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At least 379 records · Page 21Linked to original sources
PubMed2006

Volar versus dorsal locking plates with and without radial styloid locking plates for the fixation of dorsally comminuted distal radius fractures: A biomechanical study in cadavers.

PURPOSE: To compare the stability and stiffness of dorsal and volar fixed-angle distal radius constructs in a cadaveric model. METHODS: A locking distal radius system was used in a combination of a dorsal and styloid plate (group 1), a single volar plate (group 2), and a combination of a volar and styloid plate (group 3) configuration. In addition a single volar 3.5-mm steel locking plate was used in group 4. Each construct was tested on 6 fresh-frozen radii with simulated unstable dorsally comminuted extra-articular distal radius fractures. Specimens were tested on a material testing machine with an extensometer and subjected to axial compression fatigue and load-to-failure testing. RESULTS: No construct failed in fatigue testing of 250 N for 5,000 cycles. Two specimens in each group were tested for 20,000 cycles without failure. The plastic deformation in the double-plate groups was lower compared with the single-plate groups, although the difference was not statistically significant. Group 1 had the highest and group 4 the lowest failure load and stiffness, respectively. The differences between group 1 and the other groups, except failure load compared with group 3, were statistically significant. Groups 2 and 3 had a significantly higher load to failure and group 3 had a significantly higher stiffness compared with group 4. CONCLUSIONS: All constructs offer adequate stability with minimal deformation on fatigue testing under physiologic conditions. Dorsal fixed-angle constructs are stiffer and stronger than volar constructs. The addition of a styloid plate to a volar plate did not significantly improve stability in this model of simulated extra-articular dorsal comminution loaded in axial compression.

Aged↗
PubMed1994

Comparison of torsional strength of humeral intramedullary nailing: a cadaveric study.

Control of rotation after intramedullary fixation of the humeral shaft has been observed to vary clinically. Two of the newer intramedullary nails specifically designed for the humerus were tested. Transverse and spiral fractures were created in 35 fresh-frozen cadaveric humeri. The constructs were tested in a materials testing system to evaluate in vitro the torsional strength of the nailed humeral fractures. Intact bones showed a mean peak torque of 53 +/- 17 Nm. The humeri fixed with the Russell-Taylor nail (n = 18) using one interlocking screw proximally and one distally showed a mean torsional strength of 10.4 +/- 3.6 Nm. The specimens fixed with the Seidel nail (n = 17), interlocked proximally with two screws and distally by the friction of three expanded flanges against the inner cortex, had a significantly lower mean torsional strength of 1.5 +/- 0.6 Nm (p < 0.0005). When compared with intact bones, constructs using the Russell-Taylor nail achieved 20% of mean peak torque. This improved rotational strength should permit an earlier return to full functional use of the extremity.

Aged↗
PubMedDate not supplied

Dynamics of platelet adhesion to artificial materials and cultured endothelial cells under shear flow.

To evaluate the dynamic features of platelet adhesion to biomedical materials, a new shear flow testing apparatus was constructed. A cone-plate rotational viscometer, equipped with a transparent cone and transparent bottom window, was mounted on the stage of an inverted microscope. Test materials (glass, silicone, polyvinyl chloride, Thermanox, and porcine endothelial cells cultured on glass coverslips) were placed on the bottom window. Real time microscopic images of platelets adherent to the test materials in a shear rate range between 3.6 and 360 1/s were observed and recorded with a videocassette recorder. Time course changes in the number of adherent platelets were analyzed on the basis of a convective diffusion model. With respect to effective diffusivity of platelets (De) and the surface reactivity constant (K), less significant differences were found among artificial materials. In the case of cultured endothelial cells, both De and K, which were evaluated for the first time in the present study, were two to four orders of magnitude lower than those obtained with artificial materials.

Animals↗
PubMed2000

In vitro investigation of aluminum and fluoride release from compomers, conventional and resin-modified glass-ionomer cements: a standardized approach.

