Mikroleakage of Sealants Placed After Enamel Treatment With Self Etching Adhesive

Samojetkajući adhezivni sustavi istodobno s jetkanjem omogućuju penetraciju adheziva u jetkanu površinu cakline. Važne prednosti uporabe smojetkajućih adhezivnih sustava u postupku pečaćenja kao zamjeni za klasično jetkanje fosfornom kiselinom jesu: nema nanošenja kiseline i nema ispiranja. Svrha je istraživanja bila analizirati penetraciju i rubnu propustljivost pečata apliciranih nakon tretmana cakline samojetkajućim adhezivnim sustavom. 45 zuba podijelje nih u 3 skupine zapečaćeno je materijalom Concise White Sealant (3M Dental Products) nakon sljedećeg postupka pripreme površine cakline: Skupina 1: okluzalna površina jetkana je 37% fosfornom kiselinom 30 s, ispirana 15 s i sušena 15 s, nakon sušenja nanesen je materijal za pečaćenje i osvijetljen 20 s; skupina 2: Okluzalna površina tretirana je samojetkajućim adhezivnim sustavom Prompt- L-Pop (Espe Dental AG) 20 s i osvijetljen 10 s (Optilux, Demetron Research Company), materijal za pečaćenje zatim je nanesen i osvijetljen 20 s; skupina 3: Okluzalna površina tretirana ja samojetkajućim adhezivnim sustavom Prompt-L-Pop 20 s i odmah nakon tretmana nanesen je materijal za pečaćenje, oba materijala istodobno su osvijetljena 20 s. Svi su zubi termociklirani 1.800 ciklusa na temperaturi 5 - 55°C s 10 s imerzije u svakoj kupki. Rubna propustljivost ispitana je postupkom bojenja otopinom AgNO3. Zubi su uloženi u akrilnu smolu, prerezani (3-5 rezova po uzorku) i fotografirani pod 10 x povećanjem stereo mikroskopa. Rubna propustljivost mjerena je postupkom po Överböu i Raadalu. Statistička je rašlamba učinjena neparametrijskim testovima Kruskal-Wallis i Mann-Whitney. Penetracija materijala u dubinu fisura bila je između 87,8 - 92,1% bez statistički znatne razlike između skupina. Ustanovljena je statistički znatna razlika između klasičnoga postupka jetkanja i uporabe samojetkajućeg adhezivnog sustava (p = 0,003). Nije ustanovljena statistički znatna razlika u skupinama tretiranim samojetkajućim adhezivnim sustavom s polimerizacijom ili bez nje (p = 0,1234). Muguće je zaključiti da “all in one” samojetkajući adhezivni sustav Prompt-L-Pop nije tako djelotvoran kao kombinacija jetkanja fosfornom kiselinom i materijala za pečaćenje za dobivanje dobroga rubnog zatvaranja.Self-etching adhesives with enamel treatment at the same time as adhesive infiltration offers simplification of the classic technique of placing sealants. Main advantages in clinical work are: non need for applying acid, and no rinsing. Aim of the study was to evaluate both the penetration an sealing ability of a sealant applied after enamel treatment with a self-etching adhesive. The study was performed on forty-five teeth divided into three groups of fifteen teeth sealed with Concise White Sealant (3M Dental Products) after enamel surface was treated as fallows: Group 1: occlusal surface etched with 37% phosphoric acid for 30 s, rinsed for 15 s and air-dried for 15 s. After drying the sealant was applied and polymerized for 20 s. Group 2: The occlusal surface treated with self-etching adhesive Prompt-L-Pop (Espe Dental AG) for 20 s and lightened for 10 s (Optilux, Demetron Research Company). The sealant was then applied and lightened for 20 s. Group 3: The occlusal surface was treated with the selfetching adhesive Promt-L-Pop for 20 s and directly folloved by sealant application, the two materials were then simultaneously lightened 20 s. All teeth were thermocycled between 5 and 55°C for 1800 cycles with dwelling time of 10 s. AgNO3 dye solution was used for microleakage testing. After dyeing the teeth were embedded in acrylic resin, sectioned (3-5 sections per sample) and photographed under a stereo-microscope (10 X). Microleakage scores were recorded using the method of Övrebö and Raadal. Non-parametric Kruskal-Wallis and Mann-Whitney tests were used for statistical analysis. The sealant penetration rate was between 87.8 - 92.1% whatever the batch with no statistical significant difference between groups. Significant statistical difference was established between the classic H3PO4 pre-etch technique and the self-etching conditioning (p = 0.003). No significant difference was found between self-etching batches with or without polymerisation (p = 0.1234). Obtained data lead to the conclusion that the “all in one” self-etching adhesive Prompt-L-Pop is not as efficient as the classic H3PO4 etching + sealant in achieving a good enamel marginal sealing

BeppoSAX Observations of Markarian 501 in June 1999

We present the preliminary results of a long BeppoSAX observation of the BL Lac object Mkn501 carried out in June 1999. The source was fainter than found during the BeppoSAX pointings of 1997 and 1998, but is still detected with a good signal-to-noise ratio up to ~40 keV. The X-ray spectrum in the energy range 0.1-40 keV, produced through synchrotron radiation, is steeper than in the previous years, it is clearly curved, and peaks (in nu*F_nu) at ~0.5 keV. This energy is much lower than those at which the synchrotron component was found to peak in 1997 and 1998. Some intraday variability suggests that activity of the source on small time scales accompanies the large long time scale changes of brightness and spectrum.Comment: 4 pages, Latex, 2 PostScript figures, to appear in the Proceedings of the Conference "X-ray Astronomy '999: Stellar Endpoints, AGNs, and the Diffuse X-ray Background" (Bologna, 6-10 September 1999

