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Force Amplitude (force + amplitude)
Selected AbstractsAdenosine induces prolonged anti-,-adrenergic effects in guinea-pig papillary muscleACTA PHYSIOLOGICA, Issue 1 2002L. ARVOLA ABSTRACT A sustained anti- , -adrenergic effect of adenosine has been reported. This study was initiated to investigate this topic and especially elucidate the role of protein kinase C (PKC). Contractile force amplitude and action potential duration at 90% repolarization (APD90) were measured in guinea-pig papillary muscles before and after 5 min challenge with 5 nm isoproterenol. Protocols contained 30 min exposure to the test agents adenosine 33 ,m (ado), adenosine + PKC-inhibitor bisindolylmaleimide 20 nM (ado + BIM), PKC-activator 1,2-dioctanoyl-sn-glycerol 10 ,m (DOG) and , -agonist phenylephrine 5 ,m (phe). Isoproterenol was given at the end of test exposure and after 15 min washout. Results are mean ± SEM of percentage-change, P , 0.05 considered significant and labelled *. The first isoproterenol challenge significantly increased contractile force (27 ± 7%*) in the control group. Responses in the test groups were 2 ± 4 (ado), 1 ± 5 (ado + BIM), 14 ± 4* (DOG), 0 ± 2% (phe). After washout of adenosine, DOG and phenylephrine, isoproterenol induced 3 ± 8 (ado), 23 ± 5* (ado + BIM), 13 ± 5* (DOG), 15 ± 7% (phe) increase in test groups compared with 22 ± 5%* increase in contractile force in the control group. After 45 min washout of adenosine the inotropic response was still significantly reduced compared with control (29 ± 4 vs. 79 ± 8%*). Isoproterenol stimulation shortened APD90 in controls at both time points (5 ± 1%* and 4 ± 1%*), with no significant shortening in test groups. Adenosine induces sustained anti- , -adrenergic effects on contractile force as well as APD90. A role for PKC in signal transduction is supported with respect to contractile force. [source] Frictional properties of skin: proposal of a new approachINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2000Koudine Synopsis Phenomena occurring at the interface between skin and a glass pad, alternatively moved at its surface, are described by direct observation and measured by recording the force on the pad induced by the skin displacement. Static and dynamic friction coefficients are determined as a function of the load applied on the pad. Influence on the recordings of the friction coefficient of some cosmetic treatments applied on the skin are described. Results show that discontinuous phenomena, due to compression and distortion of the skin microrelief, occur during the beginning of the sliding process. Friction coefficients are depending on the load applied on the pad. Our studies confirm the increase of friction coefficient after hydration of the skin surface and suggest that the fluctuations in the frictional force amplitude could supply an objective, although indirect, measurement of skin smoothness. Résumé Un nouveau dispositif expérimental permet à la fois de décrire les phénomènes qui se passent à l'interface entre la peau et une demi-sphère en verre et de mesurer les forces induites par le déplacement de la peau. Le coefficient de friction (statique et dynamique) peut aussi être mesuré en fonction de la charge appliquée sur la demi-sphère. Les effets de quelques traitements cosmétiques sur les enregistrements des forces de frottement sont aussi discutés. Les résultats montrent que des phénomènes discontinus probablement dus à des mécanismes de compression et d'étirement du microrelief cutané, prennent place à l'interface entre la demi-sphère et la surface de la peau. D'autre part, le coefficient de friction est diminué dans le cas de fortes charges. Nos résultats confirment l'augmentation du coefficient de friction avec l'hydratation de la surface cutanée et suggèrent que l'amplitude des fluctuations de la force de frottement serait une mesure indirecte mais objective de la douceur cutanée. [source] Sensory-motor function of human periodontal mechanoreceptors,JOURNAL OF ORAL REHABILITATION, Issue 4 2006M. TRULSSON summary, Natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the basic force-encoding properties of human periodontal receptors will be presented along with a discussion about their likely functional role in the control of human mastication. Microneurographic recordings from single nerve fibres reveal that human periodontal receptors adapt slowly to maintained tooth loads. Most receptors are broadly tuned to the direction of force application, and about half respond to forces applied to more than one tooth. Populations of periodontal receptors, nevertheless, reliably encode information about both the teeth stimulated, and the direction of forces applied to the individual teeth. Information about the magnitude of tooth loads is made available in the mean firing rate response of periodontal receptors. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at very low force levels (below 1 N for anterior teeth and 4 N for posterior teeth). Thus, periodontal receptors efficiently encode tooth load when subjects contact and gently manipulate food using the teeth. It is demonstrated that signals from periodontal receptors are used in the fine motor control of the jaw and it is clear from studies of various patient groups (e.g. patients with dental implants) that important sensory-motor functions are lost or impaired when these receptors are removed during the extraction of teeth. [source] Sensory and motor function of teeth and dental implants: A basis for osseoperceptionCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2005Mats Trulsson SUMMARY 1.,When dental implants are loaded mechanically, a sensation, often referred to as osseoperception, is evoked. The sensory signals underlying this phenomenon are qualitatively different from the signals evoked when loading a natural tooth. In contrast with osseointegrated dental implants, natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the functional properties of human periodontal mechanoreceptors will be presented, along with a discussion about their likely functional role in the control of human jaw actions. 2.,Microneurographic experiments reveal that human periodontal mechanoreceptors adapt slowly to maintained tooth loads. Populations of periodontal receptors encode information about both which teeth are loaded and the direction of forces applied to individual teeth. 3.,Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at surprisingly low forces (below 1 N for anterior teeth and 4 N for posterior teeth). Accordingly, periodontal receptors efficiently encode tooth load when subjects first contact, hold and gently manipulate food by the teeth. In contrast, only a minority of receptors encodes the rapid and strong increase in force generated when biting through food. 4.,It is concluded that humans use periodontal afferent signals to control jaw actions associated with intra-oral manipulation of food rather than exertion of jaw power actions. Consequently, patients who lack information from periodontal receptors show an impaired fine motor control of the mandible. [source] Positive effect of early loading on implant stability in the bi-cortical guinea-pig modelCLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2005Els De Smet Abstract: Loading, early after implant placement, has gained rapid interest in dentistry. Primary implant stability, as e.g. defined by resonance frequency instrumentation, has been isolated as a predicator when immediate and early implant loading is applied. The aim of this study was to investigate the effect of early (after 7 days) mechanical loading on the establishment of osseointegration by means of resonance frequency analysis (RFA). Percutaneous titanium implants were installed in both tibiae of 10 guinea-pigs. One week after implant installation, one implant (test) was loaded daily for 6 weeks, while the contra-lateral served as the unloaded one (control). A sinusoidally varying bending moment was applied at a frequency of 3 Hz and a force amplitude of 5 N, for 1800 cycli. Resonance frequency was measured at implant installation and from then on weekly using the RFA-device (Osstell®). Contrary to control implants, that showed a decrease in stability 1 week after installation, reaching a minimum at 3 weeks (,200 Hz), test implants showed a progressive increase in stability over time. After 6 weeks, the mean resonance frequency of test and control implants reached the same values. As confirmed by recent literature, early loading does not have to endanger the establishment of osseointegration of titanium implants. On the contrary, controlled loading is beneficial to maintain the implant stability during the early critical healing period as determined by RFA-measurements. Résumé La mise en charge précoce après l'insertion de l'implant acquière beaucoup d'intérêt en médecine dentaire. La stabilité primaire de l'implant, qui est par exemple définie par l'instrumentation de fréquence de résonnance RFA, a été isolée comme un annonciateur lorsque la mise en charge de l'implant était précoce ou immédiate. Le but de cette étude a été d'étudier l'effet d'une mise en charge précoce (sept jours) sur l'établissement de l'ostéïntégration à l'aide de RFA (Osstell®). Des implants titane percutanés ont été