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PubMed1997

Potentially useful materials for biodegradable ureteric stents.

OBJECTIVES: To develop and test materials that may be useful in the design and further development of biodegradable ureteric stents. MATERIALS AND METHODS: Specimens of two plastics were placed in artificial urine of different pH for 30 days to examine the degree of dissolution of the plastic in alkaline and the stability in acidic conditions. RESULTS: The specimens remained stable in the artificial urine at pH < 7.0 for 30 days and dissolved completely at a pH > or = 7 within 48 h. CONCLUSION: Plastics can be designed which may be useful in the further development of biodegradable ureteric stents. The rate of dissolution could be changed by influencing urinary pH.

Biodegradation, Environmental↗

PubMed1995

Reference materials and reference measurement systems in laboratory medicine. Transfer of values to reference materials.

For concentration values assigned to reference and proficiency testing materials, and to patient samples, to be traceable to those in recognised, authoritative reference materials, the value must be transferred from these materials by precise methods. The intent of this document is to outline guidelines for transfer of values from a higher to a lower level reference material, e.g. from primary to secondary4) and from secondary to working reference materials. The guidelines are intentionally broad and relatively non-specific; they may still require revision for specific analytes.

Chemistry, Clinical↗

PubMed1995

Wear resistance of resin cements.

PURPOSE: To evaluate the in vitro wear resistance of four resin cements and a glass ionomer cement using a three-body wear test. MATERIALS AND METHODS: Each cement was evaluated as a direct restorative material as well as in conjunction with an inlay. All restorations were placed into cylindrical shaped cavity preparations generated on the flattened occlusal surface of human extracted molars. The bulk wear resistance of a cement was determined when tested as a direct restorative material. RESULTS: The wear resistance of all cements was greater when tested in conjunction with a resin composite inlay restoration. Although wear of a cement is dependent upon the method of testing, it was greater when combined with a less wear resistant resin composite inlay material. All of the cement materials used in this study exhibited less wear resistance than the resin composite inlays with which they were used. This in vitro wear testing system can be used as a screening test for the cement materials before a clinical study.

Analysis of Variance↗

PubMedDate not supplied

Biomechanical comparison of hybrid external fixators.

OBJECTIVES: To determine the stiffness characteristics of the hybrid ring fixator in the treatment of (OTA 41-C) proximal metaphyseal and shaft tibial fractures. DESIGN: Five identical composite tibiae were fixed with a Synthes, ACE Fischer, Howmedica Monticelli-Spinelli, or Smith & Nephew Trauma Ilizarov hybrid external fixator or with the conventional Ilizarov wire fixator. The Synthes and Monticelli-Spinelli fixators were tested twice, the first time with the connectors on the outside of the ring and the second time with the connectors on the inside of the ring. MAIN OUTCOME MEASUREMENTS: A materials testing machine was used to apply pure compression, anterior and posterior bending, medial and lateral bending, and torsion. Stiffness values were calculated from the load deformation and torque angle curves. RESULTS: Overall, the Synthes and Monticelli-Spinelli fixators were the most rigid of the fixators when the wire-to-ring connectors were placed inside the ring. In general, the fixators were stiffest in axial compression and least stiff in posterior bending. Wire length had a significant effect on overall stiffness. CONCLUSIONS: This study suggests that the four hybrid external fixators in standard configuration have stiffness characteristics similar to those of the conventional Ilizarov fixator when used to treat proximal metaphyseal and shaft fractures of the tibia.

Biomechanical Phenomena↗

PubMed1995

Development of photo-sensing bulge ductility tester.

The ductility of thin films is normally evaluated by conducting the bulge testing. However, the accuracy of the conventional type of mechanical bulge ductility testing unit is poor in determining the actual elongation. In this development, a photo-sensitive device is provided in the detecting portion to accurately measure the elongation. The sensitivity depends on the type of the materials tested. A Pyrex glass ball is utilized as a punching ball to provide equally distributed light. Pushing of the Pyrex glass is activated by a hydraulic media to control the punching velocity. Accuracy and reproducibility were primarily checked with copper thin foil deposited on polyimide substrates. Two types of dental articulating papers (paper-based and plastic-based) were tested. It was suggested that an appropriate selection of articulating paper to mark the occlusal interferences is essential for precise determination of occlusal harmony.

