Scanning Electron Microscopy of Dentin Caries. Experimental in vitro Studies with Streptococcus Mutans

This study was performed to gain better insight into the mechanisms involved in carious destruction of human dentin by Streptococcus mutans. In particular, bacterial colonization of dentin surfaces and bacterial invasion in dentin were studied. Streptococcus mutans (S. mutans), strain NCTC 10449, was grown on sterile dentin blocks in a 10% CO2 atmosphere at 37°C. After 72, 120, 144 and 288 h of incubation the specimens were processed for scanning electron microscopic examination. The colonization of the dentinal surface progressed slowly and was nearly complete after 288 h. Invasion of S. mutans into the dentinal tubules was found occasionally and was limited to the initial 5 μm of the tubular lumen. The acid metabolites produced by S. mutans, caused lesions of the dentinal structures in the close proximity of the bacteria. From the results of this in vitro study it appears that carious destruction of exposed dentinal surfaces by S. mutans mainly occurs at the exposed dentin after it has been colonized by bacteria. Destruction of the deeper dentinal layers by bacteria invading the dentinal tubules may play a less important role. However, in the few cases where S. mutans invaded the dentinal tubules, rapid destruction of the peritubular dentin sheath occurred. In addition, the possibility remains that acid metabolites produced by S. mutans diffuse into the dentinal tubules and cause tissue damage in the deeper parts of the dentin

The implications of K-Ar glauconite dating of the Diest Formation on the paleogeography of the Upper Miocene in Belgium

The glauconite-rich Diest Formation in central and north Belgium contains sands in the Campine subsurface and the hilly Hageland area that can be distinguished from each other. The Hageland Diest Sands member contains no stratigraphically relevant fossils while in the Campine subsurface dinoflagellate cysts are common and show a stratigraphic range covering the entire Tortonian stage. K-Ar dates were determined for glauconite from 13 selected samples spread over both areas. A glauconite date corresponding to the earliest Tortonian indicates newly formed glauconite was incorporated into a greensand at the base of the Diest Formation in the central Campine area. All other dates point at reworked glauconite and can be organized in two groups, one reflecting a Burdigalian age and another reflecting a Langhian age. These data and the thickness and glauconite content of the Diest Formation imply massive reworking of older Miocene deposits. The paleogeographic implications of these data lead to the tentative recognition of two Tortonian sedimentary sequences. An older one corresponding to dinoflagellate biochron DN8 comprises the Deurne Member, part of the Dessel Member, the Hageland Diest member, the eastern Campine Diest member and some basal sands of the Diest Formation in the central Campine. A younger sequence corresponding to dinoilagellate biochrons DN9 and 10 was strongly influenced by the prograding proto-Rhine delta front in the Roer Valley Graben to the northeast. The subsiding Campine basin was filled from east to west during this second cycle

Ultrastructural Observations on Bacterial Invasion in Cementum and Radicular Dentin of Periodontally Diseased Human Teeth

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141124/1/jper0493.pd

Geophysical Characterization, Redox Zonation, and Contaminant Distribution at a Groundwater/Surface Water Interface

Three transects along a groundwater/surface water interface were characterized for spatial distributions of chlorinated aliphatic hydrocarbons and geochemical conditions to evaluate the natural bioremediation potential of this environmental system. Partly on the basis of ground penetrating radar measurements, a conductive sediment layer was detected from the shore out to at least 300 m offshore which exhibited gradients in redox pairs and contaminant profiles. The cis-Dichloroethene and 1-chloroethene were predominant in the presence of elevated methane and ferrous iron concentrations and depressed sulfate and aquifer solids-bound iron concentrations. The shallow monitoring points were generally hypoxic to aerobic and exhibited values of specific conductance reflective of near-shore lake water, indicating reoxygenation of the contaminant plume due to wave infiltration. The barge transect yielded trace contaminant concentrations and showed evidence of sulfate reduction. These analyses contributed to the understanding of processes affecting contaminant fate and transport at near-shore mixing zones

Hierarchical cluster analysis of polychlorinated dioxins and furans in Michigan, USA, soils: Evaluation of industrial and background congener profiles

As part of the University of Michigan Dioxin Exposure Study, soil samples were collected from 766 residential properties near the Tittabawassee River between Midland and Saginaw; near the Dow Chemical Facility in Midland; and, for comparison, in the other areas of Midland and Saginaw Counties and in Jackson and Calhoun Counties, all located in the state of Michigan, USA. A total of 2,081 soil samples were analyzed for 17 polychlorinated dibenzo- p -dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). In order to better understand the distribution and sources of the PCDD/F congeners in the study area, hierarchical cluster analysis (HCA) was used to statistically group samples with similar congener patterns. The analysis yielded a total of 13 clusters, including: 3 clusters among the soils impacted by contamination present in the Tittabawassee River sediments, a cluster comprised mainly of samples collected within the depositional area of the Dow incinerator complex, a small cluster of samples with elevated 2,3,7,8-tetrachlorinated dibenzo- p -dioxin (TCDD), and several clusters exhibiting background patterns. The clusters related to the Tittabawassee River floodplain contamination all contained elevated PCDF levels and were differentiated from one another primarily by their relative concentrations of higher-chlorinated PCDDs, a difference likely related to both extent and timing of impacts from Tittabawassee sediments. The background clusters appear to be related to combustion processes and are differentiated, in part, by their relative fractions of TCDD. Thus, HCA was useful for identifying congener profile characteristics in both contaminated and background soil samples. Environ. Toxicol. Chem. 2010;29:64–72. © 2009 SETACPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64530/1/24_ftp.pd

