Magnetic fields of 10mT and 120mT change cell shape and structure of F-actins of periodontal ligament cells.

Dental magnetic attachments, usually applied locally to oral cavities, produce stray fields (flux leakage) spreading in adjacent tissues. It has been found that human periodontal ligament (PDL) cells change their geometry and the structure of their cytoskeleton F-actins when the cell cultures are exposed to B-field strengths of B = 10mT and 120mT, respectively, which are similar to those generated by dental magnetic attachments. Analytically, after long-time exposures to B-fields for 12h, 36 h and 60 h, respectively, cytoskeleton F-actins are labeled with a fluorescent dye and observed under a laser scanning confocal microscope. The geometrical cell parameters of cell length and cell width and the fluorescence emission of labeled F-actins, respectively, were determined and subjected to an automatic image analysis using a special software. The results on cell shrinkage and filament reorganizations were statistically analyzed by the program ANOVA (P < 0.05). It was found that only long-time (hours) exposure to high fields in the order of 0.1T may produce tissue irritations during long-time medical treatments using open- and closed-field dental magnetic attachments.

[Determination and Weibull analysis of the strength of dental veneering porcelains].

OBJECTIVE: To determine the strength of the veneering porcelain stored in artificial saliva. METHODS: Standard beams with a size of 3 mm x 2 mm x 20 mm made from the body, incisal, and translucent porcelains of SHOFU Vintage were stored in the artificial saliva for 30 days. Twenty samples from each material were tested for the strength by the 3-point flexural test at a crosshead speed of 0.5 mm. The data were analyzed by the two-parameter Weibull method. RESULTS: The strength, Weibull modulus (m) and characterization strength (male0) were (75.5 +/- 5.6) MPa, 17.3, and 77.6 MPa for Body porcelain, respectively; (73.6 +/- 5.0) MPa, 16.5, and 76.0 MPa for incisal porcelain, respectively; and (72.9 +/- 4.5) MPa, 16.1, and 75. 5 MPa for translucent porcelain, respectively. CONCLUSION: There are no differences in strength between the three dental porcelains. Weibull analysis describes the strength of the porcelains better than the average and standard deviation.

[Effects of static magnetic field on the activity of superoxide dismutase of human gingival fibroblasts].

OBJECTIVE: To investigate the effects of static magnetic fields (SMF) generated by the open-circuit and closed-circuit dental magnetic attachments on the enzymology of human gingival fibroblasts. METHODS: In this study, a cellular SMF exposure system developed by our department of prosthetic dentistry was used to impose the static magnetic force on the cultured human gingival fibroblasts in vitro. The activity of superoxide dismutase in those fibroblasts of the test group and that of the control group were measured and compared. RESULTS: No significant difference (P > 0.05) in superoxide dismutase activity was found between the groups when they were loaded with different intensity of magnetic fields or for different period of time. CONCLUSION: Under the conditions in this experiment, the static magnetic fields of the open-circuit magnetic attachments, and those of the closed-circuit ones as well, have no biological effects on the superoxide dismutase of human gingival fibroblasts.

[The research for magnetic attachments producing static magnetic fields to influence on cytoskeletons of human periodontal ligament cells].

OBJECTIVE: The present research aimed to investigate that the static magnetic field (SMF) generated by dental magnetic attachments influenced on the cytoskeletons of human periodontal ligament cells (HPDLCs). METHODS: In vitro cultured HPDLCs were exposed to 10 mT and 120 mT SMF which simulated those of from the closed-field and open-field magnetic attachments respectively for 12-60 hours in a cellular SMF exposure system. The control group cells were cultured outside the SMF exposure system and were only exposed to geomagnetic field of about 0.03-0.07 mT. After finishing the SMF exposure, the cytoskeletons were observed under a laser scanning confocal microscope (LSCM). The image analysis software was utilized to measure and analyze the cell area, length/width ratios and the contents of F-actin of cells. RESULTS: There were certain changes observed in the cytoskeletons after HPDLCs exposed to 10 mT and 120 mT SMF for 12-60 hours. With the SMF strength increasing and the loading time extending, the cell microfilaments got ashorened change and a disordered arrangement inside cells, and the length/width ratios of cells decreased (P < 0.05). The areas of cells decreased after SMF loading for 60 hours (P < 0.05). The cell F-actin contents decreased after SMF loading for 12 hours (P < 0.05), but in the meantime there was no significant difference happening between the 36 or 60 hours SMF loading group and the control group (P > 0.05). CONCLUSION: In this study the SMF of magnetic attachments can lead the certain changes to the cytoskeletons in HPDLCs.

