Effects of dissolved oxygen changes in the benthic environment on phosphorus flux at the sediment-water interface in a coastal brackish lake.

In semi-enclosed coastal brackish lakes, changes in dissolved oxygen in the bottom layer due to salinity stratification can affect the flux of phosphorus (P) at the sediment-water interface, resulting in short- and long-term water quality fluctuations in the water column. In this study, the physicochemical properties of the water layers and sediments at five sites in Saemangeum Lake were analyzed in spring and autumn for four years, and phosphorus release experiments from sediments were conducted for 20 days under oxic and anoxic conditions during the same period. Sediment total phosphorus (T-P) decreased in autumn compared to spring due to mineralization of organic bound phosphorus, which was the most dominant P fraction. This may be related to the increase in the ratio of PO4-P to T-P in bottom waters in autumn, when hypoxia was frequently observed. The difference in P fluxes between oxic and anoxic conditions indicated that during autumn, as compared to spring, the release of phosphorus could have a more immediate impact on the water column during the formation of hypoxia/anoxia. The main factors influencing changes in P fluxes from sediments were identified through redundancy analysis. Additionally, based on the results of multiple regression analysis, sediment TOC, sediment non-apatite phosphorus, porewater pH, and porewater PO4-P were determined to be the most significant factors affecting P fluxes from sediments, depending on the season or redox conditions. Recently, the increased influx of seawater into Saemangeum Lake has been shown to contribute to water quality improvements in the water column due to a strong dilution effect. However, the sediment environment has shifted towards a more reduced state, leading to increased P release under anoxic conditions. Therefore, for future water quality management within the lake, it is necessary to consistently address the recurring hypoxia and continuously monitor phosphorus dynamics.

Injuries and Illness during the 2019 Gwangju FINA and Masters World Championships in Elite and Amateur Athletes.

Comparative analysis of injury and illness prevalence in elite and amateur athletes provides the basis for the development of tailored prevention programs. The authors analyzed the differences in frequency and characteristics of injuries and illnesses which occurred in elite and amateur athletes during the 2019 Gwangju Federation Internationale de Natation (FINA) and Masters World Championships. The 2019 FINA World Championships hosted 3095 athletes in the disciplines of swimming, diving, high diving, artistic swimming, water polo, and open water swimming. While the 2019 Masters World Championships hosted 4032 athletes in swimming, diving, artistic swimming, water polo, and open water swimming. All medical records were electrically recorded in every venue as well as the central medical center located at the athlete's village. More elite athletes visited clinics than amateur athletes during the events (15.0 vs 8.6%, p<0.05) despite the ages of amateur athletes being higher than elite athletes (41.0±15.0 vs 22.4±5.6 years, p<0.01). Elite athletes complained mainly of musculoskeletal problems (69%), while amateur athletes complained of both musculoskeletal (38%) and cardiovascular (8%) problems. The most frequent injury in elite athletes was due to overuse in the shoulder joints, while that of amateur athletes was traumatic injuries involving feet and hands. The most common illness was respiratory infection in both elite and amateur athletes, while cardiovascular events occured only in amateur athletes. As the risk of injury varies in elite and amateur athletes, tailored preventive measures should be prepared. Furthermore, preventive measures of cardiovascular events should focus on amateur sports events.

Osseointegration of 3D-printed titanium implants with surface and structure modifications.

BACKGROUND: The purpose of this study was to establish a mechanical and histological basis for the development of biocompatible maxillofacial reconstruction implants by combining 3D-printed porous titanium structures and surface treatment. Improved osseointegration of 3D-printed titanium implants for reconstruction of maxillofacial segmental bone defect could be advantageous in not only quick osseointegration into the bone tissue but also in stabilizing the reconstruction. METHODS: Various macro-mesh titanium scaffolds were fabricated by 3D-printing. Human mesenchymal stem cells were used for cell attachment and proliferation assays. Osteogenic differentiation was confirmed by quantitative polymerase chain reaction analysis. The osseointegration rate was measured using micro computed tomography imaging and histological analysis. RESULTS: In three dimensional-printed scaffold, globular microparticle shape was observed regardless of structure or surface modification. Cell attachment and proliferation rates increased according to the internal mesh structure and surface modification. However, osteogenic differentiation in vitro and osseointegration in vivo revealed that non-mesh structure/non-surface modified scaffolds showed the most appropriate treatment effect. CONCLUSION: 3D-printed solid structure is the most suitable option for maxillofacial reconstruction. Various mesh structures reduced osteogenesis of the mesenchymal stem cells and osseointegration compared with that by the solid structure. Surface modification by microarc oxidation induced cell proliferation and increased the expression of some osteogenic genes partially; however, most of the markers revealed that the non-anodized solid scaffold was the most suitable for maxillofacial reconstruction.

