Occupational noise and hypertension in Southern Chinese workers: a large occupational population-based study.

INTRODUCTION: An increasing number of original studies suggested that occupational noise exposure might be associated with the risk of hypertension, but the results remain inconsistent and inconclusive. In addition, the attributable fraction (AF) of occupational noise exposure has not been well quantified. We aimed to conduct a large-scale occupational population-based study to comprehensively investigate the relationship between occupational noise exposure and blood pressure and different hypertension subtypes and to estimate the AF for hypertension burden attributable to occupational noise exposure. METHODS: A total of 715,135 workers aged 18-60 years were included in this study based on the Key Occupational Diseases Surveillance Project of Guangdong in 2020. Multiple linear regression was performed to explore the relationships of occupational noise exposure status, the combination of occupational noise exposure and binaural high frequency threshold on average (BHFTA) with systolic and diastolic blood pressure (SBP, DBP). Multivariable logistic regression was used to examine the relationshipassociation between occupational noise exposure status, occupational noise exposure combined with BHFTA and hypertension. Furthermore, the attributable risk (AR) was calculated to estimate the hypertension burden attributed to occupational exposure to noise. RESULTS: The prevalence of hypertension among occupational noise-exposed participants was 13·7%. SBP and DBP were both significantly associated with the occupational noise exposure status and classification of occupational noise exposure combined with BHFTA in the crude and adjusted models (all P < 0·0001). Compared with workers without occupational noise exposure, the risk of hypertension was 50% greater among those exposed to occupational noise in the adjusted model (95% CI 1·42-1·58). For participants of occupational noise exposed with BHFTA normal, and occupational noise exposed with BHFTA elevated, the corresponding risks of hypertension were 48% (1·41-1·56) and 56% (1·46-1·63) greater than those of occupational noise non-exposed with BHFTA normal, respectively. A similar association was found in isolated systolic hypertension (ISH) and prehypertension. Subgroup analysis by sex and age showed that the positive associations between occupational noise exposure and hypertension remained statistically significant across all subgroups (all P < 0.001). Significant interactions between occupational noise status, classification of occupational noise exposure combined with BHFTA, and age in relation to hypertension risk were identified (all P for interaction < 0.001). The associations of occupational noise status, classification of occupational noise exposure combined with BHFTA and hypertension were most pronounced in the 18-29 age groups. The AR% of occupational noise exposure for hypertension was 28·05% in the final adjusted model. CONCLUSIONS: Occupational noise exposure was positively associated with blood pressure levels and the prevalence of hypertension, ISH, and prehypertension in a large occupational population-based study. A significantly increased risk of hypertension was found even in individuals with normal BHFTA exposed to occupational noise, with a further elevated risk observed in those with elevated BHFTA. Our findings provide epidemiological evidence for key groups associated with occupational noise exposure and hypertension, and more than one-fourth of hypertension cases would have been prevented by avoiding occupational noise exposure.

The relationship between occupational stress and job burnout among female manufacturing workers in Guangdong, China: a cross-sectional study.

This study aims to investigate the relationship between occupational stress and job burnout in female manufacturing workers. A random sample of 1081 female workers in electronic manufacturing in Guangdong Province participated in the present study. An anonymous self-administered questionnaire that covered social-demographic characteristics, the Chinese version of the Job Content Questionnaire, the Chinese version of the Effort-reward Imbalance Questionnaire, and the Maslach Burnout Inventory for the General Survey, was used to assess occupational stress and job burnout. Independent sample t-test, one-way analysis of variance (ANOVA), correlation analysis, hierarchical multiple regression analysis and logistic regression analysis were used in data analysis. Occupational stress was positively correlated with emotional exhaustion and depersonalization and negatively correlated with personal accomplishment. After adjusting for sociodemographic characteristics, job strain was a risk factor for emotional exhaustion (OR = 2.27, 95% CI: 1.61-3.20) and depersonalization (OR = 1.96 95% CI: 1.45-2.64). Female workers with high effort-reward imbalance had an increased risk of depersonalization (OR = 1.96, 95% CI: 1.33-2.90). Furthermore, female workers with high overcommitment had an increased risk of emotional exhaustion (OR = 3.07, 95% CI: 2.06-4.58) and depersonalization (OR = 2.83, 95% CI: 1.92-4.17), while higher social support reduced the risk of emotional exhaustion (OR = 0.37, 95% CI: 0.26-0.53). The job burnout of female manufacturing workers is significantly correlated with their occupational stress. Higher job strain and overcommitment might be important contributors to job burnout. Increased worker social support can reduce job burnout.