[Compatibility between high-strength dental ceramic (type A) and vintage AL veneering porcelain].

OBJECTIVE: To investigate the interface bond strength and compatibility between High-Strength Dental Ceramic (type A) and Vintage AL veneering porcelain. METHODS: Twenty bar-shape specimens (ten Vintage AL and ten Vitadur alpha) were fabricated, and shear test was conducted to determine the bond strength. A bilayered composite (1 mm core ceramic and 0.8 mm Vintage AL) was prepared and then fractured for scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. Ten all-ceramic anterior crowns were fabricated and the temperatures of thermal shock resistance were tested. RESULTS: The mean values of the bond strength measured were (55.52 +/- 14.64) MPa and (59.37 +/- 13.93) MPa for Vintage AL and Vitadur alpha respectively (P>0.05). SEM showed tight connection between the High-Strength Dental Ceramic (type A) and the veneering porcelain. Element diffusion was also confirmed by energy dispersive spectroscopy (EDS) analysis. The temperature of thermal shock resistance of this system was (179 +/- 15) degrees C. CONCLUSION: Vintage AL veneering porcelain has good thermal and chemical compatibility with High-Strength Dental Ceramic (type A).

[Study on the interface of Ti-porcelain fused under different surface treatment].

OBJECTIVE: This study was made to observe the topography and ionic diffusion of the elements titanium, silicon, et cetera in the Ti-porcelain interface area which was pretreated with different methods. METHODS: Ti-bond porcelain was fused on commercial pure titanium (CPT) with 8 different pretreatment methods; according to the temperature of the preoxidation, there were 300 degrees C, 400 degrees C, 500 degrees C and 600 degrees C groups, and based on the oxidizing-time in the air, there were 5 min, 15 min, 2 h and 24 h groups. The topography and ionic diffusion of elements in the Ti-porcelain interface area were observed with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) respectively. RESULTS: There were clefts and exfoliations in the 500 degrees C pre-oxidation group and 600 degrees C pre-oxidation group in SEM images. The distribution of titanium in the interlayer in EPMA images decreased from the titanium surface to porcelain, which was opposite to the distribution of silicon. CONCLUSION: The clefts and exfoliations suggested the position of the fracture and brittleness of alpha-Ti[o] layer. The widths of ionic diffusion in the eight groups were different, but it was difficult to measure and compare them exactly.

Laboratory evaluation of a new denture adhesive.

OBJECTIVE: The ideal denture adhesive demonstrates a neutral or slightly basic pH, satisfactory bonding load, and minimal toxicity to the oral mucosa. The purpose of this study was to evaluate the properties of a new denture adhesive (Comfort-DA, developed by the authors). METHODS: Comfort-DA was evaluated in the laboratory to determine the clinical effect of pH, bonding strength, and cytotoxicity. Firstly, the material was diluted at 1.0, 2.0, 3.3, 5.0, and 10% concentrations. Then the pH values were measured at 1-, 2-, 3-, 4-, 5-, 6-, and 8-hour intervals. Secondly, bonding load test was performed between acrylic resin samples on a universal testing machine. An existing product, Fittydent, was used as a control. Finally, the cytotoxicity of several dilutions of Comfort-DA was recorded with a MTT assay on human oral fibroblast cells. Cell viability was recorded by optical density after culturing in an atmosphere of 5% CO2 and 95% air at 37 degrees C for 2, 3 and 4 days, respectively. Wells containing fresh medium alone served as controls. All the results were compared with ANOVA or Tukey intervals (alpha = 0.05). RESULTS: Comfort-DA remained above the critical pH for hydroxyapatite (pH 6.5) in all dilutions throughout the study. Results of bonding strength test indicated that Comfort-DA was significantly stronger than Fittydent (p < 0.05). The statistical analysis of results for cytotoxicity showed that Comfort-DA only displayed slight cytotoxicity. SIGNIFICANCE: The generally favorable laboratory performance of Comfort-DA formulations indicates that this product may be an efficacious denture adhesive.

