BACKGROUND:During the restoration of residual molar crown, a little part of tooth is still remained commonly. After the restoration, with various forces, stress distribution affects directly the results after restoration. Finite element method is gradually applied in stress analysis on artificial tooth.OBJECTIVE: To establish the three-dimensional (3-D) finite element model of post-inlay restoration of the first residual mandibular molar crown so as to provide experimental data for improving model establishment of complicated teeth and analysis on the property of stress distribution of restoring methods.DESIGN: Repeated observation and measurement were given.SETTING: Department of Stomatology and Department of Radiology of First Hospital affiliated to Sun Yat-sen University;Department of Solid Mechanics,College of Traffics and Communications, South China University of Technology; Department of Restoration of Guanghua College of Stomatology.MATERIALS: The experiment was performed in Department of Solid Mechanics, College of Traffics and Communications of South China University of Technology from November 2003 to December 2004. Six first mandibular molars on the right side with normal morphology in vitro were collected, and Toshiba Xpress/SX spiral CT machine, image photo synthesis software and finite element analysis software ANSYS were applied in the experiment.METHODS: 1 of the 6 first mandibular molars on the right side with normal morphology in vitro was selected for pulpectomy, which was the best in density and near to clinical requirement in morphology. With pulpectomy, the prosthesis of braking-lock post-inlay restoration was prepared. Spiral CT-cross scanning was performed in premolar crown before the restoration, the residual crown with post-inlay in main root canal after restoration and the residual crown with braking-lock second post-inlay restoration. With image photosynthesis software, 3-D digital model of residual tooth and metal part was established and the entire tooth model was prepared after adhesion of two parts. In order to provide better boundary conditions of simulated natural tooth in practice, alveolar bone was considered. Under Mesh order in ANSYS software, automatic mesh generation was performed in the model directly.MAIN OUTCOME MEASURES: Establishment of 3-D finite element models of residual tooth before restoration, post inlay, and alveolar bone and tooth after restoration and the results of mesh generation.RESULTS: By establishing 3-D finite element models of residual tooth before restoration, post inlay, alveolar bone and tooth after restoration and automatic mesh generation, there were altogether 117720 units and 20988nodes. Good geometric similarity presents between the construction model of 3-D finite element model and solid tissue.CONCLUSION: Combination of 3-D finite-element model with spiral Ctcross technology establishes complex dental models, simulates practical conditions authentically and is good in operation.

Objective To investigate the application of 3D ultrashort TE double echo pulse sequence in the bone and joint MR imaging. Methods Eight volunteers and a porcine fibula in vitro with intact muscle were involved in this study. Among the volunteers, one was suspected with meniscus tear, the others were asypmtomatic. MR imaging of 3D ultrashort TE double echo pulse sequence were performed on the tibial diaphysis, knee joint, ankle and wrist of each volunteer and the porcine fibula in vitro. Using the first echo images subtract with the second echo images, we observed the subtracted images from the primary double echo images and MPR images respectively. We then compared the difference of SNR. Four different echo times of the first echo (TE1) in the images were set as 0. 08 ms, 0. 16 ms, 0. 24 ms, 0. 35 ms. The quality of the subtracted images from the primary double echo images of the four different TE1 was compared.The MIP images from the primary double echo images with TE1 of 0. 08ms were performed to display the 3D structure of the ankle tendons. The data were analysed with One-Way ANOVA and Paired-Samples t test statistically. Results The 3D images of the tendons were displayed through MIP of the subtracted images from the primary double echo images. The cortical bones, periosteums, tendons and menisci of the 8 volunteers appeared as high signal intensity in UTE pulse sequence. The SNR of the subtracted images from MPR images (SNR, 3.76 ± 0. 88) was significantly higher than those from the primary double echo images(SNR,2. 82±0. 75) (t = - 4. 851, P < 0. 01). There were significant differences among the subtracted images from each of the four different TE1. The highest quality were obtained from the TE1 of 0.08ms. The CNR were as follows: CNR<,0.08ms>1.74±0. 54, CNR<,0.16ms> 1.35 + 0. 60, CNR0.24ms>1.20±0. 48,CNR<0.35ms> 0.89±0. 24 (F = 3. 681, P < 0. 05). The artifacts appeared markedly with prolonging of the TE1.Conclusion The MRI of ultrashort TE double pulse sequence may display the short T2 components that appeared as low signal with conventional clinical MR imaging, which made it pessible to quantify the tissues containing a majority of short T2 components.

nal surface coil,and it can be a promising method to diagnose interphalangeal joints lesions.

