Yinghan Wang

Accuracy of volumetric measurement of teeth in vivo based on cone beam computer tomography.

OBJECTIVES to evaluate the accuracy of cone beam computed tomography (CBCT) for volumetric measurement of teeth, using micro-computed tomography (Micro-CT) as the reference standard. SETTING AND SAMPLE POPULATION The Department of Orthodontics at Sichuan University. The sample consisted of 27 maxillary and mandibular premolars of 15 patients, planned to be extracted for orthodontic treatment. MATERIAL AND METHODS The 27 teeth were subjected to standardized CBCT scanning before extraction and Micro-CT scanning after extraction. From CBCT data, teeth were tissue segmented and then three-dimensionally (3D) reconstructed, while from Micro-CT data, teeth were 3D reconstructed directly. Tooth volumes were then calculated. The intra-observer repeatability and reproducibility of two observers and the overall between-instrument agreement of the measurements were evaluated using intra-class correlation coefficients (ICCs) and concordance correlation coefficient (CCC), respectively. RESULTS The intra-observer repeatability was high for both observers. ICCs were 0.999 and 0.998, respectively. The reproducibility of the two observers was also high (ICC, 0.740). The overall between-instrument agreement of the measurements was good, and CCC was 0.993 and its lower 95% confidence interval was 0.989. CONCLUSIONS The accuracy of the CBCT method for volumetric measurement of teeth in vivo is comparable to the Micro-CT method in vitro. The CBCT method has the potential possibility to be applied in studies on root resorption associated with orthodontic force. Further study is needed to prove the sensitivity of the method.

Fabrication of high strength PVA/rGO composite fibers by gel spinning

High strength composite fibers were prepared from poly(vinyl alcohol) (PVA) (degree of polymerization: 6100) reinforced by reduced graphene oxide (rGO). The macroscopically homogeneous PVA/rGO dispersion was obtained through solvothermal reduction of graphene oxide (GO) in PVA/dimethyl sulfoxide (DMSO)/H2O solution, and then extruded into composite fibers by gel spinning followed by hot drawing. It was found that the mechanical properties of PVA fibers were greatly improved by incorporating rGO. At 0.1 wt% rGO loading, tensile strength increased from 1.8 GPa for the pure PVA fiber to 2.2 GPa for the PVA/rGO composite fiber. The results of mechanical properties and FTIR spectra for PVA/rGO composite fibers suggest the relatively strong interfacial interactions between rGO nanosheets and PVA that improve the load transfer from the polymer matrix to the reinforcing phase. Meanwhile, the thermal stability of the composite fibers was also enhanced by rGO addition.

The effect of the reduction extent on the performance of graphene/poly(vinyl alcohol) composites

The reduction extent of graphene oxide (GO) was tailored by adjusting the solvothermal reduction time. The effects of the reduction extent of GO on the structure and properties of graphene/poly(vinyl alcohol) (PVA) composites were investigated. Results show that the mechanical properties of polymer composites are sensitive to the reduction extent of GO, and reduced graphene oxide (rGO) with an optimum reduction extent (C/O ratio = 3.94) could more efficiently improve the mechanical properties of PVA than low/high reduction extent rGO. Low reduction extent rGO could enhance the interfacial interactions through the formation of hydrogen bonds with PVA chains, but its mechanical strength is smaller. High reduction extent rGO has stronger mechanical strength while the deep deoxidation of GO significantly weakens interfacial interactions between rGO nanosheets and PVA chains. Achieving optimum reinforcing effects requires balancing and optimizing interfacial interactions and mechanical strength of rGO.

Accuracy of volumetric measurement of simulated root resorption lacunas based on cone beam computed tomography.

