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Biomedical subjects

H Y Chen

Publications and source records attributed to H Y Chen.

At least 55 records · Page 3Linked to original sources
PubMed2001

Marginal quality and microleakage of adhesive class V restorations.

OBJECTIVES: The aim of this in vitro study was to determine the marginal quality and microleakage of composite resin class V restorations. METHODS: Standardized mixed class V cavities (diameter: 4mm, depth: 2mm) with half of the finish lines limited within dentin were cut in 90 freshly extracted human molars and randomly assigned to nine groups (n=10). After etching enamel and dentin, the cavities were restored with nine different restorative systems (Syntac Sprint/Tetric Ceram=SS, Syntac Single-Component/Tetric Ceram=SC, Onestep/Aeliteflo=OS, Aquaprep+Onestep/Aeliteflo=OA, Prime & Bond 2.1/TPH=PB, Optibond Solo/Prodigy=OP, Singlebond/Z100=SB, Tenure Quik/Marathon=TQ, Solobond M/Arabesk=SM) using a wet-bonding procedure. After finishing and polishing, the teeth were stored for 24h in distilled water at 37 degrees C before they were subjected to thermocycling (5/55 degrees C, 1000x). Epoxy replicas were made for margin analysis in the SEM. Specimens were stained in methylene blue, sectioned, and evaluated for microleakage. Dye penetration was scored on a 0-3 ordinal scale. RESULTS: Statistical analysis (Kruskal-Wallis H-test, Mann-Whitney U-test) revealed significant differences (P<0.05) among the groups at dentin and enamel margins for the microleakage scores as well as for the results of the quantitative SEM margin analysis. SC revealed a significantly higher percentage of perfect margins in the SEM than OS and SM in enamel and dentin, respectively. OA exhibited significantly more leakage in enamel than all other groups. CONCLUSIONS: None of the tested restorative systems achieved a perfect seal in dentin and enamel of mixed class V cavities. Marginal quality and sealing ability of adhesive systems to dentin, using a wet-bonding procedure, is still inferior compared with enamel margins.

Barium Compounds↗
PubMed2001

Capsaicin and nonivamide as novel skin permeation enhancers for indomethacin.

The study was conducted in vitro to investigate the changes of indomethacin transdermal permeation pretreated by capsaicin and nonivamide, two compounds chemically similar to Azone. The combined effect of low frequency ultrasound (20 kHz) and enhancers on the indomethacin permeation was also evaluated. The experimental data demonstrated that capsaicin and nonivamide significantly enhanced the flux of indomethacin across nude mouse skin. Enhancement effects of both analogues were very similar and depended predominantly on the concentration tested. Histological examination coupled with visual scores indicated the safety of capsaicin and nonivamide on skin structure. Simultaneous application of ultrasound and enhancers significantly increased skin permeation of indomethacin compared with either ultrasound or enhancers alone. Better effect was obtained by the combination with capsaicin than nonivamide.

Animals↗
PubMed2001

A profile conditional likelihood approach for the semiparametric transformation regression model with missing covariates.

We propose a profile conditional likelihood approach to handle missing covariates in the general semiparametric transformation regression model. The method estimates the marginal survival function by the Kaplan-Meier estimator, and then estimates the parameters of the survival model and the covariate distribution from a conditional likelihood, substituting the Kaplan-Meier estimator for the marginal survival function in the conditional likelihood. This method is simpler than full maximum likelihood approaches, and yields consistent and asymptotically normally distributed estimator of the regression parameter when censoring is independent of the covariates. The estimator demonstrates very high relative efficiency in simulations. When compared with complete-case analysis, the proposed estimator can be more efficient when the missing data are missing completely at random and can correct bias when the missing data are missing at random. The potential application of the proposed method to the generalized probit model with missing continuous covariates is also outlined.

Humans↗
PubMed2001

Association of the vitamin D receptor gene start codon Fok I polymorphism with calcium oxalate stone disease.

