hi there, brackets are really very tiny metallic things and they will pass out in the feces without being noticed. The pain that he is feeling may be out of anxiety
about the same or could be organic.I would suggest that you give her some antispasmodics and plenty of fluids and observe for a day or two. If he still complains of the pain then you may take him to the ER and get him examined by the doctor and if required get an x-ray done. At present it does't seem to be an emergency and only reassurance and and antispasmodic should be enough. Take care.