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Biomedical subjects

Gang Shen

Publications and source records attributed to Gang Shen.

At least 37 records · Page 2Linked to original sources
PubMed2005

[Analysis of the efficacy of Twin-block appliance on maxillofacial growth of six pairs of monozygotic twins].

PURPOSE: The purpose of this study was to investigate the efficacy of Twin-block appliance on maxillofacial growth by using monozygotic twins. METHODS: 6 pairs of non-high angle monozygotic twins aged 12.2 with class II division 1 malocclusion were selected from 32 pairs of twins. In the first year Twin A of each pair was functionally treated using Twin-block appliance; meanwhile, Twin B underwent non-extracted fixed treatment without any treatment procedure which might cause changes like functional appliances such as Class II elastics. The difference of the cephalometric changes of maxilla and mandible before and after treatment between Twin A and Twin B was compared using paired-t test. RESULTS: Compared with those of Twin A after one year treatment, SNA, Cd-A and Cd-Go of Twin B had little chang (P>0.05), but Cd-S' reduced (P<0.05), Cd-Gn and SNB increased (P=0.01), (Cd-Gn)-(Cd-A) and ANB increased (P<0.05) significantly. CONCLUSION: Twin-block appliance can stimulate forward mandibular growth and cause forward mandibular displacement, but has little effect on ramus height and maxillary growth.

Cephalometry↗
PubMed2005

Physical properties of human premolar cementum: hardness and elasticity.

AIMS: To determine if the cementum on the maxillary right and left first premolars has identical physical properties. METHODS: Ten normal maxillary first premolar teeth, extracted from five orthodontic patients with a mean age of 14.0 years, were used. The teeth had not been subjected to an orthodontic force. The hardness and elastic modulus of the cementum were measured on the buccal and lingual surfaces of the roots at three locations: cervical third, middle third and apical third. RESULTS: There were no significant side-to-side differences in cementum hardness (Mean side-to-side difference: 0.0063 GPa; SD: 0.0279; p = 0.525) or elastic modulus (Mean side-to-side difference: -0.027 GPa; SD: 0.111; p = 0.814). The hardness and elastic modulus of the cementum decreased from cervical to apical regions on both root surfaces. CONCLUSIONS: Similar physical properties of the cementum on the maxillary right and left first premolars suggest that intra-arch comparisons can be used to investigate root resorption caused by orthodontic forces.

Adolescent↗
PubMed2004

Syntheses of photolabile novobiocin analogues.

Novobiocin was recently shown to inhibit Hsp90 through a previously unrecognized C-terminal ATP binding site. Although the N-terminal region of Hsp90 has been solved by X-ray crystallography, the C-terminal region has not. In an effort to elucidate the C-terminal binding site of Hsp90, four photolabile analogues of novobiocin were prepared.

Binding Sites↗
PubMed2004

X-ray photoelectron spectroscopy and infrared spectroscopy study of maleimide-activated supports for immobilization of oligodeoxyribonucleotides.

Surface-tethered nucleic acids are widely applied in solid-phase assays in which complementary strands must be detected against a complex mixture of other sequences. In response to such needs, numerous methods have been developed for immobilizing nucleic acids on solid supports. Often, detailed analysis of associated chemical transformations and of potential side reactions is difficult to obtain. Combined use of planar and high surface area powder supports allows characterization using surface as well as bulk diagnostic techniques. This approach is followed in the present study in which X-ray photoelectron spectroscopy (XPS), transmission infrared spectroscopy (FTIR) and reactivity titrations are used to investigate siliceous supports modified with an aminosilane precursor followed by a maleimide-bearing crosslinker for attachment of nucleic acids. The supports retain maleimide activity for approximately a day when stored under buffer, but deactivation is accelerated under basic conditions or by incomplete conversion of the precursor aminosilane monolayer. Reactions involving the olefinic bond of the imide as well as its carbonyl groups are observed and analyzed. Attachment of sulfhydryl-terminated oligodeoxyribonucleotides is highly site specific, and immobilized strands exhibit excellent hybridization activity. Quantitative use of XPS for label-free determination of DNA coverage based on calibration against reference materials is also described.

Electron Probe Microanalysis↗
PubMed2004

Reaction of N-phenyl maleimide with aminosilane monolayers.

