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At least 685 records · Page 38Linked to original sources
PubMed2007

Friction of conventional and silica-insert ceramic brackets in various bracket-wire combinations.

OBJECTIVE: To compare the level of friction resistance (FR) of conventional and silica-insert ceramic brackets using various bracket-wire combinations and angulations. MATERIALS AND METHODS: Four types of ceramic brackets were examined: (1) polycrystalline alumina bracket (PCA-C), (2) polycrystalline alumina bracket with a stainless steel (SS) slot (PCA-M), (3) polycrystalline alumina bracket with a silica layer (PCA-S), and (4) monocrystalline sapphire bracket (MCS). A conventional SS bracket was used as the control. The static and kinetic FR in four bracket-wire angulations (0 degrees, 5 degrees, 10 degrees, and 15 degrees) was examined using SS and beta-titanium (beta-Ti) orthodontic wires, 0.019 x 0.025 inches in size, under elastic ligature in the dry state. RESULTS: The FR generated by the PCA-S bracket was significantly lower than that generated with the other ceramic brackets, and was similar to that of the SS bracket. The PCA-S bracket showed the lowest FR with both the SS and the beta-Ti wires at zero bracket angulation. The FR to sliding increased rapidly and nonlinearly when the bracket wire angulation was >5 degrees. The PCS-S bracket showed the lowest FR from 5 degrees to 15 degrees of angulation. The MCS bracket demonstrated the highest increase in FR from 0 degrees to 15 degrees of angulation, showing the highest FR at 15 degrees of angulation. CONCLUSION: PCA-S showed minimal FR among the ceramic brackets, and was comparable to the conventional SS bracket. The silica layer and rounded edges of the ceramic slot lowered FR considerably.

Aluminum Oxide↗
PubMed2001

[A comparative study of friction behaviour matching of natural tooth and new type dental prosthetic materials--titanium].

New type dental prosthetic materials Titanium not only have excellent biocompatibility, better corrosion resistance, appropriate hardness, light density approaching to human skeleton, but also good mechanical properties as those of type II, IV gold alloy recommended by ADAS, and their strength to weight ratio is 1.3 times that of aluminum, 1.5 times that of steel. Friction wear comparative tests of natural living teeth and dental Titanium materials have been carried out against Gr15 steel ball. A reciprocating movement was realized at the modified machine of fretting to simulate the pair of real tooth. The main test parameters were: slip amplitude 500 microns, normal load 20 N, frequency 2 Hz, and number of cycles 5000. The wear behavior results show that titanium is comparatively a prospective dental materials for restoration.

Child↗
PubMed2002

Measuring principles of frictional coefficients in cartilaginous tissues and its substitutes.

The frictional properties of cartilaginous tissues, such as the hydraulic permeability, the electro-osmotic permeability, the diffusion coefficients of various ions and solutes, and the electrical conductance, are vital data to characterise the extracellular environment in which chondrocytes reside. This paper analyses one-dimensional measurement principles of these coefficients. Particular attention is given to the deformation dependence of them and the highly deformable nature of the tissues. A suggested strategy is the combination of a diffusion experiment using radiotracer methods, an electro-osmotic flow experiment and an electro-osmotic pressure experiment at low electric current.

Animals↗
PubMed2002

Utilized coefficient of friction during walking: static estimates exceed measured values.

This study compared utilized coefficient of friction (COF) measured during nonslip pedestrian gait to estimated utilized COF values calculated using anthropometric (i.e., leg length) and stride characteristic data (i.e., impact angle, step length). Twenty healthy adults walked at slow, medium, and fast speeds with kinematic and kinetic data recorded simultaneously. Estimated and measured impact angle varied with walking speed, with greater angles evident with faster speeds (p < 0.001 and p < 0.05, respectively). The estimated impact angle was greater than the measured impact angle (p < 0.05). Estimated and measured peak utilized COF values varied with walking speed, with higher utilized COF values evident with faster speeds (p < 0.001 and p = 0.001, respectively). Estimated utilized COF values were 86, 118, and 131% greater than measured peak utilized COF values for slow, medium, and fast speeds, respectively (p < 0.001). Higher estimated utilized COF values varied moderately with increased measured peak utilized COF values (r = 0.522; p < 0.001). These data suggest that impact angle and step length alone cannot be used to accurately assess the utilized COF on level walking surfaces.

Accidental Falls↗
PubMedDate not supplied

Frictional resistance of removable partial dentures with retrofitted resin composite guide planes.

