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Biomedical subjects

S M Siegel

Publications and source records attributed to S M Siegel.

At least 19 recordsLinked to original sources
PubMed1998

Treatment of patients with asymmetries using asymmetric mechanics.

The orthodontic correction of dental asymmetries is often considered a difficult and challenging process, primarily because of misdiagnosis and poorly planned treatment mechanics. A careful differential diagnosis together with a thorough treatment plan can ensure successful treatment outcomes in the management of these malocclusions. In this article, key elements of differential diagnosis and treatment planning are reviewed. Different treatment strategies, including an analysis of the side effects associated with the use of these appliance systems, are described. This approach will help the clinician to best adapt treatment mechanics to a given malocclusion.

Dental Arch↗
PubMed1996

Combined orthodontic and prosthetic therapy. Special considerations.

The adult patient may present with a complex medical and dental history. Comprehensive treatment planning with appropriate consultation among the restorative dentist and other dental specialists is a prerequisite for a successful treatment outcome. This article reviewed the role of orthodontic treatment in the restoration of the partially edentulous patient. The case illustrations presented show the value of collaborative efforts in a multidisciplinary team approach. Although there may be initial reluctance on the part of some patients to seek multiple specialty consultations, the rewards are great for the patient and the dentists who subscribe to this treatment philosophy.

Adolescent↗
PubMed1991

The protection of invertebrates, fish, and vascular plants against inorganic mercury poisoning by sulfur and selenium derivatives.

Protection of organisms against mercury (Hg) poisoning is most commonly associated with the antagonistic effects of selenium (Se)-compounds against mercury alkyls in higher animals. This study shows that there is no consistent difference among Periodic Group VIA derivatives including S(IV), S(II) organic, Se (IV), Se (II) organic, possibly Se VI, as well and Te (IV) in their ability to protect against mercury poisoning. The organisms used in assays were: Coleus explants (leaf abscission); turnip (germination); pea (growth inhibition and Hg uptake); a planarian (regeneration); the brineshrimp (excystment, phototaxy); the mealworm larva Tenebrio (metamorphosis) and the fish "tilapia" (survival, Hg uptake). Thiamine was the most effective of the Group VIA derivatives against the widest spectrum of organisms and test systems. In planarian regeneration, it was active where S and Se compounds failed. The most unexpected observation was the hastening of insect metamorphosis by HgCl2 and the enhancement of that effect by thiamine.

Animals↗
PubMed1991

Stroke as a late sequela of cranial irradiation for childhood brain tumors.

Cerebrovascular disease involving large and medium-size vessels is thought to be an uncommon sequela of treatment of childhood brain tumors. We reviewed 11 children who developed cerebrovascular disease manifested by strokes or transient ischemic attacks 6 months to 4 years after treatment of brain tumors, while their tumors were in remission. All had received radiation therapy, and seven had received chemotherapy. One child died of acute bilateral cerebral infarctions due to carotid occlusion on one side and marked stenosis on the other 2 years after receiving radiation therapy for an incompletely resected craniopharyngioma. Pathologically, there was marked subendothelial fibrosis of the vessels of the circle of Willis, with inflammatory changes surrounding some of the vessels. In addition to the widely recognized small-vessel damage caused by radiation and chemotherapy in children (mineralizing microangiopathy), damage to medium and large intracranial vessels may result in late sequelae, manifested by stroke or transient ischemic attacks.

Adolescent↗
PubMed1985

The prognostic implication of hypercholesterolemia in infants and children with hepatoblastoma.

This paper reports the relationship between serum cholesterol level and hepatoblastoma in nine patients. Four of the nine patients had a high (417-544 mg%) serum cholesterol. All of these patients were less than one year of age and had tumors of the epithelial type. Three of the infants died soon after being diagnosed. Three patients had a moderately elevated serum cholesterol (206-249mg%). One underwent primary hepatic resection. Two had nonresectable tumors that became resectable after chemotherapy. One died secondary to pulmonary metastases. The remaining two patients had a normal serum cholesterol level prior to treatment. Both patients had hepatic resection after chemotherapy and had no evidence of increased cholesterol postoperatively and are alive six years after diagnosis. From these data, it is suggested that the pretreatment level of serum cholesterol may be of prognostic significance in infants and children with hepatoblastoma.

Adolescent↗
PubMed1983

Short-term and long-term clinostat and vibration-induced biochemical changes in dwarf marigold stems.

Stems of 21-day dwarf Marigold plants cultivated on the clinostat were compared with plants cultivated on vertical axis rotators ("vibrational controls") and stationary controls for long-term changes in cell wall composition. Stems of 21-day plants grown under stationary conditions and subsequently exposed to the clinostat for 24 hours were also analyzed. Among the long-tern markers, calciun, lignin, and protein-bound hemicellulose (possibly cell wall glycoprotein) clearly differentiated the effects of vibration from those of the clinostat. Short-term differential responses included rate of ethylene production, nastic movement and peroxidase activity of the cell wall, but not of the protoplast.

