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STATEMENT OF PROBLEM: Previous research into the strength of endodontically treated or vital teeth restored with inlays or onlays has not determined which restoration method and material provide the most favorable stress distribution upon loading. PURPOSE: The purpose of this study was to calculate the von Mises stresses in a mandibular first molar using a 3-dimensional (3-D) finite element model. Models compared endodontically treated and vital teeth, a variety of restorative materials, and the use of either inlays or onlays to restore teeth. MATERIAL AND METHODS: Four 3-D models of mandibular first molars were created: (1) the IV group (inlay restored, vital pulp); (2) the OV group (onlay restored, vital pulp); (3) the IE group (inlay restored, endodontically treated); and (4) the OE group (onlay restored, endodontically treated). In each group, 3 types of restorative material were tested: (1) composite resin, (2) ceramic, and (3) gold alloy. The materials had elastic moduli of 19 GPa, 65 GPa, and 96.6 GPa, respectively. Each model was subjected to a force of 45 N directed to the occlusal surface, applied either vertically or laterally (45 degrees obliquely). The stresses occurring in dentin tissue were calculated. The stress distribution patterns and the maximum von Mises stresses were calculated and compared. RESULTS: The different restorative materials exhibited similar stress distribution patterns under identical loading conditions. In each group, the gold-restored tooth exhibited the highest von Mises stress, followed by ceramic and composite resin. The maximum von Mises stress in dentin was found in the IE group (16.73 MPa), which was 5 times higher than the highest value found in the OV group (2.96 MPa). The highest stresses, which occurred at the floor of the preparation and the cervical region in dentin, were in the IE group. The stress concentration area in the IE group was also larger. CONCLUSIONS: The results indicate that endodontic treatment caused higher stress concentration in dentin compared with vital teeth, but that proper restoration can minimize internal stresses. In the models, the von Mises stress values increased with the increasing elastic modulus of the restorative material. Composite resin onlays showed the best performance overall in minimizing internal stresses. As internal stresses are indicated as a prime failure mechanism of the restoration, composite resin onlays are expected to better restore structural integrity.
Subject(s)
Dental Materials/therapeutic use , Dental Restoration Failure , Dental Stress Analysis , Inlays/methods , Root Canal Therapy , Tooth, Nonvital , Composite Resins/therapeutic use , Computer Simulation , Dental Caries/therapy , Dental Porcelain/therapeutic use , Elastic Modulus , Finite Element Analysis , Gold Alloys/therapeutic use , Humans , Imaging, Three-Dimensional , Mandible , Molar , Stress, MechanicalABSTRACT
Modern stomatological education in China has developed into its present form over a period of 90 years. The College of Stomatology of the Fourth Military Medical University, as the only one of its kind in the Chinese army, has been playing an essential role in training professionals and guaranteeing the dental health of all officers and soldiers in the army. Its education system and five-year curricula designed for undergraduates were introduced in relation to those of China's first-rate stomatological colleges. This paper also examines in detail the problems of the current curriculum and holds up the prospect of a further improved curriculum to meet the ever increasing demand for qualified professionals in the military service.
Subject(s)
Military Dentistry/education , China , Curriculum , Education, Dental , HumansABSTRACT
Objective:To obtain mutA gene of Strepto c occus mutans (Ms),and to express it in E.coli DH5?.Methods: mutA gene was amplified by PCR with specific primers from genome of Ms CH43 strain. After sequencing, the gene segment was inserted into vector pProEX and expressed in E.coli DH5?.The protein expression was induced by ITPG an d the protein products were examined by 180 ml/L SDSPAGE electrophorosis. Results:The length of PCR product was 147 bp and was identical to mu tA gene reported by GenBank.The mutA gene product was expressed in E.col i DH5? with Mr of 5.7?10 3.The maximum mutA protein product amount (20% of the total bacterial protein) was obtained when the A 600 value of DH5? was 1.666,IPTG concerntration 1.0 mmol/L and induction time 6 h.Conclus ion:mutA of Ms CH43 can be cloned and expressed in E.coli DH 5?.
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Objective:To study the effects of parathyroid hormone (PTH) on BMP3 expression of cultured human dental papilla mesenchymal cells (DPMCs). Methods:DPMCs were obtained by cell culture, BMP3 mRNA expression was studied by in situ hybridization. BMP3 gene expression of human DPMCs after exposure to 33.3 nmol/L PTH for 5 days were measured. The cells cultured in the medium without PTH served as control.Results: Stronger BMP3 positive signals were observed in PTH treated cells than that in the control cells.Conclusion:PTH stimulats BMP3 systhesis of cultured DPMCs.