Frictional resistance to the dislodging forces of a removable partial denture with and without resin composite retrofitted guide planes was compared in vitro. Six master models of four natural teeth, each simulating a Kennedy Class III modification 1 arch, were used. Guide planes were prepared, and 18 cobalt-chromium removable partial denture frameworks without clasps were fabricated. Three resin composite materials were applied to the guide planes as retrofitting materials. Following this, the resistance to dislodgment of the removable partial denture framework was evaluated under cyclic dislodgment, and the resistance to dislodgment before and after resin composite retrofitted guide planes was compared. The dislodgment force was recorded every 500 cycles. Testing was concluded when the dislodging force value reached 50% of the initial value. There was a significant difference between the dislodging forces with and without retrofitted guide planes. Higher dislodging forces were recorded when resin composite retrofitted guide planes were used. Z100 was the most effective retrofitting material under cyclic dislodgment, and Heliomolar and Herculite XR performed similarly.

Acrylic Resins↗
PubMed1998

Material properties of commonly-used interface materials and their static coefficients of friction with skin and socks.

Compressive stiffness (CS) of different supporting materials used in prosthetics and orthotics and their static coefficients of friction (COF) with skin and socks were characterized. Materials tested included Spenco, Poron, nylon-reinforced silicone, Soft Pelite, Medium Pelite, Firm Plastazote, Regular Plastazote, and Nickelplast. A displacement-controlled testing device was constructed to assess the CS of 11.1 mm diameter material specimens under cyclic loading (1 Hz) to 220 kPa over 10- and 60-min periods. Results demonstrated local CS ranging from 687 kPa (Poron) to 3,990 kPa (Soft Pelite). To fit the cyclic stress-strain (S-S) data within an error of 4.0 percent full-scale output, the minimum order of fit required for Spenco, Poron, and nylon-reinforced silicone was a third-order polynomial; for Soft Pelite, Medium Pelite, Firm Plastazote, and Regular Plastazote, a second-order polynomial; and for Nickelplast, a linear fit. For all materials, the nonrecovered strains were related to loading time using an exponential fit. A biaxial force-controlled load applicator device was used to assess COF at skin-material, sock-material, and skin-sock interfaces for shear forces of 1 to 4 N applied to a 10.2 x 7.8 mm loading pad. COFs ranged from 0.48 (+/- 0.05) to 0.89 (+/- 0.09). COFs at skin-material interfaces were significantly (p < 0.05) higher than those at skin-sock interfaces. There was a trend of a higher COF at sock-material interfaces than at skin-sock interfaces. These data are of potential utility in finite element modeling sensitivity analysis of residual limb-prosthetic socket systems or body-orthosis systems to characterize effects of material features on interface pressure and shear stress distributions.

Biocompatible Materials↗
PubMed1997

[Materials for joint replacement and friction and wear].

Debilitating diseases such as osteo- and rheumatoid arthritis, trauma and bone cancer can be treated by using prostheses. The wear resistance of materials for joint replacement can affect the service-quality and service-life of prostheses. Materials for joint replacement and friction and wear were briefly reviewed in this paper.

Alloys↗
PubMed1976

Systemic and local complications following low-friction arthroplasty of the hip joint. A study of 800 consecutive operations.

At the New York Orthopaedic Hospital, a study was made of postoperative complications in 800 consecutive total hip replacements of the Charnley low-friction arthroplasty type. Specially designed records made it possible to document and include all systemic and local complications of this procedure. While the rate of postoperative infection was low (less than 1%), thromboembolism and deep-vein thrombosis incidence was high despite the introduction of a prophylactic anticoagulation regimen. There were no deaths during or immediately after surgery, but six occurred within the first six weeks postoperatively. Two were due to a massive pulmonary embolus (proved at autopsy), two to myocardial infarction (clinical diagnosis), and one to a perforated cecum (proved at autopsy). The incidence of mechanical and technical failures in our series was relatively low and quite comparable with results reported by others.

Aged↗
PubMed1988

Determination of molecular mass, Stokes' radius, frictional coefficient and isomer-type of non-denatured proteins by time-dependent pore gradient gel electrophoresis.

