01
The IAN Block — A Cornerstone With Limitations
The inferior alveolar nerve block — an indispensable technique with real limits
The inferior alveolar nerve (IAN) block — administered at the mandibular lingula — is the most widely used technique in endodontics for mandibular molars. It provides excellent anaesthetic spread in the majority of cases.
However, certain clinical situations — particularly irreversible pulpitis and acute inflammation — significantly reduce its effectiveness, leaving practitioners facing failures that complicate treatment and cause considerable patient discomfort.
Advantages of the classic IAN block
Mandibular lingula block — reference technique
- Anaesthesia of a wide territory (inferior alveolar + lingual nerve)
- Universally taught and mastered technique
- Effective in most non-inflammatory cases
- Anaesthetises all mandibular molars on the treated side
Limitations in inflammatory context
Irreversible pulpitis — high failure rate
- Failure rate may exceed 30–40% in irreversible pulpitis
- Vincent's sign (anaesthetised lip) is not a reliable indicator of pulpal anaesthesia
- Multifactorial mechanisms — pH, neural excitability, anatomy
- Often requires supplemental techniques
02
Failure Rates and Vincent's Sign
Vincent's sign — a false safety indicator
Lower lip numbness (Vincent's sign) only confirms that the inferior alveolar nerve has been reached. It provides no guarantee whatsoever of pulpal anaesthesia.
Key clinical data — Cohen et al.
In a group of 61 patients with a positive Vincent's sign (anaesthetised lower lip), 38 still showed a positive response to cold testing on the molar. This discrepancy confirms that soft tissue anaesthesia does not predict pulpal anaesthesia in an inflammatory context.
Failure rates by clinical context
| Clinical context | Estimated failure rate | Reliable indicator |
|---|---|---|
| Asymptomatic tooth / necrosis | 5–15% | Vincent's sign sufficient |
| Chronic apical periodontitis | 15–25% | Pulp test recommended |
| Reversible pulpitis | 20–30% | Pulp test essential |
| Symptomatic irreversible pulpitis | 30–40%+ | Pulp test + supplemental techniques |
03
Inflammatory Tissue Acidity
Tissue pH — the enemy of local anaesthetics
In pulpitis or tissue inflammation, local pH becomes significantly more acidic. This pH shift directly affects the efficacy of amide-type local anaesthetics (lidocaine, articaine, mepivacaine).
Biochemical mechanism of pH-related failure
Understanding why tissue acidity reduces local anaesthetic efficacy.
Pharmacology of local anaesthetics
- Local anaesthetics exist in two forms: ionised (BH⁺) and unionised (B)
- Only the unionised form (B) crosses the lipid nerve membrane
- The B/BH⁺ ratio depends on tissue pH according to the Henderson-Hasselbalch equation
Impact of inflammatory acidification
- Normal tissue pH: 7.4 → favourable B/BH⁺ balance for nerve penetration
- Inflammatory pH: 6.0–6.5 → shift towards the ionised form BH⁺
- Result: fraction available to cross the nerve membrane is drastically reduced
- The anaesthetic reaches the nerve sheath but cannot effectively block sodium channels
Practical implication
Reducing inflammation before the procedure (pre-operative NSAIDs) partially restores a more favourable tissue pH, increasing the fraction of anaesthetic capable of penetrating the nerve sheath.
04
Increased Neural Excitability
Inflammatory mediators sensitise nerve fibres
Pulpal inflammation triggers the release of pro-inflammatory mediators (prostaglandin E2, bradykinin, cytokines, substance P) that act directly on Aδ and C nociceptive fibres.
Neural sensitisation mechanisms
Aδ and C fibres — inflammatory hyperexcitability
- Lowering of the depolarisation threshold of nerve fibres
- Upregulation of tetrodotoxin-resistant sodium channels (Nav1.8, Nav1.9)
- These channels are particularly resistant to conventional local anaesthetics
- Increased number of fibres in spontaneous discharge state
- A hyperexcited fibre requires a higher dose or a different technique
Resistant Nav channels — pharmacological challenge
Nav1.8 and Nav1.9 — unblocked targets
- Nav1.8 and Nav1.9 preferentially expressed in C nociceptive fibres
- Relative resistance to lidocaine and articaine at standard concentrations
- Blocking them requires very high local anaesthetic concentrations
- Justifies the use of direct-diffusion techniques (intraosseous, PDL)
05
Anatomical and Technical Variations
Sources of failure of anatomical origin
- Inaccurate needle placement: too anterior, posterior, high or low relative to the mandibular foramen
- Atypical mandibular foramen: positioned higher (50% of cases) or lower than average — the classic internal ramus concavity landmark can be misleading
- Bone thickness: dense cortex or large required needle depth — the anaesthetic solution must diffuse through bone before reaching the nerve
- Nerve course variations: rare bifurcations of the inferior alveolar nerve, accessory innervation from the mylohyoid nerve
- Accessory innervation: the mylohyoid nerve and cervical nerves (C2–C3) may contribute to mandibular molar innervation, bypassing the IAN block
Accessory innervation — an underestimated cause
Up to 30% of patients have a mylohyoid nerve contribution to mandibular molar innervation. This nerve, which branches off the IAN before the foramen, cannot be blocked by the standard lingula injection and requires an additional infiltration.
