2. What is a local anaesthetic?
A local anaesthetic is a drug used to reversibly
prevent the transmission of nerve impulses in the area
where it is applied, without affecting consciousness.
3. How do local anaesthetics work?
Induce loss of sensation hence locally
preventing pain in a well-defined area of the
body.
When propagation of a nerve impulse is
prevented, then there can be no
sensation/impulse reaching the CNS/brain.
Local anaesthetics-LAs- are eliciting their
conduction-blocking effects by reversibly
blocking the movement of sodium inside the
nerve axon required for action potentials.
4.
5. Some more details
Local anaesthetics reversibly block the
movement of sodium in and out of the cell at the
region where they are applied.
Without sodium, there can be no nerve
depolarisation hence no action potentials
propagate.
Lack of action potentials/impulses implies LOSS
OF SENSATION which includes the absence of
PAINFUL sensations.
6. No action potentials = No impulses
http://esciencecentral.org/ebooks/minimally-invasive/images/anesthesia-cosmetic-procedures-image-2.jpg
7. Types of Local Anaesthetics:
There are two main types of local
anaesthetics: AMIDES & ESTERS.
All made up of three main components:
A lipophilic/hydrophobic aromatic
compound.
An intermediate chain/linage which can be
either an ester or an amide [This is the part which allows
the distinction between the esters and the amides].
A hydrophilic amine.
9. Amide vs. Ester
Esters are easily broken down by pseudocholinesterase
in the plasma therefore they have a much shorter
duration of action.
Amides are stable in plasma and they are only broken
down in the liver. Have lower potential to produce
allergic reactions than esters.
AMIDES ESTERS
Lignocaine / Lidocaine Procaine [Novacaine]
Bupivacaine Benzocaine [Topical 20%]
Prilocaine Cocaine [Rarely employed these
days]
Articaine Amethocaine [Skin topical]
Mepivicaine --
10. Contents of an LA cartridge:
Local anaesthetic drug.
Vasoconstrictor +/-.
Reducing agent: Used to
stabilize the vasoconstrictor so
it doesn’t get oxidised.
Preservatives.
Fungicide.
Isotonic solution: Modified
Ringer’s solution.
http://media.dentalcare.com/images/en-US/education/ce364/fig01.jpg
11. Lidocaine 2% [20mg/ml]:
Most common.
Gold Standard – Used for over
50 years in dentistry.
Lignospan/xylocaine.
1:80,000 adrenaline as a
vasoconstrictor.
Max. Dose = 500mg or 11x2.2ml
cartridges for a 70kg man.
Pulpal anaesthesia: 45 minutes.
Soft tissues: 2-3 hours.
Half life: 90 minutes.
Topical preparations exist.
http://www.septodont.co.uk/sites/default/files/Lignospan-Special-photo.jpg
12. Prilocaine 3%:
Citanest.
Contains felypressin
[octapressin] as a
vasoconstrictor.
Latex-free bung.
Max. Dose=400mg.
4% solution exists which is
useful in vasoconstrictor-free
anaesthesia.
Half Life: 90 minutes
EMLA topical gel: Prilocaine
2.5% + Lidocaine 2.5%.
http://www.nextdental.com/systhumbs/images/thumbs/
productvariantdetailmain-0003617_1000.jpeg
13. Articaine 4%
Available with either 1:100,000 or 1:200,000
adrenaline.
More effective than lidocaine 2% when used as
buccal infiltration to anaesthetise the lower 6’s
and lower incisors.
MUST NOT be used for nerve blocks because it
can cause temporary or permanent
paraesthesia.
Can penetrate bone more than other LA
agents, hence given buccally in patients with
coagulation defects to avoid ID blocks.
14. Articaine 4%
Metabolised more quickly
than other dental LA agents.
Metabolised partially by
plasma.
Half-life: 20 minutes.
Advantage in relation to
reduced toxicity if repeated
injections are required for a
long procedure.
Max. Dose = 500mg, hence
about 5 cartridges.
http://www.dimensionsofdentalhygiene.com/uploadedImages/
DDH/Magazine/2012/03_March/Features/ppx06.jpg
15. Mepivicaine
Two types of
formulation available
in UK.
2% [20mg/ml] with
1:100,000 adrenaline
[Scandonest].
3% [30mg/ml] plain
solution useful if
vasoconstrictor-free
LA is required. http://www.septodont.co.uk/sites/default/files/Scandonest2-Special.jpg
16. Vasoconstrictors
Adrenaline:
Naturally occurring hormone.
Gives more profound
anaesthesia.
Improves control of
haemorrhage, especially in
infiltration type anaesthesia.
Reduces systemic absorption
hence:
Prolongs the duration of pulpal
anaesthesia.
Reduces the toxicity [hence we
can probably inject more].
http://thumbs.dreamstime.com/z/structure-adrenaline-29160062.jpg
17. Vasoconstrictors
Felypressin:
A synthetic octapeptide.
Similar to the pituitary
hormone vasopressin.
In dental LA added as
0.03IU/ml to 3%
Prilocaine=Citanest.
Not as effective as
adrenaline hence poorer
haemorrhage control.
