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PubMed1988

Mechanical strength of trabecular bone at the knee.

Interest in the biomechanical properties of trabecular bone has expanded in response to the problems related to total and partial joint replacement with the knee joint constituting a main focus of attention. This relatively recent development has left a number of fundamental problems unanswered, especially related to the machining, storage and testing of trabecular bone specimens. Nevertheless, these studies have contributed to the understanding of the mechanical function of trabecular bone. Regarding the role of trabecular bone at the knee joint, the following conclusions may be emphasized (conclusions drawn from the author's previous studies (I-X) are shown in italics): (1) Trabecular bone is almost exclusively responsible for the transmission of load at the proximal tibial epiphysis from the knee joint to the metaphysis. The peripheral shell surrounding the epiphysis is not composed of cortical bone and plays a negligible role in load transmission. (2) The compressive strength and stiffness of trabecular bone is primarily dependent upon the apparent density, trabecular architecture and the strength of the bone material. Direct and indirect sources suggest that the true material strength of trabecular bone is less than that of cortical bone. The epiphyseal trabecular architecture, featuring a marked polarity with alignment of primary trabeculae at right angles to the joint surface, is responsible for functional anisotropy which points to the axial compressive properties as the more important mechanical parameters. (3) Tensile and shear properties are of special relevance to mechanical loosening of implants. These properties may be derived from the apparent density, and a close empirical relation to the axial compressive strength and stiffness is suggested. (4) The foam-like structure of trabecular bone is the basis for the large energy absorptive capacity. (5) The pattern of axial compressive stiffness and strength at the normal proximal tibia differs little among individuals. Supporting the medial tibial plateau is a large high strength area with maximal strength centrally and slightly anteriorly, while laterally there is a restricted area of relatively high strength posteriorly with a lower maximal value than medially. Bone strength is significantly reduced within ten millimeters of the subchondral bone plate, and this reduction continues distally at the lateral condyle. At both condyles strength is reduced towards the periphery with very low values being obtained at the margins of the condyles and at the intercondylar region. Absolute bone strength values are influenced by the level of physical activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Arthritis, Rheumatoid↗

PubMed1988

Trabecular bone strength at the knee.

The axial strength of trabecular bone at the knee is critical for the maintenance of support and fixation of the prosthetic components after total surface knee arthroplasty. The resistance of trabecular bone to penetration was measured posteriorly, centrally, and anteriorly in each of the tibial and femoral condyles in 150 consecutive total knee arthroplasties. Forty-seven rheumatoid knees and 88 osteoarthritic knees were evaluated. The correlation of bone strength with selected clinical parameters was found to be too poor to predict bone strength. Tibial bone strength was lower in rheumatoid than in osteoarthritic knees. Steroid medication did not influence tibial bone strength in rheumatoid arthritis. The distribution of bone strength between the medial and lateral condyles was closely dependent on knee alignment, with high medial strength in varus knees. At the unloaded condyle, strength was reduced relative to the findings for normally aligned knees. At the tibia, strength decreased with depth from the resection surface, while at the femur the converse was true. Tibial bone strength, both condylar and overall average, was lower than values reported in studies of normal cadaver knees. Evaluation of the absolute bone strength at the tibial condyles suggested that the values too low to meet load-bearing requirements after well-aligned knee replacement were infrequent.

Aged↗

PubMed2005

Strength training and aerobic exercise training for muscle disease.