[Measurements of the flux densities of static magnetic fields generated by two types of dental magnetic attachments and their retentive forces].

OBJECTIVE: To measure and analyze the flux densities of static magnetic fields generated by two types of commonly used dental magnetic attachments and their retentive forces, and to provide guidance for the clinical application of magnetic attachments. METHODS: A digital Gaussmeter was used to measure the flux densities of static magnetic fields generated by two types of magnetic attachments, under four circumstances: open-field circuit; closed-field circuit; keeper and magnet slid laterally for a certain distance; and existence of air gap between keeper and magnet. The retentive forces of the magnetic attachments in standard closed-field circuit, with the keeper and magnet sliding laterally for a certain distance or with a certain air gap between keeper and magnet were measured by a tensile testing machine. RESULTS: There were flux leakages under both the open-field circuit and closed-field circuit of the two types of magnetic attachments. The flux densities on the surfaces of MAGNEDISC 800 (MD800) and MAGFIT EX600W (EX600) magnetic attachments under open-field circuit were 275.0 mT and 147.0 mT respectively. The flux leakages under closed-field circuit were smaller than those under open-field circuit. The respective flux densities on the surfaces of MD800 and EX600 magnetic attachments decreased to 11.4 mT and 4.5 mT under closed-field circuit. The flux density around the magnetic attachment decreased as the distance from the surface of the attachment increased. When keeper and magnet slid laterally for a certain distance or when air gap existed between keeper and magnet, the flux leakage increased in comparison with that under closed-field circuit. Under the standard closed-field circuit, the two types of magnetic attachments achieved the largest retentive forces. The retentive forces of MD800 and EX600 magnetic attachments under the standard closed-field circuit were 6.20 N and 4.80 N respectively. The retentive forces decreased with the sliding distance or with the increase of air gap between keeper and magnet. CONCLUSION: The magnetic attachments have flux leakages. When they are used in patients' oral cavities, if keeper and magnet are not attached accurately, the flux leakage will increase, and at the same time the retentive force will decrease. Therefore the keeper and magnet should be attached accurately in clinical application.

[Experimental study on the reconstruction of mandibular defects with sinboneHT bone replacement in rabbits].

OBJECTIVE: After sinboneHT bone replacement (SBR) was implanted in animals, to evaluate the biocompatibility of SBR and compounded in autogenetic bone in the proportion of one to one in order to prepare for the clinical applications in the future. METHODS: Bone defects of 10 mm x l0 mm x 2 mm was made at the mandibular of rabbits, then SBR with different granule diameter and autogenetic bone was compounded in the proportion of being applied in the left defects, while autogenetic bone was implanted in the right defects and nothing was used in the right reformed defects. Animals were sacrificed at 2, 4 and 8 weeks respectively. The biologic capacity was evaluated with anatomy, X-rays studies and histology. RESULTS: SBR has better biocompatibility, which can effectively accelerate the reconstruction of bone defects and help the new bone by being compounded with autogenetic bone. It provides the appropriate scaffold or template which would allow cellular infiltration, attachment and multiplication. CONCLUSION: SBR is a kind of bone substitute material with good biocompatibility. SBR compounded with self-bone has a better regeneration function.

[Bi-axial flexure strength and fracture mode of alumina glass-infiltrated core/veneer ceramic composites].

PURPOSE: To determine the bi-axial flexural strength and fracture mode of bilayered alumina glass-infiltrated core and the veneering porcelain. METHODS: Forty disk specimens were made from alumina glass-infiltrated core (HSDC-A) and veneer porcelain (Vintage AL), and equally divided into four groups as follows: monolithic specimens of veneer(MV),monolithic specimens of core material(MC),bilayered specimens with the veneer on top (BC) and bilayered specimens with core material on top(BV). Mean flexure strength, standard deviation and associated Weibull modulus were determined using bi-axial flexure (ball-on-ring) for each group. The results were analyzed with one-way ANOVA and the Weibull distribution with SPSS 13.0 software package. Both optical and scanning electron microscopy were employed for identification of the fracture mode and origin. RESULTS: The strength in the group MC and BC were significantly stronger than that in the group MV and BV. The frequency of specimen delamination, Hertzian cone formation and sub-critical radial cracking in the bilayered discs were dependent on the surface loaded in tension. CONCLUSION: Material which lies on the bottom surface dictates the strength and fracture mode of the specimens. Supported by Shenzhen Municipal Technological Project (Grant No.200903082).