Reaction of N-phenyl maleimide (NPM) with silica surfaces modified with a self-assembled monolayer of (aminopropyl)triethoxysilane (APTES) was investigated using infrared spectroscopy (FTIR), elemental analysis, and titration assays. This reaction is of interest as a test case for using amine-maleimide coupling for immobilization of biomolecules. Addition of NPM to surface APTES residues was consistently sub-stoichiometric, with typical yields of about 75% on monolayers with a coverage of 1.15 APTES residues/nm2. Titration analysis found negligible presence of imide alkene C=C bonds in modified supports, indicating that addition of NPM to APTES proceeded via amine attack at the imide olefinic bond. FTIR measurements also revealed presence of amide bands which intensified over periods of 10 h. These observations were attributed to a slower secondary process in which APTES amines attack imide carbonyls to produce amide linkages. Stability of NPM-modified surfaces was examined under room temperature storage in pH 7 buffer up to 72 h and for 2 h exposure to buffer at temperatures up to 90 degrees C. It was found that stability was determined by robustness of APTES-silica attachment, with about 30% loss under the harshest conditions investigated.

Amines↗
PubMed2004

[A clinical study on improved herbst appliance].

PURPOSE: To observe the clinical effect of improved Herbst appliance. METHODS: Twelve patients with Class II malocclusion were selected and treated with improved Herbst appliance,The effects were observed and assessed after 6 to 8 months. The advantages and steps of this technique were also described. RESULTS: All the cases had satisfied and effective results with the help of improved Herbst appliance. The change of the ANB angle had statistical difference. CONCLUSION: Improved Herbst appliance is an be effective fixed functional appliance, it can used in adolescents (in the permanent dentition),postadolescents and young adults, instead of some orthognathic surgery especially in borderline skeletal Class II. This technique can easily be used in dental clinic.

Adolescent↗
PubMed2004

[APDI and ODI estimated from substitute palate plane].

PURPOSE: The substitute palate plane was defined at the cephalometrics of noncleft patients. APDI and ODI were estimated from substitute PP. It is expected that the APDI and ODI estimated from PP (APDI',ODI')can be extended to the cleft patients to illustrate the anteroposterior and vertical relationship between maxilla and mandible. METHODS: The cephalometrics of 30 patients of C-I,C-II and C-III were traced and so were in 30 patients of normal overbite,deep overbite and open bite. The substitute palate plane(PP') was defined. The inclination of the PP to the FH, APDI and ODI, the inclination of the substitute PP to the FH,APDI' and ODI' were measured. The APDI and APDI' of C-I, C-II and C-III patients were compared,The ODI and ODI' of normal overbite, deep overbite and open bite patients were also compared by group t test. RESULTS: There was no significant difference between APDI and APDI' in C-I, C-II and C-III patients and also no significant difference between ODI and ODI' in normal overbite,deep overbite and open bite patients. It is showed the higher the ODI',the deeper the overbite. And the higher the APDI', the more mesial the molar relationship. CONCLUSIONS: The APDI and ODI estimated from substitute PP can be used as an important criterion to judge the vertical and anteroposterior development of the the maxilla, especially in palate clefts patients.

Adolescent↗
PubMed2004

[The effects of combined reverse Nance and TPA on reinforcement of anchorage].

PURPOSE: To evaluate the effects of combined reverse Nance and TPA on anchorage control. METHODS: 16 female adults with Class II division 1 malocclusion were treated with the combined mechanism of reverse Nance and TPA in an attempt to reinforce molar anchorage. Cephalometric analysis and model measurements were conducted for the assessment of anchorage control. RESULTS: The mesial movement of the upper first molars were minimized within 1/5 extracted space, parameters such as UMVD, MP-FH, ANS-Me remained unchanged, indicating the molar anchorage was controlled effectively. CONCLUSION: The modified combination of reverse Nance and TPA might be effective in anchorage forcement.

Adolescent↗
PubMed2004

[Comparative study of craniofacial structure between UCLP and Class III malocclusions].

PURPOSE: The aim of this study was to compare the dentocraniofacial morphology between the patients with cleft lip and palate and those with Class III malocclusion without surgical treatment. METHODS: The sample included two groups, group one consisted of 39 patients with repaired completed or uncompleted unilateral cleft lip and palate, with age ranging from 12 to 15 years; group two consisted of 40 patients with Class III malocclusion without surgical treatment, with age ranging from 12 to 15 years. Cephalometrics analysis was conducted to allow for a quantitative assessment of dentocraniofacial morphology. RESULTS: The group with unilateral cleft lip and palate showed smaller SNA and SNB angle than those in the Class III group,but the ANB angle showed no significant difference between two groups. Cleft group showed significant downward and backward rotation of the mandible associated with a more obtuse gonial angle. The upper incisors in cleft group were also found to be more retroclined. The inclination of lower anterior teeth showed no difference between two groups. CONCLUSION: The cleft group showed smaller maxilla and mandible than the Class III group, with mandibular plane being clockwise rotated.

