Precision ablation of dental enamel using a subpicosecond pulsed laser.

In this study we report the use of ultra-short-pulsed near-infrared lasers for precision laser ablation of freshly extracted human teeth. The laser wavelength was approximately 800nm, with pulsewidths of 95 and 150fs, and pulse repetition rates of 1kHz. The laser beam was focused to an approximate diameter of 50microm and was scanned over the tooth surface. The rise in the intrapulpal temperature was monitored by embedded thermocouples, and was shown to remain below 5 degrees C when the tooth was air-cooled during laser treatment. The surface preparation of the ablated teeth, observed by optical and electron microscopy, showed no apparent cracking or heat effects, and the hardness and Raman spectra of the laser-treated enamel were not distinguishable from those of native enamel. This study indicates the potential for ultra-short-pulsed lasers to effect precision ablation of dental enamel.

Evaluation of postural stability in workers exposed to lead at a secondary lead smelter.

Postural sway testing was carried out on a group of 145 workers exposed to lead in a secondary lead smelter and 84 workers not exposed to lead in a hinge manufacturing plant. All workers were measured for blood lead levels (BLL) and erythrocyte zinc protoporphyrin (ZPP) concentrations at the time of testing and both a total cumulative and a time-weighted average BLL value was constructed for the lead exposed workers. The lead exposed workers mean BLL at the time of testing was 38.9 microg/dl and the non-exposed workers mean was 2.3 microg/dl. ZPP levels averaged 55.2 microg/dl for exposed workers and 18.9 microg/dl for non-exposed workers. Total cumulative BLL averaged 83476 microg/dl days for the exposed workers, with a mean time-weighted average BLL of 35.1 microg/dl. Six tests of postural stability, four two leg conditions and two single leg conditions were administered to all subjects using a force platform to produce measurements of sway for comparison purposes. The two leg conditions also manipulated the visual and proprioceptive systems. A statistically significant association was observed for sway measurements and the current BLL for all workers, but not with the current BLL of only the lead exposed workers. No statistically significant associations were present with the cumulative measures of long-term exposure. Of the six tests of sway, only the single leg conditions showed significant exposure effects. The results suggest effects of lead exposure among those with average BLL near 40.0 microg/dl, but only in the most challenging one leg conditions.

The effect of back belt use on isometric lifting force and fatigue of the lumbar paraspinal muscles.

STUDY DESIGN: A repeated measures multivariate design to assess the effect of back belts on isometric lifting force and lumbar paraspinal muscle fatigue. OBJECTIVE: To determine the efficacy of lumbar back belts in minimizing a loss in isometric force production and fatigue of lumbar paraspinal muscles. SUMMARY OF BACKGROUND DATA: Increased prevalence of back belts in industry and lack of scientific evidence supporting them suggested additional research was needed. There has been no conclusive research to substantiate manufacturer claims that use of belts reduces fatigue of lumbar paraspinals. METHODS: Twenty-four subjects, 13 men and 11 women, were tested twice: once with and once without a belt. All subjects performed a dynamic lifting task at a rate of 10 lifts per minute for 20 minutes. Surface electromyograms from the lumbar paraspinals and isometric force measurements were recorded during a static maximal isometric lift at 0, 10, and 20 minutes. Load during the dynamic task was determined as 20% of initial maximum isometric force. Electromyographic data were used to detect changes in median power spectral frequencies. Muscular fatigue was indicated by a reduction in median power spectral frequency values or a decrease in isometric force-generating capacity. RESULTS: Multivariate and univariate analyses suggest that there is no effect on lumbar paraspinal muscle fatigue or isometric lifting force production as a result of back belt use. CONCLUSIONS: These findings do not support the use of back belts for the purpose of minimizing either lumbar paraspinal muscle fatigue or a loss in isometric lifting force production.

Evaluation of tremor in aluminum production workers.

