No abstract

IN THE PAST couple of decades a variety of studies dealing with pain thresholds have been reported. Some of these studies have been concerned with thermal-pain thresholds, others with electrical-or pressurepain thresholds. Some investigators have used uninstructed and naive subjects, while others have used subjects who were both sophisticated and specifically instructed. Except for a series of studies (5) in which a small number (three) of highly sophisticated and instructed subjects was used, the most striking finding in these various studies has been the marked individual differences in thresholds obtained under identical instructions and conditions of stimulation. The present study aims to throw some light on the source of these individual differences.The problem is approached by comparing the reactions of the same subjects to three different types of noxious stimulation: heat, electric current, and pressure. Two aspects of the response to painful stimulation are studied: pain threshold and tolerance level. The latter term refers to the maximum intensity of the noxious stimulation to which the subject is willing to expose himself. It was hoped that comparison of these two measures under three types of pain stimulation would clarify the nature of the observed individual differences. METHOD SubjectsThe Ss were 46 normal adult males who had volunteered for service in the Canadian Army. All Ss had completed at least 7 years of schooling; they ranged in age from 17 to 30 years. ApparatusThe apparatus consisted of three stimulators, each designed to deliver to S's arm controllable noxious intensities of electric current, pressure, or radiant heat.Electric stimulator. The voltage for stimulation was obtained from the 110-voIt, 60-cycIe power line through a variac and a step-up transformer, the output of which could be varied between 0 and 4500 volts. The current through S was limited by a series resistance of 1.5 megohms. As the resistance of S was negligible in comparison with 1.5 megohms, a close approximation to the current passing through S is given 1 This research was supported by a grant to Professor D. O. Hebb from Foundations Fund for Research in Psychiatry.

Acid-softened bovine enamel slabs were mounted in acrylic mandibular removable appliances and worn by 8 male subjects. Control slabs were worn for 4 days without exposure to topical fluoride agents. The test slabs were brushed 4 times a day for 3 days with a 0.24% NaF dentifrice or rinsed 4 times a day for 3 days with a 0.02% APF mouthrinse and worn a 4th day without exposure to the fluoride agent. Microhardness values for both groups of test slabs were significantly higher than controls following intraoral exposure and after in vitro exposure to acid. The uptake of fluoride by both mouthrinse- and dentifrice-treated slabs was significantly higher than the controls.

Fiber dimension and concentration may vary substantially between two necropsy populations of former chrysotile miners and millers of Thetford-Mines and Asbestos regions. This possibility could explain, at least in part, the higher incidence of respiratory diseases among workers from Thetford-Mines than among workers from the Asbestos region. The authors used a transmission electron microscope, equipped with an x-ray energy-dispersive spectrometer, to analyze lung mineral fibers of 86 subjects from the two mining regions and to classify fiber sizes into three categories. The most consistent difference was the higher concentration of tremolite in lung tissues of workers from Thetford-Mines, compared with workers from the Asbestos region. Amosite and crocidolite were also detected in lung tissues of several workers from the Asbestos region. No consistent and biologically important difference was found for fiber dimension; therefore, fiber dimension does not seem to be a factor that accounts for the difference in incidence of respiratory diseases between the two groups. The greater incidence of respiratory diseases among workers of Thetford-Mines can be explained by the fact that they had greater exposure to fibers than did workers at the Asbestos region. Among the mineral fibers studied, retention of tremolite fibers was most apparent.

The purpose of this investigation was to study the intra-oral rehardening of acid-softened enamel and fluoride uptake from SnF2 gel. Bovine enamel slabs were softened with 0.1 mol/L lactate buffer at pH 4.0 for 14 hrs and then mounted in a mandibular removable Hawley appliance. Control slabs were worn for 96 hrs by seven adult males whose teeth were brushed daily with a fluoride-free dentifrice. Test slabs were exposed once/day to 0.4% SnF2 gel. The gel was swabbed onto the slabs for one minute before being replaced in the mouth unrinsed. The natural dentition was brushed 4 X /day with a fluoride-free dentifrice. Microhardness testing was performed after intra-oral exposure (IOE) and after acid-resistance-testing (ART) following immersion in 0.01 mol/L lactate buffer for 24 hrs at pH of 4.0. Fluoride uptake was measured on separate controls, test slabs, and test slabs after ART, with 0.5 mol/L HClO4 etches of from 15 to 60 sec. The F content was measured with a F-ion-specific electrode and the phosphate content by spectrophotometry. Following IOE, microhardness recovery was 35.6% for control and 37.9% for test slabs, and control slabs retained 1.4% resistance to acid, as compared with 18.6% for the test slabs. The F content of control slabs was significantly less than that of SnF2-treated slabs from 5 to 60 micron in depth, and the F content of SnF2-treated slabs after ART was significantly less at depths of from 5 to 35 micron than that of SnF2-treated slabs not exposed to ART. Both control and SnF2 enamel slabs demonstrated rehardening after IOE, but only SnF2-treated enamel retained a significant fraction of that rehardening after ART.