At the most recent Inner Space Seminar, we discussed all different kinds of cracks in teeth. We reviewed how to detect them, classify them, treat them, & prevent them. An effective way to identify cracks in the crown of a tooth is by using transillumination.
I mentioned an inexpensive light that can be used for transillumination. Thanks to Dr. Nathan Saydyk for his research, this light has been discontinued and replaced with the new Browning 2120 Microblast Pen Light with Bore Light Adapter. This is a flashlight used for firearm inspection and cleaning that can be used for transillumination.