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Biomedical subjects

H E Lee

Publications and source records attributed to H E Lee.

At least 19 recordsLinked to original sources
PubMed2004

Acute paronychia heralding the exacerbation of pemphigus vulgaris.

Acute paronychia, the suppurative inflammation involving the paronychium of the nails, is usually caused by bacterial or fungal infection and has been rarely reported as a presentation of pemphigus vulgaris (PV). We report a woman with PV who presented with suppurative paronychia of multiple fingernails and toenails, which preceded the exacerbation of other mucocutaneous lesions. A biopsy specimen of the paronychium revealed suprabasal vesicles due to acantholysis. Systemic corticosteroids and adjuvant immunosuppressants were effective in treating mucocutaneous lesions as well as nail disease. We conclude that in patients with PV, acute paronychia could be a manifestation of the disease per se, rather than an infectious process. Only the precise diagnosis with adequate immunosuppressive treatment can lead to good control of disease activity.

Anti-Inflammatory Agents↗
PubMed2003

Life-threatening thrombotic thrombocytopenic purpura (TTP) in a patient with sickle cell-hemoglobin C disease.

We report a patient with hemoglobin sickle cell-hemoglobin C disease who developed the clinical syndrome of thrombotic thrombocytopenic purpura (TTP) during admission for typical acute pain crisis. The potential for multiorgan involvement secondary to vaso-occlusive crisis complicated the diagnosis and overlapped with the patient's clinical presentation of chronic bone pain and hemolytic anemia. Clinical improvement and normalization of laboratory parameters followed rapidly in response to plasma exchange therapy.

Adult↗
PubMed2001

Highly phosphorescent bis-cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes.

The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C(**)N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C(**)N2Ir(LX). The C(**)N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all beta-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C(**)N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1-0.6), and microsecond lifetimes (e.g., 1-14 micros). The strongly allowed phosphorescence in these complexes is the result of significant spin-orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C(**)N2Ir(acac) complexes is a mixture of (3)MLCT and (3)(pi-pi) states. By choosing the appropriate C(**)N ligand, C(**)N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C(**)N ligands, which lead to bathochromic shifts of the free ligands, lead to similar bathochromic shifts in the Ir complexes of the same ligands, consistent with "C(**)N2Ir"-centered emission. Three of the C(**)N2Ir(acac) complexes were used as dopants for organic light emitting diodes (OLEDs). The three Ir complexes, i.e., bis(2-phenylpyridinato-N,C2')iridium(acetylacetonate) [ppy2Ir(acac)], bis(2-phenyl benzothiozolato-N,C2')iridium(acetylacetonate) [bt2Ir(acac)], and bis(2-(2'-benzothienyl)pyridinato-N,C3')iridium(acetylacetonate) [btp2Ir(acac)], were doped into the emissive region of multilayer, vapor-deposited OLEDs. The ppy2Ir(acac)-, bt2Ir(acac)-, and btp2Ir(acac)-based OLEDs give green, yellow, and red electroluminescence, respectively, with very similar current-voltage characteristics. The OLEDs give high external quantum efficiencies, ranging from 6 to 12.3%, with the ppy2Ir(acac) giving the highest efficiency (12.3%, 38 lm/W, >50 Cd/A). The btp2Ir(acac)-based device gives saturated red emission with a quantum efficiency of 6.5% and a luminance efficiency of 2.2 lm/W. These C(**)N2Ir(acac)-doped OLEDs show some of the highest efficiencies reported for organic light emitting diodes. The high efficiencies result from efficient trapping and radiative relaxation of the singlet and triplet excitons formed in the electroluminescent process.

Journal Article↗
PubMed2001

Numerical investigation of the factors affecting interfacial stresses in an MOD restored tooth by auto-meshed finite element method.

