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At least 127 records · Page 7Linked to original sources

PubMed2002

Highly viscous sodium hyaluronate and joint lubrication.

We studied the natural lubrication mechanism of synovial joints. We determined the effect of sodium hyaluronate (HA) on lubricating joints without the normal lubrication mechanism. The coefficient of friction (CF) of fresh pig hip joints was measured with the cartilage intact, washed, scoured with gauze and finally with sandpaper, to model cartilage degradation. Three formulas of HA (8 x 10(5) daltons 1%, 20 x 10(5) daltons 1%, 20 x 10(5) daltons 1.5%) and physiologic saline were used as lubricants. We observed the cartilage using light microscopy (LM) and scanning electron microscopy (SEM). The latter showed that the most superficial layer observed in the washed joint was disrupted after gauze scouring. Compared with intact cartilage the CF did not increase with washing. CF increased more after scouring with sandpaper than with gauze. Each formula of HA decreased the CF of joints scoured with gauze, but only the two more viscous HA formulas decreased the CF of sandpaper-scoured joints. A negative correlation was found between the CF of the sandpaper-scoured joints and the logHA viscosity (r = -0.733, P = 0.0001), suggesting that HA with higher viscosity was more effective in lubricating the joints.

Aged↗

PubMed1992

An analysis of the squeeze-film lubrication mechanism for articular cartilage.

An asymptotic analysis of a lubrication problem is presented for a model of articular cartilage and synovial fluid under the squeeze-film condition. This model is based upon the following constitutive assumptions: (1) articular cartilage is a linear porous-permeable biphasic material filled with a linearly viscous fluid (i.e. Newtonian fluid); (2) synovial fluid is also a linearly viscous fluid. The geometry of the problem is defined by assuming that (1) cartilage is a uniform layer of thickness H; (2) synovial fluid is a very thin layer compared to H; (3) the radius R of the load-supporting area (or the effective radius of curvature of joint surface, Ri) is large compared to H. Squeeze-film action is generated in the lubricant by a step loading function applied onto the two bearing surfaces. The model assumptions and the material properties yield two small parameters in the mathematical formulation. Based on these two small parameters, two coupled nonlinear partial differential equations were derived from an asymptotic analysis of the problem: one for the lubricant (analogous to the Reynolds equation) and one for the cartilage. For known properties of normal cartilage, our calculations show: (1) the cartilage layer deforms to enlarge the load-supporting area; (2) cartilage deformation acts to reduce the lateral fluid speed in the lubricant, thus prolonging the squeeze-film time which ranges from 1 to 10 s; (3) lubricant fluid in the gap is forced from the central high-pressure region into cartilage, and expelled from the tissue at the low-pressure periphery of the load-bearing region; and (4) tensile hoop stress exists at the cartilage surface despite the compressive squeeze-film loading condition. This hoop stress results directly from the radial flow of the interstitial fluid in the cartilage layer.

Biomechanical Phenomena↗

PubMed1991

Effects of lubrication on the retention of tapered and parallel cast post and cores.

The effects of lubrication on the retention of parallel-sided and tapered cast post and cores cemented with zinc phosphate-cement (ZnPO4) and glass ionomer cements were investigated. Seventy-two maxillary canine teeth of similar size were selected for direct, parallel-sided post and core castings. The canines were sectioned at the cementoenamel junction and mounted in resin blocks. A post space was prepared to 1.5 mm (d) x 10 mm (I) with a handpiece mounted in a surveyor. The teeth were divided into four groups: ZnPO4 without lubricant, ZnPO4 with lubricant rinsed with water, ZnPO4 with lubricant removed by solvent, and ZnPO4 with solvent alone. The same four groups were made by using glass ionomer cement. Retention was tested with a 4200 series Instron machine by pulling the castings out of the teeth. There were no significant differences in retention among the eight groups of parallel posts at alpha = 0.05. The testing procedure was repeated by using an 11 mm post with 6 degrees of taper. With tapered posts, a statistically significant reduction in retention was found in the lubricated samples when compared to the nonlubricated samples.

Analysis of Variance↗

PubMed1994

The effect of dowel lubrication on retention of resin-cemented dowels.

