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PubMed2002

Vascular response of current and potential dental etchants.

This study investigated the hemostatic properties of current and potential dentin conditioners by observing the contraction of blood vessels using the rat carotid artery model. Four different agents (3M Scotchbond etchant, NRC, RC-Prep, File-Eze) were used. Dose-dependent contractions/relaxations of the test materials were first compared with epinephrine, followed by administration of papaverine, which was used to reverse epinephrine-induced contractions. In all sequences, the contraction or relaxation forces produced by the test and control materials were recorded using a force displacement transducer. RC-Prep was the only agent to produce epinephrine-like contractions (vasoconstriction) in the rat carotid artery. No contraction could be achieved with 3M etchant. Dose-dependent relaxations were observed with 3M etchant, which eventually led to collapse of the vessel wall; afterward, no response could be achieved with administration of adrenalin. File-Eze and NRC also did not cause vasoconstriction. Both materials caused dose-dependent relaxations in the smooth muscle. However, subsequent administration of adrenalin and papaverine caused dose-dependent contractions and relaxations, respectively, showing that these etchant effects did not lead to collapse of the vessel wall, as did 3M etchant.

Acid Etching, Dental↗

PubMed1994

Testing of sealing ability of endodontic filling materials.

Incomplete obturation of the root canal system is the major cause of endodontic failure. Endodontic filling materials with ability to seal the root canal are, therefore, essential for successful endodontic therapy. However, assessment of sealing ability is not included in the requirements specified in the current international standard covering root canal sealers. A number of different in vitro methods have been used to evaluate the sealing quality of endodontic filling materials. The tests have usually been leakage tests, i.e. based on assessment of penetration of a tracer along the obturated root canal. Leakage tests have poor reproducibility and are, therefore, not suited for standardized test programs. By selecting the properties necessary for sealing ability and testing them separately, it might be possible to find a number of tests, which individually are suitable for a standardized test program, and which combined will give information on the sealing ability of the test material.

Animals↗

PubMedDate not supplied

Spot tests for cannabis materials.

Sensitive and specific spot tests are described for the identification of cannabis materials. These spot tests are economical since they utilize minimal amounts of cannabis derivatives and chromogenic reagents. They yield satisfactory results when applied to the cannabis materials and are sensitive at less than 10 micrograms/ml. The described spot reactions are simple, highly reliable and reproducible.

Cannabis↗

PubMed2005

A biomechanical comparison of the Mitek RapidLoc, Mitek Meniscal repair system, clearfix screws and vertical PDS and Ti-Cron sutures.

The aim of this in vitro study was to measure and compare the biomechanical properties and mode of failure of the five different methods of meniscal repair. Reproducible tears were created in 50 bovine medial menisci and repaired in a standardized fashion with one of the following devices: the RapidLoc meniscal repair device (Mitek Products, Westwood, MA), an 8 mm Mitek meniscal repair system (Mitek Products, Westwood, MA), Clearfix screw (Innovasive Devices, Marlborough, MA), a single vertical mattress suture of 2-0 Ti-Cron (Ethicon, Massachusetts) and a vertical mattress suture of No. 1 PDS II (Johnson and Johnson Int.). The repairs were tested by single cycle load to failure in a materials testing machine. The mean loads to failure for each of the repair groups were as follows: Mitek RapidLoc 44.9 N, Mitek meniscal repair system 20.3 N, Clearfix screw 37.4 N, vertical Ti-Cron 66.1 N and vertical PDS suture 103.0 N. The mean load to failure was significantly greater with PDS vertical sutures than with other techniques (P<0.05). The Mitek RapidLoc had the least extension at failure (14.8 mm) (P<0.05). This study confirms meniscal repair with vertical PDS sutures confers the highest biomechanical stability and that the new Mitek RapidLoc device offers improved load to failure than the previous generations.

Absorbable Implants↗

PubMed1997

Anterior instrumentation of the thoracolumbar spine. A biomechanical comparison.