Adolescent↗
PubMed2004

[Non-extraction approach using RPE to correct Angle Class I malocclusion with moderate crowding: A cephalometric study].

PURPOSE: To study cephalometric changes in Angle Class I malocclusion with moderate crowding treated orthodontically without extraction using rapid palatal expansion (RPE). METHODS: 9 patients with Angle Class I moderate crowding were orthodontically treated with a non-extraction approach using RPE and fixed edgewise appliances.The cephalometric analysis was performed at T1(pretreatment), T2(3 months after RPE) and T3(fixed retention period after active treatment). RESULTS: Lateronasal width, maxillary width, upper and lower first molar width significantly increased after rapid expansion (T1-T2) and after active treatment (T1-T3) with the significant difference in upper first molar width between T2 and T3. Total facial height, upper anterior facial height, the inclination of palatal plane and Y axis increased significantly (T1-T2, T1-T3). There were significant differences in the inclination of mandibular plane among T1, T2 and T3. CONCLUSION: Maxillary transverse width could increase using RPE. Rapid palatal expansion might not result in the anteroposterior changes.

Cephalometry↗
PubMed2003

Determination of triazines in soil by microwave-assisted extraction followed by solid-phase microextraction and gas chromatography-mass spectrometry.

A method for determining triazine herbicides in soil samples that combines microwave-assisted extraction with solid-phase microextraction is described. Water containing 1% methanol was employed as extractant. The parameters of solid-phase microextraction and microwave-assisted extraction were investigated. In solid-phase microextraction, particular attention was paid to the negative effect of salt on fiber stability. Our experiments showed that this effect could be effectively reduced by simply washing the fiber with deionized water. The selected triazines could be efficiently extracted by the aqueous extractant at 105 degrees C for 3 min, with 80% output of maximum power (1,200 W). The extraction procedure provided good precision (<7%) and recoveries (76.1-87.2%). The limits of detection were in the range 2-4 microg/kg. Compared with conventional liquid extraction, microwave-assisted extraction-solid-phase microextraction was more efficient, accurate and faster, and used a very small amount of organic solvent (only 250 microL methanol). The extraction of aged spiked soil samples indicated that, although the recoveries were lower than those of freshly spiked samples, they were nevertheless satisfactory for the quantitative analysis of real-world samples.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Automated hollow fiber-protected dynamic liquid-phase microextraction of pesticides for gas chromatography-mass spectrometric analysis.

Dynamic liquid-phase microextraction (LPME) controlled by a programmable syringe pump was evaluated for extracting pesticides in water prior to GC-MS analysis. A conventional microsyringe with a 1.3-cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device as well as the sample introduction device for GC-MS analysis. The attached hollow fiber served as the "holder" and protector" of 3 microl of organic solvent. The solvent was repeatedly withdrawn into and discharged from the hollow fiber by the syringe pump. Pesticides were extracted from 4-ml water samples into the organic solvent impregnated in the hollow fiber. The effects of organic solvents, plunger movement pattern, agitation and extraction time were investigated. Good repeatabilities of extraction performance were obtained, with the RSD values ranging from 3.0% (alachlor) to 9.8% (4-chlorophenol) for the 14 pesticides; most RSD values were under 5.0%. The method provided a 490-fold preconcentration of the target pesticides. The limits of detection were in the range of 0.01-5.1 microg/l (S/N = 3) in the GC-MS selected ion monitoring mode. In addition, sample clean-up was achieved during LPME because of the selectivity of the hollow fiber, which prevented undesirable large molecules from being extracted. A slurry sample (mixture of 40 mg soil/ml of water) containing seven pesticides was extracted using this method which also gave good linearity and precision (most RSDs <7.0%, n = 3).

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Headspace liquid-phase microextraction of chlorobenzenes in soil with gas chromatography-electron capture detection.

