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The management of extensive bone loss remains a clinical challenge. Numerous studies are underway to develop a combination of biomaterials, biomolecules, and stem cells to address this challenge. In particular, the systemic administration of antibodies against sclerostin, a regulator of bone formation, was recently shown to enhance the bone repair efficiency of dense collagen hydrogels (DCHs) hosting murine dental pulp stem cells (mDPSCs). The aim of the present study was to assess whether these antibodies, encapsulated and released from DCHs, could promote craniofacial bone repair by the local inhibition of sclerostin. In vitro studies showed that antibody loading modified neither the hydrogel structure nor the viability of seeded mDPSCs. When implanted in a mouse calvaria critical-size bone defect, antibody-loaded DCHs showed repair capabilities similar to those of acellular unloaded DCHs combined with antibody injections. Importantly, the addition of mDPSCs provided no further benefit. Altogether, the local delivery of antisclerostin antibodies from acellular dense collagen scaffolds is highly effective for bone repair. The drastic reduction in the required amount of antibody compared to systemic injection should reduce the cost of the procedure, making the strategy proposed here a promising therapeutic approach for large bone defect repair.

Treating large bone defects or fragile patients may require enhancing the bone regeneration rate to overcome a weak contribution from the body. This work investigates the osteogenic potential of nutrient fisetin, a flavonoid found in fruits and vegetables, as a doping agent inside the structure of a SiO 2 -CaO bioactive glass-poly(caprolactone) (BG-PCL) hybrid scaffold. Embedded in the full mass of the BG-PCL hybrid during one-pot synthesis, we demonstrate fisetin to be delivered sustainably; the release follows a first-order kinetics with active fisetin concentration being delivered for more than 1 month (36 days). The biological effect of BG-PCL-fisetin-doped scaffolds (BG-PCL-Fis) has been highlighted by in vitro and in vivo studies. A positive impact is demonstrated on the adhesion and the differentiation of rat primary osteoblasts, without an adverse cytotoxic effect. Implantation in critical-size mouse calvaria defects shows bone remodeling characteristics and remarkable enhancement of bone regeneration for fisetin-doped scaffolds, with the regenerated bone volume being twofold that of nondoped scaffolds and fourfold that of a commercial trabecular bovine bone substitute. Such highly bioactive materials could stand as competitive alternative strategies involving biomaterials loaded with growth factors, the use of the latter being the subject of growing concerns., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Background: Developmental Defects of Enamel (DDE) is a pathology of the teeth that can greatly alter the quality of life of patients (hypersensitivity, esthetic issues, loss of function, etc.). The acquired DDE may occur as a result of a wide range of acquired etiological factors and his prevalence of this pathology may reach up to 89.9%. The main objective of this research was to identify and analyze, in current literature, the factors related to acquired DDE, in order to propose a general theory about the mechanisms involved., Methods: The search of the primary literature was conducted until [December 31, 2021]. Our search strategy uses the Pubmed/MEDLINE database and was structured around 3 terms ["Development," "Defect," and "Enamel"]. To be included, references had to be primary studies, written in English. Exclusion criteria were reviews, in vitro , animal, genetic or archeology studies, and studies focused on clinical management of DDE. One hundred and twenty three articles were included in this scoping review: 4 Randomized clinical trials, 1 letter, 5 cases reports, 2 fundamentals studies, and 111 observational studies (33 Cross-sectional studies, 68 Cohort study and 10 Case-control study). The quality of evidence was assessed using the PEDro scale for clinical trials, the Newcastle-Ottawa scale for observational studies, and a published tool to assess the quality of case reports and case series., Results: A scoping review of the literature identified 114 factors potentially involved in acquired DDE. The most frequently encountered pathologies are those causing a disorder of calcium homeostasis or a perturbation of the ARNT pathway in mother or child. The link between the ARNT pathway and metabolism deficiency in uncertain and needs to be defined. Also, the implication of this mechanism in tissue impairment is still unclear and needs to be explored., Conclusions: By identifying and grouping the risk factors cited in the literature, this taxonomy and the hypotheses related to the mechanism allow health practitioners to adopt behaviors that limit the risk of developing aDDE and to set up a prevention of dental pathology. In addition, by reviewing the current literature, this work provides guidance for basic research, clinical studies, and literature searches., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Collignon, Vergnes, Germa, Azogui, Breinig, Hollande, Bonnet and Nabet.)

