Not opening mouth wide

This is most like due to tightness on the temporomandibular joint (TMJ). It can be due to the position baby was lying in before birth. Place your finger on his chin and press down to see if he will open his mouth. If he cries, stop where it hurts. Sometimes baby will keep his jaw in the same position and ‘follow down’ with his head so that he doesn’t have to open his mouth.