The amount of fluoride release from dental cements necessary for an anticariogenic effect is not established: moreover, the possible toxic effects due to high fluoride and aluminum release are not well known and the results are still controversial. The aim of our study was to evaluate fluoride (F) and aluminum (Al) release from dental cements using a 'standardized approach' according to the end-use of the materials, i.e. biocompatibility testing. Two polyacid-modified resin composites of recent application, commonly called compomers (Dyract and Dyract Cem), were compared with two conventional acid-based (Fuji I, Ketac-Cem) and two resin-modified (Vitremer, Vitrebond) glass-ionomer cements (GICs). All types of cement are used in dentistry and are commercially available. Extracts of the cements into minimum essential medium, after setting over a 1-h (group A) and 1-week (group B) period, were performed. The extraction conditions were rigorously standardized. Mean values +/- standard deviation of F- and Al-levels in such extracts were measured and were expressed as microg g(-1) (micrograms of ions per gram of cement). A great difference in the amount of ion release, both F and Al, was shown among the tested materials. The GICs, as well as Ketac-Cem, released more F and Al than the compomers. All of the materials released the greatest proportion of ions when the extraction was performed in the first hour after mixing (group A). Al- and F-values showed a highly significant positive correlation, independently from the curing time. We conclude that the biological assessment of dental cements can be performed only if a pre-evaluation of the leachables is obtained by applying a standardized protocol which allows a useful comparison between the different materials.

Aluminum↗
PubMed1994

Partition coefficients of some acetate esters and alcohols in water, blood, olive oil, and rat tissues.

Partition coefficients of hydrophilic organic solvents (C1-C5 acetate esters and alcohols) in distilled water, olive oil, human blood, and various rat tissues (blood, liver, kidney, brain, muscle, and fat) were determined. Water/air partition coefficients were measured by a new vial equilibration technique, which needs no direct measurement of the concentration in either the liquid phase or the gas phase, but only the gas chromatographic peak areas from both phases. Once the water/air partition coefficients had been measured, the blood/air, oil/air, and tissue/air partition coefficients could be measured by the previously developed vial equilibration method, which uses gas chromatographic peak areas from the gas phases in the sample (which contains test material) and the reference (which contains no test material) vessels. The alcohols tested were 32 (methanol) to 128 (n-pentanol) times more hydrophilic than the corresponding esters compared with oil/water partition coefficients. In general, water/air partition coefficients decreased and oil/air partition coefficients increased in proportion to the number of carbon atoms. Blood/air coefficients of alcohols were almost parallel to water/air partition coefficients, whereas no such relation was found with acetate esters. n-Isomers of both acetate esters and alcohols were found to be more soluble in water, blood, oil, and tissues than the corresponding iso-isomers.

Acetates↗
PubMed1994

Hygroscopic expansion of resin based composites during 6 months of water storage.

Water absorption of composite materials causes an expansion (hygroscopic) which may result in an outward force being generated against the cavity walls. The purpose of this work was to investigate the relationship between this force and the water absorption of the material over a 6 month period of water storage. This investigation was performed by measuring the force required to displace specimens of the test materials from near cylindrical cavities. An outward force developed over a period of a few days of water storage for all test materials. The magnitude of the force was greatest for a microfilled composite, which also had the greatest water absorption. The smallest forces were observed for a hybrid composite. The magnitude of the force was independent of the Young's modulus of the test material. It would appear that expansion due to water absorption is able to rapidly compensate the effects of polymerisation shrinkage. In some cases the forces produced against the cavity walls give rise to some concern for the integrity of the restored tooth.

Absorption↗
PubMed2002

Correction of analytical results for recovery: a comparison of the method performance characteristics from recent collaborative trials studies for aflatoxin quantification using conventional and robust statistics.