Asteraceae↗
PubMed1983

An extraterrestrial habitat on Earth: the algal mat of Don Juan [correction of Jaun] Pond.

On the edge of Don Juan Pond in the Wright Valley of Antarctica lies a mat of mineral and detritus cemented by organic matter. In spite of a CaCl2 concentration of about 33% (w/v), the mat contains Oscillatoria and other cyanobacteria, unicellular forms, colonial forms rich in carotenoids, and diatoms. Bacteria are rare; fungal filaments are not. Oscillatoria showed motility but only at temperatures <10 degrees C. Acetone extracts of the mat and nearby muds yielded visible spectra similar to those of laboratory grown O. sancta, with 50- to 70-fold molar ratio of chlorophyll a to b. Although rare, tardigrades were also found. The algal mat had enzymatic activities characteristic of peroxidase, catalase, dehydrogenase, and amylase. Cellulose, chitin, protein, lipid and ATP were present. Previously, algae in the Wright Valley have been described in melt water, not in the brine itself. Wright Valley has been used as a near sterile Martian model. It obviously contains an array of hardy terrestrial organisms.

Adenosine Triphosphate↗
PubMed1981

Enzyme-mimicking properties of silicates and other minerals.

The adsorptive and/or catalytic properties of clays, silicates in general, and other minerals are well known. More recently, their probable role in prebiotic syntheses of bio-organic compounds has become a matter of record. We demonstrate that, in addition to their role in de novo formation of important biomolecules, clays, micas, fibrous silicates and other minerals mimic the activities of contemporary enzymes including oxidases, esterases, phosphatases and glucosidases. The existence of such capabilities in substances likely to be represented on the surfaces of Earth-like planets may offer a challenge to the technology and design of remote life detection systems which must then distinguish between bona fide biological chemistry and mineral-base pseudometabolism. It also raises questions about the importance of mineral surfaces in post-mortem transformations of organic metabolites in our own biosphere.

Catalysis↗
PubMed1981

Effects of salts and temperatures on post-irradiation growth of Penicillium exposed to ultraviolet.

The growth of Penicillium notatum colonies after UV irradiation of dried mycelium or spores was studied in relation to post-irradiation temperature and salt environment. Dried mycelium and spores behaved differently with respect to sensitivity to temperature, salts and UV, especially the latter. Threshold inhibitory doses for spores were modified markedly either at 4 degrees C or in magnesium and calcium chlorides. It is suggested that these temperature and salt effects are related to prevention of photochemical membrane damage.

Calcium Chloride↗
PubMed1980

Further studies on the environmental capabilities of fungi: interactions of salinity, ultraviolet irradiation, and temperature in Penicillium.

A strain of Penicillium currently under study in this laboratory has revealed some unexpected features in response to salts and UV-radiation. These responses include: (a) stimulation of growth by one molar NaCl and KCl at 23 degrees but not at 5 degrees C, (b) total inhibition by LiCl and RbCl at 5 degrees but not at 23 degrees C, (c) stimulation by 254 nm radiation (2 x 10(6) erg cm-2 min-1, 30-90 minutes) at 23 degrees and 5 degrees C, and (d) very elevated growth rates at 23 degrees after incubation at 5 degrees C.

Chlorides↗
PubMed1980

Gravity and land plant evolution: experimental induction of lignification by simulated hypergravity and water stress.

The ability to lignify cell walls has long been associated with the upright condition and sometimes massive body of the land plant, and gravitational regulation of lignification has been demonstrated by clinostat/centrifuge techniques. Previous centrifuge experiments were conducted using plants in the early stages of growth, hence already programmed for immediate lignification. Elodea, an aquatic Angiosperm long believed to be incapable of lignification synthesizes lignin or lignin-like phenolics during 6 days incubation at 80 g . Yields in some cases exceeded stationary controls by as much as 300%. Supporting data were obtained using bean cotyledons. Exposure to 80 g induced lignification in extra-vascular tissue along with vascular lignin deposits. The loss of a buoyant medium also deprived early land plants of unlimited water: the lignin content in cucumber seedlings grown in water is reduced 50% or more relative to pot grown plants but water stress elevates lignin content as much as 100%. This suggests that the water status of the land environment may have provided a "backup" or "reinforcement" signal for an adaptive axial support system.

Biological Evolution↗
PubMed1979

Growth of fungi in NaCl-MgSO4 brines.

Long-term studies have shown that common fungi of the Penicillium-Aspergillus group can be grown in a variety of brines or on moist salt crystals, simulating a range of natural terrestrial habitats such as salt flats, or special water-bodies such as the Dead Sea. In general, salt media rich in KCl are favored over other alkali halides; the media become more selective as the salt concentration rises and nutrient requirements become more complex. We here demonstrate that media which resemble the Dead Sea salt mix can support the growth of selected fungal strains, even in the absence of reduced organic nutrients other than glucose. Such media may serve as models for localized microhabitats on Mars.

Aspergillus niger↗
PubMed1979

Gravity as a biochemical determinant.

