A distinction should be made between cases where the difficulty of perforation is on the cortical bone or on the cancellous bone. In the case of osteocentral technique, if the perforation is made at the top of the septum, the cortical bone is thin enough to be perforated. However, a yellow needle may be required. If the case of transcortical technique, another more convenient site should be considered. If the cancellous bone is very dense locally, another more convenient site should also be considered. If the cancellous bone is very dense overall (less than 0.5% of cases) intraosseous anaesthesia is contraindicated. In this case, another anesthetic technique must be used.