Call his office. Most states require that dentists have someone on call when they are not around. The office staff or answering service should have that connection.
Another dentist or.. There are many dentists around and so if you really need emergency dental care, then you have to see another dentist if yours is not available. You may want to check with your family doc to see if your problem is truly an emergency. Often, dental abscesses etc...Can be treated with antibiotics which your doc can prescribe and then you can wait for your dentist to return. Good luck.
Emergency Dentistry. It is required by law that your dentist leave another dentist in charge for the care of his patients during his absence. Call the office. You should be able to get a hold of one of the staff or an answering service who will direct you to the dentist covering for him. If you still can't get anyone to see you, find yourself another dentist who will care for you in your time of need.
On Call Dentist. When any doctor is away, they usually refer to an on call doctor. If not, ask your friends/family/co-workers who they would recommend. Last resort: go to your local emergency room and be prepared to wait- you are usually not very high on the priority list.