06
Pre-operative NSAIDs — Anti-inflammatory Strategy
Principle of NSAID premedication
- NSAIDs inhibit cyclo-oxygenase (COX-1 and COX-2) and reduce prostaglandin synthesis
- Reduction of local tissue acidity → improved anaesthetic dissociation
- Decreased excitability of sensitised nerve fibres
- Administration 15 to 30 minutes before injection for optimal effect at the time of the procedure
- Positive results documented in the literature (Hargreaves & Keiser, 2002)
Ibuprofen — first choice
NSAID — non-selective COX inhibitor
- Dose: 400 mg orally, 15–30 min before the procedure
- Rapid anti-inflammatory and analgesic action
- Documented efficacy in improving IAN block success rate
- Take with food for gastric tolerability
- Contraindications: NSAID allergy, peptic ulcer, T3 pregnancy, severe CKD
Alternative — Sodium naproxen
NSAID with longer half-life
- Dose: 500 mg orally, 30–45 min before the procedure
- Longer half-life (12–17 h) — extended post-operative coverage
- Option for a long session or high post-operative pain risk
- Same contraindications as ibuprofen
Evidence base
Pre-operative ibuprofen 400 mg demonstrated a significant improvement in pulpal anaesthesia success rate in irreversible pulpitis compared to placebo. It is the most accessible and best-documented preventive strategy.
07
Pulp Testing — Verify Before Starting
Never rely solely on Vincent's sign
The golden rule before beginning endodontic treatment is to verify the absence of pulpal sensitivity — not just soft tissue anaesthesia — through systematic pulp testing.
Pulpal anaesthesia verification protocol
To be performed systematically after the anaesthetic onset time (5–10 min).
Cold test — gold standard
- Refrigerant spray (Endo-Ice, Endo-Frost) or dry ice stick
- Apply to the tooth to be treated and a contralateral control tooth
- Pulpal anaesthesia confirmed if: complete absence of response to cold stimulation
- Persistent positive response → insufficient anaesthesia → do not begin treatment
Electric pulp test (if available)
- Electric pulp tester — confirms absence of pulpal excitability
- Less useful in irreversible pulpitis (erratic response possible)
- Useful to confirm necrosis before hypochlorite testing
If positive response — clinical management
- Wait an additional 5 minutes then retest
- If persistent: supplemental injection (PDL or intraosseous)
- Never begin treatment without confirmed pulpal anaesthesia
08
Supplemental Injections
Supplemental technique options
| Technique | Mechanism | Efficacy in pulpitis | Equipment |
|---|---|---|---|
| Intraligamentary (PDL) | Diffusion through the PDL space | Moderate | PDL or conventional syringe |
| Intraosseous | Direct injection into cancellous bone | High | Stabident, X-Tip, IntraFlow |
| Buccal infiltration | Transosseous vestibular diffusion | Variable | Syringe + short needle |
| Intrapulpal | Direct action on pulpal fibres | High | Syringe + fine endo needle |
Intraosseous injection
Most effective technique in irreversible pulpitis
- Perforation of cortical bone between roots with a dedicated drill
- Direct injection into cancellous bone close to the apex
- Anaesthetic penetrates without obstacle through the apical foramen
- Systems: Stabident, X-Tip, IntraFlow (motorised)
- Success rate in irreversible pulpitis: 75–100% in studies
- Risk of transient tachycardia if epinephrine is used
Intraligamentary injection (PDL)
First supplemental choice — easy technique
- Injection into the PDL space with a short needle (27G)
- Significant pressure required — PDL syringe recommended (Ligmaject)
- 2–3 injection sites per molar (inter-radicular, mesial, distal)
- Volume: 0.2–0.4 mL per site
- Efficacy increased when performed with articaine 4%
Intrapulpal injection — last resort
If all other techniques fail, direct intrapulpal injection at the time of access can complete anaesthesia. It is painful at the moment of injection but provides immediate and reliable anaesthesia. Use a very fine needle (30G) and inject under back-pressure against the tissue walls for maximum diffusion.