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Objective: To study the effects of light intensity on the compressive strength and tensile strength of light -curing composite resin. Methods: 25 samples of Shade A (Dentsply,USA) light-curing composite resion in the size of 10?5?1(mm) and equally divided into 5 groups.The light intensities (mW/cm 2?40 s) of 300,500,800,300 mW/cm 2?10 s+500 mW/cm 2?30 s,300 mW/cm 2?10 s+800 mW/cm?30 s were applied during the light-curing in group 1,2,3,4 and 5 respectively.The compressive strength and tensile strength of of the samples were measured by computer-controlled electronic testing machine (type WDW-100). Results:The compressive strengths (MPa) of group 1,2,3,4 and 5 were 228.68?20.25,274.67?6.99,380.53?9.81,345.47?10.71 and 414.06?29.34 respectively (P
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Objective:To construct a recombination plasmid containing a kanamycin resistance gene,the upstream and downstream fragment of luxS of Streptococcus mutans so that luxS can be knock out by transforming the plasmid into S.mutans later.Methods:Kanamycin resistance gene,the upstream and downstream of luxS were cloned respectively by using plasmid pEGFP-N1 and DNA of Streptococcus mutans as template.Then the genes were ligated into Multiple Cloning Site(MCS) of vector pMD19-T in certain order and transformed into E.coli Competent Cells.Finally transformants were selected for resistance to kanamycin and ampicillin.Results:Kanamycin resistance gene and the upstream and downstream of luxS were successfully ligated into accurate enzyme digestion site of vector pMD19-T,and restriction digests analysis and sequencing result was correct.Conclusion:LuxS gene knock-out of Streptococcus Mutans recombinant plasmid is constructed and built a base of constructing Streptococcus Mutans luxS mutans in the future.
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Objective:To observe the structure and formation of plaque.Methods: A 1 mm in heigth and 3 mm in diameter plastic ring was adhered to enamel slice, then the enamel slices with plastic rings were adhered to right maxillary first molars in order to establish the model of dental plaque.The specimens of dental plaque for 1 day, 5 days and 9 days were serially sectioned and were imaged by TEM. Results:The TEM results showed that there were few microorganisms in early plaques, mainly of which were coccus. With the time went on, the kind and quantity of the microorganisms became more, and bacilli and hyphomycetes also appeared. In mature plaques, there were fence-like structure with coccus in center and bacilli and hyphomyceters at both sides, in which some bacteria went to necrosis. Conclusion:The ultrasrtucture of this dental plaque model was similar to nature's with a certain extent values.
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Objective:To determine the effects of parathyroid hormone(PTH) upon dentinogenesis in rat tooth. Methods:15 SD rats aged 42 d were evenly divided into 3 groups.In the groups of control,PTT and PTX,shamoperatoin,parathyroid autotransplantation and parathyroidectomy were conducted respectively.After operation serum Ca 2+ was weekly measured with methylthymol method.30 d after operation dentinogenesis was observed with HE staining and light microscopy.Results:30 d after operation,serum Ca 2+ concentration in PTX group was lower than that in control and PTT groups(P
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Objective: To study the effects of parathyroid hormone(PTH) on the calcification characters of cultured human dental papilla mesenchymal(DPM) cells.Methods: DPM cells were cultured up to 35 days in two groups. The control group was cultured in DMEM supplemented with 15% FCS,50 ?g/ml ascorbic acid and 10 mmol/L ?-glycerophosphate. The cells in experimental group were cultured in above mentionned medium containing 33.3 nmol/L of PTH. The medium was changed every 3 or 4 days. Osteocalcin secretion of the cells was measured by radioimmunoassay.Results: Addition of TPH in medium caused a significant increase of osteocalcin secretion from 21 to 35 days culture (P
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To assess the roles of glutamate and its ionotropic receptor in processing noxious sensory input from dental pulp,glutamate NMDA receptor subtype antagonist,MK-801 and non-NMDA receptor subtype antagonist,CNQX were administrated separately into left lateral cerebral ventricle prior to exposing pulp cavity of left maxillary first molar tooth.The number of Fos-positive neurons in medulla oblongata was measured and compared with that of the group with simple exposure of dental after same survival time pulp.Fos protein expression was reduced dose-dependently by an administration of MK-801,but CNQX had little effect.The results showed that glutamate may be an excitatory transmitter of noxious dental pulp sensory input to neurons in medulla oblongata.In pain nodel of mechanical exposing dental pulp,NMDA receptor subtype has an important role in this process.
