[Effect of printing orientation on physical and mechanical properties of 3D printing prosthodontic base resin materials].

OBJECTIVE: To analyze the influence of forming direction on the surface characteristics, elastic modulus, bending strength and fracture toughness of printed parts and the relationship between forming direction and force direction, and to provide scientific basis and guidance for the clinical application of oral denture base resin materials. METHODS: The 3D printing technology was used to print denture base resin samples. The shape and size of the samples referred to the current standard for testing conventional denture base materials. The samples used for physical performance testing were cylindrical (with a diameter of 15 mm and a thickness of 1 mm) and printed at different angles along the Z axis (0°, 45°, 90°). Scanning electron microscope was used to observe the microscopic topography of the different samples. The color stability of different samples was observed by color stabilizer. The surface roughness of the samples was analyzed by using surface roughness tester. The Vickers hardness was measured to analyze the hardness of the samples. The samples used for mechanical performance testing were rectangular (elastic modulus and bending strength: A length of 64 mm, a width of 10 mm, and a height of 3.3 mm; fracture toughness: A length of 39 mm, a width of 8 mm, and a height of 4 mm), divided into two groups: W group and H group. The W group was printed from the bottom up along the Z axis with the length × width as the bottom surface parallel to the X, Y axis plane, while the H group printed from the bottom up along the Z axis with the length × height as the bottom surface parallel to the X, Y axis plane. The forming angles of both groups were equally divided into 0°, 45°, and 90°. The elastic modulus, bending strength and fracture toughness of different samples were studied through universal mechanical testing machine. SPSS 22.0 software was used for statistical analysis. RESULTS: The microscopic topography and roughness of different samples were closely related to the printing direction, with significant differences between the 0°, 45°, and 90° specimens. The 0° specimens had the smoothest surface (roughness < 1 µm). The surface of the 45° specimen was the roughest (roughness>3 µm). The microhardness of the 0° sample was the best [(196.13±0.20) MPa], with a significant difference compared with the 90° sample [(186.62±4.81) MPa, P < 0.05]. The mechanical properties of different samples were also closely related to the printing direction. The elastic modulus, bending strength, and fracture toughness of the 45° samples in the W group were the highest compared with the other groups. The results of elastic modulus showed that in the H group, the 45° specimens had the highest elastic mo-dulus, which was significantly different from the 0° and 90° specimens (P < 0.05). The elastic modulus of 0° and 45° specimens in the W group were higher than those in 90° specimens (P < 0.05). The bending strength results showed that there was no significant difference between the specimens from dif-ferent angles in the H group. The bending strength of the 90° specimens in the W group was the smallest, and there was a significant difference between 90° and the 0° and 45° specimens (P < 0.05); And the bendind strength of the 0° and 45° specimens in the W group was significantly higher than that of the 0° and 45° specimens in the H group (P < 0.05). The fracture toughness results showed that the fracture toughness of the H group specimens was lower than 1.9 MPa m1/2, which was specified in the denture base standard. The 45° samples in the W group were the highest, with significant differences compared with the 0° and 90° samples (P < 0.05). And the 90° samples of the W group specimens were lower than 1.9 MPa m1/2. And the fracture toughness of the 45° specimen in the W group was significantly higher than that of all the specimens in the H group (P < 0.05). CONCLUSION: The 0° samples had relatively better physical properties. The 45° samples had the best mechanical properties. But the fracture toughness of specimens (H group and 90° samples of W group) did not yet meet clinical requirements. That indicated that the characteristics of the 3D printing denture base resin were affected by the printing direction. Only when the performance of the printed samples in all directions met the minimum requirements of the standard, they could be used in clinical practice.

Near-infrared light responsive gold nanoparticles coating endows polyetheretherketone with enhanced osseointegration and antibacterial properties.

