I am surprised that your child has been examined by a paediatric dentist and you have not been able to find out the cause of persistent pain. The apparent pain could be due to hidden cavity between the teeth, gum disease or even erupting teeth. Since your child must have cut number of teeth between 9-13 years wherein permanent teeth erupt and milk teeth shed, can also be the cause of pain. Well it is difficult to assess the real cause of pain unless the patient is examined and investigated (X-rays etc).