Emerging regenerative approaches for periodontal reconstruction: a systematic review from the AAP Regeneration Workshop

Enhanced immunomodulation and periodontal regeneration efficacy of subgingivally delivered progranulin-loaded hydrogel as an adjunct to non-surgical treatment for Class II furcation involvement in dogs

AIM

To evaluate the effect of subgingival delivery of progranulin (PGRN)/gelatin methacryloyl (GelMA) complex as an adjunct to scaling and root planing (SRP) on an experimental periodontitis dog model with Class II furcation involvement (FI).

MATERIALS AND METHODS

A Class II FI model was established, and the defects were divided into four treatment groups: (a) no treatment (control); (b) SRP; (c) SRP + GelMA; (d) SRP + PGRN/GelMA. Eight weeks after treatment, periodontal parameters were recorded, gingival crevicular fluid and gingival tissue were collected for ELISA and RT-qPCR, respectively, and mandibular tissue blocks were collected for micro computed tomography (micro-CT) scanning and hematoxylin and eosin (H&E) staining.

RESULTS

The SRP + PGRN/GelMA group showed significant improvement in all periodontal parameters compared with those in the other groups. The expression of markers related to M1 macrophage and Th17 cell significantly decreased, and the expression of markers related to M2 macrophage and Treg cell significantly increased in the SRP + PGRN/GelMA group compared with those in the other groups. The volume, quality and area of new bone and the length of new cementum in the root furcation defects of the PGRN/GelMA group were significantly increased compared to those in the other groups.

CONCLUSIONS

Subgingival delivery of the PGRN/GelMA complex could be a promising non-surgical adjunctive therapy for anti-inflammation, immunomodulation and periodontal regeneration.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Development and In Vitro Characterization of Antibiotic-Loaded Nanocarriers for Dental Delivery

The aim of this research work was to formulate and evaluate ciprofloxacin hydrochloride-loaded nanocarriers for treating dental infections and bone regeneration. Periodontal infection is associated with inflammation, soft tissue destruction, and bone loss. The objective of the study was to extract β tricalcium phosphate (β-TCP) from coral beach sand using the hydrothermal conversion method and load these nanocarriers with ciprofloxacin hydrochloride. The developed drug-loaded nanocarriers were evaluated for various parameters. In vitro drug-loading studies showed the highest drug loading of 71% for F1 with a drug: carrier ratio compared to plain ciprofloxacin hydrochloride gel. β-TCP and nanocarriers were evaluated for powder characteristics and the results were found to have excellent and fair flowability. In vitro drug release studies conducted over a period of 5 days confirmed the percentage drug release of 96% at the end of 120 h. Nanocarriers were found to be effective against S. aureus and E. coli showing statistically significant antibacterial activity at (* p < 0.05) significant level as compared to plain ciprofloxacin hydrochloride gel. The particle size of β-TCP and nanocarriers was found to be 2 µm. Fourier transform infra-red studies showed good compatibility between the drug and the excipients. Differential scanning calorimetry studies revealed the amorphous nature of the nanocarriers as evident from the peak shift. It is obvious from the XRD studies that the phase intensity was reduced, which demonstrates a decrease in crystallinity. Nanocarriers released the drug in a controlled manner, hence may prove to be a better option to treat dental caries as compared to conventional treatments.

Layered scaffolds in periodontal regeneration

Periodontitis is a common inflammatory disease in dentistry that may lead to tooth loss and aesthetic problems. Periodontal tissue has a sophisticated architecture including four sections of alveolar bone, cementum, gingiva, and periodontal ligament fiber; all these four can be damaged during periodontitis. Thus, for whole periodontal regeneration, it is important to form both hard and soft tissue structures simultaneously on the tooth root surface without forming junctional epithelium and ankylosis. This condition makes the treatment of the periodontium a challenging process. Various regenerative methods including Guided Bone/Tissue Regeneration (GBR/GTR) using various membranes have been developed. Although using such GBR/GTR membranes was successful for partial periodontal treatment, they cannot be used for the regeneration of complete periodontium. For this purpose, multilayered scaffolds are now being developed. Such scaffolds may include various biomaterials, stem cells, and growth factors in a multiphasic configuration in which each layer is designed to regenerate specific section of the periodontium. This article provides a comprehensive review of the multilayered scaffolds for periodontal regeneration based on natural or synthetic polymers, and their combinations with other biomaterials and bioactive molecules. After highlighting the challenges related to multilayered scaffolds preparation, features of suitable scaffolds for periodontal regeneration are discussed.

A Clinical Risk Assessment of a 3D-Printed Patient-Specific Scaffold by Failure Modes and Effects Analysis

This study aims to carry out a risk assessment to identify and rectify potential clinical risks of a 3D-printed patient-specific scaffold for large-volume alveolar bone regeneration. A survey was used to assess clinicians' perceptions regarding the use of scaffolds in the treatment of alveolar defects and conduct a clinical risk assessment of the developed scaffold using the Failure Modes and Effects Analysis (FMEA) framework. The response rate was 69.4% with a total of 41 responses received. Two particular failure modes were identified as a high priority through the clinical risk assessment conducted. The highest mean Risk Priority Number was obtained by "failure of healing due to patient risk factors" (45.7 ± 27.7), followed by "insufficient soft tissue area" (37.8 ± 24.1). Despite the rapid developments, finding a scaffold that is both biodegradable and tailored to the patient's specific defect in cases of large-volume bone regeneration is still challenging for clinicians. Our results indicate a positive perception of clinicians towards this novel scaffold. The FMEA clinical risk assessment has revealed two failure modes that should be prioritized for risk mitigation (safe clinical translation). These findings are important for the safe transition to in-human trials and subsequent clinical use.

