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Introduction: The objective of this study was to investigate the characteristics of force degradation and surface morphology of 9 brands of elastic ligatures over 6 weeks, both in vivo and in vitro, to provide some reference for clinical selection of appropriate elastic ligatures and determination of appropriate follow-up visit time., Methods: Choosing 9 kinds of brands of elastic ligatures (American Orthodontics, Ormco, 3M Grey, TP Orthodontics, Xihu, Yahong, Creative, Protect, 3M dusty blue), which are common in the market. For the in vivo study, 9 volunteers (5 males, 4 females, aged 22-26 years) were chosen to wear elastic ligature fixators, which were made to fix the elastic ligature in the mouth without bonding brackets on the teeth. The residual force and percentage of force degradation of elastic ligatures were estimated after 0, 1 hour, 2 hours, 8 hours, 1 day, 2 days, 1 week, 2 weeks, 4 weeks, and 6 weeks processed in vivo and in vitro (25°C dry air condition, 37°C artificial saliva, pH = 6.7 and oral environment); A 1-way analysis of variance and t test were used to identify statistical significance (P <0.05). The surface morphology of the initial state and after a 6-week process in vivo and in vitro were observed separately., Results: The characteristics of force degradation and surface morphology of 9 brands of elastic ligatures were different over 6 weeks; With the extension of time, the tensile force declined, and the percentage of force degradation of all groups decreased sharply by about 9.1%-32.3% in the first day, then the rate reduced steadily. In addition, during the first day, the percentage of force degradation declined most sharply in the first hour (4.4%-16.5%). The percentage of force degradation of 9 elastic ligatures was reduced by about 11.3%-37.3% over 6 weeks in all groups. At the same time, the characteristics of force degradation in the same brand are that in vivo > artificial saliva > air (P <0.05). After a 6-week process, the surface morphologic defects were aggravated under a scanning electron microscope, corresponding to the change of mechanical properties in each brand., Conclusions: The mechanical properties of elastic ligatures are reduced with time extension and decreased greater in vivo than in vitro; According to the characteristics of force degradation of different brands of elastic ligatures, clinicians can choose the proper elastic ligatures at different stages of treatment, and adjust the follow-up visit time appropriately. For example, in alignment and leveling, the elastic ligatures with slow force degradation, such as Ormco, TP, and so on, maybe more suitable to ensure close contact between the archwire and the bracket. In the space-closing stage, the elastic ligatures with fast force degradation may be more appropriate to reduce the friction between the archwire and the bracket, such as 3M Grey, Yahong, Protect, and so on., (Copyright © 2022 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: This study aimed to analyze the effects of ultrasonic removal of fractured files from the middle third of root canals on the vertical root fracture resistance., Methods: This study was an extension of a previous study assessing the effects of fractured file removal on dentinal microcracks. It included 18 bilaterally matched pairs of human mandibular incisors prepared and analyzed in the previous study. Briefly, 1 member of each pair was assigned to an ultrasonic or a control group. In the ultrasonic group, K-files were fractured in the middle third of canals followed by ultrasonic file removal and canal preparation. In the control group, the root canals were simply prepared. Micro-computed tomographic imaging was performed before and after treatment, and the cross-sectional root images were screened for microcracks. For the present study, 3-dimensional reconstruction was performed for volumetric assessments. The fracture resistance was measured using a universal testing machine. All data were statistically analyzed., Results: Fracture loads were significantly smaller in the ultrasonic group (P < .05). The percentage increase in the canal volume significantly influenced the root fracture resistance (P < .05), whereas microcracks had no significant effect (P > .05)., Conclusions: Ultrasonic removal of fractured instruments from the middle third of root canals lowers the vertical root fracture resistance, with increased dentin removal being the primary cause., (Copyright © 2019 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Immobilization of trypsin onto the superparamagnetic carboxymethyl chitosan (Fe3O4 (PEG+CM-CTS)) nanoparticles was studied. FTIR and fluorescence spectroscopy data demonstrated that the Fe3O4 (PEG+CM-CTS) nanoparticles were capable of preventing the trypsin unfolding. Due to the large specific surface area and excellent dispersibility, the adsorption equilibrium of trypsin onto the nanoparticles was achieved quickly within 30min. The results of kinetic parameters (Michaelis constant, Km) with regards to the free trypsin (FT) and immobilized trypsin (IT) were 23.1 and 24.1mg/mL separately, implying that IT has less affinity to the BAEE used as the substrate. However, the MALDI-TOF MS analysis indicated that, IT could be used for fast and efficient Bovine Serum Albumin (BSA) digestion under very facile processes, thanks to the easy manipulation of the magnetic nanoparticles (MNs), as well as the greatly reduced digestion time (from 12h to 15min). IT exhibited a sound stability after re-uses for six times, with 76.3% of the initial activity thereof still retained, thus making it more attractive in the application fields. These results are expected to open up a great potential use of such Fe3O4 (PEG+CM-CTS) nanoparticles as a superior nanosupport for trypsin immobilization., (Copyright © 2013 Elsevier B.V. All rights reserved.)