Antibacterial tooth surface created by laser-assisted pseudo-biomineralization in a supersaturated solution

Mid-infrared passive spectroscopic imaging for visualizing tooth quality

Although the measurement of tooth quality is necessary for precise prediction of caries formation, typical measurement methods include tooth-hardness measurements and absorption spectroscopy, which generally use infrared light irradiation. These methods are destructive or invasive, and obtaining two-dimensional information in the oral cavity is difficult. Mid-infrared emissions from the surface of an object reflect intrinsic vibrations of molecules in the object. In this study, a mid-infrared passive spectroscopic imaging system was developed using an inexpensive uncooled microbolometer array sensor with an optimized multi-slit, which eliminated the cancellation of interference intensities between two adjacent emission points, to obtain two-dimensional information from an object without external infrared light irradiation. First, the feasibility of obtaining two-dimensional information on tooth quality using the proposed system was examined, and emission spectra attributed to phosphate ions in hydroxyapatite (HAp), the main component of enamel, were successfully obtained from bovine teeth. Further, the hardness of bovine teeth was measured, and a correlation (R2 = 0.8067) between the Vickers hardness and peak area ratio of phosphate ions assigned to the crystalline and amorphous phases of a tooth was established. Additionally, tooth-hardness visualization in a non-contact manner was demonstrated as two-dimensional information using the obtained regression equation.

Interdisciplinary-Inspired Smart Antibacterial Materials and Their Biomedical Applications

The discovery of antibiotics has saved millions of lives, but the emergence of antibiotic-resistant bacteria has become another problem in modern medicine. To avoid or reduce the overuse of antibiotics in antibacterial treatments, stimuli-responsive materials, pathogen-targeting nanoparticles, immunogenic nano-toxoids, and biomimetic materials are being developed to make sterilization better and smarter than conventional therapies. The common goal of smart antibacterial materials (SAMs) is to increase the antibiotic efficacy or function via an antibacterial mechanism different from that of antibiotics in order to increase the antibacterial and biological properties while reducing the risk of drug resistance. The research and development of SAMs are increasingly interdisciplinary because new designs require the knowledge of different fields and input/collaboration from scientists in different fields. A good understanding of energy conversion in materials, physiological characteristics in cells and bacteria, and bactericidal structures and components in nature are expected to promote the development of SAMs. In this review, the importance of multidisciplinary insights for SAMs is emphasized, and the latest advances in SAMs are categorized and discussed according to the pertinent disciplines including materials science, physiology, and biomimicry.

Oral biosciences: The annual review 2022

BACKGROUND

The Journal of Oral Biosciences is devoted to advancing and disseminating fundamental knowledge concerning every aspect of oral biosciences.

HIGHLIGHT

This review features review articles in the fields of "Bone Cell Biology," "Tooth Development & Regeneration," "Tooth Bleaching," "Adipokines," "Milk Thistle," "Epithelial-Mesenchymal Transition," "Periodontitis," "Diagnosis," "Salivary Glands," "Tooth Root," "Exosome," "New Perspectives of Tooth Identification," "Dental Pulp," and "Saliva" in addition to the review articles by the winner of the "Lion Dental Research Award" ("Plastic changes in nociceptive pathways contributing to persistent orofacial pain") presented by the Japanese Association for Oral Biology.

CONCLUSION

The review articles in the Journal of Oral Biosciences have inspired its readers to broaden their knowledge about various aspects of oral biosciences. The current editorial review introduces these exciting review articles.

