How can I safely perform an intra‑oral mental nerve block in an adult patient with no amide‑type local anesthetic allergy, no infection at the injection site, and no bleeding disorder or anticoagulant therapy?

How to Perform an Intra-Oral Mental Nerve Block

The intra-oral approach to mental nerve block is the preferred technique because it is significantly less painful than the percutaneous approach while providing equivalent or superior anesthetic efficacy for lower lip procedures. 1

Anatomic Landmarks and Preparation

• Locate the mental foramen by palpating approximately 2.5 cm lateral to the midline, between the first and second mandibular premolars, typically below the second premolar apex 2
• Evert the lower lip to expose the buccal mucosa and identify the lower canine as your reference point 2
• Apply topical anesthetic (viscous lidocaine) to the oral mucosa for 1 minute prior to injection to significantly reduce injection pain 1
• Prepare the injection site with antiseptic solution 3

Injection Technique

• Use a 23- to 27-gauge needle attached to a syringe containing 2–2.5 mL of local anesthetic 1, 2
• Insert the needle into the buccal mucosa at the level of the lower canine, advancing it posteriorly until it approximates the mental foramen 2
• Aspirate before injecting to ensure the needle is not intravascular—this step is mandatory to prevent systemic toxicity including seizures, cardiovascular collapse, and respiratory arrest 3
• Inject slowly over 20 seconds to minimize discomfort and tissue trauma 3, 1
• Repeat on the contralateral side if bilateral anesthesia is required for midline procedures 2

Anesthetic Selection and Dosing

• Use preservative-free amide-type local anesthetics (lidocaine or articaine with epinephrine) as they are preferred over ester-type agents 4, 3
• 2% lidocaine with 1:100,000 or 1:200,000 epinephrine is effective, with 2–2.5 mL per side providing adequate anesthesia 1, 2
• 4% articaine with 1:100,000 epinephrine provides higher success rates (80–93.8%), faster onset, and longer duration than lidocaine, though smaller volumes (0.6–2 mL) may suffice 5, 6
• Buffered lidocaine at room temperature is acceptable, though warming the solution may further reduce discomfort 1

Expected Onset and Duration

• Onset of anesthesia occurs within 1–2 minutes for both lidocaine and articaine 1, 5
• Duration of anesthesia is approximately 60 minutes with lidocaine and up to 20 minutes longer with articaine for premolar anesthesia 1, 5
• Wait at least 10 minutes before initiating the procedure to ensure adequate anesthesia 7, 6

Efficacy and Success Rates

• The intra-oral mental nerve block achieves lower lip anesthesia in 100% of patients when performed correctly, compared to 70% with the percutaneous approach 1
• Success rates for mandibular premolars range from 53–93.8% depending on the anesthetic used, with articaine superior to lidocaine 7, 5, 6
• For mandibular anterior teeth and canines, success rates are lower (32.5–55% with articaine), making this block less reliable for these teeth 5
• If anesthesia is inadequate for premolar procedures, adding an inferior alveolar nerve block increases success to 82% 7

Safety Considerations in Special Populations

• In very old or frail patients with significant comorbidities, bilateral mental nerve block is a safe alternative to general anesthesia and allows procedures to be performed in a beach-chair position 2
• Avoid chlorhexidine-containing antiseptic solutions because chlorhexidine allergy is more common than amide local anesthetic allergy and is a frequent cause of peri-operative anaphylaxis 8
• Ensure a latex-free environment, as latex allergy (1.4% prevalence) is far more common than true amide local anesthetic allergy (<1%) 8

Post-Procedure Monitoring

• Inform patients that sensation typically returns within 4–12 hours for standard local anesthetics 9
• Advise patients to report any sensory or motor block persisting beyond 12 hours, as this warrants urgent evaluation for complications such as nerve injury or hematoma 9
• Post-injection pain may be higher with mental nerve block than with inferior alveolar nerve block during the first 4 days, though this does not affect procedural success 6

Common Pitfalls to Avoid

• Do not proceed without aspiration—intravascular injection of local anesthetic can cause life-threatening systemic toxicity 3
• Do not inject too rapidly—this increases pain and tissue trauma 3, 1
• Do not skip topical anesthesia—it significantly reduces injection pain with the intra-oral approach 1
• Do not rely on mental nerve block alone for mandibular anterior teeth or canines—success rates are inadequate for these teeth, and alternative blocks should be considered 5
• Do not assume block failure if inadequate time has elapsed—wait the full 10 minutes before testing anesthesia 7, 6