bone), structural organization of the principal periodontal ligament connective tissue fibers, size, number and numerical density of blood vessels in the periodontal ligament. No predictable pattern was observed, except for a statistically significant increase in the area fraction of blood vessels from apical to coronal. The periodontal ligament width was up to three times wider in bovine teeth than in human teeth. The fractal analyses were in agreement with the histological observations showing frequent signs of remodeling activity in the alveolar bone - a finding which may be related to the magnitude and direction of occlusal forces in ruminants. Although samples from the apical root portion are not suitable for biomechanical testing, all other levels in the buccal and lingual aspects of the mesial and distal roots may be considered. The bucco-mesial aspect of the distal root appears to be the most suitable location.