Radiation Characteristics

What is the ethical responsibility when taking dental radiographs?

To produce the highest diagnostic quality radiographs with the lowest possible radiation dose

What makes a radiographic diagnostic?

• Structures imaged are accurate in size and shape 

• No important anatomy is cut off

• Proper exposure, density, and contrast 

What does kVp control?

• Penetrating power of x-ray

• Contrast of the image only

What are the effects of changing kVp?

• Higher kVp = more slower wavelengths → more penetration → low contrast

• Lower kVp = less penetration → high contrast

What is the normal kVp range?

60-70 kVp

What does exposure time control?

• Longer time = more x-rays = higher density (darker)

• Shorter time = fewer x-rays = lower density (lighter) 

What does mA control?

Quantity of x-rays (electrons from cathode to anode)

• Higher mA = higher density 

• Lower mA= lower density 

What is density in a radiograph?

Overall lightness or darkness

What is contrast?

Difference between black and white areas

• Higher contrast = few shades → caries detection

• Low contrast = many grays → periodontal evaluation

What is x-ray intensity?

Combines number of x-rays and energy 

• Intensity is higher when source is closer 

• Intensity is lower when source is farther

What is the inverse square law?

Intensity is inversely proportional to the square of the distance 

What is target-object distance?

From the radiation source (tungsten target) to the tooth

What is target-receptor distance?

From the radiation source (tungsten target) to the film/receptor