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The infra-orbital nerve block anaesthetises the maxillary teeth and the associated buccal soft tissues.
In recent years, the awareness among veterinarians has increased on the need to provide comprehensive pain relief (Carroll, 1999; Gayner, 1999; Hendrix and Hansen, 2000; Lascelles, 1999). Pain and inflammation evoked during dental procedures follow the same physiological pathways as other painful procedures (Barnett, 1997).
The infra-orbital nerve block anaesthetises the maxillary teeth and the buccal soft tissues associated with them. The nerve anaesthetised is the infra-orbital and anterior superior alveolar nerves. Indications for this nerve block would include treatment of the maxillary teeth and soft tissues of the anterior portion of the mouth.
Techniques for the infra-orbital nerve block
Position of the infra-orbital nerve exiting the rostral foramen of the infra-orbital canal (blue line).
Insertion of the needle through the buccal mucosa towards the rostral foramen of the intra-orbital canal.
Watch the nerve block procedure
This is an intra-oral injection. The lip should be lifted to reveal the teeth and buccal mucosa. The bone is palpated approximately 1-2cm dorsal to the maxillary third premolar tooth. An outward bulge can be palpated which is the buccal border of the infra-orbital foramen. The bone caudal to this bulge is the border of the infra-orbital canal. The palpable hollow, cranial to the bulge, is the foramen of the canal and the point where you wish to insert your needle. Maintain your finger on the edge of the bulge, applying tension to the tissues. Ideally, a 30-gauge short needle is recommended, but a 27-gauge will suffice. The bevel of the needle is orientated towards the bone. Insert the needle through the mucosa just dorsal to the muco-gingival line at the level of the second premolar tooth in a caudal direction towards the infra-orbital foramen. Advance the needle slowly until the bone is gently contacted. The point of contact should be the upper rim of the infra-orbital foramen. The general depth of penetration is to the level of the distal root of the maxillary 4th premolar tooth. Aspirate. Slowly deposit up to 0.5mls over 30 seconds. Remember your maximum safe dose/volume. No swelling should be visible and you should not be able to feel the solution under your finger. Move your finger over the exit of the foramen and slowly withdraw the needle. Maintain direct finger pressure for another 30 seconds. Await the onset of action and then commence your procedure.
The timing of administration of the local anaesthetic – ‘Pre-emptive analgesia’
In human dentistry, the use of local analgesia in conjunction with general anaesthesia is a common treatment regime. The timing of analgesic administration is important, as anaesthesia does not necessarily equate with analgesia. It has been shown that the administration of analgesics before the infliction of pain, termed ‘pre-emptive analgesia’, greatly reduces the degree of pain the central nervous system registers, and therefore post-operative pain (Woolf and Wall, 1986; Wall, 1988; Woolf, 1989; Clarke, 2004). Clarke (2004) found that the administration of pre-emptive analgesia for tooth extraction had a significant effect on the reduction of pain when compared to when no analgesia was administered in dogs undergoing surgical tooth removal.
Types of analgesic agents
The most common anaesthetics used for local analgesia in veterinary dentistry are bupivacaine, lignocaine, mepivacaine and prilocaine. The dose of local anaesthetic drugs is presented in mg/kg. The maximum dose rates for each agent are 1.3, 4.4, 6.6 and 6.0 mg/kg respectively. To increase safety, one should always use the minimum drug doses and the smallest clinically effective dose. Maximum doses are unlikely to be reached in large breed dogs, but it is very easy to overdose the small breed dogs and cats. The maximum calculated drug dose should always be decreased in medically compromised or older patients. Changes in liver function, plasma protein binding, blood volume, and other important physiological functions influence the way local anaesthetics are distributed and bio-transformed in the body (Iwatsubo et al, 1997).
Properties of the local anaesthetic agents
Lignocaine, a short-acting anaesthetic, has marked vasodilator effects, which limit the duration of action to only 30 minutes. Its onset of action is 2 – 3 minutes. Mepivacaine, a medium-acting anaesthetic, has a rapid onset of action of 2 minutes, and a longer duration than lignocaine of 2 – 3 hrs. Bupivacaine is available as a 0.5% solution combined with adrenaline. It has a long duration of action of up to 6 hours, and an onset of action of 10 minutes, so the veterinarian must plan ahead.
Dr David E Clarke, BVSc, Diplomate AVDC, Fellow AVD, MACVSc, Registered Specialist, Veterinary Dentistry, runs a specialist referral practice in Hallam, Victoria (Hallam Veterinary Clinic) and regularly conducts lectures and workshops in Australia, New Zealand and Asia. He is the owner of K9 Gums a veterinary dental wholesale company that has been supplying veterinary clinics in Australia, New Zealand and Asia with quality equipment, disposables and materials since 1997. Dr Clarke also shares his extensive knowledge through the Veterinary Dental Education Centre (VDEC) the home of his free webinar series; information on workshops and seminars and a range of case studies and videos
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