STUDY DESIGN: To evaluate the fatigue strength and stiffness of four anterior thoracolumbar fixation devices using a corpectomy model without load-sharing bone graft to test the devices under the worst case scenario of instability. OBJECTIVES: To gain a more thorough understanding of the biomechanical qualities of anterior fixation devices to improve clinical application and design. SUMMARY OF BACKGROUND DATA: For many surgeons, the anterior approach has become the treatment of choice for patients with compression of the spinal cord, whether it is caused by trauma, tumor, or infection. When stabilization is needed, anterior fixation devices have been advocated for many years to avoid the additional approach required for posterior fixation. Many of these devices, however, have an unacceptably high rate of hardware failure. Recently, several new devices for anterior fixation have been marketed with purported advantages in fatigue life and ease of use. METHODS: Four implants, the Synthes Anterior Thoracolumbar Locking Plate, the Kaneda device, a Texas Scottish Rite Hospital anterior construct, and the Z-Plate were attached to vertebral models and tested for stiffness in multiple planes on a modified Materials Testing System machine. They then were fatigued to failure on an Instron testing machine. RESULTS: The Anterior Thoracolumbar Locking Plate was the stiffest in axial compression, lateral flexion, and torsion. The Texas Scottish Rite Hospital anterior construct was the least stiff in flexion-extension, with no significant differences in the stiffness of the anterior thoracolumbar locking plate, that of the Kaneda device, and that of the Z-Plate. Fatigue life exceeded 80,000 cycles for the anterior thoracolumbar locking plate and averaged 26,472 cycles for the Z-Plate, 6915 cycles for the Teas Scottish Rite Hospital construct, and 4419 cycles for the Kaneda device. CONCLUSIONS: The significantly greater fatigue life of the Anterior Thoracolumbar Locking Plate and the Z-Plate may predict a lower incidence of hardware failure than with previous anterior devices. This has been confirmed in preliminary clinical studies with the Z-Plate. Further clinical studies are needed to show if these lower failure rates will continue over a long-term period.

Compressive Strength↗

PubMed2001

Comparison of viscoelastic, structural, and material properties of double-looped anterior cruciate ligament grafts made from bovine digital extensor and human hamstring tendons.

Due to ready availability, decreased cost, and freedom from transmissible diseases in humans such as hepatitis and AIDS, it would be advantageous to use tendon grafts from farm animals as a substitute for human tendon grafts in in vitro experiments aimed at improving the outcome of anterior cruciate ligament (ACL) reconstructive surgery. Thus the objective of this study was to determine whether an anterior cruciate ligament (ACL) graft composed of two loops of bovine common digital extensor tendon has the same viscoelastic, structural, and material properties as a graft composed of a double loop of semitendinosus and gracilis tendons from humans. To satisfy this objective, grafts were constructed from each tissue source. The cross-sectional area was measured using an area micrometer, and each graft was then pulled using a materials testing system while submerged in a saline bath. Using two groups of tendon grafts (n = 10), viscoelastic tests were conducted over a three-day period during which a constant displacement load relaxation test was followed by a constant amplitude, cyclic load creep test (first day), a constant load creep test (second day), and an incremental cyclic load creep test (third day). Load-to-failure tests were performed on two different groups of grafts (n = 8). When the viscoelastic behavior was compared, there were no significant differences in the rate of load decay or the final load (relaxation test) and rates of displacement increase or final displacements (creep tests) (p > 0.115). To compare both the structural and material properties in the toe region (i.e., < 250 N) of the load-elongation curve, the tangent stiffness and modulus functions were computed from parameters used in an exponential model fit to the load (stress)-elongation (strain) data. Although one of the two parameters in the functions was different statistically, this difference translated into a difference of only 0.03 mm in displacement at 250 N of load. In the linear region (i.e., 50-75 percent of ultimate load) of the load-elongation curve, the linear stiffness of the two graft types compared closely (444 N/mm for bovine and 418 N/mm for human) (p = 0.341). At failure, the ultimate loads (2901 N and 2914 N for bovine and human, respectively) and the ultimate stresses (71.8 MPa and 65.6 MPa for bovine and human, respectively) were not significantly different (p > 0.261). The theoretical effect of any differences in properties between these two grafts on the results of two types of in vitro experiments (i.e., effect of surgical variables on knee laxity and structural properties of fixation devices) are discussed. Despite some statistical differences in the properties evaluated, these differences do not translate into important effects on the dependent variables of interest in the experiments. Thus the bovine tendon graft can be substituted for the human tendon graft in both types of experiments.