Molecular mass, Stoke's radius, frictional coefficient and isomer-type of non-denatured proteins can be obtained by time-dependent gradient gel electrophoresis by evaluating the resulting data using a two-step mathematical procedure. Provided a histochemical staining procedure is available to locate the position of an enzyme in the gel, crude cell extracts can be used for estimating their molecular size properties. The computation of molecular properties of non-denatured proteins is demonstrated for isozymes of aspartate aminotransferase (EC 2.6.1.1), peroxidase (EC 1.11.1.42) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) from current-year needles of spruce. The resulting data as well as those which were calculated for esterase (EC 3.1.1.1), glutamate dehydrogenase (EC 1.4.1.4), isocitrate dehydrogenase (EC 1.4.1.42), and shikimate dehydrogenase (EC 1.1.1.25) are in accordance with those reported in the literature. The method described may be applied to various scientific areas such as genetics or environmental pollution. It could be shown here that current-year needles of injured spruce (damage class 3) contained two more peroxidase isozymes and one more glucose-6-phosphate dehydrogenase isozyme than those from non-injured trees. These differences may mark two genotypes of spruce of different susceptibilities towards present-day air and soil pollutants.

Calibration↗
PubMed1999

A protein friction model of the actin sliding movement generated by myosin in mixtures of MgATP and MgGTP in vitro.

The sliding movement of an actin filament generated by myosin heads with MgGTP bound is much slower than that by those with MgATP bound. Nonetheless, there is a report that the actin sliding velocity at low (11-21 microM) MgATP concentrations is increased by the addition of MgGTP in a range of 1-3 mM, although the actin sliding velocity at these MgATP concentrations is larger than the maximum sliding velocity attained in the presence of MgGTP alone. The convex rise in the velocity was called "mutual sensitization of MgATP and MgGTP" in the report. Here we propose a theoretical model to account for the mutual sensitization of MgATP and MgGTP. The model is an extension of a protein friction model, accommodating the presence of two different substrates and assuming the presence of motile and non-motile myosins. This new model is in accord with the characteristics of the actin/myosin sliding movement experimentally observed in mixtures of MgATP and MgGTP. Comparison of the model with the experimental results implies that the non-motile and motile myosins are those with the "converse and correct" orientations of their heads with respect to the direction of the actin sliding movement in vitro.

Actins↗
PubMed1989

Dynamic changes of cell-surface glycoconjugates in human palmar epidermis following friction-blisters.

Damage and repair of cell-surface glycoconjugates were examined in human palmar skin following friction-blister injury, using biotinylated lectins and the avidin-biotin complex method. In normal skin, concanavalin A, Ricinus communis, and Triticum vulgaris bound to the surface of cells from the basal layer to the granular layer. After injury, binding of concanavalin A was absent in the plasma membrane, but appeared in the cytoplasm at perinuclear sites. The surface reaction was recovered in basal and spinous cells, but not in granular cells, when cell maturation began at 5 days after injury. In contrast, binding of Ricinus communis and Triticum vulgaris was, in general, much more resistant to tissue damage. Even in some cells, where the surface staining became obscure at an early period, a normal staining pattern reappeared by 6 h after injury. Staining of Ulex europeus I and Glycine max, detected on the surface of upper spinous and granular cells in normal skin, disappeared immediately after the injury, but recovered quickly on the surfaces of the differentiated cells. These findings suggest that at least 2 oligosaccharide sequences, one binding with concanavalin A, and the other with Ricinus communis and Triticum vulgaris, may exist on epidermal cells. Addition of terminal carbohydrates, detectable with binding of Ulex europeus I and Glycine max, appears to occur on the Ricinus communis I and Triticum vulgaris-bound oligosaccharide chain.

Biopsy↗
PubMed1993

Factors influencing survival of the socket after primary low-friction arthroplasty of the hip.

Two hundred and sixty-seven consecutive primary low-friction arthroplasties, followed for 5 to 18 years after surgery, were studied to assess the factors influencing survival of the socket, using the Kaplan-Meier method. The end point of survival was defined radiologically in two ways: incipient failure (migration of 3 mm or more or rotation of 4 degrees or more) and definite failure (progressive change of position). Twenty-four sockets (9.0%) developed incipient failure, and 14 of them progressed to definite failure. Preservation of the subchondral bone plate or eburnated bone in the acetabular roof, multiple 6-mm anchor holes, and two steps of evolution in socket design (the advent of a pressure-injection socket and than an ogee-flanged socket) benefited socket survival. Polyethylene wear was considered to be the most important factor limiting longevity of the socket.

Adult↗
PubMed1989

The energy cost of level cross-country skiing and the effect of the friction of the ski.

