Long-term efficacy, safety and biocompatibility of a novel sirolimus eluting iron bioresorbable scaffold in a porcine model.

Iron is considered as an attractive alternative material for bioresorbable scaffolds (BRS). The sirolimus eluting iron bioresorbable scaffold (IBS), developed by Biotyx Medical (Shenzhen, China), is the only iron-based BRS with an ultrathin-wall design. The study aims to investigate the long-term efficacy, safety, biocompatibility, and lumen changes during the biodegradation process of the IBS in a porcine model. A total of 90 IBSs and 70 cobalt-chromium everolimus eluting stents (EES) were randomly implanted into nonatherosclerotic coronary artery of healthy mini swine. The multimodality assessments including coronary angiography, optical coherence tomography, micro-computed tomography, magnetic resonance imaging, real-time polymerase chain reaction (PCR), and histopathological evaluations, were performed at different time points. There was no statistical difference in area stenosis between IBS group and EES group at 6 months, 1year, 2 years and 5 years. Although the scaffolded vessels narrowed at 9 months, expansive remodeling with increased mean lumen area was found at 3 and 5 years. The IBS struts remained intact at 6 months, and the corrosion was detectable at 9 months. At 5 years, the iron struts were completely degraded and absorbed in situ, without in-scaffold restenosis or thrombosis, lumen collapse, aneurysm formation, and chronic inflammation. No local or systemic toxicity and abnormal histopathologic manifestation were found in all experiments. Results from real-time PCR indicated that no sign of iron overload was reported in scaffolded segments. Therefore, the IBS shows comparable efficacy, safety, and biocompatibility with EES, and late lumen enlargement is considered as a unique feature in the IBS-implanted vessels.

Biomaterials science and surface engineering strategies for dental peri-implantitis management.

Peri-implantitis is a bacterial infection that causes soft tissue inflammatory lesions and alveolar bone resorption, ultimately resulting in implant failure. Dental implants for clinical use barely have antibacterial properties, and bacterial colonization and biofilm formation on the dental implants are major causes of peri-implantitis. Treatment strategies such as mechanical debridement and antibiotic therapy have been used to remove dental plaque. However, it is particularly important to prevent the occurrence of peri-implantitis rather than treatment. Therefore, the current research spot has focused on improving the antibacterial properties of dental implants, such as the construction of specific micro-nano surface texture, the introduction of diverse functional coatings, or the application of materials with intrinsic antibacterial properties. The aforementioned antibacterial surfaces can be incorporated with bioactive molecules, metallic nanoparticles, or other functional components to further enhance the osteogenic properties and accelerate the healing process. In this review, we summarize the recent developments in biomaterial science and the modification strategies applied to dental implants to inhibit biofilm formation and facilitate bone-implant integration. Furthermore, we summarized the obstacles existing in the process of laboratory research to reach the clinic products, and propose corresponding directions for future developments and research perspectives, so that to provide insights into the rational design and construction of dental implants with the aim to balance antibacterial efficacy, biological safety, and osteogenic property.

Comparison of microstructure, mechanical property, and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys.

Mg-1 wt.% Li-1 wt.% Ca (LX11) and Mg-4 wt.% Li-1 wt.% Ca (LX41) alloys share the same hexagonal closed-packed crystalline structure. However, the differences in microstructure, mechanical properties, and degradation rates between the two alloys are not well understood. Hereby, the above three aspects of LX11 and LX41 alloys were studied via optical microscopy, tensile tests, and electrochemical polarization and electrochemical impedance spectroscopy, together with hydrogen evolution. The concentration of the released Mg2+, Ca2+, and Li+ ions was analyzed using a flame atomic absorption spectrophotometer. Results demonstrated that the LX11 alloy was composed of finer α-Mg grains, fewer twins, and smaller volume fractions of the intermetallic phases Mg2Ca than the LX41 alloy. The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys, a remarkable increase in elongation to failure, and a stable ultimate tensile strength. The LX11 alloy had better corrosion resistance than the LX41 alloy. The release rate of the cations (Mg2+, Ca2+, and Li+) varied significantly with time. The release rate of metallic ions in Hank's solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility. The dealloying corrosion mechanism of the Mg2Ca phase in Mg-Li-Ca alloys was proposed.

Antennal and proboscis sensilla characteristics of Paranthrene tabaniformis (Lepidoptera: Sesiidae).

