Reduced ammonia emissions from slurry after self-acidification with organic supplements.

Ammonia volatilisation from field applied slurries causes environmental hazards and loss of fertilizer value. Acidification of slurry, usually with inorganic or organic acids has previously been used to reduce NH3 emissions. In this study, we present an alternative technique for the acidification of slurry, namely the use of fermentation by endogenous microbes to form organic acids from readily degradable organic compounds. In laboratory experiments, the addition of different sugars (sucrose in dosages of 0.003, 0.01, 0.03, 0.1 and 0.3 mol l(-1), glucose in dosages of 0.05 and 0.1 mol l(-1)) and organic residues (sugar beet residues in dosages of 33 and 330 g fresh weight l(-1), biowaste at 50 g fresh weight l(-1)) to cattle slurry resulted in a considerable decrease in pH, with a minimum pH of 4.7. A subsequent pH increase indicated that the organic acids were probably further degraded with a resultant loss of acidity in the slurry. In a field study, the NH3 emissions from untreated and acidified (pH = 6) slurries were compared after field application (20 m3 ha(-1)). During the first 20 hours, the acidified slurry showed NH3 emissions of less than 5% of the applied ammonia compared to a 26% loss from the untreated slurry. The total emissions of NH4+-N were 32% for acidified and 54% for untreated slurry. Easily degradable organic amendments therefore have the potential to effectively reduce NH3 emissions from slurries and may be an alternative for the use of acids.

Comparison of observer performance in determining the position of endodontic files with physical measures in the evaluation of dental X-ray imaging systems.

OBJECTIVE: To examine the feasibility of substituting observers determining the accuracy of endodontic measurements for measurements of physical qualities in comparison of digital imaging systems. METHODS: Sensors from six digital imaging systems were compared for signal-to-noise ratio (SNR), modulation transfer function (MTF) and detective quantum efficiency (DQE). A total of 45 canals in teeth from human cadavers were instrumented to their apical foramina. Endodontic files, ranging in size from size 8 to size 20, were glued in place at random distances from the apical foramina spanning a range of +/- 3 mm. The teeth were imaged with the six digital systems and dental X-ray film. Fifteen dentists independently measured the distance from the end of the file to the apical foramen. Results were expressed as the measurement error. Measurement error was compared to SNR, MTF and DQE for each digital system. RESULTS: CDR (Schick, New York, NY, USA), Digora (Sordex, Helsinki, Finland) and Dexis (Provision Dental Systems, Palo Alto, CA, USA) produced the highest SNR values followed closely by RVG-4 (Trophy, Croissy-Beavborg, France). Sens-A-Ray (Dent-X/Regam Medical Systems, Sundsvall, Sweden), Dexis and the RVG-4 produced the best MTF results. Dexis had the greatest DQE. The mean measurement errors (in mm) were: Film 0.65, Dexis 0.69, CDR 0.71, RVG-4 0.74, Digora 0.89, Sens-A-Ray 0.97, and Visualix-2 (Gendex, Monza, Italy) 0.98. CONCLUSIONS: Digital systems closely approximate film in their accuracy when used for endodontic measurement providing that the assessment instruments have similar resolving power. DQE was the best physical predictor of system accuracy when compared with endodontic length measurements. MTF and SNR alone did not accurately predict observer precision.

Comparison of digital dental X-ray systems with self-developing film and manual processing for endodontic file length determination.

Human skulls were sectioned into 15 sextants. Teeth were then removed and 45 canals were instrumented to their apical foramina. Endodontic files were glued in place at random distances from the apical foramina. Image geometry was maintained by a custom mounting jig. Images were captured with self-developing film, manually processed D-speed film, and a digital radiographic system (Dexis). Digital images were read on a conventional color monitor (cathode ray tube) and a laptop screen (active-matrix liquid crystal display). Fifteen dentists measured the distance from the file tip to the apical foramen of the tooth. Results showed that the measurement error was significantly less for the digital images than for the film-based images. It is likely that these statistical differences may not be of great clinical significance because the digital images could be measured in increments < 0.25 mm.

Subtraction radiography of dentinal caries-like lesions induced in vitro by cariogenic bacteria.

PURPOSE: The objective of this project was to develop an in vitro model system for investigations of dentinal caries. METHODS: Five extracted primary molar teeth with circular cavity preparations to the depth of the dentinoenamel junction were mounted individually in cold-cure acrylic bases constructed to fit a positioning jig in a Schick-Technologies digital radiographic imaging apparatus. The mounted teeth (MT) were incubated with pure cultures of Streptococcus mutans for 7 days and Lactobacillus casei for 38 days. At baseline and on day 23 and 45, four digital radiographs of each MT were made. Subtraction radiography was performed and analyzed using custom interactive software. RESULTS: Lesions progressed roughly halfway through the dentin in all teeth at 23 days and approximated the pulp chambers at 45 days of incubation. Images resulting from subtraction procedures clearly revealed incremental caries progression which could be quantitated. CONCLUSION: The model may be useful for screening cariostatic dental materials or treatments and investigating microbial mechanisms in dentinal caries.

Accuracy of orthognathic evaluation using telemedicine technology.