Dental Materials↗

PubMed1994

Microleakage of retrograde root fillings: assessment using a novel measurement system.

In the past, measurement of microleakage has been based on measurement of dye or radioactive isotope penetration. A method has been developed to allow electronic monitoring of microflow in the same specimen over a period of time. This method was used to compare previously reported retrograde materials with an amalgam/sealer combination. The material that performed best was amalgam/sealer, particularly in the first week. The role of cavity varnish in limiting leakage has been controversial, and the results in the present study do not indicate any significant benefit. The range of leakage measured for specimens in the same group suggests that in vivo the expected leakage could be considerable for the materials tested and that small differences in experimental leakage between groups may not have any practical significance.

Calcium Sulfate↗

PubMed1975

[Effect of Solanum melongena on experimental atheromatosis. IV. Histological studies on cholesterol-induced atheromatosis in rabbits in mean- and long-term tests (author's transl)].

QUESTION: In earlier studies [see literature (2, 20, 21, 22)] observations concerning the effect of Solanum Melongena (Sol. Mel.) (violet egg plants) on experimentally induced artheromatosis in rabbits were reported. This study aims to investigate histologically the effect of Sol. Mel. on experimental atheromatosis in mean-term (2--4 weeks) and long-term (8--12 weeks) tests. MATERIALS AND METHODS: For details of the test arrangement see AUBOCK and MITSCHEK, Exp. Path. 9, 323--335 (1974). From one portion of the material for histological examination cryostat sections were prepared, the other portion was fixed in Bouin's solution or in Baker's formol and paraffin-embedded at 58--60 degrees C (cross sections of the aorta). The specimens were stained as follows: erythrosin in conjunction with haematoxylin; aqueous or alcoholic solutions of toluidine blue (pH 3.5 to 5, and 7); methylene blue (pH 2.5 to 5, and 8); alcian blue (pH 2.5); Schiff-PAS; alcian blue and PAS in combination; Sudan III; elastica-van Gieson (blue) and Weigert's iron haematoxylin. For demonstration of mucopolysaccharides (MPS) the control sections were pretreated in a 10% Takadiastase solution for 10 minutes at 37 degrees C. In liver sections PAS-reactivity was additionally blocked by dimedone (cyclohexanedione) for elective demonstration of glycogen. The tissue sections were studied in transmission--, incident- and dark field illumination. RESULTS: lipid deposits as demonstrated by surface preparation technique could not be seen in paraffin sections after just one day. In the vascular wall histological changes were earliest visible after 10 to 14 days (enlargement of the subendothelial space and honeycombed edema with fine dispersed lipids). At this stage a "haematoxylin-effect" did yet not develop. Sometimes these alterations were also present in the upper layers of the media. They always first occurred in the aortic arch. At this time the Sol. Mel.-treated animals of group II only occasionally developed superficial edemas. Enlargement of the media with edematous infiltration and loosening of the elastic fibers was similar in both cases (figs. 1a and 1b). Fatty degeneration of the liver was already macroscopically visible on day 14; in untreated animals of group I it was more expressive than in group II (figs. 2a and 2b) -- this likewise applied to the cholesterol content (figs. 3a and 3b). After about 30 days in group I the earliest macroscopically visible plaques occurred prevailingly in the aortic arch and in the thoracic aorta. The development of such small foam cell plaques could be continuously observed with a hand lens (fig. 4a). In group II, however, it was not possible to observe any development of plaques with a hand lens, persistence of edemas was demonstrable with such (fig. 4b). Within these, fine dispersed droplets were present (fig. 5) but exact localization was only possible by electron microscopy [see literature(2)].

