Comparison of measured and simulated concentrations of 133Xe in the shallow subsurface.

Radioactive isotopes of the noble gases xenon and argon are considered primary indicators of an underground nuclear explosion. However, high atmospheric concentrations from other anthropogenic sources may lead to an elevation in the underground levels of these gases, particularly in times of increasing atmospheric pressure. In 2014, a week long sampling campaign near Canadian Nuclear Laboratories in the Ottawa River Valley resulted in first of their kind measurements of atmospheric 133Xe that had been pressed into the subsurface. In an effort to better understand this imprinting process, a second follow-up sampling campaign was conducted in the same location in 2016. The results of the second sampling campaign, where samples were collected at depths of 1 m and 2 m over a 14 day period and measured for their 133Xe concentration, are presented here. Gas transport and sample concentrations were predicted using the Subsurface Transport over Multiple Phases (STOMP) simulator. These results are examined and compared to the corresponding experimental results.

Xenon adsorption on geological media and implications for radionuclide signatures.

The detection of radioactive noble gases is a primary technology for verifying compliance with the pending Comprehensive Nuclear-Test-Ban Treaty. A fundamental challenge in applying this technology for detecting underground nuclear explosions is estimating the timing and magnitude of the radionuclide signatures. While the primary mechanism for transport is advective transport, either through barometric pumping or thermally driven advection, diffusive transport in the surrounding matrix also plays a secondary role. From the study of primordial noble gas signatures, it is known that xenon has a strong physical adsorption affinity in shale formations. Given the unselective nature of physical adsorption, isotherm measurements reported here show that non-trivial amounts of xenon adsorb on a variety of media, in addition to shale. A dual-porosity model is then discussed demonstrating that sorption amplifies the diffusive uptake of an adsorbing matrix from a fracture. This effect may reduce the radioxenon signature down to approximately one-tenth, similar to primordial xenon isotopic signatures.

The potential detection of low-level aerosol isotopes from new civilian nuclear processes.

As the world faces a challenging future in maintaining the commercial availability of radioactive isotopes for medical use, new methods of medical isotope production are being pursued. Many of these are small in size and could effectively operate continuously. With the potential for much shorter retention times, a new suite of isotopes may soon be found in the environment. The authors estimate that many more aerosols containing low-level isotopes of gas/volatile origin could be detectable at short range and times, and a few at longer ranges and times as compared to those released in more common nuclear reactor operations.

Drug therapy during pregnancy: implications for dental practice.

Pregnancy is accompanied by various physiological and physical changes, including those found in the cardiovascular, respiratory, gastrointestinal, renal and haematological systems. These alterations in the pregnant patient may potentially affect drug pharmacokinetics. Also, pharmacotherapy presents a unique matter due to the potential teratogenic effects of certain drugs. Although medications prescribed by dentists are generally safe during pregnancy, some modifications may be needed. In this article we will discuss the changes in the physiology during pregnancy and its impact on drug therapy. Specific emphasis will be given to the drugs commonly given by dentists, namely, local anaesthetics, analgesics, antibiotics and sedatives.

Development of a low-level (37)Ar calibration standard.

Argon-37 is an environmental signature of an underground nuclear explosion. Producing and quantifying low-level (37)Ar standards is an important step in the development of sensitive field measurement instruments. This paper describes progress at Pacific Northwest National Laboratory in developing a process to generate and quantify low-level (37)Ar standards, which can be used to calibrate sensitive field systems at activities consistent with soil background levels. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.

Source term estimation of radioxenon released from the Fukushima Dai-ichi nuclear reactors using measured air concentrations and atmospheric transport modeling.

Systems designed to monitor airborne radionuclides released from underground nuclear explosions detected radioactive fallout across the northern hemisphere resulting from the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Sampling data from multiple International Modeling System locations are combined with atmospheric transport modeling to estimate the magnitude and time sequence of releases of (133)Xe. Modeled dilution factors at five different detection locations were combined with 57 atmospheric concentration measurements of (133)Xe taken from March 18 to March 23 to estimate the source term. This analysis suggests that 92% of the 1.24 × 10(19) Bq of (133)Xe present in the three operating reactors at the time of the earthquake was released to the atmosphere over a 3 d period. An uncertainty analysis bounds the release estimates to 54-129% of available (133)Xe inventory.

Analysis of data from sensitive U.S. monitoring stations for the Fukushima Dai-ichi nuclear reactor accident.

