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Biomedical subjects

Y Liao

Publications and source records attributed to Y Liao.

At least 55 records · Page 3Linked to original sources
PubMed2000

New selective and potent 5-HT(1B/1D) antagonists: chemistry and pharmacological evaluation of N-piperazinylphenyl biphenylcarboxamides and biphenylsulfonamides.

A series of new analogues of N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl] 2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-carboxamide (1; GR127935) as potent and selective 5-HT(1B/1D) antagonists were synthesized and evaluated pharmacologically. Their receptor binding profiles were comparable to that of 1. The 1,3,4-oxadiazole isomer 2 and the 4'-aminocarbonyl and 4'-amidinyl analogues (9 and 10) of 1 had higher affinities at the rat 5-HT(1B) receptor (IC(50) = 0.93, 1. 3, and 0.5 nM, respectively) and calf 5-HT(1D) receptor (IC(50) = 37, 10, and 3 nM, respectively) than did 1 (1.6 and 52 nM for rat 5-HT(1B) and calf 5-HT(1D) receptors, respectively). In the functional in vitro testing of 5-HT(1B/1D) antagonistic properties, 2, 9, 10, 11b (O-demethylated derivative of 2), 13a (O-methylsulfonyl analogue of 2), and 16 (which differs from 2 with a sulfonamide linker) showed more pronounced effects in the K(+)-induced 5-HT release in the cortex of guinea pig than did 1 and 3 (SB224289). Compounds 2, 9, and 10 were equally potent as 1 in rabbit saphenous vein model (pA(2) > 9). A biochemical study of 2 with in vivo microdialysis in the rat brain showed that it is capable of augmenting citalopram (a selective serotonin reuptake inhibitor, SSRI) induced 5-HT release in rat ventral hippocampus, while preventing the decrease in acetylcholine release elicited by citalopram administration. The molecular structure of 2 was determined by single-crystal X-ray analysis. The log P and log D values of these compounds were calculated. This study contributes to the SAR study of N-piperazinylphenyl biphenylcarboxamides as selective and potent 5-HT(1B/1D) antagonists.

Acetylcholine↗
PubMed2000

Synthesis and in vitro and in vivo functional studies of ortho-substituted phenylpiperazine and N-substituted 4-N-(o-methoxyphenyl)aminopiperidine analogues of WAY100635.

WAY100635 (2), N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xanecarboxamide, is a silent serotonin 5-HT(1A) antagonist, which is now widely used to study the 5-HT(1A) receptor both in vivo and in vitro. In this paper, we describe the synthesis and in vitro (5-HT(1A) affinity and pA(2) values at guinea pig ileum strips) and in vivo (hypothermia and ultrasonic vocalization) pharmacology at the serotonin 5-HT(1A) receptor of several closely related analogues of 2. Test compounds 12 and 14, in which the arylpiperazine moiety of 2 has been replaced by an arylaminopiperidine moiety, showed no affinity or antagonistic activity at the 5-HT(1A) receptor. Substitution of the o-methoxy group of 2 by larger fluoroalkoxy or sulfonyloxy substituents did not alter the in vitro or in vivo pharmacology to any great extent; in vivo both the fluoropropyl analogue 5 and the triflate analogue 7 are equipotent to WAY100635 itself. The O-desmethyl analogue 3 proved to be the most potent antagonist at the serotonin 5-HT(1A) postsynaptic receptor sites in this series.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2000

Quality of the last year of life of older adults: 1986 vs 1993.

CONTEXT: The population is aging and life expectancy is increasing, but whether morbidity and disability late in life also increase is unknown. OBJECTIVE: To examine whether the use of health care services, disability and cognitive function, and overall quality of life in the year before death among older adults has changed over time. DESIGN AND SETTING: The 1986 and 1993 National Mortality Followback Surveys, which were probability samples of all deaths in the United States with response rates of next of kin of 90% and 88% for those aged 65 years and older. PARTICIPANTS: Next of kin were asked to report the health status of a total of 9179 decedents who were 65 years and older in 1986 and 6735 in 1993, representing 1.5 and 1.6 million decedents aged 65 years and older. MAIN OUTCOME MEASURES: Days of hospital or nursing home stays, number and length of disability in 5 activities of daily living, duration of impairment in 3 measures of cognitive function, and an overall sickness score among individuals aged 65 through 84 years and those aged 85 years and older. RESULTS: Women used significantly fewer hospital and nursing home services in the last year of life in 1993 vs 1986 (mean reduction, 3.3 nights for both age groups for hospital services; mean reduction 18.4 nights for nursing home for women aged 65-84 years and 42.3 nights for women > or =85 years). Men had no changes except those aged 85 years and older had a decline in nursing home nights of 32.6. The proportion of women aged 85 years and older with restriction of at least 2 activities of daily living decreased from 62.5% in 1986 to 52.1% in 1993 (P<.01), and those with normal cognitive function increased from 50.3% to 56.2% (P<.05). Their mean overall sickness score decreased and quality-of-life improved. Among women aged 65 through 84 years, the number with normal cognitive function increased and the mean sickness score decreased, but those with at least 2 activities of daily living impairments increased and the overall quality of life declined. A similar pattern of change was found in the oldest-old men except that cognitive function worsened. Most parameters for men aged 65 through 84 years did not change significantly. CONCLUSIONS: Men and women at least 85 years old in the US experienced a better overall quality of life in the last year of life in 1993 than those in 1986. Most measures for men and women aged 65 through 84 years improved or did not change.