Animals↗

PubMed1999

Electro-ionic microclimate and materials used in the indoor environment.

In 170 experiments relationships between 31 different materials used in indoor premises and ionization of the air in their proximity were assessed. The influence of temperature and relative humidity on ionization of air was studied. It was observed that the materials tested could be divided into four groups according to their behaviour towards ambient light negative ions. From the results obtained it follows that the more humid and thus more conductive the material in question, the greater is its influence on the ionization of the air. The most important criterion influencing the relationship of the material and ambient air ionization is the magnitude of the contacting surface of the material that is given by its ruggedness and structure. In natural materials considerable porosity may be expected. In contrast smooth surfaces without pores can be expected in materials produced by melting. Other physico-chemical properties of the materials are manifested in a more discrete way.

Air Ionization↗

PubMed2006

An animal model in sheep for biocompatibility testing of biomaterials in cancellous bones.

BACKGROUND: The past years have seen the development of many synthetic bone replacements. To test their biocompatibility and ability for osseointegration, osseoinduction and -conduction requires their placement within bone preferably in an animal experiment of a higher species. METHODS: A suitable experimental animal model in sheep with drill holes of 8 mm diameter and 13 mm depth within the proximal and distal humerus and femur for testing biocompatibility issues is introduced. RESULTS: This present sheep model allows the placing of up to 8 different test materials within one animal and because of the standardization of the bone defect, routine evaluation by means of histomorphometry is easily conducted. This method was used successfully in 66 White Alpine Sheep. When the drill holes were correctly placed no complications such as spontaneous fractures were encountered. CONCLUSION: This experimental animal model serves an excellent basis for testing the biocompatibility of novel biomaterials to be used as bone replacement or new bone formation enhancing materials.

Animals↗

PubMed1988

MR imaging of metallic implants and materials: a compilation of the literature.

Ferromagnetic metallic implants and materials are regarded as contraindications for MR imaging because of the potential risks associated with their movement or displacement. To date, 14 published articles have evaluated the ferromagnetic qualities of 127 different metallic implants and other materials, including aneurysm and hemostatic clips (32); dental implants and materials (five); intravascular coils, filters, and stents (13); ear implants (14); prosthetic heart valves (29); orthopedic implants and materials (eight); penile implants (nine); and miscellaneous metallic implants and materials (17). All of these materials were evaluated by measuring the deflection forces induced by static magnetic fields at strengths ranging from 0.147 to 4.7 T. This article is a compilation of the results of these studies; it lists all 127 of the materials tested, indicates whether they were found to be deflected by the static magnetic fields, and gives the highest static magnetic field strength at which they were evaluated. Of the metallic implants tested, 66 were nonferromagnetic, and 29 exhibited only minimal deflection relative to their in vivo applications (i.e., the deflection forces were thought to be insufficient to move or dislodge the implant or material in situ). The authors of these studies concluded that patients with these particular metallic implants or materials (95/127, 75%) can be examined safely by MR imaging with scanners having static magnetic field strengths up to and including those used for the specific evaluations. Patients with other ferromagnetic materials or implants may also undergo MR imaging safely; however, both careful consideration of the factors that influence the deflection of metallic implants and prudent clinical judgment are required before patients who have these objects are examined via MR imaging.

Magnetic Resonance Imaging↗

PubMedDate not supplied

Comparative study of dimensional accuracy of different impression techniques using addition silicone impression material.

This study compared dimensional accuracy of the single, double with spacer, double with cut-out and double mix impression technique using addition silicone impression material. A typhodont containing Ivorine teeth model with six (6) full-crown tooth preparations were used as the positive control. Two stone replication models for each impression technique were made as test materials. Accuracy of the techniques were assessed by measuring four dimensions on the stone dies poured from the impression of the Ivorine teeth model. Results indicated that most of the measurements for the height, width and diameter slightly decreased and a few increased compared with the Ivorine teeth model. The double with cut-out and double mix technique presents the least difference from the master model as compared to the two latter impression techniques.

