RESUMEN
The purpose of this investigation was to evaluate the dissipation of a force applied to an assembled stack of implant components. The stack consisted of a 10-mm threaded implant, a screw-retained abutment and a screw-retained gold crown. The dissipation of force was analyzed in relation to varying the implant diameter with and without a concomitant change in abutment diameter. Two experimental groups were evaluated. The first group consisted of 25 titanium screw-form implants (Implant Innovations, Inc.). These implants measured 10 mm in length and 3.25 mm, 3.75 mm, 4.0 mm, 5.0 mm, and 6.0 mm in diameter. The second group included 15 titanium screw-form implants (Nobel Biocare, Inc.) measuring 10 mm in length and 3.75 mm, 4.0 mm, and 5.0 mm in diameter. All implants were embedded in standardized photoelastic resin blocks. Points of interest were marked on each block using standardized templates to ensure consistency. Implants were restored using system-specific conical abutments and standardized single-unit restorations. A strain gauge was affixed to each abutment, and an eccentric load of 176 N was applied to the restoration. Periimplant stresses were measured using photoelastic analysis. Abutment strain was determined using an electronic strain indicator. Data were collated and compared using ANOVA and the Duncan multiple range statistical tests. When stress was analyzed at points on the resin-implant interface or a fixed distance from the interface, stress tended to decrease from the 5-mm-wide implant to the 6-mm-wide implant. Stress in relation to the 3.25-mm, 3.75-mm, and 4.0-mm implant was not as well defined, indicating the possibility that some deformation of implants was occurring. Increased abutment width resulted in decreased abutment strain. Therefore, using a wider abutment may be helpful in preventing preload reduction in clinical applications. This may reduce the incidence of loosening and fracture of abutment and restoration screws.
Asunto(s)
Coronas , Pilares Dentales , Implantes Dentales , Diseño de Prótesis Dental , Resinas Acrílicas , Análisis de Varianza , Aleaciones Dentales/química , Fracaso de la Restauración Dental , Elasticidad , Aleaciones de Oro/química , Humanos , Luz , Ensayo de Materiales , Modelos Anatómicos , Estadística como Asunto , Estrés Mecánico , Propiedades de Superficie , Titanio/químicaRESUMEN
The effect intracerebroventricular injections of angiotensin II (0.1 nm), angiotensin-(1-7) (1 or 100 nm) and carbachol (500 ng) on c-fos expression was examined in the forebrain of Lister hooded rats. Intense staining of the c-Fos protein was found in the median preoptic nucleus, organum vasculosum of the lamina terminalis, subfornical organ, paraventricular nucleus and supraoptic nucleus after angiotensin II and carbachol Angiotensin II caused significantly more c-fos expression in the ventral median preoptic nucleus and organum vasculosum of the lamina terminalis than carbachol, whereas in the paraventricular and supraoptic nuclei this was reversed, with carbachol having a greater effect on c-fos expression in these areas. Angiotensin-(1-7), however, only induced c-Fos protein in the organum vasculosum of the lamina terminalis and median preoptic nucleus with the number and the intensity of staining of the nuclei significantly less in both areas than after angiotensin II or carbachol. Separate groups of Lister rats were given i.c.v. injections of the same substances at the same doses, but excluding the lower dose of angiotensin-(1-7), and the intakes of water and 1.8% NaCl over 60 min were measured. Angiotensin II stimulated intakes of both water and NaCl. The effect on water intake was almost immediate (<1 min), whereas NaCl intake did not usually start until at least 5 min after injection. Over 60 min, water (12.4 +/- 1.0 ml) and NaCl (4.2 +/- 0.9 ml) intakes were significantly greater than water (1.1 +/- 0.2 ml) and NaCl (0.6 +/- 0.5 ml) intakes of the controls. Carbachol caused less drinking than angiotensin II, the water intake over 60 min being significantly less (4.8 +/- 0.7 ml) and the latency of response greater (>5 min). Carbachol, unlike angiotensin II, had little effect on NaCl intake (0.7 +/- 0.4 ml). Angiotensin-(1-7) had no effect on water (1.1 +/- 0.3 ml) or NaCl (0.3 +/- 0.3 ml) intakes. The plasma levels of vasopressin were measured after i.c.v. injection of the same three substances in the same doses, again excluding the lower dose of angiotensin-(1-7), in further groups of rats. Angiotensin II and carbachol caused an approximate five-fold increase in plasma vasopressin levels compared to cerebrospinal fluid-injected rats, but angiotensin-(1-7) had no effect on vasopressin release. Therefore, three compounds with widely differing effects on thirst, sodium appetite and vasopressin release induce distinctive patterns of c-fos protein expression in the forebrain. By combining experimental approaches in this way it is possible to determine areas of the brain which are involved in certain behavioural and endocrine responses.
Asunto(s)
Apetito/fisiología , Prosencéfalo/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Sodio , Sed/fisiología , Vasopresinas/metabolismo , Angiotensina I , Angiotensina II/farmacología , Animales , Carbacol/farmacología , Conducta de Ingestión de Líquido/efectos de los fármacos , Inyecciones Intraventriculares , Masculino , Fragmentos de Péptidos/farmacología , Ratas , Ratas EndogámicasRESUMEN
OBJECTIVE: The present study investigated the antagonism of the amino-terminal heptapeptide fragment of angiotensin II ([des-Phe8]-angiotensin II; Ang(1-7)) to angiotensin II (Ang II) both in vitro in rabbit aortae and in vivo in rats. METHODS AND RESULTS: In rabbit isolated endothelium intact aortic rings Ang(1-7) caused a concentration-related rightward displacement of the Ang II curve and depressed the maximum response to Ang II. By applying the data to a Schild plot an apparent pA2 of 5.5 was calculated. This depression of maximum response could be reversed by co-incubation of Ang(1-7) with the competitive angiotensin antagonist losartan. Ang(1-7) had no effect on the contractile responses of several other agonists. Intravenous infusion of 10 or 100 micrograms/kg per min Ang(1-7) had no effect on the resting blood pressure in the anaesthetized rat but inhibited Ang II-induced pressor responses. CONCLUSION: The present results show that Ang(1-7) is a specific non-competitive antagonist of Ang II at type 1 angiotensin II receptors.
Asunto(s)
Angiotensina II/antagonistas & inhibidores , Angiotensina II/farmacología , Antagonistas de Receptores de Angiotensina , Fragmentos de Péptidos/farmacología , Angiotensina I , Animales , Compuestos de Bifenilo/farmacología , Presión Sanguínea/efectos de los fármacos , Imidazoles/farmacología , Técnicas In Vitro , Losartán , Masculino , Conejos , Ratas , Ratas Sprague-Dawley , Tetrazoles/farmacologíaRESUMEN
With the use of 99mTc-labelled stannous pyrophosphate scans positive for myocardial infarction were obtained from 28 patients in the acute stage of the disease. In some cases the scan was positive when the initial electrocardiogram gave equivocal results. Negative scans were obtained from a control group of patients and from eight patients in hospital with chest pain but with no other evidence of recent myocardial infarction.