Threaded dowels were cemented into prepared canals of extracted human teeth by use of unfilled Bis-GMA resin cement. One half the dowels were lubricated before cementation, unscrewed partially, and reseated to original length after cement had set, to assure retrievability. There was no significant difference in mean tensile force required to dislodge the dowels cemented with or without prior lubrication. Lubrication of dowels makes them predictably and easily retrievable with no short-term effect on tensile strength of the cemented lubricated dowels. Long-term effects of the lubricant on the resin are unknown.

Bisphenol A-Glycidyl Methacrylate↗

PubMed2005

Glycerin fatty acid esters as a new lubricant of tablets.

Lubrication properties were compared among glycerin fatty acid esters (Poem TR-FB and Poem TR-HB), magnesium stearate (Mg-St), and a sucrose fatty acid ester (RYOTO SUGAR ESTER S-370F: SSE). Granules containing 50% acetaminophen were prepared, and improvements in their fluidity by the lubricants were compared. The lubricant effects of TR-FB and HB during tablet punching (pressure transmission ratio, ejection force) were similar to those of Mg-St and were better than those of SSE. When the lubricant content, mixing time, and tabletting pressure were changed, TR-FB and TR-HB provided better tablet hardness than Mg-St. TR-FB and TR-HB made tablets more disintegratable than Mg-St. When the effects of these lubricants on the stability of acetylsalicylic acid (ASA) were compared, Mg-St promoted its hydrolysis, but TR-FB or TR-HB did not affect its stability.

Esters↗

PubMed2005

Effect of swing phase load on metal-on-metal hip lubrication, friction and wear.

There is renewed interest in metal-on-metal (MOM) total hip replacements (THRs), however, variable wear rates have been observed clinically. It is hypothesised that changes in soft tissue tensioning during surgery may alter loading of THRs during the swing phase of gait leading to changes in fluid film lubrication, friction and wear. This study aimed to assess the effect of swing phase load on the lubrication, friction and wear of MOM hip replacements. Theoretical lubrication modelling was carried out using elastohydrodynamic theory. All the governing equations were solved numerically for the lubricant film thickness between the articulating surfaces under the transient dynamic conditions with low and high swing phase loads. Friction testing was completed using a single axis pendulum simulator, simplified loading cycles were applied with low and high swing phase loads. MOM hip replacements were tested in a hip simulator, modified to provide different swing phase loading regimes; a low (100 N) and a high load (as per ISO 14242-1; 280 N). Results demonstrated that the performance of MOM bearings is highly dependent on swing phase load. Hence, changes in the tension of the tissues at surgery and variations in muscle forces may increase swing phase load, reduce lubrication, increase friction and accelerate wear. This may explain some of the variations that have been observed with clinical wear rates.

Arthroplasty, Replacement, Hip↗

PubMed2006

The effects of lubrication on the temperature rise and surface finish of amalgam and composite resin.

UNLABELLED: It was thought that when finishing and polishing direct filling materials lubrication would affect the surface roughness and temperature rise in samples of amalgam and composite. OBJECT: Previous work by the authors has shown that there is an optimum load, speed and time that produced the smoothest surface when finishing amalgam and composite resin using each of four grades of a disc system. This work was undertaken to examine the effects on temperature rise in samples of amalgam and composite resin of finishing dry compared to finishing with different lubricants. The experiments all used these optimum loads, speeds and times. It also compares the surface finish produced using different lubricants. MATERIALS AND METHODS: A high copper amalgam and a hybrid composite resin were finished using the four grades of abrasive discs. Samples produced were 25 mm long by 6 mm wide by 2 mm deep. A thermocouple was inserted 1 mm into the base of the samples. The thermocouple was connected via an electronic thermometer to a computer that permitted the display and recording of temperature against time. After roughening, the samples were finished and polished in a specially constructed jig that mimicked oral finishing. The pre-determined optimum loads, speeds and times were used sequentially for each of the four grades of disc. Five samples were tested for each method of finishing. Firstly, run dry, then in turn lubricated with water, walnut oil and petroleum jelly. After the use of each abrasive disc the surface roughness was measured. One of the five samples was selected at random and prepared for examination in the scanning electron microscope. All results were subjected to non-parametric statistically analyses. RESULTS: With both materials the temperature rise was greatest when run dry, followed by petroleum jelly, walnut oil and the least was when lubricated with water. With these two materials the surface roughness correlates negatively with the temperature rise. The smoothest surface being achieved when finished dry. CONCLUSIONS: To obtain the smoothest surface finish amalgam and composite should be finished dry but further work is needed to assess the effect of the temperature rise found in the materials on the pulp.

