Selecting an Appropriate Digital Radiography Sensor
Size and Placement Considerations
Scott Benjamin, DDS
Advancements in digital radiography have enticed every clinician
with improvements in speed, clarity, and patient education opportunities. No
longer are clinicians asking themselves if they want to convert their practices
to implement this technology. Now the question is "when?" While the advantages
of digital radiography over traditional radiographic methods are not in
question, the debate over system and sensor selection, sensor positioning, and
scanning processes continues.
There are two types of digital sensors offered for use in
dentistry, direct and indirect. Direct digital radiography sensors transfer
digital information adroitly to the computer; the image is obtained directly
from the sensor itself via a connection to the computer. Indirect sensors
gather digital information that must be "translated" in an
intermediary step (typically utilizing additional equipment) and then
transferred to the computer.
The two most common types of direct sensors are charged
coupled devices (CCD) and complementary metal oxide semiconductors (CMOS). The
CCD sensor, which tends to be relatively thick and inflexible, was the first
type of sensor to be used in dentistry.1 Although disadvantages of
CCD sensors are apparent, there are unquestionable advantages to their
Indirect sensors are photostimulable phosphor (PSP) storage
plates, which resemble traditional radiographic film. This type of sensor must
be "read" by a scanner that transfers the "translated"
information to the computer. The PSP plate sensors gained initial popularity
due to their flexibility and ease of placement, but recent research indicates concerns
about their durability.2
The CCD sensors are held in explicitly designed positioning
devices. The paralleling technique can be implemented, as it would be with
film-based radiography. In addition to considering the size of the sensor, the clinician
must also take into account the positioning of the plastic sleeve and the cord
when capturing the image. The plastic sleeve may prevent optimal visualization
and cause the patient to gag, while the cord may obstruct the radiation beam. When
placing the sensor intraorally, it is advised to keep the plastic sleeve taut
to increase visualization and to prevent interference with positioning. Excess
plastic sleeve can also increase salivation that will interfere with the
radiograph. To restrain the cord, some positioning devices (eg, a notch or
clamp) can help direct the cord out of the visual field.
The PSP plate sensor is similar to film in size and
thickness and does not require a cord. The PSP plates are more flexible and,
therefore, must be carefully managed. If they become scratched, a compromised
image will result. If the receptor is bent when the patient stabilizes it,
elongation of the apical portion of the image will occur. A rigid biteblock can
reduce this distortion.3
One of the greatest advantages to digital radiography is the
ability to enhance and manipulate images on screen. Typical processing tools
(ie, flip and rotate command)
Gray Scale (invert or inverse)
(for noise reduction, sharpening, and smoothing)
It has been stated, however, that the more the image is
manipulated, the less likely it is that the image is improved. Attention to
exposure factors, patient size, and projection geometry will have a greater
impact on image quality than anything that can be done to the image after it is
While there is a learning curve to mastering digital
radiography techniques, the advantages over film radiography make it an attractive
alternative to film-base dental radiography. When determining which digital
system to purchase, it is imperative that clinicians not only determine which
sensors to utilize, but also survey current computer hardware configurations and
consider associated costs (eg, replacement sensors and warranty coverage).
AG. Fundamentals of image acquisition and processing in the digital era.
Orthod Craniofacial Res 2003;6(suppl 1):17-22.
A, Davis TD, Angelopoulos C. Storage phosphor plates: How durable are they
as a digital dental radiographic system? J Contemp Dent Pract 2004;5(2):57-69.
ET. Practical Techniques to optimize digital radiographic imaging. Pract Proced
Aesthet Dent 2008;20(2):94-98.
Table 1: Comparison of Digital Receptors
0,1,2,3,4, panoramic, and cephalometric
Reusable; 400,000 exposures*
Reusable: approximately 30-50 exposures2
Average cost of size 2 sensor is $7,000
Average cost of size 2 sensor is $25
Thicker and more ridged than traditional film
Flexible and thinner than traditional film
*Warranties differ with manufacturers.