The poplar clearwing moth, Paranthrene tabaniformis (Lepidoptera: Sesiidae) is a serious wood-boring pest of several trees. The ultramorphology of the antennae and proboscis sensilla of adult P. tabaniformis was examined using scanning electron microscope to determine their structures and sex-specific differences. The results showed that the antennae of both sexes are composed of three segments: scape, pedicel and flagellum. Female antennae are clavate while male antennae are pectinate. The number of flagellomeres for females was significantly greater than for males. Seven different types of sensilla were identified on antennae of both males and females: Böhm sensilla, sensilla squamiformia, sensilla trichodea (three subtypes), sensilla chaetica, sensilla coeloconica, and sensilla auricillica (two subtypes), and apical sensors. Three different types of sensilla were found on the proboscis of adult P. tabaniformis: sensilla styloconica, sensilla chaetica, and sensilla basiconica (three subtypes). The sexual dimorphism difference in the number, distributional pattern, the length and the basal width of various sensilla on the antennae and proboscis were determined. This study clarifies the types and sexual dimorphism of the antennal and proboscis sensilla of adult P. tabaniformis and provides useful theoretical foundations for studies on behavioral mechanisms and functions of sensilla of P. tabaniformis. RESEARCH HIGHLIGHTS: Various types of sensilla on the antennae and proboscis of adults Paranthrene tabaniformis were observed. The sexual dimorphism of various sensilla on the antennae and proboscis were determined.

Biodegradation behavior of micro-arc oxidation coating on magnesium alloy-from a protein perspective.

Protein exerts a critical influence on the degradation behavior of absorbable magnesium (Mg)-based implants. However, the interaction mechanism between protein and a micro-arc oxidation (MAO) coating on Mg alloys remains unclear. Hereby, a MAO coating was fabricated on AZ31 Mg alloy. And its degradation behavior in phosphate buffer saline (PBS) containing bovine serum albumin (BSA) was investigated and compared with that of the uncoated alloy. Surface morphologies and chemical compositions were studied using Field-emission scanning electron microscope (FE-SEM), Fourier transform infrared spectrophotometer (FT-IR) and X-ray diffraction (XRD). The degradation behavior of the bare Mg alloy and its MAO coating was studied through electrochemical and hydrogen evolution tests. Cytotoxicity assay was applied to evaluate the biocompatibility of Mg alloy substrate and MAO coating. Results indicated that the presence of BSA decreased the degradation rate of Mg alloy substrate because BSA (RCH(NH2)COO‾) molecules combined with Mg2+ ions to form (RCH(NH2)COO)2Mg and thus inhibited the dissolution of Mg(OH)2 by impeding the attack of Cl‾ ions. In the case of MAO coated Mg alloy, the adsorption of BSA on MAO coating and the formation of (RCH(NH2)COO)2Mg exhibited a synergistic effect and enhanced the corrosion resistance of the coated alloy significantly. Furthermore, cell bioactive assay suggested that the MAO coating had good viability for MG63 cells due to its high surface area.

Corrosion resistance and antibacterial activity of zinc-loaded montmorillonite coatings on biodegradable magnesium alloy AZ31.

A Zinc-loaded montmorillonite (Zn-MMT) coating was hydrothermally prepared using Zn2+ ion intercalated sodium montmorillonite (Na-MMT) upon magnesium (Mg) alloy AZ31 as bone repairing materials. Biodegradation rate of the Mg-based materials was studied via potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests. Results revealed that both Na-MMT and Zn-MMT coatings exhibited better corrosion resistance in Dulbecco's modified eagle medium (DMEM) + 10% calf serum (CS) than bare Mg alloy AZ31 counterparts. Hemolysis results demonstrated that hemocompatibility of the Na-MMT and Zn-MMT coatings were 5%, and lower than that of uncoated Mg alloy AZ31 pieces. In vitro MTT tests and live-dead stain of osteoblast cells (MC3T3-E1) indicated a significant improvement in cytocompatibility of both Na-MMT and Zn-MMT coatings. Antibacterial properties of two representative bacterial strains associated with device-related infection, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), were employed to explore the antibacterial behavior of the coatings. The measured inhibitory zone and bacterial growth rate confirmed that Zn-MMT coatings exhibited higher suppression toward both E. coli and S. aureus than that of Na-MMT coatings. The investigation on antibacterial mechanism through scanning electron microscopy (SEM) and lactate dehydrogenase (LDH) release assay manifested that Zn-MMT coating led to severe breakage of bacterial membrane of E. coli and S. aureus, which resulted in a release of cytoplasmic materials from the bacterial cells. In addition, the good inhibition of Zn-MMT coatings against E. coli and S. aureus might be attributed to the slow but sustainable release of Zn2+ ions (up to 144 h) from the coatings into the culture media. This study provides a novel coating strategy for manufacturing biodegradable Mg alloys with good corrosion resistance, biocompatibility and antibacterial activity for future orthopedic applications. STATEMENT OF SIGNIFICANCE: The significance of the current work is to develop a corrosion-resistant and antibacterial Zn-MMT coating on magnesium alloy AZ31 through a hydrothermal method. The Zn-MMT coating on magnesium alloy AZ31 shows better corrosion resistance, biocompatibility and excellent antibacterial ability than magnesium alloy AZ31. This study provides a novel coating on Mg alloys for future orthopedic applications.

