H-D Analysis Employing Energy Transfer from Metastable Excited-State He in Double-Pulse LIBS with Low-Pressure He Gas.

A laser-induced-breakdown-spectroscopy (LIBS) experiment with a unique double-pulse setup and operated in low-pressure (3 kPa) He ambient gas is performed to study the detection of light elements, such as hydrogen (H) and deuterium (D), as well as elements of high excitation energies, such as fluorine (F) and chlorine (Cl), which are usually difficult to detect using ordinary LIBS techniques. A nanosecond Nd:YAG laser operated in its fundamental wavelength with energy of 54 mJ is focused onto the Al target to generate the He plasma. Another picosecond Nd:YAG laser operated in its fundamental wavelength with energy of 2 mJ is focused onto the sample surface and activated 2 µs before the operation of the nanosecond laser. The application to polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE) samples produces sharp and high-intensity Cl- and F-emission lines. Meanwhile, the sharp and well-resolved H-D-emission lines with merely 0.18 nm wavelength separation are also clearly detected from a zircaloy sample. Further measurement of a set of zircaloy samples containing different concentrations of D yields a linear calibration curve with a zero intercept. The detection limit of D is found to be about 10 ppm.

Quantitative analysis of deuterium in zircaloy using double-pulse laser-induced breakdown spectrometry (LIBS) and helium gas plasma without a sample chamber.

A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 µs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 µg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 µm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.

Complete genome sequence of the genetically tractable hydrogenotrophic methanogen Methanococcus maripaludis.

The genome sequence of the genetically tractable, mesophilic, hydrogenotrophic methanogen Methanococcus maripaludis contains 1,722 protein-coding genes in a single circular chromosome of 1,661,137 bp. Of the protein-coding genes (open reading frames [ORFs]), 44% were assigned a function, 48% were conserved but had unknown or uncertain functions, and 7.5% (129 ORFs) were unique to M. maripaludis. Of the unique ORFs, 27 were confirmed to encode proteins by the mass spectrometric identification of unique peptides. Genes for most known functions and pathways were identified. For example, a full complement of hydrogenases and methanogenesis enzymes was identified, including eight selenocysteine-containing proteins, with each being paralogous to a cysteine-containing counterpart. At least 59 proteins were predicted to contain iron-sulfur centers, including ferredoxins, polyferredoxins, and subunits of enzymes with various redox functions. Unusual features included the absence of a Cdc6 homolog, implying a variation in replication initiation, and the presence of a bacterial-like RNase HI as well as an RNase HII typical of the Archaea. The presence of alanine dehydrogenase and alanine racemase, which are uniquely present among the Archaea, explained the ability of the organism to use L- and D-alanine as nitrogen sources. Features that contrasted with the related organism Methanocaldococcus jannaschii included the absence of inteins, even though close homologs of most intein-containing proteins were encoded. Although two-thirds of the ORFs had their highest Blastp hits in Methanocaldococcus jannaschii, lateral gene transfer or gene loss has apparently resulted in genes, which are often clustered, with top Blastp hits in more distantly related groups.

Stereoscopic navigation-controlled display of preoperative MRI and intraoperative 3D ultrasound in planning and guidance of neurosurgery: new technology for minimally invasive image-guided surgery approaches.

OBJECTIVE: This paper demonstrates a method that brings together three essential technologies for surgery planning and guidance: neuronavigation systems, 3D visualization techniques and intraoperative 3D imaging technologies. We demonstrate the practical use of an in-house interactive stereoscopic visualization module that is integrated with a 3D ultrasound based neuronavigation system. MATERIALS AND METHODS: A stereoscopy volume visualization module has been integrated with a 3D ultrasound based neuronavigation system, which also can read preoperative MR and CT data. The various stereoscopic display modalities, such as "cut plane visualization" and "interactive stereoscopic tool guidance" are controlled by a pointer, a surgical tool or an ultrasound probe. Interactive stereoscopy was tested in clinical feasibility case studies for planning and guidance of surgery procedures. RESULTS: By orientating the stereoscopic projections in accordance to the position of the patient on the operating table, it is easier to interpret complex 3D anatomy and to directly take advantage of this 3D information for planning and surgical guidance. In the clinical case studies, we experienced that the probe-controlled cut plane visualization was promising during tumor resection. By combining 2D and 3D display, interpretation of both detailed and geometric information may be achieved simultaneously. The possibilities of interactively guiding tools in a stereoscopic scene seemed to be a promising functionality for use during vascular surgery, due to specific location of certain vessels. CONCLUSION: Interactive stereoscopic visualization improves perception and enhances the ability to understand complex 3D anatomy. The practical benefit of 3D display is increased considerably when integrated with surgical navigation systems, since the orientation of the stereoscopic projection corresponds to the orientation of the patient on the operating table. Stereoscopic visualizations work well on MR and CT images, although volume rendering techniques are especially suitable for intraoperative 3D ultrasound image data.