Does not have the
unwanted effects of
adrenaline i.e. palpitations.
http://www.polypeptide.com/web/upload/products/big/141087184054183220aff5d.png
18. Complications with vasoconstrictors:
Adrenaline can induce tachycardia/fainting.
Adrenaline is contraindicated in patients with
unstable hypertension and unstable angina.
Adrenaline is contraindicated in patients
taking Monoamine Oxidase Inhibitors-
MAOIs.
Felypressin is contra-indicated in the late
pregnancy stages.
19. Needle Choice:
Needle length has to be enough to reach the
area required depth before its complete depth
has entered the tissues:
Short needle 25mm for infiltration.
Long needle 35mm for ID block.
Needle gauge gives a measure of needle
thickness:
30 is thinner and is used for infiltration LA.
25-27 is thicker and is used for an inferior alveolar
nerve block, because it deflects less within the
tissues.
20. Cartridge check:
Made-up of a cap, cylinder and plunger.
Check if it’s the correct medication.
Check the expiry date and any visible
damage.
Check for air bubbles in the solution.
Check for cloudiness as this may indicate a
bacterial infection.
http://media.dentalcare.com/images/en-US/education/ce364/fig01.jpg
25. Choice of anaesthesia
Depends on the tooth that needs to be
anaesthetised.
Maxillary [Infiltration].
Mandibular [Nerve Block].
Depends on the type of treatment you are going
to carry out.
Extractions: All nerves in the area need to be
anaesthetised. Main supply plus accessory nerves!
Restorative / Perio: Usually sufficient to block main
nerve supply.
27. Infiltration Anaesthesia
Act locally to provide good LA.
Effective on local soft tissues.
Act on teeth where bone is reasonably thin.
Used for upper teeth mainly and lower
anterior teeth.
Anaesthetic diffuses through alveolar bone to
root apex.
Not as effective on posterior mandibular
teeth due to the thick cortical bone.
30. Nerve Block Anaesthesia
Anaesthetic delivered to major nerve.
Blocks all sensation downstream of the injection
site.
The more proximal the block, the greater the
area affected.
Commonly used nerve blocks in dentistry:
Inferior alveolar nerve block.
Mental nerve block.
Lingual nerve Block.
Long buccal nerve block.
Greater Palatine nerve block.
Nasopalatine nerve block.
31. Inferior alveolar nerve block
Nerves Affected:
Inferior alveolar nerve.
Mental Nerve [ & incisive nerve].
Target Area:
Mandibular foramen [within the pterygoid
space].
Tissues Anaesthetised:
All mandibular teeth; skin of chin; labial mucosa
and lower lip. Left or right depending on side of
injection.
32. Anatomical Landmarks:
Coronoid notch.
Pterygomandibular raphe.
Occlusal plane for mandibular posteriors.
DirectTechnique:
Palpate and identify injection site.
Advance needle from contralateral premolars,
horizontally 1cm above the occlusal plane.
Needle goes in 2-2.5cm, hit bone, retract needle
1mm, aspirate, inject slowly.
Inferior alveolar nerve block
35. Mental Nerve Block
Nerves Affected:
Mental Nerve and
incisive nerve.
Injection site:
Mental Foramen.
Tissues Anaesthetised:
Mandibular incisors
and canine; labial
gingiva; skin of chin. https://cchungdentalis.files.wordpress.com/2013/04/mandibular-nerves-block-3.jpg
36. Lingual Nerve Block
Nerves Affected:
Lingual nerve.
Injection site:
Anterior to inferior alveolar site. Similar
technique.
Tissues Anaesthetised:
Mucosa of anterior 2/3 of tongue.
Lingual alveolar mucosa and lingual gingivae
of all teeth ipsilateral to the injection side.
37. Long Buccal Nerve Block
Nerves Affected:
Long buccal nerve.
Injection site:
Retromolar fossa.
Tissues Anaesthetised:
Skin and mucus
membrane of cheek.
Buccal alveolar mucosa.
Gingivae of molars.
Ipsilateral to injection side. https://cchungdentalis.files.wordpress.com/2013/04/mandibular-nerves-block-2.jpg
38. Greater Palatine Nerve Block
Nerves Affected:
Greater Palatine Nerve.
Injection site:
Greater Palatine
Foramen [can be
palpated].
Tissues Anaesthetised:
All hard palatal mucosa
and gingiva posterior to
maxillary canines.
Ipsilateral to injection
side.
https://cchungdentalis.files.wordpress.com/2013/02/maxillary-local-anesthesia-5.jpg
39. Nasopalatine Nerve Block
Nerves Affected:
Nasopalatine Nerve.
Injection site:
Mouth of incisive foramen
[posterior to incisive
papilla].
Tissues Anaesthetised:
Palatal mucosa and
gingiva anterior to
maxillary canines.
Bilateral
https://cchungdentalis.files.wordpress.com/2013/02/maxillary-local-anesthesia-6.jpg
40. Complications of LA
Pain, swelling [LA into muscle].
Spread of acute infection.
Facial Nerve Palsy [LA into parotid gland].
Bleeding.
Allergy [very rare].
Trauma to anaesthetised tissues.
Notas do Editor
Safety needle with inbuilt needle protective sheaths to reduce needle stick injuries. Also disposable, except the black handle which can be autoclaved.