Sometimes a recent cold or flu can cause sinusitis, an inflammation of the lining of your sinus cavities. Swelling and irritation are often symptoms. The maxillary sinuses happen to be directly over the upper back teeth. The swelling can bear down on the teeth, creating a dull toothache. Sometimes the sinus literally elevates the teeth a tiny bit out of socket, creating a high bite and chewing difficulties.
If your dentist is not careful, you can end up with an unnecessary root canal treatment. A proper diagnosis of every toothache usually includes an x-ray, cold test, percussion (tapping test), biting test, and periodontal probing (gum check). A positive biting or tapping test during or after a recent cold or allergy event may just indicate sinusitis, not a dental problem. If dental findings are inconsistent or inconclusive, you can be referred to your medical doctor for a consult. We had one or two such cases last year, and possibly one this morning. I routinely ask my patients with dull toothaches, especially on upper teeth, if they've had recent sinus infections, colds, flu, or allergies. The best way to get correct diagnosis, as always, is to be thorough (collect a lot of data), and look at all the facts, not just the dental ones.