insérés dans les deux tibias de dix cobayes. Une semaine après le placement des implants, un implant test a été mis en charge tous les jours pendant six semaines tandis que le contralatéral servait de contrôle et n'était pas mis en charge. Un moment sinusoïdal a été appliquéà une fréquence de trois hertz et une amplitute d'une force de 5 N pour 1 800 cycles. La fréquence de résonnance a été mesurée lors de l'insertion de l'implant et ensuite hebdomadairement en utilisant le RFA. Contrairement aux implants contrôles, qui accusaient une diminution de la stabilité une semaine après leur insertion atteignant un minimum après trois semaines (,200 Hz), les implants tests ont montré une augmentation progressive de la stabilité avec le temps. Après six semaines, la fréquence de résonnance moyenne des implants tests et contrôles atteignaient les mêmes valeurs. Comme décrit dans la littérature récente, la mise en charge précoce ne met pas en danger l'établissement de l'ostéoïntégration des implants en titane. Au contraire, une mise en charge contrôlée est bénéfique au maintien de la stabilité implantaire durant la période de guérison critique précoce comme déterminée par les mesures RFA. Zusammenfassung Die Belastung kurz nach der Implantatplatzierung hat in der Zahnmedizin schnell an Interesse gewonnen. Die Primärstabilität der Implantate, bestimmt z.B. durch Messung der Resonanzfrequenz, hat sich als Voraussagewert herauskristallisiert, wenn eine Sofort-oder Frühbelastung der Implantate durchgeführt wird. Das Ziel dieser Studie war, den Einfluss der frühen (nach 7 Tagen) mechanischen Belastung auf die Ausbildung der Osseointegration mittels Resonanzfrequenzanalyse (RFA) zu untersuchen. In die beiden Tibias von 10 Meerschweinchen wurden perkutane Titanimplantate eingesetzt. Eine Woche nach der Implantation wurde ein Implantat (Test) während 6 Wochen täglich belastet, während das kontralaterale Implantat unbelastet blieb (Kontrolle). Es wurde ein Biegemoment mit sinusoidalen Schwankungen mit einer Frequenz von 3 Hz und einer Kraftamplitude von 5 N in 1800 Zyklen appliziert. Die Resonanzfrequenz wurde nach der Implantation und dann wöchentlich mit einem RFA-Gerät (Osstell®) gemessen. Im Gegensatz zu den Kontrollimplantaten, welche eine Woche nach dem Setzen eine Stabilitätsabnahme zeigten und das Minimum nach drei Wochen (,200 Hz) erreichten, konnte bei den Testimplantaten eine progressive Zunahme der Stabilität über die Zeit beobachtet werden. Nach sechs Wochen erreichten die mittleren Resonanzfrequenzen der Test-und Kontrollimplantate dieselben Werte. Die frühe Belastung gefährdet die Ausbildung einer Osseointegration bei Titanimplantaten nicht, was auch durch die neuere Literatur bestätig wird. Im Gegenteil, eine kontrollierte Belastung ist von Vorteil für den Erhalt der Implantatstabilität während der kritischen frühen Einheilphase. Dies konnte mittels RFA Messungen ermittelt werden. Resumen La carga temprana tras la colocación del implante ha ganado rápidamente interesen odontología. Se ha aislado como predictor, la estabilidad primaria del implante, definida por instrumentación de frecuencia de resonancia, cuando se aplica la carga temprana al implante. La intención del estudio fue investigar el efecto de carga mecánica temprana (tras 7 días) en el establecimiento de la osteointegración por medio del análisis de la frecuencia de resonancia (RFA). Se instalaron implantes de titanio percutaneos en ambas tibias de 10 conejos de indias. Una semana tras la instalación, un implante (prueba) se cargó diariamente durante 6 semanas, mientras que el contralateral sirvió como el implante sin carga (control). Se aplicó un momento de flexión variante sinusoidalmente a una frecuencia de 3 Hz y una amplitud de la fuerza de 5 N, durante 1899 ciclos. Se midió la frecuencia de resonancia al instalar el implante y a partir de ahí semanalmente usando el dispositivo RFA (Ostell®). Contrariamente a los implantes de control, que mostraron una disminución de la estabilidad una semana después de la instalación, alcanzando un mínimo a las tres semanas (,200 Hz), los implantes de prueba mostraron un incremento progresivo de la estabilidad a lo largo del tiempo. Tras seis semanas, la frecuencia de resonancia de los implantes de prueba y de control alcanzaron los mismos valores. Tal como se confirma por la literatura reciente, la carga temprana no debe hacer peligrar el establecimiento de la osteointegración de los implantes de titanio. Por lo contrario, la carga controlada es beneficiosa para mantener la estabilidad de los implantes durante el periodo crítico de la cicatrización determinado por las mediciones de RFA. [source] | ||||||||||