Cementogenesis and the induction of periodontal tissue regeneration by the osteogenic proteins of the transforming growth factor-beta superfamily

Exploring the mechanical and biological interplay in the periodontal ligament

The periodontal ligament (PDL) plays a crucial role in transmitting and dispersing occlusal force, acting as mechanoreceptor for muscle activity during chewing, as well as mediating orthodontic tooth movement. It transforms mechanical stimuli into biological signals, influencing alveolar bone remodeling. Recent research has delved deeper into the biological and mechanical aspects of PDL, emphasizing the importance of understanding its structure and mechanical properties comprehensively. This review focuses on the latest findings concerning both macro- and micro- structural aspects of the PDL, highlighting its mechanical characteristics and factors that influence them. Moreover, it explores the mechanotransduction mechanisms of PDL cells under mechanical forces. Structure-mechanics-mechanotransduction interplay in PDL has been integrated ultimately. By providing an up-to-date overview of our understanding on PDL at various scales, this study lays the foundation for further exploration into PDL-related biomechanics and mechanobiology.

Cementum attachment protein-derived peptide induces cementum formation

A pentapeptide AVIFM (CAP-p5) derived from the carboxy-terminus end of cementum attachment protein was examined for its role on proliferation, differentiation, and mineralization of human periodontal ligament cells (HPLC), and for its potential to induce cementum deposition in vivo. CAP-p5 capability to induce hydroxyapatite crystal formation on demineralized dentin blocks was characterized by scanning electron microscopy, μRAMAN, and high-resolution transmission electron microscopy. The results revealed that CAP-p5 promoted cell proliferation and cell differentiation and increases alkaline phosphatase activity of HPLC and mineralization at an optimal concentration of 10 μg/mL. It induced the expression of cementum molecular markers BSP, CAP, CEMP1, and ALP at the protein level. In a cell-free system, human demineralized dentin blocks coated with CAP-p5 induced the deposition of a homogeneous and continuous mineralized layer, intimately integrated with the underlying dentin indicating new cementum formation. Physicochemical characterization of this mineral layer showed that it is composed of hydroxyapatite crystals. Demineralized dentin blocks coated with CAP-p5 implanted subcutaneously in BALB/cAnNCrl were analyzed histologically; the results disclosed that CAP-p5 could induce the deposition of a cementum layer intimately integrated with the subjacent dentin with cementocytes embedded into the cementum matrix. Immunostaining showed the expression of cementum molecular markers; v.gr. BSP, CAP, CEMP1 and ALP, validating the molecular identity of the newly deposited cementum. We conclude that CAP-p5 is a new biomolecule with the potential of therapeutic application to contribute to the regeneration of cementum and periodontal structures lost in periodontal disease.

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 healthcare 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 in 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.

The Impact of Autologous Platelet Concentrates on the Periapical Tissues and Root Development of Replanted Teeth: A Systematic Review

Introduction: In many cases, the replanted teeth may undergo resorption or ankyloses. Recent studies show that autologous platelet concentrates (APCs) may improve the outcomes of tooth replantation. The aim of this systematic review was to summarize and critically appraise the currently available literature on the use of APCs before tooth replantation. Methodology: An electronic search was conducted on the following research databases: PubMed/MEDLINE, ISI Web of Science, EMBASE and Scopus. The following medical subject heading (MeSH) keywords used were: ((tooth replantation) OR (replanted tooth) OR (teeth replantation) OR (replanted teeth)) AND ((autologous platelet concentrate) OR (platelet-rich plasma) OR (platelet-rich fibrin) OR (autologous platelet)). The studies’ data was extracted, and the research’ quality was rated using the CARE and ARRIVE protocols. Results: Ten case reports and three animal studies, one cell study and one study, which included both animal and in vitro experiments, were included in this review. In majority of the studies, APCs improved the outcomes of tooth replantation. However, there were various sources of bias in the most of the research, which may have influenced the results. Conclusions: Although majority of the studies indicate that APCs may improve outcomes of tooth replantation, majority of the studies contained numerous sources of bias. Additionally, the sample size of the included subjects is inadequate to predict the clinical efficacy of APCs in management of replanted teeth. Large-scale, multi-center and long-term studies are required to ascertain the efficacy of APCs in improve the outcomes of tooth replantation.

