Bone conduction changes following successful tympanoplasty type I

Pre and one year postoperative bone conduction (b.c.) thresholds were compared for 50 ears of 48 patients, ranging in age from 14 to 42 years, in whom successful tympanic grafts resulted in at least an average improvement of 10 db for 500 to 4000 Hz. While pre and postoperative data are included for all ears and test frequencies, significant BC improvement is seen only at those frequencies, in each case, where the pre-op BC thresholds were worse than 10 db. Normal pre-op BC thresholds cannot show substantial improvement because of audiometric limitations. The amount of BC shift at each frequency for those with pre-op BC thresholds that were subnormal averaged 6 db at 500 Hz, 13.3 db at 1000 Hz, 13.8 db at 2000 Hz and 9 db at 4000 Hz, all highly significant statistically. There were no significant postoperative BC shifts related either to duration of the disease process, length of postoperative period before final test (all were more than one year) or whether the surgical procedure was tympanoplasty type I or myringoplasty.

Potential and polarization measurements in vivo of oral galvanism

Galvanic currents within the oral cavity may have harmful effects on biological tissues. In the present work 16 patients with different kinds of oral and other discomfort and pain which they attributed to oral galvanism were investigated. The potential and polarization of each metal restoration within reach of a platinum probe were measured versus a reference electrode. A recording of these measured values permits a calculation of the currents which may pass between the teeth. A control group of patients with no subjective symptoms of galvanism in the oral cavity was also investigated. The results of the electrochemical measurements showed that conditions for oral galvanism existed within the individuals of the patient group as well as within the control group. One remarkable observation was that the metallic restorations often consisted of different electrically isolated areas with different electrochemical properties. This and other factors influencing oral galvanism are discussed.

Powder data file as a tool for identification of dental gold alloys

In order to obtain data for a prospective powder data file for dental gold alloys X-ray diffraction photograms of 75 different gold alloys were taken using a Guinier-Hägg camera and CuKalpha1 radiation. Before the X-ray photograms were taken the alloys had been heat treated at 700 degrees C, 800 degrees C or 900 degrees C depending on the solidus temperatures of the alloys. The lattice parameters of the samples were determined from the X-ray photograms. These data were supplemented by a specification of the interplanar spacings of the three strongest lines on the diffraction patterns and also by the relative intensities and Miller indices of these lines. An extensive library of reference films is to be collected and this and other details of the file are discussed. It is not intended that the file be used to identify a particular alloy but merely to identify the type of alloy. Thus it can serve as a guide to facilitate the proper selection of gold alloys within practical clinical dentistry.

Dissolution and uptake of cadmium from dental gold solder alloy implants

Pure metallic cadmium was irradiated by means of thermal neutrons. The irradiated cadmium (115Cd) was placed in bags of gold foil and the bags were implanted subcutaneously in the neck region of mice. Two and 3d respectively after implantation the mice were killed, the bags removed and the animals subjected to whole-body autoradiography. The autoradiograms revealed an uptake of 115Cd in liver and kidney. In another experiment specimens of a cadmium-containing dental gold solder alloy, a cadmium-free dental casting gold alloy and soldered assemblies made of these two alloys were implanted subcutaneously in the neck region of mice. The animals were killed after 6 months; cadmium analysis showed significant increases in the cadmium concentration in liver and kidney of those mice which had been given implants of gold solder alloy. The study clearly shows that due to electrochemical corrosion cadmium can be released from implants and accumulated in the kidneys and the liver.

Age-related decrement in hearing for speech. Sampling and longitudinal studies

A 10-year study was conducted in which 282 adults in age decades of 20 through 80 were tested in a comprehensive battery of tasks requiring the perception of speech under a variety of conditions in which the speech signal was degraded. The original results were plotted to reveal the differences in performance of the population samples of each decade. In follow-up studies, after 3 years and again after 7 years, samples of the original subject population were retested. The results of the first, stratified sampling and of the longitudinal studies are compared. The two most apparent trends are: (1) the perception of degraded (distorted and competed) speech undergoes a noticeable decline beginning with the 5th decade of life, and (2) the decline is sharply steeper in the 7th decade.

Dissolution rate of cadmium from dental gold solder alloys

The dissolution rate of cadmium from six different dental gold solder alloys was determined in an in vitro potentiostatic study. The measurements were made in the potential range 740--880 mV and attempts have been made to extrapolate the results to a potential region that might in reality occur in the oral cavity. For comparison the dissolution rates of copper and zinc were also determined. Electrochemically the most interesting quantity was the logarithm of the dissolution rate because it is a linear function of the applied potential. This linear relationship was given by the Tafel equation. The dissolution rate of cadmium was shown to be rather small even under circumstances which may be said to represent very unfavourable conditions within the oral cavity.

Speech discrimination in an aging population

The Rhyme Test of speech discrimination was used to study the relationship between speech discrimination scores and aging in 55 elderly adults. Test-retest reliability of the scores, the relationships of the scores obtained under test conditions of quiet and of competing noise, and the agreement between the scores and the subjects' self-estimate of hearing handicap in everyday listening situations were examined. Rhyme Test scores tended to decrease as age increased, particularly in the age group over 60, for the test in quiet as well as in noise. Correlations between test scores and aging were higher for the quiet condition than for the noisy condition. Test-retest correlations in the quiet condition were high, despite retest intervals as long as nine months. Subjects' self-estimates of hearing handicap correlated with their speech discrimination scores.