Acrylic Resins↗

PubMed2004

Prediction of lubrication regimes in wrist implants with spherical bearing surfaces.

The wrist joint is frequently affected by rheumatoid arthritis, resulting in wrist pain, deformity and ultimately loss of function. Artificial wrist implants have been introduced to treat the rheumatoid wrist, to attempt to alleviate pain and restore some function to the joint. The aim of this study was to predict the likely lubrication regimes that occur in wrist implants with spherical bearing surfaces. The implant was modelled as an equivalent ball-on-plane. Elastohydrodynamic lubrication theory was used to determine the minimum film thickness for the implant under different load, entraining velocity, lubricant viscosity, size of implant and material combinations. The results show that the highest film thickness is found in large implants, with high viscosity, high entraining velocity and low load. Hard-on-soft material combinations will operate with a boundary lubrication regime. Material combinations involving ceramic bearing surfaces have the potential to operate with a mixed lubrication regime.

Computer Simulation↗

PubMed1996

Lubrication of saliva substitutes at enamel-to-enamel contacts in an artificial mouth.

Mechanisms of salivary lubrication can be quantitatively measured by a reduction in the coefficient of friction. It is important that lubrication be assessed under the conditions of the oral cavity to properly assess lubrication regimes. The relative lubricity of three artificial salivas and two controls were assessed at a bovine enamel interface in an artificial mouth with a range of conditions that approximate oral function. Statistical analysis indicated that the enamel lubricity of sodium dodecylsulfate (SDS) and Oracare-D saliva substitutes were different from the other saliva substitutes and water. The low friction with Oracare-D and SDS saliva substitutes was because of resident amphipaths adsorbed at the enamel interface. Amphipaths adsorbed on enamel may provide a reduction in interocculsal friction and its resulting complications for patients with xerostomia.

Animals↗

PubMed2003

Comparative study of the lubricant performance of Compritol 888 ATO either used by blending or by hot melt coating.

Compritol 888 ATO is used as a lubricant in oral solid dosage formulations. It can also be used as a hot melt coating agent sprayed onto a powder. In this study, we compare the lubricant performance of Compritol 888 ATO either used by classical blending or by hot melt coating onto Lactopress by compression tests. In physical mix, the Compritol concentration does not affect the compressibility. The same compressibility is obtained with lactose coated by 0.5 or 1% of Compritol, but a higher compressibility can be observed with 2 and 3%. Cohesiveness of lactose depends on the process: hot melt coating induces a decrease of tablet tensile strength. In terms of forces transmission during compression phase and axial ejection pressures, Compritol used by hot melt coating allows for a concentration of 0.5% to directly obtain the lubricant performance of 3% of Compritol used by blending. These results suggest that the hot melt coating process induces an homogeneous repartition of the lubricant on the lactose surface, contrary to classical blending procedure. Thus, lubrication by hot melt coating seems to be a very efficient procedure. It could be used specifically for large surface area particulate systems producing a lot of friction.

Administration, Oral↗

PubMed2005

Effect of lubricant on the formation of heavy-duty diesel exhaust nanoparticles.

The effect of lubricants on nanoparticle formation in heavy-duty diesel exhaust with and without a continuously regenerating diesel particulate filter (CRDPF) is studied. A partial flow sampling system with a particle size distribution measurement starting from 3 nm, approximately, is used. Tests are conducted using four different lubricant formulations, a very low sulfur content fuel, and four steady-state driving modes. A well-documented test procedure was followed for each test. Two different kinds of nanoparticle formation were observed, and both were found to be affected bythe lubricant but in differentway. Without CRDPF, nanoparticles were observed at low loads. No correlation between lubricant sulfur and these nanoparticles was found. These nanoparticles are suggested to form mainly from hydrocarbons. With CRDPF, installed nanoparticles were formed only at high load. The formation correlated positively with the lubricant (and fuel) sulfur level, suggesting that sulfuric compounds are the main nucleating species in this situation. Storage effects of CRDPF had an effect on nanoparticle concentration as the emissions of nanoparticles decreased over time.

Lubrication↗

PubMed2005

Discharge of lubricant from air turbine handpieces.

