Nerve blocks and extractions Flashcards
Pain pathways
Transduction
Transmission
Modulation
Projection
Perception
Transduction pain pathway
nociceptors are stimulated by tissue injury (mechanical, thermal or chemical) and produce electrical impulses
Transmission pain pathway
the electrical impulses travel to the dorsal horn of the spinal cord via fast myelinated A-delta fibres or slower unmyelinated C fibres
Modulation pain pathway
input from both ascending and descending pathways may decrease or amplify the impulses within the dorsal horn (wind-up pain)
Projection pain pathway
pain impulses are sent from dorsal horn to higher centres of conscious perception
Perception pain pathway
Subjective exerience of pain within the brain
Analgesia for dental patients
Opioids
- usually with pre-med
- can affect all levels of pain pathway
NSAIDs
- with pre-med, during, or after procedure
- can affect both transduction and transmission
Local anaesthetics
- local or regional nerve blocks
- can affect both transduction and transmission
Alpha-2 agonists
- may be used in pre-med
- can affect both modulation and perception
Ketamine
- affects modulation and perception
Which nerves supply sensory innervation to the oral cavity?
Two branches of the trigeminal nerve
- Maxillary nerve
- Mandibular nerve
Maxillary nerve
Originates from the round foramen.
At the pterygopalatine fossa it gives rise to the zygomatic and pterygopalatine nerves and continues via the maxillary foramen into the infraorbital canal as the infraorbital nerve.
Pterygopalatine nerve
Supplies the hard and soft palate
Infraorbital nerve
Gives rise the the caudal superior alveolar nerve immediately before entering the infraorbital canal - this innervates the first and second molar teeth
Within the infraorbital canal it gives rise to the middle and rostral superior alveolar nerves which supply the premolars and canines/incisors.
Exits the infraorbital foramen and splits into the external and internal nasal nerves and the superior labial nerves.
Mandibular nerve
Oginated from the round foramen.
It runs rostrally around the TMJ and gives rise to the buccal, masseteric and auriculotemporal nerves.
Mandibular nerve continues rostrally over the medial surface of the caudal mandible where it enters the mandibular canal via the mandibular foramen and continues as the inferior alveolar nerve.
Lingual nerve
arises from the mandibular nerve just caudal to the mandibular foramen and supplies sensory innervation to the rostral 2/3 of the tongue and sublingual mucosa.
Alveolar sensory branches
within the mandibular canal
supply the mandibular teeth via foramina in the canal wall.
Mental nerves
Branches of the mandibular nerve
- caudal
- middle
- rostral
exit via the respective foramina and supply the lower lip and rostral 1/3 of the intermandibular area.
Materials used for dental analgesia
23-27 gauge needles, 5/8” to 1.5” depending on site and size of patient.
Dental aspirating syringes are helpful, but bupivacaine cartridges not available
Drugs used for dental local anaesthesia
Lignocaine
Bupivacaine
Lignocaine
usually used as 2% solution with or without adrenaline.
Rapid onset of action (30-120 seconds) but limited duration (30minutes to 2 hours).
Maximum total dose 4mg/kg (need to be careful in small dogs and cats).
Bupivacaine
available in various strengths from 0.25 to 0.75%.
Slower onset (6-10 minutes) but longer duration (6-8 hours, some studies suggest may last 24-48 hour in some patients).
The addition of buprenorphine may extend the duration to up to four days.
Maximum total dose 2mg/kg.
Injection technique for dental LA
Use a fresh needle for each injection site.
Insert needle gently with bevel orientated parallel to the nerve to reduce the risk of transection.
Avoid side to side movement.
Ideally needle is placed in close proximity to target nerve without penetrating the nerve sheath.
Aspirate to ensure no vascular penetration, then rotate and re-aspirate in case bevel was against vessel wall.
Apply digital pressure immediately post injection to reduce risk of haematoma formation and encourage diffusion of the medication.