The organic solvent film formed in a microsyringe barrel was used as an extraction interface in headspace liquid-phase microextraction (HS-LPME) of chlorobenzenes. Some common organic solvents with different vapor pressures (9.33-12 918.9 Pa) were studied as extractants. The results indicated that even the solvent with the highest vapor pressure (cyclohexane) can be used to carry out the extraction successfully. In general, the reasons for successful extraction are the very small space (5 mm3) within the microsyringe barrel and the fast equilibrium between gaseous analytes and organic solvent film. Both of these factors significantly reduced the risk of solvent loss during extraction. Thus, the choice of extraction solvent for the present method was very flexible. From the viewpoint of extraction efficiency, toluene (which has relatively low vapor pressure) was found to provide the best extraction efficiency. The effects of sampling volume, organic solvent volume, syringe withdrawal rate, and number of extraction cycles were also investigated. The procedure with respect to repeatability and limits of detection was evaluated by soil spiked with chlorobenzenes. Repeatabilitywas between 5.7 and 17.7%, and the limits of detection were 6-14 ng/g. HS-LPME was shown to be an inexpensive, fast, and simple sample preparation method for volatile compounds.

Chlorobenzenes↗
PubMed2003

[Experimental study on selecting optimal time of orthodontic tooth movement into extraction sites].

OBJECTIVE: The purpose of this study was to investigate the physiological process of healing after tooth extraction and the biological reaction of tooth movement into extraction sites with the aim of selecting optimal time of tooth movement into extraction sites clinically. METHODS: Extraction of upper first molars were performed on 30 male Sprague-Dawley rats which were divided equally into 5 groups. Orthodontic appliance was placed at different time after tooth extraction in order to move the maxillary second molars mesially into the extraction spaces. The animals were injected continuously with tetracycline and calcein for two days before appliance activation and animal sacrifice. Undecalcified mesio-distal specimans 65-100 microns of thickness were prepared. The quantification of bone remodeling parameters on tooth movement into extraction sites at different time was performed by histomorphometric measurements and computer image analysis. RESULTS: 1. The bone turnover had two bone modeling processes: resorption under pressure and formation in tension. 2. The bone resorption was more active on the mesial surface (pressure side) than that on the distal surface (tension side). While bone formation was more active on the distal surface (tension side) than that on the mesial surface (pressure side). 3. Both the resorptive parameters and the formative parameters across time were manifested by a peak at day 7 after tooth extraction. CONCLUSION: 1. Orthodontic retraction into extraction sites should be initiated at an early stage after tooth extraction, so that the advantage of bone remodeling in extraction sites was used. 2. The optimal time of tooth movement into extraction sites clinically was about a week after tooth extraction.

Animals↗
PubMed2003

[An immunohistochemical study on neovascularization in TMJ during mandibular advancement].

OBJECTIVE: Neovascularization is proved to be closely correlated with ossification. This study was designed to determine the biochemical path through which the new bone formation is enhanced in TMJ during mandibular protrusion. METHODS: SD Rats were fitted with bite-jumping appliances to allow for an adequate advancement of the mandible. The animals were sacrificed 3, 7, 14, 21 and 30 days, respectively, after placement of the appliances. Slides with TMJ tissue were prepared for biochemical procedure. Immunohistochemical approaches were adopted to examine neovascularization in TMJ by immuno-localizing the newly formed endothelial cells. Computer-assisted image analysis system was applied to quantify the positive immunoreaction. RESULTS: Neovascularization in connective tissue close to the condyle was 200% higher in the experimental groups than that in the control, and, within the bony tissue of the condyle, neovascularization in experimental animals was found to be 103% higher than that of the control. CONCLUSION: Increased neovascularization triggered by mandibular protrusion might intensify new bone formation in condyle and glenoid fossa and finally lead to a growth adaptation of TMJ to bite-jumping therapy.

Animals↗
PubMed2003

[The feasibility and reliability of Pancherz's analysis in evaluating the treatment effects of bite-jumping on skeletal class II malocclusion].

OBJECTIVE: This study was designed to conduct an in-depth evaluation on Pancherz's analysis. METHODS: A typical Class II case with bite-jumping therapy was selected for the whole process of Pancherz's Analysis. The skeletal growth modification and dental compensation were examined and portioned for their respective contribution to the correction of excessive overjet and Class II molar relationship. RESULTS: The following traits and properties of Pancherz's analysis were found: (1) A fixed reference system characterized by SN and OLp was established which led to an accurate detection of the moving objects. (2) Skeletal and dental changes were separated for evaluation, which resulted in a true assessment of the bite-jumping on growth pattern modification.(3) A segmental examination for dental changes indicated the magnitude of skeletal modification. Conclusion Pancherz's analysis is a feasible and reliable evaluation system which could reflect with accuracy the skeletal and dental effects caused by bite-jumping therapy.

Activator Appliances↗