Human Bone Marrow Stromal Cell Exosomes Ameliorate Periodontitis

Human bone marrow stromal cell (hBMSC)-derived exosomes are promising therapeutics for inflammatory diseases due to their unique microRNA (miRNA) and protein cargos. Periodontal diseases often present with chronicity and corresponding exuberant inflammation, which leads to loss of tooth support. In this study, we explored whether hBMSC exosomes can affect periodontitis progression. hBMSC exosomes were isolated from cell culture medium through sequential ultracentrifugation. miRNAs and proteins that were enriched in hBMSC exosomes were characterized by RNA sequencing and protein array, respectively. hBMSC exosomes significantly suppressed periodontal keystone pathogen Porphyromonas gingivalis-triggered inflammatory response in macrophages in vitro. Transcriptomic analysis suggested that exosomes exerted their effects through regulating cell metabolism, differentiation, and inflammation resolution. In vivo, weekly exosome injection into the gingival tissues reduced the tissue destruction and immune cell infiltration in rat ligature-induced periodontitis model. Collectively, these findings suggest that hBMSC-derived exosomes can potentially be used as a host modulation agent in the management of periodontitis.

Biological Basis of Periodontal Regeneration

The ultimate goal of periodontal therapy is homeostatic regeneration of lost attachment of alveolar bone and gingival connective tissue to the exposed root surfaces with a fully functional and healthy periodontal ligament that is covered with a healthy epithelium. This goal needs a complete understanding of the biological mechanisms inherent to healing and inflammatory processes.

Tissue Adhesion-Anisotropic Polyrotaxane Hydrogels Bilayered with Collagen

Hydrogels are promising materials in tissue engineering scaffolds for healing and regenerating damaged biological tissues. Previously, we developed supramolecular hydrogels using polyrotaxane (PRX), consisting of multiple cyclic molecules threaded by an axis polymer for modulating cellular responses. However, since hydrogels generally have a large amount of water, their adhesion to tissues is extremely weak. Herein, we designed a bilayered hydrogel with a PRX layer and a collagen layer (PRX/collagen hydrogel) to achieve rapid and strong adhesion to the target tissue. The PRX/collagen hydrogel was fabricated by polymerizing PRX crosslinkers in water with placement of a collagen sponge. The differences in components between the PRX and collagen layers were analyzed using Fourier transform infrared spectroscopy (FT-IR). After confirming that the fibroblasts adhered to both layers of the PRX/collagen hydrogels, the hydrogels were implanted subcutaneously in mice. The PRX hydrogel without collagen moved out of its placement site 24 h after implantation, whereas the bilayer hydrogel was perfectly adherent at the site. Together, these findings indicate that the bilayer structure generated using PRX and collagen may be a rational design for performing anisotropic adhesion.

In vitro and in vivo evaluation of a biomimetic scaffold embedding silver nanoparticles for improved treatment of oral lesions

BACKGROUND

New materials are currently designed for efficient treatment of oral tissue lesions by guided tissue regeneration. The aim of this study was to develop a multifunctional 3D hybrid biomaterial consisting of extracellular matrix components, collagen, chondroitin 4-sulfate and fibronectin, functionalised with silver nanoparticles, intended to improve periodontitis treatment protocols.

METHODS

Structural observations were performed by autometallography, scanning and transmission electron microscopy. In vitro tests of 3D constructs of embedded gingival fibroblasts within hybrid biomaterial were performed by MTS and Live/Dead assays. Genotoxicity was assessed by comet assay. In vivo experiments using chick embryo chorioallantoic membrane (CAM) assay analysed the degradation and nanoparticles release, but also angiogenesis, new tissue formation in 3D constructs and the regenerative potential of the hybrid material. Biological activity was investigated in experimental models of inflamed THP-1 macrophages and oral specific bacterial cultures.

RESULTS

Light micrographs showed distribution of silver nanoparticles on collagen fibrils. Scanning electron micrographs revealed a microstructure with interconnected pores, which favoured cell adhesion and infiltration. Cell viability and proliferation were significantly higher within the 3D hybrid biomaterial than in 2D culture conditions, while absence of the hybrid material's genotoxic effect was found. In vivo experiments showed that the hybrid material was colonised by cells and blood vessels, initiating synthesis of new extracellular matrix. Besides the known effect of chondroitin sulfate, incorporated silver nanoparticles increased the anti-inflammatory activity of the hybrid biomaterial. The silver nanoparticles maintained their antibacterial activity even after embedding in the polymeric scaffold and inhibited the growth of F. nucleatum and P. gingivalis.

CONCLUSION

The novel biomimetic scaffold functionalised with silver nanoparticles presented regenerative, anti-inflammatory and antimicrobial potential for oral cavity lesions repair.

