Techniques of Locoregional Anesthesia of the Oral Cavity
World Small Animal Veterinary Association World Congress Proceedings, 2015
Margherita Gracis, Med Vet, DAVDC, DEVDC
Clinica Veterinaria San Siro, Milan, Italy

Many dental, oral and maxillofacial conditions, and the great majority of surgical procedures needed to address these (e.g., dental extractions, periodontal flap surgery, endodontic procedures, trauma and oncologic surgical procedures) cause some level of pain and require pain management.

A multimodal approach, with systemic as well as local analgesics, should be utilized to achieve preemptive analgesia, which improves perioperative patient's pain management, decreases intraoperative anesthetic requirements, and improves patient's recovery.

Locoregional analgesia allows minimizing the concentration of inhalant agents and the depth of general anesthesia, thus decreasing the minimum alveolar concentration and the risk of anesthetic complications such as bradycardia, hypotension and hypoventilation.

Lidocaine (short acting) and bupivacaine (long acting) are the most used local anesthetic agents in veterinary dentistry and oral surgery. Recommended dosages vary quite significantly in the literature, with an average maximum dose reported to be 1–2 mg/kg for both lidocaine and bupivacaine. They are amide-type solutions and are primarily metabolized by the liver and excreted by the kidneys. They should therefore be used with great caution in patients with significant liver, renal and heart dysfunction and failure. Infection or acute inflammation in the area of injection is a contraindication to the use of local anesthetic agents.

Nerve blocks may be performed using disposable 1.0- or 2.5-cc aspirating syringes and thin, disposable, stainless steel needles (from 25 G to 30 G, from 12 mm to 36 mm in length), or dental, breech-loading, cartridge-type, aspirating syringes.

Maxilla

Maxillary Nerve Block

This block is used to anesthetize the teeth, soft tissues (including the skin of the nose, cheek and upper lip) and hard tissues of the ipsilateral maxilla. The palate and the nasal mucosa of the same side (innervated by branches of the pterygopalatine nerve) are also likely desensitized.

The anesthetic solution is placed in the rostral part of the pterygopalatine fossa using a transcutaneous (subzygomatic) or a transmucosal (maxillary tuberosity) approach. The nerve is blocked just before it enters the maxillary foramen.

Reaching the pterygopalatine fossa through the infraorbital foramen and canal is not recommended, as the risk of injuring the neurovascular content is very high.

The subzygomatic approach is performed inserting the needle perpendicularly to the skin, just ventral to the rostral portion of the zygomatic arch, caudal to the maxillary border and rostral to the mandibular coronoid process.

The maxillary tuberosity approach requires the insertion of the needle through the oral mucosa just behind the last maxillary molar, perpendicularly to the hard palate. The needle should be inserted for a short distance (about 5 and 10 mm in cats and up to 25–30 mm in dogs).

Caudal Palatine Nerves Blocks (Block of the Major, Accessory and Minor Palatine Nerves)

This block is achieved using the same approaches described for the maxillary nerve bock, as the pterygopalatine nerve (from which the major, minor the accessory palatine nerves originate) leaves off the maxillary nerve in the rostral portion of the pterygopalatine fossa.

With this block, the hard and soft palate are desensitized. Another branch of the pterygopalatine nerve, the caudal nasal nerve, which enters the nasal cavity and supplies the mucosa of the ventral part of the nasal cavity, maxillary sinus and palate, is also likely blocked.

Rostral Palatine Nerve Block (Block of the Major Palatine Nerve)

The major palatine nerve may be blocked rostrally, at the level of the major palatine foramen. A very thin needle is inserted through the mucosa of the hard palate midway between the palate midline and the dental arcade, at the level of the mesial roots of the maxillary fourth premolar tooth in cats and the distal root of the same tooth in dogs, and a very small amount of solution is injected while retracting the needle. No attempt is made to engage the foramen.

Infraorbital Nerve Block

The infraorbital nerve is the rostral continuation of the maxillary nerve after it enters the maxillary foramen in the pterygopalatine fossa. It supplies the maxillary teeth and the soft tissues of the external nose and upper lip.

The block is performed inserting the needle for a short distance through the infraorbital foramen, which is located on the lateral side of the maxilla, rostroventrally to the eye and dorsal to the distal root of the maxillary third premolar tooth. The needle may be inserted through the vestibular mucosa or through the facial skin. Especially in cats and brachycephalic dogs, it should be kept parallel to the gingival margin or directed ventrally, to avoid injuries to the ocular globe.

