Local Anaesthesia for Dental Boards: Techniques, Landmarks and Complications

The anatomy behind every technique

Almost every local anaesthesia question can be answered from the course of the trigeminal nerve. The maxillary division (V2) supplies the maxillary teeth through the posterior, middle and anterior superior alveolar nerves, and the palate through the greater palatine and nasopalatine nerves. The mandibular division (V3) supplies the mandibular teeth through the inferior alveolar nerve, the tongue and lingual gingiva through the lingual nerve, and the buccal gingiva of the molars through the long buccal nerve.

Inferior alveolar nerve block (IANB)

The target is the inferior alveolar nerve just before it enters the mandibular foramen, which is partly covered by the lingula on the medial surface of the ramus. The key intraoral landmarks are the coronoid notch, felt with the thumb on the anterior border of the ramus, and the pterygomandibular raphe. The needle approaches from the premolars of the opposite side, enters lateral to the raphe at roughly the level of the thumb in the coronoid notch, and advances until it gently contacts bone. Aspirate before depositing.

A successful IANB anaesthetises the mandibular teeth on that side to the midline, the lower lip and chin through the mental nerve, and usually the tongue and lingual gingiva because the lingual nerve lies nearby. It does not reliably anaesthetise the buccal gingiva of the molars, which is why a separate long buccal injection is added for extractions.

Why the IANB fails

• Technique: deposition too low (below the foramen) or too anterior is the most common cause.
• Anatomy: a high foramen, a wide ramus, or a bifid mandibular canal.
• Accessory innervation: the mylohyoid nerve, cross-innervation of the incisors from the other side, or the long buccal nerve for buccal soft tissue.
• Inflammation: inflamed tissue has a lower pH, so less of the anaesthetic exists in the uncharged base form that crosses nerve membranes. This is why a "hot" tooth with irreversible pulpitis is hard to numb.

Alternatives and supplements

• Gow-Gates block: targets the neck of the condyle with the mouth wide open, anaesthetising most of V3 with a higher target.
• Vazirani-Akinosi (closed-mouth) block: useful when trismus prevents wide opening.
• Buccal infiltration with articaine: often used as a supplement to an IANB for mandibular molars.
• Intraligamentary and intraosseous injections: localised supplements for a single tooth.

Maxillary techniques

Maxillary bone is thinner and more porous than mandibular bone, so buccal infiltration usually anaesthetises maxillary teeth well. Blocks are used for wider areas:

• Posterior superior alveolar (PSA) block: inserted at the height of the mucobuccal fold above the second molar, directed upward, inward and backward. It anaesthetises the maxillary molars, although the mesiobuccal root of the first molar may be supplied by the middle superior alveolar nerve. Over-insertion risks a haematoma from the pterygoid venous plexus.
• Infraorbital (anterior superior alveolar) block: targets the infraorbital foramen to anaesthetise the incisors, canine and, in many patients, premolars, plus the lower eyelid, side of the nose and upper lip.
• Greater palatine block: at the greater palatine foramen, usually opposite the second or third molar, for the posterior hard palate.
• Nasopalatine block: at the incisive papilla for the anterior palate, one of the most uncomfortable injections, so slow deposition helps.

Pharmacology in brief

Local anaesthetics are weak bases that block voltage-gated sodium channels. Amides (lidocaine, articaine, mepivacaine, prilocaine, bupivacaine) are metabolised mainly in the liver; articaine is also rapidly broken down in plasma because of its ester group. Esters are metabolised by plasma cholinesterases and are more often associated with allergy.

Vasoconstrictors such as epinephrine slow systemic absorption, which prolongs anaesthesia, improves haemostasis and lowers peak plasma levels. For patients with significant cardiovascular disease, many references suggest limiting epinephrine to about 0.04 mg per appointment, roughly two 1.8 mL cartridges of 1:100,000.

Dose calculations

Exams often give a weight and ask for a maximum dose or number of cartridges. Convert concentration first: a percentage is grams per 100 mL, so 2% = 20 mg/mL and 4% = 40 mg/mL. Reference maximums differ between countries, manufacturers and textbooks, so use the values your exam expects. Commonly cited figures include:

Worked example: a 20 kg child, 2% lidocaine with 1:100,000 epinephrine in 1.8 mL cartridges, using 4.4 mg/kg. Maximum dose = 20 × 4.4 = 88 mg. Each cartridge holds 36 mg, so the maximum is 88 ÷ 36 ≈ 2.4 cartridges. Children reach toxic doses quickly, which is why weight-based calculation matters most in paediatric questions.

Complications examiners ask about

• Systemic toxicity: early signs are central, such as circumoral tingling, tinnitus, dizziness and slurred speech, progressing to seizures and cardiovascular depression. Aspiration, slow injection and dose limits prevent it.
• Haematoma: most often after PSA and IANB injections.
• Trismus: usually from trauma to the medial pterygoid during an IANB; infection of the pterygomandibular space is a less common cause.
• Transient facial nerve palsy: solution deposited too far posteriorly, into the parotid gland, during an IANB. The patient cannot close the eye on that side, so protect the cornea until it resolves.
• Paraesthesia: persistent altered sensation, most often of the lingual nerve.
• Needle breakage: avoid bending needles and never insert to the hub.
• Soft-tissue self-injury: lip and cheek biting in children after mandibular blocks.
• Methaemoglobinaemia: associated with prilocaine and topical benzocaine.
• Allergy: true allergy to amide anaesthetics is rare; reactions may involve the sulfite preservative in epinephrine-containing solutions.
• Syncope: the most common emergency around injections, usually anxiety-related.

Test yourself

Ten more questions are waiting in the free anaesthesia and pain control set, and the high-yield dental pharmacology guide covers the drug interactions that often appear alongside these topics.