Dental Impression Materials↗

PubMed1999

Shear bond strength of composite resin and amalgam adhesive systems to dentin.

PURPOSE: To determine the effects of several multi-purpose dental adhesive systems on the shear bond strength of both composite resin (Herculite XRV) and amalgam (Tytin) to dentin. MATERIALS AND METHODS: 160 extracted human molar teeth were randomly assigned to 16 treatment groups (n = 10/group), embedded in resin, and ground flat on both the occlusal and apical surfaces to expose a 3.0 mm thickness of dentin. In each specimen, a 3.18 mm diameter channel was drilled through the dentin perpendicular to the ground surface. The cylindrical preparations were treated with one of seven adhesive systems or one of two controls (37% H3PO4 or Copalite varnish) according to manufacturers' recommendation, then restored with either composite resin or amalgam. Specimens were thermocycled and subjected to a punch-out shear force using a materials testing machine. RESULTS: All examined multi-purpose adhesive systems provided increased shear bond strength in comparison to the controls. Although the individual performance of each adhesive system varied with specific restorative materials, OptiBond FL demonstrated the highest mean shear bond strength to both composite resin and amalgam. Mean amalgam shear bond strength was significantly greater than mean composite resin strengths.

Acid Etching, Dental↗

PubMed1998

Effect of beryllium on the castability and resistance of ceramometal bonds in nickel-chromium alloys.

STATEMENT OF PROBLEM: Castability and ceramometal bond resistance play an important role in accepting nickel-chromium alloys as a substitute for gold alloys in dentistry. PURPOSE: This study was developed to verify the effect of beryllium on these factors in several compositions of nickel-based alloys by submitting them to castability and ceramometal bonding resistance tests. MATERIAL AND METHODS: Three experimental compositions of Ni-Cr alloys with different amounts of beryllium were used. One beryllium-free alloy was used as the control. RESULTS: Analysis of variance and Tukey's test showed significant differences (alpha = .001) for the castability test results and significant differences (alpha = .05) for ceramometal bond resistance between alloys. CONCLUSIONS: Although the amounts of chromium, manganese, and niobium were maintained, the variations in the amounts of beryllium allowed the estimation that Be-containing alloys presented better castability than Be-free alloys. The 0.9% Be-containing alloy demonstrated higher resistance of the ceramometal bond than the Be-free alloy.

Analysis of Variance↗

PubMed1989

The surface pH of glass ionomer cavity lining agents.

It is considered that acid release from the surface of glass ionomer (polyalkenoate) cements may be associated with early pulpal sensitivity following the use of these materials. This study was carried out to examine the surface pH of different types of glass ionomer lining cements using a flat-ended pH electrode. It was found that the surface pH remains low for this group of materials during the first hour of setting. Different types of glass ionomer lining cement were also shown to behave differently when considering acid release from the surface. Conclusions regarding the behaviour of glass ionomers should only be made with reference to the specific material tested.

Aluminum Silicates↗

PubMed2004

The measurement of degradation and wear of three glass ionomers following peroxide bleaching.

OBJECTIVES: To investigate, for three glass ionomer dental materials, the effects of a hydrogen peroxide solution on the elution of key elements, and the effects of a novel 6% hydrogen peroxide tooth whitening gel on subsequent wear rates with a toothpaste slurry. METHODS: Discs specimens of three glass ionomers (ChemFlex, Fuji II and Ketac-Fil) were prepared. One set of discs was exposed to either 6% hydrogen peroxide in phosphate buffer, phosphate buffer, water, a carbonated beverage or 38% orthophosphoric acid for 60 min. The ions eluted from the discs were determined by inductively coupled plasma-optical emmision spectroscopy. A second set of discs were conditioned with either a 6% hydrogen peroxide gel (30 min), water (30 min), a carbonated beverage (2 min) or 38% orthophosphoric acid gel (2 min) followed by a three-body abrasive wear treatment (2 min) with a toothpaste slurry. Changes in height of the samples were measured with a digital comparitor. The conditioning and abrasive cycles were repeated thirteen times. RESULTS: For the elution study, the solutions gave only minor release of sodium except orthophosphoric acid which showed increased elution levels of aluminium, silicon and sodium ions. For the wear study, the orthophosphoric acid gave the highest level of wear whilst for the other treatments there were no statistical significant differences in the level of wear (one-way ANOVA). CONCLUSIONS: A 6% hydrogen peroxide solution did not cause significant dissolution, and a novel 6% hydrogen peroxide tooth whitening gel did not significantly increase the three-body wear rate of any of the materials tested.