Activities of Daily Living↗
PubMed2000

Prostatic levels of tocopherols, carotenoids, and retinol in relation to plasma levels and self-reported usual dietary intake.

This study evaluated how prostatic levels of antioxidants relate to plasma levels and self-reported usual dietary intake. Definition of these relations may aid in interpreting studies of antioxidant exposure and prostate cancer risk. Between July 1996 and April 1997, plasma and prostatic tissue levels of tocopherols, carotenoids, and retinol were measured in 47 men undergoing radical prostatectomy or transurethral prostatectomy at Loyola University Medical Center, Maywood, Illinois, and an affiliate hospital. Dietary intake was measured by using a 122-item version of the Block Health Habits and History Questionnaire, and correlations were assessed with Pearson's coefficients. Prostatic levels of tocopherols and carotenoids (but not retinol) were significantly correlated with plasma levels (r= 0.31-0.56, p < 0.05-0.0001); the strongest correlations were associated with lycopene, beta-carotene, and gamma-tocopherol (0.56, 0.54, and 0.52, respectively; p < 0.0001). Relative concentrations of tocopherols and carotenoids in prostate tissue were proportionate to those in plasma. No correlation between prostatic levels and reported dietary intake was observed (r = -0.09 to 0.16, p < not significant). Adjustment for energy intake, body mass index, and serum lipids did not impact these relations. These results suggest that plasma levels of tocopherols and carotenoids better reflect prostatic exposure than self-reported usual dietary intake.

Adenocarcinoma↗
PubMed2000

HLA-DRB1 gene polymorphism in patients with dilated cardiomyopathy.

To probe into the genetic background and immunopathogenesis of dilated cardiomyopathy (DCM), HLA-DRB1 gene polymorphism in 68 patients with DCM and 175 normal control subjects were analyzed by using the polymerase chain reaction/sequence specific primer (PCR/SSP) techniques. It was found that the frequencies of HLA-DRB1* 15 and HLA-DRB1* 03 alleles were significantly lower in DCM patients than those in normal controls (14.71% vs 29.71% and 4.41% vs 15.43%, respectively), the relative risks (RR) in the DCM patients being 0.41 and 0.25, respectively, all P < 0.05. However, the frequencies of HLA-DRB1* 11 and HLA-DRB1* 12 alleles were significantly higher in the DCM patients than in controls (29.4% vs 12.00% and 36.76% vs 12.57%, respectively) with the RR in the DCM patients being 3.06 and 4.04, respectively, all P < 0.01. These findings further demonstrated that immunogenetics might play a predominant pathogenetic role in partial DCM patients.

Adult↗
PubMed2000

Effect of anti-cardiac myosin antibody on prognosis of patients with acute myocardial infarction.

To study whether there was an anti-cardiac myosin antibody (AMA) in serum of patients with myocardial infarction (AMI), relationship between AMA and the prognosis in patients with AMI was investigated. In 67 patients with acute AMI, AMA was assayed by ELISA and left ventricular structure and cardiac function were examined by echocardiography at the end of the first week after infarction and during a 6-month follow-up. The patients with AMI were divided into AMA-positive group and AMA-negative group. The parameters of left ventricular end-diastolic function and prognosis were compared between the two groups. Results showed that the AMA was positive in 18 patients with AMI, with a positive rate of 26.87%, while it was negative in 20 health donors. The locations of myocardial infarction in the two groups were similar. There were significant differences in Killip class I (22.22% vs 55.10%, P < 0.05), decreasing of wall motion and ventricular aneurysm (92.85% vs 37.5%, P < 0.01) between the positive group and the negative group. During a 6-month follow-up, the mortality was higher in AMA positive group than in AMA negative group (38.89% vs 10.20%, P < 0.05). It is concluded that AMA can be detected in serum of patients with AMI and can serve as an important autoimmune marker. The autoimmune response might take place in AMI. AMA was associated with the left ventricular remodeling and the prognosis of AMI.