Bayesian 2-D deconvolution: a model for diffuse ultrasound scattering.

Observed medical ultrasound images are degraded representations of the true acoustic tissue reflectance. The degradation is due to blur and speckle and significantly reduces the diagnostic value of the images. To remove both blur and speckle, we have developed a new statistical model for diffuse scattering in 2-D ultrasound radio frequency images, incorporating both spatial smoothness constraints and a physical model for diffuse scattering. The modeling approach is Bayesian in nature, and we use Markov chain Monte Carlo methods to obtain the restorations. The results from restorations of some real and simulated radio frequency ultrasound images are presented and compared with results produced by Wiener filtering.

Bayesian 2-D deconvolution: effect of using spatially invariant ultrasound point spread functions.

Observed ultrasound images are degraded representations of the-true tissue reflectance. The specular reflections at boundaries between regions of different tissue types are blurred, and the diffuse scattering within homogenous regions causes speckle because of the oscillating nature of the transmitted pulse. To reduce both blur and speckle, we have developed algorithms for the restoration of simulated and real ultrasound images based on Markov random field models and Bayesian statistical methods. The algorithm is summarized here, although a more detailed description can be found in our companion paper [1]. Because the point spread function (psf) is unknown, we investigate the effects of using incorrect frequencies and sizes for the model psf during the restoration process. First, we degrade the images either with a known simulated psf or a measured psf. Then, we use different psf shapes during restoration to study the robustness of the method. We found that small variations in the parameters characterizing the psf, less than +/- 25% change in frequency, width, or length, still yielded satisfactory results. When altering the psf more than this, the restorations were not acceptable. The restorations were particularly sensitive to large increases in the restoring psf frequency. Thus, 2-D Bayesian restoration using a fixed psf may yield acceptable results as long as the true variant psfs have not varied too much during imaging.

SonoWand, an ultrasound-based neuronavigation system.

OBJECTIVE: We have integrated a neuronavigation system into an ultrasound scanner and developed a single-rack system that enables the surgeon to perform frameless and armless stereotactic neuronavigation using intraoperative three-dimensional ultrasound data as well as preoperative magnetic resonance or computed tomographic images. The purpose of this article is to describe our two-rack prototype and present the results of our work on image quality enhancement. DESCRIPTION OF INSTRUMENTATION: The system consists of a high-end ultrasound scanner, a modest-cost computer, and an optical positioning/digitizer system. Special technical and clinical efforts have been made to achieve high image quality. A special interface between the ultrasound instrument and the navigation computer ensures rapid transfer of digital three-dimensional data with no loss of image quality. OPERATIVE TECHNIQUE: The positioning system tracks the position and orientation of the patient, the ultrasound probe, the pointer, and various surgical instruments. This makes it possible to update the three-dimensional map during surgery and navigate by ultrasound data in a similar manner as with magnetic resonance data. METHODS: The two-rack prototype has been used for clinical testing since November 1997 at the University Hospital in Trondheim. EXPERIENCE AND RESULTS: The image quality improvements have enabled us, in most cases, to extract information from ultrasound with clinical value similar to that of preoperative magnetic resonance imaging. The overall clinical accuracy of the ultrasound-based navigation system is expected to be comparable to or better than that of a magnetic resonance imaging-based system. CONCLUSION: The SonoWand system enables neuronavigation through direct use of intraoperative three-dimensional ultrasound. Further research will be necessary to explore the potential clinical value and the limitations of this technology.

Coronally positioned flap procedures with or without a bioabsorbable membrane in the treatment of human gingival recession.