Dense collagen (DC) gels facilitate the osteoblastic differentiation of seeded dental pulp stem cells (DPSCs) and undergo rapid acellular mineralization when incorporated with bioactive glass particles, both in vitro and subcutaneously in vivo. However, the potential of DC-bioactive glass hybrid gels in delivering DPSCs for bone regeneration in an osseous site has not been investigated. In this study, the efficacies of both acellular and DPSC-seeded DC-S53P4 bioactive glass [(53)SiO 2 -(23)Na 2 O-(20)CaO-(4)P 2 O 5 , wt%] hybrid gels were investigated in a critical-sized murine calvarial defect. The incorporation of S53P4, an osteostimulative bioactive glass, into DC gels led to its accelerated acellular mineralization in simulated body fluid (SBF), in vitro, where hydroxycarbonated apatite was detected within 1 day. By day 7 in SBF, micro-mechanical analysis demonstrated an 8-fold increase in the compressive modulus of the mineralized gels. The in-situ effect of the bioactive glass on human-DPSCs within DC-S53P4 was evident, by their osteogenic differentiation in the absence of osteogenic supplements. The production of alkaline phosphatase and collagen type I was further increased when cultured in osteogenic media. This osteostimulative effect of DC-S53P4 constructs was confirmed in vivo, where after 8 weeks implantation, both acellular scaffolds and DPSC-seeded DC-S53P4 constructs formed mineralized and vascularized bone matrices with osteoblastic and osteoclastic cell activity. Surprisingly, however, in vivo micro-CT analysis confirmed that the acellular scaffolds generated larger volumes of bone, already visible at week 3 and exhibiting superior trabecular architecture. The results of this study suggest that DC-S53P4 scaffolds negate the need for stem cell delivery for effective bone tissue regeneration and may expedite their path towards clinical applications., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Organic-inorganic hybrid biomaterials stand as a promise for combining bone bonding and bone mineral-forming ability, stimulation of osteogenic cells, and adequate mechanical properties. Bioactive glass (BG)-polycaprolactone (PCL) hybrids are of special interest as they gather the ability of BG to enhance osteoblast-mediated bone formation with the slow degradation rate and the toughness of PCL. In this study, BG-PCL hybrids were synthesized in the form of scaffold, owing to a dual cortical/trabecular structure mimicking the bone architecture. Their biological potential was evaluated both in vitro using rat primary osteoblasts (RPO) and in vivo in a mice model of critical-size calvarial defects. BG-PCL scaffolds were compared to Lubboc (BTB), a commercial purified bovine xenograft widely used in orthopedics and periodontal procedures and known for its efficiency. BG-PCL hybrids were found to facilitate RPO adhesion at their surface and to enhance RPO differentiation when compared to BTB. An in vivo micro-CT study demonstrates a higher bone ingrowth with BG-PCL scaffolds and a complete chemical conversion of the remaining BG-PCL after 3 months of implantation, while histological data show the vascularization of BG-PCL scaffolds and confirm the well-advanced bone regeneration with ongoing remodeling. Finally, we evidence the complete chemical conversion of the remaining BG-PCL into a bone-like mineral.

Stem cells endowed with skeletogenic potentials seeded in specific scaffolds are considered attractive tissue engineering strategies for treating large bone defects. In the context of craniofacial bone, mesenchymal stromal/stem cells derived from the dental pulp (DPSCs) have demonstrated significant osteogenic properties. Their neural crest embryonic origin further makes them a potential accessible therapeutic tool to repair craniofacial bone. The stem cells' direct involvement in the repair process versus a paracrine effect is however still discussed. To clarify this question, we have followed the fate of fluorescent murine DPSCs derived from PN3 Wnt1-CRE- Rosa Tomato mouse molar (T-mDPSCs) during the repair process of calvaria bone defects. Two symmetrical critical defects created on each parietal region were filled with (a) dense collagen scaffolds seeded with T-mDPSCs, (b) noncellularized scaffolds, or (c) no scaffold. Mice were imaged over a 3-month period by microcomputed tomography to evaluate the extent of repair and by biphotonic microscopy to track T-mDPSCs. Histological and immunocytochemical analyses were performed in parallel to characterize the nature of the repaired tissue. We show that T-mDPSCs are present up to 3 months postimplantation in the healing defect and that they rapidly differentiate in chondrocyte-like cells expressing all the expected characteristic markers. T-mDPSCs further maturate into hypertrophic chondrocytes and likely signal to host progenitors that form new bone tissue. This demonstrates that implanted T-mDPSCs are able to survive in the defect microenvironment and to participate directly in repair via an endochondral bone ossification-like process. Stem Cells 2019;37:701-711., (© AlphaMed Press 2019.)