Design, synthesis and characterization of poly (methacrylic acid-niclosamide) and its effect on arterial function.

We have found that niclosamide induced relaxation of constricted artery. However, niclosamide is insoluble, the low bioavailability and the resultant low plasma concentration limit its potential exertion in vivo. The aim of the present study is to synthesize a soluble poly (methacrylic acid-niclosamide) polymer (PMAN) and study the effects of PMAN on arterial function in vitro and the blood pressure and heart rate of rats in vivo. We synthesized the poly (methacrylic acid-niclosamide) polymer (PMAN), the chemical structure of which was identified by FTIR and 1H NMR spectra. The average molecular weight and polydispersity index of PMAN were 5138 and 1.193 respectively. Compared with niclosamide, the water solubility of niclosamide in PMAN was significantly increased. PMAN showed dose-dependent vasorelaxation effect on rat mesenteric arteries with intact or denuded endothelium in phenylephrine (PE) and high K+ (KPSS)-induced vasoconstriction models in vitro. The efficacy of vasorelaxant effect and the cytotoxic effect of PMAN on vascular smooth muscle cells (A10) were lower than that of niclosamide. The LD50 of PMAN in mice (iv) was 80mg/kg. Venous injection of PMAN (equivalent 5mg niclosamide per kg) showed acute reduction of the rat blood pressure and heart rate in vivo. In conclusion, the solubility of niclosamide was increased in the way of poly (methacrylic acid-niclosamide) polymer, which relaxes the constricted arteries in vitro and reduces the rat blood pressure and heart rate in vivo, indicating that modifying niclosamide solubility through polymerization is a feasible approach to improve its pharmacokinetic profiles for potential clinic application.

Azo polymeric micelles designed for colon-targeted dimethyl fumarate delivery for colon cancer therapy.

UNLABELLED: Colon-targeted drug delivery and circumventing drug resistance are extremely important for colon cancer chemotherapy. Our previous work found that dimethyl fumarate (DMF), the approved drug by the FDA for the treatment of multiple sclerosis, exhibited anti-tumor activity on colon cancer cells. Based on the pharmacological properties of DMF and azo bond in olsalazine chemical structure, we designed azo polymeric micelles for colon-targeted dimethyl fumarate delivery for colon cancer therapy. We synthesized the star-shape amphiphilic polymer with azo bond and fabricated the DMF-loaded azo polymeric micelles. The four-arm polymer star-PCL-azo-mPEG (sPCEG-azo) (constituted by star-shape PCL (polycaprolactone) and mPEG (methoxypolyethylene glycols)-olsalazine) showed self-assembly ability. The average diameter and polydispersity index of the DMF-loaded sPCEG-azo polymeric micelles were 153.6nm and 0.195, respectively. In vitro drug release study showed that the cumulative release of DMF from the DMF-loaded sPCEG-azo polymeric micelles was no more than 20% in rat gastric fluid within 10h, whereas in the rat colonic fluids, the cumulative release of DMF reached 60% in the initial 2h and 100% within 10h, indicating that the DMF-loaded sPCEG-azo polymeric micelles had excellent colon-targeted property. The DMF-loaded sPCEG-azo polymeric micelles had no significant cytotoxicity on colon cancer cells in phosphate buffered solution (PBS) and rat gastric fluid. In rat colonic fluid, the micelles showed significant cytotoxic effect on colon cancer cells. The blank sPCEG-azo polymeric micelles (without DMF) showed no cytotoxic effect on colon cancer cells in rat colonic fluids. In conclusion, the DMF-loaded sPCEG-azo polymeric micelles show colon-targeted DMF release and anti-tumor activity, providing a novel approach potential for colon cancer therapy. STATEMENT OF SIGNIFICANCE: Colon-targeted drug delivery and circumventing drug resistance are extremely important for colon cancer chemotherapy. Our previous work found that dimethyl fumarate (DMF), the approved drug by the FDA for the treatment of multiple sclerosis, exhibited anti-tumor activities on colon cancer cells (Br J Pharmacol. 2015 172(15):3929-43.). Based on the pharmacological properties of DMF and azo bond in olsalazine chemical structure, we designed azo polymeric micelles for colon-targeted dimethyl fumarate delivery for colon cancer therapy. We found that the DMF-loaded sPCEG-azo polymeric micelles showed colon-targeted DMF release and anti-tumor activities, providing a novel approach potential for colon cancer therapy.