Characterization of Non-Invasively Induced Post-Traumatic Osteoarthritis in Mice.

The pathophysiology of post-traumatic arthritis (PTOA) is not fully understood. This study used non-invasive repetitive mechanical loading (ML) mouse models to study biochemical, biomechanical, and pain-related behavioral changes induced in mice. Mouse models reflected the effects of the early stages of PTOA in humans. For the PTOA model, cyclic comprehensive loading (9N) was applied to each mouse's left knee joint. ML-induced biochemical and molecular changes were analyzed after loading completion. Cartilage samples were examined using gene expression analysis. Tissue sections were used in subsequent OA severity scoring. Biomechanical features and pain-related behavior were studied after 24 h and three weeks post-ML sessions to examine the development of PTOA. The loaded left knee joint showed a greater ROS/RNS signal than the right knee, which was not loaded. There was a significant increase in cartilage damage and MMP activity in the mechanically loaded joints relative to non-loaded control knee joints. Similarly, we found a difference in the viscoelastic tangent, which highlights significant changes in mechanical properties. Biochemical analyses revealed significant increases in total NO, caspase-3 activity, H2O2, and PGE2 levels. Gene expression analysis highlighted increased catabolism (MMP-13, IL-1ß, TNF-α) with a concomitant decrease in anabolism (ACAN, COL2A1). Histopathology scores clearly indicated increases in OA progression and synovitis. The gait pattern was significantly altered, suggesting signs of joint damage. This study showed that biomechanical, biochemical, and behavioral characteristics of the murine PTOA groups are significantly different from the control group. These results confirm that the current mouse model can be considered for translational PTOA studies.

Biomechanical Efficacy and Effectiveness of Orthodontic Treatment with Transparent Aligners in Mild Crowding Dentition-A Finite Element Analysis.

Orthodontic treatment increasingly involves transparent aligners; however, biomechanical analysis of their treatment effects under clinical conditions is lacking. We compared the biomechanical efficacy and effectiveness of orthodontic treatment with transparent aligners and of fixed appliances in simulated clinical orthodontic treatment conditions using orthodontic finite element (FE) models. In the FE analysis, we used Model Activation/De-Activation analysis to validate our method. Fixed appliances and 0.75-mm and 0.5-mm thick transparent aligners were applied to a tooth-alveolar bone FE model with lingually-inclined and axially-rotated central incisors. Compared to the fixed appliance, the 0.75-mm and 0.5-mm transparent aligners induced 5%, 38%, and 28% and 21%, 62%, and 34% less movement of the central incisors and principal stress of the periodontal ligament and of the alveolar bone, respectively, for lingual inclination correction. For axial-rotation correction, these aligners induced 22%, 37%, and 40% and 28%, 67%, and 48% less tooth movement and principal stress of the periodontal ligament and of the alveolar bone, respectively. In conclusion, transparent aligners induced less tooth movement, it is sufficient for orthodontic treatment, but 0.5-mm aligners should be used for only mild corrections. Additionally, the Model Activation/De-Activation analysis method is suitable for FE analysis of orthodontic treatment reflecting clinical treatment conditions.

3D-printed, bioactive ceramic scaffold with rhBMP-2 in treating critical femoral bone defects in rabbits using the induced membrane technique.

