I developed an itchy rash on my buttocks on thursday. The only thing I did differently was I used the rest room in my dentist office.

Rash. Without a complete history it is impossible to give you a complete answer. It could be a rash that would have occurred no matter what you did. It could be an anxiety try rash from a fear since you used something different. The rest rooms in our office have an alcohol wipes to clean before use, but that is not a must... Few public restrooms have it. If it continues have it checked out at your md.