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PubMed2002

Free flap transfer to the dorsum of the rat: a new technique to avoid autocannibalization in free flap studies.

In this report the authors describe a new method that avoids autocannibalization by free transfer of a flap to the dorsum of the rat by means of a simple exposure technique. A total of 22 Wistar rats of both sexes (weight, 200-290 g) were used in this experiment. An anatomic study performed in 12 rats revealed that a wide exposure could be created in the axillary fossa by retracting the inferior tip of the scapular bone superiorly (after severing its attachments with the deep extrinsic back muscles), the latissimus dorsi muscle laterally, and the serratus anterior muscle medially. Furthermore, after obtaining vessel diameter measurements, it was ascertained that the subscapular and the lateral thoracic vessels could serve as the recipient vessels. Based on the anatomic study, a total of 10 conventional groin cutaneous flaps, measuring 2 x 3 cm in size, were harvested based on the femoral vessels and transferred to the dorsum of the same animal by the exposure method as just described, with microvascular anastomoses performed between the femoral vessels of the flap and either the subscapular artery and the lateral thoracic vein (N = 5) or the lateral thoracic artery and vein (N = 5). Results showed that 9 of the 10 transplanted flaps were totally viable on postoperative day 7, giving a success rate of 90%, with one failing flap belonging to the latter group. The authors conclude that by this simple method of recipient vessel exposure in the axillary fossa, free flap transfer to the dorsum of the rat is a simple and reproducible technique by microvascular anastomoses performed between the pedicle vessels of a flap and the subscapular artery and the lateral thoracic vein. This model offers the unique advantage of a dorsally located flap that is protected by autocannibalization. Moreover, daily observation and monitoring of the flap are easy and practical without the need to have the animal wear protective material such as vest.

Animals↗
PubMed2002

Quantification and evaluation of Joule heating in on-chip capillary electrophoresis.

We present the use of a novel, picoliter volume interferometer to measure, for the first time, the extent of Joule heating in chip-scale capillary electrophoresis (CE). The simple optical configuration for the on-chip interferometric backscatter detector (OCIBD) consists of an unfocused laser, an unaltered silica chip with a half-cylinder channel and a photodetector. Using OCIBD for millidegree-level noninvasive thermometry, temperature changes associated with Joule heating (2.81 degrees C above ambient) in on-chip CE have been observed in 90 microm wide and 40 microm deep separation channels. The temporal response of Joule heating in isotropically etched channels was exponential, with it taking an excess of 2.7 s to reach equilibrium. Buffer viscosity changes have also been derived from empirical on-chip thermometry data, allowing for the determination of diffusion coefficients for solutes when separated in heated buffers. In addition, OCIBD has allowed the reduction in separation efficiency to be estimated in the absence of laminar flow and due to increased molecular diffusion and lower buffer viscosity. A 7% reduction in separation efficiency was determined for a high current drawing buffer such as Tris-boric acid under an applied field of just 400 V/cm. Results indicate that heating effects in on-chip CE have been underestimated and there is a need to readdress the theoretical model.

Buffers↗
PubMed1988

The switch between two conformations of adenylate kinase.

Crystalline adenylate kinase from porcine muscle cytosol can assume two interconvertible structures. Here, we report the refined structure of crystal form B at 3.3 A resolution and compare it with crystal form A. Crystal forms A and B can be interconverted by protonation and deprotonation of His36, which is located deep in the active center cleft. The changes concern the molecular packing as well as the polypeptide chain conformation. On conversion from crystal form A to B, the N-terminal alpha-helix unwinds, the active center cleft opens to some extent and the nucleotide-binding glycine-rich loop 15-22 at the active center is detached from the bulk protein. This loop has counterparts in various important mononucleotide-binding proteins and is known to bind a phosphoryl group in adenylate kinase and in the oncogenic ras proteins. It is most likely involved in the phosphoryl transfer and the concomitant conformational changes. it is suggested that the two observed conformations are relevant for enzyme action in solution: they represent two of a series of three known snapshots depicting the enzyme during the substrate binding process.

Adenylate Kinase↗
PubMed2004

A new multifunctional ferrocenyl-substituted ferrocenophane derivative: optical and electronic properties and selective recognition of Mg2+ ions.