Although autogenous bone grafts are an optimal filling material for the induced membrane technique, limited availability and complications at the harvest site have created a need for alternative graft materials. We aimed to investigate the effect of an rhBMP-2-coated, 3D-printed, macro/microporous CaO-SiO2 -P2 O5 -B2 O3 bioactive ceramic scaffold in the treatment of critical femoral bone defects in rabbits using the induced membrane technique. A 15-mm segmental bone defect was made in the metadiaphyseal area of the distal femur of 14 rabbits. The defect was filled with polymethylmethacrylate cement and stabilized with a 2.0 mm locking plate. After the membrane matured for 4 weeks, the scaffold was implanted in two randomized groups: Group A (3D-printed bioceramic scaffold) and Group B (3D-printed, bioceramic scaffold with rhBMP-2). Eight weeks after implantation, the radiographic assessment showed that the healing rate of the defect was significantly higher in Group B (7/7, 100%) than in Group A (2/7, 29%). The mean volume of new bone formation around and inside the scaffold doubled in Group B compared to that in Group A. The mean static and dynamic stiffness were significantly higher in Group B. Histological examination revealed newly formed bone in both groups. Extensive cortical bone formation along the scaffold was found in Group B. Successful bone reconstruction in critical-sized bone defects could be obtained using rhBMP-2-coated, 3D-printed, macro/microporous bioactive ceramic scaffolds. This grafting material demonstrated potential as an alternative graft material in the induced membrane technique for reconstructing critical-sized bone defects.

Comparative Analysis of Stress in the Periodontal Ligament and Center of Rotation in the Tooth after Orthodontic Treatment Depending on Clear Aligner Thickness-Finite Element Analysis Study.

Lately, in orthodontic treatments, the use of transparent aligners for the correction of malocclusions has become prominent owing to their intrinsic advantages such as esthetics, comfort, and minimal maintenance. Attempts at improving upon this technology by varying various parameters to investigate the effects on treatments have been carried out by several researchers. Here, we aimed to investigate the biomechanical and clinical effects of aligner thickness on stress distributions in the periodontal ligament and changes in the tooth's center of rotation. Dental finite element models comprising the cortical and cancellous bones, gingiva, teeth, and nonlinear viscoelastic periodontal ligaments were constructed, validated, and used together with aligner finite element models of different aligner thicknesses to achieve the goal of this study. The finite element analyses were conducted to simulate the actual orthodontic aligner treatment process for the correction of malocclusions by generating pre-stresses in the aligner and allowing the aligner stresses to relax to induce tooth movement. The results of the analyses showed that orthodontic treatment in lingual inclination and axial rotation with a 0.75 mm-thick aligner resulted in 6% and 0.03% higher principal stresses in the periodontal ligament than the same treatment using a 0.05 mm-thick aligner, respectively. Again, for both aligner thicknesses, the tooth's center of rotation moved lingually and towards the root direction in lingual inclination, and diagonally from the long axis of the tooth in axial rotation. Taken together, orthodontic treatment for simple malocclusions using transparent aligners of different thicknesses will produce a similar effect on the principal stresses in the periodontal ligament and similar changes in the tooth's center of rotation, as well as sufficient tooth movement. These findings provide orthodontists and researchers clinical and biomechanical evidence about the effect of transparent aligner thickness selection and its effect on orthodontic treatment.

Modeling behaviors of permeable non-spherical micro-plastic aggregates by aggregation/sedimentation in turbulent freshwater flow.

This study developed and evaluated a behavior model for permeable non-spherical micro-plastic aggregates in a turbulent flow of freshwater based on fractal theory, as conducting experimental and modeling studies. Laboratory-scale experiments evaluated attachment efficiency α to aggregation kinetics in an aquatic environment (pH 6, 20 â„ƒ) of the electrolyte (Al3+). The experimental α was dependent on characteristics of plastics (type, size, and density) and ranged from 0.062 to 0.2772 (averaging 0.1) with a high correlation with the modeled α (R2 > 0.92). Model validation was conducted under two simulation conditions: one drawn from a previously published study of impermeable spherical aggregates and the other based on fractal theory. The simulations verified the limited primary particle size with the lowest retention rate based on the previous study but it was difficult to determine the specific particle size with the lowest retention rate as a limiting factor. The sum of residual errors for aggregation/sedimentation between the two types of structures showed an overestimation of spherical structures. Such overestimation influenced the aggregate number concentration and distribution pattern. Therefore, the model needs to more detailed express the aggregation mechanism of permeable non-spherical aggregate structures in terms of surface growth.

Mechanical Assessment of Fatigue Characteristics between Single- and Multi-Directional Cyclic Loading Modes on a Dental Implant System.