The March 11, 2011 9.0 magnitude undersea megathrust earthquake off the coast of Japan and subsequent tsunami waves triggered a major nuclear event at the Fukushima Dai-ichi nuclear power station. At the time of the event, units 1, 2, and 3 were operating and units 4, 5, and 6 were in a shutdown condition for maintenance. Loss of cooling capacity to the plants along with structural damage caused by the earthquake and tsunami resulted in a breach of the nuclear fuel integrity and release of radioactive fission products to the environment. Fission products started to arrive in the United States via atmospheric transport on March 15, 2011 and peaked by March 23, 2011. Atmospheric activity concentrations of (131)I reached levels of 3.0×10(-2) Bqm(-3) in Melbourne, FL. The noble gas (133)Xe reached atmospheric activity concentrations in Ashland, KS of 17 Bqm(-3). While these levels are not health concerns, they were well above the detection capability of the radionuclide monitoring systems within the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty.

Effect of PaCO2 and PaO2 on lidocaine and articaine toxicity.

Alterations in arterial PaCO2 can influence local anesthetic toxicity. The objective of this study was to evaluate the effect of stress-induced changes in PaCO2 and PaO2 on the seizure threshold of lidocaine and articaine. Lidocaine (2% with 1 : 100,000 epinephrine) or articaine (4% with 1 : 100,000 epinephrine) was administered intravenously under rest or stress conditions to 36 rats separated into 4 groups. Propranolol and prazosin were administered preoperatively to minimize cardiovascular effects of epinephrine. Mean arterial pressure (MAP), heart rate (HR), and arterial pH, PaCO2, and PaO2 were measured. Results showed no differences in MAP, HR, or pH. Stress significantly increased the latency period for the first tonic-clonic seizure induced by a toxic dose of both lidocaine and articaine (P < .05). Seizures were brought on more rapidly by articaine. No significant difference between toxic doses of lidocaine and articaine was noted. Stress raised the seizure threshold dose for both drugs and significantly (P < .01) increased arterial PaO2 from 94.0 ± 1.90 mm Hg to 113.0 ± 2.20 mm Hg, and reduced PaCO2 from 36.0 ± 0.77 mm Hg to 27.0 ± 0.98 mm Hg. In conclusion, reduction in PaCO2 and/or increase in PaO2 raised the seizure threshold of lidocaine and articaine. This study also confirmed that lidocaine and articaine have equipotent central nervous system toxicity.

Need and demand for sedation or general anesthesia in dentistry: a national survey of the Canadian population.

The aim of this study was to assess the need and demand for sedation or general anesthesia (GA) for dentistry in the Canadian adult population. A national telephone survey of 1101 Canadians found that 9.8% were somewhat afraid of dental treatment, with another 5.5% having a high level of fear. Fear or anxiety was the reason why 7.6% had ever missed, cancelled, or avoided a dental appointment. Of those with high fear, 49.2% had avoided a dental appointment at some point because of fear or anxiety as opposed to only 5.2% from the no or low fear group. Regarding demand, 12.4% were definitely interested in sedation or GA for their dentistry and 42.3% were interested depending on cost. Of those with high fear, 31.1% were definitely interested, with 54.1% interested depending on cost. In a hypothetical situation where endodontics was required because of a severe toothache, 12.7% reported high fear. This decreased to 5.4% if sedation or GA were available. For this procedure, 20.4% were definitely interested in sedation or GA, and another 46.1% were interested depending on cost. The prevalence of, and preference for, sedation or GA was assessed for specific dental procedures. The proportion of the population with a preference for sedation or GA was 7.2% for cleaning, 18% for fillings or crowns, 54.7% for endodontics, 68.2% for periodontal surgery, and 46.5% for extraction. For each procedure, the proportion expressing a preference for sedation or GA was significantly greater than the proportion having received treatment with sedation or GA (P < 0.001). In conclusion, this study demonstrates that there is significant need and demand for sedation and GA in the Canadian adult population.

Local anesthesia does not block mustard-oil-induced temporomandibular inflammation.

UNLABELLED: Temporomandibular joint (TMJ) disorders and rheumatoid arthritis are two conditions in which neurogenic mechanisms may play a critical role. We investigated the neurogenic contribution underlying acute TMJ inflammation by evaluating effects of local anesthetic blockade of afferent innervation on the development of mustard oil (MO)-induced edema in the rat TMJ area. Groups of eight adult male Sprague-Dawley rats were anesthetized by intraperitoneal alpha-chloralose and urethane. A saline injection into the right TMJ followed by MO (1% to 60%) 6 min later elicited dose-dependent edema development (P < 0.05, repeated measures analysis of variance). Lidocaine (5%) or bupivacaine (0.5%) followed by MO (1% or 40%) did not produce edema development different from saline controls (P > 0.05, repeated measures analysis of variance). The failure of local anesthetic blockade to prevent MO-induced edema is not consistent with MO acting through a neurogenic mechanism, as traditionally perceived. IMPLICATIONS: Inflammation found in temporomandibular disorders and rheumatoid arthritis may result from mediators released by pain-sensing neurons. Local anesthesia failed to block simulated neurogenic temporomandibular inflammation in a rat model, suggesting that functional neuronal input may not be necessary for the promotion of inflammation.