BACKGROUND: A variety of surgical techniques have been used to cover recession type defects. New data have indicated that the outcome of coronally positioned flap procedures may be augmented by supporting the flap with a membrane. METHODS: The present study aimed at comparing the clinical outcome following treatment of localized gingival recessions by a coronally positioned flap procedure alone, or combined with a bioabsorbable membrane. Twenty patients with buccal bilateral Miller Class I or Class II gingival recessions in cuspids or premolars participated in the study. The split-mouth design, randomized selection of site treatment, and blind evaluation provided 20 sites in a membrane group and 20 sites in a non-membrane group for examination at baseline, and at 3 months and 6 months postoperatively. Clinical variables included the apical extent of the gingival recession, the width of the recession defect measured at the cemento-enamel junction (CEJ), and the width of keratinized tissue at the recession site as well as probing depth and attachment level. RESULTS: Both treatments resulted in a significant gain (P <0.0001) of root coverage, amounting to an average of 2.3 mm in the membrane group and 2.5 mm in the non-membrane group at the 6-month evaluation. There was no significant difference between the treatments. Similarly, a significant gain of clinical attachment level was seen in the membrane (1.3 mm; P <0.001) as well as in the non-membrane (1.5 mm; P <0.0001) group, but without a significant difference between the groups. The reduction of the recession width from baseline to 6 months was significantly greater (P <0.01) for the non-membrane (2.3 mm) than for the membrane (1.4 mm) group. Probing depth changes were small and not significant for either of the treatments. When patients were grouped as smokers (8) and non-smokers (12), no significant differences were revealed for any of the response variables. Overall, among the 20 membrane sites, one showed no change while the remaining 19 gained root coverage at the 6-month examination. Five sites obtained coverage to the CEJ. Among the non-membrane sites, all gained root coverage at 6 months and 10 sites showed complete coverage to the CEJ. CONCLUSIONS: The coronally positioned flap operation offers a predictable, simple, and convenient approach as a root coverage procedure in Miller Class I and Class II recession defects. Combining this technique with the placement of a bioabsorbable membrane does not seem to improve the results following surgical treatment of such defects.

The inflammatory response following treatment of abdominal aortic aneurysms: a comparison between open surgery and endovascular repair.

OBJECTIVES: to compare the inflammatory response following endovascular and conventional AAA repair. DESIGN: prospective study. PATIENTS AND METHODS: ten patients were selected for open surgery (OPEN) and ten for endovascular (ENDO) AAA repair. Leukocytes, platelets, myeloperoxidase, lactoferrin, beta-thromboglobulin, C-reactive protein (CRP), interleukin 6 (IL-6), tumour necrosis factor alpha (TNF-alpha) and complement activation products were measured before, during and after surgery. RESULTS: in the OPEN group the median hospital stay was longer (6 vs. 12 days, p=0.001) and more patients required transfusion (p=0.02). IL-6 and CRP increased postoperatively, most in OPEN (p<0.01). Platelet counts decreased after the first angiography in ENDO (p<0.01) and before aortic cross-clamping in OPEN (p<0.05). The decrease was larger in OPEN (p=0.02). Leukocyte counts decreased after the first angiography in ENDO, and thereafter increased (p=0.001). An equivalent increase was observed in OPEN after declamping (p=0.001). Leukocyte and platelet degranulation products increased after the first angiography in ENDO and after declamping in OPEN. Changes in complement activation products were small. TNF-alpha did not change significantly. CONCLUSION: endovascular AAA repair caused significant leukocyte and platelet activation. Based on the timing of activation this could be caused by radiographic contrast media.

Initial experience with stereoscopic visualization of three-dimensional ultrasound data in surgery.

Initial in vivo and in vitro experiments were performed to evaluate the feasibility of stereoscopically displaying three-dimensional (3D) ultrasound data from neurosurgery, laparoscopic surgery, and vascular surgery. Stereoscopic visualization was illustrated by four video sequences, which can be downloaded from http://www.us.unimed. sintef.no/. These sequences show a brain tumor, hepatic arteries in relation to the gallbladder, a model that mimics a neuroendoscope in a cyst, and a "flight" into model of an artery with an intima flap. The experiments indicate that stereoscopic display of ultrasound data is feasible when there is sufficient contrast between the objects of interest and the surrounding tissue. True 3D vision improves perception, thus enhancing the ability to understand complex anatomic structures such as irregular lesions and tortuous vessels.

[From The Origin of Species to Artenes Oprindelse]. / Fra the origin of species til Arternes Oprindelse. Litt om darwinismens utbredelse i Norge i det 19. århundre.

