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At least 541 records · Page 30Linked to original sources
PubMedDate not supplied

[Modeling of cerebrospinal fluid circulation with consideration of a pressure-volume curve in infusion tests of patients with suspected hydrocephalus. Preliminary report].

AIM OF THE STUDY: To verify the model of CSF circulation for both the increasing and decreasing CSF pressure during and after the infusion test. MATERIAL: Computerized infusion tests of 27 patients diagnosed for communicating hydrocephalus in the Department of Neurosurgery, Medical University of Warsaw were analyzed. METHOD: Pressure-volume (P-V) curves were plotted separately for ascending and descending phases of the test for comparison purposes. RESULTS: The phenomenon of significant change of the P-V curve slope after the infusion was identified in 70% of tests. It was found that the elastance coefficient was significantly greater during the infusion than after the infusion. The pulsatile changes in cerebral blood volume were higher after the infusion in comparison to values during the infusion. The baseline pressure was higher than that before the infusion. There was a significant increase in mean arterial blood pressure after the infusion and it was not associated with any change in the heart rate. CONCLUSIONS: We hypothesized that vasogenic component of intracranial pressure is responsible for the change of P-V curve slope. We also presume that the higher value of the pressure after the infusion can be due to by the excessive accumulation of cerebrospinal fluid in the intracranial space, including extra cellular parenchymal space. Both hypotheses require further studies to be evaluated.

Adolescent↗
PubMed2005

[Evaluating the integrated force induced by high quality magnet and elastics in orthodontic fixed appliance].

PURPOSE: To investigate the stability and effective working distance of integrated forces induced by high quality magnet and elastics in orthodontic fixed appliance. METHODS: N48 NdFeB magnets resembling brackets in size and volume were combined with 1/8, 3/16, 1/4, and 3/8 inch orthodontic elastics respectively to induce integrated forces that had super-long working distance. Magnetic, elastic, and integrated forces were tested by universal material test system and curves of the forces were draw. The characteristics of integrated forces, complementary effects of magnetic and elastic forces, and the proportion between elastic and magnetic forces in integrated forces at different extension distances were analyzed. Unpaired t test was used to analyze the differences between integrated and elastic forces. RESULTS: With the increase of the extension distance, the magnitude of the magnetic forces decreased significantly and the elastic forces increased in a liner manner, while the integrated forces were stable and changed mildly. Four kinds of integrated forces achieved 86 g, 138 g, 163 g, and 192 g stable forces within super-long distance respectively. Magnetic forces accounted for 34.94%-93.98% of the integrated force at 3 mm distance, 12.60%-37.89% at 6 mm distance, and only 2.69%-5.98% at 12 mm distance. The differences between four integrated forces and elastic forces at 3 mm (P<0.01), 6 mm (P<0.01), and 9 mm distance (P<0.05) were significant. CONCLUSION: Integrated forces composed of magnetic and elastic forces were a new ideal stable orthodontic force with super-long working distance.

Dental Stress Analysis↗
PubMedDate not supplied

A biomechanical comparison of unlocked or locked reamed intramedullary nails in the treatment of mid-third simple transverse femoral shaft fractures.

BACKGROUND: Despite that a mid-third simple transverse femoral shaft fracture has been traditionally treated with an unlocked reamed intramedullary nail, recently a static locked reamed intramedullary nail has been favored by some orthopedists to avoid missing extended fracture lines. A prospective comparison of both nails was conducted to investigate the superiority between the nails from biomechanical viewpoints. METHODS: Seven pairs of fresh healthy cadaver femora underwent mid-third transverse osteotomy. Consequently, all seven left femora were stabilized using Kuntscher nails and all seven right femora, static Russell-Taylor locked nails. Finally, all 14 femora were tested using a Material Testing System (MTS) machine to investigate the sustained mechanical loads, the maximal failure load, and the relative fragment displacement. RESULTS: The locked nails produced the larger mechanical loads (p = 0.02). The unlocked nails had the larger fragment displacement (p = 0.02) and the higher maximal failure load (6090 verse 5590 newtons, p = 0.02). All tests ended due to basal neck oblique fractures. CONCLUSIONS: Biomechanically, an unlocked nail, being a load-sharing device, is superior to a static locked nail, being a load-bearing device, in the treatment of a mid-third simple transverse femoral shaft fracture. Clinically, careful investigation of the fracture types and adequate selection of the nail type should be performed in treating these types of fractures.

