Influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns using three-dimensional finite element analysis.@*METHODS@#A maxillary second premolar was scanned by Micro-CT and a three-dimensional finite element model of ceramic endocrown with 1 mm thickness of base was established. A model without base was also established as a negative control. Four kinds of conventional base materials with different elastic modulus were adopted: light cure glass ionomer(3M Vitrebond, 3 657 MPa), flowable composite resin(3M Filtek Z350XT Flowable Restorative, 7 300 MPa), high strength glass ionomer(GC Fuji Ⅸ, 13 130 MPa), and posterior composite resin(3M Filtek P60, 19 700 MPa). With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and adhesive layer were investigated by three-dimensional finite element analysis.@*RESULTS@#The maximum von Mises stress values(vertical/oblique) in dentin and adhesive layer were measured as follows: (1) no base material: 19.39/70.49 MPa in dentin and 6.97/17.97 MPa in adhesive layer; (2) light cure glass ionomer: 19.00/69.75 MPa in dentin and 6.87/16.30 MPa in adhesive layer; (3) flowable composite resin: 18.78/69.33 MPa in dentin and 6.79/16.17 MPa in adhesive layer; (4) high strength glass ionomer: 18.71/69.20 MPa in dentin and 6.74/16.07 MPa in adhesive layer; (5) posterior composite resin: 18.61/69.03 MPa in dentin and 6.70/16.01 MPa in adhesive layer. Under the same loading condition, models with different elastic moduli of base materials had similar stress distribution patterns. The von Mises stress of tooth tissue was mainly concentrated in the tooth cervix. Under oblique load, the regions where von Mises stress concentrated in were similar to those under a vertical load, but the values increased. The stress concentration in the tooth cervix was alleviated in models with base materials compared with the model without base material. The maximum von Mises stress in the tooth tissue and adhesive layer decreased when the elastic modulus of base materials increased and got close to that of dentin.@*CONCLUSION@#The posterior composite resin of which the elastic moduli is high and close to that of dentin is recommended as base material for premolar endocrowns to alleviate the concentration of stress in tooth cervix and adhesive layer.

Investigation on levels of polybrominated diphenyl ethers in retail fish and egg products in Shenzhen / 中华预防医学杂志

<p><b>OBJECTIVE</b>To reveal the levels and distribution of polybrominated diphenyl ethers (PBDEs) in fish and egg products at retail in Shenzhen, and to evaluate the local people's exposure to PBDEs from these food.</p><p><b>METHODS</b>27 fish and egg samples were collected from supermarket and farmer's market in Shenzhen during August and October in 2008. According to the guideline of USEPA1614 method, the accelerated solvent extraction (ASE) technology was used for the extraction of PBDEs from fish and egg samples. After a series of purification processes including treatments of FMS column chromatography, acidic silica gel, silica gel and Al2O3 column, the levels of eight PBDEs congeners in the samples were determined by isotope dilution high resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS) method.</p><p><b>RESULTS</b>When BDE-209 was not taken into account, the median concentrations of ΣPBDEs in fish products was 914.7 pg/g wet weight, among which the datas for fresh water fish and sea fish were 328.2 and 1108.8 pg/g wet weight, respectively, showing a statistical significant difference (P < 0.05). BDE-47 was the predominant congener in fresh water fish and sea fish by a contribution proportion of 61% and 57%, respectively. The median concentrations of ΣPBDEs in egg products were 99.8 pg/g wet weight and the predominant congeners are BDE-47 and BDE-99, with a contribution proportion above 70%. BDE-209 was not detected in fresh water fish and the median concentration in sea fish and egg products are 243.7 and 472.6 pg/g wet weight, respectively, which caused the predominant congener changed to BDE-209 in egg products when BDE-209 was take into account. The median dietary intake of PBDEs from fish and egg products among local residents in Shenzhen was estimated as 102 ng/d.</p><p><b>CONCLUSION</b>The level of ΣPBDEs in fish and egg products in Shenzhen is relatively high. The characteristics of PBDEs pollution are quite different between fish and egg products. The level of daily dietary intake of PBDEs from fish and egg products among local residents in Shenzhen is also relatively high.</p>

The levels of dioxin in 60 human breast milk samples and the exposure risk factor analysis in Shenzhen / 中华预防医学杂志