Mechanical testing based on ISO 14801 standard is generally used to evaluate the performance of the dental implant system according to material and design changes. However, the test method is difficult to reflect on the clinical environment because the ISO 14801 standard does not take into account the various loads from different directions during chewing motion. In addition, the fracture pattern of the implant system can occur both in the horizontal and the vertical directions. Therefore, the purpose of this study was to compare fatigue characteristics and fracture patterns between single directional loading conditions based on the ISO 14801 standard and multi-directional loading condition. Firstly, the static test was performed on five specimens to derive the fatigue load, and the fatigue load was chosen as 40% of the maximum load measured in the static test. Subsequently, the fatigue test was performed considering the single axial/occlusal (AO), AO with facial/lingual (AOFL) and AO with mesial/distal (AOMD) directions, and five specimens were used for each fatigue loading modes. In order to analyze the fatigue characteristics, the fatigue cycle at the time of specimen fracture and displacement change of the specimen every 500 cycles were measured. Field emission scanning electron microscopy (FE-SEM) was used to analyze the fracture patterns and the fracture surface. Compared to the AO group, the fatigue cycle of the AOFL and AOMD groups showed lower about five times, while the displacement gradually increased with every 500 cycles. From FE-SEM results, there were no different surface morphology characteristics among three groups. However, the AOMD group showed a vertical slip band. Therefore, our results suggest that the multi-directional loading mode under the worst-case environment can reproduce the vertical fracture pattern in the clinical situation and may be essential to reflect on the dental implant design including connection types and surface treatments.

Effect of guided bone regeneration on bone quality surrounding dental implants.

Bone quality as well as its quantity at the implant interface is responsible for determining stability of the implant system. The objective of this study is to examine the nanoindentation based elastic modulus (E) at different bone regions adjacent to titanium dental implants with guided bone regeneration (GBR) treated with DBM and BMP-2 during different post-implantation periods. Six adult male beagle dogs were used to create circumferential defects with buccal bone removal at each implantation site of mandibles. The implant systems were randomly assigned to only GBR (control), GBR with demineralized bone matrix (DBM), and GBR with DBM + recombinant human bone morphogenetic protein-2 (rhBMP-2) (BMP) groups. Three animals were sacrificed at each 4 and 8 weeks of post-implantation healing periods. Following buccolingual dissection, the E values were assessed at the defects (Defect), interfacial bone tissue adjacent to the implant (Interface), and pre-existing bone tissue away from the implant (Pre-existing). The E values of BMP group had significantly higher than control and DBM groups for interface and defect regions at 4 weeks of post-implantation period and for the defect region at 8 weeks (p < 0.043). DBM group had higher E values than control group only for the defect region at 4 weeks (p < 0.001). The current results indicate that treatment of rhBMP-2 with GBR accelerates bone tissue mineralization for longer healing period because the GBR likely facilitates a microenvironment to provide more metabolites with open space of the defect region surrounding the implant.

Relationships of bone characteristics in MYO9B deficient femurs.

The objective of this study was to examine relationships among a variety of bone characteristics, including volumetric, mineral density, geometric, dynamic mechanical analysis, and static fracture mechanical properties. As MYO9B is an unconventional myosin in bone cells responsible for normal skeletal growth, bone characteristics of wild-type (WT), heterozygous (HET), and MYO9B knockout (KO) mice groups were compared as an animal model to express different bone quantity and quality. Forty-five sex-matched 12-week-old mice were used in this study. After euthanization, femurs were isolated and scanned using microcomputed tomography (micro-CT) to assess bone volumetric, tissue mineral density (TMD), and geometric parameters. Then, a non-destructive dynamic mechanical analysis (DMA) was performed by applying oscillatory bending displacement on the femur. Finally, the same femur was subject to static fracture testing. KO group had significantly lower length, bone mineral density (BMD), bone mass and volume, dynamic and static stiffness, and strength than WT and HET groups (p < 0.019). On the other hand, TMD parameters of KO group were comparable with those of WT group. HET group showed volumetric, geometric, and mechanical properties similar to WT group, but had lower TMD (p < 0.014). Non-destructive micro-CT and DMA parameters had significant positive correlations with strength (p < 0.015) without combined effect of groups and sex on the correlations (p > 0.077). This comprehensive characterization provides a better understanding of interactive behavior between the tissue- and organ-level of the same femur. The current findings elucidate that MYO9B is responsible for controlling bone volume to determine the growth rate and fracture risk of bone.