The synthesis, characterisation, and X-ray structure of a new strained asymmetric diferrocene derivative (2) is reported. Compound 2 acts as a highly specific electrochemical and optical Mg(2+) ion sensor, as revealed by spectroscopic and electrochemical techniques. Thus, in the presence of Mg(2+), a new redox peak appears in the cyclic voltammogram (CV) that is anodically shifted compared to the E(1/2) of the free receptor (DeltaE(1/2)=340 mV). Diferrocene derivative 2 also gives a highly visual response upon addition of Mg(2+), namely a change of colour from orange to deep purple. In addition, compound 2 does not show any significant sensing activity in the presence of Ca(2+) or alkaline ions. On protonation, it is converted into the stable diferrocenylcarbenium salt 4, in which two different modes of stabilisation of the alpha-carbocationic centre are clearly demonstrated by a combination of (1)H NMR and (57)Fe Mössbauer spectroscopic measurements. Finally, by a partial (chemical or electrochemical) oxidation, compound 2 forms the asymmetric mixed-valence species 2(+), which can be isolated as the solid salt 6 by using CF(3)SO(3) (-) as a counterion. This mixed-valence species shows a fast intramolecular electron-transfer process, as ascertained by several spectroscopic techniques.

Electrons↗
PubMed2004

Overview of the Martian radiation environment experiment.

Space radiation presents a hazard to astronauts, particularly those journeying outside the protective influence of the geomagnetosphere. Crews on future missions to Mars will be exposed to the harsh radiation environment of deep space during the transit between Earth and Mars. Once on Mars, they will encounter radiation that is only slightly reduced, compared to free space, by the thin Martian atmosphere. NASA is obliged to minimize, where possible, the radiation exposures received by astronauts. Thus, as a precursor to eventual human exploration, it is necessary to measure the Martian radiation environment in detail. The MARIE experiment, aboard the 2001 Mars Odyssey spacecraft, is returning the first data that bear directly on this problem. Here we provide an overview of the experiment, including introductory material on space radiation and radiation dosimetry, a description of the detector, model predictions of the radiation environment at Mars, and preliminary dose-rate data obtained at Mars.

Astronauts↗
PubMed1999

Crystal structure of 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase, a potential target for the development of novel antimicrobial agents.

BACKGROUND: Folate cofactors are essential for life. Mammals derive folates from their diet, whereas most microorganisms must synthesize folates de novo. Enzymes of the folate pathway therefore provide ideal targets for the development of antimicrobial agents. 6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the transfer of pyrophosphate from ATP to 6-hydroxymethyl-7,8-dihydropterin (HP), the first reaction in the folate biosynthetic pathway. RESULTS: The crystal structure of HPPK from Escherichia coli has been determined at 1.5 A resolution with a crystallographic R factor of 0.182. The HPPK molecule has a novel three-layered alpha beta alpha fold that creates a valley approximately 26 A long, 10 A wide and 10 A deep. The active center of HPPK is located in the valley and the substrate-binding sites have been identified with the aid of NMR spectroscopy. The HP-binding site is located at one end of the valley, near Asn55, and is sandwiched between two aromatic sidechains. The ATP-binding site is located at the other end of the valley. The adenine base of ATP is positioned near Leu111 and the ribose and the triphosphate extend across and reach the vicinity of HP. CONCLUSIONS: The HPPK structure provides a framework to elucidate structure/function relationships of the enzyme and to analyze mechanisms of pyrophosphoryl transfer. Furthermore, this work may prove useful in the structure-based design of new antimicrobial agents.

Adenosine Triphosphate↗
PubMed2006

Ultrastructural and biochemical evaluation of the porcine anterior chamber perfusion model.