Searching for TeV dark matter by atmospheric Cerenkov techniques

There is a growing interest in the possibility that dark matter could be formed of weakly interacting particles with a mass in the 100 GeV - 2 TeV range, and supersymmetric particles are favorite candidates. If they constitute the dark halo of our Galaxy, their mutual annihilations produce energetic gamma rays that could be detected using existing atmospheric \u{C}erenkov techniques.Comment: 10 pp, LaTex (3 figures available by e-mail) PAR-LPTHE 92X

Complex Spectral Variability from Intensive Multi-wavelength Monitoring of Mrk421 in 1998

We conducted a multi-frequency campaign for the TeV blazar Mrk~421 in 1998 April. The campaign started from a pronounced high amplitude flare recorded by SAX and Whipple; ASCA observation started three days later. In the X-ray data, we detected multiple flares, occuring on time scales of about one day. ASCA data clearly reveal spectral variability. The comparison of the data from ASCA, EUVE and RXTE indicates that the variability amplitudes in the low energy synchrotron component are larger at higher photon energies. In TeV Gamma-rays, large intra-day variations -- which were correlated with the X-ray flux -- were observed when results from three Cherenkov telescopes are combined. The RMS variability of TeV Gamma--rays was similar to that observed in hard X-rays, above 10 keV. The X-ray light curve reveals flares which are almost symmetric for most of cases, implying the dominant time scale is the light crossing time through the emitting region. The structure function analysis based on the continuous X-ray light curve of seven days indicates that the characteristic time scale is ~0.5 day. The analysis of ASCA light curves in various energy bands appears to show both soft (positive) and hard (negative) lags. These may not be real, as systematic effects could also produce these lags, which are all much smaller than an orbit. If the lags of both signs are real, these imply that the particle acceleration and X-ray cooling time scales are similar.Comment: 10 pages, 4 figures, accepted for publication in ApJ Letter

Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope

The CAT imaging telescope, recently built on the site of the former solar plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from October 1996 to March 1997. This steady source, often considered as the standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam to probe the performances of the new telescope, particularly its energy threshold (220 GeV at 20 degrees zenith angle) and the stability of its response. Due to the fine-grain camera, an accurate analysis of the longitudinal profiles of shower images is performed, yielding the source position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba

The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy

The CAT (Cherenkov Array at Themis) imaging telescope, equipped with a very-high-definition camera (546 fast phototubes with 0.12 degrees spacing surrounded by 54 larger tubes in two guard rings) started operation in Autumn 1996 on the site of the former solar plant Themis (France). Using the atmospheric Cherenkov technique, it detects and identifies very high energy gamma-rays in the range 250 GeV to a few tens of TeV. The instrument, which has detected three sources (Crab nebula, Mrk 421 and Mrk 501), is described in detail.Comment: 24 pages, 15 figures. submitted to Elsevier Preprin

Very high energy gamma rays from the direction of Sagittarius A*.

We report the detection of a point-like source of very high energy (VHE) -rays coincident within 1' of Sgr A *, obtained with the HESS array of Cherenkov telescopes. The -rays exhibit a power-law energy spectrum with a spectral index of and a flux above the 165 GeV threshold of m -2 s -1. The measured flux and spectrum differ substantially from recent results reported in particular by the CANGAROO collaboration

A possible association of the new VHE gamma-ray source HESS J1825--137 with the pulsar wind nebula G18.0--0.7

We report on a possible association of the recently discovered very high-energy $\gamma$-ray source HESS J1825--137 with the pulsar wind nebula (commonly referred to as G 18.0--0.7) of the $2.1\times 10^{4}$ year old Vela-like pulsar PSR B1823--13. HESS J1825--137 was detected with a significance of 8.1 $\sigma$ in the Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. The centroid position of HESS J1825--137 is offset by 11\arcmin south of the pulsar position. \emph{XMM-Newton} observations have revealed X-ray synchrotron emission of an asymmetric pulsar wind nebula extending to the south of the pulsar. We argue that the observed morphology and TeV spectral index suggest that HESS J1825--137 and G 18.0--0.7 may be associated: the lifetime of TeV emitting electrons is expected to be longer compared to the {\it XMM-Newton} X-ray emitting electrons, resulting in electrons from earlier epochs (when the spin-down power was larger) contributing to the present TeV flux. These electrons are expected to be synchrotron cooled, which explains the observed photon index of $\sim 2.4$, and the longer lifetime of TeV emitting electrons naturally explains why the TeV nebula is larger than the X-ray size. Finally, supernova remnant expansion into an inhomogeneous medium is expected to create reverse shocks interacting at different times with the pulsar wind nebula, resulting in the offset X-ray and TeV $\gamma$-ray morphology.Comment: 5 pages, 3 figures, to appear in Astronomy and Astrophysics Letter

Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope

The CAT Imaging Telescope has observed the BL Lac object Markarian 501 between March and August 1997. We report here on the variability over this time including several large flares. We present also preliminary spectra for all these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late