BMS-202, a PD-1/PD-L1 inhibitor, decelerates the pro-fibrotic effects of fibroblasts derived from scar tissues via ERK and TGFß1/Smad signaling pathways.

INTRODUCTION: Hypertrophic scar (HS), a fibroproliferative disorder of the skin with some tumor-like properties, is closely related to dysregulated inflammation. PD-1/PD-L1 inhibitor is a promising medication for cancer therapy as its potent functions on adaptive immune response; whether it could be a candidate for HS therapy has aroused our interest. This study aimed to explore the effect and the mechanism of BMS-202, a PD-1/PD-L1 inhibitor, in HS. METHODS: Ten HS and adjacent normal skin tissues collected from HS patients were used to detect α-SMA, collagen I, and PD-L1 expression by Quantitative reverse transcription-polymerase chain reaction and western blot (WB) analysis. Fibroblasts derived from HS tissues (HFBs) were exposed to diverse concentrations of BMS-202, of which proliferation, migration, apoptosis, and collagen synthesis were evaluated by Cell Counting Kit-8, wound healing, terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End labeling, and [3 H]-proline incorporation assays, respectively. The effect of BMS-202 on α-SMA and collagen I expression, and transforming growth factor beta 1 (TGFß1)/Smad signaling in HFBs was also determined by WB and enzyme-linked immunosorbent assay. RESULTS: The expression level of PD-L1 was significantly elevated in both HS tissues and HFBs, which was positively correlated with α-SMA and collagen I expressions. BMS-202 exerted a significant suppression effect on the cell proliferation, migration, collagen synthesis, and α-SMA and collagen I expression of HFBs in a concentration-dependent way; but did not affect apoptosis. Finally, BMS-202 could reduce the phosphorylation of ERK1/2, Smad2, and Smad3, and the TGFß1 expression once its concentration reached 2.5 nM. CONCLUSION: BMS-202 effectively suppressed proliferation, migration, and extracellular matrix deposition of HFBs, potentially through the regulation of the ERK and TGFß1/Smad signaling pathways.

Socio-demographic factors, dental status, oral health knowledge and attitude, and health-related behaviors in dental visits among 12-year-old Shenzhen adolescents: a multilevel analysis.

BACKGROUND: Dental visits can provide education, prevention and treatment measures for teenagers, and help to form correct oral health knowledge and attitude. The purpose of this study was to evaluate the effects of socio-demographic factors, dental status, oral health literacy, and health-related behaviors on dental visits in early 12-year-old adolescents. METHODS: 953 subjects aged 12 in Longhua district of Shenzhen were investigated. The questionnaire and clinical examination were applied in schools, and two-level logistic regression models were constructed to interpret the effect of individual and contextual factors on Shenzhen adolescents' dental visits. RESULTS: A total of 27.6% of the participants had not been to a dentist. After the multiple factors binary logistic regression analysis, it confirmed that the following variables: Shenzhen Hukou (OR 2.133, 95% CI 1.429-3.185), moderate caries (OR 1.404, 95% CI 1.022-1.928) and severe caries (OR 2.546, 95% CI 1.461-4.437), Angle Class II malocclusion (OR 1.703, 95% CI 1.134-2.556), sometimes or never toothbrushing (OR 2.985, 95% CI 1.491-5.975), dental floss usage (OR 1.829, 95% CI 1.250-2.677), having had a toothache within the last 12 months (OR 1.469, 95% CI 1.086-1.986), high knowledge attitude level (OR 1.570, 95% CI 1.106-2.229), moderate knowledge attitude level (OR 1.534, 95% CI 1.073-2.193), were associated factors for dental visit experience. CONCLUSIONS: The dental visits of 12-year-old children in Longhua district of Shenzhen is affected by multi-dimensional factors. It is suggested that oral health education should be strengthened, good oral hygiene habits should be cultivated, and the needs and utilization of oral health services for non-Shenzhen Hukou adolescents should be paid attention to, so as to effectively improve the overall oral health level of adolescents.