BACKGROUND: Strength training or aerobic exercise programmes might maximise muscle and cardiorespiratory function and prevent additional disuse atrophy in patients with muscle disease. However, over-exerting might cause more rapid disease progression. OBJECTIVES: To examine the efficacy and safety of strength training and aerobic exercise training in patients with muscle diseases. SEARCH STRATEGY: We searched the Cochrane Neuromuscular Disease Group register (October 2002 and May 2004), the Cochrane Collaboration Rehabilitation and Related Therapies Field register (October 2002), MEDLINE (January 1966 to December 2002), EMBASE (January 1973 to October 2002), and CINAHL (January 1982 to August 2002) for randomised trials. We reviewed the bibliographies of trials identified and reviews covering the subject. SELECTION CRITERIA: Randomised or quasi-randomised controlled trials comparing strength training and/or aerobic exercise programmes lasting at least 10 weeks. Types of outcome measures: FOR STRENGTH TRAINING. Primary: static or dynamic muscle strength. Secondary: muscle strength (endurance or fatigue), functional assessments, quality of life, muscle membrane permeability, pain, and fatigue. FOR AEROBIC EXERCISE TRAINING. Primary: aerobic capacity expressed as work capacity. Secondary: aerobic capacity (oxygen consumption, parameters of cardiac or respiratory function), functional assessments, quality of life, muscle membrane permeability, pain, and fatigue. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed trial quality and extracted the data. MAIN RESULTS: We identified two randomised trials fulfilling all inclusion criteria. The first trial compared the effect of strength training versus no training in 36 patients with myotonic dystrophy. The other trial compared strength training versus no training combined with albuterol or placebo in 65 patients with facioscapulohumeral muscular dystrophy. Methodological quality and training programmes were graded adequate. In the myotonic dystrophy trial there were no significant differences between training and non-training groups for the primary outcome measure. In the facioscapulohumeral muscular dystrophy trial static muscle strength did not show significant differences between training and non-training groups. Only a +1.2 kg difference (95% confidence interval 0.2 to 2.1) in dynamic strength of elbow flexors in favour of the training group, reached statistical significance. For both trials there were no significant differences between groups for most of the secondary outcome measures, including those covering adverse effects. AUTHORS' CONCLUSIONS: In myotonic dystrophy and facioscapulohumeral muscular dystrophy moderate-intensity strength training appears not to do harm but there is insufficient evidence to establish that it offers benefit. Limitations in the design of studies in other muscle diseases prevent general conclusions in these disorders.

Exercise↗

PubMed2004

Quadriceps activation failure as a moderator of the relationship between quadriceps strength and physical function in individuals with knee osteoarthritis.

OBJECTIVE: To determine if quadriceps activation failure (QAF) moderates the relationship between quadriceps strength and physical function in individuals with knee osteoarthritis (OA). METHODS: Quadriceps strength and QAF were measured in 105 subjects (80 females) with radiographically confirmed knee OA using a burst-superimposition maximum voluntary isometric quadriceps torque test procedure. Subjects performed the Get Up and Go test as a physical performance measure of function and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) as a self-report measure of function. A principal component analysis was performed to combine the Get Up and Go score and the WOMAC subscores into a single function score. Hierarchical regression analysis was performed to examine the ability of 3 models to predict physical function (strength = function; strength + QAF = function; strength + QAF + [strength x QAF] = function). Partial F tests were used to compare differences in R(2) values between each model. RESULTS: Each model independently predicted the principal component score for function. Adding the strength x QAF interaction term with strength to the model resulted in the highest prediction of function. The strength x QAF interaction indicated that subjects with lower levels of quadriceps strength and higher levels of QAF had lower levels of function than those with comparable levels of weakness but low levels of QAF. CONCLUSION: The magnitude of QAF serves to moderate the relationship between quadriceps strength and physical function. Physical function may be more severely affected by weakness of the quadriceps muscles in individuals with knee OA who have higher degrees of QAF than those who may have quadriceps weakness, but do not have QAF.

Exercise Test↗

PubMed1994

Grip strength and bone mineral density in older women.

Most previous literature on muscle strength and bone density examined the association between specific muscle groups and adjacent bones. This study examined the association of grip strength with bone density at distant sites, such as the spine and hip, as well as at the wrist and radius. Subjects were 649 postmenopausal women aged 65 years and older. Bone mineral density was measured at the ultradistal wrist and midshaft radius in the nondominant arm using single-photon absorptiometry and at the lumbar spine and hip using dual-energy x-ray absorptiometry. Grip strength was measured in both the dominant and nondominant hands using a dynamometer. Overweight women had significantly stronger grip strength in both hands (p < 0.01 for dominant hand, p < 0.05 for nondominant hand grip strengths). Exercises had significantly stronger grip strength in the nondominant hand than nonexercisers (p < 0.05). Women reporting arthritis had significantly weaker grip strength in both hands than women not reporting arthritis (p < 0.001). There were no significant differences in grip strength by estrogen use, cigarette smoking, or thiazide use. Regression analyses adjusted for age, obesity, exercise, cigarette smoking, thiazide use, arthritis, years postmenopausal, and estrogen use indicated significant positive associations between grip strength and bone density at all sites. Regression analyses stratified by exercise indicated that only women who exercised had significant associations of grip strength with bone mineral density (all p < 0.05). In this cohort of older women, grip strength was an independent indicator of general bone density.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗

PubMed1997

Ionic Strength Effects on Cation Sorption to Oxides: Macroscopic Observations and Their Significance in Microscopic Interpretation

Sorption of metal ions at oxide mineral-water interfaces is a complex process involving many possible variables, one of them being ionic strength. Depending on the system, adsorption of metal ions at these interfaces has been reported to increase or decrease with increasing ionic strength. However, in most cases it appears to be insensitive to ionic strength. Insensitivity to ionic strength has been taken as an indication for inner sphere surface complexation. Decrease of sorption with increasing ionic strength has been interpreted as outer sphere surface complexation. Promotive effects of ionic strength have not been discussed at all in terms of conventional surface complexation theory. The present paper shows that the classical example of Ba sorption to goethite, where increasing ionic strength decreases Ba adsorption, can be alternatively explained by an inner sphere mechanism if ion pair formation in solution between Ba and nitrate of the swamping electrolyte is taken into account. This suggests that macroscopic observations in cation uptake experiments should not be used to obtain mechanistic interpretations, even for ionic strength effects. Promotive effects of ionic strength on Cd sorption to goethite are also discussed. The present modeling exercises with the help of a conventional one-site surface complexation model suggest that promotive ionic strength effects may be explained in terms of more effective shielding of highly charged surface complexes at high ionic strength. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1994

Muscle strength from adolescence to adulthood--relationship to muscle fibre types.

The aim of the present study was to reinvestigate muscle strength and the relationship to muscle fibre and the level of physical activity in adult men and women previously studied during adolescence. A group of 55 men and 26 women were tested for maximal strength (handgrip, Sargent jump and two-hand lift) and completed a questionnaire concerning physical activity during their leisure time (activity index) at the ages of 16 and 27 years. Biopsy specimens were taken from the vastus lateralis and analysed for fibre type (percentage of I, IIA, IIB) and fibre area (area I, area IIA, area IIB). The sex differences in strength increased from age 16 to 17 years. Body dimension, sex, percentage of type II, mean fibre area and the activity index contributed to explaining 50-75% of the strength at both ages. Different changes in relationship between fibre type composition and strength in women and men was seen with increasing age. In the women, the relationship between strength and the percentage of type II fibres changed with age (from 16 to 27 years of age) from a positive correlation (only Sargent jump) to negative correlations for all the strength tests, i.e. the more type I fibres the stronger the subject. A positive correlation between strength and the level of physical activity during leisure time was revealed in the women at both ages. The positive correlation between strength and type II fibres in the 16-year-old men had disappeared at age 27. No systematic relationships between strength and the level of physical activity were seen in the men at either 16 or 27 years of age. It is suggested that women may be more dependent on physical activity than adult men to develop strength and the percentage of type I fibres reflects the degree of physical activity among adult women but not among adolescent women.

Adolescent↗

PubMed2001

[Increase in strength after active therapy in chronic low back pain (CLBP) patients: muscular adaptations and clinical relevance].

