Basic dental and oral local anaesthesia

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CHAPTER 4 Basic dental and oral local anaesthesia

Dental pain is best managed by a dentist because a dentist knows about teeth and most doctors do not. They can also provide definitive care in an appropriate setting with the correct instruments. Dentists are often not available, however, so patients with toothache or dental injuries often present to the ED for pain relief. Although conventional analgesics are effective, performing a nerve block with a long-acting local anaesthetic will make the patient your friend for life. Dental blocks are also a good choice for pregnant women because local anaesthetics and adrenaline (epinephrine) are not teratogenic and can be administered safely without systemic side effects, if used correctly.

The maxillary dentition receives innervation from the maxillary branch of the trigeminal nerve (anterior, middle and posterior superior alveolar nerves, palatine nerves), and the mandibular dentition from the mandibular division of the trigeminal nerve (inferior alveolar nerve, accessory innervation).

Local anaesthesia for the maxillary dentition

Supraperiosteal or infiltration local anaesthesia

The maxillary teeth are innervated via a network of nerves originating from the maxillary nerve and the infraorbital nerve (Fig. 4.1). These nerves run in the cancellous bone of the maxilla, superior to the roots of the maxillary teeth. The lateral cortical plate of the maxillary alveolus is usually sufficiently thin and porous to allow for effective infiltration (supraperiosteal) local anaesthesia. This technique is not recommended for more than two adjacent teeth or when local infection or inflammation is present. To accomplish this, local anaesthetic is infiltrated along the buccal-gingival fold adjacent to the area to be blocked (e.g. adjacent to the first molar if that tooth is painful from infection or injury).

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Fig. 4.1 The maxillary nerve and its terminal branches: maxillary nerve, posterior superior alveolar nerve, infraorbital nerve, anterior superior alveolar nerves, middle superior alveolar nerves.

Technique

Identify the target area for needle insertion – the apex of the buccal-gingival fold adjacent to the target tooth or teeth.
Dry the mucosa of the target area and apply topical anaesthesia with a cotton bud. Use lidocaine 4% gel or any other topical anaesthetic (improvising with an ester such as tetracaine, which can usually be found amongst the ophthalmic medications, works extremely well).
Wait 30 seconds for the topical anaesthesia to take effect. To reduce the pain of injection, lift the lip, pull it taut and shake it as the needle is inserted.
Align the syringe parallel to the long axis of the tooth. With the bevel facing the bone, insert the needle into the target area and advance the needle until the bevel is at or beyond the apex of the tooth (usually just a few millimetres) (Fig. 4.2). There should be no resistance or patient discomfort during this procedure.
If two teeth need to be blocked, insert the needle of the syringe parallel to the maxillary buccal mucogingival line (where the cheek mucosa reflects onto the gum) opposite the teeth to be anaesthetised (Fig. 4.3).
Aspirate, and if there is no flashback of blood, inject about 2 to 4 mL of local anaesthetic slowly over 30 to 60 seconds, and continue whilst slowly withdrawing the needle.
The patient should experience numbness within 2 to 5 minutes of injection. Failure to reach the apex of the tooth when injecting anaesthetic results in varying degrees of soft-tissue numbness without anaesthesia of the tooth itself. If the first attempt at infiltration fails to provide adequate pain relief, the procedure can safely be repeated several times provided that the total amount of local anaesthetic injected is within the recommended limits.
Lidocaine provides about 1 hour of dental analgesia and 3 to 5 hours of soft-tissue analgesia. For temporary relief of pain in the ED, the preferred agent is 0.5% bupivacaine or 0.5% ropivacaine with 1:200 000 adrenaline. This provides 1 to 3 hours of dental analgesia and 4 to 9 hours of soft-tissue analgesia. The duration of analgesia is less with supraperiosteal infiltration than with regional nerve blocks. The onset of analgesia is within 3 to 10 minutes, depending on which agent is used.
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Fig. 4.2 Supraperiosteal infiltration for a single maxillary tooth. The needle is inserted at the apex of the buccal-gingival fold and advanced several millimetres before injecting local anaesthetic.

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Fig. 4.3 Supraperiosteal infiltration for two or three maxillary teeth. The needle is inserted at the apex of the buccal-gingival fold and advanced posteriorly across the teeth to be blocked. After aspirating, local anaesthetic is injected as the needle is slowly withdrawn.

Tips for the non-dentist

The orientation of the bevel is important in order to decrease the pain of injection and to control the deflection of the needle. When infiltrating, it is better to orientate the bevel towards the bone to avoid scraping the periosteum (Fig. 4.4). It is also important to remember, especially with nerve blocks, that the tip of the needle is deflected away from the side of the bevel as it passes through the tissues. This may amount to as much as 4 mm of deflection in a 30G needle inserted 25 mm into the tissues.
One cartridge of local anaesthetic (1.8 to 2 mL) is sufficient in dental anaesthesia to provide anaesthesia to most areas. Larger volumes injected over a larger area increase the likelihood of successful anaesthesia, however, especially for the non-expert. The disadvantage of this is the potential for toxic effects of the local anaesthetic and maximum doses should be carefully calculated and observed.
If local infiltration is ineffective for the maxillary tooth or teeth, a nerve block might be required. An infraorbital nerve block will anaesthetise the anterior superior alveolar nerve which innervates the anterior maxillary teeth and a posterior superior alveolar nerve block will anaesthetise the maxillary molars.
Avoid using a standard dental syringe: it is impossible to aspirate using these syringes. Use a conventional syringe with the smallest readily available needle of appropriate length (often a 23G 40-mm needle).
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Fig. 4.4 The bevel of the needle should be orientated towards the bone to avoid scraping the periosteum with the sharp tip of the needle.

 

Intraoral infraorbital nerve block

This block provides excellent anaesthesia for pain involving the upper teeth from the midline to the canine or for lacerations involving the upper lip. It also anaesthetises the maxillary premolars and part of the root of the first maxillary molar in about 70% of patients.

The infraorbital foramen can easily be identified using ultrasound to establish its exact position.

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