Oxygen consumption [(VO2) in ml.kg-1.min-1], blood lactate concentration ([La] in mM) and dynamic friction of the skis on snow [(F) in N] were measured in six athletes skiing on a level track at different speeds [(v) in m.min-1] and using different methods of propulsion. The VO2 increased with v and F, the latter depending mostly on snow temperature, as did [La]. The VO2 was very much affected by the skiing technique. Multiple regression equations gave the following results: with diagonal stride (DS), VO2 = -23.09 + 0.189 v + 0.62 N; with double pole (DP), VO2 = -30.95 + 0.192 v + 0.51 N; and with the new skating technique (S), VO2 = -32.63 + 0.171 + 0.68 N. In terms of VO2 DS is the most expensive technique, while S is the least expensive; however, as F increases, S, at the highest speed, tends to cost as much as DP. At speeds from 18 to 22 km.h-1, the speeds measured in the competitions, the F for DS and DP can represent from 10% to 50% of the energy expenditure, with F ranging from 10 to 60 N; with S this range increases to 20%-70%. This seems to depend on the interface between the skis and the snow and on the different ways the poles are used.

Energy Metabolism↗
PubMed1996

Use of the force-velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer.

A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5-7 s to reach the maximal velocity (vmax) against different braking forces (FB). Power was averaged during a complete crank rotation by adding the power dissipated against FB to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output (Wpeak), power output attained at vmax (Wvmax) calculated as the product of vmax and FB and the work performed to reach vmax expressed in mean power output (Wvmax). The relationships between these parameters and FB were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken at rest to identify muscle metabolic and morphometric properties. The Wpeak value was similar for all FB. Therefore, the average of values was defined as corrected maximal power (Wmax). This value was 11% higher than the maximal power output uncorrected for the acceleration. Whereas the Wmax determination did not require high loads, the highest Wvmax value (Wmax) was produced when loading was heavy, as evidenced by the Wvmax-FB parabolic relationship. For each subject, the braking force (FB,Wmax) giving Wmax was defined as optimal. The FB,Wmax, equal to 0.844 (SD 0.108) N.kg-1 bodymass, was related to thigh muscle area (r = 0.78, P < 0.05). The maximal velocity (vm,Wmax) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate kinase activity). Thus, from the Wmax determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer.

Adult↗
PubMed1990

[Experimental determination of sliding friction during insertion of femoral intramedullary nails].

No data have published concerning the procedure of driving in intramedullary nails. An extensive experimental device consisting of a contact-free distance measurement, a dynamograph connected to strain gages and an accelerometer now enabled this investigation. Among other things we determined the range of sliding friction for each stroke at different levels of nail-progression. Depending of the depth of nail-progression forces between 200 N und 400 N were measured. When the nail is stuck these values rise to over 1000 N. The sliding-process lasted between 10 ms and 20 ms. Knowledge of these data is of major importance for improvement of surgical technique and possible development of mechanical nail-insertion aids.

Biomechanical Phenomena↗
PubMed2001

Patellar tendon-lateral femoral condyle friction syndrome: MR imaging in 42 patients.

OBJECTIVE: To demonstrate the MR imaging findings that occur between the posterior inferolateral patellar tendon and the lateral femoral condyle in patients with chronic anterior and or lateral knee pain. PATIENTS AND DESIGN: A retrospective review of the MR images in 42 patients who presented with chronic anterior or lateral knee pain was performed by two musculoskeletal radiologists. In 15 patients, post-contrast images were available. RESULTS: Sagittal and axial imaging planes best demonstrated the patellar tendon and its relationship with the lateral femoral condyle. In 40 patients, there was obliteration of the fat planes and abnormal signal intensity in the lateral soft tissues of the inferior patellofemoral joint. Enhancement after administration of gadolinium was noted in all cases in which contrast was administered. Eighteen patients showed cystic changes in the soft tissues adjacent to the lateral femoral condyle in addition to fat plane obliteration. In two patients, only cystic changes were noted in the lateral soft tissues. Abnormal patellar alignment was noted in 37 patients. Patellar tendon pathology was seen in nine patients. CONCLUSION: In evaluating anterior knee symptoms, MR imaging allows identification of changes that may be related to patellar tendon-lateral femoral condyle friction syndrome and that should be distinguished from other causes of anterior or lateral knee pain.

Adolescent↗
PubMed1984

Immediate excision and skin graft of a friction burn in a replanted thumb with a note on its usefulness and indications.

A case is presented in which an area of friction burn was excised from the dorsum of a replanted thumb and the wound closed with a split-skin graft. In our experience successful revascularisation of similar injuries has often been followed by progressive venous failure. It is suggested that this technique, by decompressing the tissues, may prevent stagnation and propagation of thrombus, protect the interpositional graft and avoid subsequent venous failure with loss of the replanted digit.

Adult↗