Drug use for the pregnant or lactating patient.

The dental patient who is pregnant or lactating may require management involving the administration or prescription of drugs. The approach of completely avoiding all drugs may not permit appropriate treatment of the patient and most often is not warranted. This article reviews the current considerations in the use of drugs in the dental patient who is either pregnant or lactating. The safety of the local anesthetics, vasoconstrictors, analgesics, antimicrobials, and sedatives used in dentistry is discussed.

Oral and inhalation conscious sedation.

Many patients can benefit by having dental procedures carried out with conscious sedation administered by the oral or inhalation routes. Dentists who employ these techniques must be familiar with the pharmacology of the agents selected, cognizant of the risks and benefits of the technique employed, and able to manage adverse events that may arise with its use. Careful patient selection and prudent administration of one of the drugs described here is the basis for successful use of these techniques.

Adverse drug interactions in dental practice: interactions associated with analgesics, Part III in a series.

BACKGROUND: Numerous reports of drug interactions exist, yet not all are valid in or pertinent to dentistry. This article provides an overview of drug interactions with analgesics and identifies those that are clinically relevant. METHODS: The author reviewed reports of drug interactions involving nonsteroidal anti-inflammatory drugs, or NSAIDs (including aspirin), acetaminophen and opioids to determine the interactions' validity and clinical relevance. Consistent with the practice followed in other articles in this series, the author determined the significance of the proposed interaction by gauging its reported severity and the quality of the documentation. RESULTS AND CONCLUSIONS: NSAIDs should not be taken by patients taking high-dose methotrexate, anticoagulants or alcohol. They should be avoided in elderly or renally impaired patients taking digoxin, and avoided over the long term in those taking other NSAIDs. It is possible that NSAIDs should not be given to patients taking lithium, but future studies should be conducted to confirm this. Use of NSAIDs likely is appropriate in the short term with patients taking antihypertensives, unless they have severe congestive heart disease. Aspirin should not be given to patients taking oral hypoglycemics, valproic acid or carbonic anhydrase inhibitors. Acetaminophen may be given in the short term to any patient with a healthy liver, but it should not be given to a patient who has stopped drinking alcohol after chronic intake. Opioids should not be combined with alcohol, and meperidine must be avoided in the patient who has taken monoamine oxidase inhibitors in the previous 14 days. CLINICAL IMPLICATIONS: Drug interactions with analgesics are often reported, but only a small number have clinical relevance in dentistry. Awareness of the significance of these interactions will allow dentists to prescribe analgesics optimally and minimize the potential for adverse reactions.

Adverse drug interactions in dental practice. Professional and educational implications.

BACKGROUND: Rapid progress in dental pharmacotherapeutics requires that clinicians constantly update their knowledge of new drugs, drug interactions and useful therapeutic trends. This article is the first in a five-part series based on a 1998 International Association for Dental Research symposium entitled "Adverse Drug Interactions in Dentistry: Separating the Myths From the Facts." The goal of the series is to identify specific adverse drug interactions that are relevant to the therapeutic agents commonly used in general dental practice: analgesics, antibiotics, sedatives, local anesthetics and vasoconstrictors. METHODS: A group of dentist/clinical pharmacologists, with documented expertise in specific areas of dental therapeutics, reviewed the current literature regarding adverse drug interactions in dentistry. This expert panel evaluated the quality of information used to document these drug interactions and assess the severity of these drug reactions with respect to the drugs' use in dental practice. RESULTS: On the basis of the quality and severity of each reported interaction, the authors summarized the clinical importance of these drug interactions using a Significance Rating for Dental Drug Interactions. The participants presented their recommendations at the above-mentioned IADR symposium. CONCLUSIONS: Although thousands of drug interactions are described in the literature, the authors found many to be poorly documented or of minor importance to dental practitioners. For interactions that they determined to be relevant, the participants provided recommendations and precautions for preventing these potential complications. This article discusses the professional impact of drug interactions on dental practice; the classification and documentation of drug interactions; the determination of causality between drug interactions and adverse effects; risk factors; and unique characteristics of dental therapeutics. Subsequent articles will present specific summary recommendations for drug interactions associated with the use of antibiotics, analgesics, sedatives, and local anesthetics and vasoconstrictors. CLINICAL IMPLICATIONS: Although thousands of drug interactions have been reported in the literature, only a few are significantly associated with dental therapeutic agents. Avoiding these drug interactions will prevent potentially severe reactions in dental practice.

