Marginal Edge Research Articles

Penatalaksanaan Perawatan Saluran Akar pada Fraktur Gigi 21 disertai Perforasi

Root canal treatment aims to maintain the condition of the teeth in order to keep them functioning. In practice, the treatment procedure does not always run smoothly, the operator can face undesirable conditions that can affect the prognosis of treatment. A common procedural error during root canal treatment is a lateral root perforation which must be treated immediately to avoid further damage. The success of the perforation treatment is determined by the materials used. One of the bicompatible materials to seal lateral perforations using MTA (mineral trioxide aggregate). Successful root canal treatment affects treatment outcomes, so proper restoration is required to reduce the risk of marginal leakage. The choice of final restoration in post-root canal treatment depends on the amount of remaining tooth structure, horizontal pressure and chewing load. For post-root canal treatment anterior teeth with intact marginal edges, direct restoration can be performed using composite resin

DYNAMICS OF THE DEVELOPMENT SALT-DOME STRUCTURES OF THE CENTRAL PART OF THE DNIEPER-DONETS DEPRESSION

The Dniprо-Donets Depression is the main oil and gas region of Ukraine. The region is characterized by a wide distribution of salt dome structures that are objects of oil and gas exploration. The complex and long history of the region’s formation caused the creation of the structural-tectonic zonation of the Dniprо-Donets Depression, which includes: the northern and southern marginal (near-edge) zones (or seam zones of the Pripyatsky-Manitsky and Baranovitsko- Astrakhansky deep faults), pre-axial (or zones of near-ridge basement protrusions) and axial zones. The southern and northern marginal (edge) zones are the immersed slopes of the Ukrainian Shield and the Voronezh Crystalline Massif. Riftogenesis and halokinesis were the factors that have influenced the cyclical course of the evolution of salt domes, for which the asynchronous level of development was characteristic in certain geological epochs, due to their confinement to different structural and tectonic zones of the depression. The morphological features of salt structures, the distribution and nature of disjunctive dislocations, stratigraphic and lithological gaps and unconformities are reflected in the distribution of oil and gas traps. In developed oil and gas regions, where tasks of geological exploration works become more complicated, the value of paleotectonic researches for forecasting traps and their oil and gas content is substantially increased. The main stages of the formation of salt structures located in the axial, southern and northern marginal structural and tectonic zones of the depression on the graphs of sedimentation rates are considered. When comparing charts of sedimentation rates according to the wells data, in the Tournaisian through the early Permian interval there is a synchronous (according to the epochs) jump-like character of the development of structures, regardless of their location within structural and tectonic zones is observed. The general slowdown of sedimentation rates from the Paleozoic to the Mesozoic, from the Mesozoic to the Cenozoic era, is characteristic for the whole territory of the Dnipro-Donets Depression. For the Kreminkivskaya-402 borehole maximum values correspond to the Middle and Late Devonian and Bashkirian, middle values to the Late Visean, Serpukhovian, and the minimal values – to the Tournaisian and Early Visean time. For the Skorobagatkivska-2 borehole the maximum values correspond to the Middle and Late Devonian, Late Visean, Bashkirian and Late Carboniferous, the middle values correspond to the Tournaisian- Early Visean and Moscovian, and the minimal values – to the Serpukhovian and Early Permian. For the Herasymivska-1 borehole the maximum values are characteristic for the Middle and Late Devonian, Late Visean and Bashkirian; the middle values – to the Tournaisian and Moscovian, and the minimal values – for the Late Visean and Serpukhovian.