[Influence of multiple sintering on wear behavior of Cercon veneering ceramic].

OBJECTIVE: To investigate the influence of multiple sintering on wear behavior of Cercon veneering ceramic. METHODS: Samples were fabricated according to the manufacture's requirement for different sintering times (1, 3, 5, 7 times). The wear test was operated with a modified MM-200 friction and wear machine in vitro. The wear scars were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). RESULTS: With the sintering times increasing, the wear scar width became larger. The correlation was significant at the 0.01 level. Significant difference was observed in wear scar width among different samples (P < 0.05). SEM and AFM results showed that veneering ceramic wear facets demonstrated grooves characteristic of abrasive wear. CONCLUSION: Multiple sintering can decrease the wear ability of Cercon veneer, and the wear pattern has the tendency to severe wear.

[Osteoblastic early attachment onto the surface of bioadhesive peptide modified pure titanium].

OBJECTIVE: To investigate the long-term integrity and the biological function of interface between the bioadhesive peptide modified implant surface and peri-implant tissue. METHODS: A short bioadhesive peptide containing Glycine-Tyrosine-Arginine-Glycine-Asparticacid-Serine (GYRGDS) sequence was immobilized onto the titanium implant surface by means of sol-gel coating technique and self-assembled monolayers (SAM). The chemical composition and organic functional groups on the titanium surfaces were characterized using XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectrometer). The adhesive strength and stability of osteoblasts on various implant surfaces were compared under flow condition. RESULTS: The results showed that alkali/hot water aging treatment could apparently improve the content of -OH functional groups of titanium surface. The chemical reactive Ti-O-Ti bonding at the surface of titanium played a vital role in inducing the formation of organosilane SAM. GYRGDS peptide can be covalently grafted onto the surface of titanium by SAM technique. The resistance of freshly adherent osteoblasts to detachment by flow was shear time dependent. When the four groups were compared under the same flow stress condition (2.05 Pa) at three specific time spans (30 min, 1 h, 2 h), the cells retention rates in GYRGDS-grafted groups were 93.0%, 54.4%, 34.4% respectively and were much higher than those in non-coated groups. CONCLUSIONS: It was suggested that GYRGDS might have positive effects on maintaining stability and adherence of cells onto the substrates under flow condition.

[Regulation of integrin beta1 mRNA expression by mechanical stress in human periodontal ligament fibroblasts].

OBJECTIVE: To investigate the effect of different kinds of mechanical stress on the mRNA expression of integrin beta1 subunit in cultured human periodontal ligament fibroblasts (hPDLF). METHODS: To scalp and remove the periodontal ligament attached to the mid-third part of the fresh root of young premolars extracted for the cause of orthodontics. Cultured hPDLF by the method of digesting by I-type collagenase combining with tissue adhering. Then hPDLF was isolated and purified by cells passage. The sixth passage's cells were selected to be loaded. A new cyclic strain loading apparatus. Forcel four point bending device was used for mechanically loading. Cells were loaded by three levels (1000, 2000, 4000 microstrain) of tensional and compressive forces and collected at different times (0, 0.5, 1, 4, 8, 12 h) course after strain loading. The quantity of integrin beta1 mRNA in every group was analyzed by means of quantitative real-time PCR with the special primers of up- and down-regulated genes. RESULTS: Dynamic mechanical forces down-regulated the expression of integrin beta1 subunit mRNA in hPDLF and the difference in groups by different magnitude, different kinds, and different time of mechanical forces loading were statistically significant. The stronger stimulated forces, the more down-regulated expression. Compression down-regulated the expression of integrin beta1 subunit mRNA more than tension did. CONCLUSION: Dynamic mechanical forces could regulate the expression of integrin beta1 subunit mRNA. The difference among all the groups by different magnitudes, different kinds, and different time of mechanical forces loading were statistically significant.

