Radiopacity of dental materials using a digital X-ray system.

OBJECTIVES: Radiopacity is a desirable property for most intra-oral materials. There are established ISO and ANSI/ADA protocols for determining radiopacity using film-based radiography. However, these methods are not always followed by researchers. This study aims to adapt those procedures by using digital radiography, a simplified stepwedge, and examine the effects of target distance and exposure time choice. METHODS: One millimetre thick samples of three dental materials were prepared by placing the materials into a 1.00 mm thick washer sandwiched between two glass slides. The samples were digitally radiographed alongside a stepwedge of aluminum alloy 1100 with an X-ray unit at 70 kVp using five different target distance/exposure time combinations. For each combination, the grey scale values of various thicknesses of the stepwedge were converted into absorbencies and plotted against their thickness. These plots were then linearly regressed in order to correlate absorbance with a thickness of aluminum for each target distance/exposure time combination. The absorbencies of each sample were then converted into radiopacities using these correlations. RESULTS: The correlations between the absorbance of the stepwedge and its thickness were highly linear. This linearity allows the correlation to be accurately deduced from fewer data points than required by the ISO and ANSI/ADA protocols. Varying exposure time did not significantly affect the mean radiopacity measured at a target distance of 30 cm. Varying the target distance did not significantly affect the measured radiopacity as long as the samples were properly exposed. SIGNIFICANCE: A simplified, consistent digital method for determining radiopacity is presented.     

Effects of the anticholinesterase edrophonium on spectral analysis of heart rate and blood pressure variability in humans.

Edrophonium, an anticholinesterase, exerts a biphasic effect on cardiovascular autonomic drive in humans (lower doses enhance; higher doses reduce). Twenty-five anesthetized, mechanically respired (10 breaths. min(-1), constant tidal volume) patients were given either saline (n = 10) or edrophonium (0.01-1.0 mg. kg(-1), n = 15) following surgery. ECG, radial arterial pressure, and respiratory rate were sampled at 250 Hz to obtain time series for consecutive R-R intervals (RRIs), and systolic (SBP) and diastolic blood pressure (DBP). A Wigner distribution was used for time frequency mapping of spectral powers at high (HFP, 0.15-0.5 Hz) and low (LFP, 0.0-0.05 Hz) frequency. Edrophonium produced a dose-dependent decrease in heart rate [baseline 66.8 +/- 1.9 (S.E.M.) beats per minute; maximum decrease to 55.8 +/- 1.4 beats per minute with 1.0 mg. kg(-1), P < 0.01]. HFP of the RRI increased at low doses (0.2-0.4 mg. kg(-1); maximum increase to 111.0 +/- 58.2% baseline; P < 0.01) but decreased (-49.5 +/- 35.5% baseline; P < 0.01) at higher (1.0 mg. kg(-1)) doses. Edrophonium had no effect on SBP and DBP. HFP of SBP decreased with increasing doses (maximal decrease to -26.2 +/- 7.5% baseline, P < 0.01, 1.0 mg. kg(-1)). LFP of SBP was also decreased (-46.3 +/- 10.9% baseline, P < 0.01, 1.0 mg. kg(-1)). Edrophonium may enhance (lower dose) or reduce (higher dose) cardiovascular autonomic drive in humans, as evidenced by the significant changes it evokes in HFP of the RRI (parasympathetic drive), and in the HFP and LFP of SBP (sympathetic drive). These observations may account for the modest autonomic side effects of edrophonium when this drug is used clinically.     

Halothane Suppression of Spinal Sensory Neuronal Responses to Noxious Peripheral Stimuli Is Mediated, in Part, by Both GABAA and Glycine Receptor Systems

Background: A major effect of general anesthesia is lack of response in the presence of a noxious stimulus. Anesthetic depression of spinal sensory neuronal responses to noxious stimuli is likely to contribute to that essential general anesthetic action. The authors tested the hypothesis that [gamma]-aminobutyric acid receptor type A (GABAA) and strychnine-sensitive glycine receptor systems mediate halothane depression of spinal sensory neuronal responses to noxious stimuli.

