LOCAL ANAESTHESIA IN DENTAL PRACTICE

Dr. Christis Isseyegh

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.

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.

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.

No action potentials = No impulses

http://esciencecentral.org/ebooks/minimally-invasive/images/anesthesia-cosmetic-procedures-image-2.jpg

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.

Amide vs. Ester

http://media.dentalcare.com/images/en-US/education/ce449/fig03.jpg

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 ESTERSLignocaine / Lidocaine Procaine [Novacaine]

Bupivacaine Benzocaine [Topical 20%]Prilocaine Cocaine [Rarely employed

these days]Articaine Amethocaine [Skin topical]

Mepivicaine --

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

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

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

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.

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

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

VasoconstrictorsAdrenaline: 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

VasoconstrictorsFelypressin: 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

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.

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.

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

Trigeminal Nerve Anatomy CN-V

http://www.frca.co.uk/images/trigeminal_nerve_general.jpg

CN-V2 Maxillary Division

http://www.frca.co.uk/images/maxillary_branch.jpg

CN-V3 Mandibular Division

http://www.frca.co.uk/images/mandibular_branch.jpg

Innervation of teeth and soft tissues

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.

Infiltration vs. Nerve Block

Infiltration Nerve Block

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.

Buccal Infiltration

http://pocketdentistry.com/wp-content/uploads/285/QE06_Meechan_fig041b.jpg

Injected deep into vestibular fold

Palatal Infiltration

http://www.nysora.com/files/2013/oral-maxillofacial-regional-anesthesia/16.jpg

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.

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.

Anatomical Landmarks: Coronoid notch. Pterygomandibular raphe. Occlusal plane for mandibular posteriors.Direct Technique: 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

Inferior alveolar nerve block

http://www.jcda.ca/uploads/c127/fig1.jpg

http://www.pitt.edu/~regional/Dental%20Blocks/Image93.jpg

Inferior alveolar nerve block

https://cchungdentalis.files.wordpress.com/2013/04/mandibular-nerves-block-1.jpg

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

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.

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

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

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.

Bilateralhttps://cchungdentalis.files.wordpress.com/2013/02/maxillary-local-anesthesia-6.jpg

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.