The Origin of Species, Charles Darwin's most important work, was published in London in 1859. The first presentation in Norway, by P. Chr. Asbjørnsen, appeared in the journal Budstikken. About 30 years passed before it was translated into Norwegian, and it took some time before Darwin's theories were debated in Norway. The zoologist Michael Sars introduced them in the Scientific Society in Christiania (i.e., Oslo) in 1869, but he was not met with a great deal of interest. However, a new generation of scientist saw this differently, mainly the botanist Axel Blytt, the zoologist G.O. Sars and the geologist W.C. Brøgger. Two prominent professors of medicine were also involved in the debate, on different sides. The Darwinist Gerhard Henrik Armauer Hansen, who discovered the lepra bacillus, wrote several books and articles about Darwinism, while Professor Ernst Ferdinand Lochmann, though admiring Darwin as a prominent naturalist, strongly rejected Darwinism as a scientific theory.

Sulfonates as terminal electron acceptors for growth of sulfite-reducing bacteria (Desulfitobacterium spp.) and sulfate-reducing bacteria: effects of inhibitors of sulfidogenesis.

This study demonstrates the ability of Desulfitobacterium spp. to utilize aliphatic sulfonates as terminal electron acceptors (TEA) for growth. Isethionate (2-hydroxyethanesulfonate) reduction by Desulfitobacterium hafniense resulted in acetate as well as sulfide accumulation in accordance with the expectation that the carbon portion of isethionate was oxidized to acetate and the sulfur was reduced to sulfide. The presence of a polypeptide, approximately 97 kDa, was evident in isethionate-grown cells of Desulfitobacterium hafniense, Desulfitobacterium sp. strain PCE 1, and the two sulfate-reducing bacteria (SRB)-Desulfovibrio desulfuricans IC1 (T. J. Lie, J. R. Leadbetter, and E. R. Leadbetter, Geomicrobiol. J. 15:135-149, 1998) and Desulfomicrobium norvegicum; this polypeptide was not detected when these bacteria were grown on TEA other than isethionate, suggesting involvement in its metabolism. The sulfate analogs molybdate and tungstate, effective in inhibiting sulfate reduction by SRB, were examined for their effects on sulfonate reduction. Molybdate effectively inhibited sulfonate reduction by strain IC1 and selectively inhibited isethionate (but not cysteate) reduction by Desulfitobacterium dehalogenans and Desulfitobacterium sp. strain PCE 1. Desulfitobacterium hafniense, however, grew with both isethionate and cysteate in the presence of molybdate. In contrast, tungstate only partially inhibited sulfonate reduction by both SRB and Desulfitobacterium spp. Similarly, another inhibitor of sulfate reduction, 1,8-dihydroxyanthraquinone, effectively inhibited sulfate reduction by SRB but only partially inhibited sulfonate reduction by both SRB and Desulfitobacterium hafniense.

Sulfidogenesis from 2-aminoethanesulfonate (taurine) fermentation by a morphologically unusual sulfate-reducing bacterium, Desulforhopalus singaporensis sp. nov.

A pure culture of an obligately anaerobic marine bacterium was obtained from an anaerobic enrichment culture in which taurine (2-aminoethanesulfonate) was the sole source of carbon, energy, and nitrogen. Taurine fermentation resulted in acetate, ammonia, and sulfide as end products. Other sulfonates, including 2-hydroxyethanesulfonate (isethionate) and cysteate (alanine-3-sulfonate), were not fermented. When malate was the sole source of carbon and energy, the bacterium reduced sulfate, sulfite, thiosulfate, or nitrate (reduced to ammonia) but did not use fumarate or dimethyl sulfoxide as a terminal electron acceptor for growth. Taurine-grown cells had significantly lower adenylylphosphosulfate reductase activities than sulfate-grown cells had, which was consistent with the notion that sulfate was not released as a result of oxidative C-S bond cleavage and then assimilated. The name Desulforhopalus singaporensis is proposed for this sulfate-reducing bacterium, which is morphologically unusual compared to the previously described sulfate-reducing bacteria by virtue of the spinae present on the rod-shaped, gram-negative, nonmotile cells; endospore formation was not discerned, nor was desulfoviridin detected. Granules of poly-beta-hydroxybutyrate were abundant in taurine-grown cells. This organism shares with the other member of the genus Desulforhopalus which has been described a unique 13-base deletion in the 16S ribosomal DNA. It differs in several ways from a recently described endospore-forming anaerobe (K. Denger, H. Laue, and A. M. Cook, Arch. Microbiol. 168:297-301, 1997) that reportedly produces thiosulfate but not sulfide from taurine fermentation. D. singaporensis thus appears to be the first example of an organism which exhibits sulfidogenesis during taurine fermentation. Implications for sulfonate sulfur in the sulfur cycle are discussed.