Results from recently conducted collaborative trials on the determination of aflatoxin B(1) in various matrices have been evaluated to establish whether the use of recovery data would result in a distinct change of the relative between-laboratory standard deviation (RSD(R)) of the corrected data compared with the uncorrected data. In addition, we applied conventional and robust statistics to evaluate whether the impact of the use of recovery data on the estimation of RSD(R) depended on the statistical method applied for data analysis. This investigation was based on means before and after correction for recovery. The method performance characteristics were calculated using results from naturally contaminated test materials, while the results from test materials fortified with the target analytes were used to estimate the recovery. The study revealed that applying conventional and robust statistics in general led to comparable estimates for RSD(R). The comparison about the use of recovery data showed that in most cases, the RSD(R) obtained from the analysis of aflatoxin B(1) decreased after correction of the results for recovery. This tendency was similar when the comparison was done using robust or conventional statistics. However, in three cases, conventional statistics yielded a higher RSD(R) for the corrected data, whereas robust statistics showed the opposite. Looking carefully at the data, the treatment of conventional statistics indicated that the way outliers are detected and removed could result in an under- or overestimation of RSD(R). Applying the law of error propagation revealed that most likely the correlation between the uncorrected data and the recovery rate led to a reduced variability of the data corrected for recovery.

Aflatoxin B1↗
PubMed1989

Osseointegration of metallic implants. I. Light microscopy in the rabbit.

Thirty-eight adult albino rabbits received one implant of pure titanium and one implant of another, test, material in each tibia. The test materials were titanium-aluminum-vanadium alloy, chrome-cobalt alloy, and stainless steel. Observation times were 4 months and 11 months. Light microscopy of the interface revealed a direct contact between bone and implant surface (osseointegration) in 73 of the 76 cases. The exceptions were two implants of pure titanium and one of stainless steel. Thus, given identical healing conditions, the modern implant metals were accepted by the bone in the same way. It is suggested that osseointegration should be regarded not as an exclusive reaction to a specific implant material, but as the expression of a nonspecific and basic healing potential in bone.

Alloys↗
PubMed1986

Three experimental designs testing orthopedic casting material strength.

Three methods for testing the comparative strength of orthopedic casts have been considered. Two of the tests, three-point-beam-bending and diametral compression, were expected to yield information about "material" strength, and a third simulated an actual cast yielding information about "structural" strength. In one study using these three methods, differences in strength were detected in the material tests, but not in the structural test. Thus, the authors believe that tests of material strength alone are insufficient to establish clinically relevant differences between the strength of orthopedic casts. Adequate testing must include structural tests like the cast-cylinder test described in this article if meaningful and clinically relevant conclusions are to be drawn regarding the comparative strength of the actual cast. Since both the three-point-beam-bending and diametral compression tests produced essentially the same results, both tests are probably not necessary. However, each of these two tests does serve to substantiate the results of the other.

Casts, Surgical↗
PubMed2006

A pinch elastometer for soft tissue.

A prototype compression elastometer suited to the characterisation of soft tissue is analysed and tested by application to various elastomers. The test material is pinched between two rigid cylinders and the compression force and displacement interpreted to yield a measure of "effective" stiffness or to calibrate a simple non-linear-elastic material model (Neo-Hookean). This deformation suits the testing of bulk soft tissue since it effectively isolates the test material from boundary conditions such as other soft tissue, ligaments and bones. These can be highly variable in the body and can affect results greatly when employing other types of tests to determine the elastic nature of tissue. A simple linear-material analysis, based on established solutions to two-dimensional problems, is extended to take into account various geometrical complexities. This analysis permits immediate inversion of the readings from the device to yield the elastic properties of the material, without the need for complex numerical analysis. Finite element analysis is also employed to determine the range of reliable application of the linear-elastic model. In particular, this analysis permits the extension of the linear-elastic analysis to include simple forms of non-linear-material behaviour. The method is demonstrated using three elastomers having significantly different material properties. A viable range of application of the device is identified in which it yields results with reasonable precision and accuracy. The prototype device was able to measure the effective elastic modulus of the test materials with a maximum error of 13% for three material types (N=25). Repeatability error was less than 7% in all cases. Further refinement of the device and measuring system will reduce this uncertainty.

Biomechanical Phenomena↗
PubMed2005

The effect of bleaching agents on the surface hardness of tooth colored restorative materials.