INTRODUCTION: Active treatments are advocated for the management of non-specific chronic low back pain (CLBP), although few studies have documented the relative efficacy of differing types of programme. A number of the available treatments comprise exercise routines on specially designed training machines, which are ostensibly better disposed to reverse the compromised trunk muscle function displayed by these patients than are 'free exercise' programmes. However, in using these muscle-training programmes, the physiological or anatomical adaptations that might account for the improved performance are rarely investigated, let alone identified. This is an important issue, because if the 'newly-acquired strength' is mostly specific to performance on the devices on which the patient has trained and been tested, and reflects the skill in executing these particular tasks, this will not necessarily assist the patient during performance of his/her everyday activities. The aims of the present study were (1) to quantify the changes in back muscle performance in chronic LBP patients following 3 months active therapy, and (2) to analyse the corresponding changes in activation and cross-sectional area of the paraspinal muscles. METHODS: 148 individuals (57% women) with CLBP (age 45.0+/-10.0 years; duration of LBP 10.9+/-9.5 years) were randomised to a treatment which they attended 2/week for 3 months: active physiotherapy, muscle reconditioning on training devices, or low-impact aerobics. Pre- and post-therapy, assessments were made of isometric trunk muscle strength in each plane of movement and of erector spinae activation (using surface electromyography) during back extension. In a sub-group of 56 patients, the cross-sectional area of the paravertebral muscles was determined using magnetic resonance imaging (MRI). In all patients, self-rated pain intensity, pain frequency and disability were assessed before and after therapy. RESULTS: 132/148 patients completed the therapy. Isometric strength in each movement plane increased significantly in all groups post-therapy. Apart from trunk extension, the changes were significantly greater in the devices group than in the other two groups (Fig 1). Activation of the paraspinal muscles during back extension also increased significantly in all groups (Fig 2) and was weakly, but significantly (r = 0.37; p = 0.0001) correlated with increased strength in back extension. Although, at baseline, highly significant correlations were observed between the size of the paraspinal muscles (at L3/4 and at L4/5) and isometric back extension strength (r=0.75; p< 0.0001), post-training increases in strength were not accompanied by corresponding changes in muscle size. None of the improvements in strength showed any relationship with the clinical changes in pain and disability, regardless of whether the latter were examined on an individual basis or in relation to 'outcome groups'. CONCLUSION: The superior trunk strength shown by the devices group post-therapy was considered to be attributable, in part, to a 'learning effect', of the type often seen when training and testing are carried out on the same machines. These gains are considered to be mostly 'task-specific'. However, part of the improvement in strength after active therapy (in all groups) also appeared to be due to an increased neural activation of the trunk muscles. These positive effects should be transferable to the performance of everyday activities for which the same muscles are employed, although the percentage improvement is probably not as high as the measured increase in strength might suggest. Possible roles for improved co-ordination and changes in motivation and/or pain tolerance after therapy cannot be excluded. No differences in the clinical outcome were observed between the three therapy groups, and the changes in physical performance after therapy did not correlate with the clinical outcome. It is therefore questionable whether strength measurements have any clinical significance in documenting the success of rehabilitation programmes, other than on a motivational basis. The results of the present study suggest that the value of supervised active therapy programmes does not reside in the reversal of specific muscular deficiencies, but rather in the provision of a source of confirmation/encouragement for the patient, that movement is not harmful, and a foundation upon which to further build. Whether the utilisation of specific training devices, or individual instruction, is necessary to elicit these particular effects is questionable.

Adaptation, Physiological↗

PubMed1987

The decline of grip strength in the menopause: relationship to physical activity, estrogen use and anthropometric factors.

The focus of this study was the relationship of grip strength to age, physical activity and anthropometric factors, in a population of 255 post-menopausal women not on estrogen therapy (mean age = 57.6) and 55 women currently on estrogen replacement therapy (mean age = 56.9). Grip strength was measured as an indicator of muscular strength in the upper limbs. The grip strength of the estrogen users was significantly higher than that of the estrogen abstainers. Grip strength was related to age (r = -0.25, p less than 0.01), and the body habitus parameters of height (r = 0.36, p less than 0.01) and weight (r = 0.18, p less than 0.01). Although estrogen use was univariately correlated with strength (r = 0.16, p less than 0.05), multiple regression analyses revealed that only the height, age and physical activity were independent determinants of grip strength. These data suggest: height is the major determinant of upper body strength in older women; the reduction in physical activity with advancing age may contribute to strength decline, and modest increase in physical activity may retard the loss of strength that accompanies aging; the loss of ovarian estrogen in menopause may be related to the loss of strength in postmenopausal women.

Adult↗

PubMed2004

Decreased neck muscle strength is highly associated with pain in cervical dystonia patients treated with botulinum toxin injections.