OBJECTIVES To evaluate the accuracy of volumetric measurement of simulated root resorption cavities based on cone beam computed tomography (CBCT), in comparison with that of Micro-computed tomography (Micro-CT) which served as the reference. SETTING AND SAMPLE POPULATION The State Key Laboratory of Oral Diseases at Sichuan University. MATERIAL AND METHODS Thirty-two bovine teeth were included for standardized CBCT scanning and Micro-CT scanning before and after the simulation of different degrees of root resorption. The teeth were divided into three groups according to the depths of the root resorption cavity (group 1: 0.15, 0.2, 0.3 mm; group 2: 0.6, 1.0 mm; group 3: 1.5, 2.0, 3.0 mm). Each depth included four specimens. Differences in tooth volume before and after simulated root resorption were then calculated from CBCT and Micro-CT scans, respectively. The overall between-method agreement of the measurements was evaluated using the concordance correlation coefficient (CCC). RESULTS For the first group, the average volume of resorption cavity was 1.07 mm(3) , and the between-method agreement of measurement for the volume changes was low (CCC = 0.098). For the second and third groups, the average volumes of resorption cavities were 3.47 and 6.73 mm(3) respectively, and the between-method agreements were good (CCC = 0.828 and 0.895, respectively). CONCLUSIONS The accuracy of 3-D quantitative volumetric measurement of simulated root resorption based on CBCT was fairly good in detecting simulated resorption cavities larger than 3.47 mm(3), while it was not sufficient for measuring resorption cavities smaller than 1.07 mm(3) . This method could be applied in future studies of root resorption although further studies are required to improve its accuracy.

A study of the transition of liquid-crystal alignment from homeotropic to planar on a polyimide layer

The alignment of nematic liquid crystals by rubbed polyimide surfaces has been well-studied and developed. A novel polyimide film which induced a homeotropic alignment of the nematic liquid crystal without rubbing or with weak rubbing strength was presented. However, there was a transition from homeotropic to planar alignment of the nematic liquid crystal after strong rubbing. In order to study the transition, the polyimide surface was investigated by atomic force microscopy, surface free energy measurement and angle-resolved analysis X-ray photo-electron spectroscopy before and after rubbing with a velvet fabric. It was found that both the change of surface polarity and surface morphology were not the reasons for the transition. The droop of the side chain on the polyimide surface after the rubbing treatment was detected by angle-resolved analysis X-ray photo-electron spectroscopy. Owing to the special structure of the novel polyimide, the X-ray photo-electron spectroscopy was successfully used for the first time to analyse the conformational change of the side chain of a polymer. In conclusion, the transition of nematic liquid crystal alignment from homeotropic to planar after rubbing was influenced by the side chain conformation of the polyimide.

The Effects of Different Side Groups on the Properties of Polythiophene

To investigate the different side groups on the properties of polythiophenes (PTs), three kinds of samples, with alkyl [poly(3‐hexylthiophene), P3HT], alkoxy [poly(3‐hexyloxythiphene), P3HOT], aryl [poly(3‐phenylthiophene), P3PhT], were synthesized with chemically oxidized polymerization in the presence of FeCl3. It was found that the molecular weight (MW) of PTs was influenced by the steric hindrance between side groups. The results of ultraviolet‐visible (UV‐Vis) and Fourier transform infrared (FT‐IR) spectra showed that P3HOT had a longer effective conjugation length than P3HT and P3PhT, due to both the stronger electron‐donating property of the alkoxy groups and the coplanar conformation of hexyloxy. Photoluminescence quenching was observed in P3HOT, which was attributed to energy transfer and photochemical reaction. Moreover, the thermal stability of PTs was dependent on the side group, too.

Enhancement of water and organic solvent resistances of a waterborne polyurethane film by incorporating liquid polysulfide

Environmentally friendly, waterborne polysulfide-based polyurethane (WSPU) films have been successfully synthesized from liquid polysulfide (PSF), polytetramethylene ether glycol (PTMG), isophorone diisocyanate (IPDI) and dimethylolpropionic acid (DMPA). The chemical structures, mechanical and thermal properties of the chemically modified films have been carefully investigated using ATR-IR, gel permeation chromatography (GPC), tensile tests, dynamic mechanical analysis (DMA) and a thermogravimetric analyzer (TGA). As the PSF content increases from 0 to 20%, after an immersion in deionized water for 96 h, the water absorption decreases from 6.2% to 3.4% and the tensile strength retention increases from 74.3% to 91.7%. The chemical resistance to organic solvents is also improved significantly. The enhanced water and organic solvent resistances of waterborne polyurethanes (WPUs) are primarily attributed to the addition of a PSF containing sulfur group. However, the tensile strength and thermal performance are weakened to some extent. This study produces a new composite derived from polysulfide, and its high water and solvent resistance performance could contribute to surface material research.