A comparison of certain practice characteristics of dental anesthesiologists in Canada and the United States.

An existing database was used to compare aspects of dental anesthesiology practice of dental anesthesiologists in Canada (n = 32) and the United States (n = 123). Data focusing on percutaneous injuries were obtained through a mailed questionnaire that was returned anonymously. Respondents provided information on the treatment of patients under deep sedation or general anesthesia only. Eighty-one percent of Canadians and 61% of Americans returned the questionnaire. The vast majority (84%) of injuries reported were due to sharps associated with general dentistry compared with those associated with anesthesiology. Canadians were more likely to be operator-anesthetists (P < .01) and to experience a percutaneous injury (P < .01) than US practitioners. American practitioners were more likely to have a greater proportion of the caseload under the age of 20 (P < .02). No other significant differences were observed. These results illustrate a number of unique attributes of the practice of dental anesthesiology in these 2 countries.

The occupational risk to dental anesthesiologists of acquiring 3 bloodborne pathogens.

OBJECTIVE: To estimate the occupational risk to dental anesthesiologists of contracting 3 bloodborne pathogens: hepatitis B (HBV), hepatitis C (HCV), and human immunodeficiency virus (HIV). METHODS: Through an anonymously returned, mailed questionnaire, dental anesthesiologists in Canada and the United States provided information regarding percutaneous and mucocutaneous contacts with contaminated fluid during the treatment of patients under deep sedation and general anesthesia as well as other general practice information. A mathematical model was applied to determine the occupational risk. RESULTS: Of the 101 (65%) returned questionnaires, 98 reported having treated patients within the previous 6 months. Of these, 41 (42%) had at least one percutaneous accident (89 accidents in total), and the projected mean annual injury rate for dental anesthesiologists overall was 1.82. The most common causes of injury were burs, intraoral needles, and dental instruments. Operator error during use was associated with 31% of reported accidents. Significantly more injuries were reported by those who also reported a mucocutaneous contact and by those working more than 25 hours per week. The projected mean annual number of mucocutaneous exposures was 0.88 for dental anesthesiologists overall. CONCLUSIONS: The calculated annual risk to the average dental anesthesiologist of acquiring HBV (if not immune), HCV, and HIV following percutaneous injury was very low for all infections (HBV the most; HIV the least). The risk of contracting HIV following mucocutaneous contact was extremely low.

Antimicrobial resistance: dentistry's role.

The resistance of bacteria, fungi and viruses to antimicrobials is increasing rapidly, with deleterious consequences. Dentistry's role in this development is unclear, because the necessary information has not yet been collected. Nevertheless, dentists should recognize that it is essential to use antimicrobials in an appropriate and responsible manner, both to treat infection effectively, and to minimize the likelihood that the bacteria in the general population will develop resistance to antimicrobials. The purpose of this article is to make dentists aware of the concerns raised by antimicrobial resistance, and how it can be avoided.

Radiographic localization of mandibular anesthesia landmarks.

The objective of this study was to assess whether bony landmarks used for the standard inferior alveolar nerve block can be used to accurately determine the position of the mandibular foramen and whether panoramic radiographs are appropriate for this purpose. A total of 11 landmarks from 79 panoramic radiographs and 70 corresponding cases of oblique (45-degree) cephalometric radiographs were examined. Ten measurements of the distance from each landmark to the mandibular foramen, as well as 6 ratios from these distances, were calculated from all radiographs. The results showed that the position of the mandibular foramen was highly individualistic and not consistently related to traditional clinical landmarks. Panoramic radiographs were as good as oblique cephalometric radiographs for the locating of the mandibular foramen. No age or gender correlations were found. It was concluded that the mandibular foramen can be localized in panoramic radiographs but that its relation to bony landmarks is highly variable.

Localized complications from local anesthesia.

The inherent safety of local anesthetics allows practitioners to use them frequently with the confidence that adverse events are rare. Nevertheless, complications can occur. The aim of this article is to briefly review the localized adverse events that may result from local anesthetic administration. Descriptions of each complication will be followed by suggestions for prevention and management. In spite of a dentist's conscientious practice, many of these complications cannot always be prevented.