OBJECTIVES: To compare the isometric neck muscle strength of cervical dystonia patients treated with botulinum toxin injections with that of healthy control subjects and to evaluate the association between neck strength, neck pain, and disability in these patients. DESIGN: Clinical cross-sectional study. SETTING: Outpatient rehabilitation and neurology clinics in a Finnish hospital. PARTICIPANTS: Twenty-three patients with cervical dystonia with botulinum toxin-treated neck muscles and 23 healthy control subjects. INTERVENTIONS: Not applicable. Main outcome measures Isometric neck strength was measured by a special neck strength measurement system. Disability was measured by the Neck Disability Index, and pain and symptoms of cervical dystonia by a visual analog scale. RESULTS: Isometric neck strength in all directions measured was significantly lower (25%-44%) in the cervical dystonia patients than in the healthy controls. Neck pain levels reported during the strength tests (r range, -.36 to -.70) and neck pain experienced during the preceding week (r range, -.52 to -.63) were inversely associated with isometric strength results. The difference between sides in rotation strength was 35% in the patient group (P<.001), whereas no significant difference between sides was found in the healthy controls. Fifty-one percent of the patients reported moderate or severe disability. Pain, stiffness, and incorrect position of the head were the most prominent symptoms. CONCLUSIONS: Cervical dystonia patients with botulinum toxin-treated neck muscles showed significantly lower maximal neck strength than healthy controls. The patients also had a statistically significant difference between sides in neck rotation strength. Thus, strength measures may be useful to detect disturbance in the function of the neck muscles.

Botulinum Toxins, Type A↗

PubMed2005

A review of floc strength and breakage.

The main focus of the paper is to review current understanding of floc structure and strength. This has been done by reviewing current theoretical understanding of floc growth and breakage and an analysis of different techniques used for measuring floc strength. An overview has also been made of the general trends seen in floc strength analysis. The rate of floc formation is a balance between breakage and aggregation with flocs eventually reaching a steady-state size for a given shear rate. The steady-state floc size for a particular shear rate can, therefore, be a good indicator of floc strength. This has resulted in the development of a range of techniques to measure floc size at different applied shear levels using a combination of one or more of the following tools: light scattering and transmission; microscopy; photography; video and image analysis software. Floc strength may be simply quantified using the initial floc size for a given shear rate and the floc strength factor. More complex techniques have used theoretical modelling to determine whether flocs break by large-scale fragmentation or smaller-scale surface erosion effects, although this interpretation is open to debate. Impeller-based mixing, ultrasound and vibrating columns have all been used to provide a uniform, accurate and controllable dissipation of energy onto a floc suspension to determine floc strength. Other more recent techniques have used sensitive micromanipulators to measure the force required to break or compress individual flocs, although these techniques have been limited to the measurement of only a few hundred flocs. General trends emerge showing that smaller flocs tend to have greater strength than larger flocs, whilst the use of polymer seems to give increased strength to only some types of floc. Finally, a comparison of the strength of different types of floc (activated sludge flocs, organic matter flocs, sweep flocs and charge neutralised flocs) has been made highlighting differences in relative floc strength.

Bioreactors↗

PubMed2001

Evaluating acrylic and glass-ionomer cement strength using the biaxial flexure test.

Frequently, bone cement strengths are evaluated from uniaxial tests, such as three- or four-point flexure. Measurement of material strength in this manner may not provide an accurate characterisation of a bone cements true load-bearing capacity. In most orthopaedic applications, there exists a state of biaxial stress and so biaxial strength information is most useful. To address this issue, the biaxial flexure strength of two polymethylmethacrylate orthopaedic (PMMA) bone cements and two glass-ionomer dental cements have been determined. The biaxial strength of orthopaedic bone cements have been compared to the three-point bending strength. Furthermore, the calculated theoretical biaxial strength was compared with a value of biaxial strength utilising the finite element method. For all materials tested the calculated biaxial strength is significantly greater than the three-point bending strength. The biaxial test offers several advantages over three-point bending because it critically explores surface flaws--as it does not matter in which orientation the crack lies. However, it does minimise the volume or surface area investigated and also the edge effect. The difference in strength calculated for the two testing methods can be explained quantitatively in terms of the volume of material under stress. This work has demonstrated that the biaxial flexure test can be used for the testing of orthopaedic bone cements.