PURPOSE: To evaluate a porcine anterior chamber perfusion model and to test the transferability of data obtained with this model to the human system. METHODS: Porcine eyes were obtained from a local abattoir and processed within 2 hours after death. Anterior chambers of 42 pairs of eyes were dissected with removal of lens, vitreous, iris, and ciliary processes and perfused for 72 (40 pairs) or 140 (2 pairs) hours with medium or medium supplemented with 10 ng/mL transforming growth factor (TGF)-beta2. Facility was continuously measured. Afterward, trabecular meshwork (TM) specimens from all quadrants were prepared, and sections were analyzed morphologically and with immunohistochemical methods. TM sections of 10 nonperfused pairs of eyes were used as the control. RNA and protein was extracted from the TM specimens. Expression of alphaB-crystallin, fibronectin (FN), plasminogen activator inhibitor (PAI)-1, thrombospondin (TSP)-1, and connective tissue growth factor (CTGF) mRNA and protein in medium-perfused and TGF-beta2-perfused anterior segments was examined by Northern and Western blot analyses. RESULTS: The nonperfused TM showed prominent differences between the temporal and nasal quadrants. Temporally, the ciliary muscle (CM) was pronounced, the scleral sulcus was long and flat, and the scleral spur extended toward the iris root. Nasally, the CM was thin, the sulcus deep, and the spur compact. The outer TM was expanded between the scleral spur and cornea throughout the entire circumference. On the ultrastructural level, the elastic network was connected to the cribriform TM cells and the aqueous plexus endothelium. Perfusion itself had only small effects on the morphology of the outer TM. Aqueous plexus loops remained open, and TM cells showed no signs of necrosis or pyknosis. alphaB-crystallin expression was significantly increased in perfused eyes. Perfusion with TGF-beta2 for 72 hours reduced outflow facility to approximately 60% of that of the medium-perfused control. TM cells adjacent to putative drainage pathways showed enlarged cisterns of rough endoplasmic reticulum (rER), a sign of active protein synthesis. Expression of alphaB-crystallin and FN mRNA were elevated by factors of 5 and 3, respectively. The proteins were upregulated by a factor of 2.5. In addition, TGF-beta2 upregulated PAI-1 (1.7-fold) and TSP-1 (1.6-fold) proteins, two factors shown to be TGF-beta2 responsive in human TM cell culture experiments. CTGF expression was not altered. CONCLUSIONS: These new ultrastructural investigations indicate that the cribriform and subendothelial regions of the porcine TM have an architecture similar to that of the primate TM. The biochemical and physiological response to TGF-beta2 was identical with that described in human TM cell culture and anterior chamber perfusion. The porcine anterior chamber perfusion model is valid for the human system.

Animals↗
PubMed2004

From biomedicine to natural history research: EST resources for ambystomatid salamanders.

BACKGROUND: Establishing genomic resources for closely related species will provide comparative insights that are crucial for understanding diversity and variability at multiple levels of biological organization. We developed ESTs for Mexican axolotl (Ambystoma mexicanum) and Eastern tiger salamander (A. tigrinum tigrinum), species with deep and diverse research histories. RESULTS: Approximately 40,000 quality cDNA sequences were isolated for these species from various tissues, including regenerating limb and tail. These sequences and an existing set of 16,030 cDNA sequences for A. mexicanum were processed to yield 35,413 and 20,599 high quality ESTs for A. mexicanum and A. t. tigrinum, respectively. Because the A. t. tigrinum ESTs were obtained primarily from a normalized library, an approximately equal number of contigs were obtained for each species, with 21,091 unique contigs identified overall. The 10,592 contigs that showed significant similarity to sequences from the human RefSeq database reflected a diverse array of molecular functions and biological processes, with many corresponding to genes expressed during spinal cord injury in rat and fin regeneration in zebrafish. To demonstrate the utility of these EST resources, we searched databases to identify probes for regeneration research, characterized intra- and interspecific nucleotide polymorphism, saturated a human - Ambystoma synteny group with marker loci, and extended PCR primer sets designed for A. mexicanum / A. t. tigrinum orthologues to a related tiger salamander species. CONCLUSIONS: Our study highlights the value of developing resources in traditional model systems where the likelihood of information transfer to multiple, closely related taxa is high, thus simultaneously enabling both laboratory and natural history research.

Ambystoma↗
PubMed1992

Deoxyribonucleoprotein structure and radiation injury: cellular radiosensitivity is determined by LET infinity -dependent DNA damage in hydrated deoxyribonucleoproteins and the extent of its repair.

For decades, theories of cellular radiosensitivity relied upon the initial patterns of energy deposition to explain radiation lethality. Such theories are unsound: cellular (DNA) repair also underlies cellular radiosensitivity. For the charged particles encountered in deep space, both the types of DNA damage caused in cellular deoxyribonucleoproteins and the efficacies of their repair are dependent on linear energy transfer (LET infinity), and repair efficiency is also influenced by cell and tissue type, i.e., the actual recovery processes involved. Therefore, quality factors derived from radiation quality alone are inadequate parameters for assessing the radiation risks of space flight. Until recently, OH radicals formed in bulk nuclear water were believed to be the major causes of DNA damage that results in cell death, especially for sparsely ionizing radiations. That hypothesis has now been challenged, if not refuted. Lethal genomic DNA damage is determined mainly by energy deposition in deoxyribonucleoproteins, and their hydration shells, and charge (energy) transfer processes within those structures.

