Dental Materials Applied to 3D and 4D Printing Technologies: A Review.

As computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have matured, three-dimensional (3D) printing materials suitable for dentistry have attracted considerable research interest, owing to their high efficiency and low cost for clinical treatment. Three-dimensional printing technology, also known as additive manufacturing, has developed rapidly over the last forty years, with gradual application in various fields from industry to dental sciences. Four-dimensional (4D) printing, defined as the fabrication of complex spontaneous structures that change over time in response to external stimuli in expected ways, includes the increasingly popular bioprinting. Existing 3D printing materials have varied characteristics and scopes of application; therefore, categorization is required. This review aims to classify, summarize, and discuss dental materials for 3D printing and 4D printing from a clinical perspective. Based on these, this review describes four major materials, i.e., polymers, metals, ceramics, and biomaterials. The manufacturing process of 3D printing and 4D printing materials, their characteristics, applicable printing technologies, and clinical application scope are described in detail. Furthermore, the development of composite materials for 3D printing is the main focus of future research, as combining multiple materials can improve the materials' properties. Updates in material sciences play important roles in dentistry; hence, the emergence of newer materials are expected to promote further innovations in dentistry.

Poloxamer-Based Scaffolds for Tissue Engineering Applications: A Review.

Poloxamer is a triblock copolymer with amphiphilicity and reversible thermal responsiveness and has wide application prospects in biomedical applications owing to its multifunctional properties. Poloxamer hydrogels play a crucial role in the field of tissue engineering and have been regarded as injectable scaffolds for loading cells or growth factors (GFs) in the last few years. Hydrogel micelles can maintain the integrity and stability of cells and GFs and form an appropriate vascular network at the application site, thus creating an appropriate microenvironment for cell growth, nerve growth, or bone integration. The injectability and low toxicity of poloxamer hydrogels make them a noninvasive method. In addition, they can also be good candidates for bio-inks, the raw material for three-dimensional (3D) printing. However, the potential of poloxamer hydrogels has not been fully explored owing to the complex biological challenges. In this review, the latest progress and cutting-edge research of poloxamer-based scaffolds in different fields of application such as the bone, vascular, cartilage, skin, nervous system, and organs in tissue engineering and 3D printing are reviewed, and the important roles of poloxamers in tissue engineering scaffolds are discussed in depth.

Advances in Modification Methods Based on Biodegradable Membranes in Guided Bone/Tissue Regeneration: A Review.

Guided tissue/bone regeneration (GTR/GBR) is commonly applied in dentistry to aid in the regeneration of bone/tissue at a defective location, where the assistive material eventually degrades to be substituted with newly produced tissue. Membranes separate the rapidly propagating soft tissue from the slow-growing bone tissue for optimal tissue regeneration results. A broad membrane exposure area, biocompatibility, hardness, ductility, cell occlusion, membrane void ratio, tissue integration, and clinical manageability are essential functional properties of a GTR/GBR membrane, although no single modern membrane conforms to all of the necessary characteristics. This review considers ongoing bone/tissue regeneration engineering research and the GTR/GBR materials described in this review fulfill all of the basic ISO requirements for human use, as determined through risk analysis and rigorous testing. Novel modified materials are in the early stages of development and could be classified as synthetic polymer membranes, biological extraction synthetic polymer membranes, or metal membranes. Cell attachment, proliferation, and subsequent tissue development are influenced by the physical features of GTR/GBR membrane materials, including pore size, porosity, and mechanical strength. According to the latest advances, key attributes of nanofillers introduced into a polymer matrix include suitable surface area, better mechanical capacity, and stability, which enhances cell adhesion, proliferation, and differentiation. Therefore, it is essential to construct a bionic membrane that satisfies the requirements for the mechanical barrier, the degradation rate, osteogenesis, and clinical operability.

Zn and Ag Doping on Hydroxyapatite: Influence on the Adhesion Strength of High-Molecular Polymer Polycaprolactone.