Redefining the induction of periodontal tissue regeneration in primates by the osteogenic proteins of the transforming growth factor-β supergene family

The molecular bases of periodontal tissue induction and regeneration are the osteogenic proteins of the transforming growth factor-β (TGF-β) supergene family. These morphogens act as soluble mediators for the induction of tissues morphogenesis sculpting the multicellular mineralized structures of the periodontal tissues with functionally oriented ligament fibers into newly formed cementum. Human TGF-β₃ (hTGF-β₃ ) in growth factor-reduced Matrigel^® matrix induces cementogenesis when implanted in class II mandibular furcation defects surgically prepared in the non-human primate Chacma baboon, Papio ursinus. The newly formed periodontal ligament space is characterized by running fibers tightly attached to the cementoid surface penetrating as mineralized constructs within the newly formed cementum assembling and initiating within the mineralized dentine. Angiogenesis heralds the newly formed periodontal ligament space, and newly sprouting capillaries are lined by cellular elements with condensed chromatin interpreted as angioblasts responsible for the rapid and sustained induction of angiogenesis. The inductive activity of hTGF-β₃ in Matrigel^® matrix is enhanced by the addition of autogenous morcellated fragments of the rectus abdominis muscle potentially providing myoblastic, pericytic/perivascular stem cells for continuous tissue induction and morphogenesis. The striated rectus abdominis muscle is endowed with stem cell niches in para/perivascular location, which can be dominant, thus imposing stem cell features or stemness to the surrounding cells. This capacity to impose stemness is morphologically shown by greater alveolar bone induction and cementogenesis when hTGF-β₃ in Matrigel^® matrix is combined with morcellated fragments of autogenous rectus abdominis muscle. The induction of periodontal tissue morphogenesis develops as a mosaic structure in which the osteogenic proteins of the TGF-β supergene family singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis. In primates, the presence of several homologous yet molecularly different isoforms with osteogenic activity highlights the biological significance of this apparent redundancy and indicates multiple interactions during embryonic development and bone regeneration in postnatal life. Molecular redundancy with associated different biological functionalities in primate tissues may simply represent the fine-tuning of speciation-related molecular evolution in anthropoid apes at the early Pliocene boundary, which resulted in finer tuning of the bone induction cascade.

Effect of lithium ions on cementoblasts in the presence of lipopolysaccharide in vitro

The applications of lithium ions as an agent to facilitate bone formation have been widely documented; however, the effect of lithium ions in the periodontitis model has not yet been elucidated. The aim of the present study, therefore, was to investigate the effect of single lithium ions in the presence of lipopolysaccharide (LPS). A periodontitis model was induced in cementoblasts using LPS. The cytotoxic effect of the lithium ions on the cementoblasts was studied through the MTT assay. Alkaline phosphatase analysis and alizarin red staining were performed to investigate the effect of the lithium ions on differentiation. To examine the effect of lithium ions on osteoclastogenesis, osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) mRNA and protein expression levels were assessed using reverse transcription-polymerase chain reaction analysis and ELISA, respectively. Compared with the effect induced by lithium ions on normal cementoblasts, proliferation and differentiation were downregulated following the co-incubation of the cementoblasts with LPS and lithium ions. Furthermore, the lithium ions appeared to alter osteoclastogenesis by regulating the OPG/RANKL ratio. In conclusion, the present findings suggest that lithium ions can downregulate proliferation and differentiation in a periodontitis model. Further studies should be undertaken prior to the acceptance of lithium ions for use in the clinic.

Growth factors and craniofacial surgery

The specialty of craniofacial surgery is broad and includes trauma, aesthetics, reconstruction of congenital deformities, and regeneration of tissues. Moreover, craniofacial surgery deals with a diverse range of tissues including both "soft" and "hard" tissues. Technological advances in materials and biological sciences and improved surgical techniques have remarkably improved clinical outcomes. The quest to raise the bar for patient care continues to inspire advances for predictable biological regeneration of soft and hard tissues. As a consequence of this quest for advancement, a wide spectrum of biologicals is becoming available to surgeons. Is the use of recombinant DNA engineered biologicals daring? Sensible? Logical? Timely? Safe? It is crucial for the practicing craniofacial surgeon to take a step back periodically and carefully review the biological factors that have the potential for dramatically altering the discipline of craniofacial surgery. With this emphasis, the coauthors of this article will focus on growth factor technology underscoring bone tissue regeneration. As the 21st-century matures, recombinant human biologicals will have an overwhelming impact on the practice of craniofacial surgery.

Enhanced adipogenic differentiation and reduced collagen synthesis induced by human periodontal ligament stem cells might underlie the negative effect of recombinant human bone morphogenetic protein-2 on periodontal regeneration

BACKGROUND AND OBJECTIVE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a potent inducer for the regeneration of mineralized tissue, but has a limited effect on the regeneration of cementum and periodontal ligament (PDL). The aim of the present study was to determine the effects of rhBMP-2 on the in vitro and in vivo biologic activity of well-characterized human PDL stem cells (hPDLSCs) and to elucidate the underlying mechanism of minimal periodontal regeneration by rhBMP-2.

MATERIAL AND METHODS

hPDLSCs were isolated and cultured, and then transplanted into an ectopic subcutaneous mouse model using a carrier treated either with or without rhBMP-2. Comprehensive histologic, histometric and immunohistochemical analyses were performed after an 8-wk healing period. The effects of rhBMP-2 on the adipogenic and osteogenic/cementogenic differentiation of hPDLSCs were also evaluated. The effect of rhBMP-2 on both soluble and insoluble collagen synthesis was analyzed, and the expression of mRNA and protein for collagen types I, II, III and V was assessed.