Current and future trends in periodontal tissue engineering and bone regeneration

Periodontal tissue engineering involves a multi-disciplinary approach towards the regeneration of periodontal ligament, cementum and alveolar bone surrounding teeth, whereas bone regeneration specifically applies to ridge reconstruction in preparation for future implant placement, sinus floor augmentation and regeneration of peri-implant osseous defects. Successful periodontal regeneration is based on verifiable cementogenesis on the root surface, oblique insertion of periodontal ligament fibers and formation of new and vital supporting bone. Ultimately, regenerated periodontal and peri-implant support must be able to interface with surrounding host tissues in an integrated manner, withstand biomechanical forces resulting from mastication, and restore normal function and structure. Current regenerative approaches utilized in everyday clinical practice are mainly guided tissue/bone regeneration-based. Although these approaches have shown positive outcomes for small and medium-sized defects, predictability of clinical outcomes is heavily dependent on the defect morphology and clinical case selection. In many cases, it is still challenging to achieve predictable regenerative outcomes utilizing current approaches. Periodontal tissue engineering and bone regeneration (PTEBR) aims to improve the state of patient care by promoting reconstitution of damaged and lost tissues through the use of growth factors and signaling molecules, scaffolds, cells and gene therapy. The present narrative review discusses key advancements in PTEBR including current and future trends in preclinical and clinical research, as well as the potential for clinical translatability.

Periodontal surgery using rhFGF-2 with deproteinized bovine bone mineral or rhFGF-2 alone: 2-year follow-up of a randomized controlled trial

AIM

To compare outcomes of rhFGF-2 + DBBM therapy with rhFGF-2 alone in the treatment of intrabony defects. This study provides 2-year follow-up results from the previous randomized controlled trial.

MATERIALS AND METHODS

Defects were randomly allocated to receive rhFGF-2 + DBBM (test) or rhFGF-2 (control). Treated sites were re-evaluated at 2 years postoperatively, using original clinical and patient-centred measures.

RESULTS

Thirty-eight sites were available for re-evaluation. At 2 years, both groups showed a significant improvement in clinical attachment level (CAL) from baseline. A gain in CAL of 3.4 ± 1.3 mm in the test group and 3.1 ± 1.5 mm in the control group was found. No significant inter-group difference was noted. Both groups showed a progressive increase in radiographic bone fill (RBF). The test treatment yielded greater RBF (56%) compared with the control group (41%). The control treatment performed better in contained defects in terms of CAL and RBF. There was no significant difference in patient-reported outcomes between groups.

CONCLUSIONS

At 2-year follow-up, the test and cotrol treatments were similarly effective in improving CAL, whereas the test treatment achieved a significantly greater RBF. In both treatments, favourable clinical, radiographic, and patient-reported outcomes can be sustained for at least 2 years.

TRIAL REGISTRATION

The University Hospital Medical Information Network-Clinical Trials Registry (UMIN-CTR) 000025257.

Transcriptome profile of highly osteoblastic/cementoblastic periodontal ligament cell clones

Heterogeneous cell populations of osteo/cementoblastic (O/C) or fibroblastic phenotypes constitute the periodontal dental ligament (PDL). A better understanding of these PDL cell subpopulations is essential to propose regenerative approaches based on a sound biological rationale.

An in-vivo Intraoral Defect Model for Assessing the Use of P11-4 Self-Assembling Peptide in Periodontal Regeneration

Periodontal disease is one of the most common diseases worldwide. It has a significant impact on oral health and subsequently the individual’s quality of life. However, optimal regeneration of periodontal tissues, using current treatments, has yet to be achieved. Peptide self-assembly has provided a step-change in nanobiotechnology and regenerative medicine fields. Our aim was to investigate the effects of a self-assembling peptide (SAP; P₁₁-4) on periodontal regeneration in a preclinical model. Twenty-six bilateral maxillary critical-sized periodontal defects were created surgically in 13 rats. Defects on one side of the mouth were filled with P₁₁-4 hydrogel; the contra-lateral defect was untreated (control). Rats were sacrificed immediately post-surgery (time 0) and after 2 and 4 weeks. Retrieved maxillae were processed for histological, immunohistochemical, and histomorphometric assessments. The results of histological analysis showed greater organization of periodontal fibers in defects treated with P₁₁-4, at both time points, when compared to untreated defects. Histomorphometry showed that treated defects had both a significant increase in functional periodontal ligament length and a reduction in epithelial down growth after 4 weeks. At 2 weeks, treated defects showed a significant increase in expression of osteocalcin and osteoprotegerin as judged by immunohistochemistry. Also, a significantly higher osteoprotegerin/RANKL ratio was shown in treated defects. In conclusion, the results demonstrated enhanced regeneration of periodontal tissues when SAP P₁₁-4 was used to fill periodontal defects in rats. The findings of this study suggest that SAP P₁₁-4 is a promising novel candidate for periodontal regenerative therapy. Further investigations are required for optimization before clinical use.

An injectable hydrogel-formulated inhibitor of prolyl-4-hydroxylase promotes T regulatory cell recruitment and enhances alveolar bone regeneration during resolution of experimental periodontitis

The hypoxia-inducible factor 1α (HIF-1α) is critically involved in tissue regeneration. Hence, the pharmacological prevention of HIF-1α degradation by prolyl hydroxylase (PHD) under normoxic conditions is emerging as a promising option in regenerative medicine. Using a mouse model of ligature-induced periodontitis and resolution, we tested the ability of an injectable hydrogel-formulated PHD inhibitor, 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid (1,4-DPCA/hydrogel), to promote regeneration of alveolar bone lost owing to experimental periodontitis. Mice injected subcutaneously with 1,4-DPCA/hydrogel at the onset of periodontitis resolution displayed significantly increased gingival HIF-1α protein levels and bone regeneration, as compared to mice treated with vehicle control. The 1,4-DPCA/hydrogel-induced increase in bone regeneration was associated with elevated expression of osteogenic genes, decreased expression of pro-inflammatory cytokine genes, and increased abundance of FOXP3⁺ T regulatory (Treg) cells in the periodontal tissue. The enhancing effect of 1,4-DPCA/hydrogel on Treg cell accumulation and bone regeneration was reversed by AMD3100, an antagonist of the chemokine receptor CXCR4 that mediates Treg cell recruitment. In conclusion, the administration of 1,4-DPCA/hydrogel at the onset of periodontitis resolution promotes CXCR4-dependent accumulation of Treg cells and alveolar bone regeneration, suggesting a novel approach for regaining bone lost due to periodontitis.