Adult↗
PubMed1992

A model for evaluating the strength of bones lengthened by distraction osteogenesis.

In an effort to evaluate the strength of bones lengthened by distraction osteogenesis, a modified Ilizarov-type external fixator was applied to the right tibiae of five adult mongrel dogs. Diaphyseal corticotomies were performed, and distraction (lengthening) was carried out at a rate of approximately 1 mm per day for 20 days. After completion of the lengthening, the animals were killed, the fixators were removed, and the right and left tibiae were harvested and stripped of soft tissue. The ends of all harvested bones were fixated in polymethylmethacrylate to allow testing on a materials testing system (MTS) machine. Testing under torsional loads was performed on the MTS machine (50 degrees maximum angle of rotation at ten seconds) until failure. The right tibiae were lengthened an average of 12 mm (range, 7-15 mm). The slopes of the linear portion of the torque versus rotation curves were determined. A comparison of slopes revealed a mean change in stiffness between test and control bones of 20.32% (range, 0.64%-40.5%). All tibiae exhibiting mature regenerate bone demonstrated stiffness greater than the matched controls (range, 0.64-24.09% stiffer). Four of five dogs had problems with proximal and distal ring impingement. This study presents a reproducible model for evaluating the strength of bones lengthened by distraction osteogenesis. The lengthened bones that exhibited bony or mature regeneration were as strong as the control bones.

Animals↗
PubMed1982

Cellular immunity during follow-up of patients with sarcoidosis of varying duration.

Cellular immunity was followed up at 3 month intervals for 1 year in 43 patients with sarcoidosis representing three well defined categories of the disease viz acute (12), subacute (20) and chronic (11). Twelve apparently healthy individuals served as controls. Each follow-up included the following tests: total number of blood lymphocytes, T cells, B cells, leucocyte migration tests with PPD, BCG and Kveim test material and stimulation tests of lymphocytes in vitro in the presence of PHA, Con A, PPD and PWM. Statistically, the most abnormal initial findings in all the tests were noted in acute sarcoidosis, followed by the subacute group. The acute group showed the most marked changes also during the follow-up. The smallest changes during the follow-up were seen in the patients with the chronic form of the disease. However, the inter-individual variation was considerable and no definite conclusions could be drawn from findings in a given case. Alterations in cellular immunity occur in sarcoidosis. They differ between different subgroups of patients and vary differently in course of time. Well defined criteria for inclusion of patients in an investigation and repeated studies of included patients will increase the information available from investigations of cellular immunity in sarcoidosis.

Acute Disease↗
PubMed1995

Bone graft harvest site as a determinant of iliac crest strength.

Bone graft harvest site fracture can occur after removal of bone from the anterior iliac crest. No biomechanically proven guidelines for safe removal of bone exist. Cadaveric hemipelves were tested in a materials testing system machine, with the harvest site occurring 15-mm posterior to the anterosuperior iliac spine in 8 specimens and 30-mm posterior in 7 specimens. These pelves were then tested to failure by simulating avulsion fractures caused by the forces of the flexors of the hip. Average force at failure was 783 N (standard deviation, +/- 333 N) in the 15-mm group and 1917 N (standard deviation, +/- 735) in the 30-mm group. This study provides objective data which demonstrate that harvest 30 mm posterior to the anterosuperior iliac spine weakens the iliac crest less than harvest 15 mm posterior to the anterosuperior iliac crest. To minimize the possibility of iliac crest fracture after bone graft harvest, bone should be removed at least 30 mm from the anterior superior iliac spine.

Fractures, Bone↗
PubMed1998

The incidence of allergic contact dermatitis in patients with psoriasis vulgaris.