Many researches have addressed the high correlation between the fracture of restored teeth and the prepared cavity geometry. In addition, concerns about bonding versus debonding dental materials from cavity walls and different occlusal force conditions could also alter the mechanical responses in a restored tooth. This study employed an automatic mesh procedure to investigate the mechanical interactions between different interfacial conditions and cavity parameters such as pulpal wall depth under different chewing functions. The results indicated that when occlusal force was applied directly on the tooth, it could increase unfavourable stress dramatically. When interfacial fixation was simulated as the contact condition between the tooth tissue and restorative material, it might increase the fracture potential exponentially compared with the bonded interface. For pulpal wall depth analyses, greater risks of fracture for the remaining tooth were observed in deeper cavity of mesio-occlusal-distal (MOD) restorations and the existence of a pulpal wall is essential even it is only 1 mm above the gingival wall.

Bite Force↗
PubMed1999

Automatic finite element mesh generation for maxillary second premolar.

Developing three dimensional finite element mesh models for irregular geometric objects requires a large amount of manual efforts, hence limiting the three dimensional approach for dental structure analyses. An automatic procedure which can be used to generate a three dimensional finite element mesh for the maxillary second premolar was developed in this study. Firstly, a embedded second premolar was sliced and scanned parallel to the occlusal surface. A self-developed image processing system was employed to detect the boundaries of different materials within each section. An automatic mesh generation program was used on these boundaries to create tetrahedral elements based on moving nodes of uniform cube approach. Six mesh models of the second premolar with different element sizes using linear and quadratic elements were analyzed. Strain energy and von Mises stresses were reviewed for convergence in the crown regions.

Algorithms↗
PubMed1998

Methods to improve a periodontally involved terminal abutment of a cantilever fixed partial denture--a finite element stress analysis.

The two-dimensional plane stress finite element stress analysis was used to evaluate the stress of mandibular posterior cantilevers for compromised periodontal involved distal terminal abutments. Some commonly practiced methods to alleviate the stress from mastication of the cantilever FPDs were also evaluated. From the analysis the following was concluded: (1) The most distal terminal abutment of a cantilever FPD generally experienced a high stress concentration. (2) The cantilever FPDs require at least two abutments. Optimum stress reduction occurred with a splinting of three abutments. To increase the number of abutments to more than three, would not result in a proportional and meaningful reduction of stress in the periodontium. (3) To alter the bridge material with more rigid material or to have a longer marginal preparation of the terminal abutment are ineffective for better stress distribution.

Alveolar Process↗
PubMed1995

Stress analysis of four-unit fixed bridges on abutment teeth with reduced periodontal support.

The variable properties of photoelastic models and the difficulty of fabrication of the model limit experimental designs. The 'material fringe value' is introduced into the definition of the 'stress concentration index' by multiplying the fringe orders. Three levels of periodontal support in three photoelastic models (nine cases) were compared quantitatively by determining the stress concentration induced in periodontium by point loading vertically on a span of the fixed partial denture of four units length. The results indicate that comparison among photoelastic models is possible and useful. The stress concentration effects produced by the second molar were more prominent and determinant than that by the first premolar in the periodontium of the abutments.

Alveolar Bone Loss↗
PubMed1992

[The stress distribution of prefabricated screw posts. Part III: Techniques].

Some commonly used endodontic screw posts were analysed for various techniques of post insertion by photoelastic stress distribution. These endodontic dowels were installed in assumed clinical conditions. These conditions included: (1) no backing off during post installation, (2) the channelling of the post without cleaning, (3) a smaller drill was used prepare the post channel, and (4) an axis deviated contrangle was used to prepare the post channel. According to this photoelastic analysis, the techniques of post insertion may affect the stress distribution. Suggestions for post insertion are as follows: 1. The stress can be reduced by counterrotating the dowel one-fourth turn after resistance to installation has been detected. 2. The channel should be cleaned thoroughly before post insertion. 3. Because accurate post fit is important to maximize both retention and support, the screw post should be used with the matched post/reamer system; and accurate contrangle drilling should be maintained.

Humans↗
PubMed1991

[Stress distribution of prefabricated screw posts. Part II: Different designs and materials].