Aged↗
PubMed2000

Value of quantitative analysis of serum cTnT in diagnosis of cardiac disease and myocardial injury.

Serum cTnT, CK-MB and LD1 were measured in 30 patients with AMI, 76 patients with VMC, 12 patients who had undergone operation without cardioplegia, 16 patients who had received open heart operation, 15 patients who had undergone thoracotomy for non-heart surgery and 55 healthy people. Concentration of serum cTnT was 0.057 +/- 0.056 microgram/L in healthy people, 0.069 +/- 0.032 microgram/L in patients who underwent thoracotomy for non-heart surgery, 0.328 +/- 0.472 microgram/L in patients with VMC, 0.388 +/- 0.279 microgram/L in patients with DCM, 4.259 +/- 4.619 micrograms/L in patients with AMI, 8.55 +/- 6.78 micrograms/L in patients who had undergone operation without cardioplegia and 16.03 +/- 6.01 micrograms/L in heart operation patients. In patients with VCM and DCM, serum cTnT was more specific and sensitive than CK-MB and LD1 for diagnosing myocardial injury. In patients with AMI and heart operation patients, the increasing multiple of serum cTnT was obviously higher than that of CK-MB and LD1. 72 h after heart operation, cTnT was still higher than normal, while CK-MB had returned to normal level. Serum cTnT had higher specificity and sensitivity and longer diagnostic period in diagnosing myocardial injury. Moreover, cTnT assay could indicate the degree of myocardial injury. So, quantitative analysis of cTnT can be used as a routine examination in the diagnosis of myocardial injury.

Aged↗
PubMed2000

Predictive values of waist circumference for dyslipidemia, type 2 diabetes and hypertension in overweight White, Black, and Hispanic American adults.

Waist circumferences (WC) >/=102 cm for men and >/=88 cm for women have been proposed by an expert panel as cut-points for identifying increased risk for the development of obesity comorbidities for most adults. The aim of this investigation was to examine the predictive values of these WC cut-points for hypercholesterolemia, low concentration of high (HDL-C), and high concentration of low (LDL-C) density lipoprotein cholesterol, hypertriglyceridemia, type 2 diabetes, and hypertension in overweight American adults. Data from NHANES III were utilized for the analysis. Predictive abilities were determined by calculating sensitivity, specificity, positive (PV+) and negative (PV-) predictive values in overweight subjects with BMI 25-29.9 kg/m(2). Sensitivity of WC cut-point was stronger for high LDL-C compared to other risk factors with the highest values recorded in the 40-59 and 60-69 year age groups in men and women, respectively. PV+ of WC cut-points for dyslipidemia, type 2 diabetes, and hypertension were low in men compared to women. PV+ tended to increase with age, from 19-39, 40-59 to 60-90 year age groups in Whites, Blacks, and Hispanic men. In men, the highest PV+ were recorded for hypertriglyceridemia in the 60-90 years old groups, with values of 71.6%, 52.5%, and 43.3% in Whites, Blacks, and Hispanics, respectively. The CVD risk factor associated with the highest PV+ in women was diabetes with values of 97.2% in Whites and 88.9% in Blacks, and hypertriglyceridemia with a value of 93.8% in the 17-39 year age group in Hispanics. Among Black men 40-59 years of age, only 32% of a population of overweight hypertensives were detected by the WC cut-points, and among Black women, 40-59 years of age, only 54% were detected. Given the low sensitivity of these cut-points for detecting hypertension, one of the major co-morbidities of obesity, these cut-points failed to provide adequate evidence for the use of WC in determining or evaluating patients as to co-morbid states. We recommend further studies to determine a set of specific cut-points associated with increased risk of CVD in different population groups.

Adolescent↗
PubMed2000

Abdominal adiposity and clustering of multiple metabolic syndrome in White, Black and Hispanic americans.