RESULTS

In the present study, rhBMP-2 promoted both adipogenic and osteogenic/cementogenic differentiation of hPDLSCs in vitro, and the in vivo potential of hPDLSCs to form mineralized cementum and organized PDL tissue was down-regulated following treatment with rhBMP-2. Collagen synthesis, which plays a crucial role in the regeneration of cementum and the periodontal attachment, was significantly reduced, with associated modification of the relevant mRNA and protein expression profiles.

CONCLUSION

In summary, the findings of the present study suggest that enhanced adipogenic differentiation and inhibition of collagen synthesis by hPDLSCs appear to be partly responsible for the minimal effect of rhBMP-2 on cementum and PDL tissue regeneration by hPDLSCs.

Induction of bone formation by transforming growth factor-beta2 in the non-human primate Papio ursinus and its modulation by skeletal muscle responding stem cells

OBJECTIVES

Four adult non-human primates Papio ursinus were used to study induction of bone formation by recombinant human transforming growth factor-beta(2) (hTGF-beta(2)) together with muscle-derived stem cells.

MATERIALS AND METHODS

The hTGF-beta(2) was implanted in rectus abdominis muscles and in calvarial defects with and without addition of morcellized fragments of striated muscle, harvested from the rectus abdominis or temporalis muscles. Expression of osteogenic markers including osteogenic protein-1, bone morphogenetic protein-3 and type IV collagen mRNAs from generated specimens was examined by Northern blot analysis.

RESULTS

Heterotopic intramuscular implantation of 5 and 25 microg hTGF-beta(2) combined with 100 mg of insoluble collagenous bone matrix yielded large corticalized mineralized ossicles by day 30 with remodelling and induction of haematopoietic marrow by day 90. Addition of morcellized rectus abdominis muscle to calvarial implants enhanced induction of bone formation significantly by day 90.

CONCLUSIONS

In Papio ursinus, in marked contrast to rodents and lagomorphs, hTGF-beta(2) induced large corticalized and vascularized ossicles by day 30 after implantation into the rectus abdominis muscle. This striated muscle contains responding stem cells that enhance the bone induction cascade of hTGF-beta(2). Induction of bone formation by hTGF-beta(2) in the non-human primate Papio ursinus may occur as a result of expression of bone morphogenetic proteins on heterotopic implantation of hTGF-beta(2); the bone induction cascade initiated by mammalian TGF-beta proteins in Papio ursinus needs to be re-evaluated for novel molecular therapeutics for induction of bone formation in clinical contexts.

Transforming growth factor-beta isoforms and the induction of bone formation: implications for reconstructive craniofacial surgery

Craniofacial skeletal reconstruction remains a challenging problem despite major molecular and surgical developments in the understanding of bone formation by induction. The induction of bone formation has been a critical topic of research across the planet. The bone induction principle identified important cues for tissue engineering of bone, namely, osteogenic soluble molecular signals, the bone morphogenetic and osteogenic proteins, and insoluble signals or substrata including biomimetic bioactive matrices and responding stem cells. In primates, and in primates only, the osteogenic soluble molecular signals that initiate the induction of bone formation additionally include the 3 mammalian transforming growth factor-beta (TGF-beta) isoforms, members of the TGF-beta supergene family. The mammalian TGF-beta isoforms, when implanted in the rectus abdominis muscle of the nonhuman primate Papio ursinus, induce rapid and substantial endochondral bone formation resulting in large corticalized ossicles by day 30 after heterotopic implantation; in calvarial defects of the same nonhuman primates, identical or higher doses of the TGF-beta protein do not induce bone formation because of the overexpression of Smad-6 and Smad-7, gene product inhibitors of the TGF-beta signaling pathway. The addition of minced fragments of autogenous rectus abdominis muscle partially restores the osteoinductive activity of the human TGF-beta3 isoform resulting in the induction of bone formation in the treated calvarial defects. Recombinant human TGF-beta3 delivered by Matrigel matrix and implanted in class II and III furcation defects of mandibular molars of P. ursinus induce periodontal tissue regeneration. The addition of minced fragments of autogenous rectus abdominis muscle significantly enhances cementogenesis. This review highlights the induction of bone formation by the osteogenic proteins of the TGF-beta superfamily in the nonhuman primate P. ursinus and reviews combinatorial applications of myoblastic/myogenic stem cell-based therapeutics for bone induction and morphogenesis. The recruitment of myoendothelial cells is also discussed in the light of the intrinsic and spontaneous induction of bone formation by smart biomaterial matrices that induce bone differentiation in heterotopic extraskeletal sites of P. ursinus without the exogenous application of the osteogenic soluble molecular signals of the TGF-beta superfamily.