Sensory innervation of the dentition is provided by the trigeminal nerve (CNV) via the maxillary and mandibular branches.
The maxillary branch divides into the pterygopalatine, minor and major palatine nerves, caudal nasal nerve, superior alveolar nerves, and the infraorbital nerve. Caudal superior alveolar nerves are given off to supply the maxillary molars before the infraorbital nerve passes into the infraorbital canal through the maxillary foramen. Within the infraorbital canal, middle superior alveolar nerves branch off to supply the premolars. About halfway along the infraorbital canal a branch is given off medially that enters a foramen that leads to supply the canine and incisors on that side. The infraorbital nerve then exits the canal at the foramen of the same name to supply the upper lip, cheek and mucosa of these two structures.
The mandibular branch of the trigeminal nerve divides into a number of branches, the most important of which for veterinary dentistry are the buccal branch (dorsal and ventral) that supplies the mucosa of the cheek and the gingiva of the caudal maxillary and mandibular teeth on the buccal aspect; the lingual branch that branches prior to the mandibular nerve entering the foramen of the same name; and the mandibular nerve or inferior alveolar nerve. The latter nerve courses through the mandibular canal supplying the mandibular molars and premolars. At the middle mental foramen, a branch exits the canal to supply the rostral cheek and lip. The nerve then continues to supply the canine and incisors after which a small branch exits via the rostral mental foramen, situated near the alveolus of incisor 2 on the labial aspect.
Infraorbital block: administered at the opening of the infraorbital canal; blocking soft tissue rostral to the foramen.
Middle infraorbital block: administered halfway into the infraorbital canal; blocking incisors, canine and premolars (middle superior alveolar nerves).
Deep infraorbital block: administered near the maxillary foramen; blocking all teeth on that side (this is equivalent to the maxillary block - caudal superior alveolar nerves).
Maxillary block: administered at the maxillary foramen; blocking all teeth on that side.
Palatine block: administered near the major palatine artery; blocking the palatal mucosa rostral to the site of administration.
Mental block: administered at the middle mental foramen; blocking soft tissues rostral to the foramen. If blocked within the canal, incisors, canine and premolar 1 and 3 will be blocked.
Mandibular (inferior alveolar) block: administered at the mandibular foramen; blocking all mandibular teeth on that side.
Buccal nerve block: (can be palpated beneath the buccal mucosa in the caudal cheek fornix) administered where the oral mucosa covers the rostral margin of the masseter muscle. The buccal nerve must not be confused with the "ramus buccales" (branches of the maxillary branch that supply the skin of the cheek.
Lingual nerve may be blocked by administration of the local anaesthetic caudal to the mandibular foramen.
Intra-ligament block: administered into the ligament space of the affected tooth.
Intra-canal block: administered directly into the pulp chamber and should be performed in teeth that are to undergo root canal therapy if the pulp is still vital.
Local block: line blocks may be used under certain circumstances.
Lingual nerve: for glossal surgery, an intralingual block may be applied.
Local Anaesthetic Drugs
Lignocaine: onset of action about 10 minutes, duration about 60–120 minutes.
Mepivacaine: onset of action about 20 minutes, duration about 90–180 minutes.
Ropivacaine and bupivacaine: onset 20–40 minutes, duration 3–4 hours.
Local anaesthetic agents may come combined with vasoconstrictors. These help restrict bleeding and also help increase duration of effect due to vasoconstriction.
Local anaesthetics may be combined with opioids to give synergistic effects.
Multimodal anaesthesia and analgesia leads to intraoperative comfort and reduction in the levels of general anaesthesia. It also leads to reduced requirement of postoperative analgesia.
Multimodal analgesia is the concurrent or sequential administration of drugs that have different mechanisms of action leading to additive or synergistic effects. Often less of each drug is required to obtain an improved result. (Handbook of Vet Pain Management). Synergistic effects have been found when local anaesthetics have been combined with opioids or dissociative anaesthetics. Combinations of opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) have also been shown to be synergistic. (VetPain Man)
Preemptive analgesia reduces the dose and number of anaesthetic agents required to maintain general anaesthesia, improving intraoperative and postoperative analgesia.
Unmyelinated A-alpha and C nerve fibres are blocked by local anaesthetics.