Volumes used for dental LA
Cats and small dogs: 0.1-0.15ml per site
Medium dogs: 0.2-0.3ml per site
Large dogs: 0.3-0.4ml per site
What will and infraorbital block desensitise?
Ipsilateral teeth, bone, and intraoral soft tissues
Teeth affected depend on depth of needle insertion:
○ Incisors and canine if close to infraorbital foramen (rostral superior alveolar nerve)
○ Premolars 1-4 if deeper (middle superior alveolar nerve)
○ Blocking molars requires insertion of needle beyond the maxillary foramen into the pterygopalatine fossa (caudal superior alveolar nerve)
Technique for infraorbital block
Palpate submucosal neurovascular bundle dorsal to maxillary premolars and trace back to infraorbital foramen (situated dorsal to third premolar).
Insert needle rostral to foramen directed in rostrocaudal direction.
Keep needle parallel to dental arcade to reduce risk of globe penetration.
NB Infraorbital canal is very short in cats and brachycephalic dogs.
What will a maxillary block desensitise?
Will desensitise whole quadrant including teeth, alveolar bone, gingiva, mucosa and mucosa of the hard palate.
Will also block some of the extra-oral soft tissue on nose upper lip and haired skin of the rostral muzzle.
Agents are placed into the pterygopalatine fossa and includes blockade of the major palatine nerve.
Bilateral injection can also block the structures of the caudal nasal cavity.
Technique for maxillary block
Lateral approach:
○ Needle is inserted at rostro-ventral border of zygomatic arch caudal and dorsal to last molar and directed either perpendicular to the mucosa or rostrally towards the opposite nostril.
○ Needle should remain parallel to palate as it approaches the caudal opening of the infraorbital canal.
Ventral approach
○ Hold mouth wide open, insert needle into soft tissue caudal to last molar with needle directed dorsally
○ Needle tip should not need to advance more than 1-3mm into the mucosa
Infraorbital approach
What will mandibular (inferior alveolar) block desensitise?
all ipsilateral mandibular teeth, bone and intraoral soft tissue
Technique for mandibular (inferior alveolar) block
The mandibular foramen is located on the medial mandible halfway along a line drawn from the last molar to the angular process.
The foramen can usually be palpated intraorally in medium to large dogs – follow the neurovascular bundle as it enters the canal.
Agents are deposited over the foramen.
NB deposition of drugs too caudally or medially or in too large a volume can cause anaesthesia of the lingual nerve, which increased the risk of post-operative self-trauma.
Intraoral approach to mandibular block in small dogs and cats
○ Place index finger onto angular process
○ Insert needle just caudal to last molar pointing towards angular process
○ Advance needle along the medial surface of the ramus to the level of the mandibular foramen.
Intraoral approach to mandibular block in medium and large dogs
○ Palpate neurovascular bundle as it enters the mandibular foramen.
○ Insert needle just caudal to last molar and advance towards neurovascular bundle until you can palpate the needle tip under your finger.
Extraoral approach to mandibular block
○ Palpate ventral notch of mandible just rostral to angular process.
○ Insert needle through skin at the midpoint of the notch on the lingual surface of the mandible.
○ Advance the needle along the medial surface of the ramus to the level of the mandibular foramen (usually 0.5-1cm dorsal to the ventral cortex).
○ Place digital pressure intraorally to reduce haematoma formation.
Complications of dental local anaesthesia
Transient elevations in blood pressure and heart rate
Haematoma formation
Risk of LA overdose
Ensure aspiration before injection
Orbital penetration
Neuropraxia
Lingual nerve block
Infiltration anaesthesia
Avoids the risk of iatrogenic nerve damage
Technically easier to perform.
Small bleb of local injected into gingiva and alveolar periosteum in the region of the apex of the tooth to be treated, ideally on both the buccal and lingual/palatal aspects.
Local diffuses into the tissue.
Can be used for all areas apart from caudal mandibular teeth (more dense cortical bone in this area inhibits diffusion).