Effect of the functional diamine structure on the properties of a polyimide liquid crystal alignment film

A novel functional diamine containing triphenylamine moiety and biphenyl as well as a long alkyl chain, 4-dodecyloxy-biphenyl-4′,4′′-diaminotriphenylamine (DBDTA), was synthesized and characterized. A series of polyimides (PIs) were copolymerized from DBDTA, 3,3′-dimethyl-4,4′-methylenedianiline (DMMDA) and 4,4′-oxydiphthalic anhydride (ODPA) via a one-step method. The chemical structures of the diamine and PIs were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H NMR). Properties such as the solubility, rubbing resistance, thermal stability and pre-tilt angle of the PIs were investigated. Furthermore, the results were compared with the PIs-BZA derived from 4-dodecyloxy-biphenyl-3′,5′-diaminobenzoate (DBPDA). The PIs-TPA derived from DBDTA exhibited better transparency and thermal stability than the PIs-BZA from DBPDA. When the content of functional diamines was only 10%, the PI1-TPA derived from DBDTA displayed better solubility than the PI1-BZA from DBPDA. In addition, all PIs could induce uniform vertical alignment of the liquid crystals (LCs) before and after the rubbing process, but PI1-BZA only induced parallel alignment of the LCs after rubbing process. It is suggested that the PI1-TPA film is more resistant to the rubbing process than PI1-BZA.

Synthesis of soluble polyimide derived from novel naphthalene diamines for liquid crystal alignment layers and a preliminary study on the mechanism of imidization

Novel functional diamine, 6-hexyloxy-naphthalen-3′,5′-diaminobenzoate (N6) containing a rigid naphthalene unit, was molecularly designed and successfully synthesized. PIs (polyimides) were obtained by copolymerization of N6, 3,3′-dimethyl-4,4′-methylenediamine (DMMDA) and 4,4′-oxydiphthalic anhydride (ODPA). The structures of the intermediates, diamines and PIs were confirmed by FT-IR and 1H NMR spectra. All PIs obtained could be dissolved in polar aprotic solvents and low-boiling-point solvents. PI (polyimide) films attained using a casting method showed favorably high transmittance above 95% in the wave length range of 400–700 nm and could align LCs vertically before and after rubbing treatment. PI–N6 derived from N6, DMMDA and ODPA exhibited a much higher temperature at a 5% weight loss (T5) compared with the corresponding PI–C6 from 4-hexyloxy-biphenyl-3′,5′-diaminobenzoate (C6). For PI–N6, the weight ratio of the side chains was smaller than that of PI–C6, but a much higher T5 was attained. The results demonstrated that the introduction of a naphthalene unit into the side chain could effectively improve the thermal stability of PI without sacrificing its solubility. Moreover, the outstanding thermal stability of the PIs was explained in a preliminary manner by the imidization reaction mechanism.

A preliminary inquiry into the conformation of the side chains on polyimide film and the mechanism of the vertical alignment of liquid crystals induced by polyimides with side chains

A series of functional diamines, with various side chain structures and length, were designed and synthesised. Four polyimides (PIs) were copolymerised from pyromelitic dianhydride, p-phenylenediamine and four functional diamines. The conformation of the side chains on the surface of PI film was investigated through X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared dichroic spectroscopy. The results showed that the side chains on the PI film surface aligned outwards in the polymer bulk phase before rubbing. It was found that the length and the contents of the side chains influenced the conformation of the side chains. The interaction between the liquid crystals (LCs) and the side chains on the PI film surface induced the LCs to align vertically.