Mandible

Caudal and Rostral Inferior Alveolar Nerve Blocks

The inferior alveolar nerve leaves the mandibular nerve in the pterygopalatine fossa, then runs ventrorostrally, and enters the mandibular foramen on the medial side of the mandibular ramus. It runs into the mandibular canal, below the roots of the teeth, giving off caudal, middle and rostral mandibular alveolar dental branches. Rostrally, it supplies three terminal branches, the caudal, middle and rostral mental nerves, exiting through the homonymous foramina on the lateral side of the mandible and supplying the rostral lower lip and the rostral intermandibular region.

The nerve may be blocked at the mandibular foramen (caudal inferior alveolar nerve block) or at the middle mental foramen (rostral inferior alveolar nerve block).

With the caudal approach all mandibular teeth, rostral lower lip and the tissues of the rostral intermandibular region are anesthetized. Likely, the lingual nerve is also affected, desensitizing the soft tissues and periosteum of the lingual side of the mandible, floor of the mouth and rostral two-thirds of the tongue. The needle is inserted medial to the mandible either through the skin on the ventral aspect of the mandible or through the oral mucosa, and the anesthetic solution is placed next to the mandibular foramen.

If only the rostral teeth, the rostral lower lip and the rostral intermandibular region need to be desensitized, a rostral inferior alveolar nerve block may be performed instead. The needle is inserted through the vestibular mucosa at the level of the canine's root apex, at mid-height of the mandibular body, lateral to the mandible. It is then gently pushed for a short distance into the middle mental foramen. The small size of the foramen and the angle of the canal at this location often make the administration of this block impracticable, especially in cats.

Middle Mental Nerve Block

The rostral, middle and caudal mental nerves are the rostral continuation of the inferior alveolar nerve, and supply the rostral lower lip and the rostral intermandibular region. They exit through rostral (ventral to the first incisor tooth), the middle (ventral to the mesial root of the second premolar tooth) and caudal (ventral to the third premolar tooth) mental foramina, respectively. By placing the anesthetic solution at the level of these foramina (usually the middle mental foramen only), the rostral mandibular soft tissues are desensitized.

Other Techniques

When it is necessary to anesthetize a very limited area, or just one or two teeth, other techniques may be used.

Splash Block

A splash block is the placement of an anesthetic solution directly into a surgical site, such as an emptied alveolus after dental extraction. The analgesic effect occurs by diffusion of the solution into the surrounding tissues.

Infiltration Anesthesia

Infiltration anesthesia is achieved by injecting the anesthetic solution under the oral mucosa, just above the apex of the tooth of interest. In areas of thin cortical bone (e.g., rostral mandible and maxilla), the anesthetic agent will diffuse through the bone and anesthetize the pulp tissues.

Intraosseous Anesthesia

Intraosseous anesthesia is achieved by placing an anesthetic solution into the bone supporting the teeth, using dedicated devices able to perforate the bone.

Intraseptal Injection

The intraseptal injection is the placement of the anesthetic solution in the interdental papilla.

Intraligamentary Injection

The intraligamentary injection is performed injecting small volumes of anesthetic solution with special devices into the periodontal ligament space.

Intrapulpal Injection

During root canal therapy of a recently fractured tooth, the local anesthetic solution may be injected directly into the pulp system, before pulp extirpation is performed.

References

1.  Gracis M. The oral cavity. In: Campoy L, Read MR, eds. Small Animal Regional Anesthesia and Analgesia. Wiley-Blackwell; 2013:119–140.

2.  Lemke KA. Pain management II: local and regional anaesthetic techniques. In: Seymour C, Duke-Novakovski T. BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. Gloucester, UK: British Small Animal Veterinary Association; 2007:104–114.

3.  Rochette J. Regional anesthesia and analgesia for oral and dental procedures. Vet Clin North Am Small Anim Pract. 2005;35(4):1041–1058.

4.  Woodward TM. Pain management and regional anesthesia for the dental patient. Top Companion Anim Med. 2008;23(2):106–114.

  

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Margherita Gracis, Med Vet, DAVDC, DEVDC
Clinica Veterinaria San Siro
Milan, Italy


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