If you were officially dismissed from the school as a disciplinary action as it states in the question, you should answer the question appropriately if your desire is to be honest.
If you choose not to list it, I am not aware if AADSAS or individual dental schools would be able to see that you attended law school; however, if they did find out you were dismissed without you explicitly telling them, that would be a HUGE red flag.
Personally, I would be honest in the app and explain why you were dismissed; how you felt rushed into a decision to attend law school; felt it best to get out early before wasting more time/money, etc. You don't even have to admit it was about grades because you withdrew before classes were over. That is a huge plus. I'm not saying you should lie, but you should definitely manage how your story is perceived and turn it as positively as you can should you decide to list it on your app.
Just my 2c.