PURPOSE: The aim of this study was to evaluate the association of abdominal adiposity assessed by waist circumference (WC) with clustering of multiple metabolic syndromes (MMS) in White, Black and Hispanic Americans. MMS was defined as the occurrence of two or more of either hypertension, type 2 diabetes mellitus, dyslipidemia, hypertriglyceridemia or hyperinsulinemia. METHODS: The number of MMS and fasting insulin (a surrogate measure of MMS) were each used as dependent variables in gender-specific multiple linear regression models, adjusting for age, smoking and alcohol intake. The contribution of WC to interethnic differences in clustering of MMS and fasting insulin concentration was assessed in gender-specific linear regression models. The risk of MMS due to large waist was estimated by comparing odds ratio for men with WC >/= 102 cm with those with WC < 102, and women with WC >/= 88 cm with women with WC < 88 cm in the logistic regression model adjusting for age, smoking and alcohol intake. RESULTS: WC was positively and independently associated with clustering of MMS and increased fasting insulin concentration adjusting for age, smoking and alcohol intake in the three ethnic groups (p < 0.01). Black ethnicity was associated with clustering of MMS and fasting insulin concentration (p < 0.01). Hispanic ethnicity was also associated with clustering of MMS in men and associated with fasting insulin concentration in both men and women (p < 0.01). In both men and women, the risk of MMS clustering was strongly associated with increased WC in all ethnic groups independent of BMI. CONCLUSION: WC appears to be a marker for multiple metabolic syndromes in these ethnic groups. The results of this investigation lend support to the view that waist measurement should be considered as a clinical variable for assessing the risk of cardiovascular diseases.

Abdomen↗
PubMed2000

Impact of birth weight on ethnic variations in subcutaneous and central adiposity in American children aged 5-11 years. A study from the Third National Health and Nutrition Examination Survey.

OBJECTIVE: To determine the types of subcutaneous adiposity represented by different measurements of skinfold thickness that are associated with birth weight in white (n=759), Black (n=916) and Hispanic (n=813) American children aged 5-11 y. We also determined the contribution of birth weight to ethnic differences in subcutaneous and central adiposity. DESIGN AND METHODS: Data for this analysis were from the Third US National Health and Nutrition Examination Survey. The outcome measures were triceps, subscapular, suprailiac and thigh skinfold thicknesses at 5-11 y of age. Central adiposity was defined as ratios of subscapular to triceps (STR) and central-peripheral (CPR) (subscapular+suprailiac)/(triceps+thigh) skinfolds. Partial correlation analyses were used to determine the association between birth weight and measures of subcutaneous fatness, while multiple linear regression analyses were used to determine the independent contribution of birth weight to ethnicity variations in subcutaneous and central adiposity adjusting for sex, age and BMI. RESULTS: Overall, birth weight was negatively associated with subscapular skinfold and central adiposity in White, Black and Hispanic American children (P < 0.05). Birth weight was also negatively associated with suprailliac skinfold in both Blacks and Hispanics (P < 0.01) and with sum of the four skinfolds in Blacks (P < 0.05). Compared with White, Black ethnicity was negatively associated with triceps, suprailliac thigh and sum of skinfold thicknesses controlling for birth weight, sex, age and BMI (P < 0.01). Compared with White, Hispanic ethnicity was negatively associated with triceps, thigh and sum of skinfold thicknesses (P < 0.01). Both Black and Hispanic ethnicity was positively associated with STR and CPR (P < 0.01). CONCLUSIONS: In this population of American children, the association of birth weights with subcutaneous and central fat accumulation may be due to fetal programming. Since the impact of fetal conditions is likely to be modified by life course, defining the interaction between factors that are present at birth and subsequent exposures is one of the essential challenges for future research.

Adipose Tissue↗
PubMed2000

Blockade of connexin 43 expression by stable transfection of antisense cDNA in cultured vascular smooth muscle cells.

Gap junctional communication is involved in embryogenesis, cell growth control, and coordinated contraction of cardiac myocytes. It has been hypothesized that gap junctions coordinate responses of vascular cells to constrictor or dilator stimulation. Three connexin (Cx) proteins, 37, 40, and 43, are found in the vasculature. Cx43 gap junctions are widely distributed along the vascular tree, although a precise physiologic role in vascular function is unknown because of a lack of specific functional inhibitors and of suitable animal models. To investigate the role of Cx43 in intercellular communication among vascular smooth muscle (VSM) cells, we selectively modified the expression of the Cx43 gene using antisense cDNA stable transfections in culture. Results show that in cells stably transfected with antisense Cx43 cDNA, gene expression of Cx43 could be reduced to 20% of that observed in vector-transfected cells. In spite of the mRNA and protein reduction, the antisense Cx43 cDNA-transfected cells did not show a significant reduction in dye transfer or a difference in cell growth rate as compared with control. These results suggest either that the residual amount of Cx43 protein is sufficient for dye transfer and growth control or that the dye transfer in these cells can be mediated by Cx40 or other connexin proteins. Therefore, more potent approaches, such as dominant negative and gene knockout, are required to fully block gap junctional communication in VSM cells.