Animals↗

PubMed2003

Stretching and breaking characteristics of cerebrospinal fluid shunt tubing.

OBJECT: Cerebrospinal fluid (CSF) shunt system malfunction due to silastic tubing fracture necessitates revision surgery in shunt-dependent individuals. The goal of this study was to examine the mechanical stretching and breaking characteristics of new and used CSF shunt tubing catheters to determine if any inherent physical properties predispose the tubing to fracture. METHODS: Fifty-millimeter segments of new and retrieved (used) CSF shunt tubing were stretched to 120 mm in a hydraulic press to determine modulus values (modulus = stress/strain) and to measure permanent tubing deformation imparted by the applied stress and strain. Similar 50-mm tubing segments were also stretched in an electromechanical material testing system until fracture occurred; the force and strain needed to break the tubing was recorded at the time of failure. The results demonstrate that shunt tubing with a greater cross-sectional area requires greater force to fracture, and that catheters become weaker the longer they are implanted. Barium-impregnated shunt tubing, compared with translucent tubing. appears to require less applied stress and strain to break and may fracture more easily in vivo. The variety of modulus values obtained for the new catheters tested indicates that the various companies may be using materials of different quality in tubing manufacture. CONCLUSIONS: A CSF shunt catheter design that incorporates tubing with a greater cross-sectional area may lead to fewer fractures of indwelling catheters and a reduction in shunt revision surgery.

Cerebrospinal Fluid Shunts↗

PubMed1991

[Experimental comparative study on investment materials for casting high-melting dental alloys].

The physical properties of 12 investment materials produced in middle- and east european countries were tested with methods as usual in experimental practice. At that the following properties were evaluated: grain-size distribution by screen-analysis, setting behavior by penetration, setting and thermal expansion, primary and secondary hardness and porosity by water-absorption. On the basis of the results the tested materials are valuated.

Absorption↗

PubMedDate not supplied

European Community controls for high temperature testing of food contact materials.

High temperature testing above 121 degrees C is currently in accordance with national legislation, although amended Council Directive 82/711/EEC will include a framework of temperatures and times, the most stringent of which will require 2 h testing of materials and articles at 175 degrees C with olive oil. The background debate that preceded the establishment of this proposed framework is described, as well as the difficulties that were encountered over agreeing the appropriate testing for microwave susceptors. The further work that will be required for implementation (and will need to be undertaken by groups such as CEN) is outlined as are areas such as testing above 175 degrees C that may require consideration for future EC control.

Cooking↗

PubMed2002

Cytotoxicity of precious and nonprecious alloys--experimental comparison of in vitro data from two laboratories.

The aim of this investigation was to evaluate and compare the reproducibility of cytotoxicity data generated in two different laboratories using the same testing protocols. A series of dental alloys that are widely used in both countries were chosen. These alloys (five precious, two nonprecious) were wet ground up to 1200 grit SiC, sterilized in 70% ethanol, and extracted in sterile culture medium for 7 days. Pure copper was used as a positive control and Teflonreg and media only were used as negative controls. Test and control samples were randomized and blinded to each laboratory. Cells, primary human gingival fibroblasts, and immortalized 3T3 fibroblasts, were exposed to the extracts for 24 h. Extract cytotoxicity was evaluated spectrophotometrically with the use of a mitochondrial enzyme activity assay. Data were collected from both laboratories, combined, and subjected to a mixed-model analysis of variance. No statistical difference was obtained for the immortalized 3T3 cells, except for two extracts in which differences between the two labs were significant but were still not cytotoxic. Furthermore, no statistical differences were found for the primary cells. These data strongly suggest that cytotoxicity tests performed in different laboratories with the use of the same test materials may lead to comparable results if sample preparation, cells, test procedures, and data analyses are carefully considered.

3T3 Cells↗

PubMed1996

An in vivo method for testing hemocompatibility of materials used in prosthetic heart valves.

