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This paper reviews our recent results on the formation, fundamental properties and application examples of nanogranular body-centered cubic (bcc) Ti-based alloys, bulk glassy Ti-based alloys and porous Pd- and Zr-based glassy alloys with the aim of clarifying the possibility of practical uses as biomedical materials. The bcc Ti-based alloys with low Young’s modulus, large elastic elongation and high mechanical strength have already been used as eyeglass frame materials. New Ti-based bulk glassy alloys with a critical diameter of 7 mm in Ti-Zr-Cu-Pd system have been developed and tested as artificial dental root materials in various environmental conditions. The Pd- and Zr-based bulk glassy alloys can include spherical or polyhedral pores in a wide porosity range. The porous bulk glassy alloys have unique mechanical properties which are comparable to bones of human beings. These results indicate the possibility that the present nanogranular bcc Ti-based alloys as well as the bulk glassy alloys in Ti-, Pd- and Zr-based systems are used as biomedical materials in the near future.

The emergence of new technologies in biology and medicine has given new opportunities for scientific collaboration both in national and international for oral and dental research workers. Technological advances have resulted in further scientific specialisation, and the need for clinicians and basic scientists to work closely to foster innovation in research initiatives. The interests of dental research is best served by a teamwork approach, often working on basic and clinically applied research questions and utilising international contacts and collaborations. The IADR was founded to create an international organisation to further the interests of dental research by combining the talents of clinical and basic research workers and has programmes to encourage such international collaboration. Dental scientists have frequently made observations that have contributed in a major way to medical science. Examples of new technologies in the diagnosis and management of oral diseases include the use of stem cells, proteomics and genomics in oral cancer, potential in growing teeth in vitro and transgenic technologies in plants for the production of oral vaccines. Whilst the oral cavity as a unique body area allows specific oral diseases to be investigated, its anatomical position means that it is not only part of the mucosal immune system and reflective of mucosal immunity but also of dermatological, gastrointestinal and other systemic diseases. International perspectives in research are needed to maximise this potential.

The oral biofilm harbors in more than 750 species/phylotypes but even greater diversity is apparent when the genotypic diversity of individual species is considered. Analysis of individual species of the genera Streptococcus , Actinomyces , Fusobacterium , and Porphyromonas has shown that each species is genotypically diverse and that, except within closely living individuals, no two individuals harbor the same genotype. Data are presented for the relationships between the stress and the diversity of Streptococcus oralis , Actinomyces naelsundii at interproximal sites in caries-free and caries-active children, below dental restorations and of V eillonella spp. on carious and sound surfaces. The idea of “stress” requires consideration; it is relative and usually applied unevenly across the biofilm. Acidic stress increased the diversity of S. oralis , but not A. naelsundii , at interproximal sites, perhaps as a result of increased habitat diversity. While the genotypic diversity of Veillonella spp. was significantly reduced within carious lesions (acidic stress), as was the range of Veillonella spp. isolated. The diversity of the microflora surviving below dental restorations, with nutrients of limited composition, was genotypically less diverse than that of the lesion and exhibited similar phenotypic characteristics. The most stressful environments may also be the most stable. The diversity of individual species in the oral biofilm may be increased by the application of a small stress but a larger stress may “flatten” the environment, making it less subject to perturbation, reducing genotypic and phenotypic diversity. It would appear that the mechanism driving increased microbial diversity is continual perturbation of habitat diversity.

Members of the oral microbiota are responsible for the commonest bacterial diseases of man: dental caries and the periodontal diseases. Although some specific organisms have been implicated in the pathogenesis of these conditions, it is now recognised that they are not classical infectious diseases but, rather, complex diseases resulting from a breakdown in the normal homeostasis between the human host and its commensal microbiota. The first goal in understanding the mechanisms involved must be the comprehensive characterisation of the oral bacterial community. Since around half of oral species cannot be cultured on artificial media, molecular techniques have been developed based on PCR, cloning and sequencing of housekeeping genes such as that encoding 16S rRNA. These methods have revealed numerous novel bacterial lineages, including deep branches of the phyla Bacteroidetes and Firmicutes and novel phyla such as Synergistes . Taxa belonging to these newly described lineages are associated with oral diseases. In addition, novel genetic typing methods, such as multi locus sequence typing, are showing that intra-specific diversity is far greater than previously thought. Given this level of complexity, investigation of the oral bacterial metagenome is under way, which treats the oral bacterial community and its constituent genes as a whole. Functional screening of metagenomic libraries is a powerful tool for the identification of novel genes of interest in oral bacteria. These new molecular tools are revolutionising concepts of oral infectious disease pathogenesis and will enable new treatments to be developed based on modification of the composition and function of the oral microbiota.

The oral anaerobic bacterium Porphyromonas gingivalis has been implicated as a major pathogen for chronic periodontitis. The microorganism produces strong proteinases, Arg-gingipain (Rgp) and Lys-gingipain (Kgp), on the cell surface and in extracellular milieu. Gingipain genes encode polyproteins consisting of four parts: signal peptide, propeptide, proteinase, and a C-terminal adhesin domain region. The C-terminal adhesin domain region encoded by Rgp-encoding gene A ( rgpA ) comprises four domains (Hgp44, Hgp15, Hgp17, and Hgp27). A number of studies have indicated that a major hemagglutinin is derived from the gingipain genes; however, direct evidence has not yet been obtained. We showed that a fully processed recombinant Hgp44 had hemagglutinating activity, and that Hgp44 hemagglutinin bound to glycophorin on the erythrocyte membrane. P. gingivalis cells have the ability to aggregate platelets. We showed that P. gingivalis cell-mediated platelet aggregation required Hgp44 hemagglutinin on the bacterial cell surface, P. gingivalis -reactive antibody in plasma, and FcγRIIa, GPIIa/IIIb and GPIb-IX-V receptors on platelets. We also showed that a major protein of the culture supernatant of P. gingivalis , Hgp15, suppressed in vitro receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-mediated osteoclastogenesis. Hgp15 inhibited RANKL-mediated induction of c-Fos and NFATc1. These results suggest that the C-terminal adhesin domains have multiple functions associated with virulence of P. gingivalis .

