Burjor Langdana / Adventure Medic Resident Expedition Dentist
Matt Edwards / Registrar / London Air Ambulance
This article is the third of our series and aims to provide you with some guidelines on providing effective regional anaesthesia for dentistry in the field. For more in the series: check out Expedition Dentistry for Medics and the AM Guide to Dental Trauma.
Most medics will have had little experience with the specific regional blocks used in dentistry. That said, everyone should be happy to provide local infiltration of local anaesthetic and many of us will also be familiar with performing various peripheral nerve blocks. Dental anaesthesia is no different and builds on these basic skills.
One of the team is complaining of severe dental pain. He has been unable to eat or sleep. He will not let you touch the tooth and is extremely anxious about the pain getting worse. He beseeches you, “Doc, can you please numb the tooth before you go anywhere near it?” As he winces in pain, you feel far, far out of your comfort zone…
In essence, we need to locate the area with the problem, select an appropriate local anaesthetic, decide on a dose and then carefully direct our needle using anatomical landmarks.
This article and slideshow will describe the use and loading of a ‘dental syringe’ as well as number of different anaesthetic options. Dental syringes give excellent control when down deep in holes such as the mouth. They also come with specific screw-on long, thin needles and purpose-built cartridges of lidocaine and adrenaline. The disadvantages are that they are a lot of extra kit and require a little practice to use effectively. If your expedition is large or lengthy, we recommend taking a kit along.
No specific dental kit? Here are the options.
Standard needle and syringe / Can be used for blocks towards the back of the mouth, but it will be more difficult than a dental needle. The standard short 25g orange needle is not long enough for inferior alveolar block. However the blue 23g needle, while more painful and slightly more likely to cause direct damage to the nerve, should be able to reach it.
Topical anaesthetic agents / Such as Xylonor 5% lignocaine gel to numb the oral mucosa for injections. Again this may well not be carried in your kit. EMLA cream, a commonly used lidocaine and prilocaine mix, is not licensed for the use on the oral mucosa or wounds, but a number of studies have demonstrated its efficacy and safety in practice. Apply it to the mucosa under gauze for approximately 20-30 minutes. The absorption of the drugs is greater than when applied to broken skin but has still been shown to be far lower than toxic thresholds. With that in mind, it is still advisable to be very conservative with the dose of anaesthetic used for the block if EMLA has been used to numb the mucosa first. Fortunately, the amount required for any given dental block will be small.
We recommend you also use adrenaline (epinephrine) to reduce the systemic spread of local anaesthetic even further. You can mix your own quite easily. Add 50mcg of adrenaline into 10ml of 1% lidocaine and you will have a 1:200,000 mix. 50mcg is 0.05ml of 1:1000 adrenaline (the 1ml ‘anaphylaxis’ ampoule) or 0.5ml of 1:10,000 (the 10ml ‘arrest dose’ ampoule).
To block or infiltrate?
You can’t work on mandibular molars without a nerve block. They are held in very thick bone that will not be affected by local infiltration. For tooth extractions, injections on both sides are required (buccal/labial and palatal black.
However, maxillary bone and the front of the mandible bone (up to the first premolar) is porous and therefore injected anaesthetic will infiltrate around the affected tooth.
Aim for the apices of the roots of the teeth which will be approximately 20mm from the occlusal surface (the biting end) and remember canines are longer ~ 30mm.
At the front of the mouth there is little room for anaesthestic volume so infiltration should be slow or it will be extremely painful, especially on the palatal side.
Mandibular nerve block (the ‘Inferior Dental’ block)
The mandibular branch of the trigeminal nerve becomes the inferior alveolar nerve, running within the bone of the mandible itself. It enters along the medial aspect of the ramus through the mandibular foramen, supplies all the teeth of the lower half of the jaw and then exits the mental foramen supplying cutaneous sensation to the lower lip and chin. Before it enters the bone, it throws off two relevant branches, the buccal nerve and then the lingual nerve. It is not uncommon (and occasionally desirable) to block these nerves as well.