Population genomics reveals that refugial isolation and habitat change lead to incipient speciation in the Ground tit

AbstractComplex geological environments and Pleistocene glaciations contribute to speciation. For example, the unique geomorphological configuration and distinct geological evolution of the Qinghai–Tibet Plateau has led to the evolution of many endemic species adapted to a life at the plateau. Most of these endemic birds show no genetic divergence between different populations across the vast plateau region, with one particularly interesting exception. The ground tit (Pseudopodoces humilis) exhibits considerable genetic differences between the populations distributed on the central (platform) and those in the eastern margin (edge) of the plateau. Glacial refugial isolation and geographic barrier are hypotheses that have been proposed to explain this unique pattern of divergence. Here we use genome‐wide resequencing data to test these two hypotheses as explanation to the genetic divergence of the ground tit. The neighbor‐joining tree, principal component and STRUCTURE analyses suggest the presence of two incompletely diverged genetic lineages, which are geographically congruent with the populations in the platform and edge areas of the plateau. Our demographic model and population demography analyses estimated that the two populations diverged between 57 and 167 kya, and both populations experienced similar bottlenecks and expansions. Congruently, we also observed retracted suitable habitats for the two populations during the glacial time, suggesting that isolation in different glacial refugia. Interestingly, the genetic divergence between the two populations is further maintained and accumulated by habitat differentiation and morphological divergence. In accordance with this, we observed that highly divergent genomic regions harbour genes enriched in biological functions involved in muscle related processes and metabolic activities. Overall, the separation into different glacial refugia, the habitat difference and the morphological divergence contribute together to the adaptive population diversification in situ and we suggest that the platform and edge populations of the ground tit constitutes an interesting example of incipient speciation.

Research on shaping law in electrochemical machining for the leading/trailing edge of the blade

The blade is a crucial component in an aero engine. In electrochemical machining of blades, the shaping law of the leading/trailing edge is intricate because of the complexity of the flow field and electric field distributions at these locations. This paper researches the formation of the leading/trailing edge. The dissolution process of the leading/trailing edge is simulated using an initial cathode and then its forecasted profile is obtained. The cathode is then adjusted according to the deviations between the forecasted profile and the model. Meanwhile, a coefficient between the deviations and the corrected value of the cathode is obtained after optimization simulation and the optimal value is about 1.17. Then, an optimal cathode is acquired by using the optimal coefficient. In addition, the effects of the thermal and hydrogen generation are also considered. The temperature increases to 8.28 K and the bubble rate increases to 25.30% at the electrolyte outlet. Furthermore, verification experiments are performed with the optimal cathode. The results show that the margin edges are formed and the accuracy is 0.13 mm of the leading edge, while the allowance of the profile at the electrolyte outlet is larger than that at the inlet, which means that the bubble rate is dominant in the inter-electrode gap. The results indicate that the design method for the leading/trailing edge is appropriate and can be used for manufacturing other complex components such as blisks and diffusers.

Age, Growth, and Mortality Rates of the Giant Cichlid in Guatemala

AbstractAge, growth, and mortality were assessed in Giant Cichlids Petenia splendida from lakes in northern Guatemala by using cross‐sectioned sagittal otoliths. Marginal increment and edge analyses of Giant Cichlid otoliths indicated that one annulus formed per 12‐month period in Lakes Yaxhá and Petén Itza. Opaque zone formation was associated with the peak of the rainy season from May to September. Ages ranged from 0 to 8 years for Giant Cichlids in Lake Yaxhá and from 0 to 5 years in Lake Petén Itza. Within both lakes, males were larger than females, although the difference was slight in Lake Petén Itza. Lake Yaxhá Giant Cichlids had faster growth rates than those from Lake Petén Itza, and fish over 2 years old from Lake Yaxhá were larger at age than fish from Lake Petén Itza. This is counter‐intuitive because Lake Petén Itza is heavily exploited, whereas Lake Yaxhá is unfished. However, long‐term exploitation in Lake Petén Itza may have resulted in selection for fish with reduced growth rates. Alternatively, the mesotrophic state of Lake Yaxhá may explain the differences in growth, although areas of Lake Petén Itza are changing from oligotrophic to meso‐eutrophic due to rapid cultural eutrophication. Total mortality (Z) estimates for Giant Cichlids were 0.81 for Lake Yaxhá, with most of the age structured on 2–4‐year‐old fish, and 1.05 for Lake Petén Itzá, where the age structure was dominated by 0–2‐year‐old fish; these results were consistent with expectations based on the low fishing pressure in Lake Yaxhá.