OBJECTIVE: To assess the use of Fok I polymorphism (the most frequent polymorphism, at the start codon of the vitamin D receptor gene, VDR) as a convenient genetic marker in identifying the cause of urolithiasis. PATIENTS, SUBJECTS AND METHODS: A normal control group of 90 healthy subjects and 146 patients with calcium oxalate stones were examined. Using polymerase chain reaction (PCR)-based restriction analysis, the relationship between Fok I polymorphism and urolithiasis was evaluated. An unexcisable length of 265 bp was identified (allele CC) and two fragments (169 bp and 96 bp) identified as excisable lengths (allele TT). RESULTS: There was a statistically significant difference between the groups (chi-square test, P < 0.05) for the genotype of the VDR Fok I start codon polymorphism. The odds ratio (95% confidence interval) for the C allele in those at risk of stone disease was 1.672 (1.149-2.432). CONCLUSIONS: These results suggest that the VDR Fok I start codon polymorphism may be a good candidate for a genetic marker in calcium oxalate stone disease.

Adult↗
PubMed2001

Transdermal delivery of nalbuphine and nalbuphine pivalate from hydrogels by passive diffusion and iontophoresis.

The objective of this study was to evaluate the in vitro transdermal permeation of nalbuphine hydrochloride (CAS 23277-43-2) (NA) and nalbuphine pivalate (NAP), a novel prodrug of NA, from different hydrogel formulations under passive diffusion as well as iontophoresis. Various concentrations of polymers, including polyvinylpyrrolidone (PVP) and hydroxypropyl cellulose (HPC) were used in the hydrogel formulations. The passive permeation rate of NA was affected by the polymer concentrations, which can be attributed to different viscosities of the hydrated formulations; whereas the passive permeation rate of NAP was not influenced by the various polymer concentrations. Iontophoresis significantly increased the permeation rates of NA and NAP from various hydrogel formulations through skin; the enhancement ratios were higher for NA in all the formulations studied. The iontophoretic permeation rates of NA were slightly decreased by the incorporation of polymers; however, the transdermal flux and membrane potential were independent of polymer concentrations for both NA and NAP, demonstrating that the polymer concentrations in the hydrogel formulations did not have significant effects on the iontophoretic permeation of NA and NAP.

Administration, Cutaneous↗
PubMed2001

Effects of Tamm-Horsfall protein and albumin on calcium oxalate crystallization and importance of sialic acids.

BACKGROUND: Tamm-Horsfall protein and human serum albumin are common urinary proteins that show uncertain inhibitory action on the crystallization of calcium oxalate monohydrate. MATERIALS AND METHODS: Batch experiments on crystal nucleation, growth, and aggregation were performed using purified Tamm-Horsfall protein and albumin before and after enzymatic removal of sialic acids from the proteins. RESULTS: At a concentration of 100 nM, both Tamm-Horsfall protein and albumin promoted the time of crystal nucleation by 18.4% and 8.9%, respectively, relative to the control. However, both of the proteins exerted an inhibitory effect on crystal growth, with the IC(50) being 7.27 nM for Tamm-Horsfall protein and 37.5 nM for albumin. The inhibition of crystal aggregation was 81.82% by Tamm-Horsfall protein 100 nM but only 54.55% at 50 nM after enzymatic removal of the sialic acid. Instead of increasing the inhibition, the effect was changed to promotion after an increase in the concentration of Tamm-Horsfall protein to more than 500 nM for native protein and to more than 100 nM for the enzymatic digest. Albumin showed little change after enzymatic treatment and maintained a maximal inhibitory effect of 72.73% on crystal aggregation when the concentration reached to 100 nM. CONCLUSION: Because the promotion of nucleation could lessen the subsequent saturation of a calcium oxalate solution, it is concluded that Tamm-Horsfall protein and albumin show an overall effect of inhibition on crystallization in vitro. The inhibitory effect of Tamm-Horsfall protein is partly related to sialic acid.

Albumins↗
PubMed2001

No association of vitamin D receptor gene BsmI polymorphisms with calcium oxalate stone formation.