OBJECTIVE: To demonstrate and quantify the discharge of lubricating oil from high-speed air turbine handpieces whilst running. MATERIALS AND METHODS: Dye-marked oil (Kavospray, KaVo) was used to lubricate four handpieces (Quiet-Air, Midwest) and the air discharged from around the lower bearing was directed at the moving chart paper on a recorder whilst running for 40 minutes. Secondly, seven new handpieces (Quiet-Air, 300SE, Midwest; Topair 796, Topair 795, W+H; VIP-Sigma, Pana-air, NSK; Lares, Lares Research) were cleaned, weighed and then lubricated with unmarked oil (Kavospray, KaVo). Oil discharge was determined gravimetrically over runs of 240 minutes. Data were fitted to the logistic dose response function. RESULT: The dye-marked oil tests showed that oil was discharged for at least 40 minutes in the direction of the bur. The gravimetric tests showed that oil continued to be discharged up to at least 240 minutes, and that the usual practice of removing excess lubricant by running for 1-2 minutes was ineffective in preventing cut-surface contamination. SIGNIFICANCE: Bonding procedures in dentistry may be jeopardised by oil contamination from handpiece lubricants. Decontamination with a detergent is suggested as a means of ensuring effective adhesive dentistry.

Air Pollution, Indoor↗

PubMed2001

The process of lubrication impairment and its involvement in temporomandibular joint disc displacement: a theoretical concept.

PURPOSE: This article re-evaluates the chain of events leading to temporomandibular joint (TMJ) disc displacement. The joint lubrication system and the process of its breakdown are clarified and an attempt is made to evaluate the possible effect of increased friction between the disc and fossa on the anterior displacement of the disc. MATERIALS AND METHODS: The study is based on the author's accumulated clinical data and results obtained from laboratory investigations regarding TMJ lubrication and its possible breakdown, coupled with pertinent information culled from the literature. RESULTS: Translation of the disc in the TMJ is enabled due to the presence of phospholipids and hyaluronic acid, which constitute an efficient lubrication system. This system may break down in the presence of uncontrolled free radicals. In the absence of lubricants, the articular surfaces are smooth, elastic in texture, and possess strong surface energy. Such opposing planes, especially in the presence of a thin fluid film (sub-boundary lubrication) tend to generate high friction while the disc is sliding against the fossa. Such friction is probably the prime mover in loosening the disc attachments to the condyle, with subsequent disc displacement. CONCLUSIONS: Increased friction of the contiguous parts may well be a major causative factor in displacement of the articular disc. This should be taken into account in considering the appropriate treatment approach. It also raises some doubts regarding the validity of using repositioning techniques.

Elasticity↗

PubMed2004

Patient tolerance during outpatient flexible cystoscopy--a prospective, randomized, double-blind study comparing plain lubrication and lidocaine gel.

OBJECTIVE: To compare the tolerance of flexible cystoscopy with topical anesthetic versus simple lubrication when the assigned lubricant is instilled 5 min before the exploration. MATERIAL AND METHODS: A total of 185 consecutive patients were randomly assigned either to simple lubrication (Group 1) or to lidocaine hydrochloride gel (Group 2). Thirteen patients had some kind of difficulty during exploration (stenosis) that required additional manipulation or electrocoagulation for small relapses and were excluded from the final analysis, leaving 172 patients suitable for inclusion. After the intervention, all patients were surveyed regarding their discomfort and pain levels using a verbal scale and a visual analog scale ranging from zero to 10. A chi2 analysis was performed for comparison of qualitative covariables, and quantitative covariables were compared using Student's t-test. RESULTS: The 172 patients were evenly distributed between the two groups. Of those in Group 1, 89% noted little or no discomfort, compared to 84% in Group 2. Some pain or intense pain was noted by 10% and 16% in Groups 1 and 2, respectively (p > 0.05). The average value on the visual analog scale was 2.10 and 1.97 in Groups 1 and 2, respectively (p > 0.05). CONCLUSION: There are no differences in the perception of discomfort and pain by patients when anesthetic lubricant or simple lubrication are used if the waiting time before the exploration is 5 min.

Adult↗

PubMed2004

Relative safety of sexual lubricants for rectal intercourse.