Aluminum↗

PubMed1988

[Investigations on the tissue compatibility of silicon rubber materials using experimental animals].

The reaction of subcutaneous tissue in guinea-pigs at implants of six kinds of silicone rubber materials (VEB Chemiewerk Nünchritz) was investigated by semiquantitative and quantitative methods. These based on the "Programme to the Assessment of Subcutaneous Tissue Reactions at Implants" by Knöfler, Keller etc. The histocompatibility of the tested materials can be compared with that of titanium. One of the silicone rubbers differs from both the reference material and the other silicone rubber materials significantly and is assessed to be more suitable than the alloy Gisadent KCM 83 (chromium cobalt molybdenum alloy).

Animals↗

PubMed1996

Accuracy of an electromagnetic tracking device: a study of the optimal range and metal interference.

The positional and rotational accuracy of a direct-current magnetic tracking device commonly used in biomechanical investigations was evaluated. The effect of different metals was also studied to determine the possibility of interference induced by experimental test fixtures or orthopaedic implants within the working field. Positional and rotational data were evaluated for accuracy and resolution by comparing the device output to known motions as derived from a calibrated grid board or materials testing machine. The effect of different metals was evaluated by placing cylindrical metal samples at set locations throughout the working field and comparing the device readings before and after introducing each metal sample. Positional testing revealed an optimal operational range with the transmitter and receiver separation between 22.5 and 64.0 cm. Within this range the mean positional error was found to be 1.8 percent of the step size, and resolution was determined to be 0.25 mm. The mean rotational error over a 1-20 degree range was found to be 1.6% of the rotational increment with a rotational resolution of 0.1 degrees. Of the metal alloys tested only mild steel produced significant interference, which was maximum when the sample was placed adjacent to the receiver. At this location the mild steel induced a positional difference of 5.26 cm and an angular difference of 9.75 degrees. The device was found to be insensitive to commonly used orthopaedic alloys. In this study, the electromagnetic tracking device was found to have positional and rotational errors of less than 2 percent, when utilized within its optimal operating range. This accuracy combined with its insensitivity to orthopaedic alloys should make it suitable for a variety of musculoskeletal research investigations.

Alloys↗

PubMed1996

Comparison of two- and three-body wear of glass-ionomers and composites.

The two-body and three-body wear of glass-ionomers (GIC), visible light cured glass-ionomers (VLC-GIC), and composites were compared. The wear simulations were performed for the two-body wear in an artificial mouth and for the three-body wear with the so-called ACTA machine. The tested materials were different conventional glass-ionomers, light cured glass-ionomers, composites, and amalgam. The wear rates of 8 specimens of each material for the two-body and 16 for the three-body wear test were compared. After 10(5) cycles with each testing device, the wear shapes were measured. All measurements were related to the wear rate of amalgam. For the two-body wear method, the worn materials were qualitatively judged by scanning electron microscopy. The two different wear testing methods lead to similar results with slight differences in ranking. Amalgam showed the lowest wear rates with both methods. Photac Fil, a newly developed VLC-GIC, showed dramatically lower wear resistance than composites and conventional GIC with both methods. Further investigations are necessary to identify the material-specific parameters influencing the wear behaviour of a material in relation to different wear testing methods.

Acrylic Resins↗