Polyetheretherketone (PEEK) is considered as a promising dental implant material owing to its excellent physicochemical and mechanical properties. However, its wide range of applications is limited by its biologically inert nature. In this study, a near-infrared (NIR) light responsive bioactive coating with gold nanoparticles (AuNPs) and metronidazole adhered to the PEEK surface via dopamine polymerization. Compared to pure PEEK, the hydrophilicity of the treated PEEK surface was significantly improved. In addition, under NIR light, the surface coating exhibited photothermal conversion effect, and gold nanoparticles and the antibiotic can be released from the coating. This improved the antibacterial properties of PEEK materials. Moreover, the coating was more conducive to the early adhesion of bone mesenchymal stem cells. The results of in vitro and in vivo osteogenic activity studies showed that the developed coating promoted osseointegration of PEEK implants, and NIR light irradiation further improved the antibacterial ability and osteogenic activity of PEEK implants. Through RNA sequencing, the potential underlying mechanism of promoting bone formation of the AuNPs coating combined metronidazole was interpreted. In summary, the developed coating is a potential surface treatment strategy that endows PEEK with enhanced osseointegration and antibacterial properties.

Zeolite imidazolate framework-8 in bone regeneration: A systematic review.

Zeolite imidazolate framework-8 (ZIF-8) is a biomaterial that has been increasingly studied in recent years. It has several applications such as bone regeneration, promotion of angiogenesis, drug loading, and antibacterial activity, and exerts multiple effects to deal with various problems in the process of bone regeneration. This systematic review aims to provide an overview of the applications and effectiveness of ZIF-8 in bone regeneration. A search of papers published in the PubMed, Web of Science, Embase, and Cochrane Library databases revealed 532 relevant studies. Title, abstract, and full-text screening resulted in 39 papers being included in the review, including 39 in vitro and 22 animal studies. Appropriate concentrations of nano ZIF-8 can promote cell proliferation and osteogenic differentiation by releasing Zn2+ and entering the cell, whereas high doses of ZIF-8 are cytotoxic and inhibit osteogenic differentiation. In addition, five studies confirmed that ZIF-8 exhibits good vasogenic activity. In all in vivo experiments, nano ZIF-8 promoted bone formation. These results indicate that, at appropriate concentrations, materials containing ZIF-8 promote bone regeneration more than materials without ZIF-8, and with characteristics such as promoting angiogenesis, drug loading, and antibacterial activity, it is expected to show promising applications in the field of bone regeneration. STATEMENT OF SIGNIFICANCE: This manuscript reviewed the use of ZIF-8 in bone regeneration, clarified the biocompatibility and effectiveness in promoting bone regeneration of ZIF-8 materials, and discussed the possible mechanisms and factors affecting its promotion of bone regeneration. Overall, this study provides a better understanding of the latest advances in the field of bone regeneration of ZIF-8, serves as a design guide, and contributes to the design of future experimental studies.

The effect of low-frequency high-intensity ultrasound combined with aspirin on tooth movement in rats.

BACKGROUND: Given the difficulties or incapacity of teeth movement in orthodontic treatment, the ways to speed tooth movement must be investigated. Besides, nonsteroidal anti-inflammatory drugs (NSAIDs) were utilized to treat pain caused by tooth movement during orthodontic treatment. The purpose of this study is to examine the impact of aspirin and low-frequency high-intensity ultrasound (LFHIU) on rat orthodontic tooth movement in rats. METHODS: Thirty-six male Sprague-Dawley rats were divided into three groups: orthodontic (O), ultrasound-treated orthodontic (OU), and ultrasound-treated orthodontic with aspirin gavage (OUA) group. In the OU and OUA group, LFHIU (44 W/cm2, 28 kHz) was applied to the buccal side of the maxillary first molar alveolar bone for 10 s every day. In the OUA group, aspirin was given by gavage every day. The rats were sacrificed on days 1, 3, 7, and 14. RESULTS: After ultrasonic treatment, the speed of tooth movement was increased by about 1.5 times. And the number of osteoclasts considerably increased by about 2 times. However, they decreased slightly after aspirin gavage. By Applying ultrasound therapy, Receptor Activator for Nuclear Factor-κ B Ligand (RANKL) levels in periodontal tissue were elevated. Aspirin was able to reduce these increases. Results from Micro Computed Tomography (Micro-CT) revealed that bone mineral density decreased by about 1/5 after ultrasound treatment on the compression side. The rate of bone mineral apposition indicated that bone was forming under tension, and that of the OU group increased by about 1.3 times that O group. CONCLUSIONS: Although aspirin slowed this trend, LFHIU still enhanced overall tooth mobility in orthodontic treatment.

Antibacterial Properties of Gold Nanoparticles in the Modification of Medical Implants: A Systematic Review.