Study on the Effect of Petroleum Components on the Elution of Oily Sludge by a Compound Biosurfactant.

Currently, research on oily sludge treatment mainly focuses on optimizing the deoiling effect and research on the deoiling mechanism, and the influence of petroleum components on the properties and treatment of oily sludge is rarely considered. Therefore, in this study, petroleum substances in three types of oil sludge were eluted using the biosurfactant cleaning technology, and the influence of petroleum components on the cleaning process was explored. The results showed that the biosurfactants rhamnolipid and sophorolipid had a synergistic effect, and the oil-removal rate was as high as 92.2% when the SL mass fraction was 0.4 in the compound biosurfactant. Three types of oily sludge, wellsite-landing sludge, pipeline-landing sludge, and tank-bottom sludge, were cleaned by the compound biosurfactant; the results showed that the residual petroleum substance in liquid and solid phases, the turbidity value, and the zeta-potential value of the supernatant of oil sludge samples after cleaning increased with the increase in the heavy components of the oily sludge, and the oil-removal rate decreased gradually. After cleaning, the average relative molecular weight of the three oil phases increased with the heavy components, which was increased by 1.83, 4.83, and 10.72%, respectively, and the increase in molecular weight increased the difficulty of cleaning. After cleaning, the retention time and peak intensity of the oil sample changed significantly, and it had a stronger elution effect on low-molecular-weight alkanes. It was found that the compound biosurfactant had a good elution effect on polycyclic aromatic hydrocarbons, but the increase in the content of heavy components and the increase in aromatic rings increased the difficulty of cleaning. Moreover, it was found that the compound biosurfactant could not completely elute the petroleum substances on the surface of solid particles, and the asphaltene components in the oil phase were more difficult to elute than other components.

Maternal urinary cadmium concentrations in early pregnancy in relation to prenatal and postpartum size of offspring.

BACKGROUND: The impacts of environmental cadmium (Cd) exposure on birth size parameters including weight, length and head circumference (HC) have been reported in multiple studies. However, little remains known of the impacts of maternal Cd exposure during pregnancy on size during in utero development and during early childhood. The aim of this study was to comprehensively investigate impacts of maternal Cd exposure during pregnancy on the size of offspring in utero (from 24 weeks pregnancy) until six months of age. METHODS: Pregnant mothers were recruited as part of an ongoing prospective birth cohort study based in Guangdong, China. Maternal urine samples were collected in the first and third trimesters of pregnancy, in which Cd concentrations were measured by inductively couple plasma mass spectrometry (ICPMS). In utero size indicators at 24 and 32 week of gestation, including biparietal diameter (BPD), abdominal circumference (AC), femur length (FL) and HC were derived from ultrasound examinations. Anthropometric measures of weight, height and HC at birth and one, three and six months of age were also collected. Associations of size measures at the various time points with maternal urinary Cd concentrations were assessed using linear regression models. RESULTS: The median urinary Cd concentration was 1.00 and 0.98 µg/g creatinine in the first and third trimesters respectively. In univariate analysis, increased maternal Cd levels in the first trimester were associated with decreased HC (-0.17 cm/ug/g urinary Cd) at birth, and the association was particularly pronounced among males (-0.30 cm/ug/g urinary Cd). First trimester Cd exposure was also found to be significantly associated with decreased infant weight at three and six months of age among girls (-101 g/ug/g and -97 g/ug/g urinary Cd, respectively). Associations of similar magnitude were observed after adjustment for various maternal factors. No significant associations were observed with infant size measures or with measures of Cd in the third trimester. CONCLUSIONS: Our detailed study suggests that the first trimester is particularly critical window of susceptibility to sex-specific effects of Cd on size parameters at birth, with some effects persisting to six months of age. These compelling sex-dependent effects on HC and body weight warrant future studies examining longer-term health effects of pregnancy-related Cd exposures.

