By Dr. Armen Mirzayan
One of the most important lessons a digital dentist has to learn quickly is how to not introduce errors when scanning dentition. The most likely area when s/he can introduce errors is in the anterior area where the incisor are not only narrower than molars but can also have translucent enamel. Add just a little spacing between teeth with diastemas and you can quickly distort the accuracy of the model. This is true of ALL intra-oral scanners in the market.
There are a few ways you can overcome these issues and the second video highlights some of our preferred methods. The concept is easy- block the light from travelling through the tooth structure and you are set!
Here are some examples of how light shinning through the enamel and /or ceramic instead of bouncing back resulting in errors in model accuracy. Lesson #1 for every IOS user is to know when and where they are likely to introduce error. In dentate cases, it usually is right that the transition from premolar to canine to lateral. The surface area decreases dramatically and if you have translucent enamel and / or material and / or highly reflective surfaces you can “derail” the model building. Here is an exaggerated demonstration:
Translucent enamel can also play a role in distorting the cavosurface margins of a inlay or onlay restoration. When imaging from the occlusal, the gingiva below the margins acts as a barrier to block light transmission through the enamel, but as soon as you start to roll the camera to the buccal or lingual, and you have enamel with no substrate behind it to block light transmission, you can introduce errors in the equation with any scanner.
There are many ways to combat this which include powdering the tooth structure, using a rubber dam, or in Medit’s case, you can use the color subtraction filter. You selectively tell the scanner to ignore certain colors and you use that exact color (here, it is the color of the glove) to block light transmission through the enamel. So the software just ignores the blue, but the light is prevented from shining through reducing the errors you would introduce.
Dr. Armen Mirzayan is a 20+ year CAD/CAM user and Founder of CAD-Ray USA.