BACKGROUND: Contact dermatitis is said to be rare in psoriasis patients, possibly because of accelerated epidermal turnover, the isomorphic (Koebner) response, and lymphocyte functional alterations. OBJECTIVE: To identify contact allergy in patients with psoriasis. METHODS: A written questionnaire was completed by 100 patients with psoriasis about contact history, flare factors for psoriasis, topical skin care, medications, and occupational/hobby exposures. Of these patients, 20 agreed to be patch tested with a standard screening series (Hermal) and a 20-item psoriasis patch-test series that included ingredients that might be found in topical psoriasis products. RESULTS: Of the 100 patients, eight suspected a topical medication caused a reaction that worsened their psoriasis, 29 gave a history of atopy, 11 reported reactions to metal jewelry, and 29 reported an allergy to poison ivy. Patch-test results identified four of the 20 patients with six positive patch tests to the materials tested: three of the six positive tests were interpreted as relevant to the patient's psoriasis (coal tar, ethylenediamine and dithranol), two patients tested positive to nickel and one to thimerosal. Five patients had irritant reactions to dithranol. CONCLUSIONS: In this small study, 20% of self-selected psoriasis patients had positive allergic reactions on patch testing. A screening contact and atopic history in psoriasis patients may help to identify a subset of patients who could benefit from a search for more relevant contact allergens with patch test evaluation. This could improve treatment strategies and possibly reduce disability.

Dermatitis, Allergic Contact↗
PubMedDate not supplied

Depth of light-initiated polymerization of glass fiber-reinforced composite in a simulated root canal.

PURPOSE: The possibility of polymerizing glass fiber-reinforced composite (FRC) material into the root canal was preliminarily evaluated by determining the depth of light-initiated polymerization of FRC. MATERIALS AND METHODS: The material used was polymer-preimpregnated E-glass fiber reinforcement, which was further impregnated with light-polymerizable dimethacrylate monomer resin. The same resin without fiber reinforcement was used as a control. Six different lengths (range 4 to 24 mm) of light-protected cylinders filled with the test materials were light polymerized from one end. The degree of monomer conversion was determined from the other end by FT-IR spectrometry. Infrared spectra were recorded at six time points from the beginning of polymerization. The microhardness of the test materials was measured from the light-exposure surface toward the other end of the cylinder. RESULTS: Both groups showed a reduction in the degree of conversion with increased lengths of the cylinder. The FRC group showed a higher degree of conversion in the longest sample group compared to the resin group. Microhardness measurement confirmed the constant reduction of the degree of conversion by the reduced Vickers hardness values with increased cylinder length of the FRC. CONCLUSION: Generally, the glass FRC showed an almost equal degree of conversion after light curing as monomer resin without fibers. However, in the longest cylinders, FRC showed a slightly higher degree of conversion compared to resin only; this might be due to the fibers' ability to conduct light.

Bisphenol A-Glycidyl Methacrylate↗
PubMedDate not supplied

Preliminary validation of a short-term morphological assay to evaluate adverse effects on amphibian metamorphosis and thyroid function using Xenopus laevis.

Short-term static-renewal studies were performed on Xenopus laevis embryos with 16 selected test materials from day 50 (stage 60) to day 64 (stage 66) (14-day test) to evaluate effects on tail resorption and thyroid function. Of the 16 test materials, nine were found to inhibit significantly the rate of tail resorption, four were found to stimulate metamorphosis and three had no appreciable effect on the rate of metamorphosis. In an effort to determine if the morphological effects observed were related to alteration in thyroid activity, measurement of triiodothyronine (T3) in the test organisms and coadministration studies using thyroxine (agonist) or propylthiouracil (antagonist) were performed based on the morphological response noted during tail resorption. Of the nine compounds found to inhibit the rate of tail resorption, six were found to reduce the levels of T3. In each case, the inhibitory response could be at least partially alleviated by the co-administration of thyroxine. Larvae exposed to the four stimulatory agents had somewhat elevated levels of T3 and were responsive to propylthiouracil antagonism. These results suggest that 12 of the 14 compounds tested in this study that altered the rate of tail resorption did so via the thyroid axis. Overall, the X. laevis model appeared to be a suitable system for evaluating the impact of environmental agents and chemical products on thyroid function.

Animals↗
PubMed1992

Dentin thickness, hardness, and Ca-concentration vs bond strength of dentin adhesives.