Effects of intermittent treatment with parathyroid hormone (PTH) on osteoblastic differentiation and mineralization of mouse induced pluripotent stem cells in a 3D culture model

BACKGROUND/OBJECTIVES

PTH plays an important role in bone remodeling, and different actions have been reported depending on its administration method. iPSCs are promising as a cell source for regeneration of periodontal tissue due to their ability of proliferation and pluripotency. However, the effects of PTH on iPSCs remain mostly unknown. The purpose of this study was to investigate in vitro effects of parathyroid hormone (PTH) on osteoblastic differentiation of induced pluripotent stem cells (iPSCs) in a 3D culture model.

MATERIALS AND METHODS

Following embryoid body (EB) induction from mouse iPSCs (miPSCs), dissociated cells (miPS-EB-derived cells) were seeded onto atelocollagen sponge (ACS) in osteoblast differentiation medium (OBM). Cell-ACS constructs were divided into three groups: continuous treatment with human recombinant PTH (1-34) (PTH-C), intermittent PTH treatment (PTH-I) or OBM control. To confirm the expression of PTH receptor-1(PTH1R), the expression of Pth1r and cAMP production over time were assessed. Real-time PCR was used to assess the expression of genes encoding osterix (Sp7), runt-related transcription factor 2 (Runx2), collagen type 1 (Col1a1), and osteocalcin (Bglap) at different time points. Mineralization was assessed by von Kossa staining. Histochemical staining was used to analyze alkaline phosphatase (ALP) activity, and immunolocalization of SP7 and BGLAP was analyzed by confocal laser scanning microscopy (CLSM).

RESULTS

On days 7 and 14, expression of the Pth1r in miPS-EB-derived cells was increased in all groups. Production of cAMP, the second messenger of the PTH1R, tended to increase in the PTH-I group compared with PTH-C group on day 14. Expression of Col1a1 in the PTH-I group on day 14 was significantly higher than other groups. There was a time-dependent increase in the expression of Sp7 in all groups. On day 14, the expression level of Sp7 in the PTH-I group was significantly higher than other groups. In von Kossa staining, the PTH-I group showed higher level of staining compared with other groups on day 14, whereas the level was slightly attenuated in the PTH-C group. In histochemical staining, ALP-positive cells were significantly increased in the PTH-I group compared with other groups on day 14. In CLSM analysis, the numbers of SP7- and BGLAP-positive cells showed a gradual increase over time, and on day 14, a significantly greater SP7 expression was observed in the PTH-I group than other groups.

CONCLUSION

These results suggested that the intermittent PTH treatment promotes osteoblastic differentiation and mineralization of miPSCs in the ACS scaffold.

The secreted protein DEL-1 activates a β3 integrin-FAK-ERK1/2-RUNX2 pathway and promotes osteogenic differentiation and bone regeneration

The integrin-binding secreted protein developmental endothelial locus-1 (DEL-1) is involved in the regulation of both the initiation and resolution of inflammation in different diseases, including periodontitis, an oral disorder characterized by inflammatory bone loss. Here, using a mouse model of bone regeneration and in vitro cell-based mechanistic studies, we investigated whether and how DEL-1 can promote alveolar bone regeneration during resolution of experimental periodontitis. Compared with WT mice, mice lacking DEL-1 or expressing a DEL-1 variant with an Asp-to-Glu substitution in the RGD motif ("RGE point mutant"), which does not interact with RGD-dependent integrins, exhibited defective bone regeneration. Local administration of DEL-1 or of its N-terminal segment containing the integrin-binding RGD motif, but not of the RGE point mutant, reversed the defective bone regeneration in the DEL-1-deficient mice. Moreover, DEL-1 (but not the RGE point mutant) promoted osteogenic differentiation of MC3T3-E1 osteoprogenitor cells or of primary calvarial osteoblastic cells in a β3 integrin-dependent manner. The ability of DEL-1 to promote in vitro osteogenesis, indicated by induction of osteogenic genes such as the master transcription factor Runt-related transcription factor-2 (Runx2) and by mineralized nodule formation, depended on its capacity to induce the phosphorylation of focal adhesion kinase (FAK) and of extracellular signal-regulated kinase 1/2 (ERK1/2). We conclude that DEL-1 can activate a β3 integrin-FAK-ERK1/2-RUNX2 pathway in osteoprogenitors and promote new bone formation in mice. These findings suggest that DEL-1 may be therapeutically exploited to restore bone lost due to periodontitis and perhaps other osteolytic conditions.

