Surface and internal absorbed doses in mandibular and maxillary occlusal radiography.

The objective of this study was to determine the absorbed radiation doses to various structures within the head and neck as a result of routine mandibular and maxillary occlusal radiography. Five projections were investigated: the anterior mandibular; true mandibular; anterior maxillary; lateral maxillary; and maxillary vertex occlusal radiographic views. Standard thermoluminescent dosimetry methodology was employed using a humanoid phantom of the skull. Multiple exposures were done for each view to ensure adequate precision. The absorbed doses to various locations following a single occlusal exposure are presented in centiGray (cGy). It was found that the absorbed dose values for occlusal radiography observed in this study were similar in magnitude to previously reported absorbed dose values for other forms of dental radiography. Values ranged from 0.0014 cGy to 1.301 cGy. The highest absorbed doses were generally the skin entrance doses. The results of this study provide an accurate, concise summary of surface and internal absorbed radiation doses for five commonly used occlusal radiographs. They can be used in the calculation of risk estimates for dental radiography, and may assist dentists in their discussions with patients concerned about radiation exposure.

Children and adults' distance estimations in a large-scale environment: effects of time and clutter.

In two experiments adults (mean age = 19-5), sixth graders (mean age = 11-8), fourth graders (mean age = 9-8), and second graders (mean age = 7-8) walked a straight line distance through a large-scale environment. Subjects were then asked to estimate the time taken to traverse each half of the walk and to estimate the distance between objects seen along the walk. In Experiment 1 each half of the walk was traversed in the same amount of time but contained a different number of objects (clutter). Time and distance estimates were related, but were not affected by the number of intervening objects encountered between locations. In Experiment 2 subjects again encountered a different number of objects along each half of the walk but each half was traversed in varying amounts of time. Again, time and distance estimates were related, and there was no clutter effect. There were no consistent developmental differences across the two experiments. It was concluded that (1) Thorndyke's clutter effect does not occur across all types of spatial cognition tasks, and (2) children and adults tend to relate time and distance across a variety of distance estimation tasks.