OBJECTIVE: Telemedicine technology has the ability to project highly specialized medical and dental expertise anywhere in the world. This is particularly important to many small, isolated communities that do not have access to medical and dental specialists. Telemedicine also has the potential to reduce unnecessary travel, time away from work, and unneeded hospital admissions. For this technology to be successful, however, clinicians need to have confidence in its capabilities. This study was conducted to determine the accuracy of an orthognathic evaluation using telemedicine. MATERIALS AND METHODS: Thirteen patients were randomly selected for review by two surgeons each using telemedicine and clinical examinations. Clinically acceptable differences were established, and the results of the two examination methods were compared. RESULTS: A main effect of the examination method was observed in 7 of the 18 continuous measurements taken. Examination of the absolute value of the within-subject difference between the two examination methods demonstrated that the mean absolute difference was statistically different from zero for 13 of 18 measurements taken. CONCLUSIONS: These data demonstrate that a relatively accurate orthognathic examination can be performed with this technology. With this in mind, clinicians may feel comfortable using this technology for other clinical applications.

Use of the hand-held dental X-ray machine during joint operation, NATO exercise Display Determination-92.

The hand-held dental X-ray machine is a 30-pound, battery-powered X-ray machine capable of use in military medicine, humanitarian missions, and training exercises. The machine was developed for dental radiology, but with the attachment of a medical collimator, the equipment can also be used for medical exams. In 1992, the machine was tested under field conditions in a NATO joint exercise in Bolayir, Turkey. The hand-held dental X-ray machine was found easier to use than the currently deployed Siemens dental X-ray unit and than produced radiographs of equal quality.

Future trends in dental radiology.

Direct digital dental radiographic systems offer the potential to radically change the way dentists diagnose and treat dental pathoses. They offer instantaneous availability of radiographs, markedly lower patient radiation exposure, and the elimination of developing chemicals and developing equipment. The storage of dental radiographs as digital data permits their transmittal over phone lines facilitating phone consultations and may someday allow expedited authorization of treatment plans by dental insurance companies. With the use of digital subtraction radiology the dental practitioner will be able to diagnose periodontal disease progression and dental caries progression long before current techniques can detect a change. With tuned aperture computed tomography, the owner of a filmless digital system can make tomographic radiographs that allow the visualization of slices through areas of interest without having to buy additional hardware. Computer-aided diagnosis will facilitate the detection of proximal dental caries and osteoporosis, and may someday allow automated tracing of cephalometric radiographs.

Electromagnetic pulse (EMP), Part II: Field-expedient ways to minimize its effects on field medical treatment facilities.

Part I of this paper showed that a field commander can expect approximately 65% of his unprotected electronic medical equipment to be damaged by the electromagnetic pulse (EMP) from a single nuclear detonation as far as 2200 km away. Using computer modeling, field-expedient ways to minimize the effects of EMP were studied. The results were: (1) keep wiring near the ground, (2) keep wiring short, (3) unplug unused equipment, (4) run power cabling and tents in a magnetic north-south direction (avoid running power cabling in the east-west direction), and (5) place sensitive equipment in International Organization for Standardization shelters.

Electromagnetic pulse (EMP), Part I: Effects on field medical equipment.

The electromagnetic pulse (EMP) from a high-altitude nuclear detonation has the potential to cover an area as large as the continental United States with damaging levels of EMP radiation. In this study, two of seven items of medical equipment were damaged by an EMP simulator. Computer circuit analysis of 17 different items showed that 11 of the 17 items would be damaged by current surges on the power cords, while two would be damaged by current surges on external leads. This research showed that a field commander can expect approximately 65% of his electronic medical equipment to be damaged by a single nuclear detonation as far as 2,200 km away.

The effect of patient movement on resolution.

The effect of long exposure time on patient movement and resulting radiographic resolution was simulated and then measured by visual-light photographic techniques for four radiographic projections. A mathematic relation was then derived to transform these measurements to the maximum resolutions that could have been obtained with radiographs under similar conditions. The results indicate that radiographs of rigid structures such as bones and teeth can be taken with reasonable resolution at exposure times much longer than normally used in clinical practice. It was also found that radiographs taken with the film rigidly fixed to the object being studied will exhibit remarkably less blurring from patient motion than radiographs taken when the patient and the film are not coupled. In addition it was found that motion artifacts are reduced to a minimum when the plane of the film is perpendicular to the radiation beam.

Exposure reduction of 96% in intraoral radiography.

This study compared the diagnostic quality of E-speed film, xeroradiographic cassettes, and a screen-film imaging system used in medical radiology. The surfaces of defects simulating caries were scored for the presence and depth of the defects under ideal viewing conditions by independent observers. Receiver Operator Characteristics analysis of the data showed no significant differences regarding diagnostic potential among the three systems. The true-positive fraction was 1.00 for all systems and all operators, and the false-positive fraction was .011, .011, and .007, respectively. An exposure of 5.5 mR was used to produce images with the screen-film combination, and 150 mR was used for standard dental systems. This study showed that an exposure reduction of 96% is possible while maintaining high-quality radiographs for the diagnosis of caries.