Recent advances in periodontal regeneration: A biomaterial perspective

Periodontal disease (PD) is one of the most common inflammatory oral diseases, affecting approximately 47% of adults aged 30 years or older in the United States. If not treated properly, PD leads to degradation of periodontal tissues, causing tooth movement, and eventually tooth loss. Conventional clinical therapy for PD aims at eliminating infectious sources, and reducing inflammation to arrest disease progression, which cannot achieve the regeneration of lost periodontal tissues. Over the past two decades, various regenerative periodontal therapies, such as guided tissue regeneration (GTR), enamel matrix derivative, bone grafts, growth factor delivery, and the combination of cells and growth factors with matrix-based scaffolds have been developed to target the restoration of lost tooth-supporting tissues, including periodontal ligament, alveolar bone, and cementum. This review discusses recent progresses of periodontal regeneration using tissue-engineering and regenerative medicine approaches. Specifically, we focus on the advances of biomaterials and controlled drug delivery for periodontal regeneration in recent years. Special attention is given to the development of advanced bio-inspired scaffolding biomaterials and temporospatial control of multi-drug delivery for the regeneration of cementum-periodontal ligament-alveolar bone complex. Challenges and future perspectives are presented to provide inspiration for the design and development of innovative biomaterials and delivery system for new regenerative periodontal therapy.

Treatment of intrabony periodontal defects using rhFGF-2 in combination with deproteinized bovine bone mineral or rhFGF-2 alone: A 6-month randomized controlled trial

Aim

To evaluate the use of recombinant human fibroblast growth factor (rhFGF)‐2 in combination with deproteinized bovine bone mineral (DBBM) compared with rhFGF‐2 alone, in the treatment of intrabony periodontal defects.

Materials and Methods

Patients with periodontitis who had received initial periodontal therapy and had intrabony defects of ≥ 3 mm in depth were enrolled. Sites were randomly assigned to receive a commercial formulation of 0.3% rhFGF‐2 + DBBM (test) or rhFGF‐2 alone (control). Clinical parameters and a patient‐reported outcome measure (PROM) were evaluated at baseline and at 3 and 6 months postoperatively.

Results

Twenty‐two sites in each group were evaluated. A significant improvement in clinical attachment level (CAL) from baseline was observed in both groups at 6 months postoperatively. CAL gain was 3.16 ± 1.45 mm in the test group and 2.77 ± 1.15 mm in the control group, showing no significant difference between groups. Radiographic bone fill was significantly greater in the test group (47.2%) than in the control group (29.3%). No significant difference in PROM between groups was observed.

Conclusions

At 6 months, no significant difference in CAL gain or PROM between the two treatments was observed, although combination therapy yielded an enhanced radiographic outcome.

Tissue engineering in periodontology: Biological mediators for periodontal regeneration

Teeth and the periodontal tissues represent a highly specialized functional system. When periodontal disease occurs, the periodontal complex, composed by alveolar bone, root cementum, periodontal ligament, and gingiva, can be lost. Periodontal regenerative medicine aims at recovering damaged periodontal tissues and their functions by different means, including the interaction of bioactive molecules, cells, and scaffolds. The application of growth factors, in particular, into periodontal defects has shown encouraging effects, driving the wound healing toward the full, multi-tissue periodontal regeneration, in a precise temporal and spatial order. The aim of the present comprehensive review is to update the state of the art concerning tissue engineering in periodontology, focusing on biological mediators and gene therapy.

Strontium enhances proliferation and osteogenic behavior of periodontal ligament cells in vitro

BACKGROUND AND OBJECTIVE

Strontium (Sr) enhances osteogenic differentiation of certain multipotent cells. Periodontal ligament cells (PDLCs) are known to be multipotent, and Sr might be useful in periodontal bone tissue engineering. This study investigates the effect of high concentration of Sr on the proliferation and osteogenic behavior of PDLCs in vitro.

MATERIAL AND METHODS

Primary human PDLCs were cultured in MEM + 10% FBS without (Ctrl) or with Sr in four diverse concentrations: Sr1, 11.3 × 10^-3  mg/L, human serum physiological level; Sr2, 13 mg/L, typical human serum level after strontium ranelate treatment; Sr3, 130 mg/L, and Sr4, 360 mg/L. The spreading area (2, 4, 6, 24 hours), proliferation rate (1, 3, 7 days), osteogenic behavior (alkaline phosphatase - ALP activity, 7 and 14 days; expression of osteogenic genes, ALP, Runt-related transcription factor 2 - RUNX2, osteopontin - OPN, osteocalcin - OCN, and osteoprotegerin -OPG, 1, 3, 7, 14, 21 days), and formation of mineralized nodules (14 and 21 days) of the PDLCs were assessed. Data were compared group- and period-wise using ANOVA tests.

RESULTS

Periodontal ligament cells cultured with Sr4 showed increased spreading area (after 4 hours), proliferation rate (from 3 days), and OCN and OPN (from 7 days) gene expression as compared to Ctrl, Sr1, Sr2, and Sr3. Sr4 also led to lower ALP activity (from 7 days), ALP (from 3 days), and RUNX2 (at 7 and 14 days) gene expression, together with more evident formation of mineralized nodules, compared to Ctrl, Sr1, Sr2, and Sr3.

CONCLUSION

Periodontal ligament cells responded to Sr4 with increased cellular proliferation and osteogenic behavior in vitro.

