Its called a diagnodent and it is probably the best thing to happen to dentistry in 20 years in my opinion. The device measures the denisty of your teeth. Why is that important? Well teeth have a very hard outer shell called enamel. Often bacteria dig a hole throught the enamel and start to feast on the softer dentin below. The problem is that the enamel can stay intact, look normal, and not hurt.
Traditionally we would use x-rays to discover these kinds of cavities that are hiding, but they only show up on x-rays once they are large!
Well now we have the diagnodent to detect these small cavities. The diagnodent sends a light into the tooth and reads how it bounces back and generates a number. This often lets us catch thes cavities much earlier. For the patient this means less chance of having to have a rootcanal, less tooth structure drilled out, and reduction in price.
A filling typically cost 100 to 200$. If you have insurance you will only probably pay 20% percent of that.
However if the cavity is over half the tooth, you will probably need a crown. Crowns usually cost around a 1000 dollars and your out of pocket is usually 50%, so like 500 dollars. So financially it is a no brainer. As with any form of medicine prevention and early detection is most important. Hope this helps. Goodnight everyone.