In Vitro Corrosion and Cytocompatibility of a Microarc Oxidation Coating and Poly(L-lactic acid) Composite Coating on Mg-1Li-1Ca Alloy for Orthopedic Implants.

Manipulating the degradation rate of biomedical magnesium alloys poses a challenge. The characteristics of a microarc oxidation (MAO), prepared in phytic acid, and poly(L-lactic acid) (PLLA) composite coating, fabricated on a novel Mg-1Li-1Ca alloy, were studied through field emission scanning electron microscopy (FE-SEM), electron probe X-ray microanalysis (EPMA), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion behaviors of the samples were evaluated via hydrogen evolution, potentiodynamic polarization and electrochemical impedance spectroscopy in Hanks' solution. The results indicated that the MAO/PLLA composite coatings significantly enhanced the corrosion resistance of the Mg-1Li-1Ca alloy. MTT and ALP assays using MC3T3 osteoblasts indicated that the MAO/PLLA coatings greatly improved the cytocompatibility, and the morphology of the cells cultured on different samples exhibited good adhesion. Hemolysis tests showed that the composite coatings endowed the Mg-1Li-1Ca alloys with a low hemolysis ratio. The increased solution pH resulting from the corrosion of magnesium could be tailored by the degradation of PLLA. The degradation mechanism of the composite coatings was discussed. The MAO/PLLA composite coating may be appropriate for applications on degradable Mg-based orthopedic implants.

ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

INTRODUCTION: The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. METHODS: A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. RESULTS: No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P < .001). However, the transformation behavior of Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. CONCLUSIONS: The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments.

In vitro cytotoxicity of calcium silicate-containing endodontic sealers.

INTRODUCTION: The cytotoxicity of 2 novel calcium silicate-containing endodontic sealers to human gingival fibroblasts was studied. METHODS: EndoSequence BC (Brasseler, Savannah, GA), MTA Fillapex (Angelus Indústria de Produtos Odontológicos S/A, Londrina, PR, Brazil) and a control sealer (AH Plus; Dentsply DeTrey GmbH, Konstanz, Germany) were evaluated. Human gingival fibroblasts were incubated for 3 days both with the extracts from fresh and set materials in culture medium and cultured on the surface of the set materials in Dulbecco-modified Eagle medium. Fibroblasts cultured in Dulbecco-modified Eagle medium were used as a control group. Cytotoxicity was evaluated by flow cytometry, and the adhesion of the fibroblasts to the surface of the set materials was assessed using scanning electron microscopy. The data of cell cytotoxicity were analyzed statistically using a 1-way analysis of variance test at a significance level of P < .05. RESULTS: Cells incubated with extracts from BC Sealer showed higher viabilities at all extract concentrations than cells incubated with extracts from freshly mixed AH Plus and fresh and set MTA Fillapex, esspecially for the high extract concentrations (1:2 and 1:8 dilutions). Extracts from set MTA Fillapex of 2 weeks and older were more cytotoxic than extracts from freshly mixed and 1-week-old cement. With extract concentrations of 1:32 and lower, MTA Fillapex was no longer cytotoxic. After setting, AH Plus was no longer cytotoxic, and the fibroblast cells grew on set AH Plus equally as well as on BC Sealer. CONCLUSIONS: BC Sealer and MTA Fillapex, the 2 calcium silicate-containing endodontic sealers, exhibited different cytotoxicity to human gingival fibroblasts.