Fluoridated Apatite Coating on Human Dentin via Laser-Assisted Pseudo-Biomineralization with the Aid of a Light-Absorbing Molecule

A simple, area-specific coating technique for fluoridated apatite (FAp) on teeth would be useful in dental applications. Recently, we achieved area-specific FAp coating on a human dentin substrate within 30 min by a laser-assisted biomimetic (LAB) process; pulsed Nd:YAG laser irradiation in a fluoride-containing supersaturated calcium phosphate solution (FCP solution). The LAB-processed, FAp-coated dentin substrate exhibited antibacterial activity against a major oral bacterium, Streptococcus mutans. In the present study, we refined the LAB process with a combination of a dental diode laser and a clinically approved light-absorbing molecule, indocyanine green (ICG). A micron-thick FAp layer was successfully formed on the dentin surface within only 3 min by the refined LAB process, i.e., dental diode laser irradiation in the FCP solution following ICG treatment. The ICG layer precoated on the dentin substrate played a crucial role in inducing rapid pseudo-biomineralization (FAp layer formation) on the dentin surface by absorbing laser light at the solid-liquid interface. In the refined LAB process, the precoated ICG layer was eliminated and replaced with the newly formed FAp layer composed of vertically oriented pillar-like nanocrystals. Cross-sectional ultrastructural analysis revealed a smooth interface between the FAp layer and the dentin substrate. The refined LAB process has potential as a tool for the tooth surface functionalization and hence, is worth further process refinement and in vitro and in vivo studies.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Biological modification of tooth surface by laser-based apatite coating techniques

BACKGROUND

Development of new clinical regenerative procedures is needed for the reconstruction of the connective tissue attachment lost to periodontal disease. Apatite coating on the affected root surfaces could improve root surface biocompatibility and promote the reestablishment of connective tissue attachment.

HIGHLIGHT

We developed two novel techniques that use laser light for coating the tooth surface with apatite. In the laser-assisted biomimetic (LAB) process, a tooth substrate was placed in a supersaturated calcium phosphate solution and irradiated for 30 minutes with low-energy pulsed laser light. Due to the laser-assisted pseudo-biomineralization, a submicron-thick apatite film was created on the laser-irradiated tooth surface. Furthermore, we created a fluoride-incorporated apatite film on the tooth surface using the LAB process and demonstrated its antibacterial activity against Streptococcus mutans. In the laser-induced forward transfer with optical stamp (LIFTOP) process, a thin apatite film loaded with the cell-adhesion protein, fibronectin, was prepared beforehand as a raw material on the optical stamp (carbon- and polydimethylsiloxane-coated support) by a conventional biomimetic process. After irradiation with a single laser pulse, the film (microchip) was transferred onto a tooth substrate via laser ablation of the carbon sacrificial layer. The LIFTOP process requires only a short processing time and has a minimal heat effect on the film; thus, the film exhibits cell adhesion activity even after the LIFTOP process.

CONCLUSION

The LAB and LIFTOP processes have the potential as novel tools for tooth surface modification in the treatment of periodontal disease.

Laser-Induced Forward Transfer with Optical Stamp of a Protein-Immobilized Calcium Phosphate Film Prepared by Biomimetic Process to a Human Dentin

The rapid and area-specific printing of calcium phosphate with superior biocompatibility and osteoconductivity is a useful technique for the surface functionalization of biomedical devices. We recently demonstrated the laser-induced forward transfer (LIFT) of a brittle calcium phosphate film onto a soft and shock-absorbing polydimethylsiloxane (PDMS) substrate. In this work, a new LIFT using an optically transparent PDMS-coated stamp, which we hereafter call LIFT with optical stamp (LIFTOP), was introduced to achieve the transfer of brittle films to harder substrates. Cell adhesion protein fibronectin-immobilized calcium phosphate films (Fn-CaP) were prepared on the optical stamp through a biomimetic process. Then, the irradiation of a single laser pulse transferred the Fn-CaP film from the optical stamp onto relatively hard substrates, polyethylene terephthalate and human dentin. As a result of this LIFTOP process, Fn-CaP microchips with a shape corresponding to the laser beam spot were printed on the substrates. Cross-sectional observation of the interface between the Fn-CaP microchip and the dentin substrate revealed good attachment between them without obvious gaps for the most part.