If a 3 year old child still has pain after filling, the pain may be caused by the filling material stimulating the pulp, or secondary caries causing pulpitis, periapical inflammation and so on. 1. Pain caused by stimulation of pulp by filling materials: fillings need to use a variety of materials, such as resin fillings, amalgam fillings, etc., these materials may produce an irritating reaction to the gums, so initially, some children will have irritating pain, and generally after a period of time to recover, the symptoms will gradually reduce. 2. Pulpitis: If pulpitis has occurred before the filling, but it has not been treated in time, it will cause spontaneous pain after sealing. 3. Secondary caries: new caries after filling can also lead to toothache after filling, which requires further examination of the painful tooth and targeted treatment. Children with toothache after a filling may also have a tooth that is not restored with a crown after the filling, resulting in splitting of the tooth. It is now recommended to seek medical attention as soon as possible to identify the cause and receive treatment.