Effects of tobacco smoking on the human pupil.

OBJECTIVE: Determine the effects of tobacco cigarette or sham placebo-smoking on pupil diameter. SUBJECTS: Ten non-smokers and 10 tobacco smokers (all healthy, drug free adults) were studied while resting in a comfortable lounger. METHODS: Tobacco smokers abstained from smoking and all subjects abstained from caffeine-containing products for at least 8 h prior to testing. The smokers each smoked one tobacco cigarette, and the non-smokers each inhaled air through an unlit sham cigarette. Right pupil diameter, heart rate, systolic and diastolic blood pressure were measured before and after sham- or tobacco-smoking in each subject. Pupil size was measured from a colored photograph taken with a Polaroid camera equipped with a high-speed flash with the subject in a standardized, dimly lit quiet room. RESULTS: There was no significant difference in baseline pupil diameter between non-smokers and smokers prior to sham- or tobacco-smoking. After sham- or tobacco-smoking, both non-smokers and smokers showed slight but statistically significant pupillary constriction. CONCLUSIONS: Shortly after smoking one tobacco cigarette, pupillary constriction was greater than after sham-smoking.

Effects of topical metronidazole and tetracycline in treatment of adult periodontitis.

The present study was performed to assess and compare the clinical healing and the microbiological findings following local application of metronidazole or tetracycline to augment subgingival scaling in previously untreated adult periodontitis sites. Eighteen patients with moderate to severe adult periodontitis at single-rooted teeth were selected. In each patient, 3 interproximal sites having comparable root anatomy, probing depth > or =5 mm and bleeding on probing were randomly assigned to 1 of 3 treatment groups: 1) two sessions of subgingival scaling and root planing; 2) similar to 1, with each treatment supplemented with a 25% metronidazole sustained release gel; 3) similar to 1 with each treatment supplemented with a 3% tetracycline ointment. The treatments were performed by 1 operator and the clinical variables probing depth, attachment level, and bleeding on probing were evaluated at baseline, 3 months and 6 months by a second blinded examiner. The microbiological findings were evaluated using a commercial test kit. The average probing depth reduction for the 3 groups at 6 months was 1.5 mm and the average gain of clinical attachment was 0.8 mm. There were no significant differences between the effects following topical application of the metronidazole gel or the tetracycline ointment. Scaling and root planing alone appeared as effective as the drug augmented regimens, although there was a weak but non-significant tendency for better results in sites treated with the antibiotic drugs. Actinobacillus actinomycetemcomitans was generally not detected; Prevotella intermedia was not significantly reduced, while Porphyromonas gingivalis was significantly reduced in all treatment groups. It was concluded that the augmentative effect of the metronidazole gel and the tetracycline ointment was comparable but small compared to scaling and root planing alone. The clinical importance of such small augmentation effects should be further evaluated.

Ultrasound imaging during endovascular abdominal aortic aneurysm repair using the Stentor bifurcated endograft.

PURPOSE: To evaluate different ultrasound modalities during implantation and follow-up of endovascular grafts for abdominal aortic aneurysm (AAA) exclusion. METHODS: Between February 1995 and May 1996, 18 patients (14 men; aged 49 to 80 years, mean 67) were treated with endovascular intervention for infrarenal AAA. Seventeen patients received Mialhe Stentor bifurcated grafts, while one patient was treated with a straight graft for pseudoaneurysm. During and after the implantation, 3.25- and 5-MHz annular array ultrasound probes were used for transabdominal visualization of the endograft. Intravascular ultrasound was applied in combination with angiography for postoperative control. RESULTS: Intraprocedurally, transabdominal two-dimensional (2D) ultrasound successfully monitored guidewire passage from the groin into the main part of the bifurcated endograft for implantation of the second limb. All implantation procedures were technically successful, but four endoleaks were identified intraprocedurally by 2D ultrasound and angiography. One healed spontaneously, two were treated with endovascular techniques at 1 and 4 months, and the last leak was scheduled for repair when the patient died of probable myocardial infarction at 2 months. During follow-up, 2D ultrasound successfully visualized all the endografts; no endoleaks were found in up to 18 months of surveillance. CONCLUSIONS: Transabdominal ultrasound imaging could be valuable in bifurcated endograft deployment both for guiding guidewire insertion and for controlling wire position before the second graft limb is connected to the main graft. Provided that satisfactory visualization of the entire endograft can be obtained, ultrasound examination may possibly replace arteriography and computed tomographic scanning as a follow-up investigation.