Methods: Extracellular activity of single spinal dorsal horn wide dynamic range (WDR) neurons was recorded in decerebrate, spinal cord transected rats. Neuronal responses to noxious (thermal and mechanical) and nonnoxious stimuli were examined in the drug-free state. Subsequently, cumulative doses (0.1-2.0 mg/kg) of bicuculline (GABAA antagonist) or strychnine (glycine antagonist) were administered intravenously in the absence or presence of 1 minimum alveolar concentration (MAC) of halothane.

Results: Halothane, 1.1%, depressed the response of WDR neurons to both forms of noxious stimuli. Antagonists, by themselves, had no effect on noxiously evoked activity. However, bicuculline and strychnine (maximum cumulative dose, 2.0 mg/kg) partially but significantly reversed the halothane depression of noxiously evoked activity. Similar results were seen with most, but not all, forms of nonnoxiously evoked activity. In the absence of halothane, strychnine significantly increased neuronal responses to low threshold receptive field brushing.     

Challenges in geriatric oral health research methodology concerning caregivers of cognitively impaired elderly adults

Little is known about oral health care behaviors of community-dwelling, cognitively impaired elderly (CIE) persons. Few studies have been conducted regarding the actual provision of oral care for CIE persons or the attitudes and concerns about oral health among their caregivers. The CIE person's ability to perform self-care decreases over time, and the role of the caregiver in daily oral care becomes increasingly important. The purpose of this pilot study was to explore the attitudes toward oral health and identify related concerns among caregivers who care for community-dwelling CIE persons. Caregivers were surveyed by means of a self-administered, mailed questionnaire. To maintain confidentiality, an intermediary was used for recruitment and data collection. Overall, 148 caregivers were invited by an intermediary to participate in the survey; only 21 (14%) consented to participate and returned the questionnaire. This paper discusses some of the numerous methodological challenges identified when an attempt was made to survey caregivers' attitudes toward and barriers to providing oral care for a dependent CIE.     

Acute Sinusitis in the Rabbit: A New Rhinogenic Model

The objective of this study was to create a rhinogenic model of sinusitis using an implanted foreign body in the nasal cavity of the rabbit. The study design was a prospective controlled trial of the experimental design. In this model an obstructing foreign body was placed into the nasal cavity and then impregnated with pathogenic bacteria. This model was studied histologically using wholemount techniques. Quantitative assessment of the degree of inflammation was made for the maxillary and ethmoid sinus and for overall effect for each animal. Bacteriologic study was performed in a limited number of animals. The results indicated that a significant infection develops in about half of animals. This peaks in intensity between 1 and 2 weeks after implantation and subsequently subsides with some evidence of long-term changes present after 4 weeks. It is concluded that this is a viable and perhaps preferable animal model to study sinusitis. Further investigation is necessary to completely characterize this model.     

Reevaluating the carcinogenicity of ortho-toluidine: A new conclusion and its implications

The aromatic amine ortho-toluidine has been recognized by IARC as an animal carcinogen for the past decade. Three recent epidemiological studies of worker populations have now implicated this chemical as a human bladder carcinogen. In a study by E. Ward, A. Carpenter, S. Markowitz, D. Roberts, and W. Halperin ((1991), J. Natl. Cancer Inst. 83, 501–506), workers definitely exposed to ortho-toluidine for at least 10 years experienced a Standardized Incidence Ratio (SIR) of 27.2 (90% CI = 11.8–53.7). The other major exposure was to aniline, which significant epidemiological studies have failed to confirm as a human carcinogen. In retrospect, studies by G. F. Rubino, G. Scansetti, G. Piolatto ((1982) Environ. Res. 27, 241–254) and M. J. Stasik ((1988) Int. Arch. Occup. Environ. Health 60, 21–24) also support the hypothesis that ortho-toluidine is a human bladder carcinogen. Animal studies of both ortho-toluidine and its possible confounders in these epidemiological investigations further confirm this hypothesis. When evaluated in a suitably comprehensive way, according to the traditional standards for assessing causality outlined by A. B. Hill ((1977) A Short Textbook of Medical Statistics, pp. 288–294, Lippincott, Philadelphia) the evidence that ortho-toluidine causes human bladder cancer has become much more conclusive. In this case, animal tests have proven a good predictor of human carcinogenicity.