Animals↗
PubMedDate not supplied

Engineering crops, a deserving venture.

Plant transformation has had a deep impact on several aspects of basic and applied research. Genetic transformation has offered new opportunities compared to traditional breeding practises since it allows the integration into a host genome of specific sequences leading to a strong reduction of the casualness of gene transfer. One of the first target areas was plant protection against pests, pathogens and environmental stresses while the recent plant engineering programs are aimed at increasing food quality, in particular at increasing nutritional characteristics of food crops. Moreover, transgenic plants, tissue or cell cultures represent an attractive biological system for producing heterologous proteins since they offer economic and qualitative benefits. High yield production can be obtained and large-scale commercial production will take advantage of the existing infrastructure for crop cultivation, processing and storage. There are also qualitative benefits since protein synthesis secretion and post-translational modifications are similar in plants and animal cells. There are no human viral pathogens harboured by plants: thus, especially for pharmaceuticals, plants represent the safer production system. Plant transformation has become an essential instrument also for basic research, in particular for the functional characterisation of genes identified by sequencing of whole genomes. Large collections of insertion mutants have been obtained in the model plant Arabidopsis to provide a high level of genome saturation that means 95% chance of inactivating any gene at least once. To instil greater public confidence in modern plant biotechnology recent advances have already been made to overcome the potential risks for human health and environment.

Agriculture↗
PubMed2006

Development and characterization of a porous micro-patterned scaffold for vascular tissue engineering applications.

The fabrication of functional small diameter blood vessel analogs has implications in vascular disease treatment. Current 3D models of the medial vessel layer lack micron-scale topographical cues that have shown promise in vitro by recapitulating native vascular smooth muscle cell (VSMC) behavior. A major obstacle to fabricating 3D scaffolds is maintaining adequate nutrient diffusion to cells. We have developed and characterized porous micro-patterned poly-caprolactone (PCL) scaffolds using a novel technique that integrates soft lithography, melt molding and particulate leaching of polylactic-co-glycolic acid (PLGA) micro/nanoparticles. Scanning electron microscopy showed that PLGA-leached scaffolds have circular pores significantly smaller than the size scale of the grooved surface pattern (48 microm grooves; 5 microm deep; 12 microm spacing). Diffusion of media through PLGA-leached scaffolds was six-fold greater than through non-porous scaffolds, indicating successful introduction of through-pores into PCL by the PLGA leaching technique. VSMC alignment on micro-patterned PLGA-leached scaffolds was similar to that on micro-patterned non-porous scaffolds, indicating no loss in cellular organization on PLGA-leached scaffolds. In contrast, cells seeded on micro-patterned sodium bicarbonate-leached scaffolds remained un-aligned. The ability to micro-pattern cells on porous scaffolds may facilitate the transfer of micro-technology from simple 2D substrates to complex 3D architectures, allowing for tight control over cellular organization in fabricated tissues.

Animals↗
PubMedDate not supplied

Evaluation of primary critical ischemia time for the deep circumflex iliac cutaneous flap in cats.

OBJECTIVE: To evaluate the primary critical ischemia time for the deep circumflex iliac (DCI) cutaneous flap in cats. STUDY DESIGN: In vivo model. ANIMALS: Thirteen young adult female cats. METHODS: An island skin flap was created on the right side of each cat based on the angiosome of the ventral branches of the DCI vessels. The cats were randomly assigned to a flap ischemia time ranging from 1 to 3 hours in 10-minute intervals. Microvascular clamps were used to occlude the artery and vein for the designated time. Flaps were sutured into position after the ischemic period. On day 3, fluorescein dye was administered and the flaps were evaluated under ultraviolet light to assess percent area of perfusion. On days 7 and 14, the percent area of survival was determined for each flap based on cutaneous morphometry. RESULTS: All flaps had 100 percent area of survival throughout the study. On day 3, all flaps fluoresced uniformly compared with the surrounding skin. On days 7 and 14, all flaps were uniformly viable as confirmed by skin color, consistency, bleeding, and hair re-growth. CONCLUSION: The DCI cutaneous flap in cats can withstand up to 3 hours of ischemia with predictable survival. CLINICAL RELEVANCE: In a clinical setting, high success rates can be expected with microvascular transfer of the DCI cutaneous flap in cats when the ischemia time is <3 hours and precise surgical technique is used.

Animals↗
PubMed1999

Crystal structure of the first dissimilatory nitrate reductase at 1.9 A solved by MAD methods.

