Years ago I read how they perform the cementum annuli age test. They soak the teeth in a decalcifying solution (usually an acid) to soften them, then cut cross sections of the root of the tooth on a cryostat, stain the section on a slide and image it with a light microscope, counting the rings. One year I decided to try my hand at it since I have access to all the reagents and instruments. Let me tell you that though the price might seem high, it takes awhile to do the sample prep and imaging. Also, it takes a trained, skilled eye to accurately age a deer in this fashion.
Matson's did send the slides back to me as I requested, so I can look at them if I care to.