In this study, density functional theory was employed to calculate the adsorption of polycaprolactone (PCL) by pure hydroxyapatite (HA), Zn-doped HA, and Ag-doped HA, and the interaction of PCL on the surface of HA (001) was simulated. The results show that there was significant electron transfer between the carbonyl O in PCL and the Zn, Ag, and Ca in HA, forming coordinate bonds. The binding energies of Ag-doped HA/PCL and Zn-doped HA/PCL were much higher than those of HA/PCL. HA doped with Ag had the highest binding energy to PCL. Therefore, we believe that when HA is doped with Ag atoms, its adsorption capacity for PCL can be increased. The results obtained in this study can be used as a guide for the development of HA/PCL bone graft composite material doped with appropriate metal ions to improve its adsorption capacity.

Controllability of Graphene Oxide Doxorubicin Loading Capacity Based on Density Functional Theory.

Graphene can be used as a drug carrier of doxorubicin (DOX) to reduce the side effects of doxorubicin. However, there is limited research on the surface chemical modifications and biological effects of graphene oxide (GO). Therefore, it is necessary to explore the DOX affinity of different oxygen-containing functional groups in the graphene system. We constructed graphene system models and studied the structure and distribution of epoxy and hydroxyl groups on the carbon surface. Based on molecular dynamics simulations and density functional theory (DFT), we investigated the interaction between DOX and either pristine graphene or GO with different ratios of oxygen-containing groups. The hydroxyl groups exhibited a stronger affinity for DOX than the epoxy groups. Therefore, the DOX loading capacity of graphene systems can be adjusted by increasing the ratio of hydroxyl to epoxy groups on the carbon surface.

Sorption Studies of Tetracycline Antibiotics on Hydroxyapatite (001) Surface-A First-Principles Insight.

Owing to the limitations of traditional systemic drug delivery in the treatment of bone diseases with side effects on normal cells, the selection of materials with high affinities for bones, as targeting ligands to modify drug carriers, has become an important research topic. Tetracyclines (TCs) have an adsorption effect on hydroxyapatite (HAp). Thus, they can be used as bone-targeting ligands and combined with drug carriers. In this study, density functional theory is used to analyze the interaction mechanism of TC, oxytetracycline (OTC), chlortetracycline, and HAp. We calculate the electrostatic potential (ESP) and molecular orbitals to predict the possible binding sites of TCs on the HAp surface. The adsorption energy is used to compare the affinities of the three TCs to HAp. An independent gradient model analysis is performed to study the weak interaction between TCs and HAp. The coordination bond between TCs and the HAp surface is evaluated by conducting a charge density difference analysis. The results show that OTC has the highest affinity to HAp because the introduction of hydroxyl groups change the adsorption configuration of OTC. Thus, OTC adsorbed on HAp in a broken-line shape exposes more binding sites. This study provides a theoretical basis for TCs as bone-targeting ligands in treating bone diseases and in improving the safety of treatment by selecting different bone-targeting ligands.

The proliferation and migration of atherosclerosis-related HVSMCs were inhibited by downregulation of lncRNA XIST via regulation of the miR-761/BMP9 axis.

Atherosclerosis (AS) is a chronic inflammatory disease that can be caused by the proliferation and migration of human vascular smooth muscle cells (HVSMCs). Here, we found that lncRNA XIST was related to the abnormal proliferation and migration of HVSMCs, and thus, the mechanism by which XIST regulated HVSMCs was further investigated. HVSMCs were treated with oxidized low-density lipoprotein (ox-LDL, 100 µg/ml) as AS models. CCK8 assays, flow cytometry, Transwell assays and wound healing assays were applied to evaluate cell viability, cell cycle analysis, and cell migration, respectively. A dual-luciferase reporter assay was employed to verify the binding relationships between XIST and miR-761, miR-761, and BMP9. Ox-LDL induced the proliferation and migration of HVSMCs, upregulated the expression of XIST, downregulated miR-761 expression, and activated the BMP9/ALK1/endoglin pathway. Luciferase assays revealed that XIST sponged miR-761. XIST knockdown ameliorated ox-LDL-mediated effects in HVSMCs, which were largely abolished by miR-761 silencing. BMP9 was targeted-inhibited by miR-761. MiR-761 overexpression alleviated ox-LDL-mediated effects in HVSMCs. However, BMP9 overexpression abolished miR-761-mediated effects in HVSMCs treated with ox-LDL. Our findings suggested that XIST knockdown suppressed the proliferation and migration of HVSMCs by promoting miR-761, which targeted-inhibited the BMP9/ALK1/endoglin pathway.