BACKGROUND: The periplasmic nitrate reductase (NAP) from the sulphate reducing bacterium Desulfovibrio desulfuricans ATCC 27774 is induced by growth on nitrate and catalyses the reduction of nitrate to nitrite for respiration. NAP is a molybdenum-containing enzyme with one bis-molybdopterin guanine dinucleotide (MGD) cofactor and one [4Fe-4S] cluster in a single polypeptide chain of 723 amino acid residues. To date, there is no crystal structure of a nitrate reductase. RESULTS: The first crystal structure of a dissimilatory (respiratory) nitrate reductase was determined at 1.9 A resolution by multiwavelength anomalous diffraction (MAD) methods. The structure is folded into four domains with an alpha/beta-type topology and all four domains are involved in cofactor binding. The [4Fe-4S] centre is located near the periphery of the molecule, whereas the MGD cofactor extends across the interior of the molecule interacting with residues from all four domains. The molybdenum atom is located at the bottom of a 15 A deep crevice, and is positioned 12 A from the [4Fe-4S] cluster. The structure of NAP reveals the details of the catalytic molybdenum site, which is coordinated to two MGD cofactors, Cys140, and a water/hydroxo ligand. A facile electron-transfer pathway through bonds connects the molybdenum and the [4Fe-4S] cluster. CONCLUSIONS: The polypeptide fold of NAP and the arrangement of the cofactors is related to that of Escherichia coli formate dehydrogenase (FDH) and distantly resembles dimethylsulphoxide reductase. The close structural homology of NAP and FDH shows how small changes in the vicinity of the molybdenum catalytic site are sufficient for the substrate specificity.

Amino Acid Sequence↗
PubMed1991

Variations in the analytic holding environment.

The concept of the holding environment has been used previously to characterize the treatment needs of severely regressed patients (Winnicott, 1963b). This holding of dependence is contrasted with the holding needs of narcissistic, apparently disengaged patients (Modell, 1976). The present paper considers the type of holding required by difficult, borderline patients. It is suggested that these borderline patients need a holding of their ruthlessness and rage, and also of analytic self blame. Clinical vignettes describe the holding of an anxiously demanding and of an overtly hateful borderline patient. The patient in a holding environment evokes widely divergent countertransference reactions. These range from maternal nurturing feelings with extremely dependent patients (usually those emerging from profoundly schizoid states), to feelings of annihilation with narcissistic patients and of deep self doubt, anger and destructive wishes with demanding or hateful borderline patients. In the treatment of narcissistic and borderline patients, the holding environment metaphor may help the analyst tolerate these difficult countertransference feelings. Clinical examples of each type of countertransference reaction are presented.

Adult↗
PubMed2001

Haustoria in action: case studies of nitrogen acquisition by woody xylem-tapping hemiparasites from their hosts.

This review discusses studies conducted by the author and his colleagues on mistletoes and root hemiparasites native to Western Australia. Morphological characteristics of haustoria are described and their anatomical features are discussed in relation to uptake, transfer, and metabolism of xylem-borne nitrogenous solutes derived from a host. Experimental approaches used include comparisons of xylem sap composition of parasite and host(s), solute pool analyses and enzymatic properties of haustoria, host xylem feeding of 15N-labelled solutes to follow the fate of label in haustoria and body of the parasite, and studies using species-specific nonprotein amino acids to validate successful uptake from hosts or occasional backflow of xylem-borne solutes to a host. Field studies on promiscuous root hemiparasites assess frequencies of exploitation of different hosts. 15N natural abundance assays of host and parasite dry matter demonstrate marked preference by Santalum acuminatum for N2-fixing as opposed to nonfixing hosts. The ability of Olax phyllanthi to continue to exploit deep-rooted hosts ranks of importance when xylem water potentials of other hosts go out of sucking range during periods of water stress. Comparisons of xylem sap composition of parasites feeding on different hosts indicate remarkable versatility by haustoria in uptake and utilization of the different major nitrogenous solutes received from these hosts. Solute pools in parasites partly reflect metabolic transformations accentuated by haustoria while also indicating direct throughput from xylem of a host. The review concludes by showing how empirically based modelling techniques can be used to estimate proportional gains of N by parasites from single hosts and repercussions on host growth which accompany such exploitation.

Acacia↗
PubMed2004

Effect of high-dose irradiation on the optically stimulated luminescence of Al2O3:C.

