Nitrous is pretty mild, kinda feels like you're drunk and dissociated. It depends on the drug used for IV sedation really. Unless they're putting you to sleep completely, which I doubt they'll do just to fill a cavity. It'll most likely be a short acting benzo like Midazolam alone or mixed with Fentanyl or demerol, which are very commonly used in dentistry and for other quick procedures. Even if you have a benzo tolerance it won't matter really, an IV benzo would definitely still do the job, WAY stronger than poppin pills. When I had all my wisdom teeth removed they used IV ketamine and propofol, but that was for "general anesthesia" which is different than "IV Sedation". General anesthesia is when they put you to sleep completely and IV sedation is when they give you something to relax you and induce amnesia. I also had another procedure done under "IV sedation" (colonoscopy/endoscopy) and they used midazolam and Demerol together, I was still awake but completely out of it and couldn't even hold my head up or talk and was hardly able to remember anything from the procedure. I'd go with the IV option.