Spatial variability and size structure of particles and plankton in the Fram Strait

Changes within marine pelagic fields in the Arctic affect global biogeochemical cycles. The size structure and distribution of particles and plankton (P&P) were studied in the main northward passage of Atlantic water to the Arctic region, which is affected in various ways by climate change. The wide size spectrum of P&P (3 µm–5 mm) was assessed by combining measurements from two complementary optical counters, a Laser In-Situ Scattering and Transmissometry (LISST) instrument and a Laser Optical Plankton Counter (LOPC). The measurements were performed in the upper 100 m layer at 55 stations in summer in 2013. The P&P were attributed to various functional groups – particles, phytoplankton, marine snow, and zooplankton – to test their spatial coupling with hydrodynamic forcing. Although our study confirms that the Fram Strait is a region of strong biophysical contrasts, the expected coastal-offshore gradient has not been distinguished clearly. Three mechanisms could explain P&P patches: particle flocculation due to contact with fresh waters from ice and fjords, enhanced production due to coastal upwelling as well as widening the range of warm surface water advection northwards. Particularly rich biological hot spots were recognised in the northern, shallow parts of the west Spitsbergen shelf, and near the marginal ice edges, confirming that these areas are highly vulnerable to marine predators. Moreover, combining optical measurements from two size-specific optical counters contributes greatly to reducing the substantial knowledge gap regarding wide size structure and distribution of thus far neglected seawater components, such as non-living particles and marine snow aggregates, occurring in this vulnerable Arctic region.

Heterodonty and double occlusion in Manidens condorensis: a unique adaptation in an Early Jurassic ornithischian improving masticatory efficiency.

New materials of the ornithischian dinosaur Manidens condorensis highlight a strong heterodonty between the upper and lower dentitions and reveal a novel occlusion type previously unreported in herbivorous dinosaurs. The diamond-shaped maxillary teeth have prominent cingular entolophs in a V- to Z-shaped configuration that are absent in dentary teeth. These cingular entolophs bear denticles and serrations with vertical wear that is coplanar with the apical wear facets, supporting their involvement in chewing. The separated apical and basal wear in dentary teeth is consistent with the apical and cingular wear in maxillary teeth, indicating an alternate occlusion, an orthal jaw motion, and shearing interactions between marginal and cingular edges in a double occlusion. Measurements of the length and wear area along the marginal and cingular edges indicate that the latter are functionally equivalent to adding eight teeth to a maxillary toothrow of ten, almost doubling the lengths of cutting edges and the degree of intraoral processing, while maintaining a plesiomorphic skull anatomy, an adaptation to herbivory unique in Ornithischia.

Sox17 is essential for proper formation of the marginal zone of extraembryonic endoderm adjacent to a developing mouse placental disk.

In mouse conceptus, two yolk-sac membranes, the parietal endoderm (PE) and visceral endoderm (VE), are involved in protecting and nourishing early-somite-stage embryos prior to the establishment of placental circulation. Both PE and VE membranes are tightly anchored to the marginal edge of the developing placental disk, in which the extraembryonic endoderm (marginal zone endoderm: ME) shows the typical flat epithelial morphology intermediate between those of PE and VE in vivo. However, the molecular characteristics and functions of the ME in mouse placentation remain unclear. Here, we show that SOX17, not SOX7, is continuously expressed in the ME cells, whereas both SOX17 and SOX7 are coexpressed in PE cells, by at least 10.5 days postconception. The Sox17-null conceptus, but not the Sox7-null one, showed the ectopic appearance of squamous VE-like epithelial cells in the presumptive ME region, together with reduced cell density and aberrant morphology of PE cells. Such aberrant ME formation in the Sox17-null extraembryonic endoderm was not rescued by the chimeric embryo replaced with the wild-type gut endoderm by the injection of wild-type ES cells into the Sox17-null blastocyst, suggesting the cell autonomous defects in the extraembryonic endoderm of Sox17-null concepti. These findings provide direct evidence of the crucial roles of SOX17 in proper formation and maintenance of the ME region, highlighting a novel entry point to understand the in vivo VE-to-PE transition in the marginal edge of developing placenta.