Acrylic Resins↗

PubMed2001

Reproducibility and validity of a new test protocol for measuring isokinetic trunk extension strength.

OBJECTIVE: To investigate the reproducibility and validity of isokinetic trunk extension strength scores obtained using a range of motion of 20 degrees and velocities of 10 and 40 degrees /s. BACKGROUND: Common protocols for testing trunk extension strength incorporate a range of motion of 40 degrees or more and test velocities of between 30 and 180 degrees/s. These test parameters may be neither necessary for portraying the strength profile of the muscles involved nor suitable for patients impaired with low back dysfunction. DESIGN: Test-retest of maximal concentric and eccentric isokinetic trunk extension strength in healthy subjects. METHODS: 17 women and 18 men were tested twice within 1-2 weeks. Tests were performed with subjects positioned in sitting. RESULTS: The trunk extension strength scores revealed excellent agreement with the expected physiological moment-velocity curve. On average women's trunk extension strength was 62% that of men (range: 59.3-64.4%). The test-retest correlation coefficients were generally higher in women (0.70-0.87) than in men (0.52-0.78) and significant at P=0.01. The standard error of measurement ranged between 13 and 21 N m for women and between 35 and 50 N m for men, which were equivalent to 9% and 15% of the mean strength in women and men, respectively. CONCLUSION: This study indicates that the present protocol may be validly applied in assessing trunk extension strength in normal women. RELEVANCE: Reproducible and valid trunk extension strength findings are essential if measurable strength deficiency of the extensors is to be formally accepted as an impairment. The present protocol incorporates or meets most of the relevant problems associated with trunk concentric and eccentric strength testing, and hence has the potential of becoming a standard method for clinical applications.

Adult↗

PubMed1997

Effect of burnout temperature on strength of phosphate-bonded investments.

OBJECTIVE: The high-temperature strength behaviour of dental phosphate-bonded investments is not clearly understood. The present purpose was to determine their variation in strength with temperature and to seek explanations for that variation. METHODS: The clamped-edge disc-rupture test was used in a sequential testing protocol, with a variable casting metal mass, to determine the effect of burnout temperature (ranging from 400 to 1100 degrees C) on the strength of six phosphate-bonded investments. RESULTS: The strength of phosphate-bonded investment is temperature sensitive, generally showing a distinct minimum in the tested temperature range. Low temperature strength gives little information about high temperature behaviour. The variation of strength with temperature seems amenable to explanation in terms of investment composition. CONCLUSION: Since strength varies greatly with temperature and brand, the inconsistency of previous results is explained. On the other hand, low-temperature strength is no guide for the high-temperature strength, so that information on both the room and the service temperature strength is required. Inversion of silica at high temperature may decrease the strength of phosphate-bonded investments.

Chromium Alloys↗

PubMed1997

Effect of burnout temperatures on strength of phosphate-bonded investments--Part II: Effect of metal temperature.

OBJECTIVES: It had previously been found that the strength of phosphate-bonded investments is temperature sensitive. However, while the effect of heat from the cast metal is expected to have some effect on continued reactions and melting, there is no published report dealing with this. It was the purpose of this study to consider further the effects of burnout temperature on strength and the contribution of metal casting temperature and investment composition. METHODS: The disc-rupture test (Luk, H. W.-K. and Darvell, B. W., Strength of phosphate-bonded investments at high temperature. Dental Materials 1991, 7, 99-102) was employed to determine the effect of burnout temperature (ranging from 400 to 1000 degrees C) on the 'actual' strength of six phosphate-bonded investments; the cast metal temperature was controlled to be the same as that of the mould. Atomic absorption was employed to investigate aspects of the composition of the investments. RESULTS: The 'actual' strength obtained in this test was always higher than the 'service' strength observed in similar testing with the metal at a fixed temperature (1460 degrees C). The 'actual' strength was also temperature sensitive, but with a different pattern of variation compared with the 'service' values. All investments tested were found to behave plastically at high temperatures. Calcium, sodium, zinc and iron were found in appreciable quantities in the investments. CONCLUSION: Heat from the high-temperature casting metal has a material effect in decreasing the strength of phosphate-bonded investments. Such heating increases the plastic behaviour of the investment and this, together with the casting pressure, may result in a distorted mould and thus inaccurate castings, a hitherto unrecognized source of error. 'Actual' strength gives no guide to the 'service' strength, emphasizing the need for tests under service conditions. Composition affects investment high-temperature strength substantially.