OBJECTIVE: The current study was conducted to determine the relative safety of sexual lubricants for rectal use. GOAL: Our goal was to identify a sexual lubricant that would not damage the rectal epithelium. STUDY DESIGN: We describe a mouse assay to determine the degree to which lubricants cause rectal sloughing. We also tested lubricants for cytotoxicity and their effect on Herpes simplex virus (HSV-2) infection after rectal challenge. RESULTS: Of the products tested, Delube and KY-Plus are most likely to damage the rectal epithelium, whereas Viamor, Vagisil, and Astroglide would cause some degree of rectal damage. PBS, Carraguard, and methylcellulose were not toxic in any of the assays. CONCLUSION: We have developed a quantitative method to assay the degree of sloughing of the rectal epithelium. Using this and other techniques, we are able to predict the degree to which lubricants could be safe for rectal use.

Animals↗

PubMed2006

Is liquid-based pap testing affected by water-based lubricant?

OBJECTIVE: To estimate the effect of water-based lubricant on the liquid-based Pap test. METHODS: Two hundred women each had 2 simultaneous Pap test collections. One specimen was randomly contaminated with 0.5 mL of water-based lubricant after collection. The physician was blinded as to which collection was contaminated. Both specimens were sent for cytology. Cytopathologists were blinded to the study. The rate of abnormal cytology and discordance between the control and the contaminated specimens was estimated. The discordance of secondary diagnoses, such as yeast infections and bacterial vaginosis, was also estimated. RESULTS: The incidence of abnormal cytology was similar in the contaminated specimens and the control specimens (6.5%, 95% confidence interval [CI] 3.5-10.9% versus 7.0%, 95% CI 3.9-11.5%). The rate of disagreement between the 2 specimens collected from each patient was 7.5% (95% CI 4.6-12.1%) and is similar to previously published estimates of discordance using conventional cytology. Secondary diagnoses, such as yeast infections or bacterial vaginosis, were similar in both groups, suggesting no interference from the lubricant. CONCLUSION: Water-based lubricant does not affect liquid-based cervical cytology Pap testing. Water-based lubricant does not affect secondary diagnoses such as bacterial vaginosis or yeast infections. LEVEL OF EVIDENCE: II-1.

Adult↗

PubMed2005

The use of lubrication in flexible fibreoptic nasendoscopy: a randomized controlled trial.

OBJECTIVES: To determine how lubrication of the endoscope prior to flexible fibreoptic nasendoscopy affects levels of patient discomfort and pain during endoscopy. To assess the extent to which lubrication affects the ease of nasendoscopy and the quality of the image obtained. DESIGN: Single blind, randomized controlled trial. SETTING: Outpatient clinic of the Department of Otolaryngology at a secondary level referral centre. PARTICIPANTS: A total of 150 participants selected sequentially from patients requiring a nasendoscopy where the endoscope would be passed far enough to view the larynx. Patients requiring topical anaesthetic were excluded. All participants who were entered in the study completed the study. Endoscopy was performed by all grades of medical staff. MAIN OUTCOMES MEASURES: Levels of discomfort and pain experienced by the participants were assessed by a visual analogue scale (VAS). Difficulty of passing the scope was indicated by the endoscopist using a VAS, as was the quality of image obtained. RESULTS: There was no significant difference between mean scores for pain or discomfort of the lubricated and unlubricated groups (P = 0.46 and P = 0.82 respectively). Scores for difficulty of passing the scope were significantly lower in the lubricant group (P = 0.003) but loss of image was significantly greater (P = 0.008). CONCLUSIONS: Lubrication of the endoscope prior to nasendoscopy does not reduce levels of discomfort or pain for the patient, but increases ease in insertion for the operator. However, this may be at the expense of reduced image quality.

Adult↗

PubMed2002

Analysis of mixed lubrication mechanism in metal-on-metal hip joint replacements.

A simple mixed lubrication model has been developed to predict the asperity contact and wear for the metal-on-metal bearing couple for total hip joint replacements. It has been shown that the femoral head radius has a large effect on the predicted asperity contact and wear depending on the lubrication regime. An increase in the femoral head radius can lead to an increase in wear under a predominantly boundary lubrication regime, but this trend can be reversed under a mixed lubrication regime towards fluid film lubrication. These observations are consistent with the recent experimental findings from hip simulator studies by Smith and co-workers.

Arthroplasty, Replacement, Hip↗