Nanoparticles for the Treatment of Oral Biofilms: Current State, Mechanisms, Influencing Factors, and Prospects.

Due to their excellent size, designability, and outstanding targeted antibacterial effects, nanoparticles have become a potential option for controlling oral biofilm-related infections. However, the formation of an oral biofilm is a dynamic process, and factors affecting the performance of antibiofilm treatments are complex. As such, when examining the existing literature on the antibiofilm effects of nanoparticles, attention should be paid to the specific mechanisms of action at different stages of oral biofilm formation, as well as relevant influencing factors, in order to achieve an objective and comprehensive evaluation. This review is intended to detail the antibacterial mechanisms of nanoparticles during the four stages of the formation of oral biofilms: 1) acquired film formation; 2) bacterial adhesion; 3) early biofilm development; and 4) biofilm maturation. In addition, factors influencing the antibiofilm properties of nanoparticles are summarized from the aspects of nanoparticles themselves, biofilm models, and host factors. The limitations of current research and possible trends for future research are also discussed. In summary, nanoparticles are a promising antioral biofilm strategy. It is hoped that this review can serve as a reference and inspire ideas for further research on the application of nanoparticles for effectively targeting and treating oral biofilms.

Heavy metal distribution, contamination and analysis of sources - Intertidal zones of Sandu Bay, Ningde, China.

Concentrations of heavy metals in sediments and seawaters from the intertidal zone are analyzed along with cage-bred fish in the Sandu Bay of Fujian Province in China. Elements measured are As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. The concentrations of Cu and Ni found in the sediments do not meet the first standard of the Chinese National Criteria for Marine Sediment Quality. The results of Igeo, EF, and CF index calculations for the sediment samples clearly prove anthropogenic causes of contamination. The water quality standard for fisheries was exceeded by As, Hg, and Cu. Cage-bred fish show increased levels of As, Cr, and Zn. Significant associations are found for AsCu and NiZn. These findings can be related to coal and crude oil combustion and processes associated with the production of batteries, steel, and alloys. The results point to industrial source locations along discharging rivers north and northwest of the Sandu Bay.

Evidence for Adaptive Response in a Molecular Epidemiological Study of the Inhabitants of a High Background-radiation Area of Yangjiang, China.

Our previous studies have shown that cancer mortality in high background-radiation areas of China was lower than that in a control area, indicating the possibility of an adaptive response in high background-radiation areas. Our aim is to determine the effect of low-dose radiation on the level of DNA oxidative damage, DNA damage repair, antioxidant capacity, and apoptosis in high background-radiation area and control area populations of Guangdong through a molecular epidemiological study in order to identify adaptive response. Blood samples were collected from male residents aged 50 to 59 y in a high background-radiation area (Yangjiang) and a control area (Enping), and activities of superoxide dismutase, glutathione, catalase, total antioxidant capacity, and expression of O6-methylguanine-DNA methyltransferase gene (MGMT), human 8-oxoguanine DNA N-glycosylase 1 gene (hOGG1), proapoptotic genes and antiapoptotic genes, oxidative-stress-related genes, as well as concentrations of 8-OHdG, TrxR, HSP27, and MT-COX2 were determined. The activities of antioxidative enzymes, relative mRNA expression level of DNA repair genes, antiapoptotic genes, oxidative-stress-related genes HSPB1 and MT-COX2, and the concentration of antioxidant index TrxR in the high background-radiation area population increased significantly compared to the control population (p < 0.05). The relative mRNA expression level of proapoptotic genes and the concentration of DNA oxidative damage index 8-OHdG were significantly lower in the high background-radiation area compared to those in the control area (p < 0.05). In conclusion, under long-term, natural, high background, ionizing radiation, DNA damage-repair capacity and antioxidant capacity of inhabitants in the high background-radiation area may be enhanced. Additionally, it could induce up regulation of cell-survival gene expression and down regulation of apoptotic gene expression. It might be speculated that enhanced antioxidant and DNA repair capacity and inhibition of apoptosis might play important roles in adaptive response of low-dose radiation in high background-radiation areas.

