Cracked teeth can be one of the most challenging diagnosis. Bite sticks, vitality tests, and radiographs are all very important; however, transillumination is an essential tool that we often forget is at our disposal. In the case demonstrated below, you can see a clear MMR crack on tooth #5 that is deeply stained and tooth #4 appears relatively normal. However, using transillumination it is clearly evident that there is a large mesial/distal crack in tooth #4. RCT was completed after removing the entire crack under the microscope, and this patient’s pain is entirely resolved. Without transillumination, we might otherwise suspect tooth #5 as the cause of the pt’s biting pain. For demonstration purposes, a curing light was used to transilluminate the tooth as a little trick to use in your office without having to purchase an actual transilluminator!