Calcium↗

PubMed1998

Bond strength of repaired anterior composite resins: an in vitro study.

The objectives of this study were to investigate the repair potential of two commercially available composite resins in terms of bond strength, and the effectiveness of two commercially available adhesive systems used as intermediary materials in the repaired specimens. The repair strength of Helio Progress (HP) and Herculite XRV (XRV) was tested using two bonding agents: DenTASTIC (DT) and All Bond 2 (AB2). The effect of surface abrasion of specimens and the effect of time on repair strength were also investigated. Surface abrasion significantly improved the bond strength (P < 0.001) and the use of bonding agents further enhanced bond strength but not significantly. Use of bonding agents alone improved the repair bond strength significantly (P < 0.001). Repair of HP with HP after surface abrasion and application of DT produced the highest repair bond strength which was 99% of the cohesive strength of the control (unrepaired) specimens. Although there were some differences in the bond strength over the time period of the study (one month) none of these was statistically significant. It is concluded that surface abrasion coupled with the application of bonding agent produces the highest repair strength. It seems likely that clinically acceptable bond strengths are possible after repair of anterior composite resins.

Composite Resins↗

PubMed1992

The effect of elbow flexion and time of assessment on the measurement of grip strength in rheumatoid arthritis.

Grip strength is one of the traditional outcome measures commonly used in rheumatoid arthritis trials. This study evaluated the degree of morning variation and the effect of elbow flexion in the assessment of grip strength in patients with rheumatoid arthritis. Grip strength was measured in 37 patients (1987 American Rheumatism Association criteria) at 8, 10, and 12 AM with a sphygmomanometer cuff folded on itself, taped permanently, and inflated to 20 mm Hg, with the elbow flexed at 90 degrees. At 10 AM grip strength was also measured with the elbow flexed at 30 and 130 degrees. Mean values for grip strength at 8, 10, and 12 AM were, respectively, 69, 79, and 83 mm Hg. Mean grip strength values with the elbow flexed at 30, 90, and 130 degrees were, respectively, 78, 79, and 75 mm Hg. There was a statistically significant correlation between grip strength and morning stiffness, grip strength and hand function, and grip strength and number of active joints. In rheumatoid arthritis trials, grip strength should be assessed at the same time of the day. Elbow flexion does not play a role in grip strength measurement.

Adult↗

PubMed1995

Effect of ionic strength on the kinetic mechanism and relative rate limitation of steps in the model NADPH-cytochrome P450 oxidoreductase reaction with cytochrome c.

Although the kinetic mechanism of the NADPH-cytochrome P450 oxidoreductase (P450R) reaction with cytochrome c3+ has been determined at 850 mM ionic strength [Sem, D.S., & Kasper, C. B. (1994) Biochemistry 33, 12012-12021], this mechanism is no longer valid at lower ionic strength. At 850 mM ionic strength, the mechanism is two-site ping-pong, and reaction at the electron acceptor site is itself ping-pong. As the ionic strength is decreased below 850 mM, the initial velocity profiles begin to show curvature when cytochrome c3+ is the varied substrate. These data are consistent with a mechanism that is still two-site ping-pong, but now with random sequential binding of two molecules of cytochrome c3+ at the electron acceptor site. Decreasing ionic strength also causes a change in rate-limiting steps, with (V/K)cytc and (V/K)NADPH increasing while Vmax decreases (below 500 mM ionic strength). These results are consistent with favorable ionic interactions being important for binding NADPH and cytochrome c3+ and with product (NADP+) release becoming the rate-limiting step in Vmax at low ionic strength. Vmax decreases significantly at higher ionic strength (> 500 mM), while (V/K)NADPH decreases only slightly. The DV isotope effect is largest (2.4) at 500 mM ionic strength but decreases at both low and high ionic strength as steps other than hydride transfer become more rate-limiting. D(V/K)NADPH also decreases at both low and high ionic strength, but to a lesser extent than DV.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