Successful extracorporeal life support in respiratory failure after copper sulphate ingestion.

A 44-year-old woman intentionally ingested a solution of copper sulphate. She had minimal intravascular haemolysis and methemoglobinaemia but developed acute respiratory distress syndrome (ARDS) 4 hours after acute copper sulphate poisoning. This required extracorporeal membrane oxygenation (ECMO) management in the intensive care unit. Subsequently, she improved clinically and was successfully weaned from ECMO. Acute copper sulphate poisoning can cause severe pulmonary toxicity even in the absence of other serious symptoms. Therefore, a physician treating acute copper sulphate poisoning should look out for respiratory symptoms even in the absence of other common symptoms. We suggest early initiation of venovenous ECMO in those with ARDS following copper sulphate poisoning.

Immediate mechanical stability of threaded and porous implant systems.

BACKGROUND: Primary stability of a dental implant system is an essential factor to maintain its long-term success. Thus, the objective of this study was to examine whether primary stability is different between threaded and porous dental implant systems placed in artificial bone blocks and human cadaveric mandibular bone. MATERIALS AND METHODS: Forty-two threaded and 42 highly porous dental implants were placed in artificial polyurethane bone foams with 7 different thicknesses (3.5 to 12mm). In addition, 11 threaded and 11 porous implants were installed in 8 edentulous mandibles of human cadavers. Implant stability quotient values, insertion torque, static and dynamic stiffness, and viscoelastic tan δ of each implant system were measured. Mean gray values were obtained at the implantation sites in the human mandible. FINDINGS: The porous implant group had substantially lower implant stability quotient values and insertion torque values than the threaded implant group that were equal or >5.5mm in thickness of the artificial bone block (p<0.026) with the exception of 8.5mm thickness, while static and dynamic stiffness values were not different between the two implant groups greater than 5.5mm in thickness (p>0.132). Static and dynamic stiffness values of the porous group were significantly greater than the thread group in the human mandibular bone (p<0.015). INTERPRETATION: The porous layer supports axial loading better than lateral and shear loading of the dental implant system. This result indicates that trabecular shaped architecture of the porous layer may provide sufficient anchorage compromising reduction of the axial primary stability of the porous implant system to be comparable with the threaded implant system.

The RhoGAP Myo9b Promotes Bone Growth by Mediating Osteoblastic Responsiveness to IGF-1.

The Ras homolog A (RhoA) subfamily of Rho guanosine triphosphatases (GTPases) regulates actin-based cellular functions in bone such as differentiation, migration, and mechanotransduction. Polymorphisms or genetic ablation of RHOA and some of its regulatory guanine exchange factors (GEFs) have been linked to poor bone health in humans and mice, but the effects of RhoA-specific GTPase-activating proteins (GAPs) on bone quality have not yet been identified. Therefore, we examined the consequences of RhoGAP Myo9b gene knockout on bone growth, phenotype, and cellular activity. Male and female mice lacking both alleles demonstrated growth retardation and decreased bone formation rates during early puberty. These mice had smaller, weaker bones by 4 weeks of age, but only female KOs had altered cellular numbers, with fewer osteoblasts and more osteoclasts. By 12 weeks of age, bone quality in KOs worsened. In contrast, 4-week-old heterozygotes demonstrated bone defects that resolved by 12 weeks of age. Throughout, Myo9b ablation affected females more than males. Osteoclast activity appeared unaffected. In primary osteogenic cells, Myo9b was distributed in stress fibers and focal adhesions, and its absence resulted in poor spreading and eventual detachment from culture dishes. Similarly, MC3T3-E1 preosteoblasts with transiently suppressed Myo9b levels spread poorly and contained decreased numbers of focal adhesions. These cells also demonstrated reduced ability to undergo IGF-1-induced spreading or chemotaxis toward IGF-1, though responses to PDGF and BMP-2 were unaffected. IGF-1 receptor (IGF1R) activation was normal in cells with diminished Myo9b levels, but the activated receptor was redistributed from stress fibers and focal adhesions into nuclei, potentially affecting receptor accessibility and gene expression. These results demonstrate that Myo9b regulates a subset of RhoA-activated processes necessary for IGF-1 responsiveness in osteogenic cells, and is critical for normal bone formation in growing mice. © 2017 American Society for Bone and Mineral Research.

