A WNT protein therapeutic accelerates consolidation of a bone graft substitute in a pre-clinical sinus augmentation model

AIM

Autologous bone grafts consolidate faster than bone graft substitutes (BGSs) but resorb over time, which compromises implant support. We hypothesized that differences in consolidation rates affected the mechanical properties of grafts and implant stability, and tested whether a pro-osteogenic protein, liposomal WNT3A (L-WNT3A), could accelerate graft consolidation.

MATERIALS AND METHODS

A transgenic mouse model of sinus augmentation with immunohistochemistry, enzymatic assays, and histology were used to quantitatively evaluate the osteogenic properties of autografts and BGSs. Composite and finite element modelling compared changes in the mechanical properties of grafts during healing until consolidation, and secondary implant stability following remodelling activities. BGSs were combined with L-WNT3A and tested for its osteogenic potential.

RESULTS

Compared with autografts, BGSs were bioinert and lacked osteoprogenitor cells. While in autografted sinuses, new bone arose evenly from all living autograft particles, new bone around BGSs solely initiated at the sinus floor, from the internal maxillary periosteum. WNT treatment of BGSs resulted in significantly higher expression levels of pro-osteogenic proteins (Osterix, Collagen I, alkaline phosphatase) and lower levels of bone-resorbing activity (tartrate-resistant acid phosphatase activity); together, these features culminated in faster new bone formation, comparable to that of an autograft.

CONCLUSIONS

WNT-treated BGSs supported faster consolidation, and because BGSs typically resist resorption, their use may be superior to autografts for sinus augmentation.

Graphene Nanocoating: High Quality and Stability upon Several Stressors

Titanium implants present 2 major drawbacks-namely, the long time needed for osseointegration and the lack of inherent antimicrobial properties. Surface modifications and coatings to improve biomaterials can lose their integrity and biological potential when exposed to stressful microenvironments. Graphene nanocoating (GN) can be deposited onto actual-size dental and orthopedic implants. It has antiadhesive properties and can enhance bone formation in vivo. However, its ability to maintain structural integrity and quality when challenged by biologically relevant stresses remains largely unknown. GN was produced by chemical vapor deposition and transferred to titanium via a polymer-assisted transfer technique. GN has high inertness and did not increase expression of inflammatory markers by macrophages, even in the presence of lipopolysaccharides. It kept high coverage at the top tercile of tapered dental implant collars after installation and removal from bone substitute and pig maxilla. It also resisted microbiologically influenced corrosion, and it maintained very high coverage area and quality after prolonged exposure to biofilms and their removal by different techniques. Our findings show that GN is unresponsive to harsh and inflammatory environments and that it maintains a promising level of structural integrity on the top tercile of dental implant collars, which is the area highly affected by biofilms during the onset of implant diseases. Our findings open the avenues for the clinical studies required for the use of GN in the development of implants that have higher osteogenic potential and are less prone to implant diseases.

Biology of sinus floor augmentation with an autograft versus a bone graft substitute in a preclinical in vivo experimental model

OBJECTIVES

Compared to autografts, bone graft substitutes are slower to consolidate. If we understood why, this might open strategies to accelerate new bone formation and thus shorten the time to implant placement. In this study, we aimed at comparing autologous bone graft with a bovine bone graft substitute in a preclinical sinus lift model.

MATERIALS AND METHODS

The mouse posterior paranasal sinus served as a recipient site for grafting. Autograft from the oral cavity was compared against bone graft substitute using molecular, cellular, and histological analyses conducted on post-grafting days (PSD) 0, 9, 18, and 120.

RESULTS

Either autografts or bone graft substitutes were positioned on the sinus floor and remained in situ throughout the study. At the time of grafting and until day 9, bone graft substitutes were devoid of cells and alkaline phosphatase (ALP) activity while autografts were comprised of viable cells and showed strong ALP (mineralization) activity. Consequently, new bone formed faster in autografts compared to bone graft substitutes (140.21 ± 41.21 µm vs. 41.70 ± 10.09 µm, respectively, PSD9, p = .0143). By PSD18, osteogenesis was evident in autografted and xenografted sites. Osteoclasts identified by tartrate resistant acid phosphatase attached to, but did not resorb the bone graft substitute matrix. Autograft matrix, however, underwent extensive resorption. Transgenic mice revealed that Wnt-responsive osteoprogenitor cells originated primarily from the internal periosteum of the maxillary bone, and not from the Schneiderian membrane.