The existence of obvious morphological and physiological changes in living systems exposed to altered gravity immediately informs us that prior changes have taken place in the chemistry of exposed cells, tissues and organs. These changes include transients that return more or less promptly to the norm when the system is restored to the terrestrial g-field. For example, altered serum hormone and electrolyte levels in man, which appear to reflect successful adaptation to the conditions of orbital weightlessness, disappear shortly after return to Earth. Other changes--in mineral and protein constituents of the skeletal system in man, and cell wall composition in plants--are more persistent or even permanent. Hypogravitational departures from the norm include not only "weightlessness" as achieved in orbit, but also experimental modes of compensation, on the clinostat or by flotation. These techniques are useful in the study of hypogravity but cannot replace fully the weightless environment. Plant ethylene and peroxidase both increase under orbital, clinostat and/or flotation conditions whereas 3-phosphoglyceraldehyde-dehydrogenase increases under orbital but not clinostat conditions; cytochrome reductase and malic dehydrogenase levels are affected by the clinostat, but not by actual weightless conditions. How do the altered organismal biochemistries induced by the centrifuge and the clinostat relate to one another? Does gravity operate on living systems as a continuous variable from 0 to superterrestrial values, or do deviations from g(earth) generate non-uniform, discontinuous stress responses, irrespective of sign? In plants, measurements of wall lignin content and peroxidase activity yield opposite answers. Given the limited data so far available we will consider the meaning of these contradictions.

Adaptation, Physiological↗
PubMed1978

The effects of temperature, salinity, and other factors on the growth and formation of UV-absorbing substances by the fungus Aspergillus.

Aspergillus niger can be grown at 263 degrees K in a KCl-saturated medium with glucose as the sole C-source. In spite of their similarities K and Rb-ions are not equivalent, but unlike Na-ion, both support growth. The dependency of growth rate upon the nitrogen source is peptone > NH4+ > NO3-. In KCl-medium at 263 degrees K, the production of UV-absorbing aromatic substances normally elaborated by this fungus and soluble in alcohol is reduced more than 20-fold as indicated by comparisons of total absorbance per unit dry weight in the range 210-280 nm. Both the low temperature and salt contribute to alterations in the chemistry of these potential photoprotectants.

Aspergillus niger↗
PubMed1977

Symptom change and prognosis in clinic psychotherapy.

Applicants for outpatient psychotherapy completed a symptom checklist that permitted evaluation of the duration, intensity, and patterning of presenting symptoms. Random assignment of patients acceptable for psychotherapy to immediate treatment or to the waiting list resulted in two comparable groups who repeated the symptom checklist after an average interval nine months. Patients in psychotherapy showed a greater reduction in average intensity of all symptoms than was observable in the waiting list group. In the waiting list group, improvements tended to be limited to those patients whose conditions were of comparatively brief duration. In the psychotherapy group, improvements of chronic patients were frequent; however, improvements tended to occur among those patients reporting some new symptoms rather than those giving no evidence of exacerbation. A predmoninance of "neurotic" over "behavioral" complaints also appeared to be predictive of a positive response to psychotherapy.

Acute Disease↗
PubMed1977

Life and the outer planets I. Performance of terrestrial organisms in ammonia-rich systems.

Survival and growth of organisms has been demonstrated at 298 degrees K in NH3 atmospheres, including ammonia-methane mixtures. Included are bacteria such as Clostridium perfringens, Pseudomonas aeruginosa, fungi such as Penicillium notatum and Torula utilis. Although the biological response in onion and other species of Allium is limited to germination, standard metabolic poisons were active even in 15 M aqueous NH3, at 250 degrees K. The most extreme example of compatibility between NH3-rich environments and terrestrial life was the retention of metabolic capabilities by conidia of Penicillium after 6 months at 233 degrees K in a liquid ammonia-glycerol medium. Tritiated thymidine, uridine and amino acids were incorporated by these conidia unless subjected to intense gamma-radiation. Observations spanning the past decade suggest that the analogies between H2O and NH3 as solvent media or -OH and -NH2, as functional groups are probably valid. Chemical-biological evolution similar to early terrestrial evolution could be compatible with chemical conditions presumed to exist on the outer planets and some of their satellites.

Ammonia↗
PubMed1977

Life and the outer planets. II. Enzyme activity in ammonia-water systems and other exotic media at various temperatures.

Enzyme activities are customarily measured in aqueous solutions. Activity and thermodynamic parameters are based upon behavior in these solutions although they in no way represent the highly structured internal surface system of the cell. Actual environmental limits for enzyme action may be greater than generally assumed. Peroxidase, catalase, urease and amylase retain activity in drastically modified aqueous and nonaqueous media, including aprotic solvents. Examples include formic acid, methanol, formamide, nitromethane, 10 M LiCl and 15 M aqueous ammonia. Temperatures as low as 225-233 degrees K permit activity in some media. Ammonia-rich environments are compatible with some forms of terrestrial life. Enzyme activity in these exotic media and conditions is relevant to chemical evolution on Jupiter and similar planetary systems.

Ammonia↗