My jaw has been stuck for a week. how can the dentist fix it in the office?

Some dentist can: I am assuming your that you are inferring that you cannot open your mouth completely or have limited movement. There are 3 or 4 possible issues that can cause this. Find a dentist with special interest in tmj. This is a field that only a handful really understand and treat properly. Please remember that approx. 98% of these cases are non-surgical.

Manipulation: A locked jaw means one or both of your jaw joints--commonly known as the tmj's--are deranged. Pieces are out of normal position. To correct this, a dentist (or a well-trained chiropractor) will manipulate your jaw to help the pieces return to their normal positions. A dentist will then be able to help you find the cause (likely teeth clenching/grinding) and prescribe treatment. Go see a dentist.