Follow-up assessment of two cases of trichloroethylene hypersensitivity syndrome: A case report.

The present study aimed to explore the stability, curability and sequelae of cases of Trichloroethylene (TCE) Hypersensitivity Syndrome (THS), and to investigate the causal allergens of THS. Two cases of THS were followed-up in the current study; both cases were healing following glucocorticoid therapy and were discharged >10 weeks prior to follow-up. A questionnaire investigation, health examination and patch test were performed. Allergens of TCE and its metabolites, including chloral hydrate, trichloroethanol (TCOH) and trichloroacetic acid, were applied in the patch test; 4 controls were included. The two subjects were experiencing itching, pigmentation and xerosis of the skin, and had abnormal results in the ophthalmology Schirmer I test and tear break-up time. The body temperature, liver function, superficial lymph nodes, blood, urine routine and autoimmune antibodies of two subjects were shown to be normal, and no new rashes had appeared. All mass concentration of chloral hydrate and TCOH were positive; 5.0% trichloroacetic acid was weakly positive, 0.5% trichloroacetic acid and all mass concentration of TCE were negative. All patch tests were negative in the 4 control subjects. The results suggest that THS was stable following treatment with glucocorticoid therapy. Dry eye syndrome may continue as a sequelae of THS. The patch test demonstrated that the mechanism underlying THS is delayed-type hypersensitivity induced by TCE. In addition, as the hypersensitivity state in a THS rehabilitee could be sustained over a long period of time, it suggests that the metabolites of TCE, not TCE itself, are responsible for THS. Therefore, patients with THS should avoid contact with TCE and its metabolites, and avoid using hypnotic and anticonvulsive drugs containing chloral hydra as the primary ingredient.

Down-regulation of ABCG2 and ABCB4 transporters in the placenta of rats exposed to cadmium.

As a maternal and developmental toxicant, cadmium (Cd) possesses weak penetrability through the placental barrier. However, the underlying mechanism remains unclear. To gain insight into the protein molecules associated with Cd toxicity in placenta and explore their roles in Cd transportation, a reproductive animal experiment was carried out using Sprague-Dawley rats. We performed proteomic analysis of the placenta by Difference Gel Electrophoresis (DIGE) combined with Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Tandem Mass Spectroscopy (MALDI-TOF/TOF MS). The DIGE assay identified 15 protein spots that were differentially expressed with a greater than 1.5-fold change in placenta of Cd-treated rats compared to the control rats. Based on the expression patterns and biological functions of the proteins, we selected the ABCG2 and ABCB4 transporter proteins for further analysis. Western blot analysis showed that Cd exposure could down-regulate the expression of ABCG2 and ABCB4 in the placenta. There was a negative dose-response relationship between Cd exposure and the expression of ABCG2 or ABCB4 protein. These results indicated that down-regulation of ABCG2 and ABCB4 transporters may regulate Cd across through placenta and thus affect the in vivo toxic effect of Cd to fetus.

Trichloroethylene Hypersensitivity Syndrome Is Potentially Mediated through Its Metabolite Chloral Hydrate.