Mineralization Induction of Gingival Fibroblasts and Construction of a Sandwich Tissue-Engineered Complex for Repairing Periodontal Defects

BACKGROUND The ideal healing technique for periodontal tissue defects would involve the functional regeneration of the alveolar bone, cementum, and periodontal ligament, with new periodontal attachment formation. In this study, gingival fibroblasts were induced and a "sandwich" tissue-engineered complex (a tissue-engineered periodontal membrane between 2 tissue-engineered mineralized membranes) was constructed to repair periodontal defects. We evaluated the effects of gingival fibroblasts used as seed cells on the repair of periodontal defects and periodontal regeneration. MATERIAL AND METHODS Primitively cultured gingival fibroblasts were seeded bilaterally on Bio-Gide collagen membrane (a tissue-engineered periodontal membrane) or unilaterally on small intestinal submucosa segments, and their mineralization was induced. A tissue-engineered sandwich was constructed, comprising the tissue-engineered periodontal membrane flanked by 2 mineralized membranes. Periodontal defects in premolar regions of Beagles were repaired using the tissue-engineered sandwich or periodontal membranes. Periodontal reconstruction was compared to normal and trauma controls 10 or 20 days postoperatively. RESULTS Periodontal defects were completely repaired by the sandwich tissue-engineered complex, with intact new alveolar bone and cementum, and a new periodontal ligament, 10 days postoperatively. CONCLUSIONS The sandwich tissue-engineered complex can achieve ideal periodontal reconstruction rapidly.

Engineered scaffolds and cell-based therapy for periodontal regeneration

BACKGROUND

The main objective of regenerative periodontal therapy is to completely restore the periodontal tissues lost. This review summarizes the most recent evidence in support of scaffold- and cell-based tissue engineering, which are expected to play a relevant role in next-generation periodontal regenerative therapy.

METHODS

A literature search (PubMed database) was performed to analyze more recently updated articles regarding periodontal regeneration, scaffolds and cell-based technologies.

RESULTS

Evidence supports the importance of scaffold physical cues to promote periodontal regeneration, including scaffold multicompartmentalization and micropatterning. The in situ delivery of biological mediators and/or cell populations, both stem cells and already differentiated cells, has shown promising in vivo efficacy.

CONCLUSIONS

Porous scaffolds are pivotal for clot stabilization, wound compartmentalization, cell homing and cell nutrients delivery. Given the revolutionary introduction of rapid prototyping technique and cell-based therapies, the fabrication of custom-made scaffolds is not far from being achieved.

Effect of the combined use of enamel matrix derivative and atelocollagen sponge scaffold on osteoblastic differentiation of mouse induced pluripotent stem cells in vitro

BACKGROUND AND OBJECTIVE

Induced pluripotent stem cells (iPSCs) are a candidate cell source in periodontal regenerative therapy. Enamel matrix derivative (EMD) has been shown to regenerate periodontal tissues, and atelocollagen sponge (ACS) is considered a suitable scaffold or carrier for growth factors. This study aimed to investigate the effect of combined use of EMD and an ACS scaffold on cell behaviors and differentiation of mouse iPSCs (miPSCs) in vitro.

MATERIAL AND METHODS

Following embryonic body formation from miPSCs, dissociated cells (miPS-EB-derived cells) were seeded onto ACS with or without EMD, and cultured in osteoblast differentiation medium. Scanning electron microscopy and histological analyses were used to assess cell morphology and infiltration within the ACS. Cell viability (metabolism) was determined using an MTS assay, and expression of mRNA of osteoblastic differentiation markers was assessed by quantitative RT -PCR. Alkaline phosphatase (ALP) staining intensity and activity were evaluated. Mineralization was assessed by von Kossa staining, and calcium content was quantitated using the methylxylenol blue method.

RESULTS

By 24 hours after seeding, miPS-EB-derived cells in both the EMD and control groups had attached to and infiltrated the ACS scaffold. Scanning electron microscopy images revealed that by day 14, many cytoplasmic protrusions and extracellular deposits, suggestive of calcified matrix, were present in the EMD group. There was a time-dependent increase in cell viability up to day 3, but no difference between groups was observed at any time point. The levels expressed of ALP and osterix genes were significantly higher in the EMD group than in the control group. Expression of runt-related transcription factor 2 was increased in the EMD group compared with the control group on day 7. EMD upregulated the expression of bone sialoprotein and osteopontin on day 14, whereas expression of osteocalcin was lower at all time points. The staining intensity and activity of ALP were higher in the EMD group than in the control group. Mineralization levels and calcium contents were significantly higher in the EMD group throughout the observation period.

CONCLUSION

These data suggest that combining ACS with EMD increases levels of osteoblastic differentiation and mineralization in miPS-EB-derived cells, compared with ACS used alone.

Gold nanoparticles promote osteogenic differentiation of human periodontal ligament stem cells via the p38 MAPK signaling pathway

Gold nanoparticles (AuNPs) are a promising material for use in regenerative medicine due to their biocompatibility and easy functionalization with biomolecules including growth factors, DNA and peptides. In the present study, transmission electron microscopy indicated that the AuNPs were monodisperse and spherical in shape, with an estimated average diameter of 13 nm. And the cellular effects of AuNPs on the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) and the associated signaling pathways in cell differentiation were investigated based on histochemical analysis of alkaline phosphatase activity and mineralization, quantitative polymerase chain reaction, and western blotting. The results indicated that AuNPs enhanced the differentiation of hPDLSCs into osteoblasts, increasing their osteogenic transcriptional profile including alkaline phosphatase, osterix, collagen type I and runt‑related transcription factor 2 (RUNX2) and activating the p38 mitogen‑activated protein kinase (MAPK) signaling pathway. Furthermore, AuNPs increased the protein level of RUNX2, which is crucial for osteogenic differentiation. These results suggested that AuNPs stimulate the osteogenesis of hPDLSCs partially via activation of the p38 MAPK signaling pathway.