A Six-Year Prospective Comparative Study of Wide and Standard Diameter Implants in the Maxillary and Mandibular Posterior Area.

Background and Objectives: The aim of our study was to test whether wide diameter (6 mm) implants perform differently from standard diameter (4 mm) implants in terms of marginal bone level and survival rate. Materials and Methods: Our sample comprised 72 patients who underwent surgery; a total of 80 implants were placed in the maxillary or mandibular molar region. Patients were divided into two groups according to the diameter of the implant, and were followed up for six years after the final setting of the prosthetics. In the test group, 40 implants with 6-mm diameter were inserted; in the control group, 40 standard diameter implants were inserted. Using panoramic radiographs, we investigated mesial and distal marginal bone levels around the implant fixtures. Results: After the first implant surgery, three implants, including one wide diameter and two standard diameter implants, failed due to lack of osseointegration. We did not note any fixture fracture during the six-year follow-up. After loading, we observed a six-year survival rate of 97.29% with no statistically significant difference from standard diameter implants, with a survival rate of 94.87%. Conclusions: This study shows that 6-mm diameter implants may be considered in the presence of adequate alveolar ridge width in the posterior maxillary and mandibular regions.

An Overview on Thermosensitive Oral Gel Based on Poloxamer 407.

In this review, we describe the application of thermosensitive hydrogels composed of poloxamer in medicine, especially for oral cavities. Thermosensitive hydrogels remain fluid at room temperature; at body temperature, they become more viscous gels. In this manner, the gelling system can remain localized for considerable durations and control and prolong drug release. The chemical structure of the poloxamer triblock copolymer leads to an amphiphilic aqueous solution and an active surface. Moreover, the poloxamer can gel by forming micelles in an aqueous solution, depending on its critical micelle concentration and critical micelle temperature. Owing to its controlled-release effect, a thermosensitive gel based on poloxamer 407 (P407) is used to deliver drugs with different characteristics. As demonstrated in studies on poloxamer formulations, an increase in gelling viscosity decreases the drug release rate and gel dissolution time to the extent that it prolongs the drug's duration of action in disease treatment. This property is used for drug delivery and different therapeutic applications. Its unique route of administration, for many oral diseases, is advantageous over traditional routes of administration, such as direct application and systemic treatment. In conclusion, thermosensitive gels based on poloxamers are suitable and have great potential for oral disease treatment.

Hydrogen-rich water ameliorates rat placental stress induced by water restriction.

Dehydration is one of the intrauterine abnormalities that could lead to fetal growth retardation and to increase the risk of a variety of adult diseases later in life. This study were to determine the impact of hydrogen-rich water (HRW) supplementation on placental angiotensin II type 1 receptor and placental oxidative stress induced by water restriction. Pregnant Wistar rat were randomly assigned to one of the three groups (n =12 per group). In control group, pure water and food were supplied ad libitum. Water restriction group and HRW group were respectively given pure water and HRW with free access to food, excepting only one hour was available for drinking from day 7 to day 17 of pregnancy. The placental damages and biomarkers of stress were detected by histopathology, immunohistochemistry and western blot, as well as serological test were performed. We demonstrated that maternal water restriction resulted in reduced urine volume and increased serum osmotic pressure, along with decreased fetus weight and crown-rump length. Although placental weight and the number of fetuses had no significant difference among groups, the placental efficiency significantly increased after the oral administration of HRW to the mothers. Meanwhile, the serological derivatives of reactive oxygen metabolites decreased, a significant improvement of placental microstructure with more developed junctional zone and denser labyrinth was manifested, the upregulated expression of angiotensin II type 1 receptor, nuclear factoκB, malondialdehyde, 8-hydroxydeoxyguanosine, p38, c-Jun N-terminal kinase and down-regulation of superoxide dismutase were revealed in the placenta. Collectively, HRW administration is able to effectively attenuate placental stress induced by water restriction.