Fillings should not be painful. If you are having sensitivity around a filling there could be recurrent decay, leakage between composite and tooth, or your bite could be high. The filling cannot develop a cavity, but your remaining tooth can. If you have had fillings in the past you are at a higher risk to form decay in the future. For this reason, home care and routine professional cleanings are so important. A clinician may suggest a prescription-strength toothpaste to use at night to protect your teeth from needing future fillings. Another reason why you may be having discomfort is a leaky filling. Leakage usually occurs in patients that have higher acidic diets that break the seal between your filling and tooth. Lastly, you may need a modification to your bite. If are hitting your filling too hard it can cause an aching pain. Call your dentist to see if a bite adjustment is needed.