Micro-Computed Tomography of Tooth Volume Changes Following Post Removal.

PURPOSE: To measure tooth volume change before and after post removal using micro-CT and to compare the difference among various combinations of prefabricated post and cement systems. MATERIALS AND METHODS: Forty-eight extracted maxillary anterior teeth and mandibular canines were sectioned 13 mm from the apex. Root canals were properly instrumented. Preparations were filled with gutta percha using lateral condensation. Post space was prepared with a touch and heat device, leaving 5 mm of gutta percha from the apex. Specimens were scanned with micro-CT to establish objective baseline volume and divided into two groups of post systems: stainless steel (SS) ParaPost and glass-fiber reinforced composite (FRC) post. Half the posts for each group were cemented with Ketac Cem radiopaque glass-ionomer cement, and the other half with SpeedCEM dual-curing resin cement. The posts and residual cement were removed by the same operator, using the ultrasonic vibration technique under an endodontic operating microscope. The remaining tooth root structure was scanned again using micro-CT with volume reported (mm3 ). The statistical difference between the combination of posts and cements was measured using the Kruskal-Wallis ANOVA test (α = 0.001). The independent variables were evaluated separately using post hoc Tukey examination to determine which groups resulted in a statistically significant difference. RESULTS: There was a statistical difference of tooth root volume change among the groups. Post hoc exam revealed a statistically significant difference in tooth root volume change between group 1 (SS + GI) and the other groups (α = 0.0002). CONCLUSION: Compared to other post and cement combinations, serrated parallel-sided SS posts cemented with GI cement had the most tooth root structure loss upon post removal using the ultrasonic vibration technique.

Biomimetic whitlockite inorganic nanoparticles-mediated in situ remodeling and rapid bone regeneration.

Bone remodeling process relies on complex signaling pathway between osteoblasts and osteoclasts and control mechanisms to achieve homeostasis of their growth and differentiation. Despite previous achievements in understanding complicated signaling pathways between cells and bone extracellular matrices during bone remodeling process, a role of local ionic concentration remains to be elucidated. Here, we demonstrate that synthetic whitlockite (WH: Ca18Mg2(HPO4)2(PO4)12) nanoparticles can recapitulate early-stage of bone regeneration through stimulating osteogenic differentiation, prohibiting osteoclastic activity, and transforming into mechanically enhanced hydroxyapatite (HAP)-neo bone tissues by continuous supply of PO43- and Mg2+ under physiological conditions. In addition, based on their structural analysis, the dynamic phase transformation from WH into HAP contributed as a key factor for rapid bone regeneration with denser hierarchical neo-bone structure. Our findings suggest a groundbreaking concept of 'living bone minerals' that actively communicate with the surrounding system to induce self-healing, while previous notions about bone minerals have been limited to passive products of cellular mineralization.

Primary stability and viscoelastic displacement of mini-implant system under loading.

BACKGROUND: The objectives of the current study were to examine the effects of mini-implant diameters on 1) primary stability before bone properties are changed by active peri-implant bone remodeling and 2) the time-dependent displacement of mini-implant systems in bone under a functional radial loading and their associations with bone mineral density. METHODS: Twenty one, 8mm length mini-implants (7 each for 1.4mm, 1.6mm, and 2mm diameters) were placed in mandibular sections of human cadavers (4 males and 3 females, average 69.7 (SD 13.1) years of age). Displacement of the mini-implant in wet bone was assessed during initial and subsequent continuous radial loading of 2N in the mediolateral direction for 2h. Mean, standard deviation and coefficient of variation of peri-implant bone mineral density were obtained using histograms of cone-beam computed tomography attenuation values. The cortical thickness along with the miniscrew site was also measured. FINDINGS: The primary stability and displacement of mini-implants in bone were not significantly different between the 3 diameter groups (p>0.147, n=21). Moderate positive correlations of time-dependent viscoelastic displacement (creep) were found with bone mineral density variability independent of the mini-implant diameters (p>0.11). INTERPRETATION: The post-implantation displacements of mini-implant suggested that the orthodontic treatment loading can develop micromotion between the mini-implant and surrounding bone leading to reduction of its primary stability. Current findings also provide an insight that peri-implant bone mineral density variability plays an important role in controlling displacement of the mini-implant, which determine its stability during early and prolonged orthodontic treatment loading periods.