The relationship between the tensile bond strength (TBS) and three dentin characteristics: remaining dentin thickness (RDT), Ca-concentration, and hardness, were investigated. Sixty-two extracted bovine incisors, divided into four groups, were prepared using 600-grit SiC paper to create flat dentinal surfaces. The materials tested in this study consisted of three commercially available and one experimental dentin bonding systems. The TBS and modes of failure were determined after storage for 24 h in 37 degrees C water. Then RDT, Ca-concentration, and hardness were measured. Data were statistically compared with TBS of each group. The mean bond strength of the commercial materials ranged from 2.5 +/- 0.9 MPa to 7.7 +/- 2.8 MPa. Correlations with Ca-concentration and RDT varied, depending on the product. The bond strength of the experimental material was 9.2 +/- 4.4 MPa and significantly correlated with RDT and hardness. With two of the dentin bonding agents, specimens showed a high number of cohesive fractures in dentin, 40% to 82%. It was concluded that the variability of TBS was influenced by dentinal characteristics in three of the four materials tested.

Adhesiveness↗
PubMed1984

Comparison of the dimensional accuracy of a combined reversible/irreversible hydrocolloid impression system with other commonly used impression materials.

An investigation was conducted to compare the difference in dimensional accuracy of a combined reversible/irreversible hydrocolloid impression system and the dimensional accuracies of other commonly used impression systems. No statistically significant difference's were found between the measurements of the various materials tested and those of the master model, which leads to the conclusion that the dimensional accuracies of all the materials tested were similar. The advantages and disadvantages of each material observed during the study were reported.

Acrylic Resins↗
PubMed2003

Failure characteristics of various arthroscopically tied knots.

The current study evaluated multiple arthroscopic knot configurations and compared their properties with open, hand-tied square knots. This is an experimental study done on a material testing system. Number 2 Ethibond Extra and Number 1 Polydioxanone sutures were used. Four types of sliding knot configurations were tested: the Duncan loop, the Tennessee Slider, the Savoie-Modified Roeder, and the Lieurance-Modified Roeder. Two types of nonsliding knots were tested: the Revo knot and a knot consisting of alternating half-hitches tied with the Sixth Finger Knot Pusher. Ten knots were tied of each configuration, using strict arthroscopic technique. Each knot was backed-up with four half-hitches using post switching technique. Knots were tied around two rings and then transferred wet to a materials testing machine. The knots were tested until ultimate failure, with note of clinical failure at 3 mm. Ethibond suture using the Revo knot, the Lieurance-Modified Roeder knot, and the Savoie-Modified Roeder knot were similar in strength to the square knot with comparable failure modes. Polydioxanone suture was more variable; the Revo knot, the Savoie-Modified Roeder, the Tennessee Slider, and the Duncan loop were comparable with hand-tied square knots. All of the open and arthroscopic suture loops tested in this study failed by the suture loops expanding to greater than 3 mm before ultimate failure occurred. The surgeon choosing arthroscopic repair techniques should be aware of the differences in suture material and the variation in knot strength afforded by different knot configurations.

Arthroscopy↗
PubMed1983

The permeation by liquefied coal of gloves used in coal liquefaction pilot plants.

The protective capabilities of PVC, natural rubber and milled nitrile rubber gloves currently used in coal liquefaction pilot plants were assessed and the effectiveness of a laundering method was evaluated. The breakthrough times and cumulative permeation for exposure to toluene and to liquefied coal were determined by measurement of radiolabeled phenol tracer in the aqueous receiving medium. Breakthrough times, normalized by division by the square of the material thickness, agreed with the findings of other studies. On exposure to liquefied coal, the nitrile laboratory glove resisted breakthrough the longest (between 12 and 24 hours), although it was the thinnest material tested. Breakthrough times for the other gloves ranged from 2.75 to 6.5 hours with the times for the natural rubber glove materials intermediate to the two PVC glove materials tested. However, when normalized for thickness, both PVC materials were more resistant to breakthrough than rubber. It was found that the laundering method did not completely decontaminate samples of PVC glove material pre-exposed to liquefied coal for 24 hours under laboratory conditions.

Coal↗
PubMed1995

Reliable clinical determination of speech recognition scores using Swedish PB words in speech-weighted noise.

Results of speech recognition tests with competing sound obtained by the use of standard audiometric equipment will suffer from considerable systematic errors because of normal calibration variability. To avoid this, and to keep the reliability high, not only in investigative situations but also in clinical practice, it is highly recommended that test materials be used with speech and noise mixed in the recording. Considering this, a test material was developed consisting of six Swedish PB word lists and speech-weighted noise pre-mixed with a fixed speech-to-noise ratio and recorded on compact disc. This material was investigated for list equality, and normative recognition data were obtained. The material was found to be reliable and suitable for clinical use.

Adolescent↗