A pilot study comparing ketoprofen and acetaminophen with hydrocodone for the relief of postoperative periodontal discomfort.

The aim of this study was to compare ketoprofen to acetaminophen with hydrocodone (A/H) in a postoperative periodontal pain model. A double-blind protocol was used. Thirty minutes prior to each procedure, subjects were given orally either 100 mg ketoprofen or a placebo tablet. Four hours later, the subjects took either 50 mg ketoprofen (ketoprofen group) or 1000 mg acetaminophen with 10 mg hydrocodone (placebo group). Subjects reported levels of overall discomfort and pain using visual analog scales at eight hourly intervals following the first dose of ketoprofen or placebo. Information about adverse side effects was requested from the patients in the form of a checklist. The results revealed only small differences between the two drug regimens with respect to levels of pain or overall discomfort. A/H provided significantly better pain relief at Hours 5 and 6, while overall discomfort levels were significantly higher with ketoprofen than with placebo at Hours 3 and 4. Pain levels were low for both groups. It is recommended that additional analgesics for mild to moderate pain should be tested.

A correlation study of inflammatory cell mobilization in response to subgingival microbial colonization.

This study evaluated site-by-site the relations between subgingival microbial colonization and gingival tissue reactions. Experimental, deep periodontal defects were established at buccal surfaces of mandibular and maxillary canine teeth in 5 beagle dogs. The root surfaces were instrumented by a flame-shaped, fine-grained, rotating diamond point, or by a sharp curet. Following a 10-day postsurgical healing period, the dogs were fed a plaque-inducing diet for 70 days. The animals were then sacrificed and tissue blocks of the experimental sites including teeth and periodontal tissues were secured. The buccal gingiva was removed and processed for histomorphometric analysis while the teeth were prepared for scanning electron microscopic evaluation of the extent of subgingival microbial colonization. The results revealed that inflammatory cell density in the junctional epithelium and in the connective tissue were positively correlated to subgingival microbial colonization (P < 0.01). Furthermore, the degree of significance decreased with increasing distance from the plaque. The present study demonstrates that a close relation may exist between the extent of subgingival microbial colonization and inflammatory gingival tissue reactions.

Sulfonates: novel electron acceptors in anaerobic respiration.

The enrichment and isolation in pure culture of a bacterium, identified as a strain of Desulfovibrio, able to release and reduce the sulfur of isethionate (2-hydroxyethanesulfonate) and other sulfonates to support anaerobic respiratory growth, is described. The sulfonate moiety was the source of sulfur that served as the terminal electron acceptor, while the carbon skeleton of isethionate functioned as an accessory electron donor for the reduction of sulfite. Cysteate (alanine-3-sulfonate) and sulfoacetaldehyde (acetaldehyde-2-sulfonate) could also be used for anaerobic respiration, but many other sulfonates could not. A survey of known sulfate-reducing bacteria revealed that some, but not all, strains tested could utilize the sulfur of some sulfonates as terminal electron acceptor. Isethionate-grown cells of Desulfovibrio strain IC1 reduced sulfonate-sulfur in preference to that of sulfate; however, sulfate-grown cells reduced sulfate-sulfur in preference to that of sulfonate.

Cemental tear: a risk factor in periodontal attachment loss.

The objective of this retrospective study was to evaluate the influence of cemental tear as a risk factor in periodontal attachment loss. Seventeen extracted, single-rooted teeth showing loss of attachment and having one cemental tear surface and one opposite intact surface were examined. The teeth were stained in 0.1% toluidine blue to visualize attached periodontal ligament remnants and examined in a light microscope under incident light. On each tooth, loss of attachment was measured along the long axis of the root from the cemento-enamel junction to the most coronal level of the periodontal ligament on intact as well as on defect surfaces. Cemental tear surfaces demonstrated a significantly greater loss of attachment than opposite intact surfaces (P < 0.0001). In one specimen, the cemental tear fragment was partially attached to the root after the extraction procedure. This specimen was processed for light microscopy to determine the location of the cemental tear fracture. Histological examination clearly revealed that the split between the root and the fragment had occurred along the cemento-dentinal border. The results indicate that cemental tear should be considered as a possible etiologic entity in localized rapid periodontal breakdown.