Occurrence and Risk Assessment of PAHs in Surface Sediments from Western Arctic and Subarctic Oceans.

In the fourth Chinese National Arctic Research Expedition (from July to September, 2010), 14 surface sediment samples were collected from the Bering Sea, Chukchi Sea, and Canadian Basin to examine the spatial distributions, potential sources, as well as ecological and health risk assessment of polycyclic aromatic hydrocarbons (PAHs). The ∑PAH (refers to the sum of 16 priority PAHs) concentration range from 27.66 ng/g to 167.48 ng/g (dry weight, d.w.). Additionally, the concentrations of ∑PAH were highest in the margin edges of the Canadian Basin, which may originate from coal combustion with an accumulation of Canadian point sources and river runoff due to the surface ocean currents. The lowest levels occurred in the northern of Canadian Basin, and the levels of ∑PAH in the Chukchi Sea were slightly higher than those in the Being Sea. Three isomer ratios of PAHs (Phenanthrene/Anthracene, BaA/(BaA+Chy), and LMW/HMW) were used to investigate the potential sources of PAHs, which showed the main source of combustion combined with weaker petroleum contribution. Compared with four sediment quality guidelines, the concentrations of PAH are much lower, indicating a low potential ecological risk. All TEQPAH also showed a low risk to human health. Our study revealed the important role of the ocean current on the redistribution of PAHs in the Arctic.

Integrating Multiple Natural Tags to Link Migration Patterns and Resource Partitioning Across a Subtropical Estuarine Gradient

Establishing links between migration patterns and trophic dynamics is paramount to ecological studies investigating the functional role habitats provide to resident and transient species. Natural tags in fishes, such as otolith chemistry and tissue stable isotopes, can help reconstruct previous environmental and dietary histories, although these approaches are rarely combined. A novel multiproxy natural tag approach was developed to estimate immigration patterns of juvenile Atlantic croaker Micropogonias undulatus, across contrasting salinity gradients in three subtropical estuaries of the western Gulf of Mexico. Juvenile young-of-year Atlantic croaker were collected along a latitudinal gradient that included positive, neutral, and negative estuaries, based on physicochemical (temperature, salinity, dissolved element) and isotopic (δ15N and δ13C) parameters. Otolith elemental chronologies of Sr/Ca and Ba/Ca were used to classify migratory types within each estuary, while tissue-specific isotope ratios revealed time since recent (liver~weeks) and longer term (muscle~months) diet shifts. Nitrogen isotopes in both liver and muscle tissues were highly correlated, suggesting tissue equilibrium and estuarine residence of at least 3 months, with geographic δ15N gradients reflecting the magnitude of anthropogenic nutrient enrichment within each estuary. Differences in isotopic equilibrium of muscle-liver δ13C values and variation in marginal edge otolith Sr/Ca and Ba/Ca suggested recent shifts in carbon source and habitat utilization, reflecting individualized movement across seascapes and connectivity of habitat mosaics. The multiproxy approach presented here identified diverse migration patterns and linked feeding and movement on regional (inter-estuary), local (intra-estuary), and individual scales to improve our understanding of habitat function across estuarine gradients.

Are range based models good enough? Evidence from seven stock markets

We study the performance of range-based models over varying market conditions and compare their performance against a set of alterative risk measurement models, including the more widely used techniques in practice for measuring the Value-at-Risk (VaR) of seven financial market indices. In particular, we focus on model accuracy in estimated VaRs over quiet and volatile moments utilizing loss functions and likelihood ratio tests for coverage probability. The empirical estimates based on these two criteria find that the range based-model of Yang and Zhang (2000) shows some success in estimated VaR risk measure, especially during quiet periods, than is the case for the other range based models considered. Also, we find that the EWMA and RiskMetrics models have an inconsistent marginal edge over the widely used GARCH and historical simulation specifications and that there is validity in the use of the EWMA and RiskMetrics models over range-based approaches as both capture and thus provide more accurate estimated VaR risk measure of market risk.