BACKGROUND: We documented previously the entity of trichloroethylene (TCE) hypersensitivity syndrome (THS) in occupational workers. OBJECTIVES: To identify the culprit causative compound, determine the type of hypersensitivity of THS, and establish a screening test for subjects at risk of THS. METHODS: TCE and its main metabolites chloral hydrate (CH), trichloroethanol (TCOH) and trichloroacetic acid (TCA) were used as allergens at different concentrations in skin patch tests. The study included 19 case subjects diagnosed with occupational THS, 22 control healthy workers exposed to TCE (exposure >12 weeks), and 20 validation new workers exposed to TCE for <12 weeks free of THS. All subjects were followed-up for 12 weeks after the patch test. RESULTS: The highest patch test positive rate in subjects with THS was for CH, followed by TCOH, TCA and TCE. The CH patch test positive rate was 100% irrespective of CH concentrations (15%, 10% and 5%). The TCOH patch test positive rate was concentration-dependent (89.5%, 73.7% and 52.6% for 5%, 0.5% and 0.05%, respectively). Lower patch test positive rates were noted for TCA and TCE. All patch tests (including four allergens) were all negative in each of the 22 control subjects. None of the subjects of the validation group had a positive 15% CH patch test. CONCLUSIONS: Chloral hydrate seems to be the culprit causative compound of THS and type IV seems to be the major type of hypersensitivity of THS. The CH patch test could be potentially useful for screening workers at risk of THS.

[Interaction between smoking and nicotine acetylcholine receptor subunits alpha 5 gene rs17486278 polymorphisms on lung cancer].

OBJECTIVE: To investigate the association and interaction between smoking and the nicotine acetylcholine receptor subunits alpha 5(CHRNA5) gene polymorphisms on lung cancer in Chinese men. METHODS: A case-control study was employed with a total of 204 male lung cancer patients and 821 healthy control subjects enrolled in the study. All the subjects were interviewed under a structured questionnaire with the contents on socio-demographic status and smoking behavior. Venous blood samples were collected to measure single nucleotide polymorphism of rs17486278 in CHRNA5. A series of multivariate logistic regression models were performed to assess the association and interaction between smoking and the CHRNA5 gene polymorphisms on lung cancer. RESULTS: After controlling for potential confounding factors, data from the multivariate logistic regression analysis showed that individuals with smoking >15 cigarettes per day would significantly increase the risk of lung cancer when compared to the non-smokers (OR = 3.49, 95%CI:2.29-5.32). However, no associations between CHRNA5 rs17486278 polymorphisms and lung cancer were found. Furthermore, those who smoked 1-15 cigarettes per day had a positive interactive effect between rs17486278 CC genotype and lung cancer (OR = 16.13, 95% CI:1.27-205.33). Results from further stratified analysis on smoking behaviors and rs17486278 genotypes indicated that when compared with non-smokers on rs17486278 AA genotype, those individuals who smoked 1-15 cigarettes per day with rs17486278 CC genotype, individuals smoking >15 cigarettes per day with AA genotype and individuals smoking >15 cigarettes per day with AC genotype, all had a higher risk of developing lung cancer, with their OR value as 8.14(95% CI:1.17-56.56), 3.84 (95% CI:1.30-11.40) and 5.32 (95% CI:1.78-15.93), respectively. CONCLUSION: There was an interaction between smoking and CHRNA5 gene polymorphism on lung cancer.

CHRNA3 rs6495308 genotype as an effect modifier of the association between daily cigarette consumption and hypertension in Chinese male smokers.

Cigarette smoking is an important risk factor for hypertension. However, the effects on hypertension of the interaction between smoking and the genotype of the nicotinic acetylcholine receptor gene are unclear. The purpose of this study is to determine whether the CHRNA3 rs6495308 genotype affects the association between daily cigarette consumption and hypertension. We recruited 947 male smokers in southern China and used a questionnaire administered in face to face interviews to obtain information on their socio-demographic characteristics and smoking behavior. Blood samples were collected to test for CHRNA3 rs6495308 genotype variations. Three blood-pressure measurements were taken for each participant, and the average values recorded. We found that, compared with light smoking (<15 cigarettes per day), heavy smoking (≥15 cigarettes per day) yielded a greater risk of hypertension. We also observed that the interaction between daily cigarette consumption and the CHRNA3 rs6495308 genotype may affect hypertension. Heavy smokers with the homozygous mutant CHRNA3 rs6495308 genotype exhibited a significantly greater risk of hypertension than light smokers with wild-type CHRNA3 rs6495308 genotypes. The positive interaction between heavy smoking and the homozygous mutant CHRNA3 rs6495308 genotype was found to affect the likelihood of hypertension in Chinese male smokers.