Complications are rare but worth bearing in mind:
Toxicity / Direct intravascular injection can easily be avoided by aspirating prior to injection.
Neurological complications / Short-lived but can cause considerable anxiety if the patient and the medic are not prepared for them. Most commonly, the local anaesthetic agent may act on the facial nerve causing a palsy, or even on the optic nerve. A ‘direct hit’ on the nerve is possible, as is the barbing of a needle – hitting the mandible then causing damage to the nerve as it is withdrawn. Unfortunately the classic ‘electric shock’, warning the clinician of direct contact with a nerve, actually only occurs in about 5% of patients. Larger needles are more likely to cause damage and careful assessment of the anatomy is key to avoiding problems.
As with any procedure: you must do your best to gain informed consent from the patient and you should also first gain some experience with a dentist or maxillofacial department before trying these blocks on your own in the field.
See the slideshow above for diagrams.
Preparation / Kit, gloves and informed consent.
Position / Stand in such a way that you can see the site of injection clearly. Ask the patient to open their mouth as wide as possible. If you are right-handed, then position yourself behind patient to anaesthetise the lower-left quadrant and in front of the patient for the lower-right.
Target / Understand and visualise that you are aiming to place the LA just above the canal entrance (lingula). Find the intersection of the horizontal line (height of injection) and the vertical line (anteroposterior plane) on the medial aspect of the ramus.
Height of Injection / Put your thumb beside the last molar tooth. Feel the jaw bone as it turns upwards to the head. Rest your thumb in the depression there – the coronoid notch. It is about 6-10 mm above the occlusal table of the mandibular teeth. That defines your horizontal plane.
Anteroposterior Plane / Find the pterygomandiblar raphe (the muscular pillar that connects the lower third molar region to the upper third molar region) and go just lateral to it.
Angle of Approach / Approach from over the contra-lateral premolars which will be a 45 degree angle. Angle the needle backwards towards and just above the lingula.
Retraction / Using the non-dominant hand to retract the cheek with your thumb positioned in coronoid notch of mandible as above and index finger along the posterior border of the mandible from outside the mouth.
Depth / Make a visual note on the needle of 3cm. The needle should gently touch bone at 3 cm deep. Too shallow indicates you are in front of the lingula and in the wrong place. Too deep and the needle will be passing towards the posterior aspect of the mandible and all the vital neurovascular structures that will be waiting.
Aspirate and Administer / Check you are not in a blood vessel – if you are, reposition the needle and reaspirate. Once you are happy, deliver a full cartridge slowly over one minute.
Withdraw / Continue to inject slowly on withdrawal to anesthetise the lingual branch.
Consider Anaesthetising the Buccal Branch / To perform a long buccal nerve block, inject another cartridge of anaesthetic into coronoid notch region of the mandible, found in the mucous membrane distal and buccal to most distal molar.
Watch and Wait / Wait for a clear indication of anaesthetic taking effect as far as the midline of the mandible and along the full length of the side of the tongue. This may take seconds or minutes. Only start your dental work when there is a clear sensory distinction across the mandibular midline.
Larijani GE, Cypel D, Gratz I, Mroz L, Mandel R, Afshar M, Goldberg ME. The efficacy and safety of EMLA cream for awake fiberoptic endotracheal intubation. Anesth Analg. 2000 Oct;91(4):1024-6.
Smith MH, Lung KE. Nerve injuries after dental injection: a review of the literature. J Can Dent Assoc. 2006 Jul-Aug;72(6):559-64.
Vickers ER, Marzbani N, Gerzina TM, McLean C, Punnia-Moorthy A, Mather L. Pharmacokinetics of EMLA cream 5% application to oral mucosa. Anesth Prog. 1997 Winter;44(1):32-7.
The authors have made efforts to ensure that the pictures and diagrams in their slideshow are licensed for modification and dissemination. However, please contact Adventure Medic with any specific requests for attribution.