A cross-sectional study of 63 current and former aluminum potroom workers and 37 comparison workers was conducted to evaluate for evidence of neurological dysfunction, including tremor from long-term exposures to aluminum using sensitive quantitative measures of arm/hand and leg tremor. Signs of upper extremity tremor were also evaluated by neurological examination and compared with the quantitative measures of arm/hand tremor. Both arm/hand and leg tremor were measured using fatiguing test conditions, but no statistically significant differences due to exposure to aluminum were present between the potroom workers and the comparison workers. The neurological examination also showed no statistically significant differences between the groups on the evaluation of signs of tremor. These results do not support the findings of Best-Pettersen et al., who reported evidence of increased tremor in aluminum workers using the static steadiness test in the Halstead-Reitan battery. Differences between the studies that may have contributed to the contrasting results are discussed. In addition, techniques are presented for using microcomputer-controlled devices to evaluate tremor in both the visible (1-6 Hz) and nonvisible (7-18 Hz) frequencies of the tremor spectrum.

Pathogenesis of tuberculosis: pathway to apical localization.

We have examined the published work of investigators which dealt with the pathogenesis of tuberculosis, especially the following: the infective dose, the yield of bacilli from the primary lesion and primary complex, the predominant location of the minimal lesion, the hypotheses of a vulnerable region in the lung and the specific pathways (endogenous or exogenous) by which tubercle bacilli cause disease. More knowledge of the pathogenic pathway to tuberculosis would provide clues to the development of new vaccines and drug regimens that can intervene at a specific stage in the pathogenesis. Based on the examination of the literature on pathogenesis of human tuberculosis and our findings in a guinea-pig model of experimental airborne tuberculosis, we have proposed an hypothesis which integrates the endogenous and exogenous pathways to tuberculosis. This hypothesis is based on the following observations: 1. The infectious dose is very low, usually 1-5 tubercle bacilli. 2. The first implant can occur anywhere in the lungs. 3. The cavitary lesion, characteristic of tuberculous disease, is often located in the apical regions in the lungs. 4. Whereas the primary implant can occur anywhere in the lungs, for the progression from infection to disease, the tubercle bacilli must gain access to the 'vulnerable' regions in the apex of the lungs. Our hypothesis states that in areas of the world where there is a low risk of infection with tubercle bacilli low incidence of vaccination or sensitization to environmental mycobacteria, or high incidence of high virulent isolates, the virulent tubercle bacilli reach the vulnerable region via a bacillemia during the first infection. In areas of the world where there is a high risk of infection with tubercle bacilli, high incidence of vaccination or sensitization to environmental mycobacteria or a high incidence of low virulent isolates, the tubercle bacilli reach the vulnerable region via the airway, which requires repeated episodes of infection as the probability of a first implant occurring in the vulnerable regions is low.

The depressed office patient.

Depression is among the most common illnesses seen by the family physician. Untreated, it produces considerable morbidity and occasional mortality. By carefully listening not only to what the patient says, but how he says it, the physician gains valuable diagnostic information. Medication should be tailored to the patient's symptoms and medical background. An adequate dosage must be employed for several weeks to obtain a clinical response. Maintenance therapy is usually needed for six to 12 months.

Differential clearance of plutonium and americium oxides from the human lung.

External X- and gamma-ray counting techniques have been used to study the retention of 238PuO2 and 241AmO2 in the lungs of a worker between 7 and 869 days after simultaneous exposure to aerosols of both oxides. From these data and measurements of early faecal excretion, it is concluded that approx. 50% of the amount of each nuclide initially deposited in the subject was removed during the first few days by ciliary clearance mechanisms. The lung clearance patterns of the other 50% differed for the two nuclides. The 238Pu was apparently cleared with a biological half-life of approximately 800 days, predominantly by systemic or lymphatic uptake, with at least part of the translocated material being subsequently deposited in bone. There was no evidence for the presence of a 30-day component of lung clearance, such as has been suggested elsewhere. In contrast, most of the residual 241Am was cleared relatively quickly, with a half-life of approximately 11 days, although a small proportion was apparently subject to long-term retention, with a half-life of approximately 900 days. The data for both oxides conflict in important respects with the patterns of lung clearance postulated by the ICRP.