Effect of sustained PDGF nonviral gene delivery on repair of tooth-supporting bone defects

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) promotes soft tissue and bone healing, and is Food and Drug Administration-approved for treatment of diabetic ulcers and periodontal defects. The short half-life of topical rhPDGF-BB protein application necessitates bolus, high-dose delivery. Gene therapy enables sustained local growth factor production. A novel gene activated matrix delivering polyplexes of polyethylenimine (PEI)-plasmid DNA encoding PDGF was evaluated for promotion of periodontal wound repair in vivo. PEI-pPDGF-B polyplexes were tested in human periodontal ligament fibroblasts and human gingival fibroblasts for cell viability and transfection efficiency. Collagen scaffolds containing PEI-pPDGF-B polyplexes at two doses, rhPDGF-BB, PEI vector or collagen alone were randomly delivered to experimentally induced tooth-supporting periodontal defects in a rodent model. Mandibulae were collected at 21 days for histologic observation and histomorphometry. PEI-pPDGF-B polyplexes were biocompatible to cells tested and enzyme-linked immunosorbent assay confirmed the functionality of transfection. Significantly greater osteogenesis was observed for collagen alone and rhPDGF-BB versus the PEI-containing groups. Defects treated with sustained PDGF gene delivery demonstrated delayed healing coupled with sustained inflammatory cell infiltrates lateral to the osseous defects. Continuous PDGF-BB production by nonviral gene therapy could have delayed bone healing. This nonviral gene delivery system in this model appeared to prolong inflammatory response, slowing alveolar bone regeneration in vivo.

[Root coverage: Prognostic factors and surgical techniques]

Gingival recession is an oral exposure of the root surface due to an apical displacement of the gingival margin below the cemento-enamel junction. The root coverage is indicated for esthetic reasons, to reduce root hypersensitivity and to create or to augment keratinized tissue. Several surgical techniques have been described, the decision depending on anatomical and technical parameters. The main therapeutic goal is to achieve complete root coverage (CRC) and a satisfactory esthetic result. The purpose of this work was to make an update on the different factors that determine the success of root coverage and to evaluate the efficacy of different surgical techniques reported in literature.

Nanomaterials for Tissue Engineering In Dentistry

The tissue engineering (TE) of dental oral tissue is facing significant changes in clinical treatments in dentistry. TE is based on a stem cell, signaling molecule, and scaffold triad that must be known and calibrated with attention to specific sectors in dentistry. This review article shows a summary of micro- and nanomorphological characteristics of dental tissues, of stem cells available in the oral region, of signaling molecules usable in TE, and of scaffolds available to guide partial or total reconstruction of hard, soft, periodontal, and bone tissues. Some scaffoldless techniques used in TE are also presented. Then actual and future roles of nanotechnologies about TE in dentistry are presented.

Periodontal regeneration with stem cells-seeded collagen-hydroxyapatite scaffold

Re-establishing compromised periodontium to its original structure, properties and function is demanding, but also challenging, for successful orthodontic treatment. In this study, the periodontal regeneration capability of collagen-hydroxyapatite scaffolds, seeded with bone marrow stem cells, was investigated in a canine labial alveolar bone defect model. Bone marrow stem cells were isolated, expanded and characterized. Porous collagen-hydroxyapatite scaffold and cross-linked collagen-hydroxyapatite scaffold were prepared. Attachment, migration, proliferation and morphology of bone marrow stem cells, co-cultured with porous collagen-hydroxyapatite or cross-linked collagen-hydroxyapatite, were evaluated in vitro. The periodontal regeneration capability of collagen-hydroxyapatite scaffold with or without bone marrow stem cells was tested in six beagle dogs, with each dog carrying one sham-operated site as healthy control, and three labial alveolar bone defects untreated to allow natural healing, treated with bone marrow stem cells - collagen-hydroxyapatite scaffold implant or collagen-hydroxyapatite scaffold implant, respectively. Animals were euthanized at 3 and 6 months (3 animals per group) after implantation and the resected maxillary and mandibular segments were examined using micro-computed tomography scan, H&E staining, Masson's staining and histometric evaluation. Bone marrow stem cells were successfully isolated and demonstrated self-renewal and multi-potency in vitro. The porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite had average pore sizes of 415 ± 20 µm and 203 ± 18 µm and porosity of 69 ± 0.5% and 50 ± 0.2%, respectively. The attachment, proliferation and migration of bone marrow stem cells were satisfactory on both porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite scaffolds. Implantation of bone marrow stem cells - collagen-hydroxyapatite or collagen-hydroxyapatite scaffold in beagle dogs with experimental periodontal defects resulted in significantly enhanced periodontal regeneration characterized by formation of new bone, periodontal ligament and cementum, compared with the untreated defects, as evidenced by histological and micro-computed tomography examinations. The prepared collagen-hydroxyapatite scaffolds possess favorable bio-compatibility. The bone marrow stem cells - collagen-hydroxyapatite and collagen-hydroxyapatite scaffold - induced periodontal regeneration, with no aberrant events complicating the regenerative process. Further research is necessary to improve the bone marrow stem cells behavior in collagen-hydroxyapatite scaffolds after implantation.

Potential for Stem Cell-Based Periodontal Therapy

Periodontal diseases are highly prevalent and are linked to several systemic diseases. The goal of periodontal treatment is to halt the progression of the disease and regenerate the damaged tissue. However, achieving complete and functional periodontal regeneration is challenging because the periodontium is a complex apparatus composed of different tissues, including bone, cementum, and periodontal ligament. Stem cells may represent an effective therapeutic tool for periodontal regeneration due to their plasticity and their ability to regenerate different tissues. This review presents and critically analyzes the available information on stem cell-based therapy for the regeneration of periodontal tissues and suggests new avenues for the development of more effective therapeutic protocols.

