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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of pre-treatment of composite inlays on bonding performance between a resin composite inlay and a luting composite has not been fully studied. The aim of the present study was to evaluate the influence of three different pre-treatment modes on fatigue bond strength and marginal adaptation. One hundred twenty resin composite discs (Tetric Ceram) were made as simulated inlays and randomly assigned to four groups (n=30): Without treatment (WT), hydrofluoric acid etching for 15 s + silanating (HF), roughening with a silicon carbide bur (SC), and silica coating + silanating (CO). Luting composite cylinders (Variolink II low) were bonded to the discs using Heliobond, and after 24 h in water at 37 degrees C, quasistatic shear bond strengths (n=l) and fatigue bond strengths (n=20; 5,000 cycles) were measured. Thirty-two third molars received occlusomesial Class II cavities (n=8), and direct resin composite inlays were luted with identical methods and materials. Before and after thermomechanical loading (100,000x50 N, 2,500 x +5 degrees C/+55 degrees C), replicas were made and examined (SEM, x200). CO and SC exhibited significantly higher bond strengths and adhesive fatigue limits than HF and WT (P<0.05). After thermomechanical loading, CO (98% continuous margin) and SC (95% continuous margin) demonstrated that they provide significantly more fatigue resistance than HF (88%).
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PMID:Effect of surface treatment on fatigue behaviour between Tetric Ceram inlays and Variolink luting composite. 1180 Apr 40

To investigate whether there are inter-nerve differences in the extent and pattern of axonal excitability changes produced by voluntary contractions of tibialis anterior (TA) and abductor pollicis brevis (APB), threshold tracking was used to measure axonal excitability parameters [threshold, supernormality and strength-duration time constant (tauSD)] of peroneal and median motor axons in 11 healthy subjects. Maximal contractions for 1 min resulted in an increase in threshold, an increase in supernormality, a decrease in tauSD and an increase in latency, all of which indicate axonal hyperpolarization. The increase in threshold was less in peroneal axons (18 +/- 4%) than median axons (37 +/- 6%, mean +/- SEM, P < 0.001), and was accompanied by smaller absolute changes in latency, supernormality, and tauSD. Peroneal axons had less supernormality at rest but a greater change in supernormality for the change in threshold. There were major contraction-induced changes in the compound muscle action potential of TA but not that of APB. Voluntary contractions depress axonal excitability, but the changes are quantitatively different for motor axons innervating different muscles. There are three clinical implications. First, weakness and fatigue due to activity-dependent conduction block may vary for different muscles, independent of disease severity, and therapeutic strategies to overcome activity-dependent conduction block may not be equally effective for different muscles. Second, in motor control studies using the H reflex to document motoneuron excitability, a constant stimulus will not produce a constant neural volley if the stimulated axons have been activated by, for example, a voluntary contraction. Third, TA is probably not optimal for testing for activity-dependent conduction block.
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PMID:Effects of voluntary activity on the excitability of motor axons in the peroneal nerve. 1187 Jun 83