Seasonal Movements and Relative Abundance of Bearded Seals (<i>Erignathus barbatus</i>) in the Coastal Waters of the Chukotka Peninsula

Information about bearded seal seasonal distribution in the Pacific Arctic is limited. Bearded seals (Erignathus barbatus Exleben, 1777) from coastal sites along the southern, eastern, and northern Chukotka Peninsula, Russian Federation, were observed most seasons during 1993 – 96, 1998 – 2000, 2002 – 05, and 2010 – 11. These observations provide spatial and temporal information about bearded seal seasonal distribution, movements, and relative numbers in the coastal zones. In winter, bearded seals aggregate on the young ice in the northern part of the Gulf of Anadyr. Numbers gradually increase during March. In springtime (April–May), bearded seals in the northern Gulf of Anadyr are relatively numerous around Nunligran (Cape Achen), but the number is highly variable across years. During spring bearded seals move eastward along the coast from the northern part of the Gulf of Anadyr towards the Bering Strait and then to the north, as the marginal ice edge zone retreats north. These movements to the east and north continue in ice-free water, and by August, the spring migration of bearded seals along the coast of the Chukotka Peninsula ends. In the summer months of August and September, few bearded seals are present in this coastal zone. The southward autumn migration of bearded seals is not evident near the coast, which suggests that it occurs farther from shore.

Ufocandona hannaleeae gen. et sp. nov. (Crustacea, Ostracoda) from an artesian well in Texas, USA

We describe a new genus, Ufocandona gen. nov. with its type species Ufocandona hannaleeae gen. et sp. nov., from an artesian well in San Marcos, Texas, USA. The new genus has diagnostic characteristics that distinguish it from other genera in Candonidae, including the asymmetric shape of the valves, the smooth central area on the external surface of the valves, the hexagonal ornamentations around the marginal ends of the carapace, the dense spines on the marginal edges of the right valve and the dorsal prolongation and tubercles seen from inside the ventral edges of the left valve. Additional differences in the soft body parts of the male and female (e.g., claw-like uropod, shape of hemipenis, long Y aesthetascs, two short or reduced exopods on antenna, reduced numbers of setae and segments on other extremities) distinguish the new genus from others in the family. The discovery of this species from a deep artesian well contributes important information to our understanding of groundwater species diversity in a biologically diverse aquifer where the ostracod fauna has been unstudied.

Fish early life stages associated with giant kelp forests in sub-Antarctic coastal waters (Beagle Channel, Argentina)

The aim of this study was to assess seasonal and spatial variations in fish larvae abundance between areas with Macrocystis pyrifera kelp forests and areas without them off the coast of the Beagle Channel. Monthly plankton sampling at three sites was performed from June 2014 to May 2016 in two areas of each site. One area was defined along the offshore margin (edge of the forests) of M. pyrifera kelp forests and the other area parallel to the forests but 200 m offshore (out of the forests). To test for spatial and temporal differences in the abundance of fish larvae, a multiple-hypothesis model approach was adopted by fitting generalized models (GLMs) with the abundance of fishes as the response variable and possible combinations of seasons, sites, areas, and water parameters as explanatory variables. Ten fish taxa in larval stage were collected of which Patagonotothen spp. larvae were the dominant group. Season and area affected most the abundance of fish larvae along the coast of the Beagle Channel. High abundance of fish larvae was collected in spring of both years with a second peak in autumn. Harpagifer bispinis and Patagonotothen spp. peaked in spring, while Careproctus pallidus peaked in autumn. In every season of the two years sampled, the abundance of fish larvae was higher at the edge of the forests than out of them. The importance as nursery ground of M. pyrifera kelp forests for early stages of fishes that inhabit the Beagle Channel is discussed.