Regenerative Medicine for Periodontal and Peri-implant Diseases

The balance between bone resorption and bone formation is vital for maintenance and regeneration of alveolar bone and supporting structures around teeth and dental implants. Tissue regeneration in the oral cavity is regulated by multiple cell types, signaling mechanisms, and matrix interactions. A goal for periodontal tissue engineering/regenerative medicine is to restore oral soft and hard tissues through cell, scaffold, and/or signaling approaches to functional and aesthetic oral tissues. Bony defects in the oral cavity can vary significantly, ranging from smaller intrabony lesions resulting from periodontal or peri-implant diseases to large osseous defects that extend through the jaws as a result of trauma, tumor resection, or congenital defects. The disparity in size and location of these alveolar defects is compounded further by patient-specific and environmental factors that contribute to the challenges in periodontal regeneration, peri-implant tissue regeneration, and alveolar ridge reconstruction. Efforts have been made over the last few decades to produce reliable and predictable methods to stimulate bone regeneration in alveolar bone defects. Tissue engineering/regenerative medicine provide new avenues to enhance tissue regeneration by introducing bioactive models or constructing patient-specific substitutes. This review presents an overview of therapies (e.g., protein, gene, and cell based) and biomaterials (e.g., resorbable, nonresorbable, and 3-dimensionally printed) used for alveolar bone engineering around teeth and implants and for implant site development, with emphasis on most recent findings and future directions.

Periodontal Regeneration - Furcation Defects: Practical Applications From the AAP Regeneration Workshop

Focused Clinical Question: How should periodontal furcation defects be managed via periodontal regenerative therapy, and what parameters should be used for treatment selection? Summary: The treatment of furcation defects can vary based on the type and location of the furcation involvement. Attaining predictable regenerative outcomes is dependent on the control of local and systemic factors. A combined treatment approach (barrier and bone replacement graft with or without biologic) generally offers the better therapeutic outcome over monotherapy. Class I furcation defects can be managed via conventional periodontal non-surgical and/or surgical therapy, whereas Class II furcation defects generally attain better outcomes with regenerative therapy. There is weak evidence, limited to case reports, that Class III furcation defects can be treated successfully with regenerative therapy. Conclusions: In Class I furcation defects, regenerative therapy might be beneficial in certain clinical scenarios, although most Class I furcation defects can be treated successfully with non-regenerative therapy. For successful treatment of maxillary and mandibular molars with Class II furcation defects, systemic and local factors should be controlled, and surgical debridement and postoperative maintenance should be performed adequately. Although there is limited evidence for regeneration of Class III furcation defects, there may be a modest improvement allowing for tooth retention. Ultimately, the benefit of tooth retention and cost should be considered in the indication of therapy for teeth with severe furcation involvement.

Emerging regenerative approaches for periodontal reconstruction: a consensus report from the AAP Regeneration Workshop

BACKGROUND

Historically, periodontal regeneration has focused predominantly on bone substitutes and/or barrier membrane application to provide for defect fill and/or selected cell repopulation of the lesion. More recently, a number of technologies have evolved that can be viewed as emerging therapeutic approaches for periodontal regeneration, and these technologies were considered in the review paper and by the consensus group. The goal of this consensus report on emerging regenerative approaches for periodontal hard and soft tissue reconstruction was to develop a consensus document based on the accompanying review paper and on additional materials submitted before and at the consensus group session.

METHODS

The review paper was sent to all the consensus group participants in advance of the consensus conference. In addition and also before the conference, individual consensus group members submitted additional material for consideration by the group. At the conference, each consensus group participant introduced themselves and provided disclosure of any potential conflicts of interest. The review paper was briefly presented by two of the authors and discussed by the consensus group. A discussion of each of the following topics then occurred based on the content of the review: a general summary of the topic, implications for patient-reported outcomes, and suggested research priorities for the future. As each topic was discussed based on the review article, supplemental information was then added that the consensus group agreed on. Last, an updated reference list was created.

RESULTS

The application of protein and peptide therapy, cell-based therapy, genetic therapy, application of scaffolds, bone anabolics, and lasers were found to be emerging technologies for periodontal regeneration. Other approaches included the following: 1) therapies directed at the resolution of inflammation; 2) therapies that took into account the influence of the microbiome; 3) therapies involving the local regulation of phosphate and pyrophosphate metabolism; and 4) approaches directed at harnessing current therapies used for other purposes. The results indicate that, with most emerging technologies, the specific mechanisms of action are not well understood nor are the specific target cells identified. Patient-related outcomes were typically not addressed in the literature. Numerous recommendations can be made for future research priorities for both basic science and clinical application of emerging therapies. The need to emphasize the importance of regeneration of a functional periodontal organ system was noted. The predictability and efficacy of outcomes, as well as safety concerns and the cost-to-benefit ratio were also identified as key factors for emerging technologies.

CONCLUSIONS

A number of technologies appear viable as emerging regenerative approaches for periodontal hard and soft tissue regeneration and are expanding the potential of reconstructing the entire periodontal organ system. The cost-to-benefit ratio and safety issues are important considerations for any new emerging therapies. Clinical Recommendation: At this time, there is insufficient evidence on emerging periodontal regenerative technologies to warrant definitive clinical recommendations.