The transverse (T-)tubules primarily function in conducting the action potentials that initiate excitation contraction coupling in skeletal muscle but may additionally subserve longer-term roles in volume regulation, membrane fusion and other trafficking processes. Osmotic shock thus both electrically detaches the T-tubules from surface membrane ('detubulation') and produces tubular vacuolation. The present experiments separated these effects. An established, reference osmotic shock protocol that exposed muscles to Ca2+/Mg2+-Ringer and gradual cooling to 10 degrees C after 18 min in glycerol-Ringer accomplished significant detubulation (77.5+/-13.15%, mean +/- SEM; n = 4). In contrast, a test protocol conducted entirely at room temperature using Mg2+-rather than Ca2+/ Mg2+-Ringer yielded reduced (P < 0.05, post hoc Duncan's multiple range test) detubulation indices (1.67+/-1.67%, n = 6) statistically indistinguishable from findings in fibres spared osmotic shock. Yet both osmotic shocks caused a formation of closed vacuoles, demonstrated by Sulphorhodamine B trapping, that occupied statistically similar fractions of total fibre volume (reference procedure: 14.38+/-2.7%, n = 6; test procedure: 13.36+/-2.00%, n = 22) in turn higher than determinations in control fibres (P < 0.05). The findings reconcile reports associating detubulation with vacuolation in osmotically shocked muscle [S. Nik-Zainal et al. (1999) J Muscle Res Cell Motil 20: 45-53; K.N. Khan et al. (2000) J Muscle Res Cell Motil 21: 79-90] with the persistence of tubular electrical activity in extensively vacuolated amphibian fibres following fatigue [J. Lannergren and H. Westerblad (1987) Acta Physiol Scand 129: 311-318; J. Lannergren et al. (1999) J Muscle Res Cell Motil 20: 19-32]. Furthermore test protocols produced higher densities of open vacuoles (13.38+/-2.33%, n = 9) than did reference protocols (6.66+/-1.63%, n = 20) contrary to their possible involvement in the electrophysiological changes. Abolition of tubular electrophysiological activity thus either follows or is independent of tubular vacuolation whilst sharing some of its underlying osmotic mechanisms.
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PMID:Persistent tubular conduction in vacuolated amphibian skeletal muscle following osmotic shock. 1196 71

This study investigated the possibility of there being differences in respiratory muscle strength and endurance in elite and competition triathletes who have similar maximal oxygen uptakes (VO(2max)) and ventilatory thresholds (Th(vent)). Five internationally-ranked elite, [mean (SD) age 23.8 (1.4) years] and six nationally- and regionally-ranked competition [age 21.1 (1.1) years] male triathletes performed two successive trials: first an incremental cycle test to assess VO(2max) and Th(vent) and second 20 min of cycling followed by 20 min of running (C-R) at intensities higher than 85% VO(2max). Cardioventilatory data were collected every minute during the two trials, using an automated breath-by-breath system. Maximal expiratory and inspiratory (P(Imax)) strength were assessed before and 10 min after C-R from the functional residual capacity. Respiratory muscle endurance was assessed 1 day before and 30 min after C-R by measuring the time limit (t(lim)). The results showed firstly that during C-R, the competition triathletes had significantly (P < 0.05) higher minute ventilation [mean (SEM) 107.4 (3.1) compared to 99.8 (3.7) l x min(-1)], breathing frequency [44.4 (2.0) compared to 40.2 (3.4) x min(-1)] and heart rate [166 (3) compared to 159 (4) beats x min(-1)] and secondly that after C-R, they had significantly lower P(Imax) [127.1 (4.2) compared to 130.7 (3.0) cmH(2)O] and t(lim) [2:35 (0:29) compared to 4:12 (0:20) min] than the elite triathletes. We conclude that, despite similar VO(2max) and Th(vent), the competition triathletes showed less extensive adaptive mechanisms, including those in the respiratory muscles, than did the elite triathletes. This led to higher ventilation, which appeared to be the cause of the faster development of fatigue in the inspiratory muscles in this group.
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PMID:The effect of cycling followed by running on respiratory muscle performance in elite and competition triathletes. 1217 85

Different approaches have been proposed to improve the adaptation of Class II restorations, including applying low-elasticity modulus base liners. This in vitro fatigue test (or study) evaluated the influence of the compomer base-lining configuration on restoration adaptation. Direct Class II MOD box-shaped composite restorations with or without base and lining (n=3x8) were placed on intact human third molars with proximal margins 1 mm above or under the CEJ. The compomer (Dyract) was applied as a 1 mm-thick lining or as a base, closing proximo-gingival margins. Marginal adaptation was assessed before and after each phase of mechanical loading (250,000 cycles at 50N, 250,000 cycles at 75N and 500,000 cycles at 100N); internal adaptation was evaluated after test completion. Gold-sputtered resin replicas were observed in the SEM and restoration quality evaluated in percentages of continuity (C) at the margins and within the internal interface after sample section. Mechanical loading did not influence adaptation to enamel, while it adversely affected restoration adaptation to dentin for the full composite and compomer-base restorations (C varied, respectively, from 95.2 to 75.3% and from 98.0 to 10.6%). The internal adaptation quality showed the same general trend, however, with reduced scores of continuity. In this experimental condition, application of a low elasticity modulus layer under the restorative material proved advantageous but the compomer should not contact the gingival margins.
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PMID:Marginal and internal adaptation of stratified compomer-composite Class II restorations. 1221 70