Load-bearing capacity and the recommended thickness of dental monolithic zirconia single crowns.

PURPOSE: The aim of this study was to evaluate the load bearing capacity and a reasonable thicknesss of dental monolithic zirconia crowns. MATERIALS AND METHODS: Polymethyl methacrylate (PMMA) abutment tooth specimens were made by CAD/CAM technic. Monolithic zirconia crowns (MZC), monolithic lithium disilicate crowns (MLC), layered zirconia crowns (LZC) and metal ceramic crowns(MCC), of which the occlusal thickness was 1.5mm were thereafter fabricated and cemented on the abutment tooth specimens. MCC with occlusal thicknesses of 0.6mm, 0.8mm, 1.00mm, 1.2mm were also made. All specimens underwent load-to-fracture test. Weibull parameters (σ0) and (m) were calculated. Fracture modes were also evaluated. RESULTS: The mean fracture load was 1863.16±116.81 for MLC, 2284.77±355.60 for MCC, 2308.0±510.94 for LZC, 4109.93±610.18 for MZC (1.5mm), 3068.31±233.88 for MZC (1.2mm), 2429.88±315.03 for MZC (1.0mm), 1814.60±68.21 for MZC (0.8mm) and 1308.38±111.38 for MZC (0.6mm). The fracture load of MZC was significantly higher than MCC, LZC and MLC (P<0.05). The fracture loads for MCC with different thickness were significantly different (P<0.05). Similar trend was observed for the characteristic strength (σ0) and Weibull modulus (m). For MZC and MLC, the fracture mode was catastrophic failure. The predominant fracture mode for LZC was catastrophic fracture. The fracture loads of MZC(1.0mm) and MCC were not statistically different (P>0.05). CONCLUSIONS: Monolithic zirconia crowns exhibit higher fracture loads than monolithic lithium disilicate crowns, layered zirconia crowns and metal ceramic crowns. The fracture resistance of monolithic zirconia crowns with a thickness of 1.0mm can be equal to metal ceramic crowns. Doubling the monolithic zirconia core from 0.6mm to 1.5mm increases the fracture resistance of this restorative system threefold.

Biomechanical properties of nano-TiO(2) addition to a medical silicone elastomer: the effect of artificial ageing.

OBJECTIVES: The aim of this study was to evaluate the effect of TiO2 nanoparticles on the mechanical and anti-ageing properties of a medical silicone elastomer and to assess the biocompatibility of this novel combination. METHODS: TiO2 (P25, Degussa, Germany) nanoparticles were mixed with the silicone elastomer (MDX4-4210, Dow Corning, USA) at 2%, 4%, and 6% (w/w) using silicone fluid as diluent (Q7-9180, Dow Corning, USA). Blank silicone elastomer served as the control material. The physical properties and biocompatibility of the composites were examined. The tensile strength was tested for 0% and 6% (w/w) before and after artificial ageing. SEM analysis was performed. RESULTS: TiO2 nanoparticles improved the tensile strength and Shore A hardness of the silicone elastomer (P<0.05). However, a decrease in the elongation at break and tear strength was found for the 6% (w/w) composite (P<0.05). All the ageing methods had no effect on the tensile strength of the 6% (w/w) composite (P>0.05), but thermal ageing significantly decreased the tensile strength of the control group (P<0.05). Cellular viability assays indicated that the composite exhibited biocompatibility. CONCLUSIONS: We obtained a promising restorative material which yields favourable physical and anti-ageing properties and is biocompatible in our in vitro cellular studies.