AIM OF THE STUDY: The aim of this study was to evaluate the effect of at-home (Opalesence/Dr. kit 15%, Ultradent, Products, Inc. South Jordan, UT, USA) and in-office (Superoxol 35%, Sultan Chemists, Inc., Englewood, NJ, USA) bleaching on the surface hardness of the following tooth colored restorative materials: composite resin, Point-4 (P4), Kerr Corporation, Orange, CA, USA; ormocer, Admira (AD),VOCO, Germany; compomer Dyract AP (DY), Dentsply DeTrey GmbH, Germany; and resin modified glass ionomer cement, Fuji II LC (FL), GC Corporation, Japan. METHODOLOGY: Sixty specimens were prepared; 15 specimens of each material (each group n = 5, control after 15 days, at-home and in-office). All specimens were stored in distilled water at room temperature for 24 hrs before testing. A universal testing machine (Micromet 2100 series micro hardness testers) was used for testing Vicker's surface hardness for the three groups for every tested material. All results were statistically analyzed with one way analysis of variance (ANOVA), Post hoc Tukey HSD tests (P < 0.05), and percentage changes for Tukey. RESULTS: All the tested materials showed an increase in Vicker's surface hardness between base line (24 hrs) and the control group after 15 days storage in distilled water except DY which showed a decrease in surface hardness. All tested materials showed a decrease in surface hardness from control group after 15 days and both at-home and in-office bleaching agents except DY which showed increased values. SIGNIFICANCE: At-home as well as in-office bleaching agents have a softening effect on some tooth colored restorative material, and the patient must be aware before using them.

Analysis of Variance↗
PubMed1983

Biocompatibility test procedures for materials evaluation in vitro. I. Comparative test system sensitivity.

Relative sensitivity of in vitro biocompatibility test systems was explored. Cellular responses of 12 standardized cell lines to 20 materials representing a range of toxicity were measured. Each cell line and material combination was tested in duplicate using four different culture methods, and each culture plate was examined by two graders. Results of the tissue culture assays were compared to those obtained for the same materials in vivo using a 5-day rabbit intramuscular implant assay. Methods involving measurement of cellular growth (colony counts or percent of confluence) in serum-fortified media extracts of test samples were generally more sensitive and discriminating than those in which test materials were placed directly in cell cultures (measurement of zone of growth inhibition). There was good agreement between graders for all test methods. Antibiotics were not used in the test program. Based upon sensitivity, reproducibility, ability to discriminate materials, and grader agreement, 4 of the 12 cell lines and 2 of the 4 test methods appeared most suitable for screening and evaluation of materials. Agreement of results using these four cell lines with intramuscular implantation tests for the 30 materials ranged from 60 to 90%.

Animals↗
PubMed2006

Retrieval-induced facilitation: initially nontested material can benefit from prior testing of related material.

Classroom exams can assess students' knowledge of only a subset of the material taught in a course. What are the implications of this approach for long-term retention? Three experiments (N = 210) examined how taking an initial test affects later memory for prose materials not initially tested. Experiment 1 shows that testing enhanced recall 24 hr later for the initially nontested material. This facilitation was not seen for participants given additional study opportunities without initial testing. Experiment 2 extends this facilitative effect to a within-subjects design. Experiment 3 demonstrates that this facilitation can be modulated by conscious strategies. These results have implications for educational practice and the theoretical developments of the testing effect, associative memory, and retrieval inhibition.

Adult↗
PubMed1982

Migration of leukocytes in dental pulp in response to plaque bacteria.