Porphyromonas gingivalis (Pg), a Gram-negative anaerobic blackpigmented rod bacterium, has been recognized as the most potent etiologic bacterium in human chronic periodontitis. It possesses a variety of putative virulence factors providing both tissue destruction and host evasion including lipopolysaccharides (LPS), fimbriae, various proteinases, etc. These factors actively participate in periodontal tissue destruction. However, recent evidence suggests that Pg has also evolved mechanisms to inhibit or confuse host immune systems. Thus, Pg is suggested to behave not only like an “active invader”, but also like a “stealth element” in periodontal lesions. In the present study, repeated exposure of Pg components induced tolerance resulting in selective inhibition of cytokine production of both monocytes and gingival fibroblasts in a different fashion from that described for LPS in Escherichia coli . It was also revealed that Pg LPS induced a unique dendritic cell subset with a CD14^+CD16^+ phenotype that exhibited weak maturation. In animal studies, administration of live Pg or its LPS exerted a regulatory effect on systemic markers such as triglycerides or adiponectin. Taken together, these findings suggest that Pg may be able to adapt to the local immune defense, contributing to the connection between systemic and periodontal disease.

Low-rigidity β-type titanium alloys composed of nontoxic and allergyfree elements are receiving considerable attention as biomaterials. Ti-29Nb-13Ta-4.6Zr (TNTZ) composed of nontoxic and allergy-free elements exhibits low Young’s modulus of approximately 60 GPa; it is effective in inhibiting bone resorption and enhancing the remodeling of bones, which may be due to the excellent stress transmission between the bone and the implant. TNTZ exhibits multifunctional characteristics such as super elasticity and shape memory effect. It can be applicable for not only dental implants but also for dental prostheses.

In vivo bone tissue engineering is an emerging field of regenerative medicine for bone defects, which differs from classical tissue engineering. In vivo bone tissue engineering uses the body as a “bioreactor” to construct bone graft with intrinsic osteoinductive biomaterials in the non-osseous or osseous sites. This technique relies on the body’s own capacity to regenerate itself, and it does not rely on the delivery of exogenous growth factors or cells. This study has focused on the exploration of osteoinductive biomaterials, the construction of tissue engineering bone with osteoinductive biomaterials, and investigating possible applications in repairing mandibular bone defects in animals in order to develop a feasible technique for bone restoring. The results demonstrated that biomaterials without any exogenous growth factors or cells can induce bone formation in non-osseous sites, and in vivo tissue engineering bone formed with osteoinductive calcium phosphate (Ca-P) ceramics has similar histological characteristics with natural bone. It is possible to construct large bone graft with good blood supply and certain mechanical strength in vivo by using osteoinductive biomaterials. In vivo tissue engineering bone has been provided with a hope of being used to repair segmental bone defects of mandible and support dental implant.

In order to improve the phase morphology of bioabsorbable polymer blend of poly(lactic acid) (PLA) and poly (ε-caprolacton) (PCL), an additive with the isocyanate group, lysine tri-isocyanate (LTI), was used, and the effects of LTI addition on the fracture energy, J _in, and the related fracture micromechanism were investigated. The study showed that J _in effectively increases with an increase in LTI. Microscopic examination of the mode I fracture surfaces also exhibited that the size of the PCL phases dramatically decreases due to LTI addition, leading to the reduction of void formation and suppression of local stress concentration, and therefore resulting in the increase of the fracture energy. The improved miscibility also contributes to the ductility enhancement, which further increases the fracture energy. In order to improve the mechanical properties, such as the bending modulus and strength, the annealing process was conducted for PLA/PCL and PLA/PCL/LTI blends. The mechanical properties of both the blends effectively increased due to the strengthened structures by crystallization of PLA. J _in of PLA/PCL largely reduced by annealing; on the other hand, that of PLA/PCL/LTI effectively improved. The well-entangled structure of PLA/PCL/LTI results in the elongated ductile fracture of firmly connected fibrils; as a result, the energy dissipation during fracture initiation is largely increased.

A dental magnetic attachment is used for over-dentures, removable partial dentures, and orthodontic and maxillofacial prostheses. The dental magnetic attachment is composed of a magnetic assembly and a keeper. The magnetic attractive force between the magnetic assembly and the keeper is used as the retention. The magnetic assembly is composed of a small Nd—Fe—B magnet that is covered within a magnetic stainless steel yoke and a non-magnetic stainless steel spacer. The keeper is also made of magnetic stainless steel. The yoke of the magnet assembly and the keeper form a closed magnetic circuit, which is necessary to concentrate on the magnetic flux and make efficient use of it. The covering nonmagnetic stainless steel and magnetic stainless steel yoke are welded seamlessly using micro-laser to protect the magnet from corrosion. In an oral cavity, the keepers and the magnetic assemblies are contacted with root caps made of dental precious alloys. It is important to examine the galvanic corrosion behavior of those stainless steels with dental precious alloys from the electrochemical properties and released ions. The dental magnetic attachment was implanted in rabbit tibia to investigate the influence of the static magnetic flux on hard tissue.