09
Alternative Techniques to the Classic Block
Gow-Gates technique
High mandibular nerve block
- Injection point at the mandibular condyle — higher than the lingula
- Anaesthetises the mandibular nerve before division — covers the mylohyoid nerve
- Slightly higher success rate than the classic IAN block
- Longer onset (5–10 min) — requires maximal mouth opening
- Ideal when the classic technique repeatedly fails
Vazirani-Akinosi technique
Closed-mouth block — trismus
- Injection along the maxillary tuberosity — mouth closed or nearly closed
- Indicated when trismus makes the classic technique impossible
- Anaesthetises the posterior trunk of the mandibular nerve
- More challenging — risk of intravascular injection (aspiration mandatory)
- Slightly lower success rate than Gow-Gates
Escalation protocol — When anaesthesia fails
Sequence to follow when the pulp test remains positive after the initial IAN block.
Step 1 — Wait and retest
- Wait an additional 5 minutes — onset may be delayed
- Retest with refrigerant spray — persistent positive response = proceed to step 2
Step 2 — Supplemental PDL injection
- Intraligamentary injection at 2–3 sites around the molar
- Articaine 4% with epinephrine — 0.2 mL per site
- Retest with cold after 1–2 minutes
Step 3 — Intraosseous injection
- If PDL insufficient: perforation + intraosseous injection (Stabident or equivalent)
- Anaesthetic deposited directly into inter-radicular cancellous bone
- Retest with cold after 30 seconds
Step 4 — Intrapulpal if access has been started
- Direct injection into the pulp chamber via a 30G needle
- Pressure against the walls — maximum canal diffusion
- Immediate and reliable anaesthesia to complete access preparation
10
Clinical FAQ
For the trunkal IAN block, the literature does not show a clear superiority of articaine 4% over lidocaine 2% in terms of mandibular block success rate — unlike what is observed for maxillary vestibular infiltrations where articaine excels due to its high lipophilicity. However, articaine is superior for supplemental injections (PDL, mandibular buccal infiltration) because it diffuses better through cortical bone. In practice, both molecules are acceptable for the IAN block, but articaine is preferred for supplemental techniques.
Yes, with articaine 4%. Contrary to common belief, the vestibular cortex of mandibular molars — although denser than the maxilla — can be penetrated by articaine thanks to its high lipophilicity. Studies show that buccal infiltration with articaine 4% as a supplement to the IAN block significantly improves success rates in irreversible pulpitis. It does not replace the IAN block but constitutes an excellent adjunct, particularly for the first mandibular molar whose cortex is relatively accessible.
Overdose risk exists theoretically but is low under standard dental practice conditions. The maximum dose of lidocaine is 4.4 mg/kg (7 cartridges of 1.8 mL at 2% for a 70 kg adult). For articaine, it is 7 mg/kg. Respecting maximum doses by patient weight is mandatory, especially in children, elderly patients and cardiac patients. Adding 1–2 extra cartridges in a reasoned manner for supplemental techniques remains within safety margins for a normal-weight adult.
True pain (anaesthetic failure) is sharp, localised to the tooth, triggered by instruments in the pulp and often accompanied by a patient withdrawal reflex. A reflex or pressure response can occur even in the absence of pain, in response to tissue pressure, vibration or anticipation. When in doubt, a cold test during the session (on the exposed pulp or adjacent area) can confirm residual sensitivity. Stop the procedure, reinforce anaesthesia and only resume after confirming its effectiveness.
Deferral is legitimate if: (1) anaesthesia remains insufficient despite all available supplemental techniques; (2) maximum doses have been reached; (3) the patient is in a state of extreme anxiety amplifying their pain perception. In such cases, prescribe holding treatment (ibuprofen 400 mg × 3/day, paracetamol 1 g × 3/day) and recall the patient 48–72 hours later after inflammatory control. Under no circumstances does anaesthetic failure justify continuing a painful procedure — doing so generates psychological trauma and future dental avoidance.
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References
- Hargreaves KM, Keiser K. Local anesthetic failure in endodontic patients. Endodontic Topics. 2002;3:26-39.
- Reader A, Nusstein J, Drum M. Successful Local Anesthesia for Restorative Dentistry and Endodontics. Quintessence Publishing, 2011.
- Cohen HP, Cha BY, Spangberg LS. Endodontic anesthesia in mandibular molars: a clinical study. J Endod. 1993;19(7):370-3.
- Kanaa MD, Whitworth JM, Corbett IP, Meechan JG. Articaine and lidocaine mandibular buccal infiltration anesthesia: a prospective randomized double-blind cross-over study. J Endod. 2006;32(4):296-8.
- Nusstein J, Reader A, Drum M. Local anesthesia strategies for the patient with a "hot" tooth. Dent Clin North Am. 2010;54(2):237-47.
- Reisman D, Reader A, Nist R, Beck M, Weaver J. Anesthetic efficacy of the supplemental intraosseous injection in irreversible pulpitis. Oral Surg Oral Med Oral Pathol. 1997;84(6):676-82.