Animals↗
PubMed2000

Influence of the I/D polymorphism of the angiotensin-converting enzyme gene on the outcome of microalbuminuria in essential hypertension.

The objective of the present study was to analyze the influence of the I/D polymorphism of the ACE gene on the outcome of microalbuminuria in essential hypertensive patients who were receiving antihypertensive treatment. One hundred thirty-six essential hypertensive patients who were <50 years old and had never previously received treatment with antihypertensive drugs were included in the study. During a 3-year period, patients received nonpharmacological treatment consisting of moderate salt restriction and a low-calorie diet they were obese, with or without a regimen of antihypertensive drugs based on beta-blockers or ACE inhibitors. Hydrochlorothiazide was added when necessary to maintain the blood pressure goal of <135/85 mm Hg. At the beginning of the study and at yearly intervals, systolic and diastolic blood pressures (SBP and DBP, respectively), 24-hour urinary albumin excretion (UAE), renal function, and biochemical profile measurements were made. The insertion/deletion (I/D) polymorphism of the ACE gene was determined through the use of polymerase chain reaction. The variables used in the statistical analysis were the measurements at the start of the study and the increase or decrease detected during the follow-up, estimated as individual specific regression line slope values. At baseline, no differences in blood pressure or UAE values were observed among genotypes. Likewise, the genotype or allele frequency was not significantly different between normoalbuminurics and microalbuminurics. After the 3 treatment years, significant reductions in SBP, DBP, and UAE were found (SBP 151.6+/-17.3 reduced to 137.2+/-14.3 mm Hg, P<0.001; DBP 96.6+/-8.9 reduced to 84.5+/-9.8 mm Hg, P<0.001; UAE 36.7+/-71.5 reduced to 28.3+/-78.6 mg/24 h, P<0. 05). The slopes of these parameters over time did not differ significantly among genotypes. The slope of SBP was the main factor related to the slope of logUAE (P<0.003). A significant positive correlation coefficient between the SBP and logUAE slopes was observed for the DD patients (r=0.57, P<0.0001) but was absent in patients carrying the I allele (II r=-0.03, P=NS; I/D r=0.01, P=NS). Follow-up studies should be used to achieve a better understanding of the impact of candidate gene polymorphisms on the development of hypertension-induced organ damage. Assessment of the I/D polymorphism of the ACE gene may identify subjects who require a greatly lowered blood pressure to prevent organ damage and to reduce hypertension-associated complications and death.

Adult↗
PubMed2000

The effect of phenyl substituents on the release rates of esterase-sensitive coumarin-based prodrugs.

A coumarin-based prodrug system has been recently developed in our laboratory for the preparation of esterase-sensitive prodrugs of amines, peptides, and peptidomimetics. The drug release rates from this prodrug system were found to be dependent on the structural features of the drug moiety. In certain cases, the release can be undesirably slow for drugs that are secondary amines with relatively high pKa's. Aimed at finding ways to manipulate the release rates to suit the need of different drugs, we have examined the effect of the phenyl ring substitutions on the release kinetics of such prodrugs and found that appropriately positioned alkyl substituents on the phenyl ring could help to facilitate the release by as much as 16-fold. Therefore, introduction of alkyl substituents on the phenyl ring should allow us to manipulate the release rates and, therefore, time profiles for different drugs.

Coumarins↗
PubMed2000

[Investigation of infiltration glass of the machinable infiltrated ceramic(MIC)].

To explore the manufacture arts and determine the properties of the infiltration glass of the MIC. In order to determine the glass forming range of the MIC infiltration glass, molten glass was prepared in Al2O3 crucibles by heating the components to 1450 degrees C. Thermal analytic device was employed to study the thermal properties of the glass. Its crystal phases after micro-crystallization were analyzed with XRD. Flexural strength was measured by means of 3-point bending test. The chemical components of MIC glass were determined. Conventional fluorophlogopite glass was converted into an infiltration glass with low viscosity, good infiltration capability and low fusing temperature by introducing B2O3, La2O3 and Li2O into the glass. Fluorophlogopite crystals formed after crystallization. Conventional mica glass can be changed according to the requirements of properties. Modified mica MIC glass in this study has good infiltration ability in Al2O3 matrix while remains machinability.

Aluminum Silicates↗
PubMed2000

Adenovirus 5 early region 1A does not induce expression of the ewing sarcoma fusion product EWS-FLI1 in breast and ovarian cancer cell lines.

The adenovirus 5 early region 1A (E1A) can function as a tumor suppressor gene and is being used in clinical trials as a therapeutic agent for advanced breast, ovarian, and head and neck cancer. Recently, there has been a dispute regarding whether transfection with the E1A gene can induce expression of the Ewing sarcoma oncogenic fusion transcript EWS-FLI1 (Sanchez-Prieto et al., Nat. Med., 5: 1076-1079, 1999; Melot and Delattre, Nat. Med., 5: 1331, 1999; Kovar et al., Cancer Res., 60: 1557-1560, 2000). In an effort to settle the controversy, we tested several stable E1A transfectants of cell lines MDA-MB-231, MCF-7, MDA-MB-435 (breast cancer), SKOV3-ipl (ovarian cancer), and PC-3 (prostate cancer), as well as parental and vector-transfected controls, HEK 293 cells, and RD-ES (Ewing sarcoma) cells, for the EWS-FLI1 fusion product. The EWS-FLI1 transcript could not be identified with reverse transcription-PCR in any of the 13 E1A-transfected cell lines analyzed. Furthermore, the EWS-FLI1 fusion protein could not be detected by Western blot analysis in E1A-transfected cell lines. These results suggest that E1A transfection does not necessarily lead to expression of the oncogenic EWS-FLI1 fusion transcript. Thus, the potential induction of this gene rearrangement by E1A gene therapy is unlikely to be clinically significant in the treatment of advanced malignant disease.

Adenovirus E1A Proteins↗
PubMed2000

[The effect of injuries on Fn synthesized by FBs and its implication in wound timing].

cFn synthesized by FBs around the wound was detected by immunochemistry in vitro. Using the method of ELISA, The concentration of cFn in the culture media was observed. The concentration of cFn had no change within 30 minutes after injury, but started to increase after 1 hour of the injury and kept this trend within next five hours after injury. By static analysis, it can be obtained that the concentration of cFn in culture media is time-dependent after injury.

Cells, Cultured↗
PubMed2000

[Properties and infiltration arts of machinable infiltration ceramic(MIC)].

OBJECTIVE: The purpose of this study is to explore the infiltration arts of MIC and study the effects of different packing density of Al2O3 matrix on the properties of MIC. METHODS: alpha-Al2O3 specimens were fabricated by pouring alpha-Al2O3 slip with different powder/liquid ratios(P/L = 3.5, 7.5, 10.5) into a mold, and subsequently pre-fired at 1160 degrees C for 6 hours to form Al2O3 matrix. The packing density of the matrices were measured. Infiltration concepts were introduced into this study by infiltrating molten mica micro-crystalline glass into the porous Al2O3 matrix at 1160 degrees C for 6 hours to form a continuous interpenetrating composite. The composite then underwent micro-crystallization by nucleating at 550 degrees C for 1 hour and crystallizing at 900 degrees C for 1 hour, which resulted in the MIC. Mechanical properties including three point flexural strength, elastic modulus, Vicker's hardness, indentation fracture toughness and Weibull's modulus of flexural strength were determined. Parameters of machinability(H/KIC)2 of MIC were calculated. XRD and SEM were employed to study its microstructure. RESULTS: The resulted matrices reached packing densities of 63%, 76%, 78% with P/L of 3.5, 7.5 and 10.5. The MIC attained high strength and good machinability after infiltration. Three-point flexural strength and indentation fracture toughness were 342, 431, 374 MPa and 4.05, 4.14, 5.02 MPa m1/2 for MIC with packing density of 63%, 76%, 78% separately. And parameters of machinability were 5.41, 6.84 and 7.39 respectively. Packing density of Al2O3 matrix significantly influenced the mechanical properties. Maximum properties were obtained with a matrix packing density of 75%(P/L = 7.5), with a Weibull's modulus of flexural strength of 6.8. Machinability decreased with the increase of P/L ratio. Micro-crystallizing treatment resulted in the formation of evenly distributed mica crystalline in the composite, which contributed to the high strength of this composite material. CONCLUSION: MIC is a new infiltrated ceramic with favorable strength and machinability which can satisfy the prosthodontic requirements as all ceramic crown and bridge materials, it also shows promising outlook for future developments and clinical usage.

Aluminum Oxide↗