The University of Michigan Dioxin Exposure Study: Population Survey Results and Serum Concentrations for Polychlorinated Dioxins, Furans, and Biphenyls

Background: The University of Michigan Dioxin Exposure Study was undertaken to address concerns that the discharge of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from the Dow Chemical Company in the Midland, Michigan, area had resulted in contamination of soils in the Tittabawassee River floodplain and the city of Midland, leading to an increase in residents’ body burdens of these compounds. Objective: In this article we present descriptive statistics from the resident survey and sampling of human serum, household dust, and soil and compare them with other published values. Methods: From a multistage random sample of populations in four areas of Midland and Saginaw counties and from a distant referent population, we interviewed 946 adults, who also donated blood for analysis of PCDDs, PCDFs, and polychlorinated biphenyls (PCBs). Samples of household dust and house perimeter soil were collected from consenting subjects who owned their property. Results: All five study populations were comparable in age, race, sex, and length of residence in their current home. Regional differences existed in employment history, personal contact with contaminated soils, and consumption of fish and game from contaminated areas. Median soil concentrations were significantly increased around homes in the Tittabawassee River floodplain (11.4 ppt) and within the city of Midland (58.2 ppt) compared with the referent population (3.6 ppt). Median serum toxic equivalencies were significantly increased in people who lived in the floodplain (23.2 ppt) compared with the referent population (18.5 ppt). Conclusions: Differences in serum dioxin concentrations among the populations were small but statistically significant. Regression modeling is needed to identify whether the serum concentrations of PCDDs, PCDFs, and PCBs are associated with contaminated soils, household dust, and other factors

The harlequin ladybird, Harmonia axyridis: global perspectives on invasion history and ecology

The harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is native to Asia but has been intentionally introduced to many countries as a biological control agent of pest insects. In numerous countries, however, it has been introduced unintentionally. The dramatic spread of H. axyridis within many countries has been met with considerable trepidation. It is a generalist top predator, able to thrive in many habitats and across wide climatic conditions. It poses a threat to biodiversity, particularly aphidophagous insects, through competition and predation, and in many countries adverse effects have been reported on other species, particularly coccinellids. However, the patterns are not consistent around the world and seem to be affected by many factors including landscape and climate. Research on H. axyridis has provided detailed insights into invasion biology from broad patterns and processes to approaches in surveillance and monitoring. An impressive number of studies on this alien species have provided mechanistic evidence alongside models explaining large-scale patterns and processes. The involvement of citizens in monitoring this species in a number of countries around the world is inspiring and has provided data on scales that would be otherwise unachievable. Harmonia axyridis has successfully been used as a model invasive alien species and has been the inspiration for global collaborations at various scales. There is considerable scope to expand the research and associated collaborations, particularly to increase the breadth of parallel studies conducted in the native and invaded regions. Indeed a qualitative comparison of biological traits across the native and invaded range suggests that there are differences which ultimately could influence the population dynamics of this invader. Here we provide an overview of the invasion history and ecology of H. axyridis globally with consideration of future research perspectives. We reflect broadly on the contributions of such research to our understanding of invasion biology while also informing policy and people.  Additional co-authors: Artur Gil, Audrey A. Grez, Thomas Guillemaud, Danny Haelewaters, Annette Herz, Alois Honek, Andy G. Howe, Cang Hui, William D. Hutchison, Marc Kenis, Robert L. Koch, Jan Kulfan, Lori Lawson Handley, Eric Lombaert, Antoon Loomans, John Losey, Alexander O. Lukashuk, Dirk Maes, Alexandra Magro, Gilles San Martin, Zdenka Martinkova, Ingrid A. Minnaar, Oldřich Nedved, Marina J. Orlova-Bienkowskaja, Naoya Osawa, Wolfgang Rabitsch, Hans Peter Ravn, Gabriele Rondoni, Steph L. Rorke, Sergey K. Ryndevich, May-Guri Saethre, John J. Sloggett, Antonio Onofre Soares, Riaan Stals, Axel Vandereycken, Paul van Wielink, Sandra Viglášová, Peter Zach, Ilya A. Zakharov, Tania Zaviezo, Zihua Zha