Effects of 5-amino salicylic acid on the expression of multidrug resistance gene in ulcerative colitis.

BACKGROUND/AIMS: To study the effect of drugs on the expression of multidrug resistance gene in ulcerative colitis. METHODOLOGY: The expressions of multidrug resistance (MDR) 1 gene and its product P-Gp were detected by reverse transcription-polymerase chain reaction and immunohistochemistry to realize the impact of drugs on ulcerative colitis. RESULTS: MDR1 gene and P-Gp did not exhibit significant difference (P > 0.05) before and after amino salicylic acid drug treatment. Compared with the control group, their expressions before treatment in the ineffective corticosteroid- and immunosuppressant-treated groups did not exhibit significant difference (P > 0.05). Their pre- and post-treatment expressions in the ineffective groups were compared with those in the normal control group and in the effective group, and significant differences were observed (P < 0.05). CONCLUSIONS: 5-Amino salicylic acid drugs have little effect on the expression of MDR1 and its product P-Gp. The expressions of MDR1 and P-Gp were much higher in groups that showed ineffectiveness for corticosteroids and immunosuppressants after treatment.

Physical properties of 5 root canal sealers.

INTRODUCTION: The aim of this study was to evaluate the pH change, viscosity and other physical properties of 2 novel root canal sealers (MTA Fillapex and Endosequence BC) in comparison with 2 epoxy resin-based sealers (AH Plus and ThermaSeal), a silicone-based sealer (GuttaFlow), and a zinc oxide-eugenol-based sealer (Pulp Canal Sealer). METHODS: ISO 6876/2001 specifications were followed. The pH change of freshly mixed and set sealers was evaluated during periods of 1 day and 5 weeks, respectively. The viscosity was investigated at different injection rates (72, 10, and 5 mm/min) at room temperature by using a syringe-based system that was based on the Instron 3360 series universal testing system. RESULTS: The flow, dimensional change, solubility, and film thickness of all the tested sealers were in agreement with ISO 6876/2001 recommendations. The MTA Fillapex sealer exhibited a higher flow than the Endosequence BC sealer (P < .05). The MTA Fillapex and Endosequence BC sealers showed the highest film thicknesses among the tested samples. The Endosequence BC sealer exhibited the highest value of solubility, which was in accordance with 3% mass fraction recommended by the ISO 6876/2001, and showed an acceptable dimensional change. The MTA Fillapex and Endosequence BC sealers presented an alkaline pH at all times. The pH of fresh samples of the AH Plus and ThermaSeal sealers was alkaline at first but decreased significantly after 24 hours. The viscosity of the tested sealers increased with the decreased injection rates. CONCLUSIONS: The tested sealers were pseudoplastic according to their viscosities as determined in this study. The MTA Fillapex and Endosequence BC sealers each possessed comparable flow and dimensional stability but higher film thickness and solubility than the other sealers tested.

Phase transformation behavior and mechanical properties of thermomechanically treated K3XF nickel-titanium instruments.

INTRODUCTION: The bending and torsional properties of thermomechanically treated K3XF (SybronEndo, Orange, CA) nickel-titanium instruments in relation to their phase transformation behavior were evaluated. METHODS: NiTi instruments K3 (SybronEndo) and K3XF, both in sizes 25/.04 and 40/.04, were examined by differential scanning calorimetry and X-ray diffraction. The metal composition was determined by scanning electron microscopy with X-ray energy-dispersive spectrometric analyses. The bending property of K3 and K3XF instruments was measured in a cantilever-bending test with a maximum deflection of 4.00 mm. A torsional test of the instruments was evaluated according to the American National Standards Institute/American Dental Association Specification No. 28. RESULTS: K3 and K3XF instruments had approximately the same chemical composition with a nickel content of 48-49 atomic %. The differential scanning calorimetry analyses showed that each segment of the K3XF instruments (24.89°C ± 1.98°C) had a higher austenite finish temperature than the K3 instruments (17.63°C ± 1.76°C) (P < .05). The bending load values were significantly lower for K3XF than for K3 in the superelastic ranges (P < .05). There was no statistically significant difference between K3 and K3XF in the maximum torque or maximum angular deflection before failure. The torque at fracture values of K3 and K3XF increased significantly with the diameter (P < .05). CONCLUSIONS: K3XF exhibited different phase transformation behavior and flexibility when compared with K3, which may be attributed to the special heat treatment history of K3XF instruments.