Residual Stress From Cold Expansion of Fastener Holes: Measurement, Eigenstrain, and Process Finite Element Modeling

Cold expansion (CX) is a material processing technique that has been widely used in the aircraft industry to enhance fatigue life of structural components containing holes. CX introduces compressive hoop residual stresses that slow crack growth near the hole edge. The objective of this paper is to predict residual stresses arising from cold expansion using two different finite element (FE) approaches, and compare the results to measurement data obtained by the contour method. The paper considers single-hole, double-hole, and triple-hole configurations with three different edge margins. The first FE approach considers process modeling, and includes elastic–plastic behavior, while the second approach is based on the eigenstrain method, and includes only elastic behavior. The results obtained from the FE models are in good agreement with one another, and with measurement data, especially close to the holes, and with respect to the effect of edge margin on the residual stress distributions. The distribution of the residual stress and equivalent plastic strain around the holes is also explored, and the results are discussed in detail. The eigenstrain method was found to be very useful, providing generally accurate predictions of residual stress.

Otolith microchemistry: Insights into bioavailable pollutants in a man-made, urban inlet

Black bream (Acanthopagrus butcheri) were collected from an artificial inlet, Claisebrook Cove, Western Australia. Claisebrook Cove is adjacent to an historic contaminated site that was remediated during the 1990s. It was later identified as a priority area due to elevated levels of sediment contaminants including Zn, Cu, and Pb. Black bream were collected from this cove in 2005 and 2012 and their otoliths were analysed by laser ablation inductively coupled plasma mass spectrometry of the most recent growth zone. Levels of Zn and Mn, which are metabolically regulated, did not correlate with sediment contamination. However, reduction in sediment Cu levels over time coincided with reduced Cu otolith levels from 2005 to 2012. Results indicate that the elemental composition of the marginal edge of Black bream otoliths can identify bioavailable contaminants in an urban estuary and, with monitoring, can be utilized to establish long-term trends.

Velar flutter does not Occur on Persian radico-uvular /G/ sound: Case reports

Nasal turbulence with velar flutter is an obligatory symptom that occurs during production of high-pressure sounds due to a partially closed velopharyngeal (VP) port. A small VP gap creates air-pressure high enough to set the marginal edges of the velum into vibration. The flutter component is characterized spectrally by low frequencies (Zajac & Preisser, 2015) and vibratory activity through auto-correlation functions (Eshghi et al., 2015). In this study, two speech-language pathologists independently listened to the audio recordings of stops produced by two Persian-speaking children (1 male, 8 yrs and 1 female, 9 yrs) with repaired cleft palate. Speech samples consisted of Persian plosives including /p, b, t, d, k, g, G/. The two listeners achieved 100% agreement that velar flutter occurred on all stops except /G/, a voiced radico-uvular sound. Spectral evaluation indicated characteristics of flutter were present during all stops except for /G/. It is hypothesized that tissue vibration was inhibited during the production of /G/ due to the the tongue making contact with the posterior part of the soft palate and/or uvula. The findings provide cross-linguistic evidence in support of tissue vibration (velar flutter) rather than displacement of mucous (bubbling) as the primary perceptual component of nasal turbulence.

Evolution of the Arabian continental margin of the northern Dibba Zone, eastern United Arab Emirates and Oman