? Evidence for efficacy…
Likely reduced effect in inflamed tissues due to lower pH
Indications for tooth extraction
-Periodontal disease
Trauma (fractures, pulpitis)
Malocclusions
Tooth resorption
Oral inflammatory disease (FCGS, CCUS)
Persistent deciduous teeth
Unerupted teeth
Advanced caries
Contraindications for tooth extraction
Poor general health – risk of anaesthesia outweighs benefits of treatment
Coagulopathy
Teeth in an area previously treated with radiation therapy
Equipment needed for tooth extraction
Intra-oral radiography equipment
Dental machine with high-speed handpiece and range of burs
Lighting
PPE – gloves, mask, eye protection
Closed (non-surgical) extractions
Extraction is completed without raising a flap
Small single rooted teeth
Teeth with significant attachment loss
Multi-rooted teeth must be sectioned before extraction
- Each single-rooted segment is then treated like a single-rooted tooth
Open (surgical) extractions
Elevation of muco-periosteal flap
○ Improved visibility
○ Easier sectioning of multi-rooted teeth
○ Enables removal of buccal (or lingual) alveolar bone (alveolectomy)
○ Protects soft tissues from iatrogenic damage
○ Allows tension-free primary closure of soft tissues
Consider open technique for all but the simplest extractions
What do you rinse the oral cavity with before open extractions
0.12% chlorhexidine gluconate solution
Envelope flap
Sulcular incision only
Triangle flap
single vertical releasing incision
Pedicle (trapezoid) flap
Two vertical releasing incisions
Sectioning of multi-rooted teeth
Multi-rooted teeth should be sectioned so that each root can be treated like a single-rooted tooth
Always section from furcation in coronal direction
Check radiograph for abnormal root number or morphology
Coronectomy prior to extractions
Crown amputation (coronectomy) can be used as an alternative to sectioning before extracting the roots individually
○ Better visualisation of periodontal ligament all around the roots
○ Better access to roots, particularly in three-rooted upper 4th premolars
○ Enables buccal alveolectomy with cross-cut fissure (straight) bur
Post op care of tooth extractions
Analgesia as appropriate
Soft food 7-14 days
No access to hard treats or toys
Recheck at 7-14 days
Complications of tooth extraction
Fractured tooth roots
Haemorrhage
Mandibular and maxillary fractures
Oronasal fistulas
Ophthalmic complications
Fractured tooth roots
Failure to remove sufficient alveolar bone
Using extraction forceps too early and with too much force
?less likely after coronectomy
Look for bulbous or curved roots
When would a root tip be left in place?
if the risks or removing them outweigh the benefits
Fragment must be small and deep within alveolus
No sign of endodontic disease
Must not leave in Feline Chronic Gingivostomatitis (FCGS) cases
Haemorrhage caused by tooth extraction
Usually results from slipping with dental instruments
Trauma to neurovascular structures, sublingual region etc
Control via ligation, direct pressure or absorbable haemostatic agents
Avoid by employing short finger stop and using controlled force
Maxillary and mandibular fractures during tooth extraction
Most commonly associated with mandibular canine and first molar
NB small dogs
Bone loss from periodontal disease
Oronasal fistulas (ONF)
Dachshunds
Ensure flap raised and closed without tension even if tooth very loose
Once formed will not heal without surgical intervention (have healed as far as body is concerned)
Require surgical debridement and closure
Hole in bone bigger than visible hole in mucosa
Single layer closure often sufficient
First attempt is most likely to be successful
Ophthalmic complications of tooth extraction
Thin shelf of bone between orbit and roots of maxillary PM4 and molars
Orbital (or even brain) penetration if possible if instruments slip
Use short finger stop and controlled force
Key points to avoid extraction complications
Use radiographs to be prepared for difficult extractions
Make large flaps and close without tension
Remove plenty of buccal bone
Use luxators / elevators correctly to break down periodontal ligament before using forceps
Use controlled force with short finger stop
