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In recent years, the awareness among veterinarians has increased on the need to provide comprehensive pain relief, but the majority of companion animals still do not receive analgesia pre-emptively, or for an adequate duration post-operatively, when undergoing a dental procedure.
Pain and inflammation during dental procedures follow the same physiological pathways as other painful procedures (Barnett 1997) and by monitoring respiratory rate, heart rate, blood pressure and rectal temperature the companion animal veterinarian has a simple and affordable means of recognising pain experienced by dogs during dentistry (Clarke 2004).
The timing of analgesic administration is important, as general anaesthesia does not necessarily equate with analgesia. It has been shown that ‘pre-emptive analgesia’, analgesics administered before the infliction of pain, greatly reduce the degree of pain the central nervous system registers, and therefore post-operative pain (Woolf and Wall, 1986; Wall 1988; Woolf 1989).
When should you consider using a regional nerve block?
Whenever a painful procedure or inflammation is inflicted:
Extractions
Subgingival root planing – whenever a periodontal pocket is present and you are removing cementum or root
Oral surgery – including gum surgery or other soft tissue surgery
Cavities and Restorations where the tooth is cut
Jaw fractures
Types of anaesthetic
The type of anaesthetic administered is often determined by either the degree or duration of the pain and the time required for the onset of action. Lignocaine, a short-acting anaesthetic, has a duration of 30-60 minutes and takes only a couple of minutes to act. Mepivacaine, a medium-acting anaesthetic, takes 5 minutes to work and lasts approximately 4 hours. Bupivacaine often combines with adrenaline, has an onset of action of 10-15 minutes and a duration of 8 hours.
Anatomy
The maxillary branch of the trigeminal nerve is sensory to the upper teeth. In the pterygopalatine fossa the maxillary nerve gives rise to the zygomatic nerve, pterygopalatine nerve, and infraorbital nerve.
In the ptyergopalatine fossa, the infraorbital nerve gives off the caudal, middle and cranial alveolar branches. The caudal alveolar branches arise from the ventral aspect of the infraorbital nerve to enter the alveolar canals via the alveolar foramina of the maxilla to supply the 4th premolar and molars.
After the caudal superior branches are given off, the infraorbital nerve enters the infraorbital canal by passing through the maxillary foramen. Once within the canal, the infraorbital nerve gives off from its ventral border, the middle branches, which enter alveolar canals via alveolar foramina to supply the other premolars.
Just before the infraorbital nerve exits from the infraorbital canal through the infraorbital foramen, it gives off from its ventral surface the cranial branches. These branches enter the incisivomaxillary canals to supply the upper canine and incisor teeth. The infra-orbital nerve then exits the foramen at the level of the third premolar tooth and plays a sensory role to the skin and tissues of the face and lip.
Technique for infra-orbital nerve block
A 27 – 30 gauge short needle is recommended. The lip should be lifted to reveal the teeth and buccal mucosa. At the level of the maxillary third premolar tooth, the bone is palpated approximately 0.5mm in cats and 1-2cm in dogs dorsal to the 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. Maintain your finger on the edge of the bulge, applying tension to the tissues. 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 depth of penetration is to the level of the distal root of the 4th premolar tooth. Before injecting make sure: the depth of the needle is adequate to reach the foramen, any deviation of the needle away from the foramen, and orientation of the bevel. Aspirate before injecting to ensure needle is not in a vessel. Slowly deposit 0.1mls (cat) and 0.25mls per 5 kg up to 1ml maximum dose (dog) over 30 seconds. Little or no swelling should be visible. You should 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. Wait for the anaesthetic to work.
Click on the image to view the video on YouTube ‘Administering an Infra-Orbital Nerve Block’
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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