OBJECTIVE: To explore the genetic mechanism underlying a case with para-Bombay phenotype. METHODS: The ABO and Lewis phenotype were identified with serological methods. The coding regions of exons 6 and 7 of the ABO and FUT1 genes were amplified with PCR and directly sequenced. Haploid sequence analysis was carried out on the variant sites of the FUT1 gene. RESULTS: Serological analysis confirmed that the proband has a rare para-Bombay phenotype. Direct sequencing revealed that he was a B.01/O.01.02 heterozygote for the ABO gene, and had heterozygous deletion for the 768 and 881-882 sites of the FUT1 gene. Further haploid analysis showed that the c.881_882delTT deletion has occurred in one haploid while c.768delC was present in the other haploid. The proband was therefore determined as a FUT1*01N.13/01N.20 heterozygote, which have resulted in frameshift in polypeptide chain p.Phe294Cysfs*40 and p.Val257Phefs*23, respectively. CONCLUSION A rare bi-allelic heterozygous deletion of para-Bombay phenotype has been identified in a blood donor. The c.881_882delTT and c.768delC deletions may decrease the activity of α-1,2-fucosyltransferase.
Animals ; Male ; ABO Blood-Group System/genetics* ; Alleles ; Fucosyltransferases/genetics* ; Genotype ; Heterozygote ; Mutation ; Phenotype ; Humans

Objective : To study the changes of acid resistance, oxidation resistance and high osmotic pressure resistance of Streptococcus mutans after knockout of rnc gene and its possible regulatory mechanism. Methods: Through PCR ligation mutagenesis, an rnc knockout mutant (Smurnc) was constructed. Acid tolerance, oxidation tolerance and high osmotic pressure tolerance were compared between Smurnc and the wild strain respectively. Real-time RT-PCR was used to verify the changes in expression of stress tolerance related genes at the transcriptional level. Results : When rnc gene was knocked out, the acid tolerance (χ2=13.464, P=0.001) and oxidation tolerance (χ2=4.505, P=0.048) of Streptococcus mutans was significantly decreased, but the high osmotic pressure tolerance was significantly increased (χ2=11.971, P=0.001). Expression of stress tolerance related genes luxS and ropA (0.64 and 0.51 times expression of the wild strain) had been significantly downregulated (P<0.001). Expression of htrA and brpA (1.56 and 1.80 times expression of the wild strain) had been significantly upregulated (P<0.001). Conclusion The deletion of rnc gene affects the expression of the environmental tolerance related genes of Streptococcus mutans, which reduces its acid resistance and oxidation resistance, and enhances its tolerance to hypertonic pressure.

Streptococcus mutans (S. mutans) is generally regarded as a major contributor to dental caries because of its ability to synthesize extracellular polysaccharides (EPS) that aid in the formation of plaque biofilm. The VicRKX system of S. mutans plays an important role in biofilm formation. The aim of this study was to investigate the effects of vicK gene on specific characteristics of EPS in S. mutans biofilm. We constructed single-species biofilms formed by different mutants of vicK gene. Production and distribution of EPS were detected through atomic force microscopy, scanning electron microscopy and confocal laser scanning microscopy. Microcosmic structures of EPS were analyzed by gel permeation chromatography and gas chromatography-mass spectrometry. Cariogenicity of the vicK mutant was assessed in a specific pathogen-free rat model. Transcriptional levels of cariogenicity-associated genes were confirmed by quantitative real-time polymerase chain reaction. The results showed that deletion of vicK gene suppressed biofilm formation as well as EPS production, and EPS were synthesized mostly around the cells. Molecular weight and monosaccharide components underwent evident alterations. Biofilms formed in vivo were sparse and contributed a decreased degree of caries. Moreover, expressional levels of genes related to EPS synthesis were down-regulated, except for gtfB. Our report demonstrates that vicK gene enhances biofilm formation and subsequent caries development. And this may due to its regulations on EPS metabolism, like synthesis or microcosmic features of EPS. This study suggests that vicK gene and EPS can be considered as promising targets to modulate dental caries.
Animals ; Biofilms ; Dental Caries ; Dental Plaque ; Rats ; Streptococcus mutans/genetics*