BACKGROUND AND AIMS OF THE STUDY: An in vivo method for testing hemocompatibility of materials used in mechanical heart valves was developed. METHODS: Discs of test materials were glued to specially designed plastic (Delrin) buttons and implanted into the superior and inferior venae cavae of sheep through a right thoracotomy. The button and disc had such configuration that the blood flow was minimally disturbed. Up to four different materials could be tested simultaneously in each animal: two in superior vena cava and two in inferior vena cava. The materials and their respective implantation sites were changed between different animals according to the Latin square principle. Ten animals were used. Three materials currently used in mechanical heart valve prostheses-titanium, cobalt-chromium alloy (Haynes 25) and pyrolytic carbon (Pyrolite)--together with a surface modified (methylated) titanium were evaluated. No heparin was given during the experiment. After two hours of testing the discs were explanted and evaluated for hemocompatibility. The thrombus area on each disc was measured with photography and planimetry. Platelet and leukocyte adhesion on the surfaces were quantitatively assessed by scanning electron microscopy (SEM). The results showed that there were significant differences in thrombus formation (p = 0.001) and leukocyte adhesion (p = 0.002) between the materials tested. There was no difference between implantation sites but significant differences between individual animals (p < 0.05). CONCLUSION: The results indicate that the method can be used to evaluate early hemocompatibility of biomaterials.

Adhesiveness↗

PubMed1996

An in vitro study of the bond strength of light-cured glass ionomer cement in the bonding of orthodontic brackets.

The search to improve the properties of dental adhesives has lead to the development of light-cured glass ionomer cements. Using human teeth in vitro, the present study tested the shear/peel bond strengths of two light-cure materials ('Variglass VLC' and 'Fuji Lining LC') against a 'no-mix' composite orthodontic adhesive ('Right-On') and a chemically cured glass ionomer cement ('Ketac-Cem'). The light-cured materials were found to have an inferior bond strength compared with the two control adhesives. Based on the findings of this study, there is no evidence to support the use of the materials tested for the bonding of orthodontic brackets.

Acid Etching, Dental↗

PubMed2006

Promising in vitro performances of a new nickel-free stainless steel.

Stainless steel is a metallic alloy largely employed in orthopaedics. However, the presence in its composition of a high quantity of nickel, an agent known to trigger toxic and allergic responses, is cause for concern. In this study, we have investigated the in vitro biocompatibility of a new nickel-reduced stainless steel, namely Böhler P558, in comparison to the conventional stainless steel AISI 316L. The neutral red (NR) uptake and the amido black (AB) tests were performed on L929 fibroblasts and MG63 osteoblasts to assess the cytotoxicity, while cytogenetic effects were evaluated on CHOK1 cells by studying the frequency of Sister Chromatid Exchanges (SCE) and chromosomal aberrations. Ames test was used to detect the mutagenic activity. The expression of selected markers typical of differentiated osteoblasts, such as alkaline phosphatase activity (ALP), type I collagen (CICP) and osteocalcin (OC) production, were also monitored in MG63 cells cultured on the tested materials. Our results indicate the absence of significant cytotoxicity and genotoxicity for both test alloys. ALP, CICP and OC analyses confirmed that both materials support the expression of these phenotypic markers. Overall, these data show that this Ni-free alloy possesses good in vitro biocompatibility and could have a potential for orthopaedic applications.

Animals↗

PubMed1998

Effect of increasing temperature on the properties of four bone cements.

This investigation uses a laboratory model to evaluate the effects of a heated femoral stem on the biomechanical properties of four common acrylic bone cements. American Society for Testing Materials dog bone shaped acrylic cement specimens made at four test temperatures, 0 degree C, 23 degrees C, 37 degrees C and 50 degrees C, were tested for modulus, ultimate tensile strength, fracture toughness, and percent porosity. Fatigue strength was tested in Simplex P at 23 degrees C and 37 degrees C. The data allow direct comparison among four cement brands at each of the four temperature conditions. No adverse changes of the mechanical properties were found for any cement at any temperature. Modulus, fracture toughness, and fatigue strength were unaffected by increased temperature. Ultimate tensile strength increased in Simplex P and Zimmer Osteobond but was unaffected for Zimmer Regular and Palacos R cements. Percent porosity was related to temperature changes inversely in all brands studied, except for Palacos R which consistently had low porosity, unaffected by temperature variation. Fatigue strength of Simplex P was unaffected by heating to 37 degrees C. Based on this laboratory model, heating of the femoral stem could save time without sacrificing mechanical properties of acrylic bone cement.