[Effect of simulating static magnetic field of magnetic attachment on osteoblastic morphology and surface ultrastructure].

OBJECTIVE: To investigate effects of the static magnetic field (SMF) generated by dental magnetic attachment on osteoblastic morphology and surface ultrastructure. METHODS: The in vitro cultured rat osteoblasts were exposed continuously to 12.5 mT, 125 mT, and 250 mT static magnetic fields for 1, 3, 5, and 7 days. After exposed in SMF, osteoblasts were observed under a phase contrast microscope, and then HE stained and observed under a light microscope. In addition, the cells were observed under a scanning electron microscope (SEM). RESULTS: By continuous exposure, the different intensities of SMF exposure did not change the vital osteoblast growth pattern or distribution. The SEM photos showed that there were certain changes in cellular microstructures for osteoblasts after exposed to 12.5 mT for 5 to 7 days, as well as 125 mT and 250 mT for 3 to 7 days. The more exposure time increased, the more microvesicles on the surfaces of cells were observed. CONCLUSIONS: Continuous SMF-stimulation could not affect the shape, distribution, and growth pattern of osteoblasts. The SMF of magnetic attachments could lead to certain changes in surface ultrastructures of osteoblasts in this study.

[Clinical application of implant-supported restoration with all-ceramic crown fused to small-size titanium abutment].

OBJECTIVE: To get aesthetic implant-supported restorations by means of the all-ceramic crown fused to small-size titanium abutment and evaluate the quality of the restorations. METHODS: A small-size titanium abutment that had extremely thin circumferential collar and axial wall was fabricated, while a Cercon all-ceramic crown made with computer aided manufacture (CAM). The crown was fused to the abutment by firing the opaque porcelain. A total of 6 restorations in 5 patients were installed and assessed according to the California Dental Association (CDA) quality evaluation system. RESULTS: All the restorations were fabricated well and ranked in clinic evaluation excellent for surface, anatomical form, marginal quality, and color at baseline and one year after insertion, respectively. CONCLUSIONS: The restoration of all-ceramic crown fused to titanium small-size abutment is a new aesthetic alternative for the implant-supported restoration.

[Comparison of translucency between enamel, dentin and Vita veneer porcelain].

PURPOSE: To compare the translucency between enamel, dentin and dental porcelain. METHODS: 32 newly extracted vital human central incisors were collected and cut into 0.8mm enamel slices and 1.0 mm dentin slices. 1.0 mm dental porcelain specimen were made with different Vita veneer porcelain, EN1, EN2, T4, Window, A1, A2, A3, A3.5, A4, B2, C2, D2, 3 samples for each kind. The transmittance and reflectance of tooth slices and porcelain specimen were measured by PR-650 spectra scan spectrocolorimeter. The transmittance coefficients were also calculated. The 95% confidence interval was obtained by SPSS 12.0 software package. SNK method was used to compare the transmittance coefficients of different dentin porcelains. RESULTS: The transmittance coefficient of tooth enamel ranged from 0.0817 mm(-1) to 0.1009 mm(-1), which was higher than that of two kinds of enamel porcelain (0.0507 mm(-1) for EN1 and 0.0408 mm(-1) for EN2). The transmittance coefficient of dentin (0.0418-0.0482 mm(-1)) was also higher than that of dentin porcelain (0.016-0.027 mm(-1)). The transmittance coefficient of dentin porcelain decreased with the increasing of chroma (P<0.05). CONCLUSIONS: Prominent difference exists between translucency of tooth tissue and dental porcelain, especially between enamel and enamel porcelain.

[Influence of manufacture technique on translucency and color of dental porcelain].

OBJECTIVE: To study the influence of manufacture technique on the translucency and color of dental porcelain. METHODS: Specimens were made of VITA VMK 95 dentin porcelain and enamel porcelain and divided into 3 groups: Sintering times group (1, 2, 4, 6, 8 and 10 times), sintering temperature group (910, 920, 930, 940 and 950 degrees C), sintering vacuum group (95, 65, 35 and 0 kPa). Transmittance, Y, dominant wavelength and saturation were measured by PR-650 spectra scan spectrocolorimeter. RESULTS: Transmittance of dentin porcelain increased after 6 times repeated sintering. Transmittance of enamel porcelain increased first after the second sintering, and then became decreasing when sintering more than 2 times. Transmittance of enamel porcelain deceased when sintering temperature was lower than standard. Decrease of sintering vacuum caused the transmittance of dentin and enamel porcelain decreased. The changing of value was coordinated with transmittance. Dominant wavelength and saturation had negative correlation with sintering times and temperature, and positive correlation with vacuum. CONCLUSION: Sintering times, temperature and vacuum all had prominent effects on the translucency and color of dental porcelain. Comparing with dentin porcelain, enamel porcelain was more sensitive with the modification of manufacture technique.

