Get a flash light (or other light source) and look carefully at the tooth that has the ache problem. If you don't see anything obvious it may still be a good idea to see a dentist.. well maybe a general practice doctor would be a better place to start.
You seem to say the symptoms come and go during the day, this in itself is an unusual symptom in my experience. I've had bad tooth pain in my life, but while in the early going it may have been stimulated by eating something cold, when it got to really hurting, it just hurt all the time.
His symptoms could be due to an infected tooth. Infected tooth roots from the upper teeth can go inside the maxillary sinus and cause sinusitis. This can cause the headaches. He might need a CT of the sinuses for more information. However, if he does have an infected tooth, he will still need to have this addressed as dental infections can be potentially life-threatening.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. MedHelp is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.