L.R. Manson-Hing D.M.D.’s research while affiliated with University of Alabama and other places

The accuracy of an aluminum step-wedge quality-assurance test for machine and processor in dental radiography was determined. The clinical radiographic density range accepted by twenty dentists was similar to eight steps of an aluminum step-wedge test object, with dentists using six or seven steps. The test used a two-step density shift to detect and separate changes in both x-ray machine and film processing before radiographic quality becomes clinically unacceptable. Measured latent image fading of test films stored for months was small and did not affect the test performance. The accuracy of the step-wedge test in detecting eighteen machine and film-processing variables was measured with a densitometer. Possible comparisons with measurements made by an accepted densitometric method used in medical radiography showed similar results. The test can be used in lieu of more costly, time-consuming tests.

The average angles between the horizontal and occlusal planes and the ala-tragus and orbito-meatal lines were measured for 96 patients in a panoramic x-ray machine. The angles required to produce clinically acceptable radiographs are described. Some operator judgment is required when positioning each patient's head for radiographs of optimum quality.

Sharpness zones of the Orthopantomograph-5, Autopan, and Panorex were delineated with the use of a standard multiline test object at 1.7 line pairs per millimeter. In addition, Panorex zones made with medium- and high-speed screens were compared. The focal troughs of all machines covered most tooth positions. The Autopan and Orthopantomograph troughs were narrow anteriorly, while the Panorex trough was not close to the condyle posteriorly. There was little difference between focal troughs produced with the use of high- and medium-speed screens.

The effectiveness of radiographic surveys in detecting basic radiographic signs for the initial examination of patients in a specific dental clinic population was investigated. A sample of 300 patients showed that panoramic periapical and bitewing radiographs are all needed for a complete radiographic evaluation. Panoramic plus bitewings and periapical plus bitewings were the next most effective surveys with either survey being less effective than the other for some radiographic signs.

Evaluation of the effect of radiographic technique upon the prediction of tooth lengths for all major types of teeth indicated the following: 1. The paralleling technique using the Rinn XCP film holder, the paralleling technique using the hemostat with bite block, and the bisecting-the-angle technique using the Rinn XCP film holder were the most accurate systems. 2. There were no significant differences among the three most accurate techniques. 3. The paralleling technique using a 16-inch tube-to-patient distance was more accurate than the bisecting-the-angle technique using an 8-inch tube-to-patient distance. 4. A beam-guiding film holder produced a more accurate radiographic image than the other film holders used in the study. 5. For the buccal roots of maxillary molars, the bisecting-the-angle technique using the Rinn XCP film holder produced the least mean difference between radiographic image and tooth length. 6. The accuracy of predicting the length of mandibular molar teeth from the diagnostic radiograph was not affected by radiographic technique.

Intraoral radiographs were made via the bisecting-the-angle technique on patients of different ages, sexes, and races. The tooth-film angles for various areas of the mouth were measured and found to be close to 30 degrees for all areas of the mouth except the mandibular posterior regions. The study was conducted to assist in quick positioning of the x-ray beam in difficult cases.

The ability of screen-films to depict dental structures utilizing the parameters used in intraoral radiography is investigated. The resolution and contrast of a variety of screen-film combinations are determined. Radiographs made on a phantom and patient are evaluated by observers. Some film-screen combinations produce radiographs with qualities similar to conventional intraoral films and with less radiation.

Two clinical experiments were conducted to study the effect of kVp and mAs on resolution and on image contrast percentage. The resolution was measured with a "test pattern." By using a transmission densitometer, image contrast percentage was determined by a mathematical formula. In the first part of the experiment, the density of the film was kept constant by changing the kVp and mAs. In the second part of the experiment, different mAs's were chosen, and for each mAs, several kVp's were used. Five observers read the radiographs. The first experiment showed that, when the film density is kept constant, the higher the kVp, the lower the resolution and image contrast percentage; also, the higher the mAs, the higher the resolution and image contrast percentage. The second experiment showed that when the film density is not kept constant, the correlation between kVp and resolution and between kVp and image contrast percentage was the same as in the first experiment. However, there was negligible correlation between mAs and resolution and between mAs and image contrast percentage. A high positive correlation was found between resolution and image contrast percentage, but a high negative correlation was found between resolution and film density.

The effectiveness of a commercial radiographic toning solution on dental screen and nonscreen films is studied.