CONCLUSION

Autografts produce new bone sooner, but bovine bone graft substitutes eventually consolidate and then resist resorption. Enhancing osteoprogenitor cell recruitment to a bone graft substitute constitutes a viable strategy for accelerating bone formation in a sinus lift procedure.

Microbial Community-Driven Etiopathogenesis of Peri-Implantitis

Osseointegrated dental implants are a revolutionary tool in the armament of reconstructive dentistry, employed to replace missing teeth and restore masticatory, occlusal, and esthetic functions. Like natural teeth, the orally exposed part of dental implants offers a pristine nonshedding surface for salivary pellicle-mediated microbial adhesion and biofilm formation. In early colonization stages, these bacterial communities closely resemble those of healthy periodontal sites, with lower diversity. Because the peri-implant tissues are more susceptible to endogenous oral infections, understanding of the ecological triggers that underpin the microbial pathogenesis of peri-implantitis is central to developing improved prevention, diagnosis, and therapeutic strategies. The advent of next-generation sequencing (NGS) technologies, notably applied to 16S ribosomal RNA gene amplicons, has enabled the comprehensive taxonomic characterization of peri-implant bacterial communities in health and disease, revealing a differentially abundant microbiota between these 2 states, or with periodontitis. With that, the peri-implant niche is highlighted as a distinct ecosystem that shapes its individual resident microbial community. Shifts from health to disease include an increase in diversity and a gradual depletion of commensals, along with an enrichment of classical and emerging periodontal pathogens. Metatranscriptomic profiling revealed similarities in the virulence characteristics of microbial communities from peri-implantitis and periodontitis, nonetheless with some distinctive pathways and interbacterial networks. Deeper functional assessment of the physiology and virulence of the well-characterized microbial communities of the peri-implant niche will elucidate further the etiopathogenic mechanisms and drivers of the disease.

Inhibiting Corrosion of Biomedical-Grade Ti-6Al-4V Alloys with Graphene Nanocoating

The identification of metal ions and particles in the vicinity of failed implants has raised the concern that biomedical titanium alloys undergo corrosion in healthy and infected tissues. Various surface modifications and coatings have been investigated to prevent the deterioration and biocorrosion of titanium alloys but so far with limited success. Graphene is a cytocompatible atom-thick film made of carbon atoms. It has a very high surface area and can be deposited onto metal objects with complex shapes. As the carbon lattice has a very small pore size, graphene has promising impermeability capacity. Here, we show that graphene coating can effectively protect Ti-6Al-4V from corrosion. Graphene nanocoatings were produced on Ti-6Al-4V grade 5 and 23 discs and subjected to corrosive challenge (0.5M NaCl supplemented with 2-ppm fluoride, pH of 2.0) up to 30 d. The linear polarization resistance curves and electrochemical impedance spectroscopy analysis showed that the graphene-coated samples presented higher corrosion resistance and electrochemical stability at all time points. Moreover, the corrosion rate of the graphene-coated samples was very low and stable (~0.001 mm/y), whereas that of the uncoated controls increased up to 16 and 5 times for grade 5 and 23 (~0.091 mm/y) at the end point, respectively. The surface oxidation, degradation (e.g., crevice defects), and leaching of Ti, Al, and V ions observed in the uncoated controls were prevented by the graphene nanocoating. The Raman mappings confirmed that the graphene nanocoating presented high structural stability and resistance to mechanical stresses and chemical degradation, keeping >99% of coverage after corrosion challenge. Our findings open the avenues for the use of graphene as anticorrosion coatings for metal biomedical alloys and implantable devices.

LASER sintered one-piece early-loaded dental implants for mandibular premolars replacement

This study was designed to evaluate laser-sintered early-loaded 1-piece implants (OPI) based on clinical and radiographic findings. Thirty OPI were placed in the mandibular premolar area and subjected to early loading after 3 weeks of initial placement; patients were followed up for 6 months. Clinical evaluation included pocket depth, gingival health, implant stability, and esthetics. Periapical radiographs were used to measure the marginal bone loss (MBL). All implants were considered successful resulting in a survival rate of 100%. A remarkable difference (P < 0.01) existed when comparing MBL levels at 1 month with those at 3 and 6 months. Significant differences (P < 0.01) existed when comparing implant stability at 1 month to 3 months and at 3 months to 6 months. Moreover, significant differences (P < 0.01) were observed when comparing peri-implant probing depth at 1 month to that at 3 and 6 months on both the mesial and distal sides. The mean value of pink esthetic score was 11 at time of final restoration. The laser-treated early-loaded OPI design is associated with satisfactory clinical and radiographic follow-up results and it is a good alternative to the 2-piece design.