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In recent years, 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 mental nerve block anaesthetises the mandibular canine and incisor teeth and the lip rostral to the mental foramen. The nerve anaesthetised is the mental nerve, the terminal branch of the mandibular nerve. Indications for this nerve block would include treatment of the mandibular canine or incisor teeth or the rostral lip, i.e., extraction of deciduous canine teeth for a malocclusion.
The most common reason for failure to achieve adequate anaesthesia may occur when there is a significant infection or inflammation in the area the anaesthetic agent is deposited. Complications may include a haematoma but this is rare, as it is a relatively simple technique with easy-to-find landmarks.
Techniques for the mental nerve block
Position of the caudal and middle mental foramen located on the buccal surface of the mandible. The larger foramen (middle mental) is the most cranial of the two.
Insertion of the needle through the buccal mucosa towards the middle mental foramen.
Watch the Nerve Block Procedure
An intra-oral approach is used to locate the mental foramen on the buccal surface of the mandible caudal to the lip frenulum ventral to the 2nd premolar tooth. A 30-gauge short needle is recommended. The upper lip is raised and the lower lip is pulled ventrally to expose the frenulum. The bevel of the needle is orientated towards the bone. Insert the needle through the mucosa cranial to the frenulum towards the foramen. Advance the needle slowly until it enters the foramen. The general depth of penetration is 5mm in a dog. Aspirate. Slowly deposit up to 0.5mls over 30 seconds. The volume is related to the type of anaesthetic agent used. Slowly withdraw the needle. Wait for the anaesthetic to work. The onset of action is related to the type of anaesthetic used.
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 manner in which 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.
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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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