The widespread occurrence of bacterial infections and their increased resistance to antibiotics has led to the development of antimicrobial coatings for multiple medical implants. Owing to their desirable properties, gold nanoparticles (AuNPs) have been developed as antibacterial agents. This systematic investigation sought to analyze the antibacterial effects of implant material surfaces modified with AuNPs. The data from 27 relevant studies were summed up. The included articles were collected from September 2011 to September 2021. According to the retrieved literature, we found that medical implants modified by AuNPs have good antibacterial effects against gram-positive and gram-negative bacteria, and the antibacterial effects would be improved by near-infrared (NIR) radiation.

Strontium-Loaded Nanotubes of Ti-24Nb-4Zr-8Sn Alloys for Biomedical Implantation.

Ti-24Nb-4Zr-8Sn (Ti2448) alloys, with a relatively low elastic modulus and unique mechanical properties, are desirable materials for oral implantation. In the current study, a multifaceted strontium-incorporating nanotube coating was fabricated on a Ti2448 alloy (Ti2-NTSr) through anodization and hydrothermal procedures. In vitro, the Ti2-NTSr specimens demonstrated better osteogenic properties and more favorable osteoimmunomodulatory abilities. Moreover, macrophages on Ti2-NTSr specimens could improve the recruitment and osteogenic differentiation of osteoblasts. In vivo, dense clots with highly branched, thin fibrins and small pores existed on the Ti2-NTSr implant in the early stage after surgery. Analysis of the deposition of Ca and P elements, hard tissue slices and the bone-implant contact rate (BIC%) of the Ti2-NTSr implants also showed superior osseointegration. Taken together, these results demonstrate that the Ti2-NTSr coating may maximize the clinical outcomes of Ti2448 alloys for implantation applications.

Assessment of mitochondrial function in metabolic dysfunction-associated fatty liver disease using obese mouse models.

Metabolic dysfunction-associated fatty liver disease (MAFLD) is characterized by deregulated hepatic lipid metabolism; however, the association between MAFLD development and mitochondrial dysfunction has yet to be confirmed. Herein, we employed high-resolution respirometry, blue native polyacrylamide gel electrophoresis-based in-gel activity measurement and immunoblot analysis to assess mitochondrial function in obesity-induced mouse models with varying degrees of MAFLD. Results showed a slight but significant decrease in hepatic mitochondrial respiration in some MAFLD mice compared to mice fed a standard diet. However, the activities and levels of mitochondrial oxidative phosphorylation complexes remained unchanged during obesity-induced MAFLD progression. These results suggest that mitochondrial function, particularly oxidative phosphorylation, was mildly affected during obesity-induced MAFLD development. Moreover, transcriptome profiling of mouse and human liver tissues with varying degrees of MAFLD revealed that the decreased activation of mitochondria-related pathways was only associated with MAFLD of a high histological grade, whereas the major regulators of mitochondrial biogenesis were not altered in mice or humans during MAFLD development. Collectively, our results suggest that impaired hepatic mitochondrial function is not closely associated with obesity-induced MAFLD. Therefore, therapeutic strategies targeting mitochondria for the treatment of MAFLD should be reconsidered.

Comparison of the osteoblastic activity of low elastic modulus Ti-24Nb-4Zr-8Sn alloy and pure titanium modified by physical and chemical methods.

Ti-24Nb-4Zr-8Sn (Ti2448) alloy is a novel low elastic modulus ß-titanium alloy without toxic elements. It also has the advantage of high strength, so it has potential application prospects for implantation. To develop its osteogenic effects, it can be modified by electrochemical, and physical processes. The main research aim of this study was to explore the bioactivity of Ti2448 alloy modified by sandblasted, large-grit, acid-etched (SLA), micro-arc oxidation (MAO) and anodic oxidation (AO), and to determine which of the three surface modifications is the best way for developing the osteogenesis of bone marrow mesenchymal stem cells (BMMSCs). In vitro studies, the cytoskeleton, focal adhesion and proliferation of BMMSCs showed that both pure titanium and Ti2448 alloy have good biocompatibility. The osteogenic differentiation of BMMSCs with the Ti2448 alloy were examined by detecting alkaline phosphatase (ALP), mineralization nodules and osteogenic proteins and were better than that with pure titanium. These results showed that the Ti2448 alloy treated by SLA has a better effect on osteogenesis than pure titanium, and AO is the best way of three surface treatments to improve osteogenesis in this study.