Diamonds and digital sensors

by Jim Ramey

Diamonds. Most people can’t distinguish between low- and high-grade diamonds. That is why the diamond industry came up with the four C’s: cut, color, clarity, and carat. Sometimes they even add a fifth C — certification.

Just as with diamonds, it can be very difficult to tell the difference between digital sensors. In order to help dentists compare the quality of sensors, I have created the six C’s of digital sensors. And, just as with diamonds, these measurements will help you judge the quality of a digital sensor.

Clarity

With digital sensors, clarity is the quality of the image. Clarity is measured in two ways: line pair measurements and resolution.

There are two forms of line pair measurements: actual and theoretical. The larger of the two is always the theoretical line pair. Some companies will only report the theoretical line pair measurement to make their product look better. Make sure that you use the same type of line pair test results when comparing sensors.

Both the actual and theoretical line pair test numbers are useful. However, the theoretical is created through numerous mathematical calculations and does have some subjectivity. The actual pair number is a more accurate measurement of a sensor’s clarity. The actual number of line pairs per millimeter is what you can see with your naked eye, so this is the number to which you should pay the most attention. The higher the number, the better.

With today’s technology, I would expect a “high grade” sensor to provide test results of 18 or higher on its actual line pair, and 22 or higher on its theoretical line pair. By way of example only, the DentiMax sensor has an actual number of line pairs of over 20 and a theoretical of 26. You will see similar line pair results for other high-end sensors such as Kodak, DEXIS, and Schick.

“Resolution” is commonly referred to by pixel size, and more recently some companies have used the term “megapixels,” just like what is used in the digital camera industry. Resolution with a value close to or higher than a 19x19 micron pixel size is a good standard.

CMOS or CCD

These are the two types of scintillators that digital sensors use to convert an X-ray into a digital signal. The CCD technology is an older technology. It requires more power; therefore, CCD sensors need an additional component, commonly known as a “box.” CMOS is the newer technology. Most CMOS scintillators require less power, so no box is needed. A few CMOS sensors have in-line boxes — where the box is in line with the cable. The newest CMOS scintillator sensors require no box at all. Compared to the CCD sensor, the CMOS scintillator sensors provide a far superior diagnostic quality image.

Cut

This refers to how the sensor is shaped. The shape of the sensor is important for patient comfort. Most sensors on the market have one of three shapes that really come down to what kind of corners they have — square, rounded, or cut. Square-cornered sensors have pointy corners and are in a nearly perfect rectangle shape. Rounded-corner sensors are almost a perfect rectangle shape, but the corners of the sensor have been slightly rounded. Cut-corner sensors have true rounded corners. How can you tell the difference? By the image that is produced. Does the digital X-ray image have pointed corners, pointed corners with slightly rounded edges, or is part of the image actually cut off?

Cut-corner sensors are the most comfortable sensors for your patient. Sensors that have cut corners will produce an image with just the very corners cut off. You don’t lose much of the image as far as the size of the image or what teeth you can diagnostically see, and your patients will not complain that the sensor hurts. DEXIS and DentiMax are two companies that offer sensors with cut corners.

Carat

This is the size of the sensor. Most sensors are the same width and length as #1 and #2 film. Unlike cut, size will affect how many teeth you can capture in a digital X-ray image and what you can diagnostically see in that image. Just like film, the #1 and #2 size sensors allow you to switch the sensor to the appropriate size for your patient. For example, if you have a patient with a torus or something similar, you can take most of the shots in your FMX with the size 2 sensor, and then switch to the size 1 for those hard-to-reach areas.

Thickness is the other measurement for the size of a sensor. You don’t want the sensor to be overly thick. Sensors between 4 mm and 6 mm thick are in the sensor “sweet spot” for thickness.

Choice

Choice is a factor that may affect you three to five years after your initial sensor purchase. Some companies limit you as to what sensor you can use with their software. If or when your sensor breaks, you will be forced to purchase their sensor at their price — no other option. Other companies provide software that gives you the freedom to choose whatever sensor, digital pan, and/or digital camera you may want to use.

Cost

This is the one C that often results in doctors “holding off” on switching from film to digital, or why they might only purchase one sensor. Using the measurements from this article, you will find that the sensor price does not always determine the quality of the sensor, and that the market currently offers high-grade quality sensors at many different price points.

Another cost factor is monthly maintenance and warranty fees. Some companies do not charge for maintenance fees and warranties, while others charge substantial fees. When comparing sensor prices, be sure that you add up the cost of the monthly fees so you can make an accurate comparison on the true cost of the sensor.

Conclusion – It can be difficult to distinguish between low-quality and high-quality digital sensors. There are many variables, measurements, and criteria that should be considered. Fortunately, just like diamonds, the C’s of sensors can help you make the best and most informed decision possible in your next digital sensor purchase.

James W. Ramey has a bachelor of science degree in management information systems from the University of Akron. For the last eight years, he has worked exclusively with digital radiography technology and has experience with most sensors on the market, including digital, panoramic, cephalometric, and intraoral cameras. You may reach Ramey at [email protected].

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