Failure in local anaesthesia in dentistry is not uncommon with failure rates ranging approximately between 15% and 30%, especially for the inferior alveolar nerve block (IANB).
Occasionally traditional techniques of anaesthesia like infiltration and regional block injections may not provide successful anaesthesia especially in endodontics for the so-called inflamed pulp (hot tooth) or irreversible pulpitis.
When inferior alveolar nerve block alone was used only 14-39% success rate was obtained but when supplemental injections were included, success was significantly increased to 50-65% for irreversible pulpitis.
The term intra-ligamentary or periodontal ligament anaesthesia may be misleading as the anaesthetic injected into the periodontal ligament provides pulpal anaesthesia by penetrating the cancellous bone through natural perforations.
Intra-osseous injection consists of introducing the local anaesthetic directly into periradicular cancellous bone via specialized systems like Stabident (Fairfax Dental, USA) and X-Tip (X-Tip Technologies, USA).
In approximately 5-10% of mandibular posterior teeth with irreversible pulpitis, supplemental injections, even when repeated, do not produce profound anaesthesia; pain persists when the pulp is entered.
This is an indication for an intrapulpal injection.
