for the filling local anesthesia must have been given and some times the child bites from the lip when it is numb causing swelling and numbness of the lip. If this is the reason then the swelling and numbness will go with in a day or two. Other reason can be, if the filling is done and it is deep and nerve is exposed then the swelling can be there but in that case the child feels severe pain also. Most likely in case of your grandson it is due to biting the lip but still you can show to dentist in the morning to rule out other cause.
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