Exposure times are based on the assumption that the tubehead is no more than 2 centimeters away from the face of the patient. Light images can also be caused by an increase in the source-object distance, or not placing the tubehead close enough to the patient's face during exposure. Underexposed receptors result in images that are too light or low in density. Typically, child exposure time settings are lower than adult exposure time settings because of the child’s smaller size. Failing to adjust exposure time will result in images that are either too light or too dark. Usually one step up for large patients and one step down for small patients will be adequate adjustment for each periapical and/or bitewing. The operator should use longer times for larger-than-average patients and shorter times for smaller-than-average patients. Improper exposure time settings can also result from an inaccurate evaluation of patient size and stature. Therefore, time adjustments are necessary when the patient’s size deviates from the average adult. Generally speaking, the recommended time setting for each area is based on the size of an average adult patient. Refer to the manufacturer’s manual for the recommended settings for specific intraoral views or projections. Every treatment room should have an exposure factor chart to guide the operator in selecting the appropriate kVp, mA and time setting for each periapical and bitewing. The exposure time settings should be based on the receptor speed or type, the area being exposed, and patient size and stature. Time and milliamperage control density or the overall darkness of an image while kilovoltage controls contrast or the differences in darkness. Improper time selection is the most likely error because most intraoral x-ray units have fixed or unchangeable milliamperage (mA) and kilovoltage (kVp) settings. Incorrect exposure can be caused by many factors the most common being improper exposure settings.
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