Biomechanical Phenomena↗

PubMed1991

Refining the qualification process for medical materials.

This article examines the history of the use of silicone elastomers in medical devices and explains the importance of understanding a material's physical and chemical properties. Related issues of biocompatibility testing, materials biodurability, process controls, regulation, cost, FDA master files, and expedited approval also are addressed.

History, 20th Century↗

PubMed1990

The effect of various treatments on composite materials in bonding with resin cements.

The present study investigated the influence of surface treatments of composite materials using 6% hydrofluoric acid or 2% acidulated phosphate fluoride, the influence of the application of a bonding agent to the surface, and the influence of incremental curing of composite materials on the shear bonding strength between composite materials and resin cements. These results were studied statistically by analyzing variances in three-way classification and by their contributory ratios. The effects of hydrofluoric acids or acidulated phosphate fluorides on the treated surfaces of composite materials, and also the interfaces between composite materials and resin cements were further examined by mean of scanning electron microscopy (SEM). Unlike the controls, surfaces of all specimens treated with hydrofluoric acid or fluoride revealed micro-porous surfaces, but the effect of the surface treatment on the bonding strength was not equal for all the composite materials tested. The application of a bonding agent influenced some composite material, but the incremental curing of composite materials had no influence on bonding with resin cements.

Acidulated Phosphate Fluoride↗

PubMed1989

Surface changes on dental materials. The influence of two different dentifrices on surface roughness measured by laser reflexion and profilometer techniques.

Surface changes and wear resistance were investigated on eight different dental materials, using a laser reflexion technique and a profilometer. The tested materials were: (table; see text) The materials were subjected to brushing in a brushing machine, containing a toothpaste-water slurry. Two different toothpastes were used separately; Clinomyn and Colgate. The results showed that all the materials were to some extent affected by the brushing. Titanium was the most and SR Isosit N the least wear resistant material. Clinomyn and Colgate influenced the materials in different ways depending on their abrasive properties.

Acrylic Resins↗

PubMed2001

Sealing and dentin bond strength of adhesive systems in selected areas of perfused teeth.

OBJECTIVES: (1) Test the sealing capacity and tensile strength of various adhesive systems: Scotch Bond 1 (Single Bond in USA)(SB1)+Z100, Syntac Sprint (SYN)+Tetric Ceram, Prime and Bond 2.1 (PB21)+TPH Spectrum, F2000 (Adhesive+Compomer) (F2000) and Optibond Solo (OPT)+Prodigy, to perfused teeth (30 cm distilled H2O), in select areas. (2) Determine the relationship between sealing ability and size of adhesive area (BA) with tensile strength (TS). METHODS: Segments of human third molars (n=67) sealed with amalgam on their coronal side were connected to a perfusion system (30 cm distilled H2O), to measure the basal permeability. Access cavities were drilled through the amalgam to expose dentin (area range: 8.7-20.8 mm2) and measure the permeability of that area. Cavities were sealed with one of the test materials and permeability measured prior to tensile testing. The percentage of decrease in permeability (PPD) that occurred with the different combinations of materials was also measured. RESULTS. TENSILE STRENGTH: there were no statistically significant differences among groups. PERMEABILITY: ANOVA showed that there were statistically significant differences in the mean % decrease in permeability (PPD) among groups (p=0.018). Student-Newman-Keuls test (p<0.05) detected that the mean PPD of F2000 ranked statistically higher than that of SB1. Relationship among variables: a linear correlation was found defined by the formula TS=7.47+0.008 x PPD-0.23 x BA, with a significance of the model p=0.0097. SIGNIFICANCE: None of the materials studied reduced permeability up to 100%. They all produced low tensile bond strengths (maximum mean value of groups: 5.51 MPa (OPT)).

Acetone↗