In vitro cytotoxicity evaluation of a novel root repair material.

INTRODUCTION: This study examined the effect of a new bioactive dentin substitute material (Biodentine) on the viability of human gingival fibroblasts. METHODS: Biodentine, White ProRoot mineral trioxide aggregate (MTA), and glass ionomer cement were evaluated. Human gingival fibroblasts were incubated for 1, 3, and 7 days both in the extracts from immersion of set materials in culture medium and directly on the surface of the set materials immersed in culture medium. Fibroblasts cultured in Dulbecco modified Eagle medium were used as a control group. Cytotoxicity was evaluated by flow cytometry, and the adhesion of human gingival fibroblasts to the surface of the set materials was assessed by using scanning electron microscopy. The data of cell cytotoxicity were analyzed statistically by using a one-way analysis of variance test at a significance level of P< .05. RESULTS: Cells exposed to extracts from Biodentine and MTA showed the highest viabilities at all extract concentrations, whereas cells exposed to glass ionomer cement extracts displayed the lowest viabilities (P< .05). There was no significant difference in cell viabilities between Biodentine and MTA during the entire experimental period (P> .05). Human gingival fibroblasts in contact with Biodentine and MTA attached to and spread over the material surface after an overnight culture and increased in numbers after 3 and 7 days of culture. CONCLUSIONS: Biodentine caused gingival fibroblast reaction similar to that by MTA. Both materials were less cytotoxic than glass ionomer cement.

Current challenges and concepts of the thermomechanical treatment of nickel-titanium instruments.

INTRODUCTION: The performance and mechanical properties of nickel-titanium (NiTi) instruments are influenced by factors such as cross-section, flute design, raw material, and manufacturing processes. Many improvements have been proposed by manufacturers during the past decade to provide clinicians with safer and more efficient instruments. METHODS: The mechanical performance of NiTi alloys is sensitive to their microstructure and associated thermomechanical treatment history. Heat treatment or thermal processing is one of the most fundamental approaches toward adjusting the transition temperature in NiTi alloy, which affects the fatigue resistance of NiTi endodontic files. The newly developed NiTi instruments made from controlled memory wire, M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK), or R-phase wire represent the next generation of NiTi alloys with improved flexibility and fatigue resistance. The advantages of NiTi files for canal cleaning and shaping are decreased canal transportation and ledging, a reduced risk of file fracture, and faster and more efficient instrumentation. The clinician must understand the nature of different NiTi raw materials and their impact on instrument performance because many new instruments are introduced on a regular basis. RESULTS: This review summarizes the metallurgical properties of next-generation NiTi instruments, the impact of thermomechanical treatment on instrument flexibility, and the resistance to cyclic fatigue and torsion. CONCLUSIONS: The aim of this review was to provide clinicians with the knowledge necessary for evidence-based practices, maximizing the benefits from the selection and application of NiTi rotary instruments for root canal treatment.

ProFile Vortex instruments after clinical use: a metallurgical properties study.

INTRODUCTION: The aim of the study was to analyze the incidence and mode of ProFile Vortex instrument (Dentsply Tulsa Dental Specialties, Tulsa, OK) defects during a predefined schedule of clinical use by the undergraduate students in a dental school setting and to examine the metallurgical characteristics of unused and clinically used Vortex instruments. METHODS: A total of 2,203 ProFile Vortex instruments discarded after single use from the undergraduate students program over 24 months were collected and examined for defects using a stereomicrosocpe at 10× magnification. The incidence and type of instrument defects or separation were analyzed. The lateral surfaces of part of the defected instruments and fracture surfaces of fractured files were examined using scanning electron microscopy. Unused and clinically used files were examined by differential scanning calorimetry and X-ray diffraction. Vickers hardness of the files was measured with a 200-g load. RESULTS: Only 1 of the 2,203 files fractured during clinical use. The cause of fracture was shear stress, and the file also showed unwinding of the helix structure. None of the remaining 2,202 files exhibited unwinding after clinical use. Blunt apicals were detected in 86 used files (3.9%). Austenite-finish temperatures were very similar for as-received, used files with defects and used files without defects, all exceeding 50°C. No difference in microhardness was detected among these 3 instrument groups. X-ray diffraction results showed that NiTi files had austenite structure at room temperature. CONCLUSIONS: The risk of ProFile Vortex fracture is very low when files are used 1 time by undergraduate students. Unwinding of the files was not detected except for the fractured file. Clinical single use had no detectable effect on austenite-martensite phase transformation of the files. Unused and clinical single-use files contain a similar phase structure at body temperature.