Cell material from three different dental plaque bacteria (Actinomyces viscosus, Streptococcus mitis, Actinobacillus actinomycetemcomitans) were studied for their capacity to induce leukocyte migration in the dental pulp of monkeys. Altogether five animals were used to provide 123 teeth for the study. The bacterial test materials were prepared from lyophilized sonicates of pure cultures of respective bacteria mixed with crystalline bovine serum albumin (BSA) 1:1 by weight. Immediately prior to use in the experiment saline was added to render the test material into a paste-like consistency. Buccal Class V cavities were prepared in the monkey teeth leaving a thin remaining wall to the pulp. In these cavities, the test materials were enclosed for a period of 8 h. A set of control cavities received BSA alone. Placement of test and control materials were made before and after depleting the animals of serum complement by repeated injections of Cobra Venom Factor. Histologic examination of pulp tissue specimens showed that materials from two of the bacterial species (A. viscosus, Act. actinomycetemcomitans) consistently induced infiltrations of polymorphonuclear leukocytes in one to several cell layers underneath the test cavity. The material from S. mitis seemed less potent and in 11 of 22 teeth no pulpal reaction was recorded. Inactivation of complement with Cobra Venom Factor did not appear to affect the severity of the pulpal responses.

Animals↗
PubMed1992

A new procedure of the tensile fatigue test for dental materials.

A new tensile fatigue test using a stainless steel screw was introduced. A transparent PMMA rod was selected as the test material. A hole was drilled and tapped into the rod; a screw was put into the rod with dental cement or without cementation. Three types of cyclic loads were applied to the test piece; the number of times the load was applied when the initial crack was observed and when the final fracture occurred were recorded. Surface observation showed that actual fatigue fractures occurred in the test piece. The preferred applied load waveform was the cyclic haver-triangles load because of the small coefficient of variance. Fatigue strengths of test pieces with and without cementation were different. Cementation improved the fatigue properties, and the type of cement had an effect on the fatigue properties. Although the number of final fractures minus the number of initial cracks was the constant regardless of the type of cement used.

Analysis of Variance↗
PubMed1998

Comparison of three fracture toughness testing techniques using a dental glass and a dental ceramic.

OBJECTIVES: Various methods aimed at determining the fracture toughness of ceramics in mode I (KIc) have been described in the literature. The accuracy, scatter and the interexaminer reproducibility of KIc depend strongly on the procedural approach, the test parameters used and the conditioning of the specimens. The purpose of the present study was to compare fracture toughness values obtained using two indentation methods as well as a newly established fracture mechanics test. METHODS: The following methods for KIc determination were applied: (1) indentation fracture (IF), (2) indentation strength (IS) and (3) the single-edge-V-notched-beam test (SEVNB). The materials tested were a low-fusing dental glass (Duceram LFC) and a feldspar-based porcelain (IPS classic). Data were compared by ANOVA and Tukey's multiple comparison test (p < or = 0.05). RESULTS: For both materials, KIc coefficients of variation ranged between 10 and 14% for IF and 7 and 10% for IS. The IS technique demonstrated a load dependency for the IPS porcelain which was not observed when using the IF method. The SEVNB test provided consistent results with coefficients of variation between 1 and 3%. SEVNB toughness values for the IPS porcelain were in agreement with the IS technique. However, halfpenny shaped cracks were observed at the tip of the notch of all LFC specimens thus leading to underestimated KIc values. SIGNIFICANCE: The overall aim of this type of study is to select testing procedures that are as expedient and reliable as possible. This study has shown that all three methods agreed within 10%. However none of the procedures proved absolutely straightforward. Decision on which method to use should be based on a sound understanding of the conceptual limitations and technical difficulties inherent to each technique.

Aluminum Silicates↗
PubMed1996

In vitro interaction between tetracalcium phosphate-based cement and calvarial osteogenic cells.

Newly-developed tetracalcium phosphate-based cement (4CP cement) and cells derived from neonatal rat calvaria were cocultured to study the in vitro reaction of osteoblastic cells to the biomaterial at light and electron microscopic levels. Three-dimensional nodular structures covered with active osteoblastic cells were formed in the periphery of the test material and they contained a mineralized tissue that exhibited features closely resembling bone formed in vivo. Ultrastructurally, the test material was circumscribed with an electron-dense structure, and was immediately adjacent to elongated cyoplasmic processes with intact morphology or collagen fibrils with periodic structures. Furthermore, the mineralization of the extracellular collagenous matrix occurred directly on the surface of the material. These in vitro findings suggest the ability of 4CP cement to bind directly with newly-formed hard tissues.

Animals↗