<p><b>OBJECTIVE</b>To investigate the levels of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-p-furans (PCDD-Fs) in human breast milk of the mothers who lived in non-directly persistent organic pollutants (POPs) polluted area in Shenzhen, and the correlation of exposure risk factor was analyzed.</p><p><b>METHODS</b>From July to November in 2007, 60 primiparas by vaginal delivery after parturition 3 weeks to 2 months were sampled for breast milk who aged from 20 - 34 years old and has lived in Shenzhen non-directly POPs polluted areas over 5 years. PCDD-Fs were extracted from the frozen-dried samples with accelerated solvent extraction (ASE), cleaned up by fluid management system (FMS) and quantified by high-resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS) using isotope dilution methodology. TEQ were calculated. The correlation relationship among infant's birth weight and length, participatory's dietary, age, inhabitation period, environment and the body burden of PCDD-Fs in mother was statistically analyzed by SPSS 13.0.</p><p><b>RESULTS</b>The participants aged from 20 - 34 years old (28 years on average) and lived in Shenzhen for 5 - 29 years (10 years on average). The concentration of PCDD-Fs in 60 breast milk samples were 26.957 143 - 669.583 333 pg/g fat (mean: 7.224 817 pg/g fat, median: 84.176 062 pg/g fat), and TEQ-PCDD-Fs in samples were 2.420 793 - 29.014 277 pg/g fat (mean: 8.645 992 pg/g fat, median: 7.751 804 pg/g fat). 2, 3, 4, 7, 8-PeCDF, 1, 2, 3, 7, 8-PeCDD, 2, 3, 7, 8-TCDD were the dominant contributors to the total TEQ, which were 3.691 654 pg/g fat (42.689 378%), 2.478 315 pg/g fat (28.652 356%), and 0.980 995 pg/g fat (11.343 995%) respectively. Significant positive correlations were found among age (r = 0.26, P < 0.05), inhabitation period (r = 0.49, P < 0.05), the consumption of fish (r = 0.37, P < 0.05) and the concentrations of TEQ-PCDD-Fs in the study.</p><p><b>CONCLUSION</b>The levels of dioxin chemicals in the breast milk samples in non-directly POPs polluted areas of Shenzhen are high. Significant positive correlations were found among age, inhabitation period, the consumption of fish and the concentration of PCDD-Fs.</p>

Levels of PCDD/Fs, PCBs and PBDEs compounds in human placenta tissue / 中华预防医学杂志

<p><b>OBJECTIVE</b>To establish the methods of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) compounds determination by isotope dilution HRGC/HRMS simultaneously in human placenta tissue from mothers, and assess the human exposure risk to dioxins and PBDEs in study.</p><p><b>METHODS</b>Concentrations of 17 PCDD/Fs and 12 dioxin-like PCBs as well as 7 PBDEs were measured in human placenta tissue samples by isotope dilution HRGC/HRMS. SigmaTEQ (PCDD + PCDFs + PCBs) concentration using WHO-TEF factor and PBDEs concentration was calculated respectively. Risk assessment of mother exposure to dioxins and PBDEs was evaluated.</p><p><b>RESULTS</b>Median of SigmaTEQ (PCDD + PCDFs + PCBs) concentration for six samples was 18.15 WHO-TEQ pg/g lipid, ranging from 5.14 - 67.01 WHO-TEQ pg/g lipid. Although the median of SigmaTEQ (PCDD + PCDFs + PCBs) was lower than that of human blood of EU and Japan, and close to that of Korea and Taiwan non-exposure as reported in the literatures, the highest SigmaTEQ (PCDD + PCDFs + PCBs) concentration of placenta sample exceeded the value of high dioxins exposure area subjects in Taiwan. The dominant contributor congener for WHO-TEQ were 2, 3, 4, 7, 8-PeCDF, 1, 2, 3, 7, 8-PeCDD, PCB126, totally accounted for 65 percent of SigmaWHO-TEQ. Median and average of PBDE concentration for six samples were 2.73 ng/g lipid and 7.17 ng/g lipid, respectively, ranging from 0.95 - 25.99 ng/g lipid. BDE47 was the dominant contributor congener for the total concentration, accounted for 35 percent.</p><p><b>CONCLUSION</b>The methods of PCDD/Fs, PCBs and PBDEs compounds determined by isotope dilution HRGC/HRMS simultaneously in human placenta tissue from mothers were established successfully, and the human exposure risk to PCDD/Fs, PCBs and PBDEs should be surveyed for the donor with the highest SigmaTEQ (PCDD + PCDFs + PCBs) and PBDEs concentration of placenta sample in the future.</p>

Levels of polychlorinated dibenzo-p-dioxins and dibenzo-furans in sea fish samples in some sea areas in China / 中华预防医学杂志

<p><b>OBJECTIVE</b>To analyse the levels of polychlorinated dibenzo-p-dioxins and dibenzo-furans (PCDD/Fs) in sea fish samples in some sea area in China surveyed by using isotope dilution HRGC/HRMS and was evaluated the local people with PCDD/Fs exposure from eating fish.</p><p><b>METHODS</b>Seven different kinds of fish and twenty fishes were sampled totally. Dibenzo-p-dioxins and dibenzo-furans were extracted from fish samples by Soxhlet extraction, concentrated and purified by FMS column chromatograph and enriched by carbon column. Confirmation and quantitative analysis at ng/kg level of PCDD/Fs was performed by HRGC/HRMS using multiple ion detection mode (MID).</p><p><b>RESULTS</b>Carp-2 was the certified reference material obtained from the NRC Institute of Canada. The concentration of 9 compounds was consistent with the certified value, and precision was evaluated in this study. The relative standard deviation was less than 15 percent for three times determination. The average concentration of 20 sea fishes was 1.48 ng/kg wet weight, the range was in 0.21-8.10 ng/kg wet weight, and the average total toxicity equivalency factor (TEQ) was 0.292 ng TEQ/kg (wet weight basis) and the range was 0.030-1.291 ng TEQ/kg for these 20 fishes. The evaluation exposure from fish for local people was 0.58 pg WHO-TEQ/kg BW.day.</p><p><b>CONCLUSION</b>The levels of PCDD/Fs was different from sample to sample, and the exposure from fish be less than WHO tolerance limit standard, however, the status for PCDD/Fs pollution should not be ignored especially when having an intake of multi-food.</p>