The southern margin of the Musandam Mountains (UAE and northern Oman) preserves a Late Permian to Late Cretaceous Neo-Tethyan platform margin sequence that provides important insights into the switch from deposition in shallow shelf to deeper-water margin slope environments. New biostratigraphic dating resolves ambiguities in previous works and better constrains the timing of the stages in the development of the south Musandam platform margin and their link to the wider Oman tectonic framework. The accumulation of Late Permian to Late Triassic mainly dolomitised shelf carbonates along this sector of the nascent Neo-Tethyan margin was ended by a phase of margin-edge collapse linked to the onset of a major phase of Neo-Tethyan rifting and extension, and deposition of a fore-reef talus assemblage. This is newly dated as also being Late Triassic (Norian-Rhaetian) and termed the Kharas Formation. Following non-deposition, or possible erosion of Early Jurassic deposits, differential subsidence in the Middle Jurassic led to deposition of on-lapping deeper-shelf/slope facies peri-platform lime mudstones, fine grained turbidites and minor, channelised coarser-grained graded conglomerates and packstones (Sumeini Group) along the southern side of the Musandam platform. In the west, oolitic peloidal packstone and grainstone shoals were deposited, here termed the Jarief Formation. Their Bathonian-Callovian age is coeval with the regional development of oolitic facies on the carbonate platform, linked to a mid-Jurassic sea-level highstand, and their redeposition into the adjacent Hawasina Basin as turbidites of the Guwayza Formation of the Hamrat Duru Group. Uplift and destabilisation of the margin of the carbonate platform throughout Oman in the Late Jurassic during a mild compressional regime cut off the coarser sediment supply to the Jarief Formation, which was superseded by deposition of Sumeini Group slope-facies lime mudstones with numerous intraformational truncation surfaces. Slope facies sedimentation then persisted along the length of the southern edge of the Musandam platform as the margin relaxed and subsided until the end of the Early Cretaceous. Uplift of the margin edge, related to changing regional compressive stresses as seafloor spreading increased in the South Atlantic and intra-oceanic subduction in Neo-Tethys initiated creation of the Semail Ophiolite, led first to collapse along the shelf edge, generating the thick and highly channelised post Aptian Ausaq Formation mega-breccias. This marked the end of the passive margin as a thick, Late Cretaceous predominantly shale and chert succession was deposited as the margin subsided with continent-ward migration of the foredeep that developed ahead of final emplacement of the Neo-Tethyan Hawasina Nappes and Semail Ophiolite during the Santonian.

Geographies of inequalities in an area of opportunities: ambiguous experiences among young men in the Norwegian High North

AbstractResearch within the field ‘geography of education’ points to the importance of studying the relationship between social and spatial variations in educational provision and attainment. This research has mainly focused on the spatial segregation of different social groups in urban settings. There has been limited research on how geography influences youth and education in rural settings. Youth research in general is criticised for an unacknowledged ‘metrocentricity’, referring to the invisibility of how place and geography represent changeable and contingent conditions in young people's lives. This paper is based on interviews with young, unemployed men living in small places that can be termed the marginal edge of the northern periphery, in the northern part of Norway. By combining a geographical approach with theories on social learning, the paper discusses how changes in the local world of education and work are experienced by a group of young men, and how the changes influence their choices, and lack thereof, in specific rural communities. The overall aim of this paper is to demonstrate how place and geography matter, and how gender and place intersect, when it comes to young people's experiences of opportunities and options.

Impact of the intermediary layer on sealant retention: a randomized 24-month clinical trial

The aims of this study were to assess long-term impact of tooth eruption stages (ES) on sealant retention on occlusal surfaces previously coated with intermediary bonding layer and to determine caries prevention. Sixty-five school children were selected (aged 6-10years), with four non-carious permanent first molar in different ES (OP (operculum present), ME (marginal edge), CE (completely erupted)). Split-mouth and single-blind study design was used. The teeth (260) were randomly selected according to treatment (sealant/technique): F (Fluroshield), H (Helioseal Clear Chroma), SF (Single Bond+F), EH (Excite+H). Sealant retention, marginal integrity, discoloration, and caries prevention were assessed after 6, 12, 18, and 24months by calibrated examiner (Spearman=0.91) using visual inspection. Data were submitted to the Cox proportional hazard model (survival analysis) and Likelihood ratio χ 2 test (correlation), p≤0.05. At baseline, ES was 20% in OP, 54% in ME, and 26% in CE. There was no significant difference on sealant retention between the treatments (p=0.2774). However, significant differences were found regarding the ES on sealant retention (p=0.0041). The CE stage showed the highest retention survival rate during the 24months. The overall sealant prevention average was found to be about 99.4% and showed no difference between the groups. Eruption stages affect sealant retention irregardless of the intermediate layer and type of sealant. However, there was caries prevention on tooth occlusal surfaces after 24months, regardless of treatment. Sealing is recommended to prevent occlusal caries of newly erupted teeth in high-caries-risk patients. However, its application is critical on moisture limited control surfaces independently of sealer material and technique.