[Effects of simulating static magnetic fields of magnetic attachments on osteoblasts proliferation, cell cycle distribution and apoptosis ratio].

OBJECTIVE: To investigate the effects of the static magnetic field (SMF) generated by dental magnetic attachments on osteoblastic proliferations, cell cycle distribution, and apoptosis ratio. METHODS: By simulating those of the closed-field, the closure process and the open-field Magnedisc 800 magnetic attachments respectively, the in vitro cultured rat osteoblasts were exposed continuously to 12.5, 125, 250 mT SMF. The effects of the SMF on the proliferation of the cells were examined. MTT colorimetry test was performed to detect the effect of the SMF on the vitalities of cells. Flow cytometry was utilized to analyze the cell cycles and cell apoptosis rates. RESULTS: The SMF exposure didn't change the vital osteoblasts number, the cell cycle distribution and proliferation activities of osteoblasts. The cell apoptosis situation were not observed statistical differences. CONCLUSION: No matter the closed-field, the closure process and the open-field magnetic attachments respectively, continuous simulating SMF-stimulation of magnetic attachments couldn't change osteoblasts proliferation activity, cell cycle distribution, and apoptosis ratio.

[Effect of vacuum deposition technology on the metal-porcelain bond strength of a new type of CO-CR ceramic and framework dental alloy].

OBJECTIVE: To investigate the effect of a new engineering technique of vacuum deposition-plasma magnetron reactive sputter deposition technique on the metal-porcelain bond strength of a new type of Co-Cr ceramic and framework dental alloy. METHODS: Before porcelain painted on the specimens, the standardized metal strips made from DA9-4 dental alloy were coated with a thin Al2O3 ceramic film by plasma magnetron reactive sputter deposition technique. The conformation, structure and thickness of the ceramic film were analyzed. The specimens for three-point bending test made from DA9-4 alloy and VMK95 porcelain were used for metal-porcelain bond strength measurement, in the same time the interface of metal-porcelain and element distribution were also observed. RESULTS: The flexural bonding strength of metal-porcelain of sputtering group and control group were (180.55+/-16.45) MPa and (143.80+/-24.49) MPa. The flexural bonding strength of metal-porcelain of sputtering group was higher than control group significantly through statistical analysis (P<0.01). CONCLUSION: The plasma magnetron reactive sputter deposition technique has a positive effect in improving the bonding strength of DA9-4 dental alloy and ceramic.

[Wear behavior of enamel and veneering ceramics].

OBJECTIVE: To compare the wear between the enamel and two types of dental decoration porcelains for all-ceramic restorations (Vita-alpha, Vintage AL). METHODS: Friction coefficients, wear scar width, element concentrations and wear surface evolution were considered relatively to the tribology of that in vivo situation. The wear scars of the samples were characterized by means of dynamic atomic force microscopy (DFM). The different element concentrations of the surface before/after the wear test were determined with energy dispersion spectrometry (EDS). RESULTS: The friction coefficient varied from time in each kind of material. The statistical differences between materials were observed in wear scar width and properties of materials (P<0.05). DFM results showed wear surface of natural tooth full of abrasive particles and denaturation of dental texture. Wear surface of veneering ceramics consisted mainly of abrasive particles, plough and microcracking. EDS results showed that the element concentration of Fe was obviously found on the samples after wear. CONCLUSION: The main underlying mechanisms of natural teeth wear are abrasive, and denaturation of dental texture. Abrasive wear, adhesion and fatigue of veneering ceramics characterize the wear patterns which plays different role in Vita-alpha and Vintage AL. The wear patterns of veneering ceramics can be described as mild wear.