This study compared stress distribution during installation and the functions of prefabricated posts of different designs and materials. When endodontic dowels were installed in standardized models as well as simulated loads were applied, direct comparisons of stress distributing properties were analyzed by photoelastic stress analysis. Based on our findings, we concluded that: 1. During installation and under simulated functional loads, the tapered-end posts produced wedging stresses near the apex. More uniform stress distributions were observed with parallel-sided posts. 2. When the coronal flanges of flange type posts engaged the model around the occlusal portion of the channel preparation, stress concentrations occurred at the flange-dowel-dentin area. Stress levels were reduced toward the apical portion of the dowels. 3. The split shaft of Flexi-Post posts appeared to compress inward, stress concentrations occurred at the cervical and middle third and the other portion of the dowels were reduced. 4. Cementation type posts displayed a low and even distribution of dentinal stress during installation and functional loads.

Biocompatible Materials↗
PubMed1991

[Stress distribution of prefabricated screw posts. Part I: Post size].

A commonly used prefabricated screw post was analysed for its various lengths and diameters. When endodontic dowels were installed in standardized models, direct comparisons of stress distributing properties were analysed through photoelastic stress analysis. According to the analysis, installation of the post produced severe lateral stress. At shorter lengths, these stress concentrations were much more severe. However, increasing the diameter of the dowel may reduce the stress slightly. Under load conditions, the stress-producing characteristics of the dowel increased with shorter lengths and smaller diameters. It seems that increasing the surface area of insertion with the dentin improves the distribution of the load caused by the insertion of the post.

Post and Core Technique↗
PubMed1991

[Stress analysis of post-reinforced maxillary anterior teeth].

This study used plane stress analysis to survey the stress distribution of maxillary anterior teeth reinforced with posts of various materials, and maxillary anterior teeth without posts. Two-dimensional finite element models of the maxillary central incisor were subjected to a simulated biting force of 200N applied under various occlusal contact conditions. The results of this study suggest that posts can transfer stress to the dentin and supporting alveolar bone, and that there is a more even stress distribution than in teeth without posts. Also, with post reinforcement the relative stress magnitudes and concentrations at the lingual surface of the post cervical area indicates that conservative enlargement of the root canal of the lingual surface is necessary. Finally, it seems that posts material with the same elastic modulous as the dentin may be the best choice.

Dental Stress Analysis↗
PubMed1990

[Use of silicone template to prepare guide planes for removable partial denture].

Guide planes are used not only for one path of insertion and removal but also to increase both the stability of the denture and resistance to lateral movement; they also protect the abutments from displacement during insertion and removal of the denture. Therefore, it is necessary to give attention to this part of the mouth preparation in the construction of removable partial dentures. Some methods have developed to form exact guide planes. They are the free-hand method, the modeling plastic index, the acrylic index, the laboratory milling technique, and the intraoral parallelism device. However, most of these instruments are either too expensive or too sophisticated to be considered practical for removable partial denture preparations. This article describes a simple and effective method to assure the development of guide planes intraorally as they are planned on the diagnostic cast. The occlusal or incisal surface of the abutment on the prepared stone cast was completely covered with a newly mixed putty type silicone rubber base. The plastic silicone was put against the prepared guide plane on the stone cast and was compressed with a blockout trimmer held on the surveyor before the silicone setting. All of the prepared guide plane was contoured to disclose the marker and to form a ledge. After the silicone setting, the template was removed and trimmed so that soft tissue will not interfere with the intraoral reorientation. As the templates are placed on the abutments intraorally, the abutments bulging out of the template area are obviously discernible and prepared guide planes on the diagnostic cast can be easily and definitely duplicated on the abutments.

Denture, Partial, Removable↗
PubMed1989

cis-beta-acetylacrylate is a substrate for maleylacetoacetate cis-trans isomerase. Mechanistic implications.

Maleylacetoacetate cis-trans isomerase together with coenzyme glutathione catalyzes cis-trans isomerization of cis-beta-acetylacrylate strongly suggesting that the isomerase directly catalyzes isomerization of the diketo forms in addition to the ketoenol forms of maleylacetone and maleylacetoacetate. The isomerase exhibits wider substrate acceptance than previously thought.

Fatty Acids, Monounsaturated↗