Therapies using stem cells may be applicable to all fields of regenerative medicine, including craniomaxillofacial surgery. Dental pulp stem cells (DPSCs) have demonstrated in vitro and in vivo osteogenic and proangiogenic properties. The aim of the study was to evaluate whether early angiogenesis investigated by nuclear imaging can predict bone formation within a mouse critical bone defect. Two symmetrical calvarial critical-sized defects were created. Defects were left empty or filled with i) DPSC-containing dense collagen scaffold, ii) 5% hypoxia-primed DPSC-containing dense collagen scaffold, iii) acellular dense collagen scaffold, or iv) left empty. Early angiogenesis assessed by PET using 64 Cu-NODAGA-RGD as a tracer was found to be correlated with bone formation determined by micro-CT within the defects from day 30, and to be correlated to the late calcium apposition observed at day 90 using 18 F-Na PET. These results suggest that nuclear imaging of angiogenesis, a technique applicable in clinical practice, is a promising approach for early prediction of bone grafting outcome, thus potentially allowing to anticipate alternative regenerative strategies. STATEMENT OF SIGNIFICANCE: Bone defects are a major concern in medicine. As life expectancy increases, the number of bone lesions grows, and occurring complications lead to a delay or even lack of consolidation. Therefore, to be able to predict healing or the absence of scarring at early times would be very interesting. This would not "waste time" for the patient. We report here that early nuclear imaging of angiogenesis, using 64 Cu-NODAGA-RGD as a tracer, associated with nuclear imaging of mineralization, using 18 F-Na as a tracer, is correlated to late bone healing objectivized by classical histology and microtomography. This nuclear imaging represents a promising approach for early prediction of bone grafting outcome in clinical practice, thus potentially allowing to anticipate alternative regenerative strategies., (Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Bone exhibits a great ability for endogenous self-healing. Nevertheless, impaired bone regeneration and healing is on the rise due to population aging, increasing incidence of bone trauma and the clinical need for the development of alternative options to autologous bone grafts. Current strategies, including several biomolecules, cellular therapies, biomaterials, and different permutations of these, are now developed to facilitate the vascularization and the engraftment of the constructs, to recreate ultimately a bone tissue with the same properties and characteristics of the native bone. In this review, we browse the existing strategies that are currently developed, using biomolecules, cells and biomaterials, to induce, direct and potentiate bone healing after injury and further discuss the biological processes associated with this repair.

In humans, the SOST gene encodes sclerostin, an inhibitor of bone growth and remodeling, which also negatively regulates the bone repair process. Sclerostin has also been implicated in tooth formation, but its potential role in pulp healing remains unknown. The aim of this study was to explore the role of sclerostin in reparative dentinogenesis using Sost knockout mice ( Sost -/- ). The pulps of the first maxillary molars were mechanically exposed in 3-mo-old Sost -/- and wild-type (WT) mice ( n = 14 mice per group), capped with mineral trioxide aggregate cement, and the cavities were filled with a bonded composite resin. Reparative dentinogenesis was dynamically followed up by micro-computed tomography and characterized by histological analyses. Presurgical analysis revealed a significantly lower pulp volume in Sost -/- mice compared with WT. At 30 and 49 d postsurgery, a large-forming reparative mineralized bridge, associated with osteopontin-positive mineralization foci, was observed in the Sost -/- pulps, whereas a much smaller bridge was detected in WT. At the longer time points, the bridge, which was associated with dentin sialoprotein-positive cells, had expanded in both groups but remained significantly larger in Sost -/- pulps. Sclerostin expression in the healing WT pulps was detected in the cells neighboring the forming dentin bridge. In vitro, mineralization induced by Sost -/- dental pulp cells (DPCs) was also dramatically enhanced when compared with WT DPCs. These observations were associated with an increased Sost expression in WT cells. Taken together, our data show that sclerostin deficiency hastened reparative dentinogenesis after pulp injury, suggesting that the inhibition of sclerostin may constitute a promising therapeutic strategy for improving the healing of damaged pulps.

Therapies using mesenchymal stem cell (MSC) seeded scaffolds may be applicable to various fields of regenerative medicine, including craniomaxillofacial surgery. Plastic compression of collagen scaffolds seeded with MSC has been shown to enhance the osteogenic differentiation of MSC as it increases the collagen fibrillary density. The aim of the present study was to evaluate the osteogenic effects of dense collagen gel scaffolds seeded with mesenchymal dental pulp stem cells (DPSC) on bone regeneration in a rat critical-size calvarial defect model. Two symmetrical full-thickness defects were created (5 mm diameter) and filled with either a rat DPSC-containing dense collagen gel scaffold (n = 15), or an acellular scaffold (n = 15). Animals were imaged in vivo by microcomputer tomography (Micro-CT) once a week during 5 weeks, whereas some animals were sacrificed each week for histology and histomorphometry analysis. Bone mineral density and bone micro-architectural parameters were significantly increased when DPSC-seeded scaffolds were used. Histological and histomorphometrical data also revealed significant increases in fibrous connective and mineralized tissue volume when DPSC-seeded scaffolds were used, associated with expression of type I collagen, osteoblast-associated alkaline phosphatase and osteoclastic-related tartrate-resistant acid phosphatase. Results demonstrate the potential of DPSC-loaded-dense collagen gel scaffolds to benefit of bone healing process.

A mosaic minisatellite region has been identified in the mitochondrial genome of Norway spruce (Picea abies). The array was composed of three tandem repeats PaTR1 (32 bp), PaTR2a (26 bp) and PaTR2b (26 bp). PaTR2a and PaTR2b differed by one base substitution. The analysis of 92 trees covering the whole natural distribution area of the species allowed detection of 11 length variants ranging from 131 bp to 447 bp. This high intra-specific polymorphism relies on variation in the number of the tandem repeats. Population genetic parameters estimated among 14 populations suggested high population differentiation (Gst=0.749). The phylogenetic analysis of the 11 sequenced length variants has been performed using a parsimony approach. The topology of the tree showed a good association of groups with geographical origin and a low level of size homoplasy. The phylogenetic reconstruction also suggests that this minisatellite locus has mainly evolved by an increase in the repeat copy number.