This paper examines the effect of high-dose irradiation on the optically stimulated luminescence (OSL) of Al2O3:C, principally on the shape of the OSL decay curve and on the OSL sensitivity. The effect of the degree of deep trap filling on the OSL was also studied by monitoring the sensitivity changes after doses of beta irradiation and after step-annealing of samples previously irradiated with high doses. The OSL response to dose shows a linear-supralinear-saturation behavior, with a decrease in the response for doses higher than those required for saturation. This behavior correlates with the sensitivity changes observed in the samples annealed only to 773 K, which show sensitization for doses up to 20-50 Gy and desensitization for higher doses. Data from the step-annealing study leads to the suggestion that the sensitization is caused by the filling of deep electron traps, which become thermally unstable at 1100-1200 K, whereas the desensitization is caused by the filling of deep hole traps, which become thermally unstable at 800-875 K, along with a concomitant decrease in the concentration of recombination centers (F+ -centers). Changes in the shape of the OSL decay curves are also observed at high doses, the decay becoming faster as the dose increases. These changes in the OSL decay curves are discussed in terms of multiple overlapping components, each characterized by different photoionization cross-sections. However, using numerical solutions of the rate equations for a simple model consisting of a main trap and a recombination center, it is shown that the kinetics of OSL process may also be partially responsible for the changes in the OSL curves at high doses in Al2O3:C. Finally, the implication of these results for the dosimetry of heavy charged particles is discussed.

Aluminum Oxide↗
PubMed1998

The use of near-infrared spectroscopy for assessing flap viability during reconstructive surgery.

The ability to assess viability of tissues by monitoring changes in oxygenation and perfusion during harvesting and following transfer of free and pedicled flaps is potentially important in reconstructive surgery. Rapid detection of a critical change in tissue oxygenation could enable earlier and more successful surgical intervention when such problems arise. In this study near infra-red spectroscopy (NIRS) was used to assess changes in tissue oxygenation, haemoglobin oxygenation and blood volume in a porcine prefabricated myocutaneous flap model in response to pedicle manipulations. As far as we are aware this is the first usage of a NIRS instrument to assess changes in oxygenation in a flap model which closely simulates the clinical situation. A myocutaneous flap was raised (n = 9 pigs), tubed and the flap circulation allowed to readjust for periods between 7 and 9 days. The pedicle vessels were then subjected to arterial (n = 9), venous (n = 12) and total occlusion (n = 6). Repeatable and reproducible patterns of change were measured in each case. Comparison of mean values indicated that the differences between arterial and venous, and venous and total occlusions were significant for all NIRS parameters. The monitor was easily able to detect two additional features: (i) the presence of venous congestion indicated by raised levels of deoxygenated haemoglobin and an increase in blood volume; and (ii) the presence and magnitude of reactive hyperaemia. In two flaps release of arterial or total occlusion did not result in the expected reactive hyperaemia associated with an increase in blood volume (oxygenated haemoglobin) suggestive of possible damage to the vascular bed. NIRS proved able to detect and distinguish between microcirculatory changes occurring as a result of arterial, venous or total vascular occlusion. We believe that NIRS provides a sensitive and reliable postoperative monitor of tissue viability following transfer of free and pedicled flaps. It can accurately identify different types of problems with the pedicle vessels. In addition its predictive capabilities would allow assessment of flaps buried deep to the skin. This monitor is excellent for surgical and intensive care unit monitoring since it is unaffected by light, portable and is extremely easy to use.

Animals↗
PubMed1993

Stress and strain distribution in the bone surrounding a new design of dental implant: a comparison with a threaded Branemark type implant.

The stress and strain distributions in the bone surrounding a new dental implant, designed specifically for use with a bioactive porous coating and thus having a fully bonded interface to the bone, have been analysed. The new implant geometry was slightly tapered, with deep concentric grooves to allow bone ingrowth and load transfer, and had a parallel cylindrical section at the neck. The results have been compared with stress and strain predictions in the bone surrounding a 'Branemark type' threaded implant with a fully bonded interface. Under axial loading both implant types produced similar stress and strain distributions with a higher level of stress in the cortical bone surrounding the neck of the implant. Under lateral loading a high stress concentration was found in the neck region of both implants, but this was lower around the neck of the new design compared with the threaded implant. When the new implant was surrounded by cancellous bone, the reduction in the stress concentration was up to 50 per cent. This reduction should help to reduce fatigue failure and bone resorption in this area under lateral loading.

Bone Density↗