Mechanical properties of controlled memory and superelastic nickel-titanium wires used in the manufacture of rotary endodontic instruments.

INTRODUCTION: The aim of this study was to investigate the structure and mechanical properties of newly developed controlled memory (CM) nickel-titanium wires used in the manufacture of rotary endodontic instruments. METHODS: The composition and the phase transformation behavior of both types of wires were examined by x-ray energy dispersive spectroscopy and differential scanning calorimetry, respectively. Conventional superelastic (SE) nickel-titanium wire was used as a control. The mechanical properties of the wires at selected temperatures (room temperature, 37°C, and 60°C) were evaluated with tensile, cyclic tensile, and cantilever bending tests by using an Instron 3365 universal testing machine. The data of austenitic transformation finishing temperature (A(f)) were analyzed statistically by using 1-way analysis of variance test at a significance level of P < .05. RESULTS: The raw CM wires contained a nickel content of 50.7% ± 0.5% and possessed a relatively higher A(f) than SE wires (P < .05). The critical plateau stress and ultimate tensile strength of the CM wires were lower than they were for the SE wires, but the maximum strain before fracture of the CM wires (58.4% ± 7.5% to 84.7% ± 6.8%) was more than 3 times higher than it was for SE wires (16.7% ± 3.8% to 27.5% ± 5.4%). The maximum strain of the CM wires with a diameter of 1.22 mm tested at room temperature (23°C ± 2°C) was up to 84% ± 6.4%. CM wires were not SE at either room temperature or 37°C; however, they exhibited superelasticity when heated to 60°C. CONCLUSIONS: The raw CM wires exhibited different phase transformation behavior and mechanical properties when compared with SE wires, attributing to the special heat treatment history of CM wires. This study suggested greater flexibility of endodontic instruments manufactured with CM wires than similar instruments made of conventional SE wires.

Ti-Ge binary alloy system developed as potential dental materials.

As-cast Ti-xGe (x = 2, 5, 10, 20 wt %) binary alloys were produced in this work, and various experiments were carried out to investigate the microstructure, mechanical properties, in vitro electrochemical and immersion corrosion behaviors as well as cytotoxicity with as-cast pure Ti as control, aiming to study the feasibility of Ti-xGe alloy system as potential dental materials. The microstructure of Ti-xGe alloys changes from single α-Ti phase to α-Ti + Ti(5)Ge(3) precipitation phase with the increase of Ge content. Mechanical tests show that Ti-5Ge alloy has the best comprehensive mechanical properties. The corrosion behavior of Ti-xGe alloys in artificial saliva with different NaF and lactic acid addition at 37°C indicates that Ti-2Ge and Ti-5Ge alloys show better corrosion resistance to fluorine-containing solution. The cytotoxicity test indicates that Ti-xGe alloy extracts show no obvious reduction of cell viability to L-929 fibroblasts and MG-63 osteosarcoma cells, similar to pure Ti which is generally acknowledged to be biocompatible. Considering all these results, Ti-2Ge and Ti-5Ge alloys possess the optimal comprehensive performance and might be used as potential dental materials.

[Fracture analyses of casting framework removable partial dentures].

OBJECTIVE: To compare the clinical fracture rates of removable partial denture (RPD) made of titanium with that of Co-Cr alloy, to analyze the fracture modes and reasons of two kinds of metal frameworks, and to explore the effect of defects on the fracture process. METHODS: Following totally 30 618 RPDs made by titanium and by Co-Cr alloy, the fracture rates in 18-month were calculated individually. The fractured surfaces of failed RPDs were examined by fractography investigations using a field emission scanning electron microscope to disclose the fracture mode and damage character. The energy-dispersive X-ray spectroscopy analysis was performed to examine the chemical compositions. RESULTS: The fracture rate of titanium framework was 1.75%, comparing with 0.57% of Co-Cr alloy framework. The reasons included teeth preparing, framework design, and defects during casting. The fracture modes of titanium and Co-Cr alloy framework performed toughness fracture character. The fissures were found in both titanium and Co-Cr alloy frameworks, and pores were detected in titanium frameworks. CONCLUSION: The higher fracture rate of titanium framework is related to the defects during casting.