Phenomena of Nano- and Micro-Pore Formation on Ti-(10~50)Ta Alloys by Plasma Electrolytic Oxidation for Dental Implants.

In this study, the phenomena of nano and micro-pore formation on Ti-(10~50)Ta alloys by plasma electrolytic oxidation for dental implants was investigated using various experimental techniques. The Ti­xTa alloys having Ta contents of 10, 30, and 50 wt.% were prepared using arc-melting vacuum furnace. Micro-pore formation was performed using a potentiostat in 1 M H3PO4 electrolyte by using a potentiostat at various applied voltage (180 V, 210 V, and 240 V). The microstructure of Ti­xTa alloys changed from α' phase to ß + α″ phase with Ta content increased. The applied potential increased, the numbers of micro-pore per unit area decreased, whereas the area ratio of occupied by micro-pores increased. The Ta contents increased, the numbers of micro-pore per unit area decreased, whereas the area ratio of occupied by micro-pores increased at 210 V and 240 V. The thickness of oxide layer and micro-pore size can be controlled by applied potential.

Surface Characteristics of Nano-Structured Silicon/Hydroxyapatite Deposition onto the Ti-Nb-Zr Alloy.

The Ti-Nb-Zr alloy was manufactured with 35 wt% of Nb and 10 wt% of Zr by arc melting furnace to be a beta phase. Electrochemical deposition of Si substituted Ca/P was performed by pulsing the potential with a method of cyclic voltammetry, and changed cyclic time between 10, 30, 70, and 150. The electrolyte was prepared by dissolving the reagent-grade chemicals: Ca(NO3)2, NH4H2PO4, and Na2SiO3 x 9H20 to be 1.67 of Ca/P ratio and silicon contents were controlled to be 1 wt%. The surface characteristics were observed by field-emission scanning electron microscopy, X-ray diffractometer, and electrochemical corrosion as a potentiodynamic test. The Si substituted hydroxyapatite layer was successfully formed on the Ti-35Nb-10Zr alloy substrate by electrochemical deposition. A surface morphologies showed needle like shape at 10 cycles, then changed to be a circular with increment of cycles. The Ca/P ratio was the range between 1.5 and 2.0, the crystalline of hydroxyapatite could be confirmed. The corrosion behavior of Si-HA deposition was related with surface shape and thickness by increment, of cyclic times. Higher cyclic times of deposition had higher corrosion potential and current density than that of lower cyclic surface.

Mechanical properties of bone tissues surrounding dental implant systems with different treatments and healing periods.

OBJECTIVES: The objective of the current study was to examine whether the nanoindentation parameters can assess the alteration of bone quality resulting from different degrees of bone remodeling between bone tissue ages around the dental implant interface with different treatments and healing periods. MATERIALS AND METHODS: Dental implants were placed in mandibles of six male dogs. Treatment groups included: resorbable blast media-treated titanium (Ti) implants, alumina-blasted zirconia implants (ATZ), alumina-blasted zirconia implants applied with demineralized bone matrix (ATZ-D), and alumina-blasted zirconia implants applied with rhBMP-2 (ATZ-B). Nanoindentation modulus (E), hardness (H), viscosity (η), and viscoelastic creep (Creep/P max) were measured for new and old bone tissues adjacent to the implants at 3 and 6 weeks of post-implantation. A total of 945 indentations were conducted for 32 implant systems. RESULTS: Significantly lower E, H, and η but higher Creep/P max were measured for new bone tissues than old bone tissues, independent of treatments at both healing periods (p < 0.001). All nanoindentation parameters were not significantly different between healing periods (p > 0.568). ATZ-D and ATZ-B implants had the stiffer slope of correlation between E and Creep/P max of the new bone tissue than Ti implant (p < 0.039). CONCLUSIONS: Current results indicated that, in addition to elastic modulus and plastic hardness, measurement of viscoelastic properties of bone tissue surrounding the implant can provide more detailed information to understand mechanical behavior of an implant system. CLINICAL RELEVANCE: Ability of energy absorption in the interfacial bone tissue can play a significant role in the long-term success of a dental implant system.