There are a number of similarities between chronic exertional compartment syndrome (CECS) and the effects of high force eccentric contractions in healthy controls. We hypothesised that CECS patients would be particularly susceptible to pain, fatigue and swelling after eccentric exercise. Ten CECS patients [aged 30.3 (8.0) years, mean (SD)], 7 males) and 14 healthy controls [aged 32.3 (9.0) years, 7 males] performed 40 maximal eccentric contractions of the anterior tibial muscles at an angular velocity of 90(o) s(-1). Maximal voluntary isometric contractions (MVC), force generated by electrical stimulation at 10 Hz and 50 Hz and muscle thickness (measured by real-time ultrasound scanning) were measured before exercise and for 10 min afterwards. Ratings of pain and tenderness were made before exercise, then 24 h and 48 h later. The two groups were comparable for initial isometric strength and muscle size. MVC force immediately after exercise fell to 90 (2.5)% [mean (SEM)] in patients and 86.5 (2.4)% in controls (P<0.0005 for both groups) and had not recovered after 10 min. Preferential loss of force at the low stimulation frequency occurred in both groups to a similar extent (20%, P<0.0005) and continued to decline over 10 min of recovery. There was no significant change in muscle thickness in either group. Only mild pain and tenderness were reported by the controls. The patients showed great individual variation but their mean pain scores were significantly higher during dorsiflexion and palpation (P<0.05) 24 h after exercise. After 48 h the patients reported more pain during dorsiflexion (P=0.005), plantarflexion (P<0.05) and palpation (P<0.05). These results suggest that some, but not all, CECS patients may be more susceptible to the pain associated with eccentric contractions that is thought to be the cause of damage and inflammation of connective tissue.
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PMID:Effect of eccentric exercise on patients with chronic exertional compartment syndrome. 1256 Sep 56

This study investigated the effect of initial muscle glycogen on performance of repeated sprints and some potential mechanisms for an effect of glycogen on fatigue. Eight subjects performed 2 cycling trials (repeated 60-s sprints) following consumption of either a high carbohydrate (HC) or a low carbohydrate (LC) diet. Muscle biopsies and blood samples were collected at baseline, following a 15% (15% fatigue) and a 30% decline in sprint performance (30% fatigue), when exercise was terminated. Baseline muscle glycogen levels [346 +/- 19 HC (SEM) vs. 222 +/- 19 mmol/kg dw LC] and total exercise time to 30% fatigue were higher following HC than LC (57.5 +/- 10.0 vs. 42.0 +/- 3.6 min; p <.05). Similar significant (p <.05) decreases over the entire exercise bout were seen in muscle glycogen (43%), creatine phosphate (CP; 35%), and sarcoplasmic reticulum (SR) Ca2+-uptake in isolated homogenized muscle (56%) for both trials (p >.05 between trials). The percentage decline in SR Ca2+-release was less for HC than LC (36% and 53%, respectively), but this was not statistically different. In summary, HC delayed fatigue during repeated sprints. As the reductions in muscle glycogen, CP, and SR function during exercise were not different by dietary treatment, these data do not support a link between whole muscle glycogen and SR function or CP reduction during repeated sprint exercise.
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PMID:Effects of muscle glycogen on performance of repeated sprints and mechanisms of fatigue. 1266 Apr 2