BACKGROUND AND PURPOSE: The formation of urinary stones is reported to be associated with the vitamin D receptor (VDR). As the most frequently seen polymorphism within the VDR gene is BsmI, it has been used as a genetic marker in searching for the cause of urolithiasis. We aimed to evaluate the association between calcium stone disease and the BsmI polymorphisms. MATERIALS AND METHODS: A control group of 90 healthy people and a group of 124 patients with calcium oxalate stones were examined. The polymorphism was detected using polymerase chain reaction (PCR)-based restriction analysis. A PCR product length was determined to be 580 bp (BB) whereas two fragments of 405 bp and 175 bp were determined to be excisable (bb) by BsmI endonuclease. Associations between calcium stone disease and BsmI polymorphisms were evaluated. RESULTS AND CONCLUSIONS: The results revealed no significant difference between normal individuals and stone patients (P = 0.891). The allelic distribution of B and b were similar within both the normal group and the stone patients. Therefore, the BsmI polymorphism of the VDR gene at intron 8 is not a suitable genetic marker for urinary stone disease.

Calcium Oxalate↗
PubMed2001

Prognostic value of nm23 expression in stage IB1 cervical carcinoma.

BACKGROUND: The purpose of this retrospective study was to evaluate the patterns of nm23 expression in stage IB1 squamous cell carcinoma of the uterine cervix, to compare nm23 expression with clinicopathological findings and to assess its prognostic value. METHODS: Twenty-seven patients with stage IB1 squamous cell carcinoma of the uterine cervix underwent abdominal radical hysterectomy and pelvic lymph node dissection. Expression of nm23 was studied immunohistochemically, followed by amplification and direct sequencing of exons 4 and 5 of the nm23 gene. RESULTS: Overexpression of nm23 was detected in 18.5% of the tumors and low expression was seen in 33.3%, while negative expression was found in 48.1% of the tumors. Deep cervical stromal invasion (> or =1/2) was found to be associated with the increased risk of lymph node metastases (odds ratio = 17.5). A significantly lower percentage of patients survived when nm23 overexpression was observed (p = 0.0063). Univariate analysis revealed that tumor size (2-3.9 cm), lymph node metastasis, tumor invasion into parametria, tumor invasion into blood/lymph vessel, squamous cell carcinoma (> or =2 ng/ml) and nm23 overexpression had a significantly lower recurrence-free survival rate of the patients. None of the above factors was significant according to multivariate analysis. There were no mutations in exons 4 and 5 of the nm23 gene in stage IB1 squamous cell carcinoma of the uterine cervix. CONCLUSIONS: This study suggests that expression of nm23 may be indicative of an unfavorable prognosis in patients with stage IB1 squamous cell carcinoma of the uterine cervix.

Adult↗
PubMed2001

Fatal falls in the US construction industry, 1990 to 1999.

The Occupational Safety and Health Administration's (OSHA's) Integrated Management Information System (IMIS) database allows for the detailed analysis of risk factors surrounding fatal occupational events. This study used IMIS data to (1) perform a risk factor analysis of fatal construction falls, and (2) assess the impact of the February 1995 29 CFR Part 1926 Subpart M OSHA fall protection regulations for construction by calculating trends in fatal fall rates. In addition, IMIS data on fatal construction falls were compared with data from other occupational fatality surveillance systems. For falls in construction, the study identified several demographic factors that may indicate increased risk. A statistically significant downward trend in fatal falls was evident in all construction and within several construction categories during the decade. Although the study failed to show a statistically significant intervention effect from the new OSHA regulations, it may have lacked the power to do so.

Accidental Falls↗
PubMed2001

Augmented inverse probability weighted estimator for Cox missing covariate regression.

This article investigates an augmented inverse selection probability weighted estimator for Cox regression parameter estimation when covariate variables are incomplete. This estimator extends the Horvitz and Thompson (1952, Journal of the American Statistical Association 47, 663-685) weighted estimator. This estimator is doubly robust because it is consistent as long as either the selection probability model or the joint distribution of covariates is correctly specified. The augmentation term of the estimating equation depends on the baseline cumulative hazard and on a conditional distribution that can be implemented by using an EM-type algorithm. This method is compared with some previously proposed estimators via simulation studies. The method is applied to a real example.

Analysis of Variance↗
PubMed2001

Calcitonin receptor gene polymorphism: a possible genetic marker for patients with calcium oxalate stones.

OBJECTIVES: The formation of urinary stones is hypothesized to be associated with calcitonin receptors. The most commonly seen polymorphism is C/T at the 1377th nucleotide. Hence, these polymorphisms are being used as a genetic marker in the search for the cause of urolithiasis. METHODS: A normal control group of 105 healthy people and 102 patients with recurrent calcium oxalate stones were examined. The polymorphism was detected following a polymerase chain reaction-based and restriction analysis by AluI. An uncuttable length is 228 bp (CC) whereas two fragments of 120 and 108 bp are shown as cuttable lengths (TT). RESULTS: The results revealed significant differences between the normal individuals and the stone patients (p<0.01). The distribution of leucine (cuttable) homozygote in the stone group (2.0%) was higher than in the control group (0.0%). The odds ratio for the leucine allele of the calcitonin receptor gene in calcium oxalate stone disease is 5.634 (95% CI: 2.286--13.885). CONCLUSIONS: Results show that the polymorphism in the calcitonin receptor gene could be a genetic marker for urinary stone disease and therefore it is worthwhile pursuing further studies of the leucine allele of calcitonin receptor gene due to it is strongly correlated with stone disease.

Adult↗
PubMed2001

The suitability of packable resin-based composites for posterior restorations.

BACKGROUND: Packable composites, promoted for the restoration of stress-bearing posterior teeth, have captured clinicians' interest. METHODS: The authors tested three packable composites (Alert, Jeneric/Pentron; Solitaire, Heraeus Kulzer, Wehrheim, Germany; SureFil, Dentsply De Trey, Konstanz, Germany); a new packable organically modified ceramic, or ormocer (Definite, Degussa AG, Hanau, Germany); a hybrid composite (Tetric Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) and an ion-releasing composite (Ariston pHc, Ivoclar Vivadent, Schaan, Liechtenstein). They determined modulus of elasticity according to EN 24049:1993 of the European Committee for Standardization. They measured Vickers hardness using a 200-gram load for 40 seconds. To determine the materials' depth of cure, they used both a scraping method (International Standards Organization standard CD 4049:1997) and a hardness profiling method. RESULTS: The authors calculated means and standard deviations from 10 replications of each test and used one-way analysis of variance and post hoc Tukey tests (alpha = .05). The materials had significant differences (P < .001) in all characteristics. Solitaire had the significantly lowest elastic modulus and microhardness; Alert had the highest values for these characteristics. Ariston pHc exhibited the significantly lowest depth of cure. There was a significant correlation between the two methods of measuring depth of cure (r2 = 0.9945; P = .021). CONCLUSIONS: The material group of packable composites is rather inhomogeneous in terms of mechanical and physical data. Our data suggest that bulk curing of packable composites in deep cavities still is not recommendable. CLINICAL IMPLICATIONS: The clinician needs to select packable composites carefully, as it seems that not all of these materials quality for stress-loaded posterior restorations.

Analysis of Variance↗
PubMed2001

Preoperative diagnosis by electron beam computed tomography and perioperative management of primary tracheal anomalies in tetralogy of Fallot.

PURPOSE: To investigate the usefulness of electron beam computed tomography (EBCT) in the preoperative detection and perioperative management of insidious concomitant primary tracheobronchial anomalies in patients with tetralogy of Fallot (TF). METHODS: From July 1995 to October 1999, 88 children (38 girls, 50 boys) with TF were enrolled in this study. EBCT examinations provided information needed to plan management. The final diagnoses of airway abnormalities were correlated with the findings of bronchoscopy in five patients and confirmed during surgery. RESULTS: Fourteen (16%) of the 88 patients had associated primary tracheobronchial anomalies. Nine patients had tracheal bronchi, which were combined with tracheobronchial stenosis in two patients and with tracheal stenosis in one patient. Two patients had tracheal diverticulum, which was combined with lower tracheal stenosis in one patient. Two patients had congenital tracheal stenosis. Tracheomalasia was found in one patient. Three patients with ventilation difficulties died postoperatively. Special attention was given to the care of the diseased airways perioperatively, and the remaining 11 patients had a smooth course of hospitalization and discharge. CONCLUSIONS: Our results show that EBCT provides good delineation of both cardiac and tracheobronchial anomalies and suggest that it should be used perioperatively to detect associated airway anomalies in TF, to facilitate the design of an appropriate ventilation care strategy.

Adolescent↗
PubMed2001

Subtyping HIV-1 infections in Taiwan using peptide-enzyme immunoassay, reverse transcription-polymerase chain reaction, and sequencing.

BACKGROUND AND PURPOSE: There are important questions about epidemiologic transmission patterns as well as the possibility that genetic and phenotypic differences in human immunodeficiency virus type 1 (HIV-1) affect transmissibility, infectivity, pathogenicity, and response to therapy and vaccines. To delinate the genetic heterogeneity of HIV-1 and the association of subtypes with risk factors and location of residence in Taiwan, subtypes of HIV-1 in Taiwanese patients were identified and a phylogenetic study was performed. In addition, the accuracy of peptide-enzyme immunoassay (EIA) using serum samples from Taiwanese patients infected with HIV-1 was investigated. METHODS: Peptide-EIA was used to give a preliminary subtype of HIV-1-positive serum samples collected from different areas of Taiwan. Reverse transcription (RT)-polymerase chain reaction (PCR) and genetic sequencing were used to confirm the peptide-EIA results and to construct a phylogenetic tree. RESULTS: Among the 149 serum samples, 98 were subtype B (66%), 38 subtype E (25%), two subtype Thai-B (1.3%), one subtype G (0.7%), and one subtype C (0.7%). Comparison of risk factors for HIV-1 infection and subtype revealed that most B subtype infections (59/98) occurred in homosexual or heterosexual patients, whereas 28 of 38 E subtype infections occurred in heterosexual patients. The B/E ratio was significantly different (p < 0.05) in Taipei than in other areas of Taiwan. CONCLUSIONS: These results suggest that the predominant subtype of HIV-1 infection in Taiwan is B, followed by E, and that the distribution of HIV-1 subtypes in Taiwan is similar to that of Thailand, although the genetic sequences are distinct. Homosexuality, heterosexuality, bisexuality, and intravenous drug use behaviors affect the distribution of different subtypes of HIV-1 infection. Peptide-EIA in conjunction with RT-PCR and sequencing can provide accurate subtyping of HIV-1 infection.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Three-year clinical evaluation of composite and ceramic inlays.

PURPOSE: To evaluate the 3-yr clinical performance of composite and ceramic inlays in posterior teeth. MATERIALS AND METHODS: 47 composite inlays (Tetric, Blend-a-Lux, Pertac) and 24 ceramic inlays (Empress) were placed by seven student operators under supervision of an experienced dentist. Clinical assessment of 58 inlays (81.7%) was performed after 3 yrs using amodified USPHS criteria and statistically analyzed with Mann-Whitney U test and Fisher's exact test. RESULTS: A total of 100% of the ceramic inlays and 89% of the composite inlays were assessed to be clinically excellent or acceptable. Three composite inlays failed during the first yr and one had to be replaced during the second evaluation period. All composite inlay failures were recorded on molars, revealing a significantly higher failure rate compared with premolars (Fisher's test, P = 0.041). Ceramic inlays revealed a significantly better "anatomic form of the surface" (P = 0.027) and "integrity of the restoration" (P = 0.035). Inlays in small cavities performed better for "marginal integrity" (P = 0.033) and "discoloration at the margin" (P = 0.038).

Adult↗