This in vitro study generated data on the quality of marginal adaptation, fracture resistance and retention of several indirect adhesive composite configurations on root-treated premolars before and after a long-term fatigue test and compared these results to a control group of adhesive onlays on "vital" teeth. Six root-treated extracted human premolars per group, with four different restorative configurations with and without adhesive fiber posts, were evaluated. Another group of six premolars, "revitalized" by using diluted horse serum to simulate pulpal fluid and restored with adhesive composite onlays, served as the control. Marginal adaptation before and after long-term occlusal loading (1,200,000 occlusal loading cycles at max 49 N) was assessed by using the replica technique and quantitative evaluation in SEM at 200x magnification. The number of lost restorations was recorded after loading. Fracture resistance and fracture patterns were evaluated by using a universal-testing machine on the fatigued samples. No significant differences (p > 0.05) between groups were detected before and after loading for the percentage of "continuous margin" at the total marginal length. Loading had a significant (p < 0.05) effect on the percentage of "continuous margin" for the total marginal length of two groups only. No significant difference (p > 0.05) for fracture resistance was detected and no lost restorations were observed. The results suggest that for both the less decayed and the more significantly decayed devital teeth, the minimally invasive adhesive restorative approach is promising.
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PMID:Marginal adaptation, retention and fracture resistance of adhesive composite restorations on devital teeth with and without posts. 1267 67

Complete removal of failed posterior resin composite fillings is time-expensive and involves the risk of removing sound tooth substance. In any case of failure within the composite material, intra-oral repair would be favourable. This in vitro study was conducted to examine the effect of different preparation and bonding modes on integrity of repaired restorations. Forty-eight direct Class II resin composite restorations (Syntac Classic/Tetric Ceram) were placed in extracted human third molars. The specimens were stored for 365 days and then replaced partially by removing the central part of the proximal box with all margins located in composite. The partial repairs were placed with the same materials after pre-treatment with a silicon carbide bur and Syntac Classic (n = 8). Preparation modes have been (i) box-only parallel, (ii) box-only with undercuts, (iii) box with undercuts and additional occlusal retention. The repairs were performed either with (i) Tetric Ceram or with (ii) Tetric Flow as thin lining covered with Tetric Ceram. Before and after thermomechanical loading (100 000 cycles of 50 N and 2500 cycles between +5 and +55 degrees C in an artificial mouth), marginal quality between aged and freshly applied composite was evaluated by SEM at x200 magnification and microleakage was observed by light microscopy at x50 magnification. Box-only preparations exhibited a better fatigue resistance than preparations with additional occlusal retention. This observation was independent from the presence of undercuts (P < 0.05). An intermediary layer of flowable resin composite tended to result in better marginal quality, however, not being statistically significant.
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PMID:Effect of preparation mode on Class II resin composite repair. 1278 51

Failure of total hip arthroplasty femoral stems is a serious clinical complication. Even modern metal alloys and designs sometimes suffer such incidents. The reported study aimed at the investigation of the reasons leading the in vivo fracture of two Ti6Al4V femoral stems. Stems were retrieved during revision surgery approximately 2 years postoperatively. Examination and analysis included XRF spectrometry for identification of chemical composition, macroscopic examination and topographical measurements, SEM study of fracture surfaces, study of alloy microstructure by optical microscopy, and finally measurement of mechanical properties by means of tensile testing conducted on alloy samples machined from the stems themselves. Macroscopic examination and measurements showed close topographical similarity between the two fractures. XRF spectrometry, tensile testing, and microstructure analysis identified the alloy as a typical Ti6Al4V surgical titanium alloy. During SEM analysis the fracture surfaces exhibited characteristic fatigue striations tidally running on the cross sections, which were considered as the weakest ones regarding toward geometry and stress concentration. Fracture in both stems occurred due to fatigue along